Formation Of Anatase TiO2 Nanoparticles Research Articles

Insights into formation of anatase TiO2 nanoparticles from peroxo titanium complex degradation under microwave-assisted hydrothermal treatment

Several methods for the synthesis of anatase TiO2 have been reported in the literature. In particular, the microwave-assisted hydrothermal crystallization of Ti-peroxocomplexes has enabled the phase and morphological control of TiO2 nanoparticles by adjusting the synthesis conditions, such as pH, time and temperature, with significant increase in the reaction rate compared to the conventional sol-gel techniques. In this paper, we uncover the mechanism involved in the formation of anatase TiO2 nanoparticles from the Ti-peroxo complex precursor route. Structural characterizations (XRD, Raman, TEM and XANES) revealed that the Ti-peroxo complex precursor exhibits a titanate-like structure, comprised of bulk NH4+ ions and surface peroxo groups. The NH4+ ions release during hydrothermal treatment is determining on the anatase TiO2 nanoparticle formation, which occurs concomitantly with the decomposition of peroxogroups. UV-induced dye photodegradation tests involving the Ti-peroxo complex precursor and TiO2 nanoparticles showed that the precursor is not able to form hydroxyl radicals that are the main chemical species responsible for the dye photodegradation, despite the presence of peroxo groups at its surface. The results herein highlight the mechanism involved in the formation of anatase TiO2 nanoparticles, which could assist in the development of new synthesis approaches based on Ti-peroxocomplex precursors.

Effect of gamma radiation on the photocatalytic properties of Cu doped titania nanoparticles

The aim of this paper is to study the effect of gamma-rays on structural, physicochemical, optical and photocatalytic performance of TiO2 nanoparticles doped with different concentrations of copper ranging from 0 to 6 at.%. The powders have been prepared by sol-gel technique and annealed at 400 °C. They were irradiated by gamma-rays with doses varying from 14 to 60 KGy. These investigations confirm the formation of anatase TiO2 nanoparticles and Cu2+ ion substitution for Ti4+ sites within the TiO2 structure. This study also shows that, once the TiO2 structure is saturated with copper, a metallic copper segregation is formed at the crystallite surfaces. After gamma irradiation, samples present a crystalline core and a disordered shell structure as a result of the formation of oxygen vacancies. Such oxygen vacancies at the TiO2 nanocrystal surface lead to a remarkable enhancement of the photocatalytic activity of Cu-doped TiO2 catalysts.

A simple strategy for the anchoring of anatase titania on multi-walled carbon nanotubes for solar energy harvesting

Pure anatase titania (TiO2) nanoparticles were anchored on the surface of functionalized multi-walled carbon nanotubes (MWCNTs) using a solution-based synthetic method at room temperature. X-ray diffraction and Raman patterns were used to analyze the structural and phase composition of these nanocomposites, highlighting the formation of anatase TiO2 nanoparticles with MWCNTs up to 0.5wt.%. The non-spherical particles of TiO2 in the order of 7–12nm, were confirmed through transmission electron microscopy analysis and these particles were well dispersed on the MWCNTs. The optical absorption spectra of these structures were studied by diffuse reflectance UV–visible spectroscopy. The optical energy band gap of the various nanocomposites was observed from 3.2 to 2.6eV with an increasing amount of MWCNTs, up to 0.5wt.%. The generation of OH species in nanocomposites in the presence of visible light irradiation was investigated by photoluminescence spectroscopy. Photoelectrochemical cell performance of TiO2-MWCNTs for 0.5wt.% content of MWCNTs under light intensity 100mW/cm2 showed a significant improvement of short-circuit current density from 1.23 to 12.1mA/cm2 and a cell efficiency (0.090–3.46%) that is better than many reported anatase-based compositions without sensitizer.

Microwave Treated Bentonite Clay Based TiO2 Composites: An Efficient Photocatalyst for Rapid Degradation of Methylene Blue.

The composites of TiO₂ and bentonite were synthesized under microwave conditions. Formation of anatase TiO₂ nanoparticles was achieved within 10 minutes by microwave treatment at 180 °C on the clay surface. Phase composition, particle morphology, specific surface area, chemical bonding etc. of these samples were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen gas adsorption method (BET) and fourier transform infrared spectroscopy (FTIR). The photo catalytic activity of the as prepared material to degrade methylene blue resulting in complete photomineralization to CO₂ and H₂O was monitored by UV-Vis spectroscopy and gas chromatography. The effect of TiO2 content on the photocatalytic activity was also investigated. Bentonite containing 50% TiO₂ by weight showed the highest photocatalytic activity because of its relatively large specific surface area and pore volume. Overall our findings show that the photocatalytic activity of resulting composite is more efficient than commercial nano-TiO₂ and thus could therefore be an economic competitive candidate for contaminated water remediation.

