Removal Of A Typical Organochorine Pollutant 2,4,6-trichlorophenol By Biochar Supported Nanoscale Zerovalent Iron

As a typical fat-soluble organic pollutant,halogenated organic compounds（HOCs）have attracted more and more attention due to their potential ecological risks.Nanoscale zero-valent iron（NZVI）can be used for reductive dehalogenation of halogenated organic compounds due to its high specific surface area as well as high removal effectiveness.However,owing to its inherent limitations such as aggregation and passivation,the promising applications of NZVI have not been fully exploited.These limitations can be overcome by using biochar（BC）as supporting materials of NZVI.In general,the excellent physical and chemical properties of BC can improve the dispersion of NZVI,enhance electron transfer from NZVI to HOCs,and inhibit the oxidation passivation of NZVI.BC-supported NZVI is regarded as a potential alternative in in situ remediations.Sulfidized NZVI has been studied extensively in recent years due to the high reactivity of SNZVI to HOCs.The mechanism of enhanced removal of HOCs by SNZVI includes improving reaction selecticity and affinity,reducing electron transfer resistance and providing additional specific surface area and active site.Metal doping is another common method of NZVI modification.The metal with lower activity than Fe can effectively promote the corrosion of Fe⁰ and improve the reaction efficiency.In this thesis,based on the two application scenarios of pollution control in groundwater and emergency treatment of accidental leakage of HOCs in water,two environmental functional materials using agriculture wastes were developed.and used for simultaneously adsorbing and degrading of 2,4,6-trichlorophenol（2,4,6-TCP,a typical HOCs）,the main work is as follows:（1）Fourier transform infrared spectroscopy and Raman spectroscopy were used to characterize the surface functional groups and crystal structure of different agricultural wastes derived BC.The results showed that corn cob derived BC had abundant oxygen-containing functional groups,aromatic functional groups,and graphitization structure,made it the best NZVI load carrier.The optimal pyrolysis temperature of corn cob derived BC was 800℃,and the adsorption capacity of corn cob derived BC on 2,4,6-TCP was 135.432 mg·g^-1 in accordance with the pseudo-second-order adsorption kinetics model.The fitting results of particle diffusion model indicated that the adsorption of 2,4,6-TCP by corn cob derived BC was a joint action of surface adsorption and internal diffusion adsorption,in which the internal diffusion process was the main rate control step.The isothermal adsorption curve of corn cob BC to 2,4,6-TCP was more consistent with Freundlich model,and the adsorption type was single-layer adsorption.Low temperature was favorable for the adsorption of corn cob BC to 2,4,6-TCP.（2）The improved liquid phase reduction method was used to prepare BC-SNZVI.Compared with BC and BC-NZVI,BC-SNZVI had larger specific surface area(208.8 m²·g^-1),more developed microporous structure(0.117 cm³·g^-1)and more abundant surface functional groups.The Fe content increased from 11.7%to 17.7%after S doping which was attributed to the additional function groups after S doping.The influence of S/Fe ratio,curing agent and curing strategy on the synthesis of BC-SNZVI was investigated.The experimental results show that the optimal conditions for the synthesis of BC-SNZVI were:S/Fe ratio of 0.088,sulfidation agent of Na2S2O3,sulfidation strategy of Pre Sulfidation Route.The removal process of 2,4,6-TCP by BC-SNZVI was consistent with the pseudo-first-order reaction kinetics model.When reaction conditions remained unchanged(material dosage was 0.5 g·L^-1,initial 2,4,6-TCP concentration was 30 mg·L^-1,initial p H was 3.0).The observed pseudo-first-order kinetic constants of BC-SNZVI synthesized under optimal synthesis conditions were 5.11 times higher than those of BC-NZVI and 41.40 times higher than those of NZVI.The removal of 2,4,6-TCP by BC-SNZVI is an acid-promoting reaction,however,due to the change of surface charge caused by the introduction of S,the material can still remove 2,4,6-TCP by electrostatic adsorption under the condition of neutral p H.（3）Two possible removal pathways of 2,4,6-TCP by BC-SNZVI were determined which were 2,4,6-TCP→2,6-MCP→2-MCP→phenol and 2,4,6-TCP→2,4-MCP→2-MCP→phenol.The first one was the primary path.The mechanism of the removal of 2,4,6-TCP by BC-SNZVI enhanced by S element was complex,including increasing the specific surface area and micropore volume of the material,enriching the surface functional groups of BC-SNZVI,improving the dispersion and load rate of NZVI,enhancing the electrostatic adsorption,improving the hydrophobicity of the material and the affinity for HOCs,inhibiting the recombination of proton and hydrogen and reducing the electron transfer resistance.（4）BC-Ni/NZVI was prepared by an improved liquid phase reduction method.It was proved that the doping amount of Ni affects the removal of 2,4,6-TCP by BC-Ni/NZVI.The optimal doping amount of Ni is 0.6%wt,and the reaction is in accordance with the pseudo-first-order kinetic model,the kinetic constant kobs was 0.05225 min^-1 under the reaction conditions of 0.5 g·L^-1 material dosage,30 mg·L^-1 initial 2,4,6-TCP concentration and 3 initial p H.The removal of 2,4,6-TCP by BC-Ni/NZVI was further strengthened by the external magnetic field environment.Under the condition of material dosage of 0.2 g·L^-1,the initial2,4,6-TCP concentration of 20 mg·L^-1,the initial p H of 3.0,the kinetic constant kobs was0.01675 min^-1.kobs increased by about 65.7%compared with the control group without an external magnetic field.The results of XRD and SEM showed that exogenous magnetic field significantly promoted the corrosion of Fe⁰,resulting in fibrilite and iron oxide corrosion products.The experiments showed that the Lorentz force had little effect on the adsorption performance of 2,4,6-TCP,and the rapid corrosion of Fe⁰ caused by magnetic field gradient force and Lorentz force were the main mechanism of enhanced removing 2,4,6-TCP by magnetic field enhanced BC-Ni/NZVI.The hydrogen produced by Fe⁰ corrosion was adsorbated by the supported metal Ni and catalyzed to produce proton hydrogen.2,4,6-TCP was dechlorinated by highly reducing proton-hydrogen attacks.The magnetic field strengthened BC-Ni/NZVI system designed in this experiment was expected to be applied to the rapid restoration of HOCs leakage water.