ZnO nano-particle catalysts in contaminant degradation processes with solar light Naked and supported systems

The photo-catalytic degradation of organic contaminants (like dyes, insecticide, pesticide, … etc) in water, air, and soil using ZnO under UV are commonly used procedures. This is due to its low costs, use of sunlight, mild reaction conditions, high photochemical reactivity, low environmental toxicity and stability to photocorrosion. In this work commercial and synthetic nano-particles of zinc oxide and thin films were used in photodegradation of methyl orange (MO) from water under UV-light and direct solar light. ZnSO4.7H2O was used to prepare hexagonal ZnO nano-particles (20-25 nm) by direct precipitation method, and ZnO thin films by chemical bath deposition method. Supported ZnO onto other substances (Activating Carbon, Sand, and Clay to form ZnO/AC, ZnO/Sand, and ZnO/Clay) was also used here to enhance the contaminant photodegradation process. UV-visible scanning, photoluminescence measurements, XRD characterization, and SEM imaging were used to characterize the prepared catalyst systems. Effects of pH, catalytic concentration, contaminant concentration, temperature, and light concentration on photo-degradation rate were studied. Turnover number and Quantum yield were calculated for comparison study. Temperature effect was studied and activation energy was calculated. Photodegradation was faster in neutral medium pH=7. Higher catalyst concentration increased photodegradation, until certain amount then showed no systematic effect. The contaminant concentration speeded up the reaction rate. Temperature showed only small effect on the rate, with only a small calculated value of activation energy. The degradation process was enhanced by concentrating solar light with concaved mirrors. The nano-particle, thin film, and supported ZnO catalyst systems caused complete photodegradation of contaminants after enough time. The ZnO/AC system showed the highest catalyst efficiency. Pre-annealing the ZnO catalysts also enhanced the photodegradation rate.