Combining photocatalytic and electrocatalytic oxidation for dibutyl phthalate degradation: the influence of carbon-coated titanium anode and metal oxide catalysts.

Abstract

Plasticisers, such as dibutyl phthalate (DBP), are contaminants of emerging concern (CEC) that are toxic to living things and the environment. Unlike hydrophilic pollutants, DBP shows the characteristics of hydrophilic and hydrophobic nature which makes its degradation or removal difficult using conventional treatment technologies. The current study explored the potential of photocatalysis followed by electrocatalytic oxidation (PC + EC) using vanadium pentoxide (V₂O₅) and carbon-coated titanium (C/Ti) anode for the removal of 75 mg L^-1 DBP from water. The structural stability and changes in the functional groups after treatment of the catalyst were determined using powder XRD and FTIR studies that found the catalyst structure to be stable. Optimization studies showed that UV-A (315-400 nm) irradiation source, 112 mA cm^-2 current density, 50 mg L^-1 catalyst dosage, 360 min PC, 210 min EC at pH 3 and 20 mM sodium sulphate managed to degrade 99.5% of DBP with 97% COD and 87.7% TOC removal. Compared to electrocatalytic oxidation (EC), PC + EC showed 40% higher TOC removal. Reusability studies found the reduction of 45% for COD removal after four treatment cycles with V₂O₅, while the anode material showed no considerable decrease in its degradation efficiency. High-resolution mass spectrometry (HRMS) studies established that complete degradation was preceded by the oxidation of DBP to phthalic anhydride and phthalic acid responsible for the increase in TOC during the initial treatment period. Overall, this study lays out insights for the application of photo-electrocatlytic oxidation for the removal of ubiquitous poorly soluble water pollutants such as phthalates.