模拟矿物纳米孔在吸附作用中的尺寸和表面效应实验研究

Nanoporous structures are ubiquitously found in rocks, soil, sediments, minerals, organic matters, and even organisms. It was thought that sorption behavior of mineral nanopores might have played a critical role in many important earth science research areas, such as weathering, trace element enrichment, shale gas, environmental polution, bioavailability, and carbon cycling, etc. Yet, fundamental knowledge gap still exists concerning how mineral nanopores and associated pore characteristics influence sorption processes. Based on the perspective of nanogeoscience, we propose that the effects of pore size and surface chemistry are the key to the understanding of special sorption mechanism involving mineral nanopores. We will first synthesize nanoporous silica materials, quantitatively change their pore size and surface chemistry, and subsequently use them as model mineral nanopores to systematically test their role in the sorption uptake of trace elements and organic compounds. We aim to collect reliable experimental data from this controlled sorption study using model mineral nanopore, clarify the effects and microscopic mechanisms of involved experimental factors especially the pore characteristics in the sorption process, and eventually derive a reasonable sorption model that can consistently bridge the gap between mineral nanopore-associated microscopic interaction mechanisms and macroscopic experimental observations. The scientific basic results and new findings anticipated from this project are believed to have significant implications in many related areas including resources, environment, energy, ecology and so on.

纳米孔隙结构普遍存在于岩石、土壤、沉积物、矿物、有机质甚至生物体中。矿物纳米孔的吸附行为被认为在许多重要地球科学领域可能发挥关键作用，比如风化、微量元素富集、页岩气、环境污染、生物可利用性、碳循环等。然而，矿物纳米孔及其孔特征如何在吸附过程中发挥作用尚不清楚。本着纳米地球科学的认识角度，我们提出矿物纳米孔的孔尺寸和表面效应是理解其特殊吸附机制的关键。我们将定量地控制合成纳米孔二氧化硅的孔尺寸和表面化学特征，并将其作为模拟矿物纳米孔应用于微量元素和有机物吸附的系统实验研究。本项目旨在获取模拟矿物纳米孔吸附实验的可靠数据，阐明各相关因素特别是孔特征在吸附过程中的作用和微观机理，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。本项目研究获得的基础科研数据和发现将在资源、环境、能源、生态等多个领域有着潜在的应用价值。

纳米孔隙结构普遍存在于矿物、岩石、土壤、沉积物等地质介质中。矿物纳米孔的吸附行为在许多重要的地球科学领域中发挥着关键作用，如岩石风化、微量元素富集、生物可利用性、环境污染治理、页岩气储存等。然而，矿物纳米孔及其孔特征参数如何在吸附过程中发挥作用尚不清楚。本项目采用经典的Stöber和MCM-41方法分别合成了微孔和介孔二氧化硅，通过优化合成和后处理条件，揭示了相关多孔物质的成孔机理，获得了结构稳定的微孔和介孔二氧化硅样品。并进一步以微孔Stöber和介孔MCM-41二氧化硅为模拟矿物纳米孔，研究了其对重金属和有机质的吸附性能、纳米孔空间限制下物质的物理化学性质，获得了一系列新颖的研究成果。主要发现包括：微孔封堵理论可用来解释Stöber二氧化硅气体吸附结果的巨大差异，团聚加单体生长模型较符合其成孔过程；Stöber二氧化硅吸附Cu2+和Mn2+的吸附量，在20~60℃范围内随着温度升高而增加，在pH值3~6范围内随pH的升高而增加；有机分子与微孔二氧化硅的作用受分子大小及孔尺寸限制，因而影响样品孔内有机质的吸入量、表面基团反应程度及相应吸/放热效应等；MCM-41介孔中CTAB失重量随着孔尺寸越大而变大；氨气易吸附于MCM-41介孔内，其逸出温度可高达250℃；水在介孔中的凝固点可以降到低于零下40℃；介孔MCM-41二氧化硅对Cu2+的吸附24h可达到平衡，吸附量随pH值的增大而增大；25℃之前，吸附量随着温度的升高而增大，温度继续升高时吸附量降低；增大离子强度，吸附量显著降低；吸附量随着介孔孔尺寸和孔容的增大单调增大，显示了显著的纳米孔空间限制效应；MCM-41吸附Cu2+的等温线符合Langmuir模型，吸附速率符合拟二级动力学模型；Cu2+在MCM-41介孔内有较大比例以外圈络合形式存在，介孔孔壁的电势叠加作用促进了Cu2+与二氧化硅表面的相互作用，导致吸附过程中与孔径紧密关联的纳米空间限制效应。本项目目前已发表学术论文11篇，会议摘要3篇，并多次在国内学术会议作大会和分会场报告交流。以上结果进一步提高了对纳米孔吸附规律和作用机制的认识，为理解资源、环境、生态、能源等领域中纳米孔相关科学问题提供了科学依据。