Enhanced heterogeneous photodegradation of VOC and dye using microwave synthesized TiO2/Clay nanocomposites: A comparison study of different type of clays

Supply of pure drinking water and air is a perquisite for sustaining of civilization and in this respect the clays are found to have significant importance as a semiconductor support material due to their layered morphology, chemical as well as mechanical stability, cation exchange capacity, non-toxic nature, low cost and availability. In spite of availability of technique very few studies have been done on the effect of clay structure on photocatalytic efficiency of semiconductor/clay nanocomposites. The TiO2/clay nanocomposites were synthesized from different clays having textural differences (1:1 and 2:1); by a simple and time as well as cost effective method under microwave conditions. Formation of anatase TiO2 nanoparticles on surface of different clays was achieved at 180 °C within 10 min of time. Phase composition, particle morphology, specific surface area, chemical bonding, etc. of those samples were characterized by using XRD, TEM, FESEM, FTIR and nitrogen gas adsorption-desorption (BET) methods. Formation of TiO2 nanoparticles on clay surface were confirmed by monitoring peaks of anatase TiO2 with crystallite size 10–20 nm in X-Ray diffraction pattern of TiO2/Clay nanocomposites. The TiO2/clay nanocomposites exhibited high surface area and uniform pore distribution compared to pure clays and TiO2 (Degussa P25, Germany). The photocatalytic activities of the nanocomposites were found to be depended on clay texture as well as optical characteristics apart from their surface area. The 2:1 clay (bentonite, kunipia-F) was observed to act as better support for TiO2 in comparison with 1:1 clay (kaolin); regarding its photo-catalytic degradation of methylene blue (MB) and volatile organic compound (VOC) such as chlorobenzene (CB) due to their different texture and optical properties. TiO2/bentonite nanocomposite has high optical absorbance under UV spectrum. It also showed surface area of 112 m2/g with high photocatalytic activity with a rate constant 0.02886 and 0.0460 min−1 for MB and CB degradations respectively. It had also been found that, the photocatalytic activity of the TiO2/bentonite nanocomposites were 8 and 5 times higher for MB and CB degradation respectively in compare with Degussa P25.

Direct formation of anatase TiO2 nanoparticles on carbon nanotubes by atomic layer deposition and their photocatalytic properties

TiO2 with different morphology was deposited on acid-treated multi-walled carbon nanotubes (CNTs) by atomic layer deposition at 100 °C–300 °C to form a TiO2@CNT structure. The TiO2 fabricated at 100 °C was an amorphous film, but became crystalline anatase nanoparticles when fabricated at 200 °C and 300 °C. The saturation growth rates of TiO2 nanoparticles at 300 °C were about 1.5 and 0.4 Å/cycle for substrate-enhanced growth and linear growth processes, respectively. It was found that the rate constants for methylene blue degradation by the TiO2@CNT structure formed at 300 °C were more suitable to fit with second-order reaction. The size of 9 nm exhibited the best degradation efficiency, because of the high specific area and appropriate diffusion length for the electrons and holes.

Modification of acid-activated kaolinite with TiO2 and its use for the removal of azo dyes

Acid-activated kaolinite (AAK), prepared by the calcination and acid activation of coal-bearing kaolinite, was modified with TiO2 to improve its ability to adsorb and hence remove azo dyes. X-ray diffraction analysis, N2 adsorption–desorption analysis, and high-resolution transmission electron microscopy were used to characterize the synthesized samples and confirm the formation of anatase TiO2 nanoparticles on the surface of the AAK bulk. The obtained AAK/TiO2 nanocomposites retained the porous structure of AAK and exhibited a Brunauer–Emmett–Teller surface area as high as 358.6m2g−1. The dye-adsorption abilities of the synthesized samples were investigated using anionic dyes such as Congo red (CR), Direct Fast Scarlet 4BS (4BS), and weak acid dark blue 5R (5R), which are common pollutants. The dye-removal efficiency increased from 25 to 95%, 11 to 90%, and 13 to 97% for CR, 4BS, and 5R, respectively, under the same adsorption conditions, when the TiO2 content in the nanocomposite was increased from 0 to 30mass%, indicating the anionic-dye-removal ability of AAK improved significantly after modification with TiO2. The dye-adsorption kinetics fit well the pseudo-second-order rate equation, while the adsorption isotherm data could best be described by the Langmuir adsorption model.

Defective TiO2-supported Cu nanoparticles as efficient and stable electrocatalysts for oxygen reduction in alkaline media.

