Energy Band Engineering of Polymeric Carbon Nitride with Indium Doping for High Enhancement in Charge Separation and Photocatalytic Performance

Metal doping is a valid strategy to increase simultaneously photoabsorption, the charge separation efficiency, and thus the photocatalytic activity of polymeric carbon nitride (CN); however, metal elements in groups IIIA-VA in the periodic table are rarely researched in doping CN. Herein, indium (In)-doped CN (In:CN) was first synthesized with In3+ ions inserted in the interlayer, approaching the cavities in the monolayer sheets, and fixed through coordination with nitrogen atoms around them. In:CN exhibits a higher photoabsorption, specific surface area, charge separation and transfer efficiency, and photocatalytic performance in H-2 generation and environmental remediation than bulky CN. The H-2 generation and rhodamine B decomposition rates for In:CN are similar to 2.9 and 4.6 times those for CN, respectively. The apparent quantum yield (420 nm) of In:CN for H-2 production can reach 6.8%. The enhancement in charge separation plays an indispensable role for the photoactivity increase of In:CN, which originates from the generation of an impurity level above the valence band edge in the bandgap because of the In doping, i.e., the In3+-coordination structure works as a hole-capture center. This paper supplies an easy method for CN modification and illustrates the mechanism for In-doping-induced change of the energy band structure, which may guide the preparation of other CN-based photocatalysts with metal doping.