Preparation of stable anatase-type TiO2 and its photocatalytic performance

Cost-Effective Production of TiO2 with 90-Fold Enhanced Photocatalytic Activity Via Facile Sequential Calcination and Ball Milling Post-Treatment Strategy

Titanium dioxide (TiO₂), the golden standard among the photocatalysts, exhibits a varying level of photocatalytic activities (PCA) amongst the synthetically prepared and commercially available products. For commercial applications, superior photoactivity and cost-effectiveness are the two main factors to be reckoned with. This study presents the development of simple, cost-effective post-treatment processes for a less costly TiO₂ to significantly enhance the PCA to the level of expensive commercial TiO₂ having demonstrated superior photoactivities. We have utilized sequential calcination and ball milling (BM) post-treatment processes on a less-costlier KA100 TiO₂ and demonstrated multi-fold (nearly 90 times) enhancement in PCA. The post-treated KA100 samples along with reference commercial samples (P25, NP400, and ST01) were well-characterized by appropriate instrumentation and evaluated for the PCA considering acetaldehyde photodegradation as the model reaction. Lattice parameters, phase composition, crystallite size, surface functionalities, titanium, and oxygen electronic environments were evaluated. Among post-treated KA100, the sample that is subjected to sequential 700 °C calcination and BM (KA7-BM) processes exhibited 90-fold PCA enhancement over pristine KA100 and the PCA-like commercial NP400 (pure anatase-based TiO₂). Based on our results, we attribute the superior PCA for KA7-BM due to the smaller crystallite size, the co-existence of mixed anatase-srilankite-rutile phases, and the consequent multiphase heterojunction formation, higher surface area, lattice disorder/strain generation, and surface oxygen environment. The present work demonstrates a feasible potential for the developed post-treatment strategy towards commercial prospects.

Synthesis and Characterization of TiO₂ Nanoparticles for the Reduction of Water Pollutants

The aim of this manuscript was the optimization of the synthesis of TiO₂ nanoparticles (TiO₂ NPs) with conditions that could be easily reproducible at the industrial level. Several procedures were tested and those with C₁₂H₂₈O₄Ti and CO(NH₂)₂ as precursors seemed the most promising and, consequently, were improved with different molar ratios, lower temperatures and the addition of NH₄Cl as a secondary dopant of nitrogen. The obtained samples were studied with analytical techniques such as X-ray powder diffraction (XRPD) and field emission scanning electron microscopy (FESEM). To complete the study, dye degradation and bacteriological tests were also performed. The results indicate that it is possible to obtain TiO₂ NPs at lower temperatures with respect to those used in the literature; the best candidate that could satisfy all the requirements was a sample with a molar ratio of C₁₂H₂₈O₄Ti:CO(NH₂)₂ at 2:1 and obtained at 50 °C.

Buried Charge at the TiO2/SrTiO3 (111) Interface and Its Effect on Photochemical Reactivity

High-temperature annealing in air is used to produce SrTiO₃ (111) surfaces with two types of atomically flat terraces: those that promote photoanodic reactions and those that promote photocathodic reactions. Surface potential measurements show that the photocathodic terraces have a relatively more positive surface potential than the photoanodic terraces. After depositing thin TiO₂ films on the surface, from 1 to 13 nm thick, the surface of the film above the photocathodic terraces also has photocathodic properties, similar to those of the bare surface. While a more positive surface potential can be detected on the surface of the thinnest TiO₂ films (1 nm thick), it is undetectable for thicker films. The persistence of the localized photocathodic properties on the film surface, even in the absence of a measurable difference in local potential, indicates that the charge associated with specific terraces on the bare SrTiO₃ (111) surface remains localized at the TiO₂/SrTiO₃ interface and that the buried charge influences the motion of photogenerated carriers.

Litchi-like CdS/CdTiO3–TiO2 composite: synthesis and enhanced photocatalytic performance for crystal violet degradation and hydrogen production

CdS/CdTiO₃–TiO₂ composites prepared under different conditions contain a mixture of crystal phases of CdS, CdTiO₃ and TiO₂. The conditions of synthesis have an impact on the photocatalytic performance for dye degradation and hydrogen production.

TiO2 nanofibers resembling ‘yellow bristle grass’ in morphology by a soft chemical transformation

We synthesized a uniquely shaped one-dimensional (1-D) TiO₂ nanostructure having the morphology of yellow bristle grass with high surface area by the titanate route under mild reaction conditions.

