Computation of Pore Sizes from Physical Adsorption Data

Pierce, Conway

doi:10.1021/j150503a005

Cited by 317 publications

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“…For analysis of the isotherms the criteria of Broekhoff and De Boer (1967) were followed to obtain parameters SB~a-(specific surface area, calculated from the BET equation), CBEa-(energetic constant of BET theory), and Vao (pore volume as calculated with the liquid adsorptive at P/P0 = 0.98). The distribution of the pore size in the mesopore range was obtained by the method of Pierce (1953). The microporosity of the samples was analyzed using the t-method of Lippens and De Boer (1965).…”

Section: Methodsmentioning

confidence: 99%

Mechanism of Acid Activation of Magnesic Palygorskite

González

Pesquera

Benito

et al. 1989

Clays and clay miner.

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Abstract--This paper compares the texture of palygorskite after acid leaching with that of the product after extraction silica is removed. These effects were evaluated on the basis of nitrogen adsorptiondesorption and mercury penetration porosimetry. Acid leaching at reflux temperature with 2 N HC1 resulted in an increase in surface area from 138 to 399 mVg, due to a partial (~ 50%) dissolution of the octahedral sheet and the creation of microporosity. This microporosity disappeared if the silica generated by the leaching was removed. The surface area also decreased from 399 to 214 mVg, and the pore volume decreased from 0.538 to 0.507 cm3/g. The microporosity must therefore have been due to texture development in the generated silica.

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Section: Methodsmentioning

confidence: 99%

Mechanism of Acid Activation of Magnesic Palygorskite

González

Pesquera

Benito

et al. 1989

Clays and clay miner.

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“…The t-plot method of assessing the microporosity of the HFO aggregates [28,29], was applied to the N 2 gas adsorption isotherms. The size distribution of pores in the range between pore diameters 2 and 95 nm (mesopores) was evaluated by applying the Barrett-Joyner-Halenda (BJH) method [30,31] to the N 2 gas desorption isotherm data. For the BJH calculations, the pore shape was assumed to be cylindrical.…”

Section: Surface Area and Porosity By Gas Adsorptionmentioning

confidence: 99%

Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Hofmann¹,

Pelletier

Michot

et al. 2004

Journal of Colloid and Interface Science

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Hydrous ferric oxides (HFO) are efficient sorbents for inorganic and organic pollutants and therefore have great potentials in environmental science and engineering applications. Freezing and thawing of HFO suspensions leads to the formation of dense HFO aggregates. It facilitates the handling and increases the drying rate of HFO. In this study, we used a combination of pycnometry, gas adsorption (N 2 gas, water vapor), and small-angle neutron scattering (SANS) to characterize the porosity and pore size distribution of dense HFO aggregates formed by freezing dialyzed HFO suspensions at −25 • C and thawing them at room temperature. The crystallinity of the HFO, which was a 2-line ferrihydrite, was not affected by this treatment. Wet sieving and laser diffraction analysis showed that the dense HFO aggregates had a unimodal size distribution with an average diameter of 235 ± 35 µm. Increasing the freezing rate by cooling with liquid N 2 (−196 • C) resulted in much smaller aggregates with an average diameter of 20 µm. Adding NaNO 3 electrolyte to the HFO suspensions prior to freezing also resulted in the formation of smaller aggregates. The dense HFO aggregates formed at −25 • C had a porosity of 0.73 ± 0.02 l l −1 . SANS revealed a unimodal size distribution of pores, with an average pore diameter of 2.0 nm. The diameter of the HFO crystallites was estimated by transmission electron microscopy to be 1.9 ± 0.5 nm. Geometrical considerations taking into account the unit particle and average pore size suggest that the crystallites retain 1-2 layers of hydration water during the coagulation induced by freezing. Analysis by N 2 gas adsorption showed that drying the dense HFO aggregates induced a reduction in porosity by about 25% and shifted the pore size distribution to smaller diameters. Rewetting during water vapor adsorption did not induce significant changes of the aggregate structure. The specific surface area of the dry HFO aggregates was between 320 and 380 m 2 g −1 .

