Oxidative degradation of phenol by manganese dioxide

Manganese dioxides(δ-MnO2)mainly exist in the form of vernadite and birnessite in the natural environment,which are considered to be important oxidants during the abiotic transformation of phenolic compounds.In this study,δ-MnO2 was synthesized by a facile method,and its ability for the degradation of aqueous phenol was investigated.Impacts of solution pH,δ-MnO2 loading,ionic strength,coexistence metal ions,and humic acid on the degradation of aqueous phenol were studied.The optimum solution pH and δ-MnO2 loading were determined to be 3.62 and 0.13 mg·L-1,respectively.The coexistence of Na + and Mn2 + showed inhibition effect on the oxidative degradation process,while Mg2 + and Ca2 + did not show any obvious effect during the experimental process.The removal efficiency of phenol decreased from 96.9% to 78.9% when the concentration of humic acid in the reaction solution increased from 1 mg·L-1 to 5 mg·L-1.GC-MS was applied to identity the reaction intermediates,and hydroquinone was found to be the main reaction intermediate in the degradation system.Based on the above observations,the possible degradation pathway of phenol by δ-MnO2 was proposed.