In the last decade, polymeric semiconductors have attracted wide attentions owing to their potential application in organic light-emitting diodes, organic solar cell and organic field-effect transistors. Some polymer materials, especially elastomers, have excellent flexibility, such as strechability, bendability, etc., so polymeric semiconductors are considered as the most promising kind of materials in the future research of flexible electronics. The key point for the flexibility evaluation of polymeric semiconductors is intrinsic mechanical properties, for which, according to relevant works, researchers have already developed some effective approaches to determine, including stretching method, sinusoidal buckling technique, nanoindentation method, and AFM nanomechanical mapping. On the other hand, a variety of ideas for designing flexible polymeric semiconductor materials have emerged and can be classified into supramolecular strategy, "chain flexibilization" strategy, and doping/blending strategy. It is noteworthy that the orthogonal dynamic non-covalent interaction is a fundamental molecular mechanism to induce the flexibility of conjugated polymers. And the tactic based on this mechanism provides a universal method to design flexible semiconductor materials and deserves further studies. This review gives a summary on the intrinsic mechanical properties and design strategies of flexible polymeric semiconductor materials based on the state-of-the-art researches.

Scanning Kelvin probe force microscopy (SPFKM) is a material measuring and characterizing technique which applies scanning Kelvin probe on the basis of atomic force microscopy (AFM) and has been gaining momentum in recent years. It involves simultaneously the nanometer-level topography measurement and the in-situ high-resolution volta potential mapping, thereby providing a novel insight in investigating the mechanisms of materials’ corrosion behaviours. The present paper sketches out the principles with respect to the two working modes of SKPFM, summarizes the unresolved issues that have emerged in SPFKM’s application, and also renders a comparative discussion between SKPFM and the traditional SKP technique. The review offers an elaborate delineation about the application of SKPFM in corrosion science, and ends with a rough description of the opportunities and challenges.

Halide perovskite materials are currently a research hot spot in academia, but there are few comparative analyses of the properties of two-dimensional (2D) and three-dimensional (3D) halide perovskite materials. Through comparison, this article summarizes the different physical and chemical properties of the materials after the dimensional change and the reasons for the property change, and the application fields and problems faced by different properties are analyzed, which provides ideas for the future research of perovskite materials.
First of all, both 3D and 2D halide perovskites have the characteristics of adjustable band gap and high tolerance to defects, but the 2D material is more stable than the 3D material in terms of structural stability. The reason is that the 2D halide perovskite material has low combination energy and high tolerance to deformation. Secondly, since the 3D halide perovskite material is dimensionally reduced to obtain a 2D halide perovskite, the periodic metal framework is destroyed during the process. Some electron donor defects or hole acceptor defects have deep energy levels in the 2D material, resulting in the decrease of carrier concentration and the decrease of electronic transmission performance. The 2D material has poor electric mobility ability compared with the 3D material. At the same time, the quantum effect of the 2D material is prominent and the light absorption ability is reduced, so three-dimensional halide perovskites are more suitable for use in solar cell light absorption layers than two-dimensional materials. Thirdly, on the one hand, the 3D halide perovskite materials currently used in light-emitting devices have low external quantum efficiency and require the introduction of work function-matched semiconductor materials to form heterostructures in order to be efficiently applied. On the other hand, although 2D halide perovskites can achieve a variety of continuous luminous spectrum, but the processing technology needs to be improved to meet the needs of large-scale commercial production. Finally, traditional perovskites, as lead-containing compounds, decomposition will affect the environment, so we should produce the new lead-free stable halide perovskite.

Materials are the foundation of the national economy, the discovery of new materials gives impetus to the development of modern science and technological innovation. The traditional “trial and error” experimental methods are no longer applicable to the research of modern materials owing to the disadvantages of high cost, long period and great contingency. In recent years, with the rapid development of artificial intelligence and data-driven approach, as a main branch and an important tool of them, machine learning is receiving increasing attention and showing tremendous potential. The integration of machine learning into material science research can greatly improve the precision and efficiency, and provide new opportunities for the research and development of new materials and the study of the basic theory.
Machine learning technology combines knowledge of computer science, probability theory, statistics, database theory and engineering. It shows a faster computing speed and good generalization ability, and can effectively deal with some systems and problems difficult to tackle by traditional experiments and numerical simulation. In the past decade, the applications of machine learning in material science research have shown explosive growth,especially in the synthesis and design of new materials, the property prediction, characterization of the microstructure, and the improvement of material calculation and simulation methods. Machine learning will be indispensable in the development of material science and engineering in the future. At present, how to obtain a large number of experimental data and build effective data set is still a hot spot and difficulty in the application of machine learning in the field of material science.
This paper outlines the basic principles, workflows and common algorithms of machine learning, briefly describes the research focus and application progress of machine learning technology in the field of materials science, and analyzes the existing problems of machine learning in mate-rials science research. Meanwhile, some hot spots of the material field in the future are pointed out.

Ring-opening metathesis polymerization (ROMP) of cyclic olefins, a well-established reaction, is one of the most effective means to transform carbon-carbon double bonds and has been widely used in polymer science and organic chemistry. ROMP of cyclic olefins occurs in the presence of a metal carbene catalyst which breaks the carbon-carbon double bonds of the cyclic olefins and connects them into new unsaturated polymers. The research over the cyclic olefins metathesis polymerization was initiated in the 1950s, focusing originally on the catalytic polymerization of cyclic olefins using Ziegler-Natta catalytic systems consisting of transition metal complexes mainly based on Ti, Re, W, Mo, etc. Since the middle of the 1980s, the investigations were concentrated on the polymerization mechanism and alkylidene or carbene catalysts. With the establishment of well-defined, stable and efficient catalysts, the researchers’ concern has been turned to new applications of cycloolefin polymers, and also to developing new cycloolefin ROMP monomers.
For the ROMP reaction, norbornene and its derivatives have been studied extensively since they are highly reactive, easily accessible and relatively low-cost. Besides the expansion of the monomer species available for ROMP, continuous research endeavors have been made to enhance the ROMP resultant polymers’ performance and application potential, mainly from the aspects of the steric hindrance, chemical configuration, pendant polarities of norbornene-based monomers, and the copolymerization of other cyclic olefins or norbornene-based monomers, as well as conjunction with other polymerization methods.
The ROMP of norbornene and its derivatives also made certain advances in the fields of flame retardancy, ion exchange or proton exchange membranes, nanomaterials, biomedical materials and so on, in which flame retardant materials made from norbornene or norbornene derivatives have long been researched and broadly achieved industrialization. In the field of exchange membranes, researchers concentrate on applying norbornene-based polymer membranes to fuel cell due to their thermal stability, acid and alkali resistance, and electrical conductivity. Nanomaterials is one of the most popular research fields in recent years, and nano-metal/polymer composites and magnetic polymer nanocomposites have realized tentative application. The biomedical materials especially drug delivery systems which involve norbornene derivatives have displayed impressive potential, though the industrialization and commercialization still deserve further exploration. Additionally, the norbornene-derivative-based graft polymers, block polymers, liquid crystal polymers, and conductive polymers have also drawn researchers’ attention.
We herein briefly describe the reaction mechanism of ROMP with norbornene and its derivatives as monomer, as well as the ROMP catalysts’ multistage development, i.e. multi-component catalytic systems, molybdenum- or tungsten-based catalytic systems, and ruthenium-based catalytic systems. Moreover, the paper mainly focuses on the recent research progress of ROMP process and products with respect to the norbornene species in the above mentioned fields, and ends with a prospective discussion over the expected new directions of this emerging research topic.

