Rutile Polymorphs Research Articles

Sucrose-based reticulated vitreous carbon modified with N-doped TiO2 as an adsorbent and photocatalyst: Enhanced removal of methyl orange from aqueous solutions

A novel and low-cost 3D reticulated vitreous carbon (RVC) was synthesized and modified with (N-TiO2) to obtain an RVC/N-TiO2 composite, which was employed to remove methyl orange in an aqueous solution. This material was synthesized using the sacrificial template method and impregnated with an environmentally friendly sucrose resin, followed by N-TiO2 impregnation by dip-coating technique. SEM-EDS characterization confirmed the uniform covering of the TiO2, and XRD, Raman, and XPS evinced the presence of anatase and rutile polymorphs in the film and the N-doping, respectively. N-TiO2 coating onto RVC provides a higher specific surface area and electrochemical active area, boosting the wettability and the adsorption capacity. Additionally, this film favoured the photoelectrochemical response of the composite and the generation of •OH radicals. The adsorption, desorption, and photocatalytic studies demonstrated that >95 % decolorization of MO was achieved in 30 min without light irradiation and that >95.5 % degradation was attained in 120 min under visible light. The foam demonstrated reusability for over five cycles of adsorption/desorption of MO, with a capacity to recover up to 99 % of the dye after the first cycle and up to 94.07 % after the fifth cycle. Meanwhile, the minimal desorption of the dye (2.5 %) after illumination confirmed the photocatalytic degradation. This indicates that the process was not merely adsorption but also photocatalytic degradation.

Preparation of a hard AlTiVCr compositionally complex alloy by self-propagating high-temperature synthesis

In this study, an AlTiVCr compositionally complex alloy with a high hardness of 865 ± 34 HV was prepared by a one-step self-propagating high-temperature synthesis (SHS) method using TiO2, V2O5, Cr2O3, and Al as starting materials. Experimental results confirmed the formation of a two-phase alloy having BCC solid solution dendritic grains reinforced by a Ti-rich intermetallic phase. Elemental analysis results confirmed that the Ti at.% in the synthesized alloy was lower than other elements. The addition of extra TiO2 to the reactants, pre-milling of the TiO2-Al mixture, and using the Rutile polymorph of TiO2 instead of Anatase as the starting material increased the atomic percent of Ti. The composition of the proper synthesized alloy was formulated as Al27.3Ti17.2V28.7Cr26.8 which is close to the desired AlTiVCr alloy. To clarify the reaction sequence during the SHS, the binary mixtures were analyzed by thermal analysis. It was postulated that the melting of Al facilitated the reduction reaction of Cr2O3 and VxOy compounds, while TiO2 was the last oxide compound reduced by Al. This hindered the completion of the TiO2 reduction reaction and as a consequence, the unreacted TiO2 entered the slag which lowered the concentration of Ti in the composition of the final alloy.

Brookite TiO2 as an active photocatalyst for photoconversion of plastic wastes to acetic acid and simultaneous hydrogen production: Comparison with anatase and rutile

Photoreforming is a clean photocatalytic technology for simultaneous plastic waste degradation and hydrogen fuel production, but there are still limited active and stable catalysts for this process. This work introduces the brookite polymorph of TiO2 as an active photocatalyst for photoreforming with an activity higher than anatase and rutile polymorphs for both hydrogen production and plastic degradation. Commercial brookite successfully converts polyethylene terephthalate (PET) plastic to acetic acid under light. The high activity of brookite is attributed to good charge separation, slow decay and moderate electron trap energy, which lead to a higher generation of hydrogen and hydroxyl radicals and accordingly enhanced photo-oxidation of PET plastic. These results introduce brookite as a stable and active catalyst for the photoconversion of water contaminated with microplastics to value-added organic compounds and hydrogen.

Enzymatic Activity of Glucose Oxidase on Mesoporous TiO2:Mn Surfaces

Introduction: It is well known, that titanium dioxide (TiO2) nanoparticles can lead to the generation of reactive oxygen species (ROS) upon photoexcitation. Method: In this work, we investigated mesoporous surfaces based on TiO2 nanoparticles doped with 0.6-0.7% manganese (Mn), which showed reduced photoactivity and were based on the more stable rutile polymorph of titania. Result: In particular, we showed spectrophotometrically that the enzyme glucose oxidase (GOD) can be successfully adsorbed up to 80% while retaining its bioactivity in contact with the TiO2:Mn-based surface. Conclusion: We propose that this study could potentially give rise to biocompatible surfaces for biosensing applications.

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.

Multiscale modelling of CO2 hydrogenation of TiO2-supported Ni8 clusters: on the influence of anatase and rutile polymorphs

The selection of TiO2 phase, whether anatase or rutile, for supporting small Ni clusters significantly influences the activity and selectivity in CO2 hydrogenation to methane.

Pt-TiO2 catalysts for glycerol photoreforming: comparison of anatase, brookite and rutile polymorphs.

We compared the H2 production from glycerol photoreforming for different TiO2 polymorphs, highlighting an increase of activity in the order Pt-rutile < Pt-P25 ≈ Pt-anatase < Pt-brookite with a different distribution of the reaction intermediates. We show that the highest ability to adsorb water and the different distribution of Pt active sites in brookite can positively influence its photoactivity.

Non-resonant inelastic X-ray scattering for discrimination of pigments.

