表面基团对矿物纳米孔吸附重金属的影响及其机理：实验模拟研究

Nanoporous structures are ubiquitously found in minerals, rocks, soil and other geologic medium. The adsorption of heavy metal in mineral nanopores is essential to the fields including nanogeochemistry and environmental science. While most researches have studied the effects of pore size and nano-confined fluid on the adsorption performance of nanopores, much less work has focussed on the role of pore surface groups in the adsorption of mineral nanopores. In this proposed project, we will first synthesize nanoporous mineral samples with different surface groups such as silanol groups, aluminol groups, and also some organic groups, and subsequently use them as model mineral nanopores to systematically test their adsorption of heavy metal ions. We aim to collect reliable experimental data from this controlled adsorption study using model mineral nanopores, clarify the effects and the microscopic mechanisms of surface groups in the heavy metal ions adsorption process, and finally derive a reasonable adsorption model that can consistently bridge the gap between microscopic interaction mechanisms and macroscopic experimental observations associated with adsorption of mineral nanopores. It is anticipated that the scientific results and the fundamental information derived from this study are of both theoretical and experimental significance in providing a key foundation for an improved understanding of the interface reactions confined in a nanopore as well as the migration and enrichment processes of elements in geological environments, and thus facilitate the application of porous minerals and materials in the heavy metal remediation.

纳米孔隙结构普遍存在于矿物、岩石、土壤等地质介质中。矿物纳米孔对重金属的吸附行为是纳米地球化学和环境生态等领域必不可少的研究内容。目前研究主要关注矿物纳米孔孔径和孔内流体性质变化对其吸附性能的影响，表面基团（尤其是多种基团存在的情况）如何在矿物纳米孔吸附过程中发挥作用尚不清楚。本项目拟通过实验模拟的方法，合成具有不同表面基团（硅羟基、硅羟基和铝羟基共存、硅铝羟基和有机基团共存等）的模拟矿物纳米孔，并将其应用于重金属离子的吸附实验。本研究旨在获取不同表面基团的模拟矿物纳米孔吸附重金属实验的可靠数据，阐明表面基团在吸附过程中的作用和微观机制，进而推导基于矿物纳米孔微观作用机制且能够解释宏观吸附规律的吸附模型。相关结果将为地质作用中矿物纳米孔所涉表界面反应机理奠定基础，有助于深刻理解和掌握元素在地质介质中的迁移、富集过程，同时也可为多孔矿物/材料在重金属污染修复中的应用提供理论和实验依据。

地质介质中普遍存在着纳米孔隙结构，纳米孔隙结构影响岩石风化、微量元素富集、污染物治理、页岩气储存等重要地质过程。矿物纳米孔对重金属等离子的吸附行为是纳米地球科学和环境生态等领域的核心研究内容之一。本项目以实验合成模拟矿物纳米孔样品及典型天然纳米孔性矿物为对象，研究它们的结构、表面化学等性质以及其对典型阳/阴离子的吸附性能，获得了一系列新颖的研究结果。主要发现包括：介孔二氧化硅MCM-41吸附Cu2+的吸附量较低，且其不吸附I-。铝掺杂（硅/铝摩尔比为30）的介孔MCM-41吸附I-的分配系数（Kd）可达3.6 mL/g。纤蛇纹石对I-显示出强的吸附能力，当I-初始浓度为0.25 mmol/L，吸附时间为48 h时，纤蛇纹石束吸附I-的Kd值高达179.2 mL/g，比前人报道的其他矿物高出两个数量级。通过对比实验我们获得纤蛇纹石束中的楔形纳米孔是其吸附I-的主要位点，并发现了一种楔形纳米孔的独特吸附机制：楔形纳米孔的孔尺寸由孔中心到孔端元逐渐减小，在吸附过程中，孔壁电势叠加程度由孔中心到孔端元逐渐增加，在孔端元处吸附能力显著增强。纳米管状的埃洛石对IO3-具有强吸附能力，在IO3-初始浓度0.1 mmol/L、吸附时间为48 h时，湖北埃洛石和四川埃洛施吸附IO3-的Kd值分别为131.8和126.6 mL/g，是其多型矿物高岭石的13.5倍。我们提出一直基于几何尺寸匹配的吸附机制：埃洛石独特的纳米管状形貌是其吸附能力增强的根本原因，由于埃洛石的结构片层发生弯曲，使其铝氧片层中八面体空位上方的羟基之间的距离减小，进而使其尺寸和IO3-尺寸相匹配，因此形成具有三个羟基相互作用的强吸附作用。本项目目前已发表学术论文4篇，会议摘要1篇，在国内学术会议作大会和分会场报告交流6次。以上研究结果提高了对纳米孔隙结构所涉吸附规律和作用机制的认识，为环境废水溶液中Cu2+，I-和IO3-等相关阳/阴离子的治理提供了参考，为地球环境中的重金属等离子的迁移及富集提供了实验依据，也为相关纳米孔性矿物资源的高效利用提供新的方向。