Monday, July 27, 2009

Journal of Physical Chemistry C, vol. 113, Issues 25-30

29Si NMR Relaxation of Silicated Nanoparticles in Tetraethoxysilane−Tetrapropylammonium Hydroxide−Water System (TEOS−TPAOH−H2O)
Mohamed Haouas
*, David P. Petry, Michael W. Anderson and Francis Taulelle
Institut Lavoisier de Versailles, Universit de Versailles-St. Quentin en Yvelines, Versailles, J. Phys. Chem. C, 2009, 113 (25), pp 10838–10841
DOI: 10.1021/jp903454f

Abstract: Silicon-29 longitudinal (T1) and transverse (T2) NMR relaxation times have been measured in the clear solution precursor of silicalite-1 of composition 25 TEOS−5 TPAOH−400 H2O. The nanoparticles as well as the silicate oligomers are giving rise to observable resonances. An unusually long T1 relaxation time of 126 s is observed for Q4 in nanoparticles. Proper care for acquisition is therefore required for quantifying the distribution of Qn of the nanoparticles, an essential measurement to follow the nanoparticles connectivity evolution.

Clathrate Hydrate Formation: Dependence on Aqueous Hydration Number
Steven F. Dec
J. Phys. Chem. C, 2009, 113 (28), pp 12355–12361
DOI: 10.1021/jp9009977
Abstract: The formation of methane−ethane (C1−C2) clathrate hydrate was studied with high-resolution, solid-state 13C NMR and density functional theory techniques. The 13C NMR experiments yield a number of significant findings: (1) the hydration number of C2(aq) is 26, (2) the initial quantity of C2−51262 sI hydrate cages outnumber C1−512 cages at 274 K, (3) C1−C2 sII hydrate forms at a C1−C2 gas phase composition where only sI hydrate is thermodynamically stable, (4) the initial composition of C1−C2 sII hydrate at 268 K contains less than the original amount of C1, (5) a quasi-liquid water layer solvating both C1 and C2 exists at 268 K, (6) any C1(qll) and C2(qll) present at 253 K is too small to be detected, (7) the initial amounts of C1−C2 sI and sII hydrates formed at 253 K are much smaller than those formed at 268 and 274 K, and (8) C1(aq), C2(aq) and C1(qll), C2(qll) facilitate the formation of C1−C2 sI and sII clathrate hydrate at 268 and 274 K, respectively. On the basis of these experimental observations, a model is developed that states that the aqueous hydration number of the most water-soluble clathrate hydrate former controls the structure of the clathrate hydrate that forms during the initial stages of the clathrate hydrate formation reaction. For methane−ethane clathrate hydrate, this means that ethane in a water liquid phase or quasi-liquid layer eliminates or adds two water molecules to its hydration shell to form the ethane-filled 51262 or 51264 cage building blocks of structure I or structure II clathrate hydrate, respectively. Density functional theory computations on methane-filled 512, 51262, and 51264 and ethane-filled 51262, 51263, and 51264 clathrate hydrate cages yield the stabilization energy of the gas-filled cages and provide theoretical evidence consistent with the experimentally based clathrate hydrate formation model. The proposed model is found to explain the results of other clathrate hydrate formation reactions.

Hierarchical Meso-/Macroporous Aluminum Phosphonate Hybrid Materials as Multifunctional Adsorbents
Tian-Yi Ma, Xue-Jun Zhang and Zhong-Yong Yuan*
J. Phys. Chem. C, 2009, 113 (29), pp 12854–12862
DOI: 10.1021/jp903412m
Abstract: Inorganic−organic hybrid aluminum phosphonate (AlPPh) materials with hierarchical meso-/macroporous structure were synthesized by using two different kinds of organophosphonic acids: amino tri(methylene phosphonic acid) and bis(hexamethylenetriamine)-penta(methylenephosphonic acid). The preparation was accomplished both with and without the assistance of surfactant F127. All the samples possess a uniform macroporous (500−2000 nm) structure of mesoporous (4−5 nm) framework, which were characterized by SEM, TEM, N2 sorption, XRD, TGA-DSC, elemental analysis, MAS NMR, and FT-IR spectroscopy techniques. The as-prepared AlPPh materials were used as multifunctional adsorbents for the efficient removal of heavy metal ions (e.g., Cu2+) and the adsorption of proteins (e.g., lysozyme). The heavy metal ion adsorption results show that the AlPPh materials have a large adsorption capacity, comparable to those of previous reported Cu(II)-adsorbents made up of functionalized mesoporous silica. The isotherms for lysozyme adsorption are of type L (Langmuir isotherm), and different monolayer capacities were calculated using Langmuir equation. The differences between the metal ion and the lysozyme adsorption were mainly caused by the nature of inorganic ions and proteins and the interactions between the adsorbents and adsorbates. The synthesized AlPPh hybrid materials were confirmed to be useful multifunctional adsorbents for both metal ions and proteins.

Observation of Distinct Surface AlIV Sites and Phosphonate Binding Modes in γ-Alumina and Concrete by High-Field 27Al and 31P MAS NMR
George W. Wagner
* and Roderick A. Fry§
J. Phys. Chem. C, 2009, 113 (30), pp 13352–13357
DOI: 10.1021/jp902474z
Publication Date (Web): July 1, 2009
Abstract: High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.

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