Preparation Of Modified Biochar And Its Adsorption Performance On Cd(Ⅱ) In Water

In this paper,nine types of rice straw-derived biochar（BC300,BC500,BC700,HBC300,HBC500,HBC700,SBC300,SBC500,and SBC700）were prepared from rice straw with humic acid and 3-mercaptopropyltrimethoxysilane（3-MPTS）as modified reagents at different pyrolysis temperatures（300,500,and 700°C）.And the surface physical and chemical properties of the straw-derived biochars were investigated by p H value determination,specific surface area and pore structure（BET）analysis,ash content analysis,elemental analysis,zero electric point analysis,surface morphology analysis,Fourier infrared spectroscopy（FTIR）analysis,X-ray photoelectron spectroscopy,X-ray diffraction analysis,and Boehm titration analysis.Static adsorption experiments were used to study the effects of biochar and modified biochar on the adsorption performance of heavy metal Cd²⁺in water at different reaction times,initial mass concentration of Cd²⁺,p H and ionic strength,and DFT calculations and related characterization data were used to investigate the microscopic adsorption mechanism of biochar on Cd²⁺,and to quantify the effects of cation exchange,precipitation,complexation and other effects on the adsorption of Cd²⁺.adsorption.As a result of these studies,the following main conclusions were drawn.（1）The pyrolysis temperature significantly affected the physicochemical properties of biochar and modified biochar.The specific surface area,elemental composition and functional group content and species of humic acid and sulfhydryl modified biochar were effectively improved at low temperature（300℃）.However,the physicochemical properties of the modified biochar at medium and high temperatures（500～700℃）were not effectively changed.（2）The results of static adsorption experiments showed that the adsorption performance of biochar and modified biochar on Cd²⁺was in the order of SBCs>HBCs>BCs,among which,SBC300 had the largest adsorption capacity on Cd²⁺,and its adsorption on Cd²⁺was in accordance with quasi-secondary kinetics and Langmuir model.When the p H was 7.0 and the ionic strength was 0.01 mol·L^-1,its adsorption capacity for Cd²⁺was the largest,which was 46.5 mg·g^-1.（3）The results of DFT calculations showed that the regions ofπ-electron,lone pair electron and electron donor groups in the biochar structure were the main reaction sites for binding with Cd²⁺,in which the binding energy value of-COC-to Cd²⁺was the highest at-249.21 kcal·mol^-1,the bond length of O-Cd bond was the shortest in-COO-Cd,while the binding energy value of-SH to Cd²⁺was lower and the bond length of S-Cd bond was higher.and the bond length of S-Cd bond was longer.This affected the reaction rate of Cd²⁺adsorption by humic acid modified and sulfhydryl modified biochar.（4）The pyrolysis temperature affected the adsorption mechanism of biochar（BCs）and modified biochar on Cd²⁺,and cation exchange and precipitation were mainly the adsorption mechanism of biochar（BCs）on Cd²⁺.After sulfhydryl modification,precipitation became the main adsorption mechanism for Cd²⁺adsorption by SBCs,with Cd S precipitation dominating.The adsorption of Cd²⁺by complexation gradually increased after humic acid modification,and the carboxyl group（-COOH）in the oxygen-containing functional group dominated the complexation of Cd²⁺by HBCs.