Rapid Degradation Of Aniline And Rhodamine B In Aqueous Solution By Persulfate Combined With Rice Straw Biochar And Their Mechanisms

Both persulfate and biochars have been widely applied in the removal of organic contaminants.Persulfate,due to its high redox potential,has great application in oxidation degradation of organic pollutants in drinking water.Nevertheless,owing to persulfate itself is relatively stable,the reaction rate is quite slow at room temperature,the effect of the removal of organic substances is basically negligible.Thus,how to enhance the active of persulfate has received widely attention.Recently,metals and their oxides or surpported materials have been found to accelerate the decomposition of persulfate,and then generating higher oxidation capacity,such as sulfate raical(SO4·-)and hydroxyl radical(OH·),to degrade the organics.Therefore,increasing attentions have been paid in this area.At the same time,biochars have been widely used in the asorption of organic and heavy metals in wastewater because of its large specific area and abundant microporous struceture.Recently,some studies focusing on the interaction between biochar and O3,H2O2 or PS,it is speculated that the combination of biochar and these oxidants may generate higher oxidizing species to eliminate organics more effectively.In this study,the removal of organic pollutants by persulfate cooperated with rice straw biochar prepared from agricultural waste was investigated.Aniline is an important synthetic intermediates and Rhodamine B is also widely used in industrial production activities because of its color and fluorescence characteristics.Owing to its stable structure,poor biodegradability,the release of these wastewaters poses a serious threat to the water and soil,as well as human health.Thus,aniline and RhB were selected as targets to explore the synergies between PS and RSBC.Furthermore,the effect of factors on aniline and RhB degradation by persulfate assisted with rice straw biochar(RSBC)were also examined.At last,a possible interaction mechanism of PS and RSBC was given.This thesis is composed of two parts.Part Ⅰ:The removal efficiency of aniline by single RSBC,single PS and persulfate assisted with rice straw biochar(RSBC/PS)was investigated,and the influence factors including RSBC and PS dosage,solution pH,temperature and coexisting ions on aniline degradation were also explored.The results showed that the degradation and mineralization of aniline was markedly enhanced while RSBC and PS coexisted.Approximately 94.1%removal of aniline was attained by PS/RSBC system after 80 min,and nearly 52%of aniline was mineralized at the same time.Both RSBC dosage and PS concentration had a remarkably influence on aniline degradation.Both the rate and the degree of final removal of aniline markedly increased along with the increase dosage of RSBC.The analysis of kinetic experimental data demonstrated that the degradation of aniline followed a pseudo-first-order reaction kinetics and the reaction rate constants increase with the increase dosage of RSBC.The effect of initial pH(from 3 to 11)on aniline degradation was also investigated,and it is found that aniline could be effectively removed in the pH range of 3-9.The effect of coexisting anions on aniline degradation was performed.High concentrations of nitrate would inhibit the decomposition of persulfate and further inhibit the degradation of aniline.In order to explore the potential interaction between RSBC and PS for aniline degradation,the variation of solution pH and the generation rate of SO42-were further detected.At the same time,radical scavengers including Me-OH and TBA and hole trapping agent EDTA-2Na were introduced into RSBC/PS system to observe their effects on aniline degradation.Besides,the technology of EPR was used to determine the existence of SO4·-in RSBC and PS coexistence system.Based on the analysis and observation made here,it is speculated that the predominant reactive species responsible for the degradation of aniline may be holes instead of SO4·-and OH.radicals.S2O82-may first adsorbed onto the surface of RSBC and then reduced by the hydroxyl and carboxyl on thr surface of RSBC,following by the formation of holes with higher oxidation than SO4·-.It is concluded that RSBC prepared from agricultural waste could be used as an effective catalyst to activate PS for the degradation of aniline.Part Ⅱ:the degradation of Rhodamine B(RhB),one of the paraxanthine-based dyes,by different systems including single RSBC adsorption,single PS and RSBC together with PS were investigated.The results suggested that the degradation of RhB by PS alone was not satisfactory,and RSBC had a certain adsorption of RhB,However,a combination of RSBC with PS,rapidly clear RhB in the solution.The final removal rate of RhB was up to 98%.The dosage of RSBC and PS positively impacted the degradation of RhB.RhB would be well removed in acidic environment.When the solution initial pH increased from 3 to 11,the degradation rate of RhB was gradually decreased.Then,the scavengers,Me-OH,TBA and EDTA-2Na,were introduced into the RSBC/PS system.No inhibited effect was monitored when Me-OH and TBA was added.Conversely,EDTA-2Na behaved obviously inhibition on RhB degradation.Therefore,it is suggested that holes contributing to RhB degradation instead of commonly SOa·-.Full wavelength scanning and LC-MS data indicated that RhB degradation experienced deethylation,conjugate double bond broke,and then decomposed into CO2 and H2O.The reuse of RSBC for RhB degradation implied that RSBC did not behave well stablility.In summary,it could be inferred that RSBC/PS system is a potential and environmentally friendly approach for the degradation of organic pollutants.