Nanocomposites based on TiO2-supported copper nanoparticles were prepared by a hydrothermal method where copper nanoparticles with or without the passivation of 1-decyne were chemically grown onto TiO2 nanocolloid surfaces (and hence denoted as CuHC10/TiO2 and Cu/TiO2, respectively). Transmission electron microscopy measurements showed that the size of the hybrid nanoparticles was 5-15 nm in diameter with clearly defined lattice fringes for anatase TiO2(101) and Cu(111). The formation of anatase TiO2 nanoparticles was also observed by X-ray diffraction measurements. FTIR measurements confirmed successful attachment of alkyne ligands onto the surface of the copper nanoparticles via Cu-C≡ interfacial bonds in CuHC10/TiO2. XPS measurements suggested the formation of CuO in both samples with a higher concentration in Cu/TiO2, and interestingly Ti(3+) species were found in CuHC10/TiO2 but were absent in Cu/TiO2 or TiO2 nanoparticles. Electrochemical studies demonstrated that both Cu/TiO2 and CuHC10/TiO2 exhibited a markedly improved electrocatalytic performance in the oxygen reduction reaction, as compared to TiO2 nanocolloids alone, in the context of the onset potential, the number of electrons transferred and the kinetic current density. Importantly, among the series, CuHC10/TiO2 exhibited the best ORR activity with a high current density, an almost four-electron reduction pathway and long-term stability after 4000 cycles at high potentials, which may be ascribed to the defective TiO2 structures in combination with surface ligand engineering.

In situ sonosynthesis of nano TiO2 on cotton fabric

Here, titanium dioxide nanoparticles (NPs) were sonosynthesized and loaded simultaneously onto the cotton fabric. Titanium tetra isopropoxide (TTIP) was used as precursor and ultrasonic irradiation was utilized as a tool for synthesis of TiO2 in low temperature with anatase structure and loading nanoparticles onto the cotton fabric. TiO2 loaded cotton fabric was characterized by XRD, FE-SEM, EDS, and XRF. Moreover, several properties of the treated cotton fabrics such as self-cleaning, UV protection, washing durability, and tensile strength were studied. The effect of variables, including TTIP concentration and sonication time, was investigated based on central composite design (CCD) and response surface methodology (RSM). The results confirmed formation of anatase TiO2 nanoparticles with 3–6nm crystalline size loaded onto the cotton fabric at low temperature (75°C) that led to good self-cleaning and UV-protection properties. The excellent UV-protection rating of the treated fabric maintained even after 25 home launderings indicating an excellent washing durability. Interestingly, sonochemical method had no negative influence on the cotton fabric structure. The statistical analysis indicated significant effect of both TTIP concentration and sonication time on the content of the loaded TiO2 on the fiber and self-cleaning properties of the fabric.

Effects of hydrothermal temperature on formation and decoloration characteristics of anatase TiO2 nanoparticles

This paper describes the effects of temperature on the complex intermediate processes from the precursor to the fully-crystallized anatase TiO2 nanoparticles in hydrothermal synthesis. The anatase TiO2 nanoparticles were synthesized in a wide temperature range below 230°C. The composition, morphology, and methylene blue (MB) decoloration characteristics of the obtained products were investigated by X-ray diffraction, Fourier transform infrared spectroscope, X-ray photoelectron spectroscope, and scanning and transmission electron microscope. The dehydrating polycondensation of Ti(IV)-hydrates and the decomposition of (NH4)2Ti3O7 intermediates with the temperature increase lead to the direct formation of anatase TiO2 nanoparticles under the hydrothermal environments. The strong MB decoloration of the hydrothermal products obtained at the low (⩾130°C) and high (⩽180°C) temperatures are attributed to the adsorption of Ti(IV)-hydrates and the photocatalysis of anatase TiO2 nanoparticles, respectively.

Structural role of polyethylene glycol in the formation of anatase nanocrystalline titania at low temperature

AbstractAnatase nanocrystalline TiO2 thin films were obtained by a sol–gel dip‐coating method, in which the nanocrystallization is effected by a simple hot water treatment of the deposited films at temperatures below 90 °C under atmospheric pressure for 1 h. The dip‐coating sol was prepared by reacting titanium tetra‐n‐butoxide [Ti(OnBu)4] with polyethylene glycol (PEG) in ethanol. Films obtained from a sol that do not contain PEG show no sign of crystallization, demonstrating the importance of PEG in the crystallization process. Raman studies of reaction dynamics show that PEG undergoes a nucleophilic substitution reaction replacing butoxy groups in Ti(OnBu)4. Stoichiometric reactions of Ti(OnBu)4 with PEG in polar and nonpolar solvents were performed, and they yielded different titanium–PEG hybrid polymers, which were isolated and characterized by various spectroscopic techniques such as IR, Raman, solid‐state NMR and MALDI‐TOF‐MS. NMR studies evidenced the location and the way in which PEG is bonded with titanium atoms in the titanium–PEG hybrid polymers. On the basis of these studies, we have proposed structures for these polymers. It is demonstrated that the structure of the obtained polymers plays an important role in the formation of anatase TiO2 nanoparticles in hot water at temperatures below 90 °C under atmospheric pressure. Copyright © 2009 John Wiley & Sons, Ltd.