Activation Of H₂O₂by Cobalt Oxamate Complexes For The Catalytic Degradation Of Dyes

With the development of industry, water pollution becomes more and more seriousand leads to environmental and public safety issues. Industrial discharge sewage oftencontains organic aromatic compounds, such as chlorophenols、polycyclic aromatichydrocarbons、environmental hormones、dyes and other pollutants. Textile waste wateraccounts for a large part of industrial sewage, since a large mount of water andchemicals were used in textile process, and the wastewater is featured by highconcentrations of residual dyes, a high concentration of inorganic salts, high COD, hightoxicity and low biodegradability, etc. Therefore, a single methods of biological orphysical can not completely remove contaminants especially for stubborn dyes. Further,additives such as inorganic salts, the hydroxyl-containing compounds can capturehydroxyl radicals, which limited the advanced oxidation processes based on themechanism of hydroxyl radicals. Therefore, to develop more efficient and greenchemical treatment which regardless of interference of background materials, likeinorganic salt，is of great significance.Square-planar metal oxamate complexes are formed by a metal ions with oxamateligands amide nitrogen atoms and carboxylate oxygen atoms. The cobalt ions with d6configuration in a coordination environment of N2O2form square-planar cobalt(III)oxamate complexes that ground state is the spin triplet state(S=1). This is determinedby the nitrogen atoms with large electron-donor capacities and the square-planarcoordination environment. Activated H2O2by the cobalt(III) oxamate complexes toproduce high valence cobalt species which degraded organic dyes in textile wastewater.Such active species can avoid being caught by radical scavengers, like inorganic ions,hydroxyl group-containing compounds etc.In this paper，An unsubstituted, nitro and methyl group substituted cobalt(III)oxamate complexes were prepared ([Co(opbaX)],(X=H、NO2、CH3)). The structuresand cobalt valence of complexes characterized by high resolution ESI-MS and MS/MS,XPS,1H NMR, FTIR, which showd that different kinds of trivalent cobalt complexes were successfully synthesized. The catalystic performance of [Co(opbaX)]/H2O2sysstem was studied by catalystic oxidation of Acid Red1(AR1). We found that thecatalystic system not only can effectively remove a variety of organic dyes, but also hasbetter sustaining catalytic ability. Moreover, the catalystic performance of[Co(opbaNO2)]/H2O2was better than two other systems, so electron-deficientcoordination environment of oxamate cobalt complex can enhanced the ability ofactivation of H2O2. We investigated temperature, pH, H2O2concentration and inorganicsalts on [Co(opba)]/H2O2system to decolor dyes. The apparent rate constant was foundto increase with increasing temperature at pH8.0-11.0, and the maximum in the rangeof pH9.0-9.5, the activation energy is27.8KJ/mol. In addition, NaCl and Na2SO4haveno inhibitory effect on the catalytic system. EPR experiments, high-resolution ESI-MSdetection and density functional theory calculations show that cobalt complexesactivated H2O2by heterolysis and produced high valence cobalt species [CoIV=O] tooxidative degradation of organic dyes.[Co(opba)] were loaded on pyridine modified MWCNT surface (Coopba-Py-MWCNTs.) and characterized by TGA, UV-vis and XPS which showed that[Co(opba)] have successfully loaded through coordination between pyridine nitrogenatom and cobalt ion. The system of Coopba-Py-MWCNTs/H2O2is also able to removethe dye AR1, and have good performance in situ regeneration and recycling. We alsostuded pH, temperature, H2O2concentration on Coopba-Py-MWCNTs/H2O2systemrespectively. The results showed that Coopba-Py-MWCNTs/H2O2system can removeAR1effectively at pH8.0room temperature and have good pH adaptability comparedwith homogeneous [Co(opba)] used alone. The reaction rate increases with the risingof temperature and the activation energy is33.4KJ/mol. Coopba-Py-MWCNTsactivated H2O2via heterolytic cleavage of O-O bond and produced similarly highvalence cobalt species to attack the dye molecule, which verified by isopropanolexperimental.