Preparation And Catalytic Performance Of Sulfidated Nano-Zero-Valent Iron Catalyst

Sulfidated nano-zero-valent iron(S-nZVI)has been recognized as promising in groundwater pollution remediation and surface water pollution control countermeasure,and it has often become a hot spot in activating persulfate.In this study,chloramphenicol(CAP)was the target pollutant.Nano-zero-valent iron(n-ZVI)and sulfide nano-zero-valent iron(S-nZVI)were prepared by a one-step method of liquid-phase reduction.The best-performing material was selected,and then characterized and analyzed its structure and composition.The nZVI and S-nZVI materials were applied to activate persulfate(PS)to remove chloramphenicol in the water,and the influence of different reaction conditions on the system was explored.To determine the optimal reaction conditions,and study the degradation mechanism and path.In addition,under the conditions of different concentrations of anions(Cl^-,SO₄^2-,CO₃^2-),the differences and mechanisms of the removal of chloramphenicol in water by activating PS of nZVI and S-nZVI materials were explored,and the contribution of sulfate radical and hydroxyl radical in the system was quantitatively analyzed.The main research contents and conclusions are as follows:In this study,four kinds of S-nZVI materials with Fe/S molar ratio were synthesized by controlling the amount of Na₂S₂O₄ during the preparation process,and a series of characterization analyses were performed on nZVI and S-nZVI.The surface morphology of the material,chemical composition and composition structure before and after sulfidation and during the reaction process were studied by characterization methods such as specific surface area analysis(BET),elemental analysis(ICP),scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD).The results showed that specific surface area of S-nZVI increased first and then decreases with the increase of sulfur content,and the degree of agglomeration between particles was lower than that of nZVI.Many smaller iron sulfide particles were attached to the surface of the material,the roughness was slightly larger than nZVI.The surface components of S-nZVI were mainly FeS and FeSn,a small amount of FeSO₃,FeSO₄ and FeOOH.Besides,the sulfur-containing compounds generated on the surface of S-nZVI weaken the hydrophilicity of the material and inhibit oxidation.Single factor experiments explored the effects of different reaction conditions(including Fe/S molar ratio,catalyst dosage,persulfate concentration,initial pH of the reaction solution,etc.)on the degradation of chloramphenicol.The experimental results showed that as the Fe/S molar ratio increased,the reaction rate and degradation rate firstly increased and then decreased.When the Fe/S molar ratio was 20,the effect was the best;with the increase of the catalyst dosage,the reaction rate and the degradation rate also increased firstly and then decreased.The best effect was when the dosage was 0.1 g/L;with the increase of the persulfate concentration,the reaction rate and degradation rate both increased;with the increase of the initial pH of the solution,the reaction rate and degradation rate were both reduced,and the reaction rate was faster under acidic conditions.Taking into account the removal effect and actual production application,the optimal conditions for the selected reaction are:pH0=6.86,[CAP]0=20 mg/L,[PS]0=3 mM,S-nZVI(20)=0.1 g/L.After 30 minutes,the removal rate of CAP could reach 98.8%,which was higher than that of nZVI under the same experimental conditions.The removal of CAP in this study mainly included Fenton-like oxidation and adsorption.The adsorption capacity of the S-nZVI/PS system was weaker than that of the nZVI/PS system,but it had a stronger oxidation capacity,hydroxyl radicals played a leading role in the reaction.Through the calculation of DFT and Condensed Fukui function,the visualized results of CAP degradation were drawn,combined with the data of LC-MS to analyze the degradation products and infer the degradation path.The mechanism by which S-nZVI/PS could remove CAP more efficiently was that more free radicals were generated to attack chloramphenicol molecules through a series of reactions,and the increase in hydrophobicity could promote dechlorination.The presence of chloride ions(1-100 mM),sulfate ions(1-50 mM),and carbonate ions(1-50 mM)could affect the system to varying degrees,and sulfidation could improve the ability to resist anion interference and improve degradation and mineralization rate.The order of the degree of effect of the three coexisting ions on the removal rate of CAP was:chloride ion>sulfate ion>carbonate ion.The effect of chloride ions was reflected in low concentration to promote degradation,and high concentration to inhibit degradation.Compared with the nZVI system,the total removal efficiency of the sulfidation system could be increased by up to 11.0%,the mineralization rate could be increased by about 10%,and the hydroxyl radical content was significantly higher.The influence of sulfate ions was reflected in the positive correlation between the degree of inhibition and the concentration,and the content of sulfate radicals in the sulfidation system was more.The total removal rate of the sulfidation system could be increased by up to 14.8%,and the mineralization rate could be increased by 11%.The role of carbonate ion was related to its concentration.The material exhibited different oxidation and reduction properties at different CO₃^2-concentrations.The number of two free radicals in the S-nZVI system was less than that of the nZVI system.It was assumed that other factors(such as coagulation or other free radicals)play a role in promoting the degradation of CAP.It is worth noting that,based on the results of LC-MS and the concentration of chloride ions in the solution before and after the reaction,CAP can be dechlorinated during the degradation process,which makes the concentration of chloride ions in the solution increase with the progress of the reaction,while S-nZVI performed better when different concentrations of chloride ions coexisted,so it can be proved that it has stronger CAP degradation ability than nZVI.Therefore,compared with nZVI,S-nZVI may be a more promising catalytic material in activating persulfate,especially in the field of salt-containing pharmaceutical wastewater.