The commercialization of foldable mobile phones makes the year of 2019 been regarded as the starting year of flexible electronics. However, apart from the flexible displays which contribute to the foldable phones, flexible electronics products in a broader sense still remains unrea-lized. One of the key reasons is not all the functional electronic components have been successively flexibilized in commercial level. For example, there are still no flexible alternatives for the transistors and integrated circuits (ICs) which are indispensable to any electronic system. And the complete functions of an electronic system still rely on rigid IC chips and printed circuit boards (PCBs). To overcome this barrier, no other choice is practicable except fabricating flexible electronic systems that integrate traditional rigid ICs. There are currently two approaches to achieving this integration — transferring thin silicon chips onto a flexible substrate; or the so called “flexible hybrid electronics” — in which the latter is based on printing technique and is of simplicity, low cost and high throughput potential. Herein, I sketch out the technical approach of flexible hybrid electronics, and give a summary of the research progress of the ink materials and printing process for flexible electronics printing manufacturing. In addition, I also present a retrospective report showing the achievements of the author's Printable Electronics Research Center in the last 10 years in the area of printed electronics. This paper intends to prove that we can create flexible electronic products closer to practical applications and more competitive through printing conductive interconnects on flexible substrates, which can be an effective methodology, at the current technology level, to greatly advance the commercialization of flexible electronics.

As a major hydration product, calcium silicate hydrate (C-S-H) determines the properties of cementitious materials from every perspective including strength development, shrinkage, creep, and durability. Thus C-S-H is often considered as the “gene” of cementitious materials. Therefore, a comprehensive knowledge of the compositions, structures and performances of C-S-H would advance our understanding of the intrinsic properties and microstructure development of cementitious materials, thereby the macro performances of cement-based materials can be better controlled and even designed from the bottom up accordingly. In recent years, the development of the advanced characterization and analytical technology provides novel and inspiring methods to the investigation of the C-S-H. Great achievements have been made through an increa-sing number of literatures, which have reported the theories on the nucleation and growth, the improvement on mechanical properties together with morphology controlling of C-S-H.
Synthetic C-S-H which is relatively pure and with higher crystallinity is usually favored by researchers than the amorphous C-S-H gel in cementitious materials. It is demonstrated that the globular C-S-H is observed in the nucleating and growing course of C-S-H synthesized by double decomposition reaction which later on transforms to foil-like C-S-H as the final product, in line with the non-classical nucleation and growth pathway. At sub-particle level, more and more evidences suggest that C-S-H structure is closer to that of tobermorite rather than jennite. At particle level, CM colloidal models are widely used to explain the physical properties, such as specific surface area, and behaviors of the shrinkage and creep of cement-based materials. The extensive investigations on the characteristic parameters of C-S-H, including Ca/Si, the content of water, silicate chain structure and morphology provide more information for the establishment of the relationship between features at the micro/nano level and properties at macroscopic scale. Additionally, the controlling of the intrinsic C-S-H structure provides a promising way to improve the toughness of cementitious materials. Some achievements have been reached compassing the refinement of the pore structure, development of organic-inorga-nic composites and optimization of the microstructure by using nano materials.
The methods of synthesizing C-S-H, nucleation and growth theories of C-S-H as well as structural models are summarized systemically in this paper, through combining the classical theories and the latest investigations. The characteristics of C-S-H micro/nano structure are reviewed mainly from its Ca/Si, H₂O/Si, the degree of polymerization of silicate chain and morphologies. The approaches for controlling and designing C-S-H in terms of morphologies and mechanical properties are introduced. The limitations of the current researches and perspectives for the future on the investigation of C-S-H are provided in the end.

Polypyrrole is one of conductive polymers with the best conductive stability. Because of its simple preparation, environmental friendliness, high conductivity, high conductivity and unique doping, the preparation of polypyrrole composites in order to improve the stability is becoming a hot spot in the research field of conductive polymer-based supercapacitors electrode materials. Polypyrrole electrode materials and binary, ternary composite electrode materials with the carbon materials or metal oxide materials used in the research development of supercapacitors in recent years are reviewed. The charge storage mechanism, polypyrrole polymerization mechanism and preparation methods are introduced. Meanwhile, this paper prospected the current hot research fields and development prospect of the polypyrrole and its composite electrode materials.

As halogen-containing flame retardants suffers from toxicity and environmental concerns, phosphorus-containing flame retardants have received increasing attention as alternatives for their environmental friendliness. Since the emergence of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) as a kind of phosphorus-containing flame retardant, numerous efforts have been successively put in optimizing the synthetic approaches and chemical structure of the DOPO derivatives, and recently fruitful achievements have been made. DOPO-derivatives are considered as favorable alternatives for extensive applications in flame retardant polymer materials because of their high thermal stability, excellent water resistance, and versatile flame extinguishing behavior in the gas phase and condensed phase. DOPO derivatives can be used as reactive or additive flame retardants for epoxy resin, polyester and engineering plastics, according to their diverse functional groups. Various DOPO derivatives with P-C, P-N and P-O functional groups have been developed, among which a majority of P-C contained DOPO derivatives act as flame retardants in epoxy resins, while P-N and P-O contained DOPO derivatives are mostly applied in polyurethane foams, engineering plastics and epoxy resins.
The phosphinate derivatives of DOPO are prepared by replacing P-H bond with P-C bond through chemical processes, which mainly include two approaches, namely nucleophilic addition/substitution and molecular rearrangement. In addition, there are primarily two types of P-heteroatoms contained DOPO derivatives, representing by P-O contained phosphonate DOPO-derivatives and P-N contained phosphonamidate DOPO derivatives. In both cases, P-H bond activation of DOPO is crucial step to achieve P-N or P-O bond transformation. According to the literature, Atherton-Todd reaction and using DOP-Cl as starting material constitute the two major reaction pathways for synthesizing DOPO derivatives.
The addition of phosphorus flame retardants is able to endow polymer with satisfactory flame retardant performance. Nevertheless, the introduction of the phosphoric weak bonds of P-O and P-C may exert negative effects on the mechanics of flame retardant polymer. The negative effects of phosphorous groups will be weakened in DOPO derivatives with low loading amount of phosphorus. Therefore, the flame retardant macromole-cular materials with DOPO derivatives are superior in mechanical properties compared with other phosphorus flame retardants.
Understanding the principle of reaction is the key to developing novel DOPO based derivatives. This review offers a retrospection of the research efforts with respect to the synthesis principle and approaches of DOPO derivatives, and flame retardant applications, aiming at provide a refe-rence for the synthesis and application of novel flame retardant of DOPO derivatives. It has been proposed that the impact of DOPO derivatives on the mechanical properties of polymers will be the focus of research in the future.

With the development of the transportation, electric power, electronics and other fields,higher requirements have been put forward for copper alloys in strength and conductivity. The CuCrZr alloy is one of the ideal materials to meet these requirements. This paper summarizes the progress of the research on the alloying, designing and processing of CuCrZr alloy with the focus on the recent hot topics of CuCrZr alloys, discusses the influence of the processing methods presently under investigation on the microstructure and properties of CuCrZr alloy. The prospective research topics of the CuCrZr alloy have been also proposed.

MXene is a group of newly emerging two-dimensional (2-D) carbide/nitride materials, which are derived from its precursor MAX phase by selectively extracting A atoms from MX layers using chemical etching method. MXene can be denoted as M_n+1X_nT_x, where M is an early transition metal, X is carbon and/or nitrogen, and Tx represents surface termination groups (-OH, -F, =O) created in the etching progress. Single layered MXene exfoliated from multi-layered MXene resembles the morphology of graphene. Besides its merits of classical 2-D materials, MXene shows superior characteristics of high electrical conductivity, hydrophilia, transparency, flexibility and energy storage, which confer MXene on promising applications in composites, lubricant, environmental pollution abatement, batteries, capacitors, catalysts, sensors, antibacterial etc. This article presents the latest research results of the synthesis, structure, properties and potential applications for MXene, and research directions for MXene in the future are also predicted.

