Rutile Anatase Research Articles

Study on triphase of polymorphs TiO2 (anatase/rutile/brookite) for boosting photocatalytic activity of metformin degradation

The elution of pharmaceutical products such as metformin at higher concentrations than the safe level in aquatic systems is a serious threat to human health and the ecosystem. Photocatalytic technology using TiO2 semiconductors potentially fixes this problem. This study aims to synthesize triphasic anatase–rutile–brookite TiO2 using ultrasound assisted sol–gel technique in the presence of acid and its application to photodegradation of metformin under UV light irradiation. Based on X-ray diffraction analysis, a TiO2 sample consisted of anatase (76%), rutile (7%), and brookite (17%) polymorph (A76R7B17) that was fully crystallized. Scanning electron microscopy (EM)–energy dispersive X-ray spectra results showed agglomerated triphasic A76R7B17 with irregular spherical clusters. Transmission EM results revealed that the crystal size of A76R7B17 was 4–14 nm. The Brunauer–Emmett–Teller analysis showed the sample's specific surface area of 149 m2 g−1. The degradation test of metformin demonstrated that the A76R7B17 exhibited a 75.4% degradation efficiency after 120 min under UV light irradiation, significantly higher than using biphasic and single-phase TiO2 photocatalysts. This difference could be attributed to the heterojunction effect of triphasic materials that effectively reduced electron–hole recombination rate as well as the combination of effective electron transfer from conduction band of brookite and anatase and the utilization of wider range of UV–visible light using rutile.

Effect of substrate temperature and annealing on the growth of TiO2‐x thin films deposited by using DC‐magnetron sputtering technique

In this study, the effect of annealing on the structural, surface morphology and chemical structure of titanium suboxide (TiO2‐x) thin films has been investigated. TiO2‐x films had been grown on Si substrates by DC‐magnetron sputtering with different sputter powers (75 and 100 W) at room temperature (RT) and 200°C substrate temperature (ST). The films were subsequently annealed for 1 h at 300, 400 and 500°C in vacuum. The impact of ST, post‐annealing and sputter power on crystallinity, surface morphology and chemical state of the films were studied. Grazing incidence X‐ray diffraction (GIXRD) data revealed that the films were amorphous or exhibited a very low crystalline structure while deposited at RT and even after annealing. Moreover, the films showed crystallinity while deposited at ST and exhibited an anatase‐rutile (A‐R) mix phase from anatase (A) annealed at 300°C (75 W at ST). X‐ray reflectivity (XRR) data showed that the mass density of the films increased with the annealing temperature. Images obtained using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) revealed that post‐annealing increased the surface roughness of the films. X‐ray photoelectron spectroscopy (XPS) analysis indicated the films were sub stoichiometric. It was also indicated that Ti was in the form of Ti4+ and Ti3+ states in all films, and the proportion of Ti4+ slightly increased after post‐annealing at 500°C. The findings showed that post‐annealing, ST and sputtering power can all affect the growth of TiO2‐x films.

Effect of Temperature Sintering on Grain Growth and Optical Properties of TiO2 Nanoparticles

Titanium dioxide (TiO2) nanoparticles were prepared by the sol–gel method and the structural, morphological, and optical properties were investigated at different sintering temperatures of 500, 600, 700, 800, and 900°C. A tetragonal structure of anatase, mixed (anatase–rutile), and rutile phases are observed in the X-ray diffraction (XRD) analysis. Pure anatase phase formation occurred at 500°C, whereas anatase-to-rutile phase transformation began at 600°C, and reaching complete conversion to rutile at 800°C. The average crystallite size increased from 23 to 34 nm for anatase and 38 to 62 nm for the rutile when sintering temperature increased from 500 to 900°C. The scanning electron microscope (SEM) result presented the increase of grain size (25–100 nm) with increasing the sintering temperature. The Fourier transform infrared (FTIR) spectra demonstrated the presence of TiO2 vibrational bonds in all samples. The optical bandgaps of the sintered TiO2 nanoparticles decreased with rising sintering temperature. Photoluminescence spectra exhibited three characteristic peaks centered at 380, 450, and 550 nm. The emission intensity increased with increasing the sintering temperature. The Mie analysis was also studied to calculate scattering cross-section, forward scattering, and asymmetry for different grain sizes. The results showed that by increasing the nanoparticle diameters, the peaks of all spectra are redshifted for larger grain sizes and cross-section peaks shift to high values. In this study, the sintering temperature is observed to have a strong influence on crystalline phase transformation, microstructure, and optical properties of TiO2 nanoparticles. The TiO2 sample sintered at 900°C shows the best result to be used as luminescent material due to the low optical bandgap energy.

