Titania Nanocrystals Research Articles

Assessment of mutagenic, recombinogenic and carcinogenic potential of titanium dioxide nanocristals in somatic cells of Drosophila melanogaster

Nanoparticles have been widely used in several sectors and their long-term effect on the body and environment remains unknown. To evaluate the mutagenic, recombinogenic and carcinogenic potential of 11 nm titanium dioxide nanocrystals (TiO2 NCs), the Somatic Mutation and Recombination Test (SMART) and the Test for Detection of Epithelial Tumors Clones (Warts-Wts) were used, both in Drosophila melanogaster. Third-instar larvae (72 + 4 h), obtained in both tests, were treated with different concentrations of TiO2 NCs ranging from 6.25 to 100 mM. Ultrapure water and urethane were used as negative and positive controls, respectively. At ST cross, all concentrations of TiO2 NCs showed a significant increase in the frequencies of mutant spots, demonstrating higher recombination rates. At the HB cross, only the 50 mM concentration showed a negative result. In the Wts Test, all used concentrations were carcinogenic, except for the 100 mM one, which was toxic. No relationship was demonstrated between the used concentrations and the obtained responses. There was no interference of the cytochrome P450 enzyme complex in the induction of mutant spots.

Water chain formation on rutile TiO2 (110) nanocrystal: A molecular dynamics simulation approach

Understanding the properties of the interface of water nano-droplet and rutile TiO2 (110) nanocrystal has attracted the attention of many surface scientists. In this research the interface of water nano-droplet and (110) plane of Rutile titanium dioxide nanocrystal along with the formation of water chains was studied based on a molecular dynamics approach. Density profiles of oxygen and hydrogen atoms of the water molecules show less movement in hydrogen atoms that reside closer to the TiO2 surface than the ones that are further away. The calculated results indicate that the average interlayer hydrogen bonds per water molecule is about 0.51 at the interface where water molecules form two different water-water hydrogen bonds with 28.55 and 670.24ps lifetimes. The simulation data reveal the formation of one-dimensional chain structures of water on the TiO2 substrate. Certain values for the estimated angles among every three water molecules that participate in the formation of the chain structures is observed. The electrostatic energy contour map and the orientation of water molecules at the interface suggests that these molecules form ordered and periodic pair structures around the regions with high negative charge on titanium dioxide. The dynamical analysis of the water molecules indicates a dynamical independence from one another which results in their independent motion at the interface. Furthermore, the dynamical results also show that the water nano-droplet is pinned on the surface of titanium dioxide without any major movement.

Rapid one-pot synthesis of ultrafine titania nanocrystals and their conversion into transparent mesoporous thin layer films

Ultrafine titania nanocrystals were synthesized using a rapid heating, one-pot solvothermal method. These nanocrystals are extremely small with a narrow size distribution (3.0 ± 0.4 nm). The detailed structural analysis by using transmission electron microscopy reveals periodic alignment of the resultant titania nanocrystals with hexagonal symmetry due to their size uniformity. The drop-casting deposition and calcination of these nanocrystals are also enable to convert into mesoporous thin layer films with nano convex-concave surface. The resultant transparent mesoporous thin layer exhibits not only anti-reflection properties but also high photocatalytic activity.

Bionic titania coating carbon multi-layer material derived from natural leaf and its superior photocatalytic performance

Bionic titania coating carbon multi-layer material was fabricated by employing canna leaves as substrate and carbon precursor. Titania nanocrystals were assembled and coated on the natural films. The carbonation treatment under pure N2 atmosphere yielded the ultrathin multi-film hybrid material. The carbon layer was coated with small anatase titania crystallite (8–10nm) and possessed a highly specific surface area of 248.3m2g−1. Examination using UV–visible spectrophotometer (UV–vis) showed that the band gap of the multi-layer material was reduced to 2.75eV, and the hydrogen production by photocatalytic splitting of water under visible light irradiation was about 302μmolg−1 after six hour.

Distinguishing faceted oxide nanocrystals with 17O solid-state NMR spectroscopy

Facet engineering of oxide nanocrystals represents a powerful method for generating diverse properties for practical and innovative applications. Therefore, it is crucial to determine the nature of the exposed facets of oxides in order to develop the facet/morphology–property relationships and rationally design nanostructures with desired properties. Despite the extensive applications of electron microscopy for visualizing the facet structure of nanocrystals, the volumes sampled by such techniques are very small and may not be representative of the whole sample. Here, we develop a convenient 17O nuclear magnetic resonance (NMR) strategy to distinguish oxide nanocrystals exposing different facets. In combination with density functional theory calculations, we show that the oxygen ions on the exposed (001) and (101) facets of anatase titania nanocrystals have distinct 17O NMR shifts, which are sensitive to surface reconstruction and the nature of the steps on the surface. The results presented here open up methods for characterizing faceted nanocrystalline oxides and related materials.

