Novel, Simple and Low-Cost Preparation of Ba-Modified TiO2 Nanotubes for Diclofenac Degradation under UV/Vis Radiation.

A novel low-cost synthesis of barium-modified TiO2 nanotube (TNT) arrays was used to obtain an immobilized photocatalyst for degradation of diclofenac. TNT arrays were prepared by electrochemical anodization of titanium thin films deposited on fluorine-doped tin oxide (FTO) coated glass by magnetron sputtering, ensuring transparency and immobilization of the nanotubes. The Ba-modifications were obtained by annealing solutions of Ba(OH)2 spin coated on top of TNT. Three different concentrations of Ba(OH)2 were used (12.5 mM, 25 mM and 50 mM). The crystalline structure, morphology and presence of Ba were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Ba-modified TiO2 nanotubes (BTNT) were tested for photocatalytic degradation of diclofenac under UV/Vis radiation and it was proven that all of the Ba-modified samples showed an increase in photocatalytic activity with respect to the unmodified TNTs. The most efficient photocatalyst was the sample prepared with 25 mM Ba(OH)2 which showed 90% diclofenac degradation after 60 min. This result was in agreement with cyclic voltammetry measurements that showed the largest increase in photo-oxidation current densities for the same sample due to the increased generation of •OH radicals obtained by a more efficient photogenerated charge separation.

Ammonia and methane oxidation on TiO2 supported on glass fiber mesh under artificial solar irradiation.

In this work, we present the application of solar photocatalysis for air purification including toxic substances such as ammonia and methane normally related to emissions from agriculture (e.g., poultry and cattle farms), landfills, etc. The study was done in three different laboratory and semi-pilot scale reactors: annular reactor (AR), mini-photocatalytic wind tunnel (MPWT), and photocatalytic wind tunnel (PWT). Reactors present a physical model for estimation of air-borne pollutant degradation over TiO2-based photocatalytic layer in respect to optimal operating conditions (relative humidity, air/gas flow, and feed concentration). All studies were performed under artificial solar irradiation with different portions of UVB and UVA light. The application of solar photocatalysis for air purification was evaluated based on thorough monitoring of pollutants in inlet and outlet streams. The kinetic study resulted with intrinsic reaction rate constants: kp,int,NH3 = (3.05 ± 0.04) × 10-3 cm4.5 mW-0.5 g-1 min-1 and kp,int,CH4 = (1.81 ± 0.02) × 10-2 cm4.5 mW-0.5 g-1 min-1, calculated using axial dispersion model including mass transfer considerations and first-order reaction rate kinetics with photon absorption effects. The results of photocatalytic oxidation of NH3 and CH4 confirmed continuous reduction of pollutant content in the air stream due to the oxidation of NH3 to N2 and CH4 to CO and CO2, respectively. The application of solar photocatalysis in outdoor air protection is still a pioneering work in the field, and the results obtained in this work represent a good basis for sizing large-scale devices and applying them to prevent further environmental pollution. In the current study, a TiO2 P25 supported on a glass fiber mesh was prepared from commercially available materials. The system designed in this way is easy to perform, operate, and relatively inexpensive.