Synthesis Of Magnetic Biosorbents And Their Adsorption Performance For Cr(?)

Cr???caused serious water pollution due to its high biotoxicity and strong mobility.Magnetic biosorption is an effective method to purify the Cr???contaminated wastewater.However,owing to the complicated synthesis process,unstable structure and low adsorption efficiency,traditional magnetic biosorbents are inefficient to heavy mental wastewater,especially for Cr???contaminated water with acidic p H.To solve those problems,two kinds of magnetic biosorbent?i.e.MB-FS and MB?with stable structure were prepared through chemical crosslinking and solvothermal method,respectively.Systematic experiments have been conducted to inverstigated the Cr???adsorption performance and Cr???removal mechanism of those magnetic biosorbents.Moreover,hierachical porous biochar was prepared by controlling the pyrolysis condition.The effect of pore structure on Cr???removal rate was investigated through SEM,BET test and adsorption kinetic experiments,and a novel magnetic hierarchical porous biochar(i.e.MPC₈₀₀)was obtained through solvothermal method.The main contents of this thesis are as follows:1.The fabrication of magnetic biosorbent modified with Fe₃O₄@SiO₂-NH₂ particles and its adsorption performance to Cr???Fe₃O₄@SiO₂-NH₂ magnetic particles with core-shell structure were attached on carboxylated biochar?CBC?derived from phoenix tree leaves through amide bond,to synthesize a novel magnetic biochar?MB-FS?for the removal of Cr???ions from acidic solutions.FSEM,FTEM,XRD characterizations of MB-FS revealed that the Fe₃O₄@SiO₂-NH₂ magnetic particles distributed uniformly on the surface or macrospores of CBC.The result of batch adsorption experiment suggestted that the Cr???adsorption capacity of MBFS was 27.2 mg/g,and could be well fitted by Redlich-Peterson model?R²=0.98?.The adsorption mechanism was investigated through the XPS test and adsorption experiment.The result showed that adsorbed Cr???anions were reduced to Cr???cations by the functional groups of MB-FS in acidic environment,and the newly formed Cr???cations waere chelated by amine groups.The adsorption recycling test showed that MB-FS kept 85% of its initial Cr???adsorption capacity at the sixth cycle,and the Fe leakage under p H 1.0 was smaller than 0.25 mg/L.2.The synthesis of magnetic biosorbent by solvothermal method and its adsorption performance to Cr???A novel magnetic biochar?MB?was fabricated through a one-step solvothermal method,due to the complicated synthesis process and the low yield of MB-FS synthesised through the amide crosslinking.The formation mechanism of MB was studied through XRD-FTIRGC/MS analysis.A series of parameter optimization experiment were conducted to inverstigate the effect of Fe³⁺ concentration and biochar?BC?dosage on the structure and adsorption capacity of MB-FS.The results showed that Fe³⁺ concentration and BC dosage could affect the particles size and load density of Fe₃O₄ particles,MB possessed a large BET surface area and a optimal adsorption capacity to Cr???ions when the Fe³⁺ concentration was 1.47 mmol/L,and the Fe₃O₄/BC was 1.0.Batch adsorption experimental results showed that the maximum adsorption capacity of MB to Cr???ions at p H=2.0 was 56.76 mg/g,accompanied with 10 mg/L Fe dissolution.XPS and FTIR test results indicated that Cr???were reduced to Cr???ions by the functional groups of MB in acidic environment,and the formed Cr???ions were then reacted with Fe₃O₄ particles and formed Fe-Cr compunds on the surface of MB.3.The synthesis of magnetic hierarchical porous biosorbent and its rapid adsorption to Cr???To improve the adsorption efficiency and capacity of magnetic biochar,a series of biochar samples with different pore size distribution were prepared by controlling the activation agent and temperature of phoenix tree leaves.SEM and BET characterizations were employeed to analysis the pore structure of biochar,and batch adsorption experiment were conducted to inverstigate the Cr???adsorption rate and capacity of biochar samples,the result suggested biochar with hierarchical porous structure(i.e.PC₈₀₀ and PC850)possessed the higest adsorption capacity and rate to Cr???ions?Ks>0.04 g/?mg·min??.This result can be explained by the decrease of film mass transfer resistance due to the marcoporous and nanosheet structure of PC₈₀₀.In addition,an appropriate proportion of mesoporous was effective to the decrease of diffusion resistance.Then,a magnetic hierarchical porous biosorbent(MPC₈₀₀)was farbricated by a one-step solvothermal method for the removal of Cr???ions.The batch adsorption experiment suggestted MPC₈₀₀ could purify the Cr???-containing water fastly.The adsorption recycling test showed that MPC₈₀₀ kept 84.4% of its initial Cr???adsorption capacity at the fifth cycle,indicating MPC₈₀₀ haa a good reuse ability.The research results of this thesis provide a new idea for the efficient treatment of Cr???-containing wastewater and the preparation of new magnetic biosorbents.