PdNP Decoration of Halloysite Lumen via Selective Grafting of Ionic Liquid onto the Aluminol Surfaces and Catalytic Application

The synthesis of selectively deposited palladium nanoparticles (PdNPs) inside tubular halloysite lumens is reported. This specific localization was directed by the selective modification of the aluminol surfaces of the clay mineral through stable Al–O–C bonds. An ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium) was grafted onto halloysite following the guest displacement method (generally used for kaolinite) using halloysite–DMSO preintercalate. The characterization of this clay nanohybrid material (XRD, NMR, TGA) showed characteristics reminiscent of similar materials synthesized from kaolinite. The grafting on halloysite lumens was also effective without using the DMSO preintercalate. The presence of these new functionalities in halloysite directs the synthesis of uniform PdNPs with size ranging between 3 and 6 nm located exclusively in the lumens. This results from the selective adsorption of PdNPs precursors in functionalized lumens through an anion exchange mechanism followed by in situ reduction. In contrast, the unmodified clay mineral displayed nanoparticles both inside and outside the tubes. These catalysts showed significant catalytic activity for the reduction of 4-nitrophenol (4-NP). The most efficient catalysts were recycled up to three times without reducing significantly the catalytic activities

Single Kaolinite Nanometer Layers Prepared by an In Situ Polymerization–Exfoliation Process in the Presence of Ionic Liquids

A simple chemical route for the exfoliation of kaolinite in the presence of polymerizable ionic liquids and the resulting obtainment of exfoliated nanocomposites is reported. The exfoliation was achieved using three different ionic liquids structurally bearing a vinyl group: 1-methyl-3-(4-vinylbenzyl)imidazolium chloride salt (IL_1), 1-methyl-1-(4-vinylbenzyl)pyrrolidinium chloride (IL_2), and 1-methyl-3-vinyl imidazolium iodide (IL_3) and a urea-kaolinite intercalate as precursor. The reaction was done in one step by an in situ polymerization–exfoliation process. ¹³C CP/MAS NMR spectra confirmed the spontaneous polymerization of the ionic liquid during the exfoliation process to afford atactic polystyrene derivatives in the case of IL_1 and IL_2. The amount of organic material in the exfoliated nanocomposite was close to 30% as shown by thermal gravimetric analysis. This amount is small in comparison to the amount obtained when the exfoliation was done using sodium polyacrylate (Letaief and Detellier, <i>Langmuir</i> <b>2009</b>, <i>25</i>, 10975). XRD as well as SEM analysis confirmed a total exfoliation of the kaolinite when the reaction was done using urea kaolinite, whereas a microcomposite, made predominantly of kaolinite platelet aggregates dispersed in the polymeric matrix, was formed when dimethylsulfoxide kaolinite was used as the precursor

Adsorption of Indole on Kaolinite in Nonaqueous Media: Organoclay Preparation and Characterization, and 3D-RISM-KH Molecular Theory of Solvation Investigation

Current oil sand mining operations in the Athabasca basin are predominantly aqueous-based. Extracts containing large amounts of fines lead to the formation of stable organoclay suspensions in froths giving lower yields and greater tailing wastes and making the development of more efficient extraction methods desirable from both economical and environmental perspectives. We examine an indole-kaolinite system as a model for these oil fines and their resistance to washing in nonaqueous solvents. The prepared organoclays show indole loading exclusively on the external surface of the clay. Micron-scaled vermicular structures, similar to natural kaolinite, are observed. Their formation is believed to be driven by strong adsorbate–adsorbate interactions. Indole is the primary adsorbate, as solvent adsorption is shown to be minimal based on both experimental and computational results. Isotherms are constructed and parameters calculated from linear regression analysis fitted to the Brunauer–Emmett–Teller equation. Monolayer quantities calculated match well to the theoretical amount calculated from surface areas measurements. Washing the organoclays with both toluene and isopropanol results in a 50% decrease of loaded organic material, leaving a monolayer equivalent of organic matter. The statistical-mechanical 3D-RISM-KH molecular theory of solvation is employed to perform full sampling of solvent orientations around a kaolinite platelet and gain insights into the preferred orientation and adsorption thermodynamics of indole on kaolinite in toluene and heptane solvents. In its preferred orientation, indole is hydrogen-bonded to one or two O atoms at the aluminum hydroxide surface of kaolinite. The calculated solvation free energy and potential of mean force for adsorption of indole and solvents on kaolinite in solution yield the increasing adsorption strength order of heptane < toluene < indole on the aluminum hydroxide surface. Multilayer adsorption profiles are predicted based on the integrated three-dimensional distribution functions of indole, toluene, and heptane