Triboelectric Charging Behaviors of Polyester Films Doped with Titanium Dioxide Nanoparticles of Various Crystal Structures

It is empirically known that titanium dioxide nanoparticles stabilize the contact and frictional charge of the host polymers to which they are added. However, the mechanism for the stabilization process has not yet been elucidated. In this study, polyester films doped with titanium dioxide nanoparticles of different crystalline forms were triboelectrically charged and the effect of humidity on their charging characteristics was subsequently investigated to elucidate the charge stabilization mechanism. Our first finding was that the rutile-, rutile–anatase mixed crystal (P25)-, and amorphous-dominant-type titanium dioxide nanoparticles reduced the sensitivity of the films to humidity (humidity dependence), while the anatase-type titanium dioxide enhanced the humidity dependence. This difference in action was explained by associating it with the different water adsorption forms on the major crystalline surface of each titanium dioxide type. The second finding was that doping with titanium dioxide nanoparticles, particularly rutile and P25 nanoparticles, reduced fluctuations in the amount of tribocharges of the polyester film. This crystalline-form-dependent difference in action was considered to be based on the depth of the electron traps involved in each titanium dioxide type. The above two findings have allowed us to propose the first mechanism of tribocharge stabilization by titanium dioxide.

Copper and nanostructured anatase rutile and carbon coatings induce adaptive antibiotic resistance

Contaminated surfaces are vehicles for the spread of infectious disease-causing microorganisms. A strategy to prevent their spread is applying antimicrobial coatings to surfaces. Both nanostructured anatase rutile and carbon (NsARC), a TiO2 formulation, and copper are examples of antimicrobial agents that are used in making or coating door handles and similar surfaces, to reduce microbial loads. Antimicrobial surfaces have been extensively tested for antimicrobial activity but not sublethal effects, such as exposure-associated multiple antibiotic resistance phenotypes usually caused by induction of efflux pump genes. The possibility of NsARC and copper inducing indicative efflux pump pathways was investigated by monitoring the expression of mScarlet fluorescent protein (FP) in two reporter strains of Escherichia coli. There was an increase in the expression of FP in the reporter strains exposed to NsARC and copper relative to the inert control composed of stainless steel. Furthermore we tested E. coli and Staphylococcus aureus following 8 h of exposure to NsARC for changes in resistance to selected antibiotics. E. coli that were exposed to NsARC became more susceptible to kanamycin but there was no significant change in susceptibility of S. aureus to any tested antibiotics. These findings suggests that even though NsARC and copper are antimicrobial, they also have some potential to cause unintended phenotypes.

Effect of the Deposition Time on the Structural, 3D Vertical Growth, and Electrical Conductivity Properties of Electrodeposited Anatase-Rutile Nanostructured Thin Films.

TiO2 time-dependent electrodeposited thin films were synthesized using an electrophoretic apparatus. The XRD analysis revealed that the films could exhibit a crystalline structure composed of ~81% anatase and ~6% rutile after 10 s of deposition, with crystallite size of 15 nm. AFM 3D maps showed that the surfaces obtained between 2 and 10 s of deposition exhibit strong topographical irregularities with long-range and short-range correlations being observed in different surface regions, a trend also observed by the Minkowski functionals. The height-based ISO, as well as specific surface microtexture parameters, showed an overall decrease from 2 to 10 s of deposition, showing a subtle decrease in the vertical growth of the films. The surfaces were also mapped to have low spatial dominant frequencies, which is associated with the similar roughness profile of the films, despite the overall difference in vertical growth observed. The electrical conductivity measurements showed that despite the decrease in topographical roughness, the films acquired a thickness capable of making them increasingly insulating from 2 to 10 s of deposition. Thus, our results prove that the deposition time used during the electrophoretic experiment consistently affects the films’ structure, morphology, and electrical conductivity.

