Open Access
Article
03 April 2025Design, Building and Performance of a New Photocatalytic Reactor Using TiO2-Coated Rings Synthesized by Plasma Electrolytic Oxidation
An annular UV photocatalytic reactor with recirculation in batch was designed and built. The design considered low construction, simple operation and maintenance costs, availability and durability of the materials used, easy cleaning, and high standards of hygiene and safety. The TiO2 photocatalysts were synthesized by plasma electrolytic oxidation (PEO) on commercial Ti rings were compared with coatings obtained on Ti plates as a reference, and no influence of the substrate geometry on the morphology, crystallinity, or bandgap of the coatings was observed. The efficiency of the photocatalytic reactor using 10 TiO2-coated rings was tested by Cr(VI) transformation in the presence of EDTA. The Cr(VI) transformation after 5 h irradiation attained 95%; a rather high photocatalytic activity (62%) was maintained after the third use of the rings without reactivation of the photocatalyst. These coatings synthesized by PEO have not been applied in modular photocatalytic reactors until now.
Open Access
Opinion
11 June 2025Reflections on Photocatalysis Progress Since the Inspiration of Prof. David Ollis in 1992
Why has photocatalysis not gained the wide-ranging commercial applications in environmental purification of air and water that seemed promising 30+ years ago since the first international conference on TiO2 photocatalytic purification and treatment of water in 1992? The primary reason lies in its low intrinsic efficiency. The progress of R&D to enhance this efficiency has been slow, possibly due to an incomplete understanding of the underlying mechanisms of photocatalysis. There is also the possibility that certain factors, with effects comparable to those of the band gap, significantly influence photocatalytic performance but remain underexplored. Additionally, challenges such as mass transfer limitations and surface contamination hinder the industrial application of photocatalysts. It may be time for scientists to reconsider and address the limitations and practical application scenarios of photocatalysis.
Open Access
Review
27 June 2025Study of Self-Sensitization of Wide-Gap Oxides Photocatalysts
The self-sensitization of wide-gap oxide photocatalysts to the region beyond the long-wave edge by changing the stoichiometry is discussed. The results of in situ investigations in three phases: gas—adsorbate—surface obtained by a variety of complementary experimental methods are analyzed. Dielectrics (MgO, Al2O3, BeO) were sensitized by creating colored F- and V- type photocatalysis centers via the thermal reduction of oxides in a vacuum. For semiconductors, the 2D structures of ZnO/ZnO1−x and TiO2/TiO2−x were formed through surface photo-reduction. In all self-sensitization cases, enhanced photosorption activity was observed. The quantum yields in the model POIE (photo-induced oxygen isotope exchange) redox reaction under VIS illumination of 2D structures and resonant exciton illumination of a layered 2D structure ZnO/ZnO1−x/O− are 5–7 times higher than those of the initial samples. Both 2D structures showed stable activity in the redox reaction $$\mathrm{CO+NO}\overset{\mathrm{hv}}{\operatorname*{\rightarrow}}1/2\mathrm{N}_{2}\uparrow+\mathrm{CO}_{2\mathrm{ads}}$$ with quantum yields 5–7 times higher than those of the initial oxides in their intrinsic absorption region.