Geopolymer concrete, a class of newly emerging green building materials prepared from the readily obtainable industrial solid waste, possess a variety of advantages such as low energy consumption & carbon emission and facile production process, as well as excellent compressive strength, acid and alkali resistance, freezing and thawing performance and carbonation resistance. It has displayed notable application potential, and become one of the most promising alternatives to ordinary Portland cement. This paper renders a retrospection of the domestic and overseas research endeavors, a vivid description for the raw materials, mix design, mechanical property, workability and durability of geopolymer concrete, as well as a critical discussion upon the technological problems confronting this novel and prospective engineering material.

magnesium alloys have been extensively applied in the field of aeronautics and space, transportation and electric devices, thanks to their high specific strength, specific stiffness and good processing and machinery ability. Unfortunately, magnesium alloys bear relatively low absolute strength, which seriously hinders their application as structural components. In recent years, employing rear earth element to enhance the strength of magnesium alloys has been a research hot spot, especially the research of mg-Zn-Y alloy. In mg-Zn-Y alloy, the variation of m(Y)/m(Zn) ratio will lead to the alteration of the strengthening phase. When m(Y)/m(Zn) ratio exceeds 1, a unique phase, named as long-period ordered stacking phase (LPSO), was found in mg-Zn-Y alloy, which possesses complete coherent interface with α-mg matrix, both structural and chemical order, and rich of Y and/or Zn. In compared with other secondary phases, the LPSO phase is superior in hardness, thermal stability, dam-ping property, creep resistance and modulus. Accordingly, the impact of this novel structural strengthening phase on the mechanical properties of magnesium alloys has aroused numerous interests of researchers, and become the focus of research on the strengthening and toughening of magnesium alloys.
Recent researches are mostly concentrate on preparing magnesium alloys containing LPSO phase by means of rapid solidification powder metallurgy, copper mold casting, melt stripping and so forth; exploring the effect of LPSO phase on the properties of magnesium alloys by changing the types, amounts and proportions of solute atoms; improving the properties of magnesium alloys by regulating the amount, size and distribution of LPSO phase through heat treatment, extrusion and rolling processes. Concerning the research of microstructure of the LPSO phase, including the arrangement of each atom in the LPSO phase structure, and their specific location, first principle calculation, electoral electron diffraction (SADP), high resolution transmission (HRTEm) and high angle annular dark field image scanning electron microscope (HAADF-STEm) have been introduced in these studies, and a well-developed LPSO phase structure model has been established. A breakthrough has been achieved in the study of the movement of atoms in the LPSO phase structure during the solidification and deformation of magnesium alloys in recent years. In the early 21st century, the yield strength and elongation of the mg97Zn1Y2 (atom fraction)alloys prepared by rapid solidification and hot extrusion reached 610 mPa and 5%, respectively, and these excellent mechanical properties were attributed to the nanoscale LPSO phase.
In thisarticle, we provide a detailed review on the formation mechanism, type of LPSO phase and alloy system with LPSO phase in magnesium alloys, as well as the order of structure and chemical composition in LPSO, and a deep analysis on the mechanism of enhancing strength, plasticity, creep resistance and high damping performance of magnesium alloys by LPSO phase. We also summarize the impact of the preparation process of LPSO contained magnesium alloys on their properties. Finally, we look forward the development direction of LPSO phase magnesium alloy.

As a biodegradable and renewable material, poly(lactic acid) (PLA) has attracted numerous attention for its excellent biocompatibility and mechanical performance (high strength and high modulus). PLA matrix biocomposites have been seriously blocked by its poor ductility, low impact strength, low crystallization rate and low crystallinity since it entered people’s eye shot. Continuous efforts have been put into the modification research of PLA in the past ten years,which primarily focus on plasticizing, strengthening and toughening. Specifically speaking, plasticizing modification is adding the small molecular compound like lactic acid oligomer, citrate and polyethylene glycol into PLA, for the sake of reducing the interaction between PLA chains, improving the plasticity of PLA, and increasing the elongation at break. Yet the plasticizers are likely to exude and migrate, which is a crucial problem now. Reinforcement modification, namely heterogeneous nucleation of PLA with inorganic fillers or nanoparticles like silica (SiO₂), titanium dioxide (TiO₂), calcium carbonate (CaCO₃), talcum powder (Talc), montmorillonite, which can improve the crystalline properties of PLA, but can not fundamentally enhance the brittleness of the material toughening modification refer to the addition of rubber particles or thermoplastic elastomer such as natural rubber (NR), thermoplastic polyurethane (TPU), polycarbonate (PC) into PLA. Although the toughness of the composite is improved to some extent, the biodegradability cannot be preserved. With the production of some degradable polyester including polycaprolactone (PCL), poly (butylene succinate) (PBS), poly (butylene adipate-co-terephthalate) (PBAT), PLA can be effectively toughened without sacrificing the degradation performance. It is the main direction and research hotspot of PLA modification. PBAT, a degradable polyester polymer, possesses the flexibility of aliphatic hydrocarbon and the rigidity of aromatic ring, which makes PBAT emerge as the best candidate for PLA toughening. In the early research of PLA/PBAT, it was found that the poor compatibility of PBAT and PLA resulted in unsatisfactory mechanical properties of the blends, which is primarily caused by the tremendous differences in the structure of molecular chain segment. In the last decade, on the basis of polymer blending modification, researchers have selected the appropriate third component to modify the PLA/PBAT blend system, and achieved fruitful results. Presently, the impact strength of the PLA/PBAT blend system after toughening has been raised from 2.3 kJ/m² to 61.9 kJ/m². This review offers a retrospection of the research efforts with respect to the progress of modification PLA/PBAT blends, and provides elaborate descriptions about physical blend (inorganic filler or nanoparticles and physical compatibility agent) and reactive blending compatibilizer modified PLA/PBAT blends. Finally, we focus on the problems faced by PLA/PBAT blending modification system, aiming at providing a reference for the preparation of high performance fully biodegradable PLA/PBAT composites.

Metal organic frameworks are a kind of porous crystalline material with periodic multidimensional network structure formed by metal ions and organic ligands self-assembly process, which have been applied widely in catalysis, sensing, storage of gas and medicine, etc. The ZIF-90 nanostructured material with particle sizes below 300 nm was prepared. The structure of the metal-organic framework was characterized by FTIR and XRD. Scanning electron microscopy (SEM) characterized the morphology and particle size. The results of loading and releasing anti-cancer drug 5-fluorouracil on ZIF-90 nano-drug carrier showed that the loading ability of the material was up to 1.245 g/g, and the release rate was over 95%. The stability of the drug carrier at different pH showed that the drug carrier could rapidly release the drug with the skeletal collapse in the acidic condition of the tumor cells, therefore, ZIF-90 has potential ability of the tumor to target the drug delivery.

Lignin is rich in nature, it is also renewable and with high carbon content. The application of lignin in the preparation of carbon fiber has an unparalleled cost advantage.The development of lignin-based carbon fiber is briefly introduced. The progress of the source, structure difference and carbon fiber preparation methods of kraft lignin, organosolv lignin and steam-explosion lignin is discussed in detail. As a result, the kraft lignin has been chosen as the best raw material for the preparation of low cost carbon fiber. Furthermore, the future direction of lignin-based carbon fiber is pointed out, which aims to provide reference for the initial research of lignin-based carbon fiber.

