The Preparation Of Iron-modified Biochar-based Composites And Study On The Removal Of Dyes And Cr(Ⅵ)

Dye and heavy metal pollution in the environment have aroused worldwide concern,and effective remediation of the polluted environment is urgent.Biochar is widely available,eco-friendly,low cost,and contains unique physicochemical properties.Converting biomass waste into biochar solves the problem of high-value utilization of waste,and also effectively eliminates different pollutants,which embodies the concept of"treating waste with waste".However,biochar has a limited ability to remove pollutants and is hard to regenerate and separate.Iron-modified biochar could change the structure of biochar and improve the regeneration performance and adsorption capacity of pollutants.In this thesis,a series of iron-modified biochar composites were prepared,and the removal capacity and removal mechanism of biochar composites for dyes and Cr（Ⅵ）were investigated.This thesis contains three main sections:（1）Fe-modified lignin-based biochar（Fe-LB）was fabricated via a facile one-step carbonization method for methylene blue（MB）removal from wastewater.Compared with LB（746.40 m²/g,0.25 m³/g）,Fe-LB showed a higher specific surface area and micropore volume（885.97 m²/g,0.32 m³/g）,and the removal capacity of Fe-LB for MB was increased.Results showed that the MB removal efficiency of LB was 18.4%at 60 min.The quick adsorption could be achieved by Fe-LB in 15 min with the MB removal efficiency of 100%and the adsorption capacity of 200 mg/g.Pore adsorption,electrostatic attraction,hydrogen bond,andπ-πinteraction were the major MB adsorption mechanisms of Fe-LB.In addition,selective adsorption studies indicated that Fe-LB preferentially adsorbed MB in high salt and binary dye systems.Fe-LB possessed great potential in the treatment of MB polluted dye wastewater.（2）Chitosan coated biochar-supported nano zero-valent iron aerogel（C-nZⅥ@BC）was successfully synthesized,the aerogel had a three-dimensional network structure and abundant functional groups.The adsorption capacity of Cr（Ⅵ）by pristine BC was very poor while C-nZⅥ@BC achieved rapid and efficient removal of Cr（Ⅵ）.C-nZⅥ@BC could achieve ultrafast adsorption of Cr（Ⅵ）with 61%,77%,and 87%of Q_max obtained at 1 min with the Cr（Ⅵ）concentrations at 100,300,and 600 mg/L,respectively.Results showed that the coating of chitosan and the support of BC could prevent the oxidation and agglomeration of nZⅥ.nZⅥ and nZⅥ@BC were strongly dependent on p H for the removal of Cr（Ⅵ）,while C-nZⅥ@BC exhibited high Cr（Ⅵ）removal rates in the wide p H range（>83%）.C-nZⅥ@BC could be applied as a direct reducing agent for Cr（Ⅵ）and an activator of persulfate for antibiotics.The fixed-bed column adsorption experiment,the removal of low concentration Cr（Ⅵ）,and the simulated wastewater experiment indicated that the environment application potential of C-nZⅥ@BC was good.（3）The bifunctional Fe₃O₄ modified lignin-based biochar（LMB）was fabricated with the one-step solvothermal method.Compared with biochar,LMB combined the advantages of biochar and Fe₃O₄ and could be used as a bifunctional material for the removal of Cr（Ⅵ）and CR.The spherical Fe₃O₄ was successfully loaded on the lignin-based biochar.LMB could efficiently remove Cr（Ⅵ）and Congo red（CR）synergistically with the adsorption of biochar and the catalytic/reduction of Fe₃O₄.LMB showed a removal efficiency of 100%for Cr（Ⅵ）（100 mg/L）at 30 min.The LMB could be a catalyst to activate persulfate（PS）.The LMB+PS system showed a removal efficiency of 94.3%for CR at 60 min.Moreover,LMB could simultaneously remove 41.5%of Cr（Ⅵ）and 91.5%of CR in the mixed Cr（Ⅵ）and CR solution.The regeneration and simulated wastewater experiments showed that LMB had good reusability and stability.