Activated Carbon/Transition Metal (Ni, In, Cu) Hexacyanoferrate Nanocomposites for Cesium Adsorption.

Transition metal hexacyanoferrate/microporous activated carbon composites were obtained using a simple successive impregnation approach. The effect of metal type (nickel, indium, or copper), and the carbon oxidation on the composite characteristics (porosity, metal structure, and particle size), as well as on the removal efficiency of cesium from aqueous solution was investigated. Successful formation of the desired metal hexacyanoferrate phase was achieved and the size of the metallic nanoparticles and their dispersion in the carbon network was found to depend on the metal type, with the indium and nickel-based materials exhibiting the smallest particle size distribution (< 10 nm). Adsorption tests performed under batch conditions demonstrate that the copper hexacyanoferrate/activated carbon composite present the highest cesium removal capacity from aqueous solution (74.7 mg·g-1) among the three studied metal-based nanocomposites. The carbon oxidation treatment leads to the increase in the number of functional groups to the detriment of the porosity but allows for an improvement in the Cs adsorption capacity. This indicates that the Cs adsorption process is governed by the carbon surface chemistry and not its porosity. Moreover, combining oxidized carbon support with copper hexacyanoferrate induces the highest cesium adsorption capacity (101.5 mg·g-1). This could be related to synergistic effects through two absorption mechanisms, i.e., a cation exchange mechanism of Cs with the metallic hexacyanoferrate phase and Cs adsorption via carbon oxygen surface groups, as demonstrated using X-ray photoelectron spectroscopy (XPS) analyses.

Optimization of the synthesis of Pd-Au nanoalloys confined in mesoporous carbonaceous materials.

Pd-Au nanoalloys confined in mesoporous carbonaceous materials were synthesized by a rapid one-pot microwave assisted approach. Green polymer resins based on phloroglucinol/glyoxylic acid or glyoxal were co-assembled in the presence of a template and metallic salts followed by microwave treatment between 40 and 80°C and subsequent thermal annealing, allowing simultaneous formation of mesoporous carbonaceous materials with in-situ confined Pd-Au nanoparticles. Several Pd-Au compositions were prepared (PdxAu100-x, where x=90; 80; 70 and 50) and their impact on the alloy structure and particle size/distribution evaluated. For Pd90Au10, homogeneously dispersed nanoalloy particles (∼8nm) are obtained in the carbonaceous framework. The increase in the Au content in the alloy gradually induces an increase in the particle size and agglomeration of the particles along with the formation of multiphased alloys, i.e., segregated Pd- and Au-rich nanoparticles. The particle agglomeration was avoided by decreasing the thermal annealing time. The homogeneity of the alloy structure was found to strongly depend by two parameters, the chelating/cross-linker agents and the microwave temperature, i.e., the chelating/cross-linker agents containing carboxylic groups and the higher temperatures inducing more heterogeneous structures. The hydrogen absorption in Pd90Au10 particles with different homogeneity degree was studied at room temperature up to 1bar. Generally, hydrogen absorbs in Pd-rich nanoalloys forming a hydride phase whereas Au-rich phases do not absorb hydrogen under the present conditions.

One-pot laser-assisted synthesis of porous carbon with embedded magnetic cobalt nanoparticles.

A novel one-pot laser-assisted approach is reported herein for the synthesis of ordered carbons with embedded cobalt nanoparticles. The process is based on a UV pulsed laser exposure of an ethanolic solution consisting of green carbon precursors, a structure directing agent and a cobalt salt. Very short irradiation times (5 to 30 min) are only required to polymerize and cross-link carbon precursors (i.e. phloroglucinol and glyoxylic acid) independent of a catalyst presence. The influence of three metallic salts (acetate, nitrate and chloride) on the phenolic resin and carbon characteristics (structure, texture and particle size/distribution) was systematically studied. When exposed to UV laser, the metallic salt exhibited a strong influence on the particle size and distribution in the carbon matrix rather than on the textural carbon properties. Using cobalt acetate, very small (3.5 nm) and uniformly dispersed particles were obtained by this simple, fast and green one-pot synthesis approach. An original combined (13)C CP-MAS and DP-DEC solid state NMR spectroscopy analysis allowed to determine the structure of phenolic resins as well as the location of the cobalt salt in the resin. Complementarily, the (1)H solid-state and relaxation NMR provided unique insights into the rigidity (cross-linking) of the phenolic resin and dispersion of the cobalt salt. The magnetic properties of cobalt nanoparticles were found to be size-dependent: large Co nanoparticles (∼50 nm) behave as bulk Co whereas small Co nanoparticles are superparamagnetic.