Porous materials have been widely applied in adsorption and separation, catalyst supports, thermal insulating materials, energy storage, sensors, etc., owning to their high porosity, high surface area, low thermal conductivity and bulk density, and good chemical inertness. Porous materials can be classified into three categories according to pore size: macroporous materials with the aperture greater than 50 nm, mesoporous materials that possess a pore size between 2 nm to 50 nm and microporous materials with pore diameter less than 2 nm. However, their applications suppressed to a certain extent owing to the limited pore size. Hierarchical porous materials enjoy the advantages compared to the conventional porous materials including high permeability, elaborate pore structure, low bulk density, large surface area and pore volume, and have been provoking continuously increasing research interest. On the other hand, the conventional preparation process for hierarchical porous materials still suffer several problems, including complicated preparation process, high-cost preparation and difficulty in controlling pore structure. Thus, researchers endeavor to optimize hierarchical porous materialsfabrication process and reduce the cost of preparation, aiming to prepare uniform-and controllable-sized hierarchical porous materials.   Hierarchical porous materials mainly include macro-mesoporous materials, macro-mesoporous materials and meso-mesoporous materials with bimodal or multiple mesopores. Macro-mesoporous materials can be produced by a variety of methods including template method, foam-gelcasting, sol-gel method and molten salt method. The major routes to preparing micro-mesoporous materials are chemical activation, template method and hydrothermal method. Meso-mesoporous materials are commonly fabricated through hydrothermal method, template method, sol-gel method and self-assembly synthetic procedure. This paper gives a summary of research efforts in recent years with respect to the hierarchical porous materials, and introduces the fabrication process of macro-mesoporous, micro-mesoporous materials and meso-mesoporous materials. The development trends of the future research are also discussed.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted widespread attention due to their high power conversion efficiency (PCE) and low fabrication costs. Their excellent photoelectric performances are mainly attributed to the unique physical properties of perovskites, such as high light absorption coefficient, high carrier mobility, long carrier life, tunable band gap. They have quickly become a star of new-generation thin-film solar cells, because they can be manufactured on large scale via solution processing method. In the past decade, the PCE of small-area devices (<1 cm²) of PSCs has skyrocketed from 3.8% in 2009 to 25.2% now; the efficiency on small module-level device (10—800 cm²) has been increased to 18.04%; the PCE on module-level device (>800 cm²) has also been refreshed to 16.1%. One of the key factors for the performance mismatch between small-area and module-level devices is the limitation of the deposition methods for large-area perovskite thin films with high quality and uniformity. The general deposition method of perovskite films for small-area devices is spin-coating. However, this met-hod exhibits the disadvantages of uninform thickness and the waste of raw materials in scalable fabrication; so, it is not suitable for fabricating large-area perovskite thin films. Currently, the deposition scheme of large-area perovskite thin films is under diversified research, and the stable industrial production scale has not yet been formed. So far, the mainly reported methods of the deposition of large-area perovskite films including doctor blading, slot-die coating, spraying coating, inkjet printing, soft-cover deposition and the vacuum vapor deposition. This review has summarized the recent research progresses on the preparation methods of large-area perovskite thin films; the basic deposition principles as well as the advantages and disadvantages of various deposition technologies have also been introduced. Finally, the problems they will be faced in the follo-wing study and in the process of industrialization have been outlined, aiming at improving the understanding of the deposition methods of large-area perovskite thin films for readers and providing useful reference for the study of large-area and high-efficiency perovskite solar modules.

Hydrogels are three-dimensional networks of hydrophilic polymers formed by chemical and/or physical crosslinking. They have favorable water absorption and water retention, and will not overflow under a certain pressure. Since hydrogels entered people's eye shot, the preparation process and application range of hydrogels have been continuously optimized and enlarged. Nevertheless, hydrogels still suffer from poor water absorption, water retention, salt tolerance, mechanical strength, and degradability. Especially, hydrogels are mostly prepared by taking petro-leum products as raw materials, and the lack of oil resources in China seriously blocks the further development of hydrogels.
For the sake of solving the above problems, researchers have gradually turned their attention to the natural macromolecules. Usually, natural macromolecules exist in nature and are rich in resources. Starch, cellulose, chitosan, etc. are the earliest natural polymers that have been found to be satisfactory for introducing in hydrogels. Among them, cellulose is the most abundant one, and it has been widely used in various fields because of its non-toxic, favorable biodegradable and biocompatible properties. However, the poor water solubility and poor mechanical properties of cellulose have prompted certain hindrance in the preparation process, despite the improved effect of water absorption and water retention. Accor-dingly, the modification of cellulose has become a hot topic. Although a series of derivatives like carboxymethyl cellulose can solve the problem of cellulose insoluble in water, the gel strength and salt tolerance of hydrogel still remain unsolved. It is universally known that nanoparticles exhibit certain rigidity and are able to regulate the mechanical property of materials. Consequently, nanocellulose, one of the modified derivatives of the cellulose has attracted numerous research interests. Thanks to the nano scale size, nanocellulose not only possesses the advantages of non-to-xic, easy degradation, but also show low density, good mechanical properties, strong hydrophilicity, low coefficient of thermal expansion, etc. Compared with tranditional hydrogel, the nanocellulose-based hydrogel is superior in the following three aspects: enhanced water absorption, considerable salt tolerance, and high gel strength.
In this article, we summarize the preparation approaches ofnanocellulose and nanocellulose-based hydrogels, including physical, chemical and physico-mechanical combined methods, and analyze the merits and drawbacks of each method. Besides, we introduce the application and develo-pment of nanocellulose-based hydrogels in agriculture, biological ,water treatment and other fields. Finally, we point out the challenges in the preparation and application of nanocellulose-based hydrogels and proposed the future prospect.

Since the emergence of organic-inorganic hybrid perovskite materials as light harvesters, the perovskite solar cells have attained a considerable efficiency improvement due to notable achievements in optimizing the fabrication process and device structure, while nevertheless been suffering increasingly serious challenges, especially instability. Layered (low-dimensional) perovskite materials are constructed based on a periodical (or quasi-periodical, or hybridized) structure which is composed of alternate layers of organic amines and metal halide perovskite crystals. The layered structure approximates to a two-dimensional structure whilst the number (n) of planes, which consist of the pyramids’ squares of the perovskite octahedrons, within one separated perovskite layer approaches 1. For photovoltaic application, these low-dimensional perovskite structures have two advantages compared to their three-dimensional counterparts: I. remarkably enhanced moisture resistance and thermal stability; II. tunable optical and electrical characteristics by varying n and selecting different organic amines.

On the other hand, poor carrier mobility (a consequence of the inhibition of out-of-plane charge transport by the organic amine cations) and wide band gap contribute to a far lower efficiency of low-dimensional perovskite solar cell than three-dimensional perovskite device. This urges intensive research endeavors to seek favorable organic amines and optimize perovskite film fabrication process, aiming at boosting photovoltaic efficiency while exploiting layered perovskite’s stability. And in the past three years, impressive strides have been made in promoting the low-dimensional perovskite solar cells, with a giant leap in the reported power conversion efficiency (PCE) from 4.37% to 13.7%.

Phenethylamine (PEA), n-butylamine (n-BA), isobutylamine (iso-BA), polyethylenimine (PEI), etc. have been found to be satisfactory as the hydrophobic amine interlayers for relatively-high-efficiency layered perovskite solar cells. PEA is the first to be involved in the attempts, and the n-BA-intercalated perovskite hold the currently highest efficiency of this new type of photovoltaic devices. PEI intercalation appears to result in narrower band gap and higher moisture resistance, but also leads to a larger inhibition to the carrier transport. Although one-step spin coating provides a facile route to obtain layered perovskite films, this method will cause the horizontal growth (i.e. interlayers parallel to substrate) of the layered structure and in consequence, an extremely low cell efficiency. Works in the past two years have established a new avenue to overcome the low-efficiency bottleneck, by introducing various techniques into the spin coating process, e.g. hot casting, immersion (in short-chain amines), antisolvent dripping, all of which have successfully achieved the preferential out-of-plane alignment of the inorganic perovskite layers. Besides, researchers also have demonstrated that the 2D-3D hybrid perovskite structures, which can be constructed on the basis of 3D perovskite with the presence of organic amine additives, can gain improvements in terms of both efficiency and stability.

This review offers a retrospection of the research efforts with respect to the layered (low-dimensional) perovskite photovoltaic devices, and provides elaborate descriptions about the structure of low-dimensional perovskite, the selection of the intercalating organic amines, and the film fabrication process. We then pay attention to the problems confronting the current state-of-the-art low-dimensional perovskite solar cells. We have confidence that the low-dimensional perovskite solar cells have a bright future in the development and innovation of stable and environmental-friendly photovoltaic devices.

Pure Friedel salt (3CaO·Al₂O₃·CaCl₂·10H₂O, main corrosion product of cement-based materials by chloride ions) and ettringite (AFt, 3CaO·Al₂O₃·3CaSO₄·32H₂O, main corrosion product of cement-based materials by sulfate ions) were chemically synthesized and then characterized via X-ray diffraction and TG-DSC test to investigate their stabilities and transform mechanism. The interaction between different corrosion ions was explored by immersion experiment. The results indicated that sulfates have a significant impact on Friedel salt, as sulfate ions can substitute for chloride ions in Friedel salt and convert Friedel salt into ettringite. Chloride salts can also react with ettringite, leading to ettringite's decomposition. There is an equilibrium between Friedel salt and ettringite, and the inter-transform of them can be achieved under certain conditions. The study verified the interaction effect during the corrosion process of the compound solution of chloride salt and sulfate toward hardened cement paste.

