Synthesis Of Anatase TiO2 Nanocrystals Research Articles

Enhanced photocatalytic activity of N-doped TiO2 nanocrystals with exposed {001} facets

N-doped TiO2 nanocrystals with exposed {001} facets have been synthesized by a two-step method. Firstly, we synthesized anatase TiO2 nanocrystals with exposed {001} facets by an original hydrothermal method using HBF4 and n-BA to coordinated the regulation of size and morphology. Then, ethylenediamine has been used as N dopant source to dope with the as-prepared TiO2 nanocrystals. The effects of both HBF4 and n-BA in synthesis of anatase TiO2 nanocrystals with exposed {001} facets have been investigated. The enlarged localized profiles of the XRD pattern and XPS spectra demonstrate the existence of N element. The photocatalytic property studies showed that the N-doped TiO2 nanocrystals with exposed {001} facets exhibited much higher photocatalytic activity than that of the N-doped P25, which might be ascribed to the high percentage of exposed {001} facets. In addition, the stability study suggests that the as-synthesized photocatalyst is a promising material for the application of wastewater purification.

Fluoride-assisted synthesis of anatase TiO2 nanocrystals with tunable shape and band gap via a solvothermal approach

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO2 nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5mmol, and the optical band gap decreased from 3.47eV to 3.29eV accordingly. However, when the fluoride was changed to NH4F, the resultant TiO2 nanocrystals possessed an anatase phase but were made up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO2 nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH4F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.

Management on the location and concentration of Ti3+ in anatase TiO2 for defects-induced visible-light photocatalysis

The defect-induced “black-and-white” issue of TiO2 keeps this material under spotlight in the past decade. This work exhibits an oxidation-based synthesis of anatase TiO2 nanocrystals with various Ti3+ concentrations via a solvothermal process in combination with post-annealing at different temperatures. Strikingly, we found that by simply controlling the annealing temperature, both concentration and location of the Ti3+ defects can be well managed to reside predominately in the subsurface/bulk regions of the post-annealed anatase TiO2 nanocrystals, a highly desired feature for stable visible light-active photocatalysis. The location and quantity of the Ti3+ in anatase nanocrystals pinpointed by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) suggest that this temperature-mediated management of the location and concentration of Ti3+ defects is achieved through a Ti3+ reversible-diffusion mechanism. As an applicable verification, the sample attained by post-annealing treatment at 500°C, which has the highest Ti3+ concentration predominately in the bulk region, exhibits a 30-fold enhancement in visible-light decomposition of methylene blue and 4 times improvement in the maximal transient photocurrent density compared with P25. This work reveals that managing the location and concentration of Ti3+ defects in TiO2 is a decisive process toward defects-induced visible-light photocatalysis.

High-yield, additive-free and tailored synthesis of anatase TiO2 nanocrystals: Exposed {001} facets and enhanced visible photocatalytic activities

Uniform and monodispersed TiO2 nanocrystals (TONs) were synthesized via a novel and direct hydrothermal method, using controlled hydrolysis of tetrabutyltitanate (TBOT) in a mixed solution of ethanol and acetic acid (HAc) without adding any capping or toxic template reagents. The physical and chemical properties of TONs were studied by FESEM, XRD, HRTEM, and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the TONs was evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under visible light irradiation. The experimental results showed that the TONs exhibited a much better photocatalytic activity than that of PT (pure TiO2) and P25 (commercial TiO2).

Fluoride free synthesis of anatase TiO2 nanocrystals with exposed active {001} facets.

A novel fluoride free protocol for highly truncated anatase TiO2 nanocrystals with exposed {001} facets by preferential adsorption of CO3(2-) ions is developed. Experimental observations were corroborated by first principle quantum chemical DFT calculations. The synthesized anatase TiO2 showed improved photocatalytic activity.

Selective synthesis of TiO2 nanocrystals with morphology control with the microwave-solvothermal method

In this paper, a method to synthesize anatase TiO2 nanorods by hydrolysis of titanium(IV) isopropoxide (TTIP) in the presence of benzyl alcohol and acetic acid at 210 °C was tested. The novelty of the present approach relies on the evaluation of the shape-controlled synthesis of anatase TiO2 nanocrystals via a microwave-solvothermal method in 45 min. The different TiO2 nanocrystals were obtained by tuning the TTIP/acetic acid ratio under optimized synthetic conditions and were characterized in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), micro Raman (together with microphotoluminescence) and FT-IR spectroscopies. The acetic acid coordinated on the nanocrystal surface was removed by the reduction of its carboxyl group via a “super-hydride reaction”, and the photocatalytic activity of bare TiO2 nanocrystals, under visible light irradiation, was also evaluated: the best performing TiO2 anatase nanocrystals exhibited a discrete photoactivity, completely degrading Rhodamine B solution in five hours.

Synergy of Low-Energy {101} and High-Energy {001} TiO2 Crystal Facets for Enhanced Photocatalysis

Controlled crystal growth determines the shape, size, and exposed facets of a crystal, which usually has different surface physicochemical properties. Herein we report the size and facet control synthesis of anatase TiO2 nanocrystals (NCs). The exposed facets are found to play a crucial role in the photocatalytic activity of TiO2 NCs. This is due to the known preferential flow of photogenerated carriers to the specific facets. Although, in recent years, the main focus has been on increasing the surface area of high-energy exposed facets such as {001} and {100} to improve the photocatalytic activity, here we demonstrate that the presence of both the high-energy {001} oxidative and low-energy {101} reductive facets in an optimum ratio is necessary to reduce the charge recombination and thereby enhance photocatalytic activity of TiO2 NCs.

