Adsorption Properties Of Modified Cellulose For Typical Pollutants And The Interaction Mechanism

Recently,the residue of organic matters?herbicides,antibiotics,phthalates,etc.?and heavy metals?Cd,Cr,Pb,Hg,etc.?in farmland soil has endangered ecological security and food safety,and then posed a potential threat to human health and plant growth.Cellulose is an abundant biomass resource with low price,and it is also one of the main components of agricultural waste straw and industrial waste wood chips.Regarding cellulose as the raw material to prepare adsorbents can not only solve soil pollution problems,but also provide a new strategy for cellulose utilization.In this work,we designed and prepared three cellulose modified adsorbents for heavy metal cadmium,herbicides,sulfonamides and phthalates removal.Through the combination of experimental,theoretical analysis and computer simulations,we deeply researched the relationship between adsorbents structure and adsorption performance,as well as the macroscopic and microscopic mechanism.A novel multi-functional group?carboxyl,amide,carbonyl sulfide and secondary amino group?modified cellulose adsorbent was prepared for heavy metal cadmium adsorption.The results of XRD,FTIR,¹³C NMR and XPS confirmed that the carboxyl,amide,carbonyl sulfide and secondary amino groups were grafted onto the cellulose backbone successfully.Moreover,compared to raw cellulose,both the thermal stability,porosity and electronegativity of modified cellulose were obviously improved.The Cd²⁺adsorption capacity of the Modified-cellulose was pretty good,up to 401.1 mg/g and with 3 times enhancement.The binding energy of different functional groups modified cellulose and Cd²⁺was calculated based on density functional theory?DFT?of quantum chemical simulation,the binding ability of multi-functional modified cellulose was comparatively stronger due to the synergy effect of the functional groups.The HOMO of adsorbent and LUMO of Cd²⁺were analyzed based on Frontier orbital theory?FOT?of quantum chemical simulation,the preferential adsorption sites were mainly distributed on secondary amino groups and carbonyl sulfides.Three mesoporous cellulose biochar?MCB?adsorbents were prepared through a 300? carbonization-KOH activation-700? carbonization-HNO₃ oxidation process.The Cd²⁺adsorption performance of three MCB with the different surface area?about 600 m²/g?,pore size?about 3.2 nm?,O and N functionalities content was compared,and the MCB-1 h exhibited best Cd²⁺adsorption capacity?368.8 mg/g?,remained 89%after 5 cycles.DFT calculations identified that MCB-1 h had the comparatively stronger Cd²⁺binding ability,and the results were well consistent with the experimental data.The microscopic adsorption mechanism was analyzed in the view of classical theory and electron-scale.The classical theory results proposed that the adsorption process was dominated by chemisorption,and the existence of electron sharing or electron exchange between Cd²⁺and biochar adsorbent.Electron-scale mechanism analysis found that the functional groups and aromatic could provide lone pair electrons and?electrons for the Cd²⁺adsorption,respectively.The N functionalities such as amino,pyridine and pyrrole groups could raise the adsorption ability of the biochar adsorbent.In addition,the interfacial phenomena associated with the adsorption of sulfamethazine?SMT?onto MCB adsorbents was studied,as well as the influence of pH value,cations and humic acid?HA?on this interfacial interaction.A?-electron interaction,not electrostatic interactions,is the main interfacial interaction mechanism.A thermodynamic and kinetic study revealed that the monolayer adsorption occurred and was dominated by chemisorption.Quantum chemical simulations were conducted to further explore the interfacial interaction micro-mechanism at the molecular and electronic levels.The adsorption equilibrium configurations confirmed that SMT was adsorbed onto MCB in the V-shape configuration,mainly through?-?EDA interactions.DFT simulations showed that increasing the?electron density of the biochar favored its adsorption of SMT and that the pyrrole groups might be the most effective functionalities for this adsorption due to its same HOMO orbital with SMT.Furthermore,taking MCB as an adsorbent,and five different carbon chain structure phthalates?DMP,DEP,DBP,DOP,DEHP?as adsorbates.The effect of the carbon chain structure of PAEs on the adsorption behavior and mechanism was studied by the combination of experimental and molecular dynamics simulations.The order of adsorption capacity of MCB to the five PAEs was as follows:DOP>DMP>DEP>DBP>DEHP;the adsorption process was multi-layer adsorption,and main controlled by chemisorption.When the carbon chain of PAEs is short,the adsorption mechanism of PAEs onto porous biochar is mainly pore-filling and?-?EDA interaction.With the increase length of carbon chain,the pore-filling and?-?EDA interactions were weakened,and the hydrophobic interaction was enhanced.Under the same length of the carbon chain,the branched structure will accelerate the agglomeration of adsorbate molecules and weaken the adsorption force.In order to adsorb negatively charged glyphosate?GLY?,we prepared a positively charged MnFe₂O₄@CAC hybrid composite by immobilizing the MnFe₂O₄ nanoparticles on the CAC surface via a simple one-pot solvothermal method.The SEM,BET,TEM,IR,Raman,XRD and XPS proved the successful synthesis of MnFe₂O₄ with particles size of 100?300 nm,and the formation of MnFe₂O₄@CAC hybrid.The hybrid was positively charged at pH below 6 and has good magnetic properties.The dispersion stability of the hybrid was close to CAC,and was significantly higher than that of MnFe₂O₄ nanoparticles.Moreover,the maximum GLY adsorption capacity of MnFe₂O₄@CAC?167.2 mg/g?was much higher than that of MnFe₂O₄nanoparticles?93.48 mg/g?and CAC?61.44 mg/g?,and the result was inconsistent with the DFT calculated adsorption energy.The multi-layer adsorption occurred due to the electrostatic repulsion between the adsorbate molecules and was dominated by chemisorption.Quantum chemical simulations were conducted to further explore the electron transfer in the adsorption process.The results showed that GLY could form new chemical bonds with MnFe₂O₄ with any valences,owing to the conjugation between the p electron of adsorbent and d electron of adsorbate.Therefore,the three cellulose modified adsorbents may offer an attractive adsorbent candidate for highly efficient removal of heavy metal cations and organic matters.In addition,the mechanistic results were also useful to the design and prepare of ideal adsorbents,and provided a roadmap and technical base for the removal of farmland soil contaminants.