Characterization of mesoporous silicas by in situ small angle neutron scattering during isothermal gas adsorption

Ramsay, J.D.F.; Kallus, S.

doi:10.1016/s0022-3093(01)00445-8

Cited by 11 publications

(18 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…SANS has been widely used for characterizing the structure of porous materials as well as investigating the adsorption of liquids in small pores. 14,[26][27][28][29][30][31][32] This paper describes a new methodology which can be used for studying adsorption of supercritical fluids in porous media by the combination of SANS and neutron transmission techniques. This methodology was applied for the evaluation of the adsorption of SC CO 2 in Vycor porous glass as well as in oxidized and nonoxidized aerogels at constant temperature as a function of pressure.…”

Section: Discussionmentioning

confidence: 99%

Adsorption of supercritical CO2 in aerogels as studied by small-angle neutron scattering and neutron transmission techniques

Melnichenko

Wígnall

Cole

et al. 2006

The Journal of Chemical Physics

View full text Add to dashboard Cite

Small-angle neutron scattering (SANS) has been used to study the adsorption behavior of supercritical carbon dioxide (CO2) in porous Vycor glass and silica aerogels. Measurements were performed along two isotherms (T=35 and 80 degrees C) as a function of pressure (P) ranging from atmospheric up to 25 MPa, which corresponds to the bulk fluid densities ranging from rho(CO2) approximately 0 to 0.9 gcm3. The intensity of scattering from CO2-saturated Vycor porous glass can be described by a two-phase model which suggests that CO2 does not adsorb on the pore walls and fills the pore space uniformly. In CO2-saturated aerogels an adsorbed phase is formed with a density substantially higher that of the bulk fluid, and neutron transmission data were used to monitor the excess adsorption at different pressures. The results indicate that adsorption of CO2 is significantly stronger in aerogels than in activated carbons, zeolites, and xerogels due to the extremely high porosity and optimum pore size of these materials. SANS data revealed the existence of a compressed adsorbed phase with the average density approximately 1.07 gcm3, close to the density corresponding to closely packed van der Waals volume of CO2. A three-phase model [W. L. Wu, Polymer 23, 1907 (1982)] was used to estimate the volume fraction phi3 of the adsorbed phase as a function of the fluid density, and gave phi3 approximately 0.78 in the maximum adsorption regime around rho(CO2) approximately 0.374 gcm3. The results presented in this work demonstrate the utility of SANS combined with the transmission measurements to study the adsorption of supercritical fluids in porous materials.

show abstract

Section: Discussionmentioning

confidence: 99%

Adsorption of supercritical CO2 in aerogels as studied by small-angle neutron scattering and neutron transmission techniques

Melnichenko

Wígnall

Cole

et al. 2006

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…Small-angle scattering techniques are widely used for the determination of the specific surface area, pore size, and wall architecture of mesoporous and microporous materials. For the in situ investigation of liquid sorption effects by scattering of x rays [10][11][12][13] or neutrons, [14][15][16] special adsorption cells were developed. An overview is given by the review article of Hoinkis.…”

Section: Introductionmentioning

confidence: 99%

Physisorbed films in periodic mesoporous silica studied byin situsynchrotron small-angle diffraction

et al. 2006

View full text Add to dashboard Cite

Adsorption and capillary condensation of an organic fluid in a periodic mesoporous silica ͑SBA-15͒ are studied by in situ synchrotron diffraction. Powder diffraction patterns resulting from the two-dimensional hexagonal packing of the cylindrical pores of SBA-15 are collected as a function of vapor pressure during continuous adsorption and desorption of the fluid ͑perfluoropentane C 5 F 12 ͒, using a specially designed sorption cell. Seven diffraction peaks with systematic changes of the intensity are resolved as the adsorbed film thickness increases along the adsorption isotherm. The integrated intensities of the diffraction peaks are analyzed with a structural model involving four levels of electron density ͑dense silica matrix, microporous corona around the pores, adsorbed film, and core space of the pores͒. The model provides quantitative information about the structure of the evacuated specimen, the filling of the corona, and the growing thickness of the liquid film with increasing pressure. A very good fit of the data by this model is found for relative pressures up to p / p 0 Ϸ 0.5, but the fit of the high-indexed diffraction peaks becomes poor close to the capillary condensation pressure ͑p / p 0 Ϸ 0.68͒. Tentatively, this fact may be attributed to a deviation of the liquid film structure from the simple flat geometry close to the phase transformation, presumably caused by density fluctuations.

show abstract

“…The enhanced information obtained by such combined methods has motivated the development of several ͑usually low pressure͒ adsorption-in situ-scattering setups and cells. [34][35][36][37][38][39][40][41][42][43][44] Our long-term aim is the development of a generic combined adsorption/diffraction technique for investigating the structural properties of adsorbed fluids in porous solids. In the present study, as the first step, we have performed in situ diffraction measurements of adsorbed carbon dioxide on purely siliceous MCM-41 along an isotherm ͑253 K͒ at pressures varying between 0 and 18 bar.…”

Section: Introductionmentioning

confidence: 99%

In situneutron diffraction study of adsorbed carbon dioxide in a nanoporous material: Monitoring the adsorption mechanism and the structural characteristics of the confined phase

et al. 2008

View full text Add to dashboard Cite

The behavior of molecules confined in a nanoporous material was studied by adsorption from the gas phase with in situ neutron diffraction, with the aid of a high-pressure adsorption apparatus and the General Materials diffractometer ͑GEM, ISIS͒. The aim of this work is to establish the combined adsorption/neutron diffraction technique as a unique tool to elucidate both the adsorption mechanism and the structure of molecules confined in nanoporous materials. For this reason, a well-defined mesoporous system ͑MCM-41͒ was selected as adsorbent and carbon dioxide as adsorbate, while diffraction measurements have been carried out along a CO 2 adsorption isotherm ͑T = 253 K͒ in the pressure range of 0-18 bar. Small-angle results at low pressures favor the development of an adsorbed film rather than filling of wall microporosity, while diffraction data provide evidence of a distinct molecular arrangement of this adsorbed layer. At higher pressures diffraction data reveal that the structure of the condensed phase is directly comparable to that of bulk liquid CO 2 .

show abstract

Characterization of mesoporous silicas by in situ small angle neutron scattering during isothermal gas adsorption

Cited by 11 publications

References 16 publications

Adsorption of supercritical CO2 in aerogels as studied by small-angle neutron scattering and neutron transmission techniques

Adsorption of supercritical CO2 in aerogels as studied by small-angle neutron scattering and neutron transmission techniques

Physisorbed films in periodic mesoporous silica studied byin situsynchrotron small-angle diffraction

In situneutron diffraction study of adsorbed carbon dioxide in a nanoporous material: Monitoring the adsorption mechanism and the structural characteristics of the confined phase

Contact Info

Product

Resources

About