Photocatalytic degradation of diclofenac using a novel double Z-scheme catalyst (O-g-C3N4/ZnO/TiO2@halloysite nanotubes): Degradation mechanism, identification of by-products and environmental implementation

Abstract

It is challenging and expensive to synthesize multivariate composites with high photocatalytic efficiency and recyclability. Herein, a novel direct double Z-scheme O-g-C3N4/ZnO/TiO2@halloysite nanotubes (HNTs) photocatalyst was synthesized using a simple and low-cost method to degrade and mineralize diclofenac (DCF). During 50 min, O-g-C3N4/ZnO/TiO2@HNTs degraded DCF completely at pH 6.83, 10 mg/L DCF concentration, and 1.0 g/L catalyst, which was 1.66 and 2.4 times higher than ternary O-g-C3N4/ZnO/TiO2 and O-g-C3N4/HNTs/TiO2. Under the same conditions, 35.12 % of DCF was removed from urban wastewater. A negative effect of anions on the process was observed as follows: CO32− > HPO42− > Cl− > NO3−. Under the same conditions, 39.23 % of total organic carbon (TOC) was removed. Moreover, Mott-Schottky analysis and active species trapping experiments were performed to investigate the photodegradation mechanism systematically. It was observed that O2− played a minor part in the photodegradation process, while hole and OH were the more critical reactive species. Several intermediate compounds formed during the photocatalytic reaction were identified by LC-MS analysis. The results showed that a simple design and synthesis of multi-component complex catalysts presented a new insight into removing emerging pollutants from the aquatic environment and apprehending the enhanced photocatalytic mechanism.