微孔模拟物Stöber二氧化硅与有机质相互作用的实验研究

地球环境中普遍存在的纳米孔与有机质的相互作用对资源和环境领域许多重要科学问题(如有机质的吸附与保存、油气的赋存与采收以及二氧化碳的地质封存等)起着关键作用。然而,目前关于纳米孔特别是微孔(<2 nm)与有机质作用的系统研究还比较少。本文选择实验室合成的Stber二氧化硅作为模拟矿物微孔,采用热红联用技术(TG/DSC-FTIR)来研究其与系列有机溶剂(乙醇、正丙醇、正丁醇、正庚醇)作用后的热化学性质。结果表明,乙醇和正丙醇较易进入Stber二氧化硅微孔(孔径0.8 nm)。在NH_3催化作用下,醇与孔内外硅羟基发生烷氧基化作用,孔外烷氧基的脱除温度随着溶剂碳链增加而降低,放热效应逐渐增强;相反,孔内烷氧基的脱除温度随碳链增加而增加,放热效应逐渐减弱。在无NH_3存在条件下,由于烷氧基化作用减弱,乙醇与正丙醇能在孔内游离存在,孔内烷氧基的脱除温度随溶剂碳链增加呈下降趋势。Stber二氧化硅的微孔结构直接影响了醇类有机质在不同气氛下的热解行为,甲烷、乙烯、丙醛等分子的逸出也为纳米孔隙结构束缚下的有机质的深部热行为提供了参考。

Interaction between Micropore Model Stöber Silica and Organic Matter: An Experimental Study

The ubiquitous interaction between nanopores and organic materials in the earth environment is critical to many substantial scientific issues, such as adsorption and preservation of organic matter, storage and recovery of oil and gas, and geological sequestration of carbon dioxide, etc. Yet, so far it still lacks systematic investigations of the interaction between nanopores especially micropores (<2 nm) and organic materials. In this work, we synthesized Stöber silica as a mineral micropore model and investigated its thermochemical properties by using TG/DSC-FTIR after the interaction with a series of organic solvents (including ethanol, n-propyl alcohol, n-butyl alcohol, and n-heptyl alcohol).Our results indicate that ethanol and propyl alcohol can easily enter Stöber silica''s micropores (pore diameter 0.8 nm). Under the catalysis of NH₃, alkoxylation takes place between alcohols and surface silanol groups in and outside of the micropores. The removal temperature of alkoxyl groups outside of the pores decreases while the exothermic effect intensifies with increasing carbon chain length of the solvent. In contrast, the removal temperature of alkoxyl groups inside the pores increases with increasing carbon chain length, while the exothermic effect declines gradually. Without NH₃ catalysis, due to the weakening of the alkoxylation, free ethanol and propyl alcohol molecules could exist inside the micropores and the removal temperature of alkoxyl groups inside the pores tends to decline with increasing carbon chain length of the solvent. Stöber silica''s microporous structure directly modulates the thermolysis behavior of organic alcohols under different atmospheres, and the evolved methane, ethylene, and propionic aldehyde may provide a reference for deep thermal behavior of organic materials confined in nanoporous structure.