Synthesis of anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure and liquid-phase photocatalytic reduction and oxidation activity orders

Anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure were controllably synthesized from potassium titanate (PT) without fluorine and organic capping surfactants, and characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and fast Fourier transformation (FFT). The liquid-phase photocatalytic reduction (O2˙− generation) and oxidation (˙OH generation) activity orders of anatase TiO2 facets are {001} > {101} > {010} upon removing facet synergetic effect and surface fluorine effect. UV-vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra showed that absorbance edge order, and separation efficiency order of photoexcited holes and electrons are {001} > {101} > {010}, which explains the photocatalytic activity order well together with the atomic arrangement of different facets.

Microwave-assisted rapid synthesis of anatase TiO2 nanocrystals with exposed {0 0 1} facets

Anatase TiO2 nanocrystals with tunable percentage of reactive {001} facets were rapidly synthesized by a microwave-assisted hydrothermal treatment of the mixed solution of tetrabutyl titanate (20g), HF solution (3ml) and additional water (0–21g) at 200°C for 30min. The resulted sample is denoted as Wx, where x represents the volumes of additional water. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The photocatalytic activity of the photocatalyst was evaluated by degradation of brilliant red X3B (X3B), an anionic dye, and by a photoluminescence technique using coumarin as a probe molecule. With increasing the amount of additional water from 0 to 21ml, the shapes of TiO2 nanocrystals evolve from nanosheets to truncated octahedral bipyramids, resulting in a steady decrease in the percentage of exposed {001} facets (from 71% to 23%). The photocatalytic activity of the resulted surface fluorinated TiO2 nanocrystals increases first and then decrease with increase in the amount of water, and W3 sample with exposed 60% of {001} facets shows the highest photocatalytic activity. However, for the surface clean TiO2 samples by washing with NaOH solution, W9 with 51% of {001} facets shows the highest photocatalytic activity. Our experimental results reflect that both crystal planes and surface chemistry play very important roles on the photocatalytic activity of anatase TiO2 nanocrystals.

Solvothermally controllable synthesis of anatase TiO2 nanocrystals with dominant {001} facets and enhanced photocatalytic activity

A new non-hydrolytic approach was developed to synthesize anatase TiO2 nanocrystals with dominant {001} facets by solvothermal alcoholysis of TiF4, which was relatively green since the direct use of HF was avoided and less HF released from alcoholysis. These TiO2 nanocrystals displayed uniform shape and could be easily controlled owing to the smooth alcoholysis process. Using tert-butanol as the initial alcohol source, the total surface area was 103 m2 g−1 with small crystal sizes around 23 nm. By changing different alcohols, both the percentage of exposed {001} facets and the particle size could be adjusted. The results show that alcohols play important roles in the present strategy (1) oxygen donor to provide mild condition for crystal growth and (2) assistant agent to stabilize F species for dominant {001} facets. In further application, the absolute surface area of the {001} facets, instead of total surface area, has become the most important factor for influencing the activity of TiO2 crystals under photocatalytic selective oxidation of toluene to benzaldehyde.

Synthesis of Anatase TiO2 Nanocrystals with Exposed {001} Facets

This paper reports a facile synthesis of anatase TiO(2) nanocrystals with exposed, chemically active {001} facets. The nanocrystals were prepared by digesting electrospun nanofibers consisting of amorphous TiO(2) and poly(vinyl pyrrolidone) with an aqueous acetic acid solution (pH = 1.6), followed by hydrothermal treatment at 150 degrees C for 20 h. The as-obtained nanocrystals exhibited a truncated tetragonal bipyramidal shape with 9.6% of the surface being enclosed by {001} facets. The use of electrospinning is critical to the success of this synthesis as it allows for the generation of very small particles of amorphous TiO(2) to facilitate hydrothermal crystallization, an Ostwald ripening process. The morphology of the nanocrystals had a strong dependence on the pH value of the solution used for hydrothermal treatment. Low pH values tended to eliminate the {001} facets by forming sharp corners while high pH values favored the formation of a rodlike morphology through an oriented attachment mechanism. When acetic acid was replaced by inorganic acids, the TiO(2) nanocrystals further aggregated into larger structures with various morphologies.

Catalyst-free low temperature synthesis of discrete anatase titanium dioxide nanocrystals with highly thermal stability and UVC-cut capability

A novel, facile, catalyst-free, and low temperature process for the synthesis of discrete anatase TiO2 nanocrystals has been developed in the absence of stabilizing agent. The product was shown to be discrete anatase TiO2 nanocrystals with a mean diameter of 4.97 ± 0.9 nm and a specific surface area of 393 m2/g. By varying the water content and precursor concentration, the particle size could be tuned. Also, the resultant colloid solution was quite stable even in the absence of stabilizing agent because of the coverage of EG molecules on the particle surface. In addition, the anatase TiO2 nanocrystals obtained in this work had highly thermal stability even at temperatures up to 800 °C. Also, as compared to Degussa P25 TiO2 powders, they exhibited stronger absorption at 200–350 nm and higher transmittance in the visible light region. Thus, the new approach proposed in this work was practicable for the synthesis of anatase TiO2 nanocrystals, particularly for those requested to have highly thermal stability and UVC-cut capability.