Novel Cyclic Process Mediated by Copper Oxides Active in the Degradation of Nitrophenols:  Implications for the Natural Cycle

Direct photolysis was not found to be effective in the degradation of nitrophenols. Biological degradation is known to be slow (a few days) and not to proceed at all in the case of dinitropenols. These later compounds are not biocompatible toward common biological degradation. Different copper oxides were used in the present study in thermal and light-induced reactions to degrade a variety of nitrophenols in the presence of oxygen. The highest rate of degradation was observed with a large surface area CuO aerogel (20 m2/g). The aim of this study was threefold: (1) to report the details of the reaction leading to nitrophenols degradation by different copper oxides or Cu salts, (2) to use dioxygen as the oxidant instead of the more costly peroxides currently used, and (3) to explore the effect of the number and position of the substituent groups on the rate of degradation. The results obtained indicate that up to 10 consecutive catalytical degradation cycles for 2-nitrophenol were successfully mediated by CuO aerogel under light. The oxidant used was air (O2) at pH 2.5. The oxidation potential for the couple Cu+/Cu2+ in the CuO aerogel, was found to be different from the standard values reported in solution. Photodegradation of dinitrophenols were observed via the CuO aerogel, but the mineralization was not completed over 24 h. The degradation and photodegradation via the Cu catalyst used led to partial mineralization of the substrate with the formation of CO2, H2 (relatively small amounts), nitrite, nitrate, ammonia, and insoluble polymer.