Aqueous zinc ion batteries (ZIBs), a new type of aqueous secondary batteries proposed in recent years, show great practical value and developmental prospects in the field of scale energy storage including electric vehicle and energy storage grid owing to their high energy density and high power density, safe and efficient discharge processes, cheap and nontoxic electrode materials and simple manufacturing process.
At present, one of the main factors hindering the further development of ZIBs is the lack of suitable cathode materials. Due to the large ion radius of Zn²⁺ and its hydrated ions, it will cause irreversible deformation or structural collapse of the cathode electrode material during insertion/desorption process, resulting in a rapid decline in battery capacitance. The poor conductivity of the cathode electrode material and serious electrode polarization during charging and discharging cause the charging voltage of cathode partially overlaps with the oxygen evolution voltage. As a result, the cathode electrode material will catalyze the water to produce oxygen, causing the battery flatulence to invalid during the charging process.Moreover, the strong electrostatic interaction between the divalent Zn²⁺ and the crystal structure of the cathode electrode material leads to unsatisfactory Zn²⁺ insertion capacitance. Therefore, it is crucial to develop a cathode material that can provide high capacity and maintain good structural stability during Zn²⁺ insertion/desorption process.
In view of the shortcomings of the cathode material of the ZIBs, a variety of modification methods are used to improve their performance: (Ⅰ) guest particles, such as metal ions, organic molecules and water molecules, are introduce in to the host so a more stable frame can be obtained through its structural changes; (Ⅱ) intrinsic mixed valence materials are prepared because of their better adaptability to the volume changes and valence changes of the cathode electrode material during charging and discharging; (Ⅲ) introduce oxygen vacancies to increase active sites to promote Zn²⁺ diffusion kinetics and increase material capacity; (Ⅳ) conductive materials are composed to improve the overall conductivity of the material and enhance structural stability; (Ⅴ) the nanostructure modification is carried out to enlarge specific surface area of cathode material, shorten the Zn²⁺ diffusion distance and increase the contact area of electrochemical reaction.
This article gives a brief introduction to ZIBs, its advantages and its energy storage mechanisms. Based on the key role of cathode materials in ZIBs, several common cathode materials such as manganese-based oxides, vanadium-based oxides, and prussian blue analogs are emphatically reviewed. Moreover, the structures, properties and defects of all above cathode materials are expounded, and the modification methods including doping guest particles, compositing with conductive materials, preparing intrinsic mixed valence states and constructing nanostructures are primarily discussed. At the end of this view, we pointed out several promising directions of the development of cathode materials for ZIBs.

High-entropy alloy has attracted masses of attention due to its unique alloy design concept and excellent properties. The previous high-entropy alloys, whose density is relatively high, are mainly based on transition group elements, refractory elements or rare earth elements, which greatly limits their application. With the trend of material lightweight, the research on light-weight high-entropy alloys are gradually increasing. Light-weight high-entropy alloy is a new branch of high-entropy alloy based on light elements such as Al, Li, Mg, Ti, etc. Light-weight high-entropy alloys have unique advantages of low density, low modulus, high specific strength and high specific hardness. In addition, light-weight high-entropy alloys also have high strength, high hardness, excellent wear resistance, good oxidation resistance, excellent corrosion resistance, good high temperature oxidation resistance, high temperature softening resistance and good biocompatibility. The superior properties of light-weight high-entropy alloys have significant potential to be applied to aerospace and biotechnology.
At present, the research of light-weight high-entropy alloys mainly involve the development of composition, preparation, characterization and properties. The development and design of new components mainly use the method of combination of empirical parameters, CALPHAD and DFT (Density functional theory) calculation. The main methods of alloys preparation are induction melting, arc melting and mechanical alloying. The phase composition and structure of light-weight high-entropy alloys usually include amorphous structure, single-phase polycrystalline structure, multiphase complex structure, etc. The research of performance mainly involves mechanical properties, include strength, hardness, high tempe-rature creep, etc., and also includes oxidation resistance, corrosion resistance, biocompatibility, etc. In this paper, the composition design, pre-paration, microstructure and properties of light-weight high-entropy alloy are reviewed. Meanwhile, the problems and challenges for light-weight high-entropy alloy are prospected.

The ω phase and its phase transformation in titanium alloys have great influence on the microstructure and properties of the alloys. Therefore, the study of ω phase transformation in titanium alloys becomes one of the hot issues in recent years. In this paper, the related research reports are summarized, including ω phase formation, ω phase decomposition, ω phase morphology and ω -assisted α nucleation. The advantages and disadvantages of the related models are compared, and some scientific problems with academic disputations are expounded.

In recent years, perovskite quantum dots stand out for their excellent photoelectric properties among all kinds of optoelectronic materials. Compared with organic-inorganic hybrid perovskite quantum dots, all-inorganic perovskite quantum dots (IPQDs) show higher chemical stability. IPQDs have aroused tremendous interest owing to their high absorption coefficient, narrow full-width at half maximum, high photoluminescence quantum yield (PLQY), controllable composition and size, tunable emission spectrum, photoluminescence and electroluminescence dual characteristics. These excellent properties have made IPQDs become one of the most promising optoelectronic materials, and widely used in light emitting diodes (LEDs), solar cell, photodetector, laser and other fields.
Unfortunately, there still exist many problems in IPQDs. Ⅰ.The luminescence mechanism of IPQDs is not clear enough. A large number of comprehensive and systematic studies are still needed to reveal the mechanism for their excellent photoelectric performance. Ⅱ. The PLQY of CsPbCl₃ is low and needs further improvement. Ⅲ. Pb in IPQDs is toxic. Further analysis of the impact of Pb in IPQDs should be carry out so as to lay a theoretical foundation for development of lead-free or lead-less QDs materials. Ⅳ.IPQDs are unstable, and they are easy to decompose or agglomerate in polar solvents. The IPQDs, especially CsPbI₃, exhibit poor stability under light, oxygen, high humidity and temperature. Anion exchange can occur easily when different IPQDs are mixed. Ⅴ. Long chain insulation ligands on the surface of QDs hinder the charge-transfer between crystal grains. On the premise of sufficient passivation of quantum dots surface, an effective way to develop highly efficient LEDs is to minimize the hindrance of ligands to charge transfer. Ⅵ. Further optimization of preparation process is required for the sake of adapting to large-scale production.
Researchers have devoted themselves to reduce the toxicity and improve the stability, and significant progress has been made in recent years. Effective ways have been developed to solve the toxicity of IPQDs by completely or partially replacing Pb with non-toxic or low toxic metals (like Mn and Sn), and coating IPQDs with polymers or metal oxides. Moreover, doping Mn²⁺ into IPQDs can increase formation energy of perovskite lattice, and thereby enhance the thermal stability of IPQDs. Besides, using organic, inorganic or polymer materials to coat IPQDs can avoid the contact of IPQDs with external environment, thus the stability of IPQDs can be also improved.
This article provides an overall review on the recent advances in all-inorganic perovskite quantum dots, including synthesis methods, morphology, optical and surface properties of IPQDs. The stability of IPQDs, the toxicity of Pb and the current solutions are analyzed. The application prospects of IPQDs in light-emitting diodes, solar cells, photodetectors and lasers are discussed. Finally, some problems and outlook of future deve-lopment directions of IPQDs are pointed out.

The over-exploitation and over-utilization of fossil fuel resources such as petroleum and coal has aggravated energy and environment problem in the 21st century, and urged the development of highly-efficient and cost-effective energy conversion and storage devices to become the research topic of this new era. Among many candidates of energy conversion and storage devices, metal-air batteries and intermediate-low temperature solid oxide fuel cells can efficiently convert chemical energy into electric energy, and enjoy the advantages of low cost, high efficiency and environmental friendliness. Hence, they have provoked intensive and fruitful research endeavors with amazing achievements over the past decade. However, the sluggish kinetics of the oxygen reduction and evolution reactions greatly reduces the energy conversion efficiency, and consequently increases the application cost and severely hinders the commercialization of these two devices. Cobalt-based electrocatalysts, as highly efficient cathode materials with lower cost than noble metals, feature mixed ionic and electronic conductivity which can effectively reduce polarization and contribute to high catalytic activity for oxygen reduction and evolution reactions, and thereby have been holding growing interest recently.

