Metal oxychlorides as robust heterogeneous Fenton catalysts for the sonophotocatalytic degradation of 2-nitrophenol

Metal oxychlorides of Fe, Cu, Bi and Zn were prepared and tested in heterogeneous Fenton degradation of 20 ppm of 2-Nitrophenol (2-NP) in the presence of ultrasonic (US, 20 kHz), ultraviolet (UV, 6 W, λ = 254 nm), and US/UV coupled irradiations. The different experimental conditions including the catalysts dosages, hydrogen peroxide concentration, pH value, temperature, pollutant concentration and irradiation time were optimized and the reusability of the tested metal oxychlorides was investigated as well. The capability of 2-NP degradation follows the order US/UV > UV > US. The rate constant of degradation using sonophotocatalytic system was even higher than the sum of rates of individual systems due to its synergistic performance. Times of 30, 40, 50 and 50 min were respectively needed for Fe, Cu, Bi and Zn oxychlorides to accomplish complete degradation under the experimental conditions of 0.1 gL−1 solid, 5 mM H2O2, pH 7 and 25 °C. The rate constant of degradation followed the same order of mentioned metals with values of 0.15, 0.0871, 0.0964, 0.0806, and 0.0738 min−1 for Fe, Cu, Bi and Zn oxychlorides, respectively. The mechanism proposed considers a major role of produced hydroxyl radicals while the difference in band gap energy was emphasized in case of Bi and Zn oxychlorides.