Abstract: As a cost-effective, chemical stability, narrow energy band gap photocatalyst,graphitic carbon nitride (g-C3N4) has been noticed in the materials science. Pure g-C3N4 suffers from the fast recombination of photoinduced electron-hole pairs, insufficient sunlight absorption, low surface area. Typically, element doping and heterojunction based on g-C3N4 is known to be an efficient method to improve its photocatalytic performance, because g-C3N4 is polymer which is suitable for preparing composites based on its matrix. Different from the covalent bonding of non-metal doping, alkali metal-doped g-C3N4 and alkali-earth metal-doped g-C3N4 has been a hotspot due to the delocalization of metal doping,which endows the doped system with unique photocatalytic properties by providing more active sites, lowering the recombination of photoinduced electron-hole pairs and changing the band position. Considering economy and practicality,g-C3N4 modified with alkali metal and alkali-earth metal has been mostly prepared via lithium (Li), So-dium (Na), potassium (K), barium (Ba), magnesium (Mg) and calcium (Ca). The researches show that Li and Ca have better effect on the photocatalytic performance of g-C3N4, especially Ca. Moreover, the photocatalytic activity of g-C3N4 is expected to be further improved by diffe-rent preparation technology, such as different precursors selection, mesoporous material as catalyst carrier, the heating mode selection (controlling the heating rate, temperature and duration). The theoretical basis of alkali metal-doped or alkali-earth metal-doped g-C3N4 is the introduction of metal ions will have an impact on the band structure and carrier mobility. But the interaction of metal ions with surrounding atoms and the mechanism of modifying bandgap have not been determined, the realization of the controllable modification of alkali metal-doped or alkali-earth metal doped g-C3N4 is still to be studied. The syste-matic research of alkali metal-doped and alkali-earth metal doped g-C3N4 needs lots of experiments to form the basis of analysis and verification. This review concludes the development status of alkali metal-doped g-C3N4 and alkali-earth metal-doped g-C3N4, and provides elaborate descriptions about the preparation and application of modified g-C3N4. The photocatalytic activities of different modified g-C3N4 in practical application fields (nitrogen oxides removal, photocatalytic hydrogen evolution, degradation of organic pollutants) are compared. According to the types and quantities of doped elements, the catalyst is divided into single-doping and co-doping, and the enhancement mechanism is reorganized. This article presented the crucial issues of alkali metal-doping and alkali-earth metal-doping that need to be addressed in future research.
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