腐植酸和巯基改性生物炭对水中Cd2+的吸附性能和机制研究

本研究以水稻秸秆为原料制备生物炭（BC300），通过使用腐植酸和3-巯丙基三甲氧基硅烷（3-MPTS）丰富其表面官能团，得到腐植酸改性生物炭（HBC300）和巯基改性生物炭（SBC300）两种改性生物炭，分析改性生物炭对Cd²⁺的吸附能力，借助FT-IR、XPS和Boehm滴定等表征手段和密度泛函理论（DFT）计算探究改性生物炭的理化性质及官能团对吸附Cd²⁺的作用。结果表明：改性过程改变了生物炭的理化性质，HBC300表面增加了COOH和OH官能团，而SBC300表面COC、CO和SH官能团增多。通过丰富其生物炭表面官能团提升了生物炭对Cd²⁺吸附反应速率和吸附性能，表现出改性生物炭在水中去除Cd²⁺的潜力。其中，SBC300对Cd²⁺吸附效果最佳，其最大平衡吸附容量为49.5 mg·g^-1，但吸附反应速率小于HBC300，符合准二级动力学方程和Langmuir等温吸附模型，此吸附过程为单分子层吸附并受化学吸附控制。表征数据及DFT计算拟合数据结果表明，生物炭表面修饰官能团加快了对Cd²⁺吸附反应速率，但COC和CO官能团限制了SBC300对Cd²⁺的吸附反应速率。

Adsorption performance and mechanism of biochar modified by humic acid and thiol for Cd2+ removal in water

This study presents the preparation of biochar(BC300)using rice straw as raw material, and the modification of its surface with humic acid and 3-mercaptopropyltrimethoxysilane, providing two modified biochars:HBC300 and SBC300, respectively. Herein, the ability of the modified biochars to adsorb Cd²⁺ was analyzed, and the physicochemical properties of the modified biochars and the effects of functional groups on the adsorption of Cd²⁺ were explored using Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, Boehm titration, and density functional theory(DFT)calculations. The results showed that the modification process changed the physicochemical properties of biochar. The HBC300 surface presented an increased number of COOH and OH functional groups, while in the SBC300 surface, the number of COC, CO, and SH functional groups increased. By enriching the surface functional groups of biochar, the adsorption reaction rate and adsorption performance of biochar for Cd²⁺ were improved, showing the potential of modified biochar to remove Cd²⁺ from water. Among them, SBC300 showed the best adsorption performance on Cd²⁺, with a maximum equilibrium adsorption capacity of 49.5 mg·g^-1, but an adsorption reaction rate lower than that of HBC300. SBC300 conformed to the Pseudo-second-order kinetic equation and Langmuir isothermal adsorption model. The adsorption process consisted of a monolayer adsorption controlled by chemical adsorption. The characterization and DFT calculation fitting data results showed that the functional groups of surface-modified biochar accelerated the adsorption reaction rate of Cd²⁺; however, COC and CO functional groups limited the adsorption reaction rate of SBC300 to Cd²⁺.