Study On Functional Modification Of Biochars And Their Adsorption Property And Mechanism

The problem of water pollution has been concerned for a long time.In order to reduce the harm of heavy metals and organic pollutants,there have been a lot of researches on the treatment of heavy metal and organic wastewater.A variety of processing technologies have been developed.For example,redox,solvent extraction,membrane separation,biological treatment,adsorption.Different methods have their own advantages and disadvantages.Among them,adsorption has the advantages of simple operation,economic efficiency,low energy consumption,and no secondary pollution,and is considered to be the most promising wastewater treatment method.Therefore,the development and research of adsorbents for heavy metals and organic pollutants has attracted widespread attention.Biochar is a porous carbon material obtained by thermochemical conversion technology under oxygen-limited conditions.Biochar has unique physical and chemical properties,such as a rich porous structure,a large specific surface area,and a large number of surface functional groups.These characteristics give biochar the potential to be used as an adsorbent for environmental restoration.In order to improve the adsorption performance of biochar materials,various chemical reagents can be used for functional modification.In this study,a series of functional modified materials were prepared for pyrolytic biochar and hydrothermal biochar.The adsorption behavior and mechanism of these materials as adsorbents in the treatment of heavy metal pollutants and organic pollutants in wastewater were studied in detail.The main research work and results of this article can be summarized as the following five aspects:(1)Through the combined action of chitosan and pyromellitic dianhydride,a functional modified biochar material(CPMB)was synthesized to remove Pb(II),Cd(II)and Cu(II)in water.The physical and chemical characteristics of CPMB were analyzed by a series of characterization techniques such as SEM,FTIR and XPS.The adsorption characteristics and mechanism of CPMB were investigated by examining the effects of solution pH on adsorption,competitive adsorption experiments in mixed solutions,adsorption kinetics and isotherm experiments.The results show that CPMB had a better selective adsorption capacity for Cu(II);the maximum adsorption capacities for Pb(II),Cd(II),and Cu(II)were 9.24 mg/g,30.12 mg/g,and 89.69 mg/g;rich oxygen-containing functional groups and nitrogen-containing functional groups were the main mechanism for the removal of heavy metal ions by the biochar.They could participate in adsorption through complexation,ion exchange and electrostatic interaction.(2)A novel modified biochar material(SA-CaRB)was synthesized through the impregnation of biomass with calcium ions and the cross-linking reaction between sodium alginate and calcium ions.The physical and chemical characteristics of SA-CaRB were analyzed by a series of characterization techniques such as SEM,BET,FTIR and XPS.The adsorption properties of biochar materials prepated in this wotk were compared under different pH conditions.Through adsorption kinetics and isotherm experiments,seven different metal ions were selected as interference ions to investigate the adsorption characteristics and mechanism of SA-CaRB.The adsorption of lead ions by SA-CaRB was affected by chemical interaction.At the same time,the intra-particle diffusion model illustrated that the existence of liquid film diffusion and internal diffusion during the adsorption process.According to the Langmuir model,the maximum adsorption of Pb(II)by SA-CaRB was about 209 mg/g.The adsorption of Pb(II)by SA-CaRB had strong anti-interference ability.It was found that the oxygen-containing functional groups on SA-CaRB could interact with lead ions through chelation,complexation,and ion exchange.(3)Nicotinamide was used as a modifying agent under acidic conditions to prepare a novel amino-functionalized hydrochar(NMSH)for removing Cr(VI)and Sb(V).Biochar samples were analyzed by SEM,TEM,BET,elemental analysis,FTIR and XPS.The effects of contact time and solution concentration on the adsorption performance of NMSH were investigated in single system and binary system.The effects of pH,inorganic ions,and organics on adsorption were investigated.Under single system,the maximum adsorption capacities of Cr(VI)and Sb(V)by NMSH were132.7 mg/g and 241.9 mg/g,respectively.The coexisting Cr(VI)and Sb(V)had inhibitory effects on each other due to competitive adsorption.When the initial concentration exceeded 80 mg/L,NMSH had a better selectivity for Sb(V)so that Sb(V)could take away part of the adsorption site occupied by Cr(VI).NMSH had good anti-interference performance for a variety of inorganic ions and organics.There were differences in the adsorption mechanisms of Cr(VI)and Sb(V)by NMSH.The functional groups on NMSH played different roles in removing Cr(VI)and Sb(V).Some O-containing functional groups could reduce Cr(VI)to Cr(III),but Sb(V)was not reduced.NMSH had good regeneration performance and could be recycled.This result showed that NMSH had good economic effects and application prospects.(4)A novel hydrochar adsorbent derived from sawdust(SAHC)was prepared for highly efficient simultaneous removal of benzotriazole(BTA)and Cu(II)from aqueous solution.The prepared adsorbent was characterized by several methods such as SEM,FTIR,and XPS.Batch adsorption experiments showed that the maximum adsorption capacity of SAHC for BTA and Cu(II)was 159.91 and 298.86 mg/g,respectively.Additionally,the study of competitive adsorption showed that the adsorption of Cu(II)was barely affected by the existence of BTA while the BTA adsorption was significantly improved with the coexistence of Cu(II).The study of adsorption mechanism found that Cu(II)could chelate with BTA to form complex,and the complexing-bridging interaction improved BTA adsorption.SAHC exhibited high adsorption ability after six adsorption cycles,which indicated excellent stability and regeneration performance of SAHC.All the results suggested that SAHC could be a promising adsorbent for simultaneous removal of BTA and Cu(II)from wastewater.(5)A novel cost-effective hydrochar composite(MgSi-HC)prepared by a simple one-step process using waste sawdust,inexpensive silicate and magnesium salts as raw materials was used to remove Cu(II),Zn(II),and tetracycline(TC)from aqueous solution.The novel hydrochar material was characterized by SEM,TEM,XRD,BET specific surface area,ATR-FTIR spectra,and X-ray photoelectron spectroscopy.The values of surface area(107.7 m~2/g)and pore volume(0.489 cc/g)of MgSi-HC indicated that it had a large specific surface area and well-developed pore structure.Adsorption isotherm showed that the maximum adsorption capacity of MgSi-HC for Cu(II),Zn(II),and TC was 214.7 mg/g,227.3 mg/g,and 361.7 mg/g,respectively.In addition,the effects of heavy metals and tetracycline on each other in binary adsorption systems were different.Meanwhile,the study of mechanism indicated that various interactions might be involved in the adsorption process,and the adsorption mechanisms of heavy metal and TC were different.The potential of MgSi-HC for practical environmental remediation was evaluated,the result demonstrated that MgSi-HC still had high performance after 5 adsorption-desorption cycles,and it had stable adsorption ability in different water samples(150.2-156.2 mg/g for Cu,159.6-167.4 mg/g for Zn,and183.9-189.8 mg/g for TC),implying that the novel hydrochar could be a promising adsorbent for removal of heavy metal and antibiotics from real wastewater.This work provided a reference on the coadsorption of heavy metal and antibiotics,and indicated the potential application of MgSi-HC in complex pollutant adsorption.