Synthesis and optic properties of titanium dioxide nanostructures doped with alkali metals

The synthesis of nanotubes and faceted nanocrystals of titanium dioxide doped with alkali metals cations has been performed. It has been established that TiO2 nanotubes with lengths of up to 100 nm and thicknesses of 50–500 nm obtained by solvothermal synthesis have an anatase structure in the direction of crystal growth. Faceted TiO2 particles with sizes of 80–150 nm doped with Na and K cations (2–7 at % calculated to a yield of TiO2 yield) preserve the anatase structure, whereas doping with Li induces the formation of a mixture of anatase and rutile. An analysis of the diffuse reflectance spectra showed that dopants had an insignificant effect on optic properties of TiO2 nanoparticles. The high activity of these catalysts is explained by a decrease in the rate of recombination of charge carriers, rather than by the increase of their photo-generation yield.

Synthesis and characterization of visible-light-active mesoporous titania by doping Ni and N

Ultrafine TiO2 nanoparticles with a narrow size distribution were designed for extending the light absorption wavelength from ultraviolet to visible light with the increased photocatalytic activity. The mesoporous spherical TiO2 nanoparticles and the Ni doped TiO2 nanoparticles were prepared by sol–gel method, with the Ni molar fraction ranged from 0.5, 1, 2, 3, 4 to 5%. Samples were calcined at 550 °C to form crystallized TiO2 and eliminate organic impurities. The Ni and N co-doped TiO2 nanocrystals were prepared by heating Ni doped TiO2 powders in NH3 flow at 650 °C. All the doped titania nanocrystals are well crystallized anatase with a tetragonal structure. 0.5% Ni–TiO2 exhibited optimum photocatalytic activity for MB degradation under UV-light irradiation, which was about twice compared to that of the blank TiO2. The visible light photocatalytic activity of 5% Ni/N-TiO2 was remarkably raised up to 4 times by contrast with the blank TiO2 while the photocatalytic activity of N-TiO2 only increased to 2 times compared to that of the blank TiO2.

Synthesis, characterization and optical studies of gallium activated titania nanoparticles

The gallium ion doped and undoped titania nanocrystals were synthesized by non aqueous sol–gel technique at low temperature. They were characterized structurally and optically with the used of X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Photoluminescence (PL) and UV–visible spectrophotometer (UV–Vis). The anatase-to-rutile phase transition was observed at 550°C and reflection peaks (101) of the tetragonal phase of each sample is shifted to lower 2θ of XRD pattern which indicates the occupancy of Ga3+ ion by substituting in Ti4+ lattice sites. Crystal lattice distortion ratios are found to decrease with increase in temperature, whereas the crystallite sizes are increased with the increase in temperature. The emission spectrum is recorded under excitation wavelength 258 nm transition of the Ga3+ ion and five emission bands at 408, 444, 468, 490 and 538 nm are observed after deconvolution of the spectra. The average decay lifetimes of this sample are found to increase as the concentration of dopant increases.

High-energy {001} crystal facets and surface fluorination engineered gas sensing properties of anatase titania nanocrystals

Controllable crystal facets exposing is an efficient approach for enhancing gas sensing performances of semiconductor nanomaterials. In order to study the crystal-facets-dependent gas-sensing properties of TiO2 systematically and exactly, a series of anatase TiO2 nanocrystals with different percentage of high-energy {001} crystal facets exposure (from 6% to 91%) were designed and synthesized by a simple hydrofluoric acid-assisted hydrothermal method. Gas sensing tests suggested that gas response of the TiO2 nanocrystals increased with the percentage of high-energy {001} crystal facets, although the specific surface areas gradually decreased. The results unquestionably confirmed the enhanced gas sensing activity of anatase TiO2 high-energy {001} crystal facets. Moreover, it was found that surface fluorination of high-energy {001} crystal facets played a negative role on the gas sensing activity. The relevant sensing mechanism was discussed in detail based on combination of experimental characterization and first-principle calculations, which showed that gas adsorption properties made a great contribution to gas sensing performance. By providing a comprehensive understanding of the crystal-facets-dependent gas-sensing properties of TiO2, the present work will be helpful for the designing of TiO2-based gas-sensing materials.

