Simultaneous formation of mesopores and homojunctions in graphite carbon nitride with enhanced optical absorption, charge separation and photocatalytic hydrogen evolution

Graphite carbon nitride (CN) is considered as a promising photocatalyst for solving current energy and environmental crises, but its practical application is still restricted by fast recombination of photogenerated charge carriers, low specific surface area, and narrow visible light absorption range. Herein, oxygen-modified CN (MCN) with simultaneous formation of massive mesopores and homojunctions was successfully synthesized by calcining the precursor, a cyanuric acid (CYA)-loaded melamine (MA) hierarchical structure composed of nanobelts, which was prepared for the first time. MCN exhibits accelerated charge separation, increased specific surface areas, and enhanced visible light absorption, compared with CN, and these jointly render the photocatalytic hydrogen evolution rate of MCN (934 μmol h −1  g −1 ) be about five times higher than that of CN (163 μmol h −1  g −1 ). MCN also exhibits much faster singlet oxygen generation and higher photoactivity in organic degradation. The MA hierarchical structure and CYA synergistically formed the new mesopores and C O C bonds in MCN, which cause prominent upper shift of the Fermi level and enhanced photoabsorption of MCN. Besides, electronic microscopy images distinctly show two different sorts of regions in MCN, i.e. those with massive and few mesopores (marked as MPCN and NPCN), respectively. Therefore, MPCN/NPCN homojunctions were probably constructed in MCN, which leads to the accelerated charge separation. This work gives a way to form simultaneously mesopores and homojunctions in CN and illustrates the formation mechanism, which can effectively direct synthesis of similar photocatalysts.