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“…A micro e mesoporosidade das amostras foi avaliada quantitativamente aplicando, respectivamente, a equação de Dubinin-Raduskevich (DR) 28 e método α S 28 e o método de Pierce 29 , estando os resultados expressos na tabela 2.…”

Section: Resultsunclassified

Desaluminação do zeólito ofretita por efeito da radiação gama

Carvalho¹,

Carvalho²

1998

Quím. Nova

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Recebido em 23/7/97; aceito em 7/4/98 DEALUMINATION OF OFFRETITE THROUGH γ-IRRADIATION. Protonic offretite samples were modified by γ-irradiation under different conditions of humidity. The results of infrared spectroscopy and X-ray diffraction reveal that the presence of water is essential to promote dealumination, as the samples irradiated in vacuum only show crystallinity loss. The degree of dealumination is, mainly, controlled by the γ-irradiation dose while the textural modifications depend also on the percentage of water.Keywords: dealumination; offretite; γ-irradiation. ARTIGO INTRODUÇÃOAs propriedades dos zeólitos como catalisadores, adsorventes e permutadores iônicos, estão diretamente relacionadas com o teor em alumínio da rede cristalina, constatando-se, por exemplo, que o aumento da razão Si/Al da rede zeolítica se traduz numa maior estabilidade térmica e em alterações significativas da acidez destes materiais.Na medida em que a maioria das estruturas zeolíticas só pode ser sintetizada num intervalo muito estreito de razões Si/Al, revestem-se de grande importância os tratamentos de desaluminação que, como o nome indica, permitem remover uma fração dos áto-mos de alumínio da estrutura zeolítica, sem que tal afete de forma muito acentuada a rede cristalina das amostras.A primeira referência a este tipo de tratamentos pós-síntese é um estudo realizado nos anos 60 por Barrer e Makki 1 sobre a modificação do zeólito clinoptilolita por tratamentos ácidos. Desde este trabalho pioneiro encontram-se propostos na literatura diversos outros processos de desaluminação de estruturas zeolíticas, sendo os tratamentos hidrotérmicos (calcinações a temperaturas superiores a 773 K, em regime de steaming ou self-steaming, isto é, introduzindo ou não um fluxo contínuo de vapor de água no sistema reaccional) 2,3 e os tratamentos com SiCl 4 4 os mais vulgarmente usados. Dos restantes salientam-se reações com EDTA 5 ou outros agentes quelantes 6 e tratamentos com soluções de (NH 4 ) 2 SiF 6 7 , cuja aplicação é relativamente frequente, e reações com F 2 8 , com compostos fluorados 9,10 e compostos clorados 11,12 , que são empregues de modo esporádico.As estruturas zeolíticas podem ainda ser modificadas por efeito da radiação γ, encontrando-se, de fato, na literatura, alguns trabalhos em que por este processo se promovem alterações das propriedades ácidas das estruturas irradiadas [13][14][15][16][17] . Revendo estes estudos conclui-se que, por um lado, nenhum deles teve em vista a desaluminação das estruturas e, por outro, constata-se que em nenhum dos casos as estruturas foram irradiadas em atmosfera de umidade.Considerando que a presença de água é determinante para promover a desaluminação das estruturas zeolíticas por tratamentos térmicos, o trabalho que agora se apresenta teve por objetivo realizar um estudo preliminar sobre o efeito da radiação γ, nomeadamente do calor gerado por esta radiação, sobre estruturas zeolíticas, em diferentes condições de umidade. A estrutura selecionada para este estudo foi a do zeólito ofr...

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Computation of Pore Sizes from Physical Adsorption Data

Cited by 317 publications

References 0 publications

Mechanism of Acid Activation of Magnesic Palygorskite

Mechanism of Acid Activation of Magnesic Palygorskite

Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Desaluminação do zeólito ofretita por efeito da radiação gama

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