Catalytic degradation of real-textile azo-dyes in aqueous solutions by using Cu–Co/halloysite

Abstract

Catalytic degradation of textile dyes in diluted aqueous solutions with minimal consumption of energy is a great challenge for wastewater treatment and environmental protection. Efficient heterogeneous catalysts are needed to completely oxidize azo-dyes under soft conditions. In this work, catalysts of Cu–Co oxide (1:2 molar ratio) supported on halloysite (Ha) nanotubes (CuCo(5%)/Ha and CuCo(10%)/Ha) were synthesized and used in the catalytic wet peroxide oxidation of reactive yellow 145 (RY-145) and basic red 46 (BR-46). The catalysts were characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, \(\hbox {N}_{2}\) adsorption isotherms, scanning electron microscopy and transmission electron microscopy. The results showed that the synthesized catalysts possess nanotubular structure with good mesoporosity, and the spinel structure \(\hbox {CuCo}_{2}\hbox {O}_{4}\) was identified as the active phase deposited on Ha. The catalysts degraded these azo-dyes in diluted solutions (\(22\, \hbox {mg l}^{-1}\) of RY-145 and \(35\, \hbox {mg l}^{-1}\) of BR-46) under mild reaction conditions (\(25^{\circ }\hbox {C}\), atmospheric pressure, pH 4 and minimum amounts of both catalyst and \(\hbox {H}_{2}\hbox {O}_{2})\). Significant levels of dye conversion (\(93.1\pm 2.2\%\) for RY-145 and \(54.4 \pm 2.0\%\) for BR-46) were achieved in a relatively short time. In addition, significant values of total organic carbon removal (\(59.5 \pm 1.8\%\) for RY-145 and \(33.9 \pm 1.4\%\) for BR-46) were obtained, indicating the total oxidation of a significant fraction of these dyes to \(\hbox {CO}_{2}\) and \(\hbox {H}_{2}\hbox {O}\).