Herein, the preparation of nanotubular and porous TiO₂ structures (TNS) is presented for photocatalytic applications. Different TNS were prepared in three different types of glycerol- and ethylene glycol-based electrolytes on a large area (approx. 20 cm²) via anodization using different conditions (applied potential, fluoride concentration). Morphology, structure, and optical properties of TNS were characterized by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD), and Diffuse Reflectance Spectroscopy (DRS), respectively. All TNS possess optical band-gap energy (E_BG) in the range from 3.1 eV to 3.2 eV. Photocatalytic degradation of caffeine was conducted to evaluate the efficiency of TNS. Overall, nanotubular TiO₂ possessed enhanced degradation efficiencies (up to 50% degradation) compared to those of porous TiO₂ (up to 30% degradation). This is due to the unique properties of nanotubular TiO₂, e.g., improved incident light utilization. As the anodization of large areas is, nowadays, becoming a trend, we show that both nanotubular and porous TiO₂ are promising for their use in photocatalysis and could be potentially applicable in photoreactors for wastewater treatment. We believe this present work can be the foundation for future development of efficient TiO₂ nanostructures for industrial applications.

TiO₂ nanotube layers (TNT) are prepared by electrochemical anodization of Ti foil in an electrolyte composed of ethylene glycol, ammonium fluoride, and water. The surface of TNT is modified by iron using spin-coating of Fe(NO₃)₃/IPA (isopropyl alcohol) solution of different concentrations (10 µM−100 mM). The as-prepared materials are annealed at 450 °C for 2 h to form crystalline Fe-TNT. The phase identification and surface morphology of the materials are investigated by XRD and SEM/EDX, respectively. The novelty of this work is based on the investigation of different photochemical processes that could occur simultaneously, and it includes mainly photocatalysis and Fenton-based processes since iron is a Fenton-active element and TiO₂ is a photocatalyst. To this end, the degradation of caffeine, an organic pollutant, is performed under solar-like radiation at pH = 3 using different systems that are: (i) Fe-TNT material alone; (ii) a radical precursor alone (H₂O₂ = 1 mM); and (iii) Fe-TNT combined with H₂O₂. It is worth noting the degradation mechanism of the organic pollutants occurs via advanced oxidation processes where hydroxyl radicals have been identified as the main reactive oxygen species. One of the main goals of this work is to determine the contribution of the different involved photochemical processes (photocatalysis, photo-Fenton, and photolysis) along with the potential synergy between all these processes. To resume, this work provides new insights into the concept of photochemical versatility (using Fe-TNT), which is scarcely described in the literature.

Here, synthesis, characterisation, and photocatalytic properties for versatile applications were investigated using 2D TiO2 aerogel powders decorated by 0D BiVO4nanospheres (TiO2/BiVO4). First, 2D TiO2 was prepared via lyophilisation and subsequently modified by 0D BiVO4 using wet impregnation method. Morphology, structure, composition, and optical properties were evaluated by transmission electron microscopy (TEM), X-ray diffractometry (XRD), laser-induced breakdown spectroscopy (LIBS), and diffuse reflectance spectroscopy (DRS), respectively. Significantly enhanced photocurrent densities (3-15 times) were obtained for TiO2/BiVO4 compared to pure TiO2 and BiVO4. The reduction of toxic Cr(VI) to less-toxic Cr(III) was assessed, including the effect of pH on the overall photocatalytic efficiency. Under acidic conditions (pH ~ 2), the Cr(VI) reduction efficiency reached 100 %. In the case of photocatalytic CO2 reduction, the yields of CH4, CO, and H2 were the highest over TiO2/BiVO4. The higher efficiency for both photocatalytic reactions was achieved due to better separation of electron-hole on the TiO2/BiVO4 photocatalyst. Electrochemical measurements also demonstrated the highest photocurrent responses by TiO2/BiVO4, confirming the previous results. The excellent stability of the TiO2/BiVO4 upon repeated runs highlights its potential use in versatile environmental applications. The efficiency of TiO2/BiVO4 is due to the interplay of the structure, morphology, composition, and photoelectrochemical properties that favour the material for the presented herein photocatalytic applications.