Electrochemically assisted photocatalytic degradation of Orange II: Influence of initial pH values

Abstract

The effect of initial pH values in solution was studied in the process of electrochemically assisted photocatalytic degradation (EAPD) of an azo-dye Orange II using a ␤-PbO 2 electrode modified by TiO 2 . The removal of color and total organic carbon (TOC) from the simulated dye wastewater was experimentally investigated at pH 2.29 and 11.52. The degradation products were examined by means of HPLC, UV-vis and FTIR spectra analyses. Similar color removal rate was achieved at pH 2.29 and 11.52, but the removal of TOC at pH 2.29 was 20.0% higher than that at pH 11.52. The dye was oxidized the most completely at pH 2.29 than at 11.52 and 6.88. There was a new absorbance peak at ca. 255 nm generated at ca. 40 min only at pH 11.52, which was ascribed to the quinonic compounds resulted from 1-amino-2-naphtol. A reductive degradation pathway by reductive species such as active electrons was proposed, which only led to the removal of color in parallel with the oxidative degradation pathway. Hole process was proved to be the dominating process at pH 2.29 and the effect of the reductive species was also significant at pH 11.52. Initial pH values were proved to have only influenced the degradation pathways to some extent, and therefore resulted in the disparity of the removal of color and TOC. High mineralization rate was still achieved in spite of the initial pH values in solution due to the prevailing photocatalytic oxidation mechanism.

Study of the degradation of a toxic dye by the catalytic system (H1.5Fe1.5P2W12Mo6O61, 22H2O)/H2O2

“…6, it is clear that the discolorization efficiency decreases with increasing initial concentration of the dye. This result is in good agreement with results reported in the literature, and can be explained by the fact that increasing the initial dye concentration increases the ratio of AY99 molecules to hydroxyl radicals (as the concentrations of H 2 O 2 and the catalyst are fixed), thereby decreasing the discolorization efficiency (Ramirez et al 2007;Li et al 2006;Ji et al 2011). Fig.…”

Electrodeposited lead dioxide coatings

“…152 Recently, the PbO 2 /TiO 2 composites have attracted considerable attention due to their potential application in photoelectrocatalytic oxidation of organics in wastewater. 92,[155][156][157][158] Qu et al 155,156 reported the electrochemically assisted photocatalytic degradation of Acid Orange 7 and an azo-dye Orange II using the PbO 2 /TiO 2 composite electrodes. The degradation efficiencies improved slightly with the TiO 2 content and with increase in potential.…”

Electro-photocatalytic degradation of acid orange II using a novel TiO2/ACF photoanode

“…A major difference can be seen by comparing the percentage of AOII removal with that of TOC removal by the EPC process. The degree of mineralization was lower than that of the decomposition of AOII, which is not uncommon in heterogeneous catalysis (Fernandes et al, 2004;Li et al, 2006;Murugananthan et al, 2007). The cleavage of the AOII molecular structure first occurs at positions that are susceptible to free radical attack with the production of various intermediates.…”