Investigation of the physico-chemical properties of Ni-Mg-Al-La catalysts from ultrasound-assisted synthesis.

This work reports on the ultrasonic synthesis of layered double hydroxides (LDH), also known as hydrotalcite-type materials. We have studied the influence of ultrasonic irradiation parameters (power, time, temperature) on the physicochemical properties of Ni2Mg4Al1.8La0.2 hydrotalcite-type precursors and related mixed oxides (MO). The low-frequency acoustic cavitation (22 kHz) was applied during the precipitation and aging steps of co-precipitation synthesis and the results were compared to the classical preparation route. The materials were characterized by ATR-FTIR, XRD, N2 adsorption-desorption, SEM-EDX, S/TEM-HAADF, and XPS. Using the combination of acoustic cavitation-assisted precipitation and aging steps, XRD experiments show a higher purity hydrotalcite phase and a better incorporation of lanthanum ions into the LDH structure. As expected, morphological characterization shows a reduction in average crystallite size and an increase in surface area and pore volume, combined with a drastic reduction in synthesis time (45 min at room temperature versus 19 h at 60 °C in conventional synthesis). The insertion of a larger quantity of La is observed by S/TEM-EDSX mapping which also shows a better distribution of lanthanum atoms within the LDH and mixed oxide structures.

Immobilization of fluorescent chemosensor on pyrogenic silica: a promising device for gaseous detection.

A new approach to enhance performances of a cyclodextrin-based fluorescent chemosensor combining grafting on a silica matrix and quaternization reaction is presented. The full characterization of new fluorescent hybrid material has clearly revealed the embedding of cyclodextrin inside the siliceous material. Finally, through a comparison with previous aqueous studies, a preliminary test of toluene detection was presented and highlighted the high potential of this approach, which opens attractive perspectives of evolution toward more sensitive and selective VOC's sensing in air or in hot industrial gaseous waste.

Rapid synthesis of a versatile organic/inorganic hybrid material based on pyrogenic silica.

An efficient approach has been developed to synthesize a new versatile organo-silica material by non-conventional method (microwave irradiation and ultrasonic vibration) from amorphous pyrogenic silica and has been compared with thermic procedure. The samples were fully characterized by FTIR, solid-state (29)Si and (13)C CP/MAS NMR, thermogravimetric analysis (TGA), elemental analysis, scanning electron microscopy (SEM) and by N(2)-sorption isotherms measurements. The functionalization of silicon dioxide by 4-(chloromethylphenyl) trichlorosilane has been easily achieved by ultrasound irradiation in a very short time with high loading of organic fragments. Significant different sizes of pores were observed according to conventional or non-conventional synthesis procedure. In addition, new structural properties have been created with the emergence of a mesoporosity.