Synthesis and characterization of catalytic metal semiconductor-doped siliceous materials with ordered structure for chemical sensoring

Sensing materials based on doped mesoporous silica of SBA-15 type were obtained by repeated wet impregnation of the solid with semiconductive oxides (Sn and In) and noble metal (Pt). The mesoporous structure of SBA was preserved during the doping and calcination of the solid, although slight pore size narrowing occurred as shown by the BET adsorption analysis. The solid was deposited by the casting technique as a thin layer on a finger structure. The modifications of its electrical resistance values in the presence of hydrogen and propene (50–400 ppm), at temperature values of 450 °C was used as sensing parameter, in the presence of propene and hydrogen. The sensitivity to propene was higher than that to hydrogen

Chromium(VI) Ion Removal from Aqueous Solutions Using a Zn–Al-Type Layered Double Hydroxide

This paper deals with the structural and adsorptive characterisation of a Zn–Al-type layered double hydroxide to be used for the retention of chromate ions from aqueous media. Structural characterisation by X-ray diffraction and FT-IR spectroscopy showed that the material was a layered double hydroxide with carbonate in the interlayer; however, certain impurities were also identified. Thermogravimetric analysis allowed appropriate calcination temperatures to be chosen for the sorption studies. The equilibrium adsorption of the Cr(VI) ion was best described by the Langmuir–Freundlich equation. Calcining the material at 500 °C led to a product containing mostly stable zinc oxide with low adsorptive properties. The kinetics of Cr(VI) ion retention on the uncalcined layered double hydroxide obeyed the pseudo-first-order model as described by the Lagergren equation. Structural analysis of the product obtained after Cr(VI) ion sorption onto Zn–Al–CO 3 showed that the carbonate anion was not replaced in the interlayer and that the Cr(VI) ion was adsorbed within cavities formed by three adjacent metal hydroxide octahedra situated at the edge of the brucite-like layer

Sorption of phosphates and thiocyanates on isomorphic substituted Mg/Zn–Al-type hydrotalcites

The sorption equilibriums of phosphate and thiocyanate anions on isomorphic substituted Mg/Zn–Al-type hydrotalcites were investigated in this study. Langmuir and Freundlich isotherms were used to interpret the equilibrium data for phosphate. The sorption equilibriums of phosphate on Mg3Al, Mg2ZnAl and Mg1.5Zn1.5Al hydrotalcites were well described by the Langmuir isotherm. The highest maximum sorption capacities for these adsorbents were as follows: 111, 101 and 95 mg g-1. The equilibrium constant and standard Gibbs energy changes were also calculated from the sorption data. Standard Gibbs energy changes of about –20 kJ mol-1 indicated that the process might be considered as physical adsorption. The sorption equilibriums of phosphate on isomorphic substituted samples of MgZn2Al and Zn3Al were well described by the Freundlich isotherm. Thiocyanate showed a relative low affinity for the studied materials, as indicated by both the “S”-shaped isotherms and low sorption capacities. The sorption of phosphate and thiocyanate on the investigated hydrotalcites showed a continuous decrease of the sorption capacity in the following order: Mg3Al > Mg2ZnAl > Mg1.5Zn1.5Al > MgZn2Al > Zn3Al

Shaping hydrotalcite-like materials into microspheres and their use for sorption applications

Hydrotalcite-type materials, also called layered double hydroxides (LDHs), are a family of naturally occurring anionic clays. They are represented by the empirical formula [M2+1-xM3+x(OH)2]x+ (An-x/n) · mH2O, where: M2+ are divalent cations (Mg2+, Zn2+, Ca2+, etc.), M3+ are trivalent cations (Al3+, Fe3+, Mn3+, etc) and An- are interlayer anions (CO32-, NO3-, etc). These materials can be used in sorption applications, e. g. sorption of phosphates, due to their large surface areas, high anion-exchange capacity, and flexible interlayer region accommodating various anionic species. Moreover, their chemical composition can be easily tuned allowing not only a high ion exchange capacity but also high selectivity towards phosphate ions. However, a powder form of these sorbent materials are not suitable in wastewater treatment systems due to the mass transfer limitations or difficulties in handling and recovery at the end of the process. The focus is on structuring the powder into an optimal architecture, e.g. porous microspheres. This study explores the added value of structuring the sorbent powders into porous microspheres, with controlled porosity and pore structure. These shaping efforts should lead to a decrease of the mass transfer limitations, a lower pressure drop and faster sorption kinetics. Pural MG63HT commercial Hydrotalcite-type clay material used in the present study was provided by Sasol Germany GmbH. The powder was processed into suspensions by mixing with sodium alginate polymer which was further cross-linked into a coagulation bath containing Ca2+ ions. The shaped products were obtained using both the gravitational as well as the vibrational drip casting technique using a BRACE GmbH device for microsphere production. The research combines physico-chemical characterization (XRD, SEM, porosity measurements), material shaping (zeta potential and viscosity measurements of the slurries and suspensions) and phosphate sorption testing by UV-vis Spectroscopy