Preparation of inorganic crystalline compounds induced by ionizing, UV and laser radiations

γ-ray induced formation of oxygen vacancies and Ti3+ defects in anatase TiO2 for efficient photocatalytic organic pollutant degradation

Oxygen vacancies and Ti³⁺ defects in anatase TiO₂ have attracted great attention to address the insufficient optical absorption and photoinduced charge-carrier separation in photocatalysis. In this study, we demonstrate a superficial and innovative approach for synthesizing anatase TiO₂ nanoparticles with abundant oxygen vacancies via γ-ray irradiation reduction at room temperature. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) confirm that oxygen vacancies and Ti³⁺ defects can be quantitatively and extensively obtained by merely regulating the irradiation dosage. Photoelectrochemical measurements suggest that oxygen vacancies and Ti³⁺ defects promoted the separation of electron-hole pairs and then enhanced the photocatalytic degradation performance for organic pollutant. In comparison with TiO₂ (no irradiation), the sample (49.5 kGy irradiation) exhibited a 20.0-fold enhancement in visible-light decomposition of phenol. In addition, the results of scavenge experiments and mechanism analysis revealed that O₂^- are the dominant active species. The excited electrons generated at the conduction band and oxygen vacancy level of TiO_2-x-49.5 conspicuously contributes to generate much more ·O₂^- species. This novel study shows at room temperature, the γ-ray approach of irradiation leads to faster formation and quantification of oxygen vacancies in the semiconductor materials.

At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

Formation yields of ˙OH radicals were precisely determined in aqueous solutions of coumarin-3-carboxylic acid and ferrous sulfate (i.e., Fricke dosimeter) exposed to 253.7 nm radiation delivered from a continuous source. Quantum yield of ˙OH radicals was determined as ∼0.08, i.e., roughly one out of twelve photons, efficiently absorbed in UV-illuminated solutions, produced one ˙OH radical. Energetically, a water molecule should undergo a correlated action of at least two 4.9 eV photons delivering enough energy for direct H-OH dissociation (5.0-5.4 eV). We suggest a mechanism based on an interaction of two water molecules, both in long-living triplet states. An intermolecular transfer of excitation energy provided a sufficient amount of energy for the dissociation of one water molecule into ˙OH and H˙ radicals. In an aqueous solution of phospholipids, quantum yields of hydroperoxides formed under these irradiation conditions decreased with total effectively absorbed energy (i.e. a dose), similar to the radiation chemical yields obtained during an exposure to ionizing radiation, such as gamma rays from radionuclide sources. Under 253.7 nm irradiation, one ˙OH radical causes a peroxidation of 34 phospholipid molecules. This implicates chain mechanism of the reaction.