Recent advances in metal nanocluster-modified g-C3N4 for photocatalysis
In recent years,industrialization and urbanization have led to global energy shortages and environmental pollution.There is an urgent need to explore new green technologies to address the energy and environmental crises.Semiconductor photocatalytic technology has been widely applied in various fields,such as carbon dioxide reduction to produce methane,water splitting to generate hydrogen or oxygen,and environmental purification,owing to its economic adaptability and mild reaction conditions.The rapid development of photocatalytic technology has become an effective means of solving energy and environmental issues,with the development of efficient photocatalysts at the core.Semiconductor graphitic carbon nitride(g-C3N4)is an organic polymer semiconductor composed of sp2-hybridized carbon and nitrogen atoms interconnected by covalent σ bonds and π bonds.It forms a network structure consisting of infinite extension of triazine or tri-s-triazine ring units.g-C3N4 functions as a non-metallic and attractive photocatalytic material owing to its visible-light response,earth abundance,chemical-thermal stability and high yield.Therefore,g-C3N4 is a suitable environmentally friendly photocatalysts.However,the C-N forming π-conjugated planes along with relatively small electron mean free path(～10nm)can result in the rapid recombination of photogenerated electron and hole pairs,which behaves with limited photocatalytic performance.Theoretically,g-C3N4 shares the interlayer bonding form of van der Waals forces with graphene.Bulk g-C3N4 samples prepared by the thermal polymerization of nitrogen-containing precursors,however,always exhibit limitations such as a narrow visible light absorption range and a deficiency of active sites.Therefore,we aim to tune the internal electron arrangement,change the surface microstructures,and create new and similar electron excitation orbital directions to improve the photocatalytic performance of g-C3N4.Metal cluster modification exhibits high catalytic activity and selectivity owing to its unique structural advantages,surface effects and quantum size effects.The introduction of metal clusters into g-C3N4 offers multiple advantages:(1)Providing increased specific surface area and rich active sites for surface reactions;(2)enabling precise control of the number and structure of constituent atoms,thereby establishing a clear structure-activity relationship and offering an ideal theoretical model for studying photocatalytic mechanisms;(3)serving as a structural basis to construct a variety of metal nanocluster-derived materials,thus expanding the functionality and activity of catalysts;(4)altering the chemical composition and geometric structure to regulate the electronic band structure and optical properties,effectively improving the performance of photocatalysts and promoting synergistic interactions between components;(5)being easy to recover and reuse,meeting the needs of large-scale production and green chemistry.This article reviews recent studies on the enhancement of the redox properties of g-C3N4 through its combination with metal clusters.This paper provides a detailed introduction to various types of metal clusters and explores multiple modification methods,such as heterostructure construction,elemental doping,and defect engineering.Additionally,we systematically categorize and summarize these modification strategies,covering the current preparation methods and their impact on improving the performance of photocatalysts.This article also highlights the challenges faced by metal cluster-modified g-C3N4 in applications,such as photocatalytic hydrogen evolution,carbon dioxide reduction in the energy sector,and the removal of gaseous pollutants,wastewater treatment,and elimination of organic pollutants in the environmental sector.Finally,we propose suggestions for future research directions,particularly further studies on modification strategies and their preparation methods,to enhance the application efficacy of g-C3N4 in the areas mentioned above.
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