M. Ischia

Pyrolysis study of sol—gel derived TiO2 powders: Part III. TiO2-anatase prepared by reacting titanium(IV) isopropoxide with acetic acid

A homogeneous TiO2 gel was obtained by hydrolysing titanium(IV) isopropoxide that was previously modified by reaction with acetic acid. The so stabilized precursor was hydrolysed under strong acidic medium (pH=0 by HCl). Dried TiO2 powders were characterized by FT-IR, XRD, N2 adsorption analyses, coupled thermogravimetric (TG) gas chromatographic (GC) and `mass spectrometric (MS) analyses. A semiquantitative analysis of the main evolved chemical species allowed to depict both the chemical rearrangements occurring in the TiO2 matrix during pyrolysis and the chemical composition of the initial gel.

Sol-Gel Synthesis and Pyrolysis Study of Oxyfluoride Silica Gels

Silicon oxyfluoride materials are synthesized by the sol-gel method using triethoxyfluorosilane as precursor, bearing the Si—F bond. SiO(2−0.5x) Fx gel preparation requires peculiar experimental control of hydrolysis and condensation reactions. Maintenance of the Si—F bond during gelling, heating and aging was studied in the case of processes carried out under an argon atmosphere or in air. Fluorine contents in resulting samples were quantified by FT-IR and X-ray photoelectron spectroscopy (XPS); specific surface area and porosity of powdered samples were determined by N2 adsorption. The thermal stability of oxyfluoride gels was studied by thermogravimetric-mass spectrometric (TG-MS) coupled analyses during heat treatment, under He flow. Mass spectra recorded during principal weight losses indicate the release of variously fluorinated silicon species resulting from Si—F/Si—O exchange reactions. The evolution of these species was observed at different temperatures, depending on gelling conditions. In particular, degradation of ≡Si—F moieties was prominent for gels aged in air, whereas samples processed under an argon atmosphere preserve the ≡Si—F bond up to 300°C.

Clay-sewage sludge co-pyrolysis. A TG-MS and Py-GC study on potential advantages afforded by the presence of clay in the pyrolysis of wastewater sewage sludge

Wastewater sewage sludge was co-pyrolyzed with a well characterized clay sample, in order to evaluate possible advantages in the thermal disposal process of solid waste. Characterization of the co-pyrolysis process was carried out both by thermogravimetric-mass spectrometric (TG-MS) analysis, and by reactor tests, using a lab-scale batch reactor equipped with a gas chromatograph for analysis of the evolved gas phase (Py-GC). Due to the presence of clay, two main effects were observed in the instrumental characterization of the process. Firstly, the clay surface catalyzed the pyrolysis reaction of the sludge, and secondly, the release of water from the clay, at temperatures of approx. 450-500 °C, enhanced gasification of part of carbon residue of the organic component of sludge following pyrolysis. Moreover, the solid residue remaining after pyrolysis process, composed of the inorganic component of sludge blended with clay, is characterized by good features for possible disposal by vitrification, yielding a vitreous matrix that immobilizes the hazardous heavy metals present in the sludge.

Synthesis and structural evolution of mesoporous silica?silver nanocomposites

Mesoporous silica materials were prepared by a sol?gel procedure using Si(OCH2CH3)4 (TEOS) as the silica source and the non-ionic alkyl-poly(ethyleneoxide) oligomer Brij76 as the structure-directing agent. Pure inorganic hexagonal-like mesostructured SiO2 powders were obtained after annealing, performed in air between 400 and 600??C. Upon calcination, the organic template was removed and silica networks with a different amount of Si?OH groups as well as porous features were prepared. Ag?SiO2 nanocomposites were obtained by metallation of the mesoporous silica powders with aqueous solutions of silver acetate. Ag+ ions were chemically grafted on the silica pores by taking advantage of the basic character of acetate anions and the acidic properties of Si?OH groups. Different silver concentrations were achieved on the mesostructured silica powders, depending on their former annealing treatment. For all samples the formation of silver nanoclusters occurred spontaneously at room temperature. Monodispersed, spherical Ag crystallites, with an average diameter of a few nanometres, were obtained starting from the 400??C-treated silica, whereas clusters with different sizes (3?20?nm) and irregular shapes were grown for metallation of the 600??C-heated SiO2 matrix. The samples chemical composition was studied by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES), whereas the porous features were investigated by N2 BET adsorption. Information concerning structure and microstructure was obtained by x-ray diffraction (XRD) and transmission electron microscopy (TEM).

Rh Inclusion in Sol-Gel SiO2. Effects of Rh Precursors on Metal Dispersion and SiO2-Rh Thermal Behavior

RhCl3·nH2O and [RhCl(C2H4)2]2 are used as precursors for the preparation of 1%Rh in sol-gel derived SiO2. The gelling process of Si(OEt)4 is carried out in the absence of solvent and under strong acid catalysis. The thermal behavior of Rh precursors, of SiO2 gel and Rh-SiO2 composites is independently studied by analysing organic species released at definite temperature intervals and concomitantly collecting infrared, XPS, TEM, XRD and porosity data. Results indicate that nanometric Rh particles may be obtained from [RhCl(C2H4)2]2, their dispersion being homogeneous, dense and stable up to 250°C, whereas RhCl3·nH2O affords less metallic dispersion with other crystalline Rh-species; in both cases, well-shaped Rh metal crystallites are obtained at 650°C. The different synthetic approaches used for the preparation of RhCl3- and [RhCl(C2H4)2]2-derived samples, are invoked to account for the features of Rh dispersion obtained by mild temperature treatment. Moreover, the particular procedures for sol-gel SiO2 synthesis are related to the high-temperature maintenance of great porosity and elevated specific surface area.