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Superfast crystallization of TiO2 nanotubes at low energy budget (bath temperature starting from 2 °C).

Cost effectiveness and reducing the energy and time consumption are crucial factors of concern while material preparation for device fabrication is considered. Here a simple electro chemical reductive method of self-doping is proved for first time to achieve efficient ultrafast (5 s) low temperature (15 °C) crystallization of well aligned TiO 2 nanotubes (TONT). Moreover, the so prepared self-doped TONTs are demonstrated to exhibit superior photocatalytic performance over the undoped in the degradation of the organic pollutant methylene blue. The effect is correlated with the tailoring of the crystallinity and red shift in band gap on self-doping due to the introduction of Ti 3+ ions and oxygen vacancies.

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Modified hybrid structures of TiO2 nanotubes (TONT), p-Al doped TONT/n-TONT with an additional overlayer of alumina, are constructed to achieve 99.57% photodegradation of the stable organic pollutant methylene blue (MB) within 180 min, a degradation rate 17 times higher than pure TONTs. The anodization at three different temperatures 2, 28 and 40 °C followed by impregnation of Al is used for their preparation. The analyses of structure, chemical composition and morphology are completed using x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and high resolution transmission microscopy, respectively, Rutherford back scattering and field emission scanning electron microscopy confirm the formation of the hybrid structure. This structure exhibits the highest photodegradation rate with TONT based catalysts to date for MB blue, by enhancing the electron—hole separation, the absorption of visible photons and the adsorption sites for the pollutant. The optical data coupled with valence band XPS is used for elucidating the energy band structure of the p-n junctions and to gain insight into the effect of the junction mechanism on photoactivity. The rectification ratios of the impregnated p-n junctions, determined by current—voltage measurements, are found to vary from 102 to 106.

Herein, the effect of magnesium doping on hematite nanostructures prepared by a simple and cost‐effective electrochemical method is reported. Photocatalytic and antibacterial studies on the undoped and doped samples suggest improved performance for the Mg‐doped samples. Structural studies using X‐ray diffraction, Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS) in combination with field‐emission scanning electron microscopy for surface morphology confirm the Mg presence in the nanostructured hematite phase of iron oxide. Analyses of the valence band (VB) XPS spectra along with optical reflectance spectra indicate a shift in VB edge, characteristic of a conductivity type conversion from n‐type in hematite to p‐type in Mg‐doped hematite. The room temperature electrical conductivity is increased by three orders, and the optical bandgap is reduced by around 0.08 eV for moderately doped hematite nanostructures.

The photodegradation rate of anatase TiO 2 is enhanced by about 11 times (from 0.0015 to 0.016 min À1) by construction of a type-II p-n heterostructure of configuration n:In 2 O 3 /p:In-doped TiO 2. A simple and cost-effective two-stage electrochemical anodization is used for the fabrication of this comparatively stable and recyclable photocatalyst of vertically aligned indium-doped TiO 2 nanotubes with an overlayer of n-type In 2 O 3 nanoparticles. The modified structural, morphological, compositional, optical, and electrical properties of the TiO 2 nanotubes are studied in detail by X-ray diffraction, X-ray photoelectron spectroscopy, Rutherford backscattering, field-emission scanning electron microscopy, reflectance measurements, and electrical conductivity measurements. The enhancement in device performance by the heterostructure is attributable to the tuning of optical bandgap to the visible energy region of solar spectrum, the effective electron-hole pair separation at the potential barrier, and the increase in surface-to-volume ratio and effective adsorption area of the photocatalyst by the structural modification with nanoparticles and the nanotube formation.

This paper reports the accomplishment of a noticeable enhancement in the photodegradation and antibacterial activity of α-Fe 2 O 3 by a heterostructure formation between α-Fe 2 O 3 and ZnO flakes. The heterostructure yields 97% photodegradation of methylene blue pollutant in water within 180 min, which is a fourfold increase compared to that observed with a pure α-Fe 2 O 3 nanostructure. Further characterisations indicate that the improved results are attributable to the reduction in optical band gap, the increased electrical conductivity, the improved spatial separation of carriers and the enhanced amount of available hydroxyl radicals for the reaction. The stability and reusability of the photocatalysts are confirmed for four consecutive cycles of operations. The phase identification and structural studies are done using x-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy in conjunction with surface morphology from field emission scanning electron microscopy. The enhancement of room temperature electrical conductivity by five times and band gap reduction from 1.98 eV to 1.75 eV for the heterostructures, when compared with α-Fe 2 O 3 nanostructures, are obtained from voltage-current measurements and optical reflectance spectra.