Sorption Behavior And Mechanism Of Organic Pollutants By Biochars Mediated By Their On Three-dimensional Structures

With the rapid development of industrialization,a large number of organic pollutants are discharged into the environment,resulting in the direct or indirect ecotoxicity to the ecosystem and human health.Biochar is widely used as an adsorbent in organic pollution control due to its high sorption efficiency and low cost.The interaction between organic pollutants and biochar is very complex,because of the apparently non-ideal behavioural processes,there are problems such as the co-existence of multiple mechanisms and the complexity of environmental influences.Through macroscopic experiments and classical sorption model analysis,the interaction between biochar and organic pollutants can only be described from the macroscopic level,and the microscopic information such as the action mode of organic pollutants in the three-dimensional matrix pore of biochar can not be fully described,which may lead to inadequate understanding of the environmental behavior of organic pollutants.In order to fully understand the environmental behaviour of organic pollutants and to promote the practical engineering application of biochar,it is necessary to investigate the interaction between biochar and organic pollutants under the mediation of its three-dimensional matrix.Biochar nanoparticles and three-dimensional multi-stage pore biochar were prepared from chicken feathers by a programmed warming combined with a cross-linking procedure.The liquid phase system of biochar nanoparticles with different concentrations was constructed to investigate the aggregation behavior of biochar nanoparticles,forming biochar agglomerates considered as natural three-dimensional matrix.Bisphenol A（BPA）was used as the object of study to investigate the effect of the formation of three-dimensional agglomerates of biochar on its BPA adsorption.The three-dimensional multi-stage pore biochar was prepared by modifying biochar with KOH.Pollutants of different molecular sizes,such as benzoic acid（BA,7.624（?））,naphthalene（NAP,7.785（?））,chloramphenicol（CAP,10.811（?））,bisphenol A（BPA,12.430（?））and sulfamethoxazole（SMX,13.415（?））,were selected as model organic pollutants to investigate the sorption of organic matter by the three-dimensional multi-stage pore biochar.Combined with elemental analysis,Fourier infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）and specific surface area analysis（BET）,the physicochemical properties of the biochar were characterised and a three-dimensional pore model of the biochar was constructed based on their physicochemical properties.The interaction mechanism of biochar with organic pollutants mediated by the three-dimensional matrix was investigated by combining batch sorption experiments and molecular dynamics（MD）simulations.The results of Xigo nanotools,dynamic light scattering（DLS）and atomic force microscopy（AFM）measurements of biochar showed that the specific surface area in the liquid phase decreased,the height and thickness of agglomerates and the aqueous kinetic diameter（D_h）of biochar increased significantly with increasing biochar concentration.In addition,the polymer dispersion index（PDI）value of approximately0.3 indicates that the hydrodynamic diameter of the biochar agglomerates fluctuates within a narrow range.This confirms the formation of three-dimensional agglomerates of biochar.Molecular dynamics（MD）simulations show that the aggregation effect is more pronounced at higher biochar particle concentrations,with biochar nanosheets showing V-shaped and parallel aggregation configurations between them.The oxygen-containing functional groups and nitrogen-containing functional groups,hydrophobic carbon chains and aromatic rings in biochar promote hydrogen bonding,hydrophobic andπ-πinteractions between biochar nanoparticles,leading to the formation of biochar agglomerates.The sorption kinetic data were fitted using calibrated pseudo primary and pseudo secondary kinetic equations.The R²values fitted to the pseudo-secondary equations were consistently higher than those fitted to the pseudo-first-order equations.The sorption rate constant（k₂,g/（mg·h））also decreased with increasing biochar concentration,with k₂for CFBC-W being less than that for CFBC-F and CFBC-R at the same biochar concentration.The effect of biochar aggregation on BPA adsorption was investigated using molecular dynamics（MD）simulations.In the adsorption system containing one or two biochar lamellae,in addition to some BPA molecules being free near the biochar lamellae,some BPA molecules were adsorbed on the sides and edge functional groups,and some BPA molecules were embedded in the V-shaped aggregates,while no BPA molecules were adsorbed in the interlayer of parallel aggregated nanosheets.the abundant functional groups on the outer surface of the V-shaped biochar aggregates could provide reactive sorption sites for BPA sorption.The rich functional groups on the outer surface of the V-shaped biochar aggregates can provide reactive sorption sites for BPA sorption.The radial distribution function（RDF）describes the range of distances over which the forces act,identifying the contribution of hydrogen bonding,π-πinteractions and hydrophobic effects in the sorption process.On the other hand,sufficient intercalation space can also provide reactive sites for the sorption of BPA.Due to the small layer spacing in the parallel aggregates,BPA molecules are unable to enter the parallel interlayer,resulting in a sharp decrease in BPA adsorption in the 5 sheets system.Overall,the heterogeneous aggregation between the biochar nanoparticles consumed a large number of BPA sorption sites,thereby inhibiting their sorption performance.Experimental data on the sorption kinetics of the five pollutants on the 3D multi-stage pore biochar showed that the largest unit sorption was for NAP（344.85mg/g-359.84 mg/g）and the smallest unit sorption was for BA（100.23 mg/g-137.05mg/g）.By fitting the kinetic data to the experimental data,it was found that the multi-stage pore biochar for the five pollutants The sorption kinetic data were found to be more consistent with a two-chamber first-order kinetic model,which better described the contribution of the fast and slow chambers to the sorption process,and an intraparticle diffusion model,which described the staged sorption process,and it was found that intraparticle diffusion was not the only factor limiting the rate.The equilibrium concentration distribution curves obtained from molecular dynamics（MD）simulations showed that the smaller molecular size BA and NAP adsorbed inside the biochar pore channel,while the larger molecular size CAP,BPA and SMX molecules were distributed to a lesser extent inside the pore channel,indicating that when the molecular size was close to the pore diameter,it was more difficult for the molecules to enter the interior of the pore structure due to molecular size effects and spatial site resistance effects.The slope of the mean square displacement（MSD）curve describes the diffusion of adsorbed and unadsorbed contaminant molecules.It was found that the slope of the MSD curve for adsorbed contaminant molecules was significantly lower than that for unadsorbed molecules,and the slope of the MSD curve for adsorbed molecules decreased with increasing molecular size,which was attributed to the folding and entanglement of larger molecules due to intermolecular interactions,forming larger molecular The slope of the MSD curve decreases as the size of the molecule increases.The radial distribution function（RDF）function curves show opposite results for benzoic acid（BA）,which is attributed to deviations between the settings of the simulation parameters and the actual experiments.By studying the sorption behavior of organic pollutants on multi-stage pore biochar,it was found that the sorption between the two was mainly contributed by various mechanisms such asπ-πinteraction,electrostatic interaction and pore channel sorption.It should be noted that for electrostatic interactions,the Zeta potential value of the biochar and the p H of the solution system directly influenced the strength of the electrostatic interaction,which in turn affected the sorption behaviour of the biochar on the organic pollutants.In summary,this thesis investigates the interaction between biochar and organic pollutants mediated by the natural three-dimensional matrix of biochar and three-dimensional multi-stage pore biochar,combined with molecular dynamics simulations,and theoretically elucidates the mechanism of its action on organic pollutant sorption mediated by the three-dimensional matrix of biochar,which helps to better advance the engineering application of biochar and the understanding of organic pollutant This will help to better advance the engineering applications of biochar and the understanding of the environmental behavior of organic pollutants.