木质素/石墨烯复合水凝胶的多孔微结构可控制备及重金属吸附性能研究

Lignin-based hydrogels have attracted a great deal of attentions in treating wastewater containing heavy metal ions because of their multifunction, large specific surface areas and high porosity. However, most of the reported lignin-based hydrogels are prepared through covalent approaches to form chemically cross-linked frameworks. The porous microstructures of these hydrogels are difficult to be precisely controlled. On the other hand, the adsorption performances are limited to be improved. Furthermore, the structure-function relationship and influencing mechanism cannot be clearly revealed. Developing controlled preparation methods for porous microstructure is critical to solve these problems. Graphene possess the ability of three-dimensional self-assembly, controlled microstructure and structural fundamentation in composition with lignin. It may provide an effective method to prepare controlled porous microstructure. This project aims to prepare cheap, strong, highly adsorptive physically cross-linked hydrogels by structural controlled graphene sheets and adsorbing functional lignin. Focus on the controllable microstructure of graphene, modulating the size and surface nanopore structure of graphene sheets can control the porous microstructures of the composite hydrogels. Then we will establish the structure-function relationship between microstructure factor and adsorption performance. Furthermore, the influencing mechanism of adsorption performance can also be studied based on the controlled microstructure. At last, this project will construct an unified system of controlled microstructure, adsorption performance and influencing mechanism. Prospective results of this project will provide new ideas for the design and preparation of highly adsorptive lignin materials, and are important for developing economical and effective heavy metal adsorbents.

木质素基水凝胶因其多官能团活性、高比表面积和高孔隙率在重金属废水处理中备受关注。然而，目前采用的化学交联制备方法使其多孔微结构难以被精确调控，吸附性能提升空间有限，构效关系及影响机制难以深入研究，开发孔结构可控的制备方法是破解这一问题的关键。石墨烯具有三维自组装能力、可控的微结构以及与木质素复合的结构基础，有望为木质素基水凝胶多孔微结构的可控制备提供有效途径。本项目以石墨烯为组装模板，木质素为主要吸附功能单元，物理交联制备低成本、高强度、高吸附性能的复合水凝胶。重点通过调节石墨烯的片层尺寸、表面纳米孔结构实现复合水凝胶多孔微结构的可控制备；建立水凝胶微结构与吸附性能之间的构效关系；揭示多孔微结构对吸附性能的影响机制，最终构建结构与性能统一的“可控微结构－吸附性能－影响机制”关联系统。本项目预期成果将为高吸附性能木质素材料的设计与制备提供新思路，对经济高效的重金属吸附剂的开发具有重要意义。

近年来，绿色、廉价、可再生生物质资源的开发和利用逐渐引起研究者的研究兴趣，人们逐渐开始利用生物质资源部分替代或取代传统的功能组分。木质素基水凝胶因其多官能团活性、高比表面积和高孔隙率在含重金属废水处理中备受关注，多孔空间结构设计对水凝胶的吸附性能影响显著。目前主要通过化学交联技术制备木质素基水凝胶，很难进行多孔微结构的精确调控，因此开发孔结构可控的水凝胶制备方法具有重要的研究意义。石墨烯具有水凝胶的有序自组装性质、可控的微结构以及与木质素复合的结构基础，有望提供木质素基水凝胶多孔微结构的可控设计途径。本项目以石墨烯片为组装模板，以木质素为主要吸附功能结构单元，通过木质素与石墨烯片之间的非共价相互作用，制备低成本、高强度、高吸附性能的复合水凝胶材料，在弥补原有多孔碳材料功能性缺陷的同时，实现生物质资源的高值化应用。研究通过一步水热法制备了木质素/石墨烯复合水凝胶，借助具有多种含氧官能团的木质素磺酸盐对石墨烯三维多孔水凝胶进行功能性修饰。由于该复合水凝胶具有较大的比表面积，丰富的孔隙结构及大量的活性位点，其对水中Pb(II)的吸附能力高达1210mg/g，远高于纯石墨烯水凝胶(385mg/g)，是目前所报道的铅离子吸附材料中吸附性能最高的材料之一。此外，该水凝胶具有良好的机械强度、易回收性和可操纵性。将具有自支撑性能且柔韧的木质素/石墨烯复合水凝胶放置于柱状吸附装置中，提供了一种快速高效去除水中重金属离子的方法，在40min内其吸附量高达1308mg/g。更为重要的是该水凝胶吸附材料可以循环使用，在循环5次后其吸附能力可保持90%，循环10次后仍可保持82%的吸附能力。本项目研究成果为木质素的高值化利用提供新思路，对经济高效的重金属吸附剂的开发具有重要意义。