Catalytic reduction of organic pollutants, antibacterial and antifungal activities of AgNPs@CuO nanoparticles-loaded mesoporous silica.

In this work, the mesoporous silica MCM-41 was prepared by a hydrothermal method and then modified using silver and copper. The obtained samples were used as antibacterial/antifungal agents and as catalysts for the reduction of the following dyes: Methylene Blue (MB), Congo Red (CR), Methyl Orange (MO), and Orange G (OG). Several parameters affecting the reduction of dyes were investigated and discussed such as the catalyst nature, the initial concentration of the dye, the dye nature, the selectivity of the catalyst in a binary system as well as the catalyst reuse. The catalysts were characterized using XRD, nitrogen sorption measurements, XRF, FTIR, XPS, SEM/EDS, and TEM. XRD, XPS, and TEM analysis clearly showed that the calcination of copper- and silver-modified silica leads to the formation of well-dispersed CuO and AgNPs having sizes between 5 and 10 nm. As determined by XRF analysis, the content of silver nanoparticles was higher compared to CuO in all samples. It has been shown that the dye reduction is influenced by the size and the content of nanoparticles as well as by their dispersions. The catalytic activity was shown to be the highest for the Ag-Cu-MCM(0.05) catalyst with a rate constant of 0.114, 0.102, 0.093, and 0.056 s-1 for MO, MB, CR, and OG dyes in the single-dye system, respectively. In the binary system containing MB/OG or MB/MO, the catalyst Ag-Cu-MCM(0.05) was more selective toward the MB dye. The reuse of the catalyst for three consecutive cycles showed higher MB conversion in a single system with an increase in reaction time. For antifungal and antibacterial properties, the application of calcined and uncalcined materials toward six different strains showed good results, but uncalcined materials showed the best results due to the synergistic effect between CuO and unreduced species Ag+ which are considered responsible for the antibacterial and antifungal action.

Metal-Free Phosphated Mesoporous SiO2 as Catalyst for the Low-Temperature Conversion of SO2 to H2S in Hydrogen.

Highly active metal-free mesoporous phosphated silica was synthesized by a two-step process and used as a SO2 hydrogenation catalyst. With the assistance of a microwave, MCM-41 was obtained within a 10 min heating process at 180 °C, then a low ratio of P precursor was incorporated into the mesoporous silica matrix by a phosphorization step, which was accomplished in oleylamine with trioctylphosphine at 350 °C for 2 h. For benchmarking, the SiO2 sample without P precursor insertion and the sample with P precursor insertion into the calcined SiO2 were also prepared. From the microstructural analysis, it was found that the presence of CTAB surfactant was important for the incorporation of active P species, thus forming a highly dispersed, ultrafine (uf) phosphate silica, (Si-P) catalyst. The above approach led to the promising catalytic performance of uf-P@meso-SiO2 in the selective hydrogenation of SO2 to H2S; the latter reaction is very important in sulfur-containing gas purification. In particular, uf-P@meso-SiO2 exhibited activity at the temperature range between 150 and 280 °C, especially SO2 conversion of 94% and H2S selectivity of 52% at 220 °C. The importance of the CTAB surfactant can be found in stabilizing the high dispersion of ultrafine P-related species (phosphates). Intrinsic characteristics of the materials were studied using XRD, FTIR, EDX, N2 adsorption/desorption, TEM, and XPS to reveal the structure of the above catalysts.

Crystal and electronic facet analysis of ultrafine Ni2P particles by solid-state NMR nanocrystallography.

Structural and morphological control of crystalline nanoparticles is crucial in the field of heterogeneous catalysis and the development of "reaction specific" catalysts. To achieve this, colloidal chemistry methods are combined with ab initio calculations in order to define the reaction parameters, which drive chemical reactions to the desired crystal nucleation and growth path. Key in this procedure is the experimental verification of the predicted crystal facets and their corresponding electronic structure, which in case of nanostructured materials becomes extremely difficult. Here, by employing 31P solid-state nuclear magnetic resonance aided by advanced density functional theory calculations to obtain and assign the Knight shifts, we succeed in determining the crystal and electronic structure of the terminating surfaces of ultrafine Ni2P nanoparticles at atomic scale resolution. Our work highlights the potential of ssNMR nanocrystallography as a unique tool in the emerging field of facet-engineered nanocatalysts.