微孔模拟物Stber二氧化硅与有机质相互作用的实验研究
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摘要
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Stber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Stber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。Stber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。
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 Stber 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 Stber silica's micropores( pore diameter 0. 8 nm). Under the catalysis of NH_3,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 NH_3 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. Stber 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.
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 Stber 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 Stber silica's micropores( pore diameter 0. 8 nm). Under the catalysis of NH_3,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 NH_3 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. Stber 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.
引文
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[16]St9ber W,Fink A,Bohn E.Controlled growth of monodisperse silica spheres in the micron size range[J].Journal of Colloid and Interface Science,1968,26(1):62-69.
[17]Li S S,Wan Q,Qin Z H,et al.Understanding St9ber silica's pore characteristics measured by gas adsorption[J].Langmuir,2015,31(2):824
[18]Li S,Wan Q,Qin Z,et al.Unraveling the mystery of St9ber silica's microporosity[J].Langmuir,2016,32(36):9180-9187.
[19]Zhuravlev L T.The surface chemistry of amorphous silica.Zhuravlev model[J].Colloids and Surfaces a-Physicochemical and Engineering Aspects,2000,173(1-3):1-38.
[20]Iler R K,The chemistry of silica:Solubility,polymerization,colloid and surface properties[M].The United States of America:A Wiley-lnterscience publication.1979.
[21]Ying J Y,Benziger J B,Navrotsky A.Structural evolution of alkoxide silica-gels to glass-effect of catalyst p H[J].Journal of the American Ceramic Society,1993,76(10):2571-2582.
[22]Mitropoulos A C.The Kelvin equation[J].Journal of Colloid and Interface Science,2008,317(2):643-648.
[2]Wang Y F,Bryan C,Xu H F,et al.Nanogeochemistry:Geochemical reactions and mass transfers in nanopores[J].Geology,2003,31(5):387-390.
[3]Xu H F,Chen T H,Nie Z M,et al.Self-Assembled nanostructures in biomineralization[J].Geochimica et Cosmochimica Acta,2003,67(18):A541-A541.
[4]Loucks R G,Reed R M,Ruppel S C,et al.Morphology,genesis,and distribution of nanometer-scale pores in siliceous mudstones of the mississippian barnett shale[J].Journal of Sedimentary Research,2009,79(11-12):848-861.
[5]Denoyel R,Pellenq R J M.Simple phenomenological models for phase transitions in a confined geometry.1:Melting and solidification in a cylindrical pore[J].Langmuir,2002,18(7):2710-2716.
[6]Jahnert S,Chavez F V,Schaumann G E,et al.Melting and freezing of water in cylindrical silica nanopores[J].Physical Chemistry Chemical Physics,2008,10(39):6039-6051.
[7]Feng X,Fryxell G E,Wang L Q,et al.Functionalized monolayers on ordered mesoporous supports[J].Science,1997,276(5314):923-926.
[8]Wu D,Navrotsky A.Small molecule-silica interactions in porous silica structures[J].Geochimica et Cosmochimica Acta 2013(109):38-50.
[9]Hochella M F,Banfield J F.Chemical weathering of silicates in nature:A microscopic perspective with theoretical considerations in Chemical weathering rates of silicate minerals[J].Reviews in Mineralogy&Geochemistry,1995,31:353-406.
[10]Hochella M F.There's plenty of room at the bottom:Nanoscience in geochemistry[J].Geochimica et Cosmochimica Acta,2002,66(5):735-743.
[11]Zimmerman A R,Chorover J,Goyne K W,et al.Protection of mesopore-adsorbed organic matter from enzymatic degradation[J].Environmental Science&Technology,2004,38(17):4542-4548.
[12]Rother G,Krukowski E G,Wallacher D,et al.Pore size effects on the sorption of supercritical CO2in mesoporous CPG-10 silica[J].Journal of Physical Chemistry C,2012,116(1):917-922.
[13]Tobler D J,Shaw S,Benning L G.Quantification of initial steps of nucleation and growth of silica nanoparticles:An in-situ SAXS and DLS study[J].Geochimica Et Cosmochimica Acta,2009,73(18):5377-5393.
[14]Tobler D J,Benning L G.In Situ and time resolved nucleation and growth of silica nanoparticles forming under simulated geothermal conditions[J].Geochimica Et Cosmochimica Acta,2013,114:156-168.
[15]Wu D,Hwang S-J,Zones S I,et al.Guest-host interactions of a rigid organic molecule in porous silica frameworks[J].Proceedings of the National Academy of Sciences of the United States of America,2014,111(5):1720-1725.
[16]St9ber W,Fink A,Bohn E.Controlled growth of monodisperse silica spheres in the micron size range[J].Journal of Colloid and Interface Science,1968,26(1):62-69.
[17]Li S S,Wan Q,Qin Z H,et al.Understanding St9ber silica's pore characteristics measured by gas adsorption[J].Langmuir,2015,31(2):824
[18]Li S,Wan Q,Qin Z,et al.Unraveling the mystery of St9ber silica's microporosity[J].Langmuir,2016,32(36):9180-9187.
[19]Zhuravlev L T.The surface chemistry of amorphous silica.Zhuravlev model[J].Colloids and Surfaces a-Physicochemical and Engineering Aspects,2000,173(1-3):1-38.
[20]Iler R K,The chemistry of silica:Solubility,polymerization,colloid and surface properties[M].The United States of America:A Wiley-lnterscience publication.1979.
[21]Ying J Y,Benziger J B,Navrotsky A.Structural evolution of alkoxide silica-gels to glass-effect of catalyst p H[J].Journal of the American Ceramic Society,1993,76(10):2571-2582.
[22]Mitropoulos A C.The Kelvin equation[J].Journal of Colloid and Interface Science,2008,317(2):643-648.
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