Resourceful Treatment Of Aniline Wastewater Using Persulfate Activated By Copper-Based Catalysts

The advanced oxidation processes（AOPs）on the basis of persulfate（PS）have been paid more attention in the oxidation of various organic pollutants,and how to resourceful utilization of the organic contaminants from wastewater is still a problem that needs to be solved.In this study,we used CuO and uniformly dispersed Cu-N-C as catalysts to activate PS to oxidize aniline to polyaniline polymers under pH-neutral and alkaline conditions,and then analyzed the structure of the oxidaiton products and investigate the reaction mechanism.Our results show that PS can be effectively activated by CuO and remove aqueous aniline under pH-neutral and alkaline conditions.Under the conditions of pH7.0,1 g L^-1 CuO and 2.3 mM PS,95.2%of 1.2 mM aniline could be removed within60 min,and the reaction rate constants（k）increased with increasing pH values,indicating that aniline oxidation was more favorable at high concentrations of OH^-.The experimental results also show that the PS required to remove 1 mol of aniline was relatively low（1.19 mol at pH 7.0 and 1.68 mol at pH 12.0）,whereas 18 mol aniline was required to completely mineralize 1.0 mol aniline theoretically.Such a difference indicates that aniline was not completely mineralized.The quenching experiments and EPR analysis ruled out contributions of sulfate radical(SO4^·-),hydroxyl radical（·OH）and superoxide radical(O₂^·-),indicating that PS was activated on the surface of CuO by via a non-free radical mechanism.By means of FTIR,¹H NMR and other characterization methods,we deduce that the insoluble solid products are primarily composed of polyaniline（PANI）with the structural unit of-C6H4-NH-.EPR,UV-vis and GC-MS analyses further suggested that an electron is transferred from aniline to the activated PS to form PhNH2^·+,followed by abstraction of H⁺from PhNH₂^·+to generate PhNH·and subsequently polymerization of PhNH·to PANI.PANI generated under different pH conditions show high thermal stability and ideal pseudocapacitance,indicating that PANI generated from aniline wastewater can be used as high-temperature resistant materials or capacitors.To further determine the role of Cu in the catalytic process,we prepared uniformly dispersed Cu-N-C and used them to activate PS to remove aniline under pH-neutral and alkaline conditions.Under the conditions of pH 7.0,0.2 g L^-1 Cu-N-C and 2.3 mM PS,more than 98%of 1.2 mM aniline could be removed within 3 h with the reaction rate constant of 1.9×10^-1mM^-1min^-1.Although EPR analysis indicates the presence of·OH,SO₄^·-and CCRs in the reaction system,quenching experiments rule out contributions of·OH and SO₄^·-,implying that PS is activated on Cu-N-C via the nonradical mechanism.XPS analysis of Cu-N-C before and after the reaction indicate that Cu（I）on the surface of Cu-N-C play important roles in PS activation,followed by subsequent oxidation of Cu（I）to Cu（II）.UV-vis,GC-MS and FTIR analyses further indicate that aniline was first converted into polyaniline radical,and then the polyaniline radical was decomposed to hydroxyl aniline,p-iminoquinone and aniline dimers.This study provides a new insight on the resourceful utilization of aniline contaminants from wastewater.