Computational and Experimental Investigations of the Role of Water and Alcohols in the Desorption of Heterocyclic Aromatic Compounds from Kaolinite in Toluene

Nonaqueous extraction is an attractive alternative to the currently employed warm water process for extraction of bitumen from oil sands, as it could use less energy and water. Hydroxylated cosolvents, such as alcohols, that compete for the adsorptive clay surfaces and help release bitumen components could help improve bitumen recovery. The water naturally present in oil sand also affects oil–mineral interactions. Electronic structure methods and the statistical-mechanical 3D-RISM-KH molecular theory of solvation as well as experimental desorption measurements are employed to study the effects of water and aliphatic alcohol cosolvents in toluene solvent on the desorption of fused pyridinic heterocycles (ArN) from kaolinite. The geometries of phenanthridine and acridine (representative of pyridinic heterocycles of petroleum asphaltenes) adsorbed on the kaolinite clay surface are optimized in periodic boundary conditions using density functional theory. The 3D-RISM-KH method is employed to calculate the solvation free energy and potential of mean force for adsorption of the heterocycles on kaolinite in pure and alcohol-containing toluene. The potentials of mean force show that the adsorption of the fused pyridines on kaolinite is stronger in pure toluene than in toluene mixed with aliphatic alcohol. Analysis of the mechanism of desorption of phenanthridine and acridine from kaolinite in toluene containing alcohol reveals that the alcohol stabilizes both the pyridinic moiety and kaolinite platelet by hydrogen bonding, thus disrupting the ArN···HO–Al­(kaolinite) hydrogen bond. A mechanism for retention of toluene on kaolinite is also highlighted. Experimental studies of the desorption of fused pyridines from an ArN–kaolinite aggregate show that in water-saturated toluene the rate of desorption of the phenanthridine from kaolinite is twice as high as that in dry toluene. The experimental and computational results show that water and aliphatic alcohols in toluene help desorb pyridinic heterocycles from kaolinite, a clay mineral abundant in the oil sands. The presented insights are valuable for understanding the molecule-clay interactions in solution and relevant to improving the nonaqueous extraction of bitumen from oil sand

Molecule–Surface Recognition between Heterocyclic Aromatic Compounds and Kaolinite in Toluene Investigated by Molecular Theory of Solvation and Thermodynamic and Kinetic Experiments

Molecular recognition interactions between kaolinite and a series of heterocyclic aromatic compounds (HAC) representative of the N- and S-containing moieties in petroleum asphaltene macromolecules are investigated using the three-dimensional reference interaction site model with the Kovalenko–Hirata closure approximation (3D-RISM-KH) theory of solvation and experimental techniques in toluene solvent. The statistical-mechanical 3D-RISM-KH molecular theory of solvation predicts the adsorption configuration and thermodynamics from the 3D site density distribution functions and total solvation free energy, respectively, for adsorption of HAC and toluene on kaolinite. Spectrophotometric measurements show that, among the HAC studied, only acridine and phenanthridine adsorb quantitatively on kaolinite. For these pyridinic HAC, the adsorption results fitted to the Langmuir isotherm in the monolayer domain suggest a uniform monolayer of HAC molecules. The 3D-RISM-KH studies predict that the aluminum hydroxide surface of kaolinite is preferred for HAC adsorption due to strong hydrogen bonding with the pyridinic N atoms, while the rest of the HAC adsorb weaker. Adsorption on the silicon oxide side is weak and delocalized, as evident from the 3D solvation free energy density. Toluene sites effectively compete with non-hydrogen bonding HAC, such as fused thiophenes, for the kaolinite surface. The adsorption enthalpy and phenanthridine-acridine loading ratio are calculated and correlated with the experimentally determined Langmuir constant and adsorption loading. This combined experimental and computational modeling approach is aimed to provide insight into the specific interactions among clays, bitumen, and solvents so as to help accelerate the development of environmentally friendly and efficient desorption systems for nonaqueous extraction of bitumen from Oil Sands, an important unconventional petroleum reserve