Photocatalytic activity of ZnO impregnated Hβ and mechanical mix of ZnO/Hβ in the degradation of monocrotophos in aqueous solution

Abstract

Adsorption experiments were carried out with monocrotophos (MCP) over supports (Hβ, HY and HZSM-5), ZnO, supported ZnO (ZnO/Hβ(I), ZnO/Hβ(M), ZnO/HY(I), ZnO/HZSM-5(I)) and TiO 2/Hβ. The results revealed that Hβ has better adsorption than HY and HZSM-5. Among the supported catalysts, ZnO/Hβ(I) showed higher percentage of adsorption than others. A series of supported catalysts (impregnation and mechanical mix) were prepared with different ZnO loadings and characterised by X-ray diffraction (XRD), SEM and BET surface area analysis. The photocatalytic degradation of monocrotophos in aqueous solution was carried out by using ZnO, supports and supported ZnO with low pressure mercury lamps. The influence of various parameters such as initial concentration of MCP, pH, catalyst loading and light intensity on the degradation was optimised. It was found that degradation of MCP followed first order kinetics. The experimental results demonstrated that the presence of zeolite in ZnO could enhance adsorption as well as degradation of MCP in aqueous suspension. The optimum loading for impregnated catalysts is 5 wt% whereas 1 wt% for mechanical mix catalyst. The time required for complete mineralisation of MCP under optimal experimental conditions over ZnO, 1 wt% ZnO/Hβ(M) and 5 wt% ZnO/Hβ(I) was 600, 360 and 240 min, respectively. The higher activity of ZnO/Hβ(I) is mainly due to fine dispersion of ZnO and hydrophobicity of the support.