　For metal-air batteries, cobalt-based electrocatalysts such as simple oxides, spinel oxides, perovskite oxides, and others can significantly improve the discharge capacity and cycle life, and simultaneously, lower the charge voltage and polarization. On the other hand, the catalytic activity and stability need to be further enhanced, and the catalytic mechanisms and active sites deserve further rational exploration and ascertainment. Similarly, cobalt-based electrocatalysts including La_1-xSr_xCoO_3-δ, La_1-xSr_xCo_1-yFe_yO_3-δ, Ba_1-xSr_xCo_yFe_1-yO_3-δ and cobalt-based double perovskites show evident efficacy in reducing the cathode polarization resistance and area specific resistance as well as increasing the power density, while nonetheless sustaining a generally higher thermal expansion coefficient and a rather poor stability compared to some other competitors.

　To further improve the catalytic performance of cobalt-based electrocatalysts for metal-air batteries and intermediate-low tempe-rature solid oxide fuel cells, researchers have developed many useful and productive methods, exemplified by metal elements doping, composite cathode materials preparation, and noble metals decoration.

　This review provides a brief introduction of the structure and working principle of metal-air batteries and intermediate-low temperature solid oxide fuel cells, and a vivid description upon the latest attempts and achievements for the fabrication, modification and performance of the rich variety of cobalt-based electrocatalysts, mainly including simple oxides, perovskites oxides, spinel oxides and double perovskites.

Photoelectrochemical (PEC) sensor is a recently developed analytical device based on the process of chemical or biological recognition, which has the advantage of rapid response, high sensitivity. Moreover, the PEC sensor is simple, cheap and easy to realize miniaturization. As a result, PEC sensors have received intense interest in the fields of biological and environmental analysis. The basic principle, classification of PEC sensors, and the photoelectric active nanomaterials for the fabrication of PEC sensors are reviewed. Finally, the applications of PEC sensors in the fields of bioanalysis such as DNA detection, immunosensing and enzyme analysis are presented.

Gate-all-around (GAA) transistors are the most competitive device structure to replace existing fin field effect transistors(FinFET) below the sub-3 nm node, effectively improve the short-channel effect caused by the continuous shrinking of device size along Moore's Law. In the process flow of GAA device preparation, inner spacer preparation and channel release are newly introduced process modules relative to FinFET, and both require SiGe selective etching technology. SiGe is required to be removed as a sacrificial layer by selective etching with as little damage as possible to the Si channel. This paper presents a review of the SiGe selective etching techniques required in the gate-all-around (GAA) transistor fabrication process. Firstly, we analyze the development trend of device structure and the application of SiGe selective etching. Secondly, the development of conventional SiGe selective etching methods and new selective etching techniques are categorized and reviewed. After that the advantages and shortcomings of each technique are summarized. Finally, this study analyzes the challenges faced by SiGe selective etching technology, and prospects the possible future development trends.

In a world with rising concern about energy security, environmental crisis, and global warming, exploring superior catalysts for oxygen evolution reaction, super capacitor, and the treatment of pollutant ions in waste water are getting more and more attention. Layered double hydro-xide (LDH) has many properties such as memory effect, nice catalysis ability, anion exchange, acid-base and thermal stability, which has been widely concerned in various fields to solve the above problems.
LDH has excellent performance for oxygen evolution electrocatalysis, low cost, adjustable structure. The intercalation reaction can be carried out between layers of LDH. However, the poor electron conductivity of LDH reduces its electrochemical performance. Moreover, the LDH layers are easy to agglomerate in the synthesis process, resulting low conductivity and low catalytic activity. These problems can be solved by improving the synthesis method of LDH and compounding LDH with various functional materials.
In recent years, in order to improve the conductivity of LDH, researchers have in situ grown LDH on various conductive substrate, which can expose more active sites and as a result improve the catalytic activity of LDHs. By compounding LDH with graphene, the specific capacitance, conductivity and cycle stability of LDH/graphene composites can be enhanced, and the adsorption capacity of LDH for CO₂ can also be improved, making LDH widely used to solve energy crisis and environmental pollution problems.
This article reviews the synthesis methods of LDH and LDH composites, and summarizes the applications of LDH and its composites in catalysis, energy storage, and environmental protection in recent years. First, the application of LDH in electrocatalytic water oxidation and photocatalysis is introduced, and then the application of LDH materials in supercapacitors and environmental problems such as water pollution treatment is described.

High-entropy alloys (HEAs), also known as multi-principal component solid solution alloys, have attracted widely attention of scholars at home and abroad due to its unique alloy design concepts and excellent comprehensive properties, which have gradually become a research hot spot in the field of metal materials. Refractory high-entropy alloys (RHEAs) are thought to be a new type of superalloys designed and deve-loped based on HEAs of refractory elements. Compared with traditional high-temperature alloys, RHEAs have higher high-temperature strength, high-temperature oxidation resistance and high-temperature phase stability, implicating broad application prospects in the field of aerospace and petrochemical. Since it was proposed in 2010, RHEAs have become an important branch in the research field of HEAs.
So far, 4th, 5th, 6th periods and Ⅳ, Ⅴ, Ⅵ subgroup of 9 elements (Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) and additional elements, such as Al, C, Co, Ni, were used as principal component of RHEAs by scholars, and formed a complex alloy system. There are more than 100 alloy systems reported, the phase structure of these alloys ranges from single-phase BCC structure to double-phase, such as BCC1+BCC2, BCC+Laves, etc., and to multi-phase structure, showing structural diversity. The microstructure of RHEAs includes dendrite, equiaxed crystal, eutectic structure or deformation twin structure, etc., and the properties determined by microstructure have its own strong points. The preparation of RHEAs first adopted melting methods, including arc melting and induction melting, which required repeated remelting under high-purity protective gas. In recent years, research has also been conducted on the preparation of RHEAs by powder metallurgy, which has obtained fine particle size and relatively uniform composition. In addition, laser cladding, magnetron sputtering, etc. are also used to prepare materials or coatings for RHEAs. It can be seen that with the deepening of research, RHEAs are constantly making new progress in the research of composition design, preparation process, phase structure and microstructure, room temperature and high temperature performance.
In this review, according to the research status in RHEAs at home and abroad in the past few years, its principal composition, phase structure and preparation method were systematically introduced, and the evolution of RHEAs properties, including density, strength and plasticity, high-temperature oxidation resistance, wear resistance and corrosion resistance, were summarized. Finally, it points out the challenges faced by RHEAs and puts forward suggestions on future research priorities.

Lack of resources, shortage of energy and environmental degradation have become three essential problems faced by the sustainable deve-lopment of today's society. As the forerunner and foundation of social progress, traditional materials have brought great material wealth to mankind. Meanwhile, it has also caused the problems of excessive consumption of energy and resource as well as surge in environmental load during the material manufacturing, use and waste. As people's awareness of environmental protection, fitness, and public health security markedly enhances, ecological environment functional material, with a composite of design philosophy “material-environment-ecology-health”, has been paid wide attention by academic, industrial, and educational personnels, and therefore it has been gradually considered as the new growth point of the development of material science and engineering discipline, and its related strategic emerging industry. The research and design of ecological environment functional material not only follows the principle of life cycle assessment but also, by advocating the green material technology, it endows functional materials with the characteristics such as excellent environmental coordination, preferable environmental purification and environmental restoration, and promoting good health. Non-metallic minerals not only have a great variety, abundant reserves and low price, but also have the best compatibility with the natural environment, which gives them a natural advantage in the process of preparing ecological environment functional materials. At present, the ecological environment functional material developed with natural mineral resource as the main raw material has exhibited great practical potential in environmental pollution prevention and microenvironmental regulation. This review introduced the connotation and conception as well as the recent development of ecological environment functional material, and further presented the recent advances and development trends of the typical ecological environment functional materials such as sepiolite, montmorillonite, tourmaline, diatomite, biochar, and iron ore tailing. In order to provide reference for the future development of ecological environment functional materials industry and corresponding innovating personnel training mode, this review finally summarized the development trend of the study on ecological environment functional material and the related industry.