N-doped TiO2 nanotube arrays with mixed phase for enhanced photocathodic protection of 304 stainless steel under visible light

Effective N-doped TiO2 nanotube arrays with rutile–anatase mixed phase were fabricated by two-step anodization method and annealing in a NH3 atmosphere. Compared with pure anatase TiO2 nanotube arrays, the photocurrent density of N-doped TiO2 nanotube arrays with mixed phase increased by about three times under visible light. Moreover, the open circuit potential of 304 stainless steel obviously negatively shifted when coupled with N-doped TiO2 nanotube arrays with mixed phase under visible light. The enhancement was mainly because N-doping extends light absorbance and the mixed phase is beneficial for the separation of photoexcited electrons–holes. Therefore, N-doped TiO2 nanotube arrays with mixed phase showed highly effective photogenerated cathodic protection of 304 stainless steel under visible light. Interestingly, the photoelectrode also displayed a cathodic protection effect after removing irradiation, which is meaningful for practical applications.

Low Doses of Anatase and Rutile Nanoparticles Differently Modulate Photosynthesis and Regulatory Genes: A Contribution to the Nanoagroindustry

Industrial applications of titanium dioxide nanoparticles (TiO2 NPs) are wide, and their use in nano-fertilizing technology has been proposed in the last few years. Bioactivity evaluation of different TiO2 NPs formulations is therefore crucial, not only to select the most appropriate formulation but also to validate potential agro-applications. In the current work, we compared the bioactivity of the two most used TiO2 NPs formulations (anatase and rutile–anatase) on the photosynthesis of Lactuca sativa. Seeds were exposed to concentrations of 0, 10, and 50 mg L−1 of anatase (A) or rutile–anatase (RA). Germination rate was not affected by NPs, but root growth was stimulated mainly by RA50. Compared with control, RA showed positive effects on photophosphorylation-related parameters. A50 was more efficient in promoting the gas exchange phase (PN, Ci, gs, and E) and in stimulating the absorption of some nutrients. Expanding on the biochemical and physiological data, we show that RA50 stimulated several genes coding for proteins involved in the electron transport in thylakoids (psbA, petB, petA, psaA, psaC, ndhA, ndhD) and ATP synthesis (atpA, atpB). The transcript coding for the large subunit of RuBisCO (rbcL), was stimulated by lower concentration (RA10). This suggests that RuBisCO is highly sensitive to these NPs even at low doses. RA at low doses has been demonstrated to be the most promising NP. These discriminative effects of TiO2 NPs, based on their formulation and dose, may present advantages for their use in the precision nanoagroindustry.

Defective Grey TiO2 with Minuscule Anatase–Rutile Heterophase Junctions for Hydroxyl Radicals Formation in a Visible Light-Triggered Photocatalysis

The novelty of this work was to prepare a series of defect-rich colored TiO2 nanostructures, using a peroxo solvothermal-assisted, high-pressure nitrogenation method. Among these solids, certain TiO2 materials possessed a trace quantity of anatase–rutile heterojunctions, which are beneficial in obtaining high reaction rates in photocatalytic reactions. In addition, high surface area (above 100 m2/g), even when utilizing a high calcination temperature (500 °C), and absorption of light at higher wavelengths, due to the grey color of the synthesized titania, were observed as an added advantage for photocatalytic hydroxyl radical formation. In this work, we adopted a photoluminescent probe method to monitor the temporal evolution of hydroxyl radicals. As a result, promising hydroxyl radical formations were observed for all the colored samples synthesized at 400 and 500 °C, irrespective of the duration of calcination.

