The Role of Nb Addition in TiO2 Nanoparticles: Phase Transition and Photocatalytic Properties (original) (raw)
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Preparation, Characterisation and Photocatalytic Activity of Nb2O5/TiO2 Coupled Semiconductor Oxides
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The nanocomposite of TiO 2-MWCNTs has been synthesised by simple hydrothermal route showing significant enhancement in the photocatalytic activity for the degradation of methyl orange dye (MO). Several characterisations employed were X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energydispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), Raman spectroscopy.XRD pattern shows the formation of anatase phase in prepared TiO 2 which was retained in TiO 2-MWCNTs composite as well. The Raman spectrum of prepared TiO 2-MWCNT shows the interface integration of TiO 2 and MWCNTs which is further supported by TEM data. Complete decolorisation and degradation of dye using TiO 2-MWCNTs nanocomposite has been observed only in 45 minutes of UV irradiation. 65 per cent reduction in chemical oxygen demand (COD) value of treated dye shows substantial mineralisation of dye by composite catalyst. Dye degradation reactions were found to follow first order kinetics.
2007 Cleantech Conference and Trade Show Cleantech 2007, 2019
Thermostability study of commercial P25 TiO 2 nanoparticles was carried out by ascending annealing temperature from 400 to 1100 o C. The thermostability of TiO 2 structure was measured by X-ray diffraction (XRD). Anatase-Rutile phase transition occurred only when temperature exceeds 600 o C. Rutile weight fraction increased from 25 to 100 % between 400 to 840 o C. Phase transition activation energy was calculated by using Arrenhius plot to be 27 kJ/mol. Transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), and dynamic light scattering (DLS) techniques were applied to determine the size of grown particles. Results of particle size analysis using TEM imaging method were the same as those using BET instruments up to 840 o C. BET measurements tend to overestimate the particle size at temperature greater than 840 o C. In contrast, DLS overestimate the size of TiO 2 particles due to agglomeration in solution. Mean TiO 2 particle sizes grew from 25 to 450 nm when temperature increased from 400 to 1100 o C. Furthermore, the photocatalytic reactivity in the degradation of dye decreased with the increase of particle size and rutile fraction.
Catalysis Science and Technology 4 (2014) 2134-2146, 2014
Titanium dioxide (TiO2) nanoparticles are attracting increasing interest because of their superior photocatalytic and antibacterial properties. Here, aqueous titanium oxy-hydroxide sols were made, using a green synthesis method, from the controlled hydrolysis/peptisation of titanium isopropoxide. Three different mineral acids were used to peptise the sol (HNO3, HBr and HCl), and provide counter-ions. The influence of nitrate or halide sol counter-ions on size distributions of the starting sols were measured via photon correlation spectroscopy (PCS). Semi-quantitative phase composition analysis (QPA), on the gels thermally treated at 450 and 600 °C, was carried out via Rietveld refinement of the X-ray powder diffraction (XRD) patterns. Photocatalytic activity of the prepared samples was also assessed, in the gas-solid phase, monitoring NOx degradation using both solar and white lamps (artificial indoor lightning). Both halides (chlorine or bromine) encouraged the anatase-to-rutile phase transition (ART), resulting in powders containing up to 77 wt% rutile and only 5 wt% brookite after heating to only 450 °C, with particle sizes ∼50 nm, and these produced 100% rutile at 600 °C. Photocatalytic tests in the gas phase, using a white lamp, showed that the halide-stabilised sols, thermally treated at 450 °C, gave titania with the highest NOx conversion rate-twice that of Degussa P25.
Materials Today Sustainability, 2020
We have synthesized and characterized a series of TiO 2 (B)/anatase photocatalysts in the form of nanobelts. Spectroelectrochemical measurements (SE-DRS) revealed the staggered type of the band alignment for anatase and TiO 2 (B) composites, with higher potentials of band edges for anatase. The photoactivity of the materials and photocurrent generation have been studied. Similarly to anatase/rutile composites, a synergistic effect of the presence of two phases has been observed for TiO 2 (B)/anatase (2:98) material in the reaction of hydroxyl radicals generation. In the case of hydrogen generation reaction, such synergy was not noticed, likewise in the case of IPCE measurements. On the other hand, singlet oxygen generation takes place preferably at TiO 2 (B), despite worse oxygen adsorption at this polymorph. Our findings shed new light on the general understanding of the photocatalytic activity of TiO 2 (B) and its composites with anatase. Unlike suggested elsewhere, instead of facilitating hydrogen evolution reaction, TiO 2 (B), as a minor admixture, should rather be considered as a component of photocatalysts optimized for oxidation reactions involving hydroxyl radicals.
