Micromorphological Control Of Lignin-derived Carbon Material And Its Applications In Adsorption And Photocatalysis

With the rapid development of the society,resources shortage and environmental pollution have aroused people's wide concern.Researchers start to turn attention to the high-value development of renewable and abundant biomass resources in the field of environmental restoration.Lignin is considered to be the most abundant and renewable aromatic compound in the nature.Industrial lignin as a byproduct is mainly derived from the papermaking and cellulosic bioethanol process,which is source widely and cheap.The carbon content of lignin can reach up to 60%,which indicates it is an ideal carbon precursor.Moreover,there are many active functional groups such as phenolic hydroxyl,alcoholic hydroxyl,carboxyl,carbonyl,etc in lignin.The structure and morphology of lignin are easily adjusted through different methods.Thus,lignin as carbon precursor also exhibits excellent flexibility and designability.High value-added carbon-based function materials are prepared with industrial lignin,and applied into the treatment of antibiotic wastewater.This realizes the high value utilization of industrial lignin and protects the environment,which has great significance for the sustainable development of economy.In this paper,we designed and fabricated ligin-derived carbon(LC)with different micromorphologies using industrial lignin.Then the LC was used as carbon-based adsorbent materials or photocatalyst support materials according to the characteristics of micromorphology in the treatment of simulated antibiotic wastewater.Firstly,we prepared lignin-derived porous carbon(LPC)with high specific surface area by addition of potassium compound pore former,and illustrated the influence mechanism of structure and microstructure of lignin on the carbonization and activation process.The adsorption property and mechanism of antibiotic was analysed onto LPC.Secomdly,lignin-derived carbon nanosheet(LCN)was prepared by basic magnesium carbonate(BMC)as template,and then was used as photocatalyst support to fabricate cadmium sulfide/lignin-derived carbon nanosheet(Cd S/LCN)composite with excellent photocatalytic performance.The antibiotic in water was mineralized completely by photodegradation.Furthermore,lignin-based hollow carbon sphere(LHC)composite with opening structure was prepared by spherical nano-magnesia as template,and then was used to couple environmentally-friendly zinc oxide.The obtained zinc oxide/lignin-based hollow carbon sphere(Zn O/LHC)composite presented excellent photocatalytic performance in the photodegradation of antibiotic.Finally,we integrated the characteristic of two-dimensional structure and hollow nanostructure.Lignin-based flower-like carbon(LFC)assembled with ultrathin carbon nanosheets was prepared by flaky nano-magnesia as template,and then was coupled with Zn O.The obtained zinc oxide/lignin-based flower-like carbon(Zn O/LFC)composite presented more excellent photocatalytic performance in the photodegradation of antibiotic.The main conclusions are as follows:(1)KOH,K₂CO₃ and KHCO₃ were selected as pore former.A series of LPC were fabricated using alkali lignin and lignosulfonate as raw materials at 800°C.The influence mechanism of structure and microstructure of lignin on the carbonization and activation process was deduced through characterization methods such as AFM,QCM-D,SEM,BET,TG,TG-MS,etc.AL is serious aggregated,and its microstructure is dense because of lacking hydrophilic functional groups.KHCO₃ can release a large amount of gas before pyrolysis of AL.The expansion effect could promote pyrolysis of AL,which is beneficial to the activation pore-forming.On the contrary,LS has a highly dispersed and loose microstructure due to lots of hydrophilic functional groups.KOH can restrict the release of gas during pyrolysis of LS.The stabilizing effect could protect the microstructure,which is beneficial to the pore formation.Thus,AL with activation of KHCO₃ and LS with activation of KOH presented the higher specific surface area,which were 2084 and 2770 m²·g^-1,respectively.Above two LPC were used as adsorbent material for removing the sulfamethazine(SMT)in water environment.Adsorption kinetics study indicated the adsorption process of SMZ on these two LPC followed the pseudo-second-order model,and adsorption rate of SMZ on LSC-KOH was faster.Adsorption thermodynamics model and thermodynamic parameters analysis indicated adsorption process of SMZ on LPC followed the Langmuir model,and the maximum monolayer adsorption uptake of SMT were 884.1 and 1012.6 mg·g^-1at room temperature,respectively.The adsorption process was a spontaneous endothermic process.The fixed-bed column and recyclability experiments indicated LPC have the potential for application.Finally,the adsorption mechanism was elucidated,and the cation-?interaction between LPC and SMT was the main force.