CdS QDs modified three-dimensional ordered hollow spherical ZnTiO3-ZnO-TiO2 composite with improved photocatalytic performance

Three-dimensional ordered hollow spherical ZnTiO3-ZnO-TiO2 composite (3DOH ZnTiO3-ZnO-TiO2) was prepared by vacuum impregnation combined with calcination method using polystyrene (PS) colloidal microspheres as the template, and the CdS QDs were modified into 3DOH ZnTiO3-ZnO-TiO2 by water bath method. The crystal structure, chemical composition, surface morphology, optical absorption and surface physicochemical properties of CdS QDs modified 3DOH ZnTiO3-ZnO-TiO2 (CdS QDs 3DOH ZnTiO3-ZnO-TiO2) composite were well characterized. The results show that the three-dimensional ordered hollow spherical CdS QDs 3DOH ZnTiO3-ZnO-TiO2 composite mainly composes of anatase phase TiO2, rutile phase TiO2, and hexagonal phase ZnTiO3 and hexagonal phase ZnO. Among them, a homojunction is formed between the mixed crystal phase of TiO2 (anatase–rutile), and a heterojunction is found between hexagonal phase ZnTiO3 and hexagonal phase ZnO. In addition, the composite treated by the polystyrene (PS) colloidal microspheres template has formed the three-dimensional ordered hollow sphere structure, the hollow spheres are arranged neatly and orderly, and the sphere wall is formed by stacking nanoparticles. At the same time, the three-dimensional ordered hollow spherical structure of CdS QDs 3DOH ZnTiO3-ZnO-TiO2 composite provides more transfer paths for material transport and promotes repeated light absorption, prolonging the lifetime of photogenerated charge carriers. Moreover, due to the close connection between CdS QDs, ZnTiO3, ZnO and TiO2, the separation of electrons and hole pairs is facilitated, and the recombination of electron and hole pairs is effectively suppressed, so that CdS QDs 3DOH ZnTiO3-ZnO-TiO2 composite exhibits extremely high photocatalytic activity. Its hydrogen production is more than 300 times that of pure TiO2, moreover, of which cycle stability also shows better.

Effect of Ag doping on phase-change and photocatalytic performance of rutile–anatase mixed-phase titanium dioxide (TiO2) nanoparticles

Effect of Ag doping on phase-change and photocatalytic performance of rutile–anatase mixed-phase titanium dioxide (TiO2) nanoparticles

Enhanced photocatalytic ethylene decomposition with anatase-rutile mixed nanostructures formed by He plasma treatment

In order to realize high-performance titanium dioxide (TiO2) photocatalysts for ethylene decomposition, titanium (Ti) thin film samples with fiberform nanostructures were prepared by helium (He) plasma treatment. Then, the oxidation condition for ethylene decomposition were optimized in terms of the oxidation temperature and duration. It is shown that He plasma irradiation with Ti deposition followed by oxidation in the air formed anatase-rich TiO2. The rutile anatase transition temperature increased to higher than 1000 K on the He treated samples and the best photocatalytic performance is twice higher than that on TiO2 sample formed in a magnetron sputtering device. Helium plasma treatment induces vacancies, He clusters, and He bubbles together with formation of nanostructures. The results suggested that those morphology changes lead to the formation of stable anatase structure, which is likely the key factor for the enhancement of photocatalytic activity. Based on the obtained ethylene decomposition rate, we will discuss the necessary light source and amount of photocatalysts to keep vegetables fresh in a long-distance transport cargo.

Growth of binary anatase-rutile on phosphorylated graphene through strong P-O-Ti bonding affords a stable visible-light photocatalyst.

Titanium dioxide is an ubiquitous photocatalyst in water-cleaning technologies, being presently the most promising tools to resolve the global issue of sewage treatment. In this framework, titanium dioxide–graphene nanocomposites are discussed as promising visible-light activated photocatalysts but little is hitherto known about the surface and interface chemistry bridging the metal oxide and carbon phases. In an attempt to spotlight this overlooked issue, we herein designed two different hybrid nanocomposites through covalent grafting and growth of titanium dioxide clusters on graphene oxide and on phosphorylated graphene oxide, which affords GO@TiO2 and PGO@TiO2, respectively. While anatase could be selectively harvested on the surface of GO@TiO2, biphasic anatase–rutile nucleates could be obtained on PGO@TiO2. Thermal annealing treatments improve the metal oxide crystallization and further remove oxygenated groups from the surface of graphene. The interfacial stability of these photocatalysts was also investigated under irradiation, with the graphene support being sensitive to the proximal presence of titanium dioxide. The resulting nanocomposites were also assessed for methylene blue removal through adsorption and photocatalysis. Regardless of their composition, superior photoactivity was noticed for the nanocomposites compared to commercially available degussa that display marginal visible-light photoactivity (11% removal). Within our study, PGO@TiO2-500 stands as the most active catalyst, allowing nearly quantitative removal of the pollutant from water. The superior performance of PGO@TiO2-500 can be explained by the highest stability reached through P–O–Ti bonding, its improved crystallinity, and the reduction of the graphene surface during thermal treatment. On a whole, this study provides a blueprint for comparing semiconducting metal oxide grown on tuneable surface-interfacial graphene environments and highlights the utility of surface-engineering graphene sheets to access efficient visible-light oxidation photocatalysts.