Simple Fabrication of Titanium Dioxide/N-Doped Carbon Hybrid Material as Non-Precious Metal Electrocatalyst for the Oxygen Reduction Reaction.

We report a new approach for the fabrication of hybrid titanium dioxide/carbon materials derived from a porous titanium coordination polymer composed of a catechol-substituted porphyrin and Ti4+. Titanium dioxide nanocrystals were formed distributed in a nitrogen-doped carboniferous matrix after the thermolysis of the coordination polymer. The identity of the titanium dioxide phase, i.e., anatase or rutile, could be controlled by varying the thermolysis temperature. Electrochemical performances of the composites were explored with results demonstrating that the hybrid materials are promising cathodic materials for the oxygen reduction reaction.

Comparison of Titanium Dioxide Nanocrystal with Hydrothermal Method and P25 Degussa for Photocatalytic Arsenic

Abstract : Arsenic is one of 10 chemicals which is harmful to human health, according to WHO. Arsenic that harmful to human health is generally in the form of inorganic compounds with oxidation number of 3 (As(III)). One of the best known method to remediate As(III) is an oxidation method. Titanium dioxide (TiO 2 ) can be used as a photocatalyst to oxidize As(III). The photocatalytic activity of TiO 2 is highly dependent on the size and composition of the crystal phase. Smaller size of TiO 2 crystal can be obtained by using hydrothermal method. This study aimed to compare the synthesized TiO 2 with P25 Degussa to As(III) reduction. Materials used are TiCl 4 as a precursor and H 2 SO 4 and t-butanol as solvents. The crystal structure of synthesized TiO 2 is a mixture of anatase and rutile with a greater composition of anatase than rutile. The TiO 2 crystal size is calculated using scherrer equation and showed that the crystal size is less than 60 nm. The ability of synthesized TiO 2 using H 2 SO 4 2.0 M in the reduction of As(III) concentration is 72% exceeded the capability of P25 Degussa is 35%. Keywords: As(III), hydrothermal, H 2 SO 4 , t-butanol, TiO 2 photoactivity

Ilmenite type nano-crystalline Co–Ti–O ternary oxides: sol–gel thin film on borosilicate glass, characterization and photocatalytic activity in mineralization of reactive red 198

The sol–gel preparation of cobalt titanium oxide nano-crystals using the reaction between cobalt chloride (CoCl2·6H2O) and tetraisopropyl orthotitanate (Ti[OCH(CH3)2]4) with 1:1 molar ratio was studied. The nano-crystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDAX), fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG-DTG) analysis and UV–Vis diffuse reflectance spectra (UV–Vis DRS) spectroscopy. TG-DTG results revealed that the weight loss with peak temperatures of 189, 267 and 692 °C. The XRD results showed that the sample calcinated at 550 and 750 °C were mixtures of CoTiO3, Co3O4, and TiO2 phases while at 650 °C a single crystalline phase of CoTiO3 was formed. FESEM results of the cobalt titanium oxide nanocrystalles demonstrate that CoTiO3 is nano-particles with an average size of 70 nm. FTIR results showed the formation of cobalt–oxygen, titanium–oxygen, and titanium–oxygen–cobalt bonds. DRS spectroscopy results of the sample calcinated at 650 °C showed band gap of 1.734 eV (715 nm) and 2.389 eV (519 nm) well in the visible portion of sun light. The cobalt titanium oxide nano crystales thin films on borosilicate glass showed an excellent photocatalytic activity on mineralization of Reactive Red 198 textille dye as environmental pollutant of industrial wastewater. An excellent photocatalytic activity in mineralization of Reactive Red 198 is related to the efficient separation of cobalt titanium oxide nano-crystals and visible-light absorption.

{101}-{001} Surface Heterojunction-Enhanced Antibacterial Activity of Titanium Dioxide Nanocrystals Under Sunlight Irradiation.

