Performance deterioration of Sb-SnO2/C membrane anode treating phenolic wastewater and anode regeneration: Adsorption and physicochemical change of catalysts

Stability of anodes is the core of electrochemical oxidation (EO), but there still lacks systematic investigation on the stability of anodes under the conditions of long-term wastewater treatment. Sb-SnO2 anode was selected for investigation in this study due to its outstanding electrocatalytic activity. The sol–gel method was utilized to coat the Sb-SnO2 onto a carbon membrane to form the Sb-SnO2/C membrane anode, and its stability during long-term treatment of phenol was studied in an electrocatalytic membrane reactor. The results showed that the COD removal efficiency of Sb-SnO2/C dropped from 80.6% to 41.3% after 6 days. Carbonaceous intermediates were found to be adsorbed onto Sb-SnO2/C, mainly including aromatic intermediates and fatty acids. The adsorption of benzoquinone had a significant adverse impact on the phenol degradation of Sb-SnO2/C, leading to a decreased COD removal efficiency. The formation of Sn(OH)4, decreased crystallinity of Sb-SnO2, and the reduced Sb/Sn of the used Sb-SnO2/C were also proposed to lead to the performance deterioration. NaOH cleaning (pH = 11.9) was able to remove the adsorbed carbonaceous intermediates and improved the COD removal from 41.3% to 64.3%. Recalcination after chemical cleaning could further improve the COD removal efficiency to 89.7%, close to the initial value.