甘蔗渣生物炭吸附-还原Cr(Ⅵ)的反应研究

Adsorption-reduction reaction between bagasse-prepared biochar and Cr(Ⅵ)

以甘蔗渣为原材料,在限氧条件下经600℃碳化制备生物炭RC,经800℃碳化制备生物炭HC,分别研究两者对Cr(Ⅵ)的吸附-还原反应。采用扫描电子显微镜-能谱(SEM-EDS)、比表面积和孔隙分析(BET)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和拉曼光谱(RS)等对甘蔗渣生物炭表面性质进行表征,从吸附等温线、吸附动力学等角度探讨甘蔗渣生物炭对Cr(Ⅵ)的吸附-还原反应特征及其机理。结果表明:甘蔗渣生物炭具有丰富的孔隙结构和表面活性基团,且随着碳化温度升高,甘蔗渣生物炭表面孔隙度和芳香化程度增加,而含氧官能团OH、C O等相对含量则降低。HC对Cr(Ⅵ)的吸附-还原去除效果最好,总去除量高达117.28 mg·g^(-1),较RC增加了82.42 mg·g^(-1),其中吸附反应的去除量为76.00 mg·g^(-1),比RC增加了67.99 mg·g^(-1)。随着碳化温度升高,生物炭缺陷程度降低,电子传递能力增强。HC对Cr(Ⅵ)的还原量为87.40 mg·g^(-1),较RC增加了57.03 mg·g^(-1)。吸附等温线和吸附动力学拟合结果显示,甘蔗渣生物炭对Cr(Ⅵ)的吸附更符合拟二级动力学模型。Langmuir模型适用于HC对Cr(Ⅵ)的吸附,Freundlich模型适用于RC对Cr(Ⅵ)的吸附。XPS和FTIR分析结果显示,甘蔗渣生物炭对Cr(Ⅵ)的去除机理为静电吸附、还原和络合作用,其中RC、HC吸附作用的相对贡献率分别为22.98%、64.80%,还原反应的相对贡献率分别为87.12%、74.52%,表明甘蔗渣生物炭对Cr(Ⅵ)的去除过程以还原为主。

With the strict exclusion of oxygen,two kinds of biochar(RC and HC)were prepared from bagasse by carbonization at 600℃and 800℃,respectively.By combining several techniques,including scanning electron microscope-energy spectrum(SEM-EDS),surface area and pore analysis(BET),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),and Raman spectroscopy(RS),the surface properties of these two biochars were well characterized.The Cr(Ⅵ)adsorption isotherm and kinetics of the biochars were examined,and the focus was placed on elucidating the underlying mechanisms thereof.The results showed that these two bagasse biochars had rich pore structures and surface active groups.The increase in carbonization temperature could increase the surface porosity and the degree of aromatization but decrease the relative contents of oxygen-containing functional groups such as OH and C O.The HC exhibited the highest efficiency for removing Cr(Ⅵ),with maximum removal amounts as high as 117.28 mg·g^(-1).By discriminating the relative contribution of adsorption and reduction from the Cr(Ⅵ)removal,the amounts of Cr(Ⅵ)removed by adsorption alone could be 76.00 mg·g^(-1),with 8.01 mg·g^(-1) for RC.With the increase in carbonization temperature,the degree of the defect was reduced,and the electron transport ability was enhanced.The reduction amounts of Cr(Ⅵ)by HC were 87.40 mg·g^(-1),which was 57.03 mg·g^(-1) higher than that for RC.Additionally,the kinetics of adsorption of Cr(Ⅵ)by bagasse biochar obeyed the pseudo-second-order kinetic model.The adsorption isotherm of Cr(Ⅵ)by HC was well described by the Langmuir model,with the Freundlich model more applicable for the Cr(Ⅵ)adsorption by RC.The XPS and FTIR analysis showed that the removal mechanisms of Cr(Ⅵ)by bagasse biochar involved three steps:the electrostatic adsorption of Cr(Ⅵ)by the surface,reduction of Cr(Ⅵ)to Cr(Ⅲ),and the complexation of Cr(Ⅲ).The relative contribution of adsorption reaction to Cr(Ⅵ)removal by RC and HC accounted for 22.98%and 64.80%,respectively,with 87.12%and 74.52%via the reduction reaction,respectively.The results indicate that the reduction reaction plays a major role in removing Cr(Ⅵ)from aqueous solutions using bagasse biochar.