Mechanism Of Adsorption Of Organic Pollutants By Bio-carbon Composites

The risk of soil contamination by organic compounds has been recognized as a global environmental threat because of the potential negative consequences for human health and environment.Phthalic acid esters(PAEs)and tetracyclines(TCs)are two main kinds of organic pollutants with high residual concentrations in the soil,thus the remediation and control technology is urent needed for PAEs and TCs contaminated Soil.Biochar(BC)has great surface area,well-developed micropore and large number of function groups.BC can enhance the adsorption and fixation capacity of soil with organic contaminant through altering soil physical and chemical properties,reduce the degree of ecotoxity to soil.In this work,the com stalk biochar was modified to enhance its Di-n-butyl Phthalate(DBP)and oxytetracycline(OTC)adsorption capacities,and the adsorption mechanism for DBP and OTC were systematically investigated.Furthermore,the effects of modified BC application on the adsorption ability of DBP and OTC in brown soil were investigated.The main results are as following.The MnO2 nanosheets synthesised on BC surface has sphere-like structures,the XPS analysis indicated that the oxidation of Mn was Mn(IV).SEM images of BZnc revealed the ZnO nanorods with fusiform shap evenly dispersed on the BC surface,the XPS analysis indicated Zn contains two components,ZnO and Zn(OH)2.Both BMnc and BZnc exhibited much better DBP and OTC removal capacity compared to original BC,MnO2 and ZnO loading rate had large impact to the adsorption of DBP and OTC.The mass ratio of BC and MnO2 at 20:1 and 10:1 in BMnc showed the best DBP and OTC removal ability,respectively.However,the best nass ratio of BC and ZnO in BZnc for DBP and OTC removal is 20:1.The model fitting of kinetics showed that the process of DBP and OTC adsorption fitted the pseudo-seond-order kinetic model well,indicating it is mostly controlled by chemical interactions.Both Langmuir isotherm model and Freundlich isotherm model were well fitted to the experimental equilibrium data,the adsorption process of DBP and OTC on on raw and modified BC contain both physical adsorption and chemical interactions.The main sorption foreces involved were Van der Waals force,hydrogen bonding,π-π EDA interactions and chemical reaction.Both BMnc and BZnc improved the retention of DBP/OTC in the brown soil.The results revealed that with increasing amounts of amended BMnc or BZnc,the adsorption of DBP and OTC in brown soil significantly increased.The result showed that BMnc was more effective than BZnc and has great potential in repairing the soil polluted by PAEs and TCs.The amount of DBP and OTC adsorption in both raw and ameded brown soil decreased with the increase of pH,this may be the ruselt of electrostatic repulsive forces between soil and DBP/OTC increased with increase in pH from 4.0 to 10.0.