Study On Green Synthesis Of Biochar Supported Iron Sulfide Composites For Removal Of Pb²⁺ From Aqueous Solution

With the development of agriculture and industrialization in China,heavy metals water pollution is becoming more and more serious,which poses a great threat to China’s future development.Lead is especially common in wastewater containing heavy metals.In view of the pollution of water sources caused by the use of lead salt pesticides in the agricultural production process,it is urgent to explore and research its treatment met hods.Nano-zerovalent iron material has many advantages which its strong adsorption and strong reduction combined with the removal of lead in water.However,the traditional method of preparing nano zero valent iron has many disadvantages.In this study,green tea extract was used as the reducing agent to reduce zero-valent iron,which made the reaction process green and environmentally friendly.At the same time,ferrous sulfide was used to modify zero-valent iron so as to improve the oxidation resistance of zero-valent iron.The biochar was used as carrier to improve its dispersion and avoid the agglomeration of nanoparticles.The porous hydrophilic biochar supported iron sulfide composites（S-nZVI@HPB）was prepared for the study of lead-contaminated wastewater.In this study,the physical and chemical properties of S-nZVI@HPB were firstly determined by means of scanning electron microscopy（SEM）,specific surface area（BET）,thermogravimetric analysis（TGA）,Fourier transform spectroscopy（FTIR）and X-ray diffraction（XRD）characterization,and the composition,surface structure and functional groups of the material were analyzed.Then a series of experiments were carried out to study the influence of factors on the adsorption amount of lead in water,including pH,time,temperature,material dosage and initial lead ion concentration of aqueous solution.Finally,the mechanism of removing lead ions from water was studied and analyzed by means of kinetic model,thermodynamic model and X-ray photoelectron spectroscopy（XPS）,the main results are:（1）SEM,BET,TGA,FTIR and XRD characterization results:green synthetic S-nZVI@HPB materials are not easy to aggregate,relatively dispersed,have a large specific surface area,good thermal stability and contain rich functional groups.After the material reacted with lead,the characterization found that ferrous sulfide and zero-valent iron reacted with lead,indicating that the green synthetic S-nZVI@HPB material is feasible for the removal of lead.（2）The results of batch experiments show that:Changing the pH value of the solution,the initial concentration of the Pb²⁺ion solution,the dosage of S-nZVI@HPB,the reaction temperature and the reaction time will have a significant impact on the removal of lead ions.Increasing the initial concentration of the solution,increasing the reaction temperature and extending the reaction time are beneficial to S-nZVI@HPB material removes Pb²⁺ions in water samples.（3）The results of adsorption models analysis:the pseudo-second-order kinetic model is more suitable for the adsorption process of S-nZVI@HPB materials,so it is speculated that the adsorption method of S-nZVI@HPB for Pb²⁺ions is mainly chemical adsorption.Langmuir isotherm model has better linear fit,this indicates that S-nZVI@HPB material exhibits monolayer adsorption during the adsorption of Pb²⁺ions.Thermodynamics research results:S-nZVI@HPB removal in the process of the Pb²⁺ions in aqueous solution,the gibbs free energy changeΔG⁰<0,confirmed in S-nZVI@HPB Pb²⁺adsorption on spontaneous characteristics,enthalpy changeΔH⁰>0,indicating that the materials in the process of adsorption of Pb²⁺is endothermic.（4）The results of mechanism analysis:the reaction mechanism between S-nZVI@HPB and Pb²⁺was explored by XPS characterization.The mechanisms of removing Pb²⁺include physical adsorption（electrostatic attraction,void filling）and chemical adsorption（ion exchange,reduction reaction,surface complexation）.