| Adsorption is a well-known and an effective method for water decontamination application.Biochar is a successful absorbent for this purpose due to its powerful potential for removing pesticide from aqueous solutions.But they usually need to be modified by different methods to improve their adsorption properties.Herein,Biochars from corn were synthesized.They were low-cost,eco-friendly and easy-recycle.Two of them were screened by the adsorption performances of the pesticides from water.The mechanisms for pesticides removal from water were also discussed systematically.The research results were as follows:(1)Methods have been established for the detection of 6 triazines herbicides(TRZs)in water based on HPLC-MS-MS and for the detection of 6 organophosphorus insecticides(OPPs)in water based on GC(FPD).The pesticides all had good linearity and the correlation coefficients were more than 0.99.The recovery rates of the TRZs and OPPs in water were 81%~113% and 71%~110% with all RSD below 6.9%,which were in accordance with requirements for residual detection.(2)Biochars of corn straw,corncob,corn starch,and cellulose from corn straw were systhesized by pyrolysis and hydrothermal carbonization(HTC)with different modified methods.These biochars had been fully characterised.When biomass was pyrolyzed with H3PO4,the physicochemical properties of biochars would be improved,and the types of functional groups on the surface of biochars were increased.As for the biochars systhesized by HTC,KOH heat-treated was the key process to improve the characteristics of materials.After hydrothermal carbonization with GO(KOH-HTC-CE/G),the characteristics of the materials were further enhanced.Compared with KOH-HTC-CE,KOH-HTC-CE/G showed wrinkled nanosheet morphology,the stronger level of aromatization,and fewer oxygen-containing functional groups.(3)The systhetic methods and the variety of precursors could both affect the adsorption properties of biochars.Biochar systhesized by pyrolysis with the existence of H3PO4 from corn straw(CSWP)showed the best adsorption efficiency for TRZs.Compared to AC,PSA,GCB,and C18,CSWP showed higher adsorption capacity.More than 96% of the six TRZs(2mg/L,10 m L)could be removed of via 50 mg CSWP only by shaking five times.Alkaline condition was not beneficial for the adsorption.The adsorption efficiency of the CSWP for atrazine was still over 97% after five cycles.For the biochars synthesized by HTC,KOH-HTC-CE/G expressed the best adsorption capacities for OPPs.50 mg of KOH-HTC-CE/G could remove six OPPs(2mg/L,10 m L)more than 90% by vortexing for 2.5 min.Compared to MCNT,AC,PSA,GCB,and C18,KOH-HTC-CE/G showed higher adsorption efficiency.After eight cycles,the adsorption efficiency of the KOH-HTC-CE/G for chlorpyrifos was still over 93%.The adsorption rates of KOH-HTC-CE/G for TRZs were more than 97% by only shaking five times as well.Both of the two biochars were easier to separate from water.(4)The mechanisms of CSWP and KOH-HTC-CE/G for removal of pesticides from water were discussed systematically.The properties of pesticides were the main factors influencing the adsorption mechanism of biochar.The adsorption mechanisms of CSWP and KOH-HTC-CE/G for atrazine were similar,including van der Waals force,hydrogen-bond,and electrostatic interaction.The pseudo-second-order model could better describe the adsorption of atrazine on the two biochars.Freundlich model gave the best fit for the isotherm data,which could be employed to describe multilayer adsorption.The adsorption was a spontaneous,exothermic,and decreasing disorder process.The adsorption mechanisms of KOH-HTC-CE/G for chlorpyrifos were hydrophobic interaction and ?-? interaction.The pseudo-second-order model could better describe the adsorption.Langmuir model gave the best fit for the isotherm data,which indicated that chlorpyrifos could form monolayer coverage on the surface of KOH-HTC-CE/G.The adsorption was a spontaneous,endothermic,and increasing disorder process. |
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