不同pH值和O_(2)条件下硝酸改性生物炭去除六价铬机理  

Removal mechanisms of Cr(VI)by HNO_(3) modified biochar under different pH and O_(2) conditions

作　　者：尹茜艳 文嘉[1,2] 薛壮壮 杨翠莲 李杨芳 袁利 YIN Xiyan;WEN Jia;XUE Zhuangzhuang;YANG Cuilian;LI Yangfang;YUAN Li(College of Environmental Science and Engineering,Hunan University,Changsha 410082;Key Laboratory of Environmental Biology and Pollution Control(Hunan University),Ministry of Education,Changsha 410082)

机构地区：[1]湖南大学环境科学与工程学院,长沙410082 [2]环境生物学与污染控制教育部重点实验室(湖南大学),长沙410082

出　　处：《环境科学学报》2022年第10期274-283,共10页Acta Scientiae Circumstantiae

摘　　要：为改善生物炭对Cr(Ⅵ)的去除性能并探究溶液初始pH值和O_(2)对生物炭的氧化还原活性物质(RAMs,即含氧官能团和环境持久性自由基(EPFRs))还原Cr(Ⅵ)的影响,用硝酸(HNO_(3))改性玉米秸秆生物炭(NBC),采用电子扫描显微镜-能谱仪(SEM-EDX)、比表面积及孔隙测定仪(BET)、Zeta电位仪和红外光谱仪(FTIR)分析生物炭性质,通过X射线光电子能谱仪(XPS)、Boehm滴定和电子顺磁共振波谱仪(EPR)测定生物炭RAMs含量变化.结果表明,HNO_(3)改性增加了生物炭的比表面积、总孔体积、含氧官能团和表面电位,从而能更有效地去除Cr(Ⅵ)(在pH 2.0时去除率达到100%,其表面吸附的铬89.12%被还原为Cr(Ⅲ)).动力学实验表明,NBC可以直接还原Cr(Ⅵ),也可以通过还原O_(2)产生的•O_(2)^(−)间接还原Cr(Ⅵ);直接还原途径占主导地位,间接还原途径对Cr(Ⅵ)的还原贡献率随着pH值的升高而增加.此外,酸性条件下含氧官能团(-OH和C-O-C)是还原反应的主要电子供体,而中性条件下EPFRs主导还原.因此,HNO_(3)改性提高了生物炭对Cr(Ⅵ)的去除能力,NBC可以通过直接途径和间接途径还原Cr(Ⅵ),并且在不同pH值下通过不同电子供体主导NBC还原Cr(Ⅵ)的过程.Corn straw-derived biochar was modified with HNO_(3) to prepare NBC with oxygen-containing functional groups and environmentally persistent free radicals(EPFRs),and the key roles of these two redox-active moieties(RAMs)in the Cr(Ⅵ)removal at varying initial pH and O_(2) in water were investigated.Scanning electron microscopy energy-dispersive X-ray spectroscopy(SEM-EDX),specific surface area and porosity(BET),zeta potential and Fourier transform infrared spectroscopy(FT-IR)were used to analyze the properties of biochar.Boehm titration and electron paramagnetic resonance spectrometer(EPR)were used to determine the RAMs content of NBC.The HNO_(3) oxidation induced the increase of BET surface area,pore volume,and RAMs content,and changed zeta potentials of biochar to improve Cr(Ⅵ)adsorption(The Cr(Ⅵ)removal rate reached 100% at pH 2.0 and 89.12% of the Cr species adsorbed on the biochar existed in the form of Cr(Ⅲ)after reduction).Kinetics study revealed that NBC can either directly reduce Cr(Ⅵ)or activate O_(2) to produce•O_(2)^(−)for indirect Cr(Ⅵ)reduction.The direct reduction dominated the Cr(Ⅵ)removal and the contribution of indirect reduction increased with the increasing pH.In addition,oxygen-containing functional groups(-OH and C-O-C)were the main electron donors for Cr(Ⅵ)reduction under acidic conditions,while the neutral condition was more favorable for EPFRs-dominated reduction of Cr(Ⅵ).Therefore,HNO_(3) modification improves the ability of biochar to remove Cr(Ⅵ).NBC can reduce Cr(Ⅵ)directly and indirectly,and the main electron donors for NBC to reduce Cr(Ⅵ)were different at different pH.

关 键 词：改性生物炭 六价铬 吸附还原 含氧官能团 环境持久性自由基 

分 类 号：X703[环境科学与工程—环境工程]