(2)Lignosulfonate and basic magnesium carbonate were selected as raw material and template,respectively.Porous LCN with abundant oxygen-containing functional groups was designed and prepared through the vapor-phase peeling and self-template of BMC.The LCN was characterized by SEM,TEM,AFM,BET,Raman,etc,and the formation mechanism was deduced.The thickness of LCN can be adjusted according to the addition of BMC,and LCN-1:3 presented the thinnest with the mass ratio of 1:3 for LS to BMC.The thickness of LCN-1:3 was about 9 nm,and its specific surface area was 749 m²·g^-1.Subsequently,Cd S/LCN-1:3 composite was prepared by in-situ growth,and Cd S nanoparticles with a diameter of about 10 nm were well dispersed in LCN.Cd S/LCN-1:3 with the addition of 5%LCN-1:3 exhibited the highest photodegradation rate for SMT,which was about 1.6 times that of pure Cd S.Enhancement mechanism of photocatalytic activity was analyzed.The introduction of LCN-1:3 can inhibit the agglomeration of Cd S nanoparticles and increase the active sites of photocatalyst.On the other hand,the strong interaction between Cd S and LCN-1:3 can promote the separation of photogenerated electron-hole pairs.In addition,the absorption ability of LCN-1:3 also can enhance the photocatalytic degradation reaction,and suppress photocorrosion.(3)Enzymatic hydrolysis lignin and spherical nano-magnesia were selected as raw material and template,respectively.LHC with opening structure and abundant oxygen-containing functional groups was designed and prepared through evaporation-induced self-assembly and carbon process.The LHC was characterized by SEM,TEM,BET,Raman,XRD,etc,and the formation mechanism was deduced.The addition of Mg O and volatile temperature of solution were explored for the effect of morphology.The ideal LHC was obtained with the mass ratio of 2:1 for EHL to Mg O and 90°C of volatile temperature.LHC with a wall thickness of about 20 nm presented an opening structure of about 70 nm,and its specific surface area was 412 m²·g^-1.Subsequently,Zn O/LHC composite was prepared by in-situ growth,and Zn O nanoparticles with a diameter of about 10 nm were uniformly immobilized on the exterior and interior surface of LHC.Zn O/LHC with the addition of 5%LHC exhibited the highest photodegradation rate for CPX,which was about 2.0 times that of pure Zn O.Enhancement mechanism of photocatalytic activity was analyzed.The introduction of LHC can inhibit the agglomeration of Zn O nanoparticles and increase the active sites of photocatalyst.Simultaneously,this hollow and opening structure can generate multiple scattering of light,which is beneficial for light-harvesting.On the other hand,a joint electronic system was formed between carbon shell and Zn O,which can promote the separation of photogenerated electron-hole pairs and extend the optical absorption.In addition,the absorption ability of LHC with porous structure can capture substrates and enhance the efficiency of photocatalytic reaction.(4)EHL and flaky nano-magnesia were selected as raw material and template,respectively.LFC assembled with ultrathin carbon nanosheets was designed and prepared through evaporation-induced self-assembly and carbon process.Moreover,LFC presented abundant oxygen-containing functional groups.The LFC was characterized by SEM,TEM,BET,Raman,XRD,etc,and the formation mechanism was deduced.The addition of Mg O and volatile temperature of solution were explored for the effect of morphology.The ideal LFC was obtained with the mass ratio of 2:1 for EHL to Mg O and 100°C of volatile temperature.The LFC was assembled with carbon nanosheets of about 4 nm thick,and its specific surface area was 827 m²·g^-1.Subsequently,Zn O/LFC composite was prepared by in-situ growth,and Zn O nanoparticles with a diameter of about 10 nm were uniformly immobilized on the ultrathin carbon nanosheets.Zn O/LFC with the addition of 4%LFC exhibited the highest photodegradation rate for SMT,which was about 3.0 times that of pure Zn O.Enhancement mechanism of photocatalytic activity was analyzed.The Zn O nanoparticles can be well immobilized on ultrathin carbon nanosheets and greatly increase the active sites of photocatalyst.Simultaneously,this flower-like structure assembled with ultrathin carbon nanosheets was beneficial to transmission and multiple scattering of light,which is beneficial for light-harvesting.On the other hand,the carbon nanosheets with high graphitization degree can promote the separation of photogenerated charge carriers and extend the optical absorption.In addition,LFC also can enrich substrates,and enhance the efficiency of photocatalytic reaction.