Gustave Kenne Dedzo

Kaolinite–ionic liquid nanohybrid materials as electrochemical sensors for size-selective detection of anions

Functionalized nanohybrid materials based on clay minerals were obtained by grafting ionic liquids (trihydroxyethylmethylammonium iodide (AE1), 1-(2-hydroxyethyl)-3-methylimidazolium chloride (AE2) and 1-benzyl-3-(2-hydroxyethyl) imidazolium chloride (AE3) of different sizes in the interlayer spaces of kaolinite. The grafting was confirmed by several characterization techniques (XRD, 13C CP/MAS NMR and thermal analysis). The interlayer distances of the grafted materials were 4.1 A, 6.0 A and 8.7 A for AE1, AE2 and AE3, respectively. These materials have an anion exchange capacity related to the mobility of the counter anions of grafted cations. In aqueous medium, the anion exchange capacity does not allow a variation of the interlayer distance of kaolinite, as confirmed by XRD measurements. The interlayer distance of the nanohybrid materials is controlled by the grafted cations. These properties of anion exchangers have been used to achieve the voltammperometric detection of some anions with different sizes (thiocyanate, sulphite and ferricyanide ions), using glassy carbon electrodes coated with a thin film of the modified kaolinite. There is a good correlation between the size of the analyzed anion and the basal spacing of the material used for the electrode modification: depending on the system, the presence of the thin film induces an increase of the current intensities when the anion can easily diffuse through the interlayer space or acts as a barrier when the basal spacing does not allow its insertion. This work shows that derivatives of kaolinite can be used for the selective detection of anions in aqueous solution, using their size as a differentiating factor.

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.

Characterization and Applications of Kaolinite Robustly Grafted by an Ionic Liquid with Naphthyl Functionality

Functionalization of the kaolinite (K) interlayer space is challenging. In this work, a new kaolinite-based nanohybridmaterial (K-NI) was successfully synthesized by grafting on the interlayer aluminol surfaces the ionic liquid, 1-(1-methylnaphthyl)-3-(2-hydroxyethyl) imidazolium chloride (NI), using a guest displacement strategy. A substantial increase of the basal spacing (10.8 Å) was obtained. This is a grafted derivative of kaolinite possessing one of the largest d-values. Washing in water for several days and other vigorous treatments such as sonication showed a minor effect on the integrity of the material. FTIR and 13C NMR confirmed the conservation of the structure of the ionic liquid after the grafting. Thermal analysis confirmed the presence of grafted material and was used to estimate the abundance of the grafted ionic liquid (0.44 mole per mole of kaolinite structural formula, (Al2Si2O5(OH)4)). By using cyclic voltammetry, the permeability of a film of K-NI for the bulky ferricyanide ions was demonstrated. The accumulation of nitrophenolate anions was effective (maximum capacity of 190 μmol/g), but was less important than what was expected due to the steric hindrance of the bulky grafted NI. Although the presence of chloride anions reduced the adsorption capacity, the affinity of the modified kaolinite interlayer space for the nitrophenolate anions was demonstrated.

Amination of pretreated ayous (Triplochiton scleroxylon) sawdust with two organosilanes: characterization, stability, and permselective property

Abstract Sawdust samples of ayous wood (Triplochiton scleroxylon) have been submitted to a warm pretreatment with NaOH and functionalized in dimethylformamide (DMF) by grafting with two amino organosilanes. The reagents were chosen for their ability to bind hydronium ions in acidic medium: 3-aminopropyltriethoxysilane (APTES) and 3-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS). The resulting materials were characterized by Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (NMR) spectroscopies, which revealed the Si-O-C covalent bond and the polymerization of the grafted silanes through siloxane bridges (Si-O-Si) leading to the stabilization of the structure. The cyclic voltammetry analyses were performed on a glassy carbon modified with native or functionalized sawdust films in contact with electrochemical probes ([Fe(CN)6]3- and [Ru(NH3)6]3+). By means of this method, the permselectivity and accumulation capacity of these functionalized materials could be evaluated. The presence of silanes in the functionalized sawdust leads to a progressive accumulation of anionic species, while the cationic species were repelled when the solution is gradually acidified.