Modification of Carbon Nitride Photocatalysts by Copolymerization with Diaminomaleonitrile

g-C3N4 photocatalysts were synthesized by copolymerization of diaminomaleonitrile (DMNA) with dicyanodiamide (DCDA) at high temperatures. The effect of copolymerization on the crystal structure, chemical structure, band structure, texture, optical property, and photocatalytic performance of g-C3N4 was studied by such characterization techniques as X-ray diffraction (XRD) patterns, Fourier transformed infrared (FTIR), transmission electron microscopy (TEM), nitrogen-sorption (N-2-sorption), electron paramagnetic resonance (EPR), ultraviolet-visble diffuse reflectance spectra (UV-Vis DSR), and photoluminescence (PL) analyses. Results demonstrated that the graphitic-like layer packing structure of g-C3N4 remained unchanged after the modification; however the copolymerization with DMNA can efficiently extend the delocalization of pi-electrons and induce the formation of surface junctions, greatly enhancing the light-harvesting ability of g-C3N4 in visible light region and promoting the separation of photogenerated charge carriers, respectively. Photocatalytic performance showed that all DMNA-modified samples presented an enhanced H-2 evolution activity under visible light irradiation. The optimized weight-in amount of DMNA is found to be 0.01 g, by which the modified sample shows the highest hydrogen evolution rate of 45.0 mu mol . h(-1). This value is 4.5 times as high as that of the unmodified carbon nitride sample.