Tuning oxygen vacancy content in TiO2 nanoparticles to enhance the photocatalytic performance

Applications of TiO2 nanomaterials in photocatalysis, batteries, supercapacitors and solar cells, have seen widespread development in recent decades. Nowadays, black TiO2 have earned won attention due to enhancing the solar light absorption by the formation of oxygen vacancies and Ti3+ defects, to promote the separation of photo-generated charge carriers leading to the improvement of the photocatalytic performance in H2 production and pollutants degradation. The enhanced photocatalytic activity of black TiO2 is also due to a lattice disorder on the surface and the presence of oxygen vacancies, Ti3+ ions, Ti-OH and Ti-H groups. Enhancing the optical absorption characteristics of TiO2 and change of energy level and band-gap of materials have been successfully demonstrated to improve their photocatalytic activities, especially for black TiO2 nanoparticles, which promote the visible light absorption. The current review focuses on the investigation of the chemical reduction synthetic route for black TiO2 nanomaterials, and their propose associated with the green application such as photodegradation of organic pollutants and photocatalytic water splitting. The synthesis methods of black TiO2 involves the changes from Ti4+ to Ti3+ state, into different strategies (1) The use of hydrogen highly active hydrogen species such as H2, H2/Ar or H2/N2 gases, and metal hydrides (NaBH4, CaH2), (2) The reduction by active metals such as aluminium, magnesium and zinc (3) Organic molecules such as imidazole and ascorbic acid.

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Black TiO2 Synthesis by Chemical Reduction Methods for Photocatalysis Applications.

The prospect of engineering the bandgap in semiconductor nanostructures all the way from ultraviolet to visible is highly significant in various applications such as photocatalysis, sensing, optoelectronics and biomedical applications. Since many semiconductors have their bandgaps in the UV region, various techniques are used to tune their bandgaps to the visible region. Doping and co-doping with metals and non-metals have been found to be highly effective in bandgap narrowing as doping creates a continuum of mid-bandgap states which effectively reduces the bandgap. Other than these techniques, the modulation of intrinsic vacancies is an effective way to control the bandgap. Among all semiconductors, titanium dioxide (TiO2) is a well-studied material for UV photocatalytic applications. TiO2 has oxygen and titanium vacancies as intrinsic defects which influence the bandgap based on its phase of existence. The oxygen vacancies generate unpaired electrons associated with Ti3+ species, resulting in the creation of donor levels within the bandgap. Trivacancies give a p-type nature to TiO2 due to excess holes and generate acceptor levels in the bandgap. The existence of a continuum of such intrinsic defect states within the bandgap appears to narrow the bandgap and enhances the visible light absorption in TiO2, although the effect is an apparent narrowing. Doping and co-doping of TiO2 with metals such as Au, Ag, Fe, Co, Ni, Pt and Pd and non-metals such as B, C, N, Br and Cl, doping with Ti3+ ions and hydrogenation have all been found to narrow the bandgap of TiO2. In this review, we focus on such intrinsic vacancy-modulated bandgap narrowing in TiO2. This review covers significant recent advancements in bandgap engineering of TiO2.

A review on optical bandgap engineering in TiO2 nanostructures via doping and intrinsic vacancy modulation towards visible light applications

In the work, we firstly report the facile and large-scale synthesis of defective black TiO2−x(B) nanosheets via a dual-zone NaBH4 reduction method. The structure, physico-chemical, and optical properties of TiO2−x(B) nanosheets were systematically characterized by powder X-ray diffraction, Raman spectroscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy, etc. The concentration of Ti3+ can be well tuned by NaBH4 reduction. With increasing the mass ratio of NaBH4 to TiO2(B), the generation of Ti3+ defects gives rise to the increased intensity of a broad band absorption in the visible wavelength range. It is demonstrated that the TiO2−x(B) photocatalyst synthesized with the mass ratio of NaBH4 to TiO2(B) of 3:1 exhibited an optimum photocatalytic activity and excellent photostability for hydrogen evolution under visible-light irradiation. By combining the advantages of 2D TiO2(B) nanosheets architecture with those of Ti3+ self-doping and simultaneous production of oxygen vacancy sites, the enhanced photocatalytic performance of the defective TiO2−x(B) nanosheets was achieved.

