NaNO2/FeCl3 catalyzed wet oxidation of the azo dye Acid Orange 7

A combination of ferric chloride and sodium nitrite significantly improved the wet oxidation of the azo dye Acid Orange 7 (AO7) in acid aqueous media (pH 2.6) under moderate conditions (T = 150 °C; oxygen pressure = 0.5 MPa). To evaluate the catalytic system, wet oxidation of AO7 was carried out at temperatures between 90 and 150 °C and oxygen pressures ranging from 0.1 to 0.5 MPa. The effect of initial solution pH from 2.6 to 11.4 and the amount of catalyst on the degradation of AO7 were also investigated. AO7 initial concentration was kept 200 mg L−1. The degradation process was monitored by UV–visible spectroscopy, HPLC, IC (ion chromatography), GC–MS and TOC analysis. At 150 °C and 0.5 MPa oxygen pressure, 56% TOC was removed after 4 h of treatment, while no obvious TOC removal were achieved without catalyst at the same experimental condition. The main degradation products were some small organic acids: formic acid, acetic acid, pyruvic acid, oxalic acid, succinic acid (identified and quantified by IC) and phthalic acid (identified by GC–MS).