As the earliest alloy in human history, the invention of bronze opened a new chapter in the history of metal smelting. There are more than 30 practical alloy systems that have been used for industrial sectors so far. Eutectic alloys, such as steel (Fe-C), Al-Si alloy, Ag-Cu alloy, have been widely used because of special properties such as low melting point and good fluidity.
High entropy alloys are known as one of the three major breakthroughs in alloying theory in recent decades. Theoretically, more than 7 000 high entropy alloy systems can be designed from 13 kinds of arbitrarily selected common elements. Compared with traditional alloys that based on one element, the design space of high entropy alloys are much larger. Moreover, it is found that high entropy alloys can form simple microstructures such as a simple face-centered cubic, single body-centered cubic or face-centered cubic and body-centered cubic while conventional alloys gene-rally form complex intermetallic compounds. Hence, high entropy alloys owe high strength, high wear resistance, high corrosion resistance and other excellent properties. Specific performance changes can be achieved by controlling the composition of high entropy alloys to meet different design needs, so high entropy alloys have great research value and application space.
Eutectic high entropy alloys (EHEAs) have composition characteristics of eutectic alloys and high entropy alloys. EHEAs have gained extensive attention in recent years because of the super strength, plasticity, resistance to friction and corrosion. So far, a variety of new eutectic high entropy alloys have been successfully prepared. The scholars have carried out in-depth research on the growth mechanism and strengthening mechanism of the first eutectic high entropy alloy AlCoCrFeNi_2.1 designed by Professor Yiping Lu. EHEAs have gained extensive attention in recent years because of the super strength, plasticity, resistance to friction and corrosion. In this paper, the production of eutectic EHEAs is briefly described, and the achievements are reviewed. Moreover, the composition design, preparation method and studies about EHEAs' properties are mainly introduced, and the prospects for their future development are discussed.

Since the discovery of penicillin in 1928, the application of antibiotics has greatly reduced the morbidity and mortality of bacterial infectious di-seases, and numerous lives are survived from bacterial infection. However, with the widespread use and abuse of antibiotics, antimicrobial resistance has become a global public health issue. In addition, there are several problems that traditional antibiotic therapies encounter. Specifi-cally speaking, the antibiotics are rapidly metabolized and excreted from body after administration, only a few drugs reach the infected site and the bioavailability was low. In this case, high doses and long period treatments are required in clinical application, which lead to notable side effects. Besides, the poor therapeutic effect of antibiotics against biofilm infections and intracellular infections is also a pressing issue, leading to chronic infections and recurrent infections.
In view of the problems existing in the traditional antibiotic delivery mode, the delivery of antibiotics by nanoparticles is proposed and shows great potential in the treatment of bacterial infection, which can improve the solubility of poorly soluble drugs, improve the pharmacokinetics and biodistribution of antibiotics, and overcome the tissue and cell barriers. Inspired by the fact that the physiological and physical microenvironment of bacterial infection sites is different from normal tissues, polymeric nanoparticles, that are responsive to the unique infectious microenvironments, have been developed to deliver antibiotics. These strategies remarkably improve the bioavailability and biodistribution of antibiotics, enhance the therapeutic efficacy of antibiotics against intracellular and biofilm infections, as well as attenuate the side effects.
However, the delivery of antibiotics by nanoparticles shows limitations in the treatments of drug-resistant bacteria and especially for multidrug-resistant bacteria. Aiming at the problems of antibiotic resistance, antimicrobial peptides and their analogues have attracted extensive attention worldwide, since they exhibit broad-spectrum antibacterial activity with the less like-hood to develop drug resistance. Nevertheless, the cytotoxicity of these antibacterial agents hinders their clinical applications. For the sake of solving this problem, researchers designed responsive antimicrobial polymers that exhibited low toxicity in normal tissues, and transformed to active form to effectively kill drug-resistant bacteria when triggered by the acid infectious environment or bacterial enzymes in the infectious environment.
In this review, we gave a brief introduction on the existing issues on traditional antimicrobial therapy, and an overview and current perspectives on the development infection-microenvironment responsive polymeric nanoparticles as carriers of antibiotics and the infection-responsive antimicrobial polymers for the treatment of bacterial infectious diseases over the past decade.

Graphite-like carbon nitride(g-C₃N₄) with lamellar structure was prepared using melamine as raw material via a facile thermal polymerization method at different temperatures in air and argon atmosphere. The effects of melamine pyrolysis in different atmospheres and the thermal stability of g-C₃N₄ products were studied by TG-DSC, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and Raman. The results showed that the pure phase g-C₃N₄ with high crystallinity and lamellar structure could be synthesized via the pretreated melamine by thermal polymerization method.In argon atmosphere, g-C₃N₄ with smooth and compact surface is more favorable than air atmosphere. g-C₃N₄ with lamellar structure could be observed at 500 ℃, and it could still exist stably at 700 ℃. The thermal stability of g-C₃N₄ synthesized in argon atmosphere was better than g-C₃N₄ in air atmosphere.

The lightweight of automobile has become more and more widely concerned with the needs of energy conservation, environmental protection and economy. The low density and high strength steel of the Fe-Mn-Al-C system combines the low density and excellent mechanical properties, which complies with this topic.The earliest information on low-density steels dates back to 1933 which was related to the first development of Fe-Mn-Al-C system.Until 1958, the Fe-Mn-Al-C system of low-density steel was developed to replace the Fe-Cr-Ni system of stainless steels (added too many expensive Ni and Cr elements).At present, the Fe-Mn-Al-C system low-density steel is a kind of steel with high lightweight potential in the automotive industry, in which the addition of Al element leads to a decrease in density and Young’s modulus. Adding 1wt% Al, the steel density is reduced by 1.3%, and the Young’s modulus is reduced by 2%. Simultaneously,the addition of a large amount of Al,Mn and C elements resulted in the smelting, continuous casting, formability, weldability, microstructure evolution and deformation mechanism of Fe-Mn-Al-C system steels, which are quite different from those of traditional steels.
The lightweight Fe-Mn-Al-C system steel can be classified into four categories: single ferritic steels,ferrite based duplex steels, austenite based duplex steels and austenitic steels, according to the composition of the alloy and the main composition phase of room temperature.The single ferritic steel has similar tensile properties of 200—600 MPa as the conventional high-strength low-alloy steel (HSLA) and belongs to the first generation of advanced high-strength steel (1G-AHSS).Ferrite-based Fe-Mn-Al-C system duplex steels are another promising lightweighting scheme with a lower alloy content that can be produced using ferrite plastic deformation and retained austenite TRIP and TWIP effect to increase steel strength and plasticity.The ferrite based Fe-Mn-Al-C double phase steel has superior strength and ductility compared with the first advanced high strength steel, and the middle and upper level of their performance belongs to the category of the third generation advanced high-strength steel (3G-AHSS).The austenitic-based duplex steel is similar to ferritic-based duplex steel, but it has higher alloy content than ferritic-based dual-phase steel, and its lower limit of performance belongs to the 3G-AHSS category.The austenitic steels are the most promising in terms of properties and processing.The main constituent phases of austenitic steel are austenite, a small amount of ferrite and κ-carbide.The mechanical properties of austenitic steels are determined by the deformation of austenite and the interaction of carbide-austenite.The tensile properties of austenitic light steel are similar to those of high manganese TWIP steel, the strength of 600—1 500 MPa and the plasticity can reach of 30%—80% (even up to ~100%), it belongs to the category of the second generation advanced high strength steel (2G-AHSS).
The stacking fault energy (SFE) of Fe-Mn-Al-C system low-density high-strength steel increases and short-range ordered (SRO) phase and κ-type carbide are precipitated with the addition of Al content in steel.High-SFE low-density Fe-Mn-Al-C system steel with various deformation mechanisms such as novel microband induced plasticity (MBIP), dynamic slip band refinement (DSBR), shear band induced plasticity (SIP) deformation mechanism, transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) deformation mechanisms.These deformation mechanisms are consistent with the B2 and DO3 type of ordered phases, uniformly arrange of the intragranular nano-sized κ-carbides, dislocation slips, twins and phase transitions.The precipitation of intragranular κ-carbide is a unique strengthening mechanism of austenitic Fe-Mn-Al-C steel containing a large amount of Al and C elements.
The applications of the Fe-Mn-Al-C system steels in the automobiles are still not prevalent due to the lack of knowledge related to application properties so far.The most important reason is that high Al content leads to high Young’s modulus reduction and high Mn content leads to problems such as smelting, continuous casting, and machining.The future developments will therefore have to concentrate on the alloying and processing strategies and also on the methods to increase the Young’s modulus. An improved processing strategy and a high value for the Young’s modulus will go a long way towards upscaling these steels to real automotive applications.
The fundamental research situation and devoment of Fe-Mn-Al-C low-density high-strength steel were summarized.The composition design and the role of alloying elementsof Fe-Mn-Al-C low-density high-strength steel were introduced.The microstructures of Fe-Mn-Al-C low density high strength steel were analyzed.The mechanism of formation of toughness and toughness, stacking fault energy, physical and mechanical properties of Fe-Mn-Al-C series low density and high strength steels were revealed, and the application properties of Fe-Mn-Al-C alloys were discussed.Finally, some future directions of research on Fe-Mn-Al-C system low density steels have been proposed.

