Photocatalytic degradation of highly refractive phenolic polymer - Mechanistic insights as revealed by Electron Spin Resonance (ESR) and solid-state 13C NMR spectroscopy

•Photo catalytic degradation of recalcitrant phenolic polymer was studied.•pH and concentration was affected the adsorption of syntan on TiO2 surface.•EPR study was conformed that OH is a major radical for syntan degradation.•Possible pathway of phenolic degradation is proposed by magnetic resonance study.•Electro-oxidation was attempted to achieve complete mineralization.

The degradation of phenolic syntan by photocatalytic process was studied in a re-circulated batch reactor. Degradation was followed by analysing the Total Organic Carbon (TOC) of syntan solution. The effect of solution pH and the initial concentration of phenolic syntan on photocatalytic degradation rate were discussed. It was observed that the degradation is better under alkaline pH and very low concentration of phenolic syntan. The adsorption of phenolic syntan on TiO2 surface was also considered using in situ ATR FT-IR spectroscopy. It was observed that the adsorption of syntan on TiO2 catalyst is prominent at acidic pH. Poor degradation under acidic conditions was attributed to the adsorbed syntan which act as barrier for the penetration of UV radiation. The generation of hydroxyl free radicals during photo-oxidation was investigated by ESR spectroscopy and found that above pH 9.0 is more congenial for hydroxyl radical generation. The degradation of phenolic syntan was found to follow the first-order kinetics. The samples of syntan solution collected during the course of photocatalysis, were analyzed by NMR spectroscopy to understand the degradation path. The presence of aromatic moiety in the samples clearly revealed that the degradation is incomplete even after three hours of photocatalysis. Since the degradation is incomplete, electro-oxidation was attempted to achieve the complete mineralization of phenolic syntan.