Surface Acidity of Montmorillonites

Frenkel, M.

doi:10.1346/ccmn.1974.0220510

Cited by 119 publications

(54 citation statements)

References 22 publications

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“…The formation of XCd(OH) is reasonable (X represents surface groups on red mud) since the degree of dissociation of a water molecule adsorbed on mineral surface is 10 7 times higher than in liquid water (Frenkel, 1974). The greater affinity of hydroxyl metal ions from dissociation over metal ions is also apparent due to the lower degree of hydration of the former which leads to both steric and electrostatic favoritism in the sorption process (Ma and Uren, 1998;Naidu et al, 1994).…”

Section: Xanes Spectroscopy Analysismentioning

confidence: 98%

New insights into the sorption mechanism of cadmium on red mud

Luo

Chen

Ying

et al. 2011

Environmental Pollution

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Cadmium can be strongly sorbed and partially forms inner-sphere complexes on red mud. Effectiveness and mechanism of cadmium (Cd) sorption on original, acidified and ball milling nanoparticle red muds were investigated using batch sorption experiments, sequential extraction analysis and X-ray absorption near edge structure (XANES) spectroscopy. The maximum sorption capacity of Cd was 0.16, 0.19, and 0.21 mol/kg for the original, acidified, and nano-particle red muds at pH 6.5, respectively. Both acidification and ball-milling treatments significantly enhanced Cd sorption and facilitated transformation of Cd into less extractable fractions. The Cd L III -edge XANES analysis indicated the formation of inner-sphere complexes of Cd similar to XCdOH (X represents surface groups on red mud) on the red mud surfaces although outer-sphere complexes of Cd were the primary species. This work shed light on the potential application of red mud to remediate Cd-contaminated soils and illustrated the promising tool of XANES spectroscopy for speciation of multicomponent systems of environmental relevance. a r t i c l e i n f o

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Section: Xanes Spectroscopy Analysismentioning

confidence: 98%

New insights into the sorption mechanism of cadmium on red mud

Luo

Chen

Ying

et al. 2011

Environmental Pollution

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“…Figures 2 and 3 are histograms which relate some of the features of the reactions to the number of acid sites of montmoril- lonite with pKa <3.2. The acid sites (strength and number) were determined in a previous study using Hammett indicators (Frenkel, 1974). In fact, the values are merely approximations, because the number of acid sites determined by a Hammett indicator is strictly correct only for the specific experimental conditions of the measurement.…”

Section: Resultsmentioning

confidence: 99%

“…Pure d-limonene (Fluka) was reacted with homoionic samples (Na, Mg, AI, and H) of montmorillonite from Makhtesh Ramon, Israel (sample MF 14), prepared as previously described (Frenkel, 1974). For comparison, reactions were also carried out with homoionic samples of A.P.I.…”

Section: Methodsmentioning

confidence: 99%

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Interlayer Cations as Reaction Directors in the Transformation of Limonene on Montmorillonite

Frenkel

Heller-Kallai

1983

Clays and clay miner.

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Abstract--Clays may catalyze chemical reactions by acting as Br6nsted acids, Lewis acids, and/or Lewis bases. The changes occurring when limonene (p-menthadiene) is heated in the presence of montmoriUonite illustrate how Brrnsted and Lewis acidity may operate competitively, the nature of the interlayer cations determining which reaction dominates. The rate at which the starting material disappears increases with the acidity of the clay, which depends upon the interlayer cations (Na < Mg < A1 < H). The concentration of disproportionation and isomerization products reaches a maximum after reaction times which decrease with increasing surface acidity of the clay. p-cymene is produced by oxidation in concentrations inversely related to the surface acidity of the clay. The course of the chemical reaction can thus be steered in the preferred direction by an appropriate choice of interlayer cations.

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“…6). The Brønsted acidity of Mt is derived from the polarization of interlayer water molecules by interlayer-hydrated cations (Frenkel 1974;Heller-Kallai 2006;Rupert et al 1987;Mortland and Raman 1968). The cations attract the electron pairs of the hydrated water and weaken the -OH bond in H 2 O, making it easier to break.…”

Section: Solid Acidity Of Cation-exchanged Montmorillonitementioning

confidence: 99%

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

Liu

Yuan

et al. 2013

Phys Chem Minerals

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The effects of heating and cation exchange on the solid acidity of montmorillonite were investigated using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared spectroscopy. The number of total, Brønsted, and Lewis acid sites showed the same modulation tendency with increasing heating temperature, reaching a maximum at 120°C and subsequently decreasing until it reaches a minimum at 600°C. The Lewis acid sites result from unsaturated Al 3? cations, and their number increased with the heating temperature due to the dehydration and dehydroxylation of montmorillonite. The generation and evolution of Brønsted acidity were mainly related to interlayer-polarized water molecules. Water adsorbed on the unsaturated Al 3? ions also acted as a Brønsted acid. The acid strength of the Brønsted acid sites was dependent on the polarization ability of the exchangeable cation, the amount of interlayer water, and the degree of dissociation of the interlayer water coordinated to exchangeable cations. All cation-exchanged montmorillonites exhibited different numbers of acid sites and various distributions of acid strength. Brønsted acidity was predominant in Al 3? -exchanged montmorillonite, whereas the Na ? -and K ? -exchanged montmorillonites showed predominantly Lewis acidity. Moreover, Mg 2? -and Li ? -exchanged montmorillonites exhibited approximately equal numbers of Brønsted and Lewis acid sites. The Brønsted acidity of cation-exchanged montmorillonite was positively correlated with the charge-to-radius ratios of the cations, whereas the Lewis acidity was highly dependent on the electronegativity of the cations. The acid strengths of Al 3? -and Mg 2? -exchanged montmorillonites were remarkably higher than those of monovalent cationexchanged montmorillonites, showing the highest acid strength (H 0 B -3.0). Li ? -and Na ? -exchanged montmorillonites exhibited an acid strength distribution of -3.0 \ H 0 B 4.8, with the acid strength ranging primarily from 1.5 to 3.3 in Li ? -exchanged montmorillonite, whereas only weaker-strength acid sites (1.5 \ H 0 B 4.8) were present in K ? -exchanged montmorillonite. The results of the catalysis experiments indicated that montmorillonite promoted the thermal decomposition of the model organic. The catalytic activity showed a positive correlation with the solid acidity of montmorillonite and was affected by cation exchange, which occurs naturally in geological processes.

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Surface Acidity of Montmorillonites

Cited by 119 publications

References 22 publications

New insights into the sorption mechanism of cadmium on red mud

New insights into the sorption mechanism of cadmium on red mud

Interlayer Cations as Reaction Directors in the Transformation of Limonene on Montmorillonite

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

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