Layered double hydroxide/eggshell membrane: An inorganic biocomposite membrane as an efficient adsorbent for Cr(VI) removal

Hexavalent chromium, Cr(VI), is carcinogenic and mutagenic to the living organisms, and hence more hazardous than other heavy metals. The choice of Cr(VI) removal adsorbents has always been a hot issue in environmental protection. Here we report a novel inorganic biocomposite membrane, layered double hydroxide/eggshell membrane (LDH/ESM) as adsorbent for Cr(VI) removal, in which ESM serves as the substrate and template to immobilize the LDH formed by an in situ hydrothermal crystallization method. X-ray diffraction (XRD) and scanning electron microscope (SEM) images showed that MgAl-CO32--LDH grown on the fibers of ESM, and the final LDH/ESM composite membrane both maintained the network structure of the ESM substrate. After being treated with an NaCl/HCl mixed solution, the interlayer CO32- anions in the LDH portion of the composite membrane were exchanged for Cl-. The ESM, MgAl-CO32--LDH/ESM and MgAl-Cl--LDH/ESM composite membrane were evaluated as adsorbent to remove Cr(VI), respectively, and the effect of the pH values on the adsorption was mainly investigated. It showed that the MgAl-Cl--LDH/ESM composite membrane had a higher adsorption capacity than ESM and MgAl-CO32--LDH/ESM even when the pH value of the Cr(VI) solution was not further adjusted by addition of acid, which is of practical significance in a wastewater treatment plant. The adsorption isotherm of the MgAl-Cl--LDH/ESM composite membrane showed a good fit with the Langmuir isotherm model. (C) 2010 Elsevier B.V. All rights reserved.

六价铬（Cr(VI)）对生物体具有致癌性和致突变性，因此比其他重金属更具危害性。六价铬去除吸附剂的选择一直是环境保护中的一个热点问题。在此我们报道了一种新型无机生物复合膜，即层状双氢氧化物/蛋壳膜（LDH/ESM）作为去除六价铬的吸附剂，其中ESM作为基底和模板来固定通过原位水热结晶法形成的LDH。X射线衍射（XRD）和扫描电子显微镜（SEM）图像显示，MgAl - CO32 - - LDH生长在ESM的纤维上，并且最终的LDH/ESM复合膜都保持了ESM基底的网络结构。用NaCl/HCl混合溶液处理后，复合膜中LDH部分的层间CO32 - 阴离子被交换为Cl - 。分别评估了ESM、MgAl - CO32 - - LDH/ESM和MgAl - Cl - - LDH/ESM复合膜作为吸附剂去除六价铬的性能，并主要研究了pH值对吸附的影响。结果表明，即使不通过添加酸进一步调节六价铬溶液的pH值，MgAl - Cl - - LDH/ESM复合膜也比ESM和MgAl - CO32 - - LDH/ESM具有更高的吸附容量，这在废水处理厂中具有实际意义。MgAl - Cl - - LDH/ESM复合膜的吸附等温线与朗缪尔等温线模型拟合良好。（C）2010爱思唯尔B.V.版权所有。