Spectroscopic analyses of the photocatalytic behavior of nano titanium dioxide
Nano titanium dioxide TiO2was synthesized using hydrolysis method then subjected to several characterizations. XRD revealed that the as-prepared sample is pure anatase phase and after calcinations at 500C for 3 h the crystallinity has increased. The crystallite size calculated by Debye–Scherrer’s formula is 8 nm. The HRTEM image shows an average size of about 9 nm, which is close to the XRD calculation from Scherrer’s formula. PM3 semiempirical quantum mechanical calculations were conducted to present the electronic as well as thermal properties for TiO2. FTIR spectra between 800 and 400 cm 1 are the verification for the lattice vibrations of anatase TiO2. The photo catalytic degradation of methylene blue (MB) was tested by the prepared nano TiO2. Results indicate that, the maximum degradation efficiency reached 94.4% after 120 min of UV irradiation. This increase in the degradation efficiency of TiO2 could be attributed to the reduction in particle size that enhanced the crystallinity as a result of heat treatment
Synthesis and photocatalytic activity of TiO2 Nanoparticles
Titanium dioxide (TiO2) nanoparticles have been synthesized by sol gel method. The synthesized nanoparticles followed by calcinations at different temperatures in the range 200-800°C for 2 hours. Both the evolution of the crystal size and nature of the phases were studied as a function of annealing temperatures. These materials display a good thermal stability up to 400°C, in term of crystal size، and up to 600°C, regarding the crystalline phase. The phase purity and crystallite size of as grown TiO2 particles were characterized via X-ray diffraction (XRD). The characterized results indicated that the synthesized TiO2 powders had a pure two phases anatase and rutile structures and the average particle sizes were about 5-53 nm. The synthesized TiO2 nanoparticles exhibited 1.0053% time higher photocatalytic activity for Bismarck Brown R than that of commercial Hombikate (UV100) .
American Journal of Nanomaterials, 2019
This paper describes the photocatalytic degradation of methylene blue (MB) in aqueous solution in the presence of TiO 2 nanoparticles (NPs) in different compositions of anatase and rutile phases under UV light irradiation. The different compositions of crystalline phases of TiO 2 NPs were synthesized using sol-gel method at the same temperature for various calcination times. The TiO 2 NPs were subjected to crystal phase, vibrational, size, and morphological characterizations. The photocatalytic degradation of MB revealed that anatase TiO 2 NPs have a superior catalytic activity in the front of rutile phase. This finding further suggested that low charge resistance and low electron-hole recombination probability lead to the acceleration of the OH• formation on the surface of anatase TiO 2 NPs.
Effect of physical chemistry parameters in photocatalytic properties of TiO2 nanocrystals
Comptes Rendus Chimie, 2013
We used a new synthesis of TiO 2 anatase 6 nm nanocrystals prepared at room temperature (Hegazy and Prouzet, 2012 [10]) to explore the influence of different physical-chemical parameters on photocatalysis, and bench-tested the material against two commercial powders made of either pure anatase (Sigma TM), or composite anatase-rutile particles (P25 Degussa TM). The initial as-synthesised material demonstrates a low photocatalytic activity, which is greatly improved after thermal activation as a result of improved crystallinity without any drastic change in crystal size. The influence of several other parameters was studied, the resulting tests being compared with commercial products. The cumulative improvement provided by these different parameters led finally to a material that exhibits a higher photocatalysis compared to commercial anatase, and similar to the commercial material usually used for reference (P25). This study, which can apply to other titania materials, illustrates how the post-treatment and process adaptation can help to optimise an initial material.
2017
A Ni 2+ -TiO 2 photocatalyst, efficient and highly active in sunlight has been prepared by a simple hydrothermal method using titanium isopropoxide (TTIP) precursor. The synthesized nanoparticles (NPs) have been analysed to determine its structural, optical, morphological and compositional properties using X-ray diffraction, Raman, UV-DRS, photoluminescence, XPS, TEM and EDS. The EDS micrograph confirms the existence of Ni 2+ atoms (0.65, 1.32 and 1.60 wt.%) in the TiO 2 matrix. The average particle size obtained from TEM is 8-11 nm and is in good agreement with XRD results. Raman bands at 641.44 cm -1 , 517.42 cm -1 and 398.43 cm -1 further confirm pure phase anatase in all samples. XPS shows the substitution of Ti 4+ ions by Ni 2+ ions in the TiO 2 host lattice. The photocatalytic activity of these nanoparticles have been studied using malachite green dye under UV light, visible light and direct sunlight. The crystallite size and band gap decreases with increase in Ni 2+ concentra...
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The properties and photocatalytic performance of anatase nanoparticles of pure TiO 2 and a core-shell structure of TiO 2 on calcined vetiver grass leaves have been compared. Samples were fabricated by sol-gel and heating at 450 • C for 5 h. The comparison was based on data for X-ray diffraction (XRD), UV-Vis spectrophotometry, photoluminescence, transmission electron microscopy, specific surface area measurement, pore volume assessment, and methylene blue degradation testing. The results showed that the pure TiO 2 consisted of agglomerated equiaxed nanoparticles of individual grain sizes in the range 10-20 nm. In contrast, the TiO 2-vetiver composite exhibited a core-shell structure consisting of a carbonaceous core and TiO 2 shell of thickness 10-15 nm. These features influenced the photocatalytic performance in such a way that the lower cross-sectional area, greater surface area, and higher pore volume of the TiO 2 shell increased the number of active sites, reduced the charge carrier diffusion distance, and reduced the recombination rate, thereby improving the photocatalytic activity. This improvement derived from morphological characteristics rather than crystallographic, semiconducting, or optical properties. The improved performance of the TiO 2-vetiver core-shell was unexpected since the X-ray diffraction data showed that the crystallinity of the TiO 2 was lower than that of the pure TiO 2. These outcomes are attributed to the reducing effect of the carbon on the TiO 2 during heating, thereby facilitating the formation of oxygen vacancies, which enhance charge separation and hence photocatalysis by TiO 2 .