Studies on mass production and highly solar light photocatalytic properties of gray hydrogenated-TiO2 sphere photocatalysts

Highly visible-light-active sulfur and carbon co-doped TiO2 (SC-TiO2) heterogeneous photocatalysts prepared by underwater discharge plasma

To promptly and simply create highly crystalline S/C co-doped TiO2 (SC-TiO2) photocatalysts at room temperature and atmospheric pressure, we suggest a novel plasma-assisted sol-gel synthesis method. This method is a simultaneous synthetic process, in which an underwater plasma undergoes continuous reactions to generate high-energy atomic and molecular species that enable TiO2 to achieve crystallinity, a large surface area, and a heterogeneous structure within a few minutes. In particular, it was demonstrated that the heterogeneously structured TiO2 was formed by doping that sulfur and carbon replace O or Ti atoms in the TiO2 lattice depending on the composition of the synthesis solution during underwater plasma treatment. The resultant SC-TiO2 photocatalysts had narrowed bandgap energies and extended optical absorption scope into the visible range by inducing the intermediate states within bandgap due to generation of oxygen vacancies on the surface of TiO2 through synthesis, crystallization, and doping. Correspondingly, SC-TiO2 showed a significant degradation efficiency ([k] = 6.91 h-1) of tetracycline (TC, antibiotics) under solar light irradiation, up to approximately 4 times higher compared to commercial TiO2 ([k] = 1.68 h-1), resulting in great water purification. Therefore, we anticipate that this underwater discharge plasma system will prove to be an advantageous technique for producing heterostructural TiO2 photocatalysts with superior photocatalytic efficiency for environmental applications.

High removal efficiency of industrial toxic compounds through stable catalytic reactivity in water treatment system

We identified optimal conditions for the disposal of high concentration of organic contaminants within a short time using a hybrid advanced oxidation process (AOP) combining various oxidizing agents. Plasma-treated water (PTW) containing many active species, that play dominant roles in the degradation of organic substances like hydroxyl radicals, atomic oxygen, ozone, and hydrogen peroxide, was used in this study as a strategy to improve degradation performance without the use of expensive chemical reagents like hydrogen peroxide. In particular, the optimal decomposition conditions using PTW, which were combined with 10 mg/h ozone, 2 g/L iron oxide, and 4 W UV light, demonstrated excellent removal abilities of a high concentration of reactive black 5 (RB5; 100 mg/L, >99%, [k] = 4.15 h^-1) and tetracycline (TC; 10 mg/L, >96.5%, [k] = 3.35 h^-1) for 25 min, approximately 1.5 times higher than that without PTW (RB5; 100 mg/L, 94%, [k] = 2.80 h^-1). These results confirmed that the production of strong reactive hydroxyl radicals from the decomposition process, as well as various reactive species included in PTW efficiently attacked pollutant substances, resulting in a higher removal rate. This suggests that a water treatment system with this optimal condition based on complex AOP systems using PTW could be useful in critical environmental and biomedical applications.

Synthesis of Oxygen Deficient TiO2 for Improved Photocatalytic Efficiency in Solar Radiation

The photocatalytic activities of TiO2 have been limited mainly to absorbing in the ultraviolet spectrum which accounts for only 5% of solar radiation. High energy band gap and electron recombination in TiO2 nanoparticles are responsible for its limitations as a photocatalyst. An oxygen deficient surface can be artificially created on the titanium oxide by zero valent nano iron through the donation of its excess electrons. A visible light active TiO2 nanoparticle was synthesized in the current investigation through simple chemical reduction using sodium boro-hydride. The physical and textural properties of the synthesized oxygen deficient TiO2 photocatalyst was measured using scanning/ transmission electron microscopy while FTIR, XRD and nitrogen sorption methods (BET) were employed for its further characterizations. Photochemical decoloration of orange II sodium dye solution in the presence of the synthesized TiO2 was measured using an UV spectrophotometer. The resulting oxygen deficient TiO2 has a lower energy band-gap, smaller pore sizes, and enhanced photo-catalytic properties. The decoloration (88%) of orange (II) sodium salt solution (pH 2) under simulated solar light was possible at 20 min. This study highlights the effect of surface oxygen defects, crystal size and energy band-gap on the photo-catalytical property of TiO2 nanoparticles as impacted by nano zero valent iron. It opens a new window in the exploitation of instability in the dopant ions for creation of a visible light active TiO2 photocatalyst.

Development of TiO2-coated YSZ/silica nanofiber membranes with excellent photocatalytic degradation ability for water purification

Numerous reports have elucidated that TiO2 nanoparticles (TiO2-NPs) exhibit respectable photocatalytic degradation capacities due to their high specific surface areas. However, the current recovery process leads to a loss of TiO2-NPs; therefore, there is a need to immobilize TiO2-NPs on the substrate used. Herein, TiO2-coated yttria-stabilized zirconia/silica nanofiber (TiO2-coated YSZ/silica NF) was prepared by coating TiO2 on the surface of YSZ/silica NF using a sol-gel process. The TiO2 coating layer on the nanofiber surface improved the separation ability of the membrane as well as the photocatalytic degradation ability. The pore size of the TiO2-coated YSZ/silica NF membrane was less than that of the pristine YSZ/silica NF membrane, and it rejected over 99.6% of the 0.5 μm polymeric particles. In addition, the TiO2-coated YSZ/silica NF membrane showed excellent adsorption/degradation of humic acid (HA, 88.2%), methylene blue (MB, 92.4%), and tetracycline (TC, 99.5%). Six recycling tests were performed to evaluate the reusability of the TiO2-coated YSZ/silica NF membrane. The adsorption/degradation efficiency for HA, MB, and TC decreased by 3.7%, 2.8%, and 2.2%, respectively. We thus verified the high separation ability, excellent photocatalytic degradation ability, and excellent reusability of the TiO2-coated YSZ/silica NF membranes.

Enhanced Photocatalytic Degradation of Organic Dyes via Defect-Rich TiO2 Prepared by Dielectric Barrier Discharge Plasma

The dye wastewater produced in the printing and dyeing industry causes serious harm to the natural environment. TiO₂ usually shows photocatalytic degradation of dye under the irradiation ultravilet light rather than visible light. In this work, a large number of oxygen vacancies and Ti³⁺ defects were generated on the surface of the TiO₂ nanoparticles via Ar plasma. Compared with pristine TiO₂ nanoparticles, the as-obtained Ar plasma-treated TiO₂ (Ar-TiO₂) nanoparticles make the energy band gap reduce from 3.21 eV to 3.17 eV and exhibit enhanced photocatalytic degradation of organic dyes. The Ar-TiO₂ obtained exhibited excellent degradation properties of methyl orange (MO); the degradation rate under sunlight irradiation was 99.6% in 30 min, and the photocatalytic performance was about twice that of the original TiO₂ nanoparticles (49%). The degradation rate under visible light (λ > 400 nm) irradiation was 89% in 150 min, and the photocatalytic performance of the Ar-TiO₂ was approaching ~4 times higher than that of the original TiO₂ nanoparticles (23%). Ar-TiO₂ also showed good degradation performance in degrading rhodamine B (Rho B) and methylene blue (MB). We believe that this plasma strategy provides a new method for improving the photocatalytic activity of other metal oxides.