Designing an in-situ embedment of citric acid@HAp/ZnO as a Z-scheme heterojunction for substantial enhancement in photocatalytic degradation of malachite green under visible light

Abstract

The infiltration of organic dye pollution into aquatic ecosystems presents a serious hazard to the health of humans and animals, as well as the stability of the ecological system. Malachite green (MG) is one of the refractory contaminants that is frequently found in textile effluent. This study focused on examining the photocatalytic degradation of MG dye with the use of a heterogeneous hybrid citric acid modified Hydroxyapatite and Zinc oxide (CA@HAp/ZnO) photocatalyst. The CA@HAp/ZnO photocatalyst was synthesized and characterized through various analytical techniques such as FTIR, SEM, EDX, XRD, XPS, BET, TGA, PL, and UV-DRS. Optimization of parameters including solution pH, dose of the prepared photocatalyst, irradiation time, and initial dye concentration was carried out using the batch method. The enhanced photocatalytic performance is observed due to the direct Z-scheme mechanism which successfully separated electron-hole pairs, acquired within a minimum dosage of 10 mg and after 40 min at near neutral pH, reached its maximum degradation efficiency of 98.75% under visible light. Additionally, in five consecutive cycles CA@HAp/ZnO demonstrated excellent photocatalytic-stability for the degradation of MG with a negligible decrease in catalytic activity. The application of LC-MS enabled the identification of potential oxidative pathways for MG, along with the detection of reaction intermediates. This research offered a realistic arrangement and boosted photocatalytic activity for the beneficial clean-up of dyes from contaminated water without generating any secondary pollution.