Mechanistic understanding of the increased photoactivity of TiO2 nanosheets upon tantalum doping

Microbial synthesis of titanium dioxide nanoparticles and their importance in wastewater treatment and antimicrobial activities: a review

Nanotechnology (NT) and nanoparticles (NPs) have left a huge impact on every field of science today, but they have shown tremendous importance in the fields of cosmetics and environmental cleanup. NPs with photocatalytic effects have shown positive responses in wastewater treatment, cosmetics, and the biomedical field. The chemically synthesized TiO2 nanoparticles (TiO2 NPs) utilize hazardous chemicals to obtain the desired-shaped TiO2. So, microbial-based synthesis of TiO2 NPs has gained popularity due to its eco-friendly nature, biocompatibility, etc. Being NPs, TiO2 NPs have a high surface area-to-volume ratio in addition to their photocatalytic degradation nature. In the present review, the authors have emphasized the microbial (algae, bacterial, fungi, and virus-mediated) synthesis of TiO2 NPs. Furthermore, authors have exhibited the importance of TiO2 NPs in the food sector, automobile, aerospace, medical, and environmental cleanup.

Adsorption and Photocatalytic Degradation of Methylene Blue on TiO2 Thin Films Impregnated with Anderson-Evans Al-Polyoxometalates: Experimental and DFT Study

In this work, we fabricated a TiO2 thin film, and the same film was modified with an Anderson aluminum polyoxometalate (TiO2-AlPOM). Physical-chemical characterization of the catalysts showed a significant change in morphological and optical properties of the TiO2 thin films after surface modification. We applied the kinetic and isothermal models to the methylene blue (MB) adsorption process on both catalysts. The pseudo-second order model was the best fitting model for the kinetic results; qe (mg/g) was 11.9 for TiO2 thin films and 14.6 for TiO2-AlPOM thin films, and k2 (g mg-1 min-1) was 16.3 × 10-2 for TiO2 thin films and 28.2 × 10-2 for TiO2-AlPOM thin films. Furthermore, the Freundlich model was suitable to describe the isothermal behavior of TiO2, KF (5.42 mg/g), and 1/n (0.312). The kinetics of photocatalytic degradation was fitted using the Langmuir-Hinshelwood model; kap was 7 × 10-4 min-1 for TiO2 and 13 × 10-4 min-1 for TiO2-AlPOM. The comparative study showed that TiO2 thin films reach a 19.6% MB degradation under UV irradiation and 9.1% MB adsorption, while the TiO2-AlPOM thin films reach a 32.6% MB degradation and 12.2% MB adsorption on their surface. The surface modification improves the morphological, optical, and photocatalytic properties of the thin films. Finally, the DFT study supports all the previously shown results.

Reduced TiO2with prolonged electron lifetime for improving photocatalytic water reduction activity

The reduction of anatase TiO₂with NaBH₄under argon atmosphere at a high temperature resulted in a longer electron lifetime and a larger electron population. The reduced gray anatase sample with disorder layer showed a higher evolution rate of H₂(130.2μmol h^-1g^-1) compared to pristine TiO₂(24.1μmol h^-1g^-1) in the presence of Pt co-catalyst in an aqueous glucose solution under exposure to ultraviolet light (λ⩽ 400 nm). Ti³⁺and oxygen vacancy defects were proposed to exist in the reduced TiO₂. A continuum tail forms above the valence band edge top as a result of these two defects, which contribute to the lattice disorder. This is presumably also the case with the conduction band, which has a continuum tail composed of mid-gap states as a result of the defects. The Ti³⁺and oxygen vacancy defects operate as shallow traps for photoexcited electrons, thereby preventing recombination. Since the defects are primarily located at the surface, i.e. in the disorder layer, the photoexcited electrons in shallow traps hence become readily available for the reduction of H₃O⁺into H₂. The prolonged electron lifetime increases the photoexcited electron population in the reduced TiO₂, resulting in enhanced water reduction activity.

Efficient electron extraction by CoS2loaded onto anatase TiO2for improved photocatalytic hydrogen evolution

Titanium dioxide (TiO₂) as a benchmark photocatalyst has been attracting attention due to its photocatalytic activity combined with photochemical stability. In particular, TiO₂with anatase polymorph holds promise for driving reduction reactions, such as proton reduction to evolve H₂via photocatalysis. In this study, anatase TiO₂is loaded with CoS₂through the hydrothermal route to form a CoS₂@TiO₂photocatalyst system. X-ray absorption near edge structure confirms the +2-oxidation state of the Co cation, while extended x-ray absorption fine structure shows that each Co²⁺cation is primarily coordinated to six S^-anions forming a CoS₂-like species. A small fraction of the Co²⁺species is also coordinated to O^2-anions forming Co_xO_yspecies and substitutionally resides at the Ti⁴⁺-sites. Further investigations with steady-state IR absorption induced by UV-light and time-resolved microwave conductivity suggest an efficient electron transfer from the conduction band of TiO₂to the surface-loaded CoS₂which acts as a metallic material with no bandgap. The CoS₂shallowly traps electrons at the host surface and facilitates proton reduction. An appreciably enhanced H₂evolution rate (8 times) is recognised upon the CoS₂loading. The CoS₂is here proposed to function as a proton reduction cocatalyst, which can potentially be an alternative to noble metals.