Small molecule – Silica interactions in porous silica structures

Wu, Di; Navrotsky, Alexandra

doi:10.1016/j.gca.2013.01.038

Cited by 34 publications

(36 citation statements)

References 73 publications

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“…S1). Interestingly, analogous adsorption behavior has also been observed on mesoporous silica, with ethanol showing much stronger binding with the surface than water (35).…”

Section: Discussionsupporting

confidence: 55%

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Navrotsky

2015

Proc. Natl. Acad. Sci. U.S.A.

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Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic-NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces.thermodynamics | adsorption calorimetry | ligand-capped nanocrystal | biomineralization | carbonate formation

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“…S1). Interestingly, analogous adsorption behavior has also been observed on mesoporous silica, with ethanol showing much stronger binding with the surface than water (35).…”

Section: Discussionsupporting

confidence: 55%

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Navrotsky

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Despite the variety and complexity of organic -silica interactions, they seem to be largely governed by hydrophobicity/hydrophilicity and/or acidity/basicity 19,20 . Numerous studies were performed on the structure of silica polymorphs [21][22][23][24][25] and kinetics of surface binding 26,27 .…”

Section: Introductionmentioning

confidence: 99%

Energy Landscape of Water and Ethanol on Silica Surfaces

Guo

Sun

et al. 2015

J. Phys. Chem. C

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Fundamental understanding of small molecule -silica surface interactions at their interfaces is essential for the scientific, technological and medical communities. We report direct enthalpy of adsorption (∆h ads ) measurements for ethanol and water vapor on porous silica glass (CPG-10), in both hydroxylated and dehydroxylated (hydrophobic) forms. The results suggest a spectrum of energetics as a function of coverage, stepwise for ethanol but continuous for water.The zero coverage enthalpy of adsorption for hydroxylated silica shows the most exothermic enthalpies for both water (-72.7 ± 3.1 kJ/mol water) and ethanol (-78.0 ± 1.9 kJ/mol ethanol).The water adsorption enthalpy becomes less exothermic gradually until reaching its only plateau (-20.7 ± 2.2 kJ/mol water) reflecting water clustering on a largely hydrophobic surface, while the enthalpy of ethanol adsorption profile presents two well separated plateaus, corresponding to strong chemisorption of ethanol on adsorbate-free silica surface (-66.4 ± 4.8 kJ/mol ethanol), and weak physisorption of ethanol on ethanol covered silica (-4.0 ± 1.6 kJ/mol ethanol). On the other hand, dehydroxylation leads to missing water -silica interactions, whereas the number of ethanol binding sites is not impacted. The isotherms and partial molar properties of adsorption suggest that water may only bind strongly onto the silanols (which are a minor species on silica glass), whereas ethanol can interact strongly with both silanols and the hydrophobic areas of the silica surface.

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“…Slightly stronger interactions were found by Trofymluk et al (22) for mesoporous silica phases containing long-chain molecules. Recently, Wu et al (23) measured the enthalpy of interaction of various small molecules with mesoprous silicas using immersion calorimetry. The hydration enthalpies of a series of cation exchanged aluminosilicate or gallosilicate zeolites were studied by .…”

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Guest–host interactions of a rigid organic molecule in porous silica frameworks

Hwang

Zones

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Molecular-level interactions at organic-inorganic interfaces play crucial roles in many fields including catalysis, drug delivery, and geological mineral precipitation in the presence of organic matter. To seek insights into organic-inorganic interactions in porous framework materials, we investigated the phase evolution and energetics of confinement of a rigid organic guest, N,N,N-trimethyl-1-adamantammonium iodide (TMAAI), in inorganic porous silica frameworks as a function of pore size (0.8 nm to 20.0 nm). We used hydrofluoric acid solution calorimetry to obtain the enthalpies of interaction between silica framework materials and TMAAI, and the values range from −56 to −177 kJ per mole of TMAAI. The phase evolution as a function of pore size was investigated by X-ray diffraction, IR, thermogravimetric differential scanning calorimetry, and solid-state NMR. The results suggest the existence of three types of inclusion depending on the pore size of the framework: single-molecule confinement in a small pore, multiple-molecule confinement/adsorption of an amorphous and possibly mobile assemblage of molecules near the pore walls, and nanocrystal confinement in the pore interior. These changes in structure probably represent equilibrium and minimize the free energy of the system for each pore size, as indicated by trends in the enthalpy of interaction and differential scanning calorimetry profiles, as well as the reversible changes in structure and mobility seen by variable temperature NMR.mesoporous silica | thermodynamics | porous materials K nowing both the structure and molecular mobility of guest matter in nanosized pores and channels, which often differ from those in the bulk unconfined material or solution, is essential for fundamental understanding of processes in both science and technology, with applications including natural processes such as biomineralization (1-3) and membrane transport (4, 5), engineering processes such as oil recovery (6-8), CO 2 sequestration (9-11), catalysis (12-14), and biomedical processes including diagnostics and drug delivery (15-17). Most of the pioneering research has used soft matter as guests, including gas and liquid phases, low-melting point organic solids, and longchain polymers (18)(19)(20).In our earlier studies, various calorimetric methods have been designed to investigate guest-host interactions. Piccione et al.(21) developed a novel system for hydrofluoric acid (HF) solution calorimetry to study the interactions of four different silica zeolite frameworks with several quaternary ammonium structure-directing agents (SDAs). The enthalpies of interaction were measured to be −32.0 to −181.0 kJ per mole of SDA. Slightly stronger interactions were found by Trofymluk et al. (22) for mesoporous silica phases containing long-chain molecules. Recently, Wu et al. (23) measured the enthalpy of interaction of various small molecules with mesoprous silicas using immersion calorimetry. The hydration enthalpies of a series of cation exchanged aluminosilicate or gallosilicate ze...

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Small molecule – Silica interactions in porous silica structures

Cited by 34 publications

References 73 publications

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Energy Landscape of Water and Ethanol on Silica Surfaces

Guest–host interactions of a rigid organic molecule in porous silica frameworks

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