TiO2–mesoporous silica nanocomposites: cooperative effect in the photocatalytic degradation of dyes and drugs

Titania nanoparticles were confined inside the pore channels of preformed mesoporous silica nanoparticles (MSNs) for the photodegradation of dyes and drugs.

Photostability and optical properties of modified titanium dioxide

The influence of different modifiers, P2O5, K2O, Al2O3, SiO2, CeO2, and ZrO2, on the optical properties and photostability of rutile titanium dioxide was studied. The research was aimed at obtaining pigmentary rutile titanium dioxide with the enhanced photostability. The optical properties such as brightness, white tone, and gray tone were improved when titanium dioxide samples were modified with zirconium instead of cerium. Titanium dioxide products modified additionally with Al2O3 displayed improved optical properties by comparison with appropriate titanium dioxide products lacking introduced aluminum. In comparison with unmodified material (∆E* = 21.8), a considerable increase of the photostability of modified titanium dioxide was observed. The lowest photoactivity, in the range of ∆E* = 0.96–2.45, was measured for the TiO2-PKAlSiCe series. A selective leaching method and X-ray diffraction (XRD) analysis were used to determine the distribution of modifiers in titanium dioxide materials. It was concluded that the differences in both photoactivity and optical properties of modified titanium dioxide depend on its phase composition.

A one-step process for the antimicrobial finishing of textiles with crystalline TiO2 nanoparticles

Titanium oxide (TiO(2)) nanoparticles (NPs) in their two forms, anatase and rutile, were synthesized and deposited onto the surface of cotton fabrics by using ultrasonic irradiation. The structure and morphology of the nanoparticles were analyzed by using characterization methods such as XRD, TEM, STEM, and EDS. The antimicrobial activities of the TiO(2)-cotton composites were tested against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) strains, as well as against Candida albicans. Significant antimicrobial effect was observed, mainly against Staphylococcus aureus. In addition, the combination of visible light and TiO(2) NPs showed enhanced antimicrobial activity.

Preparation of TiO₂ nanocrystallite powders coated with 9 mol% ZnO for cosmetic applications in sunscreens

The preparation of TiO₂ nanocrystallite powders coated with and without 9 mol% ZnO has been studied for cosmetic applications in sunscreens by a co-precipitation process using TiCl₄ and Zn(NO₃)₂·6H₂O as starting materials. XRD results show that the phases of anatase TiO₂ and rutile TiO₂ coexist for precursor powders without added ZnO (T-0Z) and calcined at 523 to 973 K for 2 h. When the T-0Z precursor powders are calcined at 1273 K for 2 h, only the rutile TiO₂ appears. In addition, when the TiO₂ precursor powders contain 9 mol% ZnO (T-9Z) are calcined at 873 to 973 K for 2 h, the crystallized samples are composed of the major phase of rutile TiO₂ and the minor phases of anatase TiO₂ and Zn₂Ti₃O₈. The analyses of UV/VIS/NIR spectra reveal that the absorption of the T-9Z precursor powders after being calcined has a red-shift effect in the UV range with increasing calcination temperature. Therefore, the TiO₂ nanocrystallite powders coated with 9 mol% ZnO can be used as the attenuate agent in the UV-A region for cosmetic applications in sunscreens.

Synthesis and photocatalytic activity of TiO2 nanoparticles prepared by chemical vapor condensation method with different precursor concentration and residence time

Nanosized TiO(2) photocatalysts were synthesized using a chemical vapor condensation method under a range of synthesis conditions (precursor vapor concentration and residence time in a tubular electric furnace). X-ray diffraction showed that the prepared TiO(2) powders consisted mainly of anatase (>94%) with a small amount of rutile. The mean particle diameter from the Brunauer-Emmett-Teller surface area and transmission electron microscopy measurements ranged from 9.4 to 16.6 nm. The specific surface area (92.5-163.5 m(2) g(-1)) of the prepared TiO(2) powders was found to be dependent on the synthesis conditions. The content of hydroxyl groups on the surface of the prepared TiO(2) sample was higher than those on commercial TiO(2), resulting in increased photocatalytic oxidation. The photocatalytic activity of the TiO(2) samples prepared in a methylene blue solution was strongly dependent on the crystallinity and specific surface area, which were affected by the TTIP vapor concentration and residence time.

