Photocatalytic air-cleaning using TiO2 nanoparticles in porous silica substrate

For air-cleaning, TiO₂ photocatalysis represents one of the very efficient advanced oxidation processes (AOPs) that can decompose chemically and microbiologically stable volatile organic compounds (VOCs). However, the photocatalytic activity of nanocrystalline TiO₂ powders can be significantly suppressed due to TiO₂’s poor adsorption characteristics for organic compounds and its relatively low surface area. The present study sought to solve this problem by immobilising nanocrystalline TiO₂ in the porous silicate substrate. Two titania sources were used in an aqueous solution form: a suspension from a TiO₂ producer in Slovenia, Cinkarna Celje (CC-40) and a TiO₂ sol, prepared by a low-temperature synthesis developed at the University of Nova Gorica (TiO₂-UNG). Two different types of mesoporous silica were used: SBA-15 with an ordered hexagonal pore arrangement and KIL-2 with disordered inter-particle mesoporosity. The structural characteristics, adsorption properties and photocatalytic activity of catalysts deposited on aluminium plates as thin films were investigated. CC-40 exhibited higher adsorption and photocatalytic activity than TiO₂-UNG due to the greater quantity of Ti-OH groups on its surface. The addition of mesoporous silica led to higher adsorption and catalytic activity for both TiO₂ sources. SBA-15 was more efficient than KIL-2.     

Thermochemistry of Gd2BaCuO5 and LuBa2Cu3Ox

Solution calorimetry, using 6.0 M HCl as a solvent, is used to study the thermochemistry of Gd2BaCuO5 and the high-temperature superconductor LuBa2Cu3O6.92. For the first time, the standard formation enthalpies of these phases have been determined as follows: DeltafH(o)(Gd2BaCuO 5, s, 298.15 K) = -2618.6 +/- 7.4 kJ/mol; DeltafH(o)(LuBa2Cu3O6.92, s, 298.15 K) = -2693.1 +/- 11.9 kJ/mol. The thermodynamic stability at room temperature has been assessed. The results show that Gd211 and Lu123 are thermodynamically stable with respect to binary oxides and unstable with respect to interaction with CO 2 at ambient temperatures. Lu123 is thermodynamically stable with respect to assemblages containing combinations of Lu2O3, CuO, and BaCuO2 and thermodynamically unstable with respect to interactions with water.     

Development and validation of a sensitive and fast solid-phase spectrophotometric procedure for phenol determination in pharmaceuticals

A very sensitive, simple, and fast solid-phase spectrophotometric procedure for the determination of phenol using the p-nitrobenzenediazonium reagent (DAR reagent) was developed. This procedure is based on the simultaneous concentration of the orange product on a Dowex 1-X2 anion exchanger within 15 min, and a direct absorbance measurement of the sorbed species at both 530 nm (the absorption maximum of the phenol-DAR in the resin phase) and 700 nm (the range where only the resin absorbs light). Quality control and evaluation of the analytical parameters was carried out using a comprehensive prevalidation strategy. The linearity of the method was confirmed within an analyte working range from 0.01 to 0.10 μmol (0.2 to 2.0 nmol mL(-1)). The precision ranged from ±1.17 to ±9.61%; the accuracy ranged from -17.50 to +17.81%. The evaluated limiting values were L(D) = 0.0013 μmol and L(Q) = 0.0082 μmol. The DAR-SPS method was successfully applied to the determination of phenol in a pharmaceutical sample of salicylic acid (98.0-100.0%) and vaccines (98.0-103.4%).     

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements

In recent years, operando/in situ X-ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA-spectra with a satisfactory signal-to-noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion- and mass-transport limitations. To shed light on the impact of this variable on the spectro-electrochemical results, in this study we investigate Pd-hydride formation in carbon-supported Pd-nanoparticles (Pd/C) and an unsupported Pd-aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL-thickness largely determines the hydride formation trends inferred from spectro-electrochemical experiments, therewith calling for the minimization of the CL-thickness in such experiments and the use of complementary thin-film control measurements.