Fabrication and Enhanced Photocatalytic Activity of p–n Heterojunction CoWO/g-CN 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 CoWO/g-CN heterojunctions by a modified polyacrylamide gel method combined with a facile ultrasound-assisted route. Phase structure and elementary composition characterization confirm that the CoWO/g-CN heterojunctions consist of CoWO and g-CN and no other impurities. Scanning electron microscopy and transmission electron microscopy results demonstrate that CoWO and g-CN 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 CoWO/g-CN heterojunctions with a mass ratio 1:2 of CoWO to g-CN. The photocatalytic efficiency is about 7.8 and 1.5 times that of pure CoWO and g-CN, respectively. The enhanced photocatalytic activity is mainly ascribed to the synergistic effect between CoWO and g-CN. A possible photocatalytic mechanism of CoWO/g-CN heterojunctions was proposed. Trapping experiments confirm that hydroxyl radical (·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.