Enhanced Photocatalytic Response of N Doped Niobium Titanates Prepared by Ion Exchange Process (original) (raw)
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Materials Research
Plasma Electrolytic Oxidation (PEO) was employed for the generation of porous niobium-containing surfaces with enhanced photocatalytic activity. Pulses of 500 and 600 V, with a repetition rate of 60 Hz, were applied to titanium disks immersed in niobium-containing electrolytic solutions. The treatment time ranged from 180 to 600 s, and the surface morphology was analyzed by scanning electron microscopy, while X-ray diffraction was employed in the evaluation of crystallographic structure. The optical gap of the samples was determined from UV-Vis reflection spectra, and an automated goniometer was used for contact angle and surface energy measurements. More than 35% of Nb has been incorporated into the samples. Under certain conditions, the treatments resulted in a reduction of the optical gap from 3.18 to 2.63 eV as compared to as-received samples. Photocatalytic degradation rates of methylene blue as high as 70% have been reached after 120 minutes under irradiation with UV-Vis light.
Enhanced photocatalytic activity of TiO2 assisted by Nb, N and S multidopants
Materials Research Bulletin, 2015
A novel visible light active photocatalyst is synthesized by doping TiO 2 with multiple dopants like Nb, N and S. TiO 2 exists as anatase phase and the particle size is in the range of 10-25 nm. A significant red shift of the absorption edge and increased visible light absorption is shown by multidoped TiO 2 compared to undoped TiO 2 . The tri-doped TiO 2 has the highest activity for the photodegradation of methyl orange and the activity shows the order: 0.6NbNS-TiO 2 > P25 > 0.6Nb-TiO 2 > NS-TiO 2 > pristine TiO 2 . The enhanced photocatalytic activity of tri-doped TiO 2 is due to the reduction of band gap and enhancement of lifetime of photogenerated charge carriers. This multidoped catalyst is found to be stable and only a marginal decrease in the activity is observed upto 3 cycles. Experiments with quenchers suggest that all super oxide, hydroxyl radicals and photogenerated holes are active species for the oxidation reaction.
Enhanced photocatalytic activity of TiO2–niobate nanosheet composites
Journal of Materials Research, 2013
Protonated niobate nanosheets, H 1.8 Bi 0.2 CaNaNb 3 O 10 (BCNN), were synthesized using a new organicfree simultaneous ion exchange and exfoliation process from the Aurivillius phase Bi 2 CaNaNb 3 O 12 . Nanosheet/TiO 2 composites were prepared by thermal treatment of physical mixtures of commercially available anatase TiO 2 and the nanosheet suspension. Methylene blue (MB) dye degradation studies for the composite show a clear correlation between the MB surface adsorption and the degradation rate. The composite exhibits strongly enhanced photocatalytic activity as the calcination temperature increases, suggesting the possibility of charge transfer at the BCNN-TiO 2 interface and the existence of Nb 51 and O 2À acid-base pairs. Both phenomena are attributed to the processing approach, which includes topochemical dehydration of the BCNN nanosheets during heat treatment.
International Journal of Photoenergy, 2008
This article briefly reviews some factors that have impacted heterogeneous photocatalysis with next generation TiO 2 photocatalysts, along with some issues of current debate in the fundamental understanding of the science that underpins the field. Preparative methods and some characteristics features of N-doped TiO 2 are presented and described briefly. At variance are experimental results and interpretations of X-ray photoelectron spectra (XPS) with regard to assignments of N 1s binding energies in N-doped TiO 2 systems. Relative to pristine nominally clean TiO 2 with absorption edges at 3.2 eV (anatase) and 3.0 eV (rutile), N-doped TiO 2 s display red-shifted absorption edges into the visible spectral region. Several workers have surmised that the (intrinsic) band gap of TiO 2 is narrowed by coupling dopant energy states with valence band (VB) states, an inference based on DFT computations. With similar DFT computations, others concluded that red-shifted absorption edges originate from the presence of localized intragap dopant states above the upper level of the VB band. Recent analyses of absorption spectral features in the visible region for a large number of doped TiO 2 specimens, however, have suggested a common origin owing to the strong similarities of the absorption features, and this regardless of the preparative methods and the nature of the dopants. The next generation of (doped) TiO 2 photocatalysts should enhance overall process photoefficiencies (in some cases), since doped TiO 2 s absorb a greater quantity of solar radiation. The fundamental science that underpins heterogeneous photocatalysis with the next generation of photocatalysts is a rich playing field ripe for further exploration.
