| In recent years,the continuous use and accumulation of drugs and personal care products(PPCPs)cause a serious threat to the ecological environment and human health,and it is of great significance to develop efficient physical and chemical treatment methods.Advanced oxidation technology based on·OH or SO4·-has attracted wide attention because of its strong oxidative decomposition ability of refractory organic pollutants.At present,one of the research hot areas focuses on highly efficient heterogeneous catalysts as well as their solid-liquid interfacial catalytic oxidation mechanism.In this study,composites were prepared by carbon quantum dotsand maghemite(CQDs@?-Fe2O3)using the hydrothermal method,and the efficient degradation of typical pharmaceutical sulfamethoxazole(SMX)in visible light activated PDS(vis-CQDs@?-Fe2O3/PDS)and UV-oxalic acid chemical in-situ oxidation(UV-CQDs@?-Fe2O3/OX)systems were demonstrated respectively.Effects of important operational parameters were investigated and the realted solid-liquid interfacial degradation mechanisms were revealed.As well,the role of CQDs was further evidenced by the density functional theory(DFT)calculation.The main results are listed as follows:(1)CQDs@?-Fe2O3 would perform best in activating PDS under visible light irradiation as the ratio of CQDs/?-Fe2O3 equal to 0.05 g/g.Increase of catalyst dosage,PDS concentration and reaction temperature would beneifit for the degradation of SMX.Based on the invesiation of the iron evolution,it could be concluded that a heterogeneous-homogeneous iron cycle would occur in the Vis-CQDs@?-Fe2O3/PDSsystem,while CQDs would accelerate the interfacial transfer of the photo-generated electron from?-Fe2O3 to the surface adsorbed or homogeneous Fe3+,resulting ingeneration of Fe2+for PDS activation to produce SO4·-.(2)UV-CQDs@?-Fe2O3/OX system could achieve complete degradation of SMX within 30min of reaction time,which was rather more rapid than the related UV/?-Fe2O3/OXsystem.Reaction conditions were optimized as:p H of 3.0,[OX]of 0.2 m M,and catalyst of 0.1 g/L.The main reactive species in the system were examined as O2·-and·OH,also a little of CO2·-,and an accelerated solid-liquid interface Fe(III)/Fe(II)cycle was revealed.The introduction of CQDs would enrich the electrons generated by photochemical reduction of complex[?Fe III(C2O4)n]2-2n on the?-Fe2O3 surface,and activate the adsorbed molecular oxygen to O2·-on the CQDs surface.O2·-would then transform to·OH and rapidly oxidize SMX.(3)It was found that the bonding mode between CQDs and iron oxide crystal planes was highly related to the degradation of SMX in the above two systems.Based on the DFT theoretical calculations and the related experimental results,it was indicated thatcrystal planes of Fe3O4(100)and?-Fe2O3(110)would be favorable for the photo-electron transfer,since O-C bonds would be formed between the crystal plane and CQDs surface.However,crystal planes of Fe3O4(111),?-Fe2O3(001)and?-Fe2O3(012)led to the formation of Fe-O bonds which would inhibit the function of CQDs.In addition,it was found that the three crystal planes of?-Fe2O3,i.e.(220),(113),and(311)would all lead to the formation of O-C bonds with CQDs,revealing its best catalytic oxidation performance among the all investigated CQDs modified iron oxides. |
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