Facile and Large-scale Synthesis of Defective Black TiO2−x(B) Nanosheets for Efficient Visible-light-driven Photocatalytic Hydrogen Evolution

Highly crystalline anatase titanium dioxide (TiO2) nanocuboids were synthesized via a hydrothermal method using ethylenediamine tetraacetic acid as a capping agent. The structural study revealed the nanocrystalline nature of anatase TiO2 nanocuboids. Morphological study indicates the formation of cuboid shaped particles with thickness of ∼5 nm and size in the range of 10–40 nm. The UV-visible absorbance spectra of TiO2 nanocuboids showed a broad absorption with a tail in the visible-light region which is attributed to the incorporation of nitrogen atoms into the interstitial positions of the TiO2 lattice as well as the formation of carbonaceous and carbonate species on the surface of TiO2 nanocuboids. The specific surface areas of prepared TiO2 nanocuboids were found to be in the range of 85.7–122.9 m2 g−1. The formation mechanism of the TiO2 nanocuboids has also been investigated. Furthermore, the photocatalytic activities of the as-prepared TiO2 nanocuboids were evaluated for H2 generation via water splitting under UV-vis light irradiation and compared with the commercial anatase TiO2. TiO2 nanocuboids obtained at 200 °C after 48 h exhibited higher photocatalytic activity (3866.44 μmol h−1 g−1) than that of commercial anatase TiO2 (831.30 μmol h−1 g−1). The enhanced photoactivity of TiO2 nanocuboids may be due to the high specific surface area, good crystallinity, extended light absorption in the visible region and efficient charge separation.

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Highly crystalline anatase TiO2 nanocuboids as an efficient photocatalyst for hydrogen generation

In‐situ UV‐irradiation activation leads to an intense visible‐light absorption of up to 700 nm in ethylene glycolate‐stabilized TiO2(B) nanosheets. It is ascribed that the creation of abundant subsurface/lattice oxygen vacancies and Ti3+ centers, along with UV‐induced breakdown of Ti−O bonds between ethylene glycolate and TiO2(B). Consequently, the enhanced and stable visible‐light‐driven photocatalytic H2 evolution is obtained on defect‐rich TiO2(B) nanosheets.

In‐situ Photosynthetic Route to Tailor Point Defects in TiO2(B) Nanosheets for Visible Light‐Driven Photocatalytic Hydrogen Production

Radiation resistance and unsatisfactory efficacy of radioimmunotherapy are important barriers to non-small cell lung cancer (NSCLC) treatment. The impacts of anlotinib on radiation and tumor immune microenvironment (TIME) in NSCLC remain to be resolved. Here, we find anlotinib enhances radiosensitivity, and further increases radiotherapy-stimulated CD8+ T cell infiltration and activation via triggering cGAS/STING pathway. Moreover, anlotinib shows significant effects on radioimmunotherapy (radiotherapy plus anti-PD-L1). The addition of anlotinib alleviates CD8+ T cell exhaustion, promotes the cytotoxicity and proliferation of CD8+ T cells, and boosts immune memory activation. Our work reveals the crucial role of anlotinib in antitumor immunity, and provides preclinical evidence for the application of anlotinib combined with radioimmunotherapy in NSCLC treatment. 

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Anlotinib enhances the antitumor immunity of radiotherapy by activating cGAS/STING in non-small cell lung cancer

Dual-Purpose Nickel-Iron Layered Double Hydroxides by Controlled Lanthanide and Phosphide Incorporation for Promoting Overall Water Splitting Efficiency

The work aims to elucidate the importance of hybrid microwave annealing technology (HMA) in ultrafast fabrication of deficient cadmium stannate (Cd2SnO4) photoanodes with a worm-like porous structure and significant enhancement of solar water oxidation performance and stability. Comparison of three synthetic routes and experimental characterization revealed that relative to conventional thermal annealing (CTA) or even with extra HMA for 5 min (optimal), direct HMA for only 8 min can form cubic Cd2SnO4 thin films of unique worm-like and highly porous nanostrucures with a large interfacial surface area, high degree of phase crystallinity and high-concentration defects. The obtained results from the photoluminescence spectra and the charge efficiency measurements collaboratively verified that compared to using CTA treatment solely, the HMA treatment is effective in significantly improving charge separation, recombination and transfer processes, mainly by an over 13.5-fold increase in the bulk charge separation efficiency. Benefiting from these merits, under optimized conditions the HMA treated Cd2SnO4 film exhibited a remarkable 6-fold and 2-fold solar photocurrent enhancement compared with those of the CTA treated one and the combined CTA-HMA treated one, respectively, and an IPCE of 39% at 300 nm and 18% at 350 nm at 1.7 V versus RHE. Despite a high external bias required in this case, the study provides a simple route for synthesis of ideal Cd2SnO4 photoanodes which can be further extended to doping engineering and non-noble metal cocatalyst deposition.

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Jiajia Zhang

Papers

Facile and Large-scale Synthesis of Defective Black TiO2−x(B) Nanosheets for Efficient Visible-light-driven Photocatalytic Hydrogen Evolution

In‐situ Photosynthetic Route to Tailor Point Defects in TiO2(B) Nanosheets for Visible Light‐Driven Photocatalytic Hydrogen Production

Anlotinib enhances the antitumor immunity of radiotherapy by activating cGAS/STING in non-small cell lung cancer

Dual-Purpose Nickel-Iron Layered Double Hydroxides by Controlled Lanthanide and Phosphide Incorporation for Promoting Overall Water Splitting Efficiency

Worm-like porous and defect-structured cadmium stannate photoanodes for enhanced solar water oxidation