ZIF-67/CoOOH cocatalyst modified g-C3N4 for promoting photocatalytic deep oxidation of NO

Abstract

The removal of nitrogen oxides (NOX) by semiconductor photocatalysis is an emerging technology in recent years. However, due to incomplete oxidation, the photocatalytic oxidation of NOX is usually accompanied by the generation of toxic intermediate by-products nitrogen dioxide (NO2), which causes secondary pollution and seriously limits its practical application. To tackle the issue, ZIF-67/CoOOH (ZIF-CH) cocatalyst was constructed via flexible strongly alkali oxidation treatment to modify g-C3N4, in which ZIF-67 was selected as a cobalt source of CoOOH. XRD, SEM, TEM and XPS demonstrated the ZIF-CH was successfully synthesized and anchored on CN. UV–vis, PL, EIS, transfer photocurrent response and DFT indicated that the introduction of ZIF-CH enlarged the response range to visible light, favored the separation and transfer of carriers and improved NO/NO2 adsorption ability. Consequently, the optimized ZIF-67/CoOOH/g-C3N4 (ZIF-CH/CN) exhibited a superior NO removal efficiency of 52.5% without any generation of toxic by-product NO2, and the cycling tests indicated the high stability of ZIF-CH/CN was obtained. In-suit DRIFTS and ESR were used to investigate the reaction pathway by comparing adsorption energy and detecting the reaction intermediates and products. More importantly, this result reveal that amount of hydroxyl radical (·OH) increased after introducing ZIF-CH cocatalyst, which promotes the deep oxidation of NO. These findings could supply a convenient and effective strategy for the design of a cocatalyst to enhance the photocatalytic oxidation performance of NO and inhibit the production of toxic by-product NO2.