Ag nanoparticles decorated Z-scheme CoAl-LDH/TiO2 heterojunction photocatalyst for expeditious levofloxacin degradation and Cr(VI) reduction

Abstract

Conventional type-II heterojunctions are unable to degrade pollutants efficiently owing to their insufficient redox capacities. Z-scheme heterojunctions have therefore been considered as potential heterojunctions for the efficient degradation of organic pollutants due to their ability to maintain an adequate concentration of redox holes and electrons. In this paper, the preparation of Ag nanoparticles (NPs) decorated Z-scheme heterojunction photocatalyst composed of a CoAl-layered double hydroxide (LDH) and TiO2 is reported. This system was found to exhibit a superior photocatalytic activity in the degradation of the levofloxacin (LVFX) and Cr(VI). The Ag-CAT (12 h) catalyst exhibited the highest kinetic constant for the photocatalytic degradation of LVFX (K = 0.02588 min−1), and this value was 5.93 and 6.95 times greater than the corresponding values for TiO2 (K = 0.00476 min−1) and CoAl-LDH (K = 0.00372 min−1), respectively. A similar effect was also observed for the reduction of Cr(VI). Upon investigating the source of this excellent catalytic activity, it was found that the internal electric field in the CoAl-LDH/TiO2 heterojunction functions as a driving force to facilitate the efficient separation of photogenerated charge carriers, thereby generating holes and electrons with a high redox ability and realizing the effective elimination of a pharmaceutical and a heavy metal pollutant. Finally, the formation of internal electric field dominated Z-scheme CoAl-LDH/TiO2 heterojunction and the photocatalytic mechanism of Ag NPs decorated Z-scheme CoAl-LDH/TiO2 heterojunction photocatalyst was described in detail.