UV-photoexcitation of TiO₂ in contact with aqueous solutions of azo dyes does not imply only its photocatalytic degradation, but the reaction fate of the dye depends on the experimental conditions. In fact, we demonstrate that the presence of sodium formate is the switch from a degradative pathway of the dye to its transformation into useful products. Laser flash photolysis experiments show that charge separation is extremely long lived in nanostructured TiO₂ thin films, making them suitable to drive both oxidation and reduction reactions. ESR spin trapping and photoluminescence experiments demonstrate that formate anions are very efficient in intercepting holes, thereby inhibiting OH radicals formation. Under these conditions, electrons promoted in the conduction band of TiO₂ and protons deriving from the oxidation of formate on photogenerated holes lead to the reductive cleavage of N=N bonds with formation and accumulation of reduced intermediates. Negative ion ESI–MS findings provide clear support to point out this new mechanism. This study provides a facile solution for realizing together wastewater purification and photocatalytic conversion of a waste (discharged dye) into useful products (such as sulfanilic acid used again for synthesis of new azo dyes). Moreover, the use of TiO₂ deposited on an FTO (Fluorine Tin Oxide) glass circumvents all the difficulties related to the use of slurries. The obtained photocatalyst is easy to handle and to recover and shows an excellent stability allowing complete recyclability.

New composite photocatalysts have been obtained by chemical bath deposition of CdS on top of either nanostructured crystalline ZrO₂ or TiO₂ films previously deposited on conductive glass FTO. Their morphological, photoelectrochemical and photochemical properties have been investigated and compared. Time resolved spectroscopic, techniques show that in FTO/TiO₂/CdS films the radiative recombination of charges, separated by visible illumination of CdS, is faster than in FTO/ZrO₂/CdS, evidencing that carrier dynamics in the two systems is different. Photoelectrochemical investigation evidence a suppression of electron collection in ZrO₂/CdS network, whereas electron injection from CdS to TiO₂ is very efficient since trap states of TiO₂ act as a reservoir for long lived electrons storage. This ability of FTO/TiO₂/CdS films is used in the reductive cleavage of N=N bonds of some azo-dyes by visible light irradiation, with formation and accumulation of reduced aminic intermediates, identified by ESI-MS analysis. Needed protons are provided by sodium formate, a good hole scavenger that leaves no residue upon oxidation. FTO/TiO₂/CdS has an approximately 100 meV driving force larger than FTO/ZrO₂/CdS under illumination for azo-dye reduction and it is always about 10% more active than the seconds. The films showed very high stability and recyclability, ease of handling and recovering.

Contamination by pharmaceuticals adversely affects the quality of natural water, causing environmental and health concerns. In this study, target drugs (oxazepam, OZ, 17-α-ethinylestradiol, EE2, and drospirenone, DRO), which have been extensively detected in the effluents of WWTPs over the past decades, were selected. We report here a new photoactive system, operating under visible light, capable of degrading EE2, OZ and DRO in water. The photocatalytic system comprised glass spheres coated with nanostructured, solvothermally treated WO₃ that improves the ease of handling of the photocatalyst and allows for the implementation of a continuous flow process. The photocatalytic system based on solvothermal WO₃ shows much better results in terms of photocurrent generation and photocatalyst stability with respect to state-of-the-art WO₃ nanoparticles. Results herein obtained demonstrate that the proposed flow system is a promising prototype for enhanced contaminant degradation exploiting advanced oxidation processes.

In quest of a substantial reduction in potentially toxic gas emissions into the air from industrial plants, dry flue gas desulfurization (FGD) systems offer several advantages, such as reduced operational costs, adaptability, ease of use, and the elimination of liquid waste. This study describes the development of a laboratory-scale pilot system for conducting SO₂ abatement experiments using a fixed-bed reactor. To validate the experimental setup, the reactor was equipped with a control system for measuring and monitoring relative humidity, temperature, and total flux composition. The study utilized two standards, slaked lime and 13X zeolite, under identical experimental conditions to ensure comparability. This research will significantly advance the understanding of adsorbent materials for capturing low SO₂ concentrations by measuring adsorption kinetics and equilibrium data. The findings highlight the impact of distinct morphological, chemical, and crystallographic properties on the efficiency of dry FGD systems.