Upper temperature limits of orogenic gold deposit formation: Constraints from TiO2 polymorphs in the Dongyuan Au deposit, Jiangnan Orogen, China

Abstract Gold (Au) deposits have formed in orogenic belts throughout Earth’s history. However, the upper temperature limits of orogenic Au vein formation are difficult to constrain because measurements made on fluid inclusions focus on intermediate to late-stage minerals (e.g., quartz and calcite) or are based on P-T estimates for the metamorphic mineral assemblages of the host rocks. We conducted a study of TiO2 polymorphs that are among the earliest minerals that grew in Au-bearing veins of the Dongyuan deposit, Jiangnan orogenic Au belt, South China. Based on Raman analyzes, we identified TiO2 polymorphs of anatase (with Raman peaks at 396, 515, and 638 cm−1), rutile (with Raman peaks at 235, 447, and 613 cm−1), and anatase–rutile intergrowths. Transmission electron microscope (TEM) confirmed the polymorphs identifying the [111] zone axis of anatase, [110] zone axis of rutile, and [111] and [111] zone axes of rutile–anatase intergrowths. The TiO2 polymorphs in the Dongyuan Au veins constrain a temperature range for early mineral precipitation in the veins of 450–550 °C. The results show that ore-forming fluids for this orogenic Au deposit emplaced in the shallow crust originated from deeper and hotter crustal levels (e.g., high-grade metamorphic rocks in the middle to lower crust).

Facile Synthesis of Anatase–Rutile Diphase N-doped TiO2 Nanoparticles with Excellent Visible Light Photocatalytic Activity

To further boost the charge separation and photocatalytic activity of TiO2 under visible light, the anatase–rutile mixed-phase nitrogen-doped (N-doped) TiO2 nanoparticles were successfully synthesized through a facile one-step calcining procedure using TiN as raw materials. The crystal phases, morphologies, chemical compositions, textural structures, and optical properties of as-obtained N-doped TiO2 were characterized by the corresponding analytical techniques. The photocatalytic activities of as-fabricated samples were evaluated by degrading 4-chlorophenol (4-CP) and methylene blue (MB) aqueous solution under visible light irradiation. The results revealed that the ratio of rutile to anatase increased with the improvement of sintering temperature, and the sample prepared at 500 °C had the best photocatalytic activity. This might be because it possessed the most appropriate rutile/anatase proportion as well as the nitrogen doping. The transient photocurrent responses, photoluminescence spectra (PL) measurements, and active species trapping experiments were implemented to disclose the photocatalytic mechanism. This work will provide a further insight into the synthesis of highly efficient N-doped TiO2 photocatalysts for organic contaminant removal.

Anatase–Rutile Transition and Photo-Induced Conductivity of Highly Yb-Doped TiO2 Films Deposited by Acid Sol–Gel Dip-Coating Method

A method to prepare Yb-doped TiO2 is proposed, using titanium isopropoxide and ytterbium oxide. Thin films and powders are produced through the sol–gel technique where the Yb concentrations are 0.01 at.%, 0.02 at.%, 1 at.%, 2 at.% 4 at.% and 8 at.%. The increase in the doping concentration intensifies gradually the sample transparency for the whole observed spectrum and reaches the transparency degree of the undoped sample with the highest concentration of ytterbium. By means of x-ray diffraction (XRD) we find that the solution’s pH leads to the formation of a rutile structure which is compensated for by lanthanide doping, inhibiting the anatase–rutile phase transformation. Then, the XRD profile depends on the Yb concentration, being mostly anatase for undoped and highly (8 at.%) doped samples, with mixed ratios of these two phases in other concentrations. Maintaining an acid solution leads to fewer intergrain defects in the rutile structure contributing to higher conductivity. Photo-induced investigation of 8 at.% Yb-doped thin film, using several light sources leads to distinct behavior concerning the excitation of intra-bandgap states and/or electron–hole pairs. This result helps to understand the electronic transport in Yb-doped TiO2 and shows that devices based on its conductivity may have improved performance by irradiation with controlled light energy.

