Removal Of Pb(Ⅱ) And Cu(Ⅱ) From Aqueous Solution By Biochar-based Materials:Properties And Mechanism

Increasingly serious heavy metal pollution poses a serious threat to human health and environment.Biochar made from waste biomass is an an environmentally friendly and effective way to remove heavy metals from water.Modification and loading can give biochar more developed pore structure and richer surface functional groups,and significantly enhance its adsorption effect.In this study,hydrochloric acid modified biochar（HBC）and citric acid modified biochar（CBC）were obtained by modifying the prepared corncob biochar（BC）,the composite materials n ZVI@CBC and Mn O₂@CBC were prepared by loading nano zero-valent iron（n ZVI）and Mn O₂ on CBC with stronger adsorption property.The materials were used to efficiently remove Pb（II）and Cu（II）from water,and the effects of various environmental factors on the removal effect and possible reaction mechanism were investigated.The main conclusions of this study are as follows:1)The surface morphology of HBC and CBC is not significantly different from that of BC,the phase composition is amorphous carbon.The modification significantly increases the number and types of oxygen-containing functional groups and greatly improves the pore parameters.The two composites were successfully and uniformly loaded on the surface of CBC,but the specific surface area and pore volume of the two composites decreased due to pore clogging and collapse.Part of the loaded n ZVI was oxidized.Mn O₂ is amorphous structure and has stronger adsorption capacity.2)The pH of the solution has a significant inhibition effect on the adsorption of the modified and composite materials when the solution is strongly acidic.Low concentration of co-existing Na（Ⅰ）and humic acid（HA）can promote the adsorption of BC,HBC and CBC,while higher concentration will have an adverse effect and HA only has a negative effect on the composite.Competitive adsorption experiments show that biochar preferentially adsorbs Pb（II）and has a larger adsorption capacity for Pb（II）,but coexistence of Cu（II）inhibited Pb（II）adsorption by biochar more obviously.3)Pseudo-second-order kinetic model and Langmuir isothermal adsorption model can describe the adsorption process of the five materials well.The modified and loaded biochar has higher adsorption performance and faster reaction rate.The adsorption capacities of Pb（II）and Cu（II）for the five materials are in the order of Mn O₂@CBC>n ZVI@CBC>CBC>HBC>BC.Compared with HBC and BC,the improvement of adsorption performance of CBC is related to the optimization of structural parameters and oxygen-containing functional groups.The high reactivity of n ZVI@CBC and more abundant functional groups of Mn O₂@CBC are the reasons for the further improvement of adsorption performance of CBC.The removal effect of n ZVI@CBC is lower than that of Mn O₂@CBC because it is more filled into the pores and oxidized.4)The large surface area and pore parameters of biochar-based materials make it possible for physical adsorption.The results of pH drift experiments show that the electrostatic effect is the main mechanism of adsorption of heavy metal ions by HBC and CBC,and sedimentation is an important factor in BC.The results of XPS and FTIR show that the removal of heavy metal ions by CBC and Mn O₂@CBC is mainly due to ion exchange and complexation,while n ZVI@CBC is due to oxidation and reduction.This study proved that biochar prepared from corn cob and then modified with citric acid and loaded with Mn O₂ has good removal effect on Pb（II）and Cu（II）pollution in water,which can provide technical support and basis for the application of modified biochar in heavy metal pollution adsorption.