2021
Dion-Jacobson type layered perovskite niobium oxides KCa2Nb3O10 and KSr2Nb3O10 were prepared via molten salt method, and the potassium cations were exchanged by protons using nitric acid. Different degrees of proton exchange were adjusted, and the dependence of photocatalytic activity for hydrogen evolution on proton exchange was investigated. Moreover, proton exchange leads to different amounts of water incorporated into the interlayer spaces, also influencing photocatalytic performance significantly. Decoupling water intercalation and proton exchange, the photocatalytic activity of proton exchanged KCa2Nb3O10 and KSr2Nb3O10 can be revealed and tailored for maximum activity.
A Low-Band Gap, Nitrogen-Modified Titania Visible-Light Photocatalyst
The Journal of Physical Chemistry C, 2007
Low-Band gap nitrogen-modified titania photocatalysts were prepared by calcining titanium hydroxide and urea at 400°C. Different from previously known nitrogen-doped titania (TiO 2-N), which exhibits a strong band-to-band absorption in the ultraviolet and only a weak shoulder in the visible, the new materials (TiO 2-N1 and TiO 2-N2) have an intense band-to-band absorption in the range of 400-500 nm, resulting in corresponding band gaps of 2.46 and 2.20 eV. As compared to unmodified titania, the quasi-Fermi level of electrons is anodically shifted by 0.07-0.16 eV. Whereas TiO 2-N is inactive in visible-light mineralization (λ g 420 nm) of formic acid, TiO 2-N1 is highly active.
N and N,S-doped TiO2 photocatalysts and their activity in NOx oxidation
Catalysis Today, 2013
a b s t r a c t N-doped and N,S-codoped titania powders were prepared applying simple chemical treatment with various modifiers. The N and S were introduced preserving the crystalline structure, morphology and specific surface area of the initial TiO 2 . The level of N, S doping varied depending on the modifier two of which were structural isomers. In all samples, N was found interstitially incorporated in the TiO 2 lattice. S was recorded in ionic states S 6+ and S 4+ . All modified powders exhibited enhanced visible light absorption and narrower energy band gap in comparison to the initial titania. Except for the N-doped titania, the photocatalytic activity in NOx oxidation under UV light decreased after doping, while the activity under visible light did not increase for all modified samples. This outcome was related to the high level of N and S doping and intense e − -h + recombination on dopants' sites. The activity of the photocatalysts in NOx oxidation processes was also connected to the type of non-metal dopant in the lattice of TiO 2 . The beneficial effect of N-doping was ascribed to the preferential formation of • OH species on N-doped surface, whereas the detrimental effect of N,S-codoping was credited to the suppressed • OH production on S-doped surface.
Photoelectrochemical Behavior of Nb-Doped TiO 2 Electrodes
The photoelectrochemical behavior of degenerate Nb-doped TiO 2 (Ti 1-x Nb x O 2 : x) 0, 0.01, 0.03, 0.06, 0.1) electrodes prepared by pulsed laser deposition on LaAlO 3 (LAO) and SrTiO 3 (STO) was examined, revealing that an increase in Nb concentration causes a significant decay of titania photoactivity. One reason for such behavior may be a Burstein-Moss effect, which leads to a blue shift of the spectral limit of photoactivity. Another reason typical for metal-doped photocatalysts is the increase of the efficiency of charge carrier recombination.