Fabrication and Enhanced Photocatalytic Activity of p-n Heterojunction CoWO4/g-C3N4 Photocatalysts for Methylene Blue Degradation

Heterojunction materials have attracted tremendous interest for their potential application in optics and photocatalysis. Herein, we report the synthesis of CoWO4/g-C3N4 heterojunctions by a modified polyacrylamide gel method combined with a facile ultrasound-assisted route. Phase structure and elementary composition characterization confirm that the CoWO4/g-C3N4 heterojunctions consist of CoWO4 and g-C3N4 and no other impurities. Scanning electron microscopy and transmission electron microscopy results demonstrate that CoWO4 and g-C3N4 have particle-like and sheet-like morphologies, respectively. UV-visible absorption spectra reveal that the synthesized heterojunctions have wide visible light absorption over a wavelength range of 500-800 nm. Photoluminescence spectra show that the synthesized heterojunctions possess a strong emission centered at around 440 nm. Time-dependent photocatalytic degradation of methylene blue (MB) indicates that the highest photocatalytic efficiency up to 94.5% after 100 min is achieved over CoWO4/g-C3N4 heterojunctions with a mass ratio 1:2 of CoWO4 to g-C3N4. The photocatalytic efficiency is about 7.8 and 1.5 times that of pure CoWO4 and g-C3N4, respectively. The enhanced photocatalytic activity is mainly ascribed to the synergistic effect between CoWO4 and g-C3N4. A possible photocatalytic mechanism of CoWO4/g-C3N4 heterojunctions was proposed. Trapping experiments confirm that hydroxyl radical (center dot OH) is the main active species in the process of MB degradation. The prepared heterojunctions exhibit considerable potential for use as functional optical materials and photocatalysts.