Zinc ferrite is a n-type semiconductor with high photocatalytic activity and visible light sensitive, the unique magnetic properties and chemical stability make it widely used in the field of photocatalysis. For various morphology of zinc ferrite, different modification methods can be taken to make it more efficient and practical. In recent years, taking advantage of the zinc ferrite characteristics, the preparation of magnetic recovery and stable performance of the composite photocatalyst has attracted the attention of researchers. In this paper, the basic properties of zinc ferrite as photocatalyst and the preparation methods of various morphology are introduced. The modification technology and modification mechanism of zinc ferrite in photocatalysis are discussed. At the same time, the existing problems and prospects are pointed out.

In the Li-ion batteries (LIBs), one of the main functions of binder is used to stabilize the electrode structure. Although the content of binder is little, it has great influence on the performance of the battery. Polyvinylidene fluoride (PVDF) is the main commercial binder at present, but its application in different kinds of active substances has different defects. Therefore, the appropriate binders should be selected for different cathode or anode active materials. In cathode, lithium iron phosphate (LFP) and ternary materials (NCM) exihibit poor conductivity and ionic conductivity due to their intrinsic crystal constructure. Therefore, the binder with higher ion diffusion coefficient can obviously improve the performance of battery. During the process of charging and discharging, “shuttle effect” is one of the main factors leading to poor performance of lithium sulfur battery. The binders with oxygen-containing functional groups have strong capture ability to lithium polysulfide, which can significantly improve battery performance.
For anode materials in LIBs, traditional PVDF binder is easy to react with carbon based materials to form SEI film. Lithium salt is easily deposited on the surface of the active material, which affects the performance of the battery. Therefore, during the charging and discharging process, the binder that can produce a uniform and stable SEI film can significantly improve the battery performance. Because the SEI film can prevent the active material from falling off and promote Li⁺ migration. Then, the volume of silicon-based anode material changes greatly during the process of charging and discharging, and these volume changes make the active material fall off from the collector easily. The binders with moderate viscoelasticity and three-dimensional network structure can make the volume expanded of the silicon-based anode reversibly and the loss of active material is reduced. Therefore, this type of binder can significantly improve the battery performance. In addition, spinel-structured lithium titanium oxide (LTO) exhibit poor conductivity, conductive polymer binder will be one of main research directions in the future.
This article reviewed the binder applied in different active materials based on Li-ion batteries in recent years. The effects of binders on the Li-ion cells performance were mainly introduced, and future prospects of research and applications of binders in different kinds of LIBs were presented.

Undoubtedly, crystalline silicon solar modules represented by polycrystalline silicon (poly-Si) and monocrystalline silicon (c-Si) play a dominant role in the current photovoltaic market. At present, poly-Si solar modules with low production cost occupy a large market share, but they show relatively low conversion efficiencies. On the contrary, c-Si solar modules with relatively high production cost occupy a smaller market share compared to poly-Si modules, but they behave higher conversion efficiencies. With the progress of silicon material and c-Si wafer cutting technology, the cost of c-Si solar modules is continuously decreasing. There is a booming demand for high-efficient photovoltaic products in the future market. Accordingly, high efficiency c-Si solar cells and modules will be expected to receive more and more attention.
Aiming at further enhancing the device performance of c-Si solar cells, numerous research efforts have been performed, which mainly focus on improving the quality of Si wafers to reduce bulk defects, seeking novel passivation materials to reduce surface and interface defects, developing advanced anti-reflection technology (novel light trapping structures and materials) to raise incident light utilization, introducing low-resistant contact technology to cut down series resistance, optimizing PN junction fabrication and device designs et al. Since 2014, successive breakthroughs of conversion efficiency of c-Si silicon solar cells have been achieved with a current record of 26.6% reported by Kaneka Corp., Japan. c-Si solar cells with efficiency 25% or above include Passivated Emitter and Rear Locally diffused (PERL) cells, Interdigitated Back Contact (IBC) cells, Silicon Heterojunction (SHJ) cells, Interdigitated Back Contact and Silicon Heterojunction (HBC) cells, Tunneling Oxide layer Passivation Contact (TOPCon) cells and polysilicon on oxide (POLO) cells, etc. By analyzing the key technologies of these typical c-Si solar cells, it can be concluded that the contact recombination of metal grid electrodes and c-Si at the surface becomes the key influencing factors for the device efficiency. For the sake of weaken such recombination, one approach is to reduce the direct contact area between metal and semiconductor, such as Passivated Emitter and Rear Cell(PERC), PERL and Passivated Emitter and Rear Totally-diffused(PERT)solar cells. Another approach is to develop novel carrier-selective passivation contact, such as SHJ and TOPCon cells, which can achieve excellent surface passivation, separate and transport carriers without opening holes. In addition, the combination of interdigitated back contact and other device structures has become an inevitable choice to maximize light utilization, including IBC and HBC cells.
In this paper, the typical high-efficiency c-Si solar cells with conversion efficiencies of 25% or above are firstly summarized. The corresponding device structure, key technology and materials are analyzed in detail, respectively. At last, the development trends and future prospects of high-efficiency c-Si solar cells are performed.

The lithium-ion battery anode material have been prepared from humic acid through high-temperature heat treatment. The morphology, microcrystalline structure and electrochemical properties of as-prepared activated material were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical testing system. The results indicated that the humic acid-based graphitized materials showed a more regular graphite lamellar structure, and the degree of graphitization of the materials was also getting higher and higher with the increase of graphitization temperature. The humic acid-based graphitized mate-rials all presented good electrochemical performance. The graphitized material with the temperature of 2 800 ℃ had a first discharge specific capacity of 356.7 mAh/g and a charge capacity of 277.6 mAh/g, and the initial coulombic efficiencies was 77.81%. The capacity retention rate after 50 cycles at 1C and 2C rates was as high as 99.4% and 95.9%, respectively. The above results suggest that the humic acid-based graphitized material is an ideal lithium ion battery anode material.

Synthetic polypeptides from the ring-opening polymerization (ROP) of amino acid N-carboxyanhydrides (NCAs) are a type of natural protein mimics. The unique features of these synthetic polypeptides, including the chemical diversity of amino acids, the unique self-assembly structures and conformation transition, and the desired biological activity and good biocompatibility, enable their broad biological applications. The new ROP method represented by auto-accelerated cooperative covalent polymerization provides a new direction for the efficient preparation of polypeptide materials. Additionally, polypeptides with α-helical or β-sheet conformations can be used as building blocks for self-assembly, forming unique chiral and nanomaterials, which benefit the research on structural and functional biomimetics and biomedical applications. The conformational transitions of polypeptide materials, triggered by pH, light, heat, redox, etc, are always accompanied by the changes in their physical pro-perties (such as hydrophobicity), chemical structures (such as charge reversion), and biological activity (such as cytotoxicity), offering a new strategy for materials to adapt to the changes of biological microenvironment and targeted delivery. As a result, polypeptide materials have shown great potentials in biological applications such as antibacterial, antifouling, antitumor, gene delivery, tissue engineering, and immune regulation. This review offers a retrospection of the research process of synthetic polypeptides materials, which covered advanced preparation methods, assembly structure, conformation transition, and biological applications. In order to provide reference for the further research of synthetic polypeptides, we also raised some important questions for this field.