Ultrasound with low intensity assisted the synthesis of nanocrystalline TiO2 without calcination

A novel method has been developed for the preparation of nano-sized TiO(2) with anatase phase. Nanoparticles with diameter about 6 nm were prepared at a relatively low temperature (75 degrees C) and short time. The synthesis was carried out by the hydrolysis of titanium tetra-isopropoxide (TTIP) in the presence of water, ethanol, and dispersant under ultrasonic irradiation (500 kHz) at low intensity. The results show that variables such as water/ethanol ratio, irradiation time, and temperature have a great influence on the particle size and crystalline phases of TiO(2) nanoparticles. Characterization of the product was carried out by different techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV-vis spectroscopy.

Critical nuclei size, initial particle size and packing effect on the phase stability of sol-peptization-gel-derived nanostructured titania

The influence of the initial particle size and packing of anatase crystallites on the phase stability of nanostructured titania was investigated. Dried anatase gels with different degrees of particle packing were prepared through the peptization-induced electrostatic stabilization of primary particles in the sol. The initial size of anatase primary particles was varied by precalcination prior to the anatase-rutile phase transformation that occurred during final calcination. In the case of well-packed titania, the initial size of anatase primary particles does not influence the phase-transformation behavior whereas loosely packed titania shows a strong initial anatase primary particle size dependence on the phase-transformation behavior.

Photocatalytic activity of TiO2 doped with boron and vanadium

Boron (B)- and vanadium (V)-doped TiO(2) photocatalysts were synthesized using modified sol-gel reaction processes and characterized by X-ray diffraction (XRD), Raman spectroscopy and N(2) physisorption (BET). The photocatalytic activities were evaluated by monitoring the degradation of methylene blue (MB). The results showed that the materials possess high surface area. The addition of B favored the transformation of anatase to rutile, while in the presence of V, anatase was the only phase detected. The MB degradation on V-doped TiO(2) was significantly affected by the preparation method. In fact while the presence of V in the bulk did not influence strongly the photoreactivity under visible irradiation, an increase of surface V doping lead to improved photodegradation of MB. The degradation of MB dye indicated that the photocatalytic activities of TiO(2) increased as the boron doping increased, with high conversion efficiency for 9mol% B doping.

Low-temperature preparation and microwave photocatalytic activity study of TiO2-mounted activated carbon

TiO2 thin films were deposited on granular activated carbon by a dip-coating method at low temperature (373 K), using microwave radiation to enhance the crystallization of titania nanoparticles. Uniform and continuous anatase titania films were deposited on the surface of activated carbon. BET surface area of TiO2-mounted activated carbon (TiO2/AC) decreased a little in comparison with activated carbon. TiO2/AC possessed strong optical absorption capacity with a band gap absorption edge around 360 nm. The photocatalytic activity did not increase when the as-synthesized TiO2/AC was thermally treated, but was much higher than commercial P-25 in degradation of phenol by irradiation of electrodeless discharge lamps (EDLs).

Dependence of photocatalytic activity of anatase powders on their crystallinity

Structural changes in anatase phase in four TiO(2) photocatalysts with annealing at high temperatures were followed by evaluating crystallite size and lattice strain of anatase phase separately and measuring the content of anatase. The rate constant k for the decomposition of methylene blue in its aqueous solution under UV irradiation was determined as a measure of photocatalytic activity. Marked dependences in crystallinity improvement, i.e., the growth of crystallite and the decrease in lattice strain, and in phase transformation from anatase to rutile phases of TiO(2) on annealing temperature was observed above 500 degrees C, depending on starting photocatalysts used. The phase transformation to rutile started after reaching of crystallite size to about 32 nm and of lattice strain to about 0.5 x 10(-3). Rate constant k was found to depend on both crystallite size and lattice strain of anatase; it increased with increasing crystallite size up to about 32 nm and decreasing lattice strain down to about 0.5 x 10(-3). Further increase in crystallite size and decrease in lattice strain induced the decrease in rate constant k, mainly due to the partial transformation of anatase to rutile. The present results showed that the activity of the photocatalysts was possible to be improved by annealing at a high temperature, by selecting an optimal condition of annealing for getting a high crystallinity in anatase phase and no phase transformation to rutile phase.