Performance And Mechanism Of Catalytic Ozonation Of Sulfamethoxazole In Water By Composite Iron–manganese Silicate

With the improvement of people's living standards and health awareness,as well as the rapid development of the chemical technical field,various antibiotic drugs with different therapeutic effect are developed.However,antibiotic have been frequently detected in the aquatic environment due to its huge consumption and unreasonable disposal.Sufficient evidences have proved the unsatisfactory removal of antibiotic in conventional treatment plant.Therefore,the researchers have developed a series of advanced treatment processes to improve the removal efficiency of antibiotic existed in the drinking water and to ensure the water quality safety.Heterogeneous catalytic ozonation combines ozone with the adsorptive and catalytic properties of solid catalyst to completely mineralize organic compounds or decompose them into easily biodegradable compounds at relatively mild operational conditions.In this study,composite iron–manganese silicate oxide(FMSO),a laboratory-synthesized metal silicate oxide,was prepared by a copolymerization precipitation method and used as a heterogeneous ozonation catalyst.The characterization results indicated that the synthesized FMSO was of amorphous structure.The surface morphologies of FMSO presented regular structures,and there were abundant highly dispersed uniform particles on the surface of FMSO.Meanwhile,the interior of FMSO seemed to possess a well-developed porosity structure.FMSO possesses large surface area,high pore volume,and abundant surface hydroxyl groups.The p Hpzc of FMSO was close to neutral.The oxygen element of FMSO' surface mainly belongs to chemisorbed state.Sulfamethoxazole(SMX)was selected as the target compound,the catalytic performance of FMSO for the ozonation of SMX was investigated under semi-continuous mode.Results showed that the presence of FMSO significantly improved the mineralization efficiency of SMX,TOC removal was significantly increased by 52.8% compared to sole-ozonation.In the FMSO catalytic ozonation,the increase of FMSO and ozone dosage have a positive effect on the TOC removal,while the initial concentration of SMX has less relativity with the TOC removal.The present of impurities in the tap water exerted a negative effect on the TOC removal.The presence of Ca2~+,Mg2~+,Na~+,K~+ and NO3-have insignificant effect on the TOC removal,while the presence of Cl-,SO42-and PO43-exerted a remarkable inhibition effect on the TOC removal.The optimum temperature for TOC removal was 25? during catalytic ozonation.The catalytic performance of FMSO remained stable after several times of recycled use and its metal ion leaching is apparently negligible during catalytic ozonation.The physical structures and surface chemical properties of FMSO maintained a good stability during the ozonation process.The kinetics of heterogeneous catalytic ozone decomposition in aqueous solution over FMSO was investigated.Results showed that the presence of FMSO significantly accelerated ozone decomposition rate from 0.022 min-1(without FMSO)to 0.101 min-1.The heterogeneous reactions taken place on the surface of FMSO played a predominant role during the ozone decomposition process.The increase of initial ozone concentration has a positive effect on ozone decomposition.The present of impurities in the tap water could promote the ozone decomposition process,while the presence of HCO3-could inhibit the ozone decomposition process.Effect of inorganic anions and solution p H indicated that surface hydroxyl groups on FMSO were the active sites for catalyzing ozone decomposition and neutral charge surface seemed to show the highest catalytic performance.The increase of calcination temperature exerted a negative effect on the catalytic activity of FMSO.FMSO has a high stability during the ozone decomposition process.A systematic investigation of the cooperation mechanism between adsorption and catalytic reaction during the catalytic ozonation of SMX by FMSO was carried out.The presence of FMSO in the ozonation process effectively enhanced the ozone utilization efficiency and accelerated the transformation of ozone into ·OH radicals.The latter result was verified by the indirect method,using NaHSO3 as the scavenger,and the direct electron spin resonance(EPR)determination technology.The adsorption of SMX on FMSO was minimal(1.8%).However,ozone rapidly converted SMX into various intermediates,which was exhibited by the much higher adsorption affinity on the surface of FMSO than that of SMX.The accumulation of various intermediates on the FMSO surface also increased their contact probability with the ·OH radicals generated by the ozone decomposition.The continuous interaction of intermediates with ·OH radicals could further promote the benign cycling of the release of adsorption sites and the succeeding adsorption/decomposition of ozone and intermediates on FMSO.This could be another reason for the higher and faster TOC removal rate.In both non-catalytic ozonation and catalytic ozonation with FMSO,the degradation of SMX was mainly the direct oxidation of ozone molecules in the initial stage.Meanwhile,large amounts of refractory intermediates such as carboxylic acids were generated.The presence of FMSO could effectively remove these refractory intermediates,leading to the higher TOC removal efficiency.The degradation pathways of SMX was subsequently proposed.