Study On The Mechanism Of Photolysis And Photocatalysis With Persulfate For The Degradation Of PPCPs

The extensive production and use of pharmaceutical person care product including non-steroidal anti-inflammatory drugs(NSAIDs)and antibiotics have increased the volume of downstream residues that contaminate the environment,which pose great threats to ecosystems and human health.Photolysis and Photocatalysis with Persulfate can remove PPCPs effectively,which possessed promising potential application in water treatment process.It's necessary to further investigate the mechanism of the generation of reactive species and the transformation of the target compound.On the one hand,the transformation pathway and toxicity variation of target compound were elucidated in the photolysis with persulfate system;on the other hand,metal and non-metal modification of g-C3N4 with persulfate serving as photo-electron to produce more reactive radicals,which can degrade emerging pollutants effectively under visible light,providing theoretical support for practical application.The main research contents and results are as follow:The decomposition of peroxydisulfate(PDS),which is activated by UV-vis to produce a potent oxidizing sulfate radical,comprises a new type of advanced oxidation technology.The degradation of indomethacin(IM)by the UV-vis activation of peroxydisulfate was investigated.The results demonstrated that IM degradation followed pseudo-first-order reaction kinetics.UV-vis irradiation led to the direct albeit slight photolysis of IM,whereas the addition of an oxidant significantly enhanced the removal efficiency.The IM degradation efficiency was increased when the pH was elevated from 5 to 7;however,the elimination of IM was reduced when the pH was elevated from 7 to 9 due to the conversion of SO4·-to·OH.A low concentration of Cl-had a dual effect,while a high concentration led to a dramatic inhibitory effect.Fulvic acid(SRFA)inhibited the decomposition of IM through the light screening effect and the quenching of radicals.A quenching experiment revealed that SO4·-was the primary free radical,which is confirmed by electron spin resonance spectroscopy.The second order rate constants of IM and SO4·-were also determined.The photobacterium was selected to assess the toxicity of the transformation products,which was further confirmed by quantitative structure active relationship analysis.The cleavage of the bond between C on the benzene ring and N on the indole group,the hydroxylation of the benzene ring,and the decarboxylation of the aliphatic chain were the main pathways for the degradation of IM in the UV-vis/peroxydisulfate system.A copper ferrite modified graphitic carbon nitride(CuFe2O4/g-C3N4)nanocomposite was successfully synthesized for the utilization as a visible-light responsive photocatalyst.The as-synthesized catalysts were characterized using X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV-vis diffuse reflectance spectra(UV-vis/DRS),photoluminescence(PL)analysis,and an electrochemical workstation.Compared to g-C3N4 and CuFe2O4,the CuFe2O4/g-C3N4 composites possessed excellent photocatalytic performance for the destruction of propranolol(PRO).A removal efficiency of 82.2%was achieved with 1 g/L catalyst and 1mM peroxydisulfate(PDS)under visible light irradiation within 120 min.The g-C3N4 coupled with CuFe2O4 improved the capacity for visible light capture,whereas the presence of PDS enhanced the transfer of photogenerated electron.Quenching experiments and electron spin resonance(ESR)suggested that the reactive oxygen species(ROS)were superoxide radicals(O2·-),h+,hydroxyl radicals(·OH),and sulfate radicals(SO4·-).Moreover,the byproducts of PRO were investigated by HPLC-MS/MS,and the transformation pathways under the Vis/CuFe2O4/g-C3N4/PDS process were tentatively proposed based on the intermediates.The research provided a potential approach of CuFe2O4 modified g-C3N4 as a photocatalyst combined with PDS for the treatment of contaminated water.Fe-doped g-C3N4/graphene(rGO)composites were investigated as catalysts for the activation of peroxymonosulfate(PMS)to degrade Trimethoprim(TMP)under visible light irradiation.The rapid recombination of photogenerated electron-hole pairs in g-C3N4 may be suppressed by doping with Fe and incorporating rGO.The TMP degradation efficiency using 0.2%Fe-g-C3N4/2wt%rGO/PMS was 3.8 times than that of g-C3N4/PMS.The degradation efficiency of TMP increased with higher catalyst dosages and PMS concentrations.Acidic condition(pH=3)was observed to significantly enhance the TMP degradation efficiency from 61.4%at pH=6 to nearly 100%.By quenching experiments and electron spin resonance(ESR),O2·-was found to play an important role for the activation of PMS to accelerate the generation of reactive radicals for the TMP degradation.A total of 8 intermediates derived from hydroxylation,demethoxylation and carbonylation were identified through theoretical calculations and the HRAM/LC-MS-MS technique,and transformation pathways of TMP oxidation were proposed.TOC removal rate of TMP increased as reaction time was prolonged.Acute toxicity estimation by quantitative structure-active relationship analysis indicated that most of the less toxic intermediates were generated.The aim of this study was to elucidate and validate the functionality of a promising polymeric catalyst for the environmental remediation of organic contaminants.As prepared visible-light-sensitive MoS2/g-C3N4 nano-composite couple with PMS was employed in the photocatalytic degradation of Ibuprofen(IBP).The XRD,FT-IR,SEM,TEM,BET,UV-Vis-DRS,and photoluminescence(PL)techniques were used to characterize the composite.A lower PL intensity of the composite than the individual semiconductors confirmed that the photogenerated electron-hole recombination in the composite is lower than those of individual components.The MoS2/g-C3N4 composite combined with PMS accelerated photocatalytic degradation of IBP due to the improved visible light absorption,separation efficiency of photogenerated charges and the larger generation of reactive species.During 60 min of photodegradation experiment,complete removal of IBP was achieved in the MoS2/g-C3N4/PMS process at pH 3.The effects of catalyst concentration and PMS concentration was investigated.Meanwhile,the quenching experiments and ESR measurement were also performed to identify the major reactive species.The results showed that SO4·-,·OH,O2·-,1O2,and h+played role in the degradation of IBP.Three-dimensional excitation-emission matrix fluorescence spectra(3D EEMs)were used to further monitor the IBP degradation.The transformation products of IBP were identified through HRAM/LC-MS-MS analysis and theoretical calculation,and the transformation pathway of IBP was tentatively proposed.The as-synthesized materials combined with PMS possessed a potential application for emerging pollutant removal in environmental remediation.