Synergistic Design of Anatase–Rutile TiO2 Nanostructured Heterophase Junctions toward Efficient Photoelectrochemical Water Oxidation

Synergistically designing porous nanostructures and appropriate band alignment for TiO2 heterophase junctions is key to efficient charge transfer, which is crucial in enhancing photoelectrochemical (PEC) water splitting for hydrogen production. Here, we investigate the efficiency of PEC water oxidation in anatase–rutile TiO2 nanostructured heterophase junctions that present the type-II band alignment. We specifically prove the importance of a phase alignment in heterophase junction for effective charge separation. The TiO2 heterophase junctions were prepared by transferring TiO2 nanotube (TNT) arrays onto FTO substrate with the help of a TiO2 nanoparticle (TNP) glue layer. The PEC characterization reveals that the rutile (R)-TNT/anatase (A)-TNP heterophase junction has a higher photocurrent density than those of A-TNT/R-TNP junction and anatase or rutile single phase, corresponding to twofold enhanced efficiency. This type-II band alignment of R-TNT/A-TNP for water oxidation, in which photogenerated electrons (holes) will flow from rutile (anatase) to anatase (rutile), enables to facilitate efficient electron-hole separation as well as lower the effective bandgap of heterophase junctions. This work provides insight into the functional role of heterophase junction for boosting the PEC performances of TiO2 nanostructures.

Hydro-thermal performance of normal-channel facile heat sink using TiO2-H2O mixture (Rutile–Anatase) nanofluids for microprocessor cooling

Thermal management of microelectronics is a challenging task in modern high heat generating devices. In this work, thermal performance of normal-channel facile heat sink has been investigated using water and TiO2-H2O (mixture of Rutile and Anatase) nanofluids with volumetric concentration of 0.005% and 0.01%. The maximum reduction in base temperature was noted for TiO2-H2O (∅ = 0.01%) and TiO2-H2O (∅ = 0.005%) as 8.2% and 5.5%, respectively, when compared with water. The thermal performance of normal-channel facile heat sink was then compared with the mini-channel integral fin heat sink. The base temperature of normal-channel facile heat sink was found very close to mini-channel integral fin heat sink with a maximum difference of 1.8%. The total cost to fabricate mini-channel heat sink was almost 5.3 times greater than normal-channel heat sink. So, the normal-channel heat sink has economical advantage over the mini-channel heat sink in terms of lower fabrication cost with similar thermal performance. However, the pressure drop was found greater for normal-channel as compared to mini-channel heat sink. The experimental results of normal-channel facile heat sink were also validated numerically, and a good agreement was found.

Enhancing electrochemical properties of TiO2 nanotubes via engineered defect laden crystal structures

This study identifies the dependence of electrochemical properties of titanium dioxide nanotubes (NTs) containing specific concentrations and locations of defects within the crystal structure. NTs, formed through electrochemical anodization, were annealed at 500˚C in either oxygen (O2-NTs) or 2% hydrogen with nitrogen balance (2%H2/N2-NTs). Examination of the NTs using scanning/transmission electron microscopy showed that the O2-NTs were comprised of a mixed phase anatase–rutile, while the 2%H2/N2-NTs were primarily anatase with a defect laden disordered surface layer. Electrochemical impedance measurements showed enhanced electrochemical behavior of the 2%H2/N2-NTs compared to the O2-NTs as a result of the defect-laden structure.

Low-temperature One-pot Aqueous Synthesis and Application of Anatase/Rutile TiO2 Composite Nanoparticles

TiO2 nanoparticles composed of rutile nanothorns and anatase nanoparticles deposited on the base of the nanothorns are obtained via a low-temperature (<100 °C) one-pot aqueous route. Heating of ana...