Hafedh Kochkar

Shape-Controlled Synthesis of Silver and Palladium Nanoparticles Using β-Cyclodextrin

Shape-controlled silver and palladium nanoparticles were for the first time synthesized by seed-mediated techniques in the presence of β-cyclodextrin (β-CD). Palladium and silver seeds were prepared by reduction of palladium or silver ions with sodium borohydride in the presence of sodium citrate dihydrate as a stabilizer. Seeds were then injected into a growth solution containing the same Pd (or Ag) precursor, ascorbic acid (as a weak reducing agent), and β-CD. Using β-cyclodextrin impacts the final morphology of silver nanoparticles through a strong capping effect slowing down the growth regime and shifting it to thermodynamic-controlled conditions. Adjusting the β-CD/Ag molar ratio can lead to the selective formation of multiply twinned icosahedral particles presenting mainly {111} facets. On palladium, β-cyclodextrin selectively led to the controlled aggregation of primary nanoparticles into nanodendrites or multipods. After deposition on TiO 2 , these nanostructured Pd catalysts show excellent activity for the hydrogenation of cinnamaldehyde.

Study of Pd(II) adsorption over titanate nanotubes of different diameters

Hydrogenotitanates (HNTs) nanotubes with different diameters were prepared by hydrothermal treatment of TiO(2) (P25) followed by washing with HCl aqueous solution. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal analysis and N(2) adsorption/desorption. In order to determine the palladium uptake ability of different HNT samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH(+)(4)/NH(3) buffer). Transmission electron microscopy showed that the diameter of the nanotubes depends on the preparation conditions. Chemical analysis of residual sodium and thermal studies showed that the chemical formula of the two prepared HNT was H(x)Na(2-x)Ti(2)O(5)H(2)O with x=1.61 or 1.65. The HNTs are mesoporous materials with a multi-walled nanotubular structure and high specific surface area. In order to determine the capacity of palladium retention of different HNTs samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH(+)(4)/NH(3) buffer). The adsorption kinetics of Pd(II) on the HNTs was very fast. The isotherms of Pd(II) on the HNTs showed that the adsorption occurred (1) initially through cationic exchange and (2) when the concentration of Pd(II) is high by precipitation of different Pd salts. The adsorption capacity of Pd(II) is strongly altered by the morphology of the HNTs samples.

One-pot deposition of palladium on hybrid TiO2 nanoparticles and catalytic applications in hydrogenation.

One-pot deposition of Pd onto TiO(2) has been achieved through directly contacting palladium(II) salt with nanosized functionalized TiO(2) support initially obtained by sol-gel process using titanium isopropoxide and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various palladium salts (Na(2)PdCl(4) and Pd(NH(3))(4)Cl(2)·H(2)O) and titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used in order to study the effect of the nature of the precursor and of the citrate content on the final Pd particle size and catalytic properties of the as-obtained Pd/TiO(2) systems. Characterization was performed using N(2) adsorption-desorption isotherms, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained hybrid Pd/TiO(2) catalysts were tested in the selective hydrogenation (HYD) of an α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Citrate-free Pd/TiO(2)-based catalysts present lower selectivity into saturated alcohol. However, citrate-functionalized Pd/TiO(2) catalyst seems to control the selectivity, the particle size and dispersion of Pd NPs leading to high intrinsic activity.

Design of β-cyclodextrin modified TiO2 nanotubes for the adsorption of Cu(II): Isotherms and kinetics study

This paper builds on previous literature showing the interesting adsorptive properties of TiO2 nanotubes. It further explores the positive effect of β-cyclodextrin on these properties. Hence, β-cyclodextrin modified TiO2 nanotubes were successfully prepared and characterized by XRD, N2 physisorption at 77K, Raman, FTIR-ATR, 1H NMR, TEM and EPR. The adsorptive interaction of Cu(II) with materials was investigated in aqueous solution at pH 9.25 (NH4+/NH3). The main conclusion is that copper(II)-ammonia complexation equilibria play an important role in the adsorption process. The β-cyclodextrin was found to improve the Cu(NH3)42+ adsorption mainly by retarding its precipitation to high concentrations values (>400mgL-1). Adsorption experimental data showed good fit with the pseudo-second-order model and the Langmuir isotherm model.

p-Hydroxybenzoic acid degradation by Fe/Pd-HNT catalysts with in situ generated hydrogen peroxide

Abstract Pd- and Fe/Pd-HNT were elaborated by successive ionic exchange and wet impregnation at room temperature of hydrogenotitanate nanotubes (HNT) nanomaterials. Hydrogen peroxide was generated in situ via reaction of oxygen and formic acid (FA) over Fe/Pd-HNT catalysts. A high p-hydroxybenzoic acid (p-HBz) mineralization was achieved (52%) using Fe/Pd-HNT/FA/O 2 /UV system compared to the simulated reaction using Fe/Pd-HNT/H 2 O 2 /UV system (34%). The rate of hydrogen peroxide formation over Pd-HNT catalyst, during in situ generation, probably plays a key role in controlling the kinetics of the p-HBz degradation.

One-Pot deposition of palladium on hybrid TiO2 nanoparticles: Application for the hydrogenation of cinnamaldehyde

Abstract One-pot deposition of Pd onto TiO 2 has been achieved by direct impregnation in excess of Na 2 PdCl 4 contacted with citrate-functionalized TiO 2 support initially obtained by sol-gel process techniques using Ti(O i Pr) 4 and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used to prepare the hybrid TiO 2 support in order to study the effect of citrate on the final catalytic properties of Pd/TiO 2 catalysts. Characterizations were performed using N 2 adsorption-desorption, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained Pd/TiO 2 catalysts were tested in the selective hydrogenation (HYD) of cinnamaldehyde. Using citrate-functionalized TiO 2 support increases both the activity and the selectivity to saturated alcohol.

Catalytic activity of nanostructured Pd catalysts supported on hydrogenotitanate nanotubes

Abstract Palladium nanoparticles (NPs) with well-controlled morphologies (cubes, rods, icosahedra) and with preferential crystallographic planes were prepared through a seed-mediated colloidal approach. Pd NPs were then impregnated onto high surface area hydrogenotitanate nanotubes before being evaluated in the selective hydrogenation of a α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Their preferential exposition of crystallographic planes (mainly (100) and (111) sites) offers the unique ability to determine the influence of the structure-sensitivity of this selective hydrogenation reaction in real experimental conditions. Results show that the selectivity to saturated alcohol increases with increasing proportion of Pd(111) sites.