Highly efficient photocatalytic degradation of lignin by hydrogen peroxide under visible light

The photooxidative degradation of lignin, a common constituent of waste water effluent discharged from paper and pulp industry, is investigated via representative model compound, guaiacylglycerol-beta-guaiacyl ether and alkaline lignin under UV-vis radiation. Hydrogen peroxide along with visible irradiation is found to be a clean homogenous photocatalytic system for effective deconstitution of highly intricate structure of lignin. Reactions were conducted in the range of 30 200 mg L-1 of lignin with varying molar H2O2: lignin ratios. About 95 % degradation was achieved for model compound, whereas maximum of 90 % of decomposition was obtained for alkaline lignin within duration of 45 60 min. Almost total discoloration of alkaline lignin along with 64 % decrease in chemical oxygen demand value, was obtained within 1 h of photodegradation. Both hydydroxyl (OH) and superoxide (O2.-) radicals, generated from hydrogen peroxide interact with the phenolic moeties in an integrated manner, resulting in complete photodegradation of lignin.