凹凸棒石@C纳米复合材料对Cr(Ⅵ)吸附-还原作用

Adsorption and reduction of Cr( Ⅵ) by attapulgite@C nanocomposite

以凹凸棒石和葡萄糖为原料,通过设置凹凸棒石与葡萄糖不同质量比,采用水热碳化法制备凹凸棒石@C纳米复合材料,并选择出去除Cr（Ⅵ）效果最佳的凹凸棒石@C纳米复合材料.同时,利用傅里叶红外光谱（FT-IR）、X射线衍射（XRD）、Zeta电位仪（Zeta）、X光电子能谱（XPS）手段对复合材料进行了表征,考察了时间和p H对其去除水中Cr（Ⅵ）的影响,探讨了其吸附-还原机制.结果表明,最佳复合材料的凹凸棒石与葡萄糖质量比为1∶4;吸附平衡时间约为6 h,动力学过程符合准二级动力学模型.在p H为1～10时,Cr（Ⅵ）去除率随p H升高而减小,p H=1时Cr（Ⅵ）去除率最大,高达92.7%,吸附率为48.5%,还原率为44.2%;而总铬吸附率则随p H升高先增大后减小,p H=2时最大,吸附率为50.2%,还原率为13.0%,表明对Cr（Ⅵ）去除存在吸附-还原作用,酸性越强,越容易发生还原反应.FT-IR分析结果表明,凹凸棒石@C纳米复合材料表面存在含氧基团和还原性基团（Cx—OH、—CH等）;XPS分析结果表明其对Cr（Ⅵ）的去除是吸附-还原相互作用的结果,包括Cr（Ⅵ）在复合材料表面与含氧基团络合配位吸附和静电吸附,以及Cr（Ⅵ）还原Cr（Ⅲ）再吸附,其中,Cr（Ⅲ）再吸附主要通过与Mg2＋、Al3＋等阳离子交换作用实现的.

A series of attapulgite@ carbon nanocomposite have been synthesized by hydrothermal carbonization method with various ratios of attapulgite to glucose. The attapulgite@ C nanocomposite with the best removal of Cr（ Ⅵ） was selected. The structures of samples were characterized by using Fourier transform infrared spectroscopy（ FT-IR）,X-ray diffraction（ XRD）,Zeta instrument（ Zeta） and X photoelectron spectroscopy（ XPS）. The effects of time and p H on the removal of Cr（ Ⅵ） from aqueous solution were investigated,and the mechanism of Cr（ Ⅵ） adsorption and reduction was explored.The results show that the adsorbent achieved its optimal condition with attapulgite to glucose mass ratio of 1： 4,its adsorption equilibrium time is about 6 h and its adsorption kinetics process meets pseudo-second-order kinetics model. In the p H range of 1 ~ 10,the removal rate of Cr（ Ⅵ） decreased with the increase of p H. The maximum removal rate reached up to 92.7% at p H = 1,with adsorption rate of 48.5% and reduction rate of 42.2%. The adsorption rate of total chromium increased initially and then decreased with the increase of p H. The maximum adsorption rate reached up to 50.2% at p H = 2,with the reduction rate of 13.0%,indicating that both adsorption and reduction resulted in the removal of Cr（ Ⅵ）. The reduction reactions favored acid condition.In addition,the result from the FT-IR analysis shows that the attapulgite@ C nanocomposite possess the oxygen-containing groups and the reducing groups（ Cx—OH,—CH. etc.）. The XPS analysis results indicate that the removal of Cr（ Ⅵ） by the attapulgite@ C nanocomposite is a adsorption and reduction process. The process includes the adsorption of Cr（ Ⅵ） onto the surface of composite materials through the complexation and electrostatic mechanisms,and then part of the absorbed Cr（ Ⅵ） was reduced to Cr（ Ⅲ） which is further absorbed through the Mg2＋,Al3＋etc. ion exchange.