The {101}-{001} surface heterojunction constructed on polyhedral titanium dioxide (TiO2) nanocrystals has recently been proposed to be favorable for the efficient electron-hole spatial separation due to the preferential accumulation of electron and hole on {101} and {001} facets, respectively. The formed free electron and hole can promote reactive oxygen species (ROS) production, which potentially can be used for inactivation of bacteria. In the present study, a series of truncated octahedral bipyramid TiO2 nanocrystals (T1, T2, T3, and T4) coexposed with {101} and {001} facets were prepared to form various ratios of {101} to {001} facet for optimization of electron-hole spatial separation efficiency. All these polyhedral TiO2 nanocrystals could more significantly produce ROS than spherical TiO2 nanocrystals (Ts), exhibiting the higher antibacterial activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria under simulated sunlight irradiation. Among these polyhedral TiO2 nanocrystals, T3 with a {101}/{001} ratio of 1.78 was found to be the best one showing the highest ROS and the most potent antibacterial performance. Scanning electron microscope images of bacteria displayed that the surface membrane structure of both E. coli and S. aureus bacteria was influenced to different extents by these TiO2 nanocrystals, where T3 caused the most severe membrane damage. The molecular mechanism underlying the high antibacterial activity of TiO2 nanocrystals was ascribed to activation of oxidative stress as evidenced by intracellular ROS production, glutathione depletion, and membrane lipid peroxidation in bacteria. The surface heterojunction as a completely new strategy holds great promise to develop effective antibacterial nanomaterials.

Defect states determined the performance of dopant-free anatase nanocrystals in solar fuel cells

Solar-driven water splitting promises a step towards large-scale solar energy storage. However, the bottleneck is always the poor performance of the used photoanodes, particularly in their capability to harvest the visible light. Herein, we report the design of visible-light active anatase titanium dioxide nanocrystals (sub 10nm in size and with a surface area of ∼99m2/g) using the sol-gel method followed by hydrothermal treatment with H2O2 at relatively low temperature (180°C). The fabricated nanocrystals demonstrate a band gap of 2.85eV, with an increased amount of surface defects that overcome the negative effects of bulk defects as revealed by the positron annihilation measurements. These prepared nanocrystals have notable enhancement in solar light harvesting and water splitting efficiency compared to the commercial Degussa P25 counterpart. The photoactivity, structural and electrochemical behavior of the synthesized nanocrystals were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), photocurrent measurements, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), positron annihilation, and Doppler broadening analysis.

Thermal and mechanical performance of rigid polyurethane foam added with commercial nanoparticles

This study investigates the effects of commercial nanoparticles on thermal and mechanical performance of rigid polyurethane foams. Two different types of nanoparticles are considered as fillers, spherical titania and rod-shaped halloysite clay nanotubes. The aim of this study was to produce rigid polyurethane foams modified with titania nanocrystals and nanohalloysite in order to obtain polyurethanes with improved properties. The laboratory scale-up will be suitable for the production in many branches of industry, such as construction and automotive production. In particular, these foams, added with commercial nanoparticles, characterized by better thermal and mechanical properties, are mainly used in construction for thermal insulation of buildings. The fillers were dispersed in the components, bringing rates up to 10%. In these investigations, the improvement of the thermal properties occurs by adding nanoparticles in the range 4–8% of titania and halloysite. The mechanical properties instead have been observed an improvement starting from 6% of nanoparticles addition. All data are in agreement with scanning electron microscope observations that shown a decrease in the average cell size and an increase in the cell density by adding nanoparticles in foams.

Synthesis and characterization of barium-doped TiO2 nanocrystals for photocatalytic degradation of Acid Red 18 under solar irradiation

Addition to the aesthetic negative environmental impacts, dyes have serious negative biological and chemical effects on the environment. The aim of this study was to investigate the removal of acid red 18 from aqueous solution using novel barium oxide added to titanium oxide nanocrystals. Moreover, these doping conditions resulted in reducing the bandgap energy significantly, which in turn makes them active under sunlight illumination. The barium doped TiO2 nanocrystals were synthesized under mild hydrothermal conditions and were characterized by XRD, FTIR, SEM, and EDS to investigate the structure and textural features of the nanocrystals. The photodegradation experiments were conducted through the influence of batch degradation parameters such as pH, illumination time, nanocrystals dosage, and initial dye concentration. The results revealed that the removal efficiency of Acid Red 18 was 98.6 under acidic conditions. Moreover, the removal efficiency increased by reducing the initial dye concentration, increasing illumination time, and nanocrystals dosage. The characterization results confirmed the high crystallinity, lack of agglomeration and excellent dispersion of the barium doped TiO2 nanocrystals in the media. Therefore, the barium doped TiO2 nanocrystals could be used for photodegradation of organic pollutants from the aqueous media. © 2017 Desalination Publications. All rights reserved.

