Heat treatment effect of zinc oxide on the sonocatalytic degradation of organic dyes

Abstract

Sonocatalytic degradation of Methyl Orange in a 40 kHz, 124 W ultrasonic bath was carried out in the presence of zinc oxide (ZnO) catalyst. The catalysts were subjected to heat treatment from 200 °C to 800 °C for 2 hours and were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. XRD confirmed that no phase change occurred even though calcined up to 800 °C whereas SEM showed that catalysts started to undergo aggregation when the heat treatment temperature was raised to 600 °C. The effect of initial dye concentration, catalyst loading, pH and hydrogen peroxide (H2O2) concentration on the sonocatalytic activity were carried out at 2.5 mg/L to 12.5 mg/L, 0.2 g/L to 1.0 g/L, pH 2 to pH 10 and 0.5 to 2.5 mmol/L, respectively. The optimum operating conditions discovered were 2.5 mg/L initial dye concentration, 0.8 g/L catalyst loading, pH 6 solution and 1.0 mmol/L H2O2 concentration, which successfully removed 71.42 % of Methyl Orange in 1 hour. The sonocatalytic degradation efficiency of the reused catalyst were 64.4 % and 59.6 % in the subsequent usage.