Formation of a Dimeric Precursor Intermediate during the Nonaqueous Synthesis of Titanium Dioxide Nanocrystals

AbstractFor tailoring the size and morphology of nanoparticles, a deep knowledge of the mechanism leading to particle formation is required. We have investigated the reaction mechanisms in the synthesis of anatase nanocrystals by the so‐called benzyl alcohol route as a model for binary metal oxides, and elucidated the chemical structure of cluster species involved in the reaction using NMR spectroscopy and single crystal X‐ray structure analysis. In the first reaction step, a novel dimeric coordination complex is formed via ligand exchange, and was identified as the crucial compound initiating particle formation in the synthesis process.

Titania Nanocrystal Surface Functionalization through Silane Chemistry for Low Temperature Deposition on Polymers.

A method to obtain photocatalytically active thin films of anatase nanocrystals on polymer substrates was explored. Anatase nanocrystals were synthesized by a fast hydrolysis synthesis in an apolar solvent and characterized with regard to their crystallinity, size, and dispersibility and the stability of the resulting suspensions. The stable titania nanocrystal suspensions were further processed for their use in polar solvents using ligand exchange. Oleic acid was exchanged for 3-aminopropyltriethoxysilane (APTES), resulting in aqueous suspensions of charge-stabilized nanocrystals. These were adapted for use as coating suspensions for surface-treated PMMA substrates in order to obtain thin films containing anatase nanocrystals covalently coupled to the surface of the PMMA substrates. Thereby, the ligand exchange was beneficial for increasing the compatibility and durability of the inorganic/organic composite, by the formation of a covalent amide bond between the silane ligands on the nanocrystals and the carboxylic acid groups on the polymer substrate. The surface morphology, transparency, and photocatalytic activity toward the degradation of organic pollutants of the coatings, obtained through dip-coating, were evaluated.

A Modified Thermal Treatment Method for the Up-Scalable Synthesis of Size-Controlled Nanocrystalline Titania

Considering the increasing demand for titania nanoparticles with controlled quality for various applications, the present work reports the up-scalable synthesis of size-controlled titanium dioxide nanocrystals with a simple and convenient thermal treatment route. Titanium dioxide nanocrystals with tetragonal structure were synthesized directly from an aqueous solution containing titanium (IV) isopropoxide as the main reactant, polyvinyl pyrrolidone (PVP) as the capping agent, and deionized water as a solvent. With the elimination of the drying process in a thermal treatment method, an attempt was made to decrease the synthesis time. The mixture directly underwent calcination to form titanium dioxide (TiO2) nanocrystalline powder, which was confirmed by FT-IR, energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. The control over the size and optical properties of nanocrystals was achieved via variation in calcination temperatures. The obtained average sizes from XRD spectra and transmission electron microscopy (TEM) images showed exponential variation with increasing calcination temperature. The optical properties showed a decrease in the band gap energy with increasing calcination temperature due to the enlargement of the nanoparticle size. These results prove that direct calcination of reactant solution is a convenient thermal treatment route for the potential large-scale production of size-controlled Titania nanoparticles.

Evaluation of titanium dioxide nanocrystal-induced genotoxicity by the cytokinesis-block micronucleus assay and the Drosophila wing spot test

Titanium dioxide nanocrystals (TiO2 NCs) crystalline structures include anatase, rutile and brookite. This study evaluated the genotoxic effects of 3.4 and 6.2 nm anatase TiO2 NCs and 78.0 nm predominantly rutile TiO2 NCs through an in vitro micronucleus (MN) assay using V79 cells and an in vivo somatic mutation and recombination test in Drosophila wings. The MN assay was performed with nontoxic concentrations of TiO2 NCs. Only anatase (3.4 nm) at the highest concentration (120 μM) induced genotoxicity in V79 cells. In the in vivo test, Drosophila melanogaster larvae obtained from standard (ST) or high bioactivation (HB) crosses were treated with TiO2 NCs. In the ST cross, no mutagenic effects were observed. However, in the HB cross, TiO2 NCs (3.4 nm) were mutagenic at 1.5625 and 3.125 mM, while 78.0 nm NCs increased mutant spots at all concentrations tested except 3.125 mM. Only the smallest anatase TiO2 NCs induced mutagenic effects in vitro and in vivo. For rutile TiO2 NCs, no clastogenic/aneugenic effects were observed in the MN assay. However, they were mutagenic in Drosophila. Therefore, both anatase and rutile TiO2 NCs induced mutagenicity. Further research is necessary to clarify the TiO2 NCs genotoxic/mutagenic action mechanisms.