Inelastic X-ray scattering (IXS) spectroscopy has been used in many fields of solid-state physics and theoretical chemistry as an accurate and quantitative probe of elementary excitations. We show that non-resonant IXS spectra in the energy loss range below 100 eV exhibit a strong contrast across a wide range of commercially available pigments, opening new routes for their discrimination. These signatures combine plasmonic transitions, collective excitations and low energy absorption edges. We have performed IXS to discriminate different artists' pigments within complex mixtures and to quantitatively determine rutile and anatase polymorphs of TiO2. The integration of experimental data on pigment powders with suitable ab initio simulations shows a precise fit of the spectroscopic data both in the position of the resonances and in their relative intensity.

The optical properties and spectroscopic limited maximum efficiency of SnO2 polymorphs for solar cell applications: A first-principles analysis

Considerable research has been focused on the synthesis and characterization of several polymorphs of tin dioxide (SnO2). However, these polymorphs remain somewhat rare in modern photovoltaic applications. Due to their low cost and ultrahigh power conversion efficiency, hybrid organic-inorganic lead perovskites have caused a revolution among solar cell researchers. This study provides crucial insights into the optical behavior of SnO2 polymorphs, offering a valuable foundation for their potential applications in advanced electronic and photovoltaic technologies. The effective mass of stable SnO2 polymorphs has been computed and the charge carrier dynamics of SnO2 polymorphs, informing the selection and design of materials. Moreover, the SLME of SnO2 polymorphs was also computed and compared to that of other efficient perovskite solar cells. Both Pnnm and Pbca have equivalent efficiency in comparison to the rutile polymorph. Three of the seven stable polymorphs are effective in solar cell applications. This research represents the initial effort to investigate the atomic composition and electrical characteristics of different SnO2 polymorphs by the utilization of XANES, specifically at the Sn-K-edge and O-K-edge wavelengths. Our findings, as mentioned in this paper, may be an important advancement in the understanding of these materials, thereby facilitating the development of more efficient photovoltaic devices.

Elektrolit içerisindeki bor miktarının PEO ile kaplanan Ti45Nb'nin korozyon özelliklerine etkisi

Developing more biocompatible biomaterials with mechanical properties similar to those of cortical bone has long been a challenge for scientists. They are still working on new alloys and coating processes to meet this challenge. Among these biocompatible materials, ß-titanium alloys, which will prevent stress-shielding and have a Poisson’s ratio very close to the cortical bone, have been attracting the attention of scientists for a long time. In addition to this, the PEO method, which makes it possible to embed ions into the oxide layer, has also come to the fore in recent years as a surface treatment in order to increase the corrosion resistance, wear resistance and biocompatibility of biomaterials and also to provide antibacterial/antimicrobial properties. In this study, Ca and P-containing oxide layers with two different boron content and no boron content were successfully formed on Ti45Nb ß-titanium alloy substrate by using the PEO method. Surface characterization and corrosion resistance tests of these layers were carried out. The obtained results were compared with each other and with the uncoated substrate. XRD analysis showed that the coatings are primarily composed of two major polymorphs of TiO2, anatase and rutile. Static electrochemical measurements were made in diluted Foetal Bovine Serum (FBS) and hydrogen peroxide added serum. H2O2 was added to simulate the inflammatory state in the body. The measurements showed that all the coated samples had lower corrosion current densities compared to the uncoated ones both in serum and H2O2-added serum.

Quantification of titanium dioxide (TiO2) anatase and rutile polymorphs in binary mixtures by Raman spectroscopy: an interlaboratory comparison

This article presents an interlaboratory comparison (ILC) on Raman spectroscopy as a technique for relative quantification of the two most common polymorphs of titanium dioxide (TiO2)—anatase and rutile—in binary mixtures. Some standard methods are currently employed internationally for the determination of TiO2 content in samples (ISO 591-1, ASTM D3720-90), but require extensive sample preparation, do not distinguish between the two polymorphs or are accurate only for small fractions of either polymorph. Raman spectroscopy is a well-suited characterization technique for measuring and differentiating TiO2 in a fast, non-invasive way, while requiring no particular reagent or sample preparation. Eleven international participants conducted the study under the framework of Versailles Project on Advanced Materials and Standards. The collected data was analyzed by means of partial least squares regression after spectral preprocessing. The resulting models all show discrepancies of lower than 2% from the nominal values in the quantitative analysis over the concentration range of 5%–95% mixture fractions, with many datasets showing substantial improvement margins on this figure. The results of this ILC provide validation of Raman spectroscopy as a reliable method for quantification of TiO2 phases.

Electroabsorption as a Probe of Electrons Injected into Nanocrystalline SnO2/TiO2 Core/Shell Thin Films

Core/shell nanoparticles comprised of a SnO2 core and a TiO2 shell, SnO2/TiO2, present in a mesoporous thin film, are of practical interest for applications in dye-sensitized water splitting as they outperform sensitized materials based on SnO2 or TiO2 (anatase or rutile polymorphs) for the water oxidation half-reaction. Here we report electroabsorption studies designed to quantify the surface electric field and the ability of the shell to screen an electric field from a surface anchored dye. The metal-to-ligand charge transfer (MLCT) absorbance of [Ru(bpy)2(4,4′-(PO3H2)2-2,2′-bipyridine)](PF6)2, abbreviated RuP, was indeed sensitive to electron injection into the oxide support. When a fixed charge of 1 mC was injected, the electric field magnitude (in MV/cm) increased in the order 0.15 TiO2 (rutile) < 0.35 TiO2 (anatase) ≪ 1.4 SnO2 (rutile). This order tracks the reported bulk dielectric constants of the oxide materials. Comparative studies with SnO2/TiO2 core/shell materials, fabricated by atomic layer deposition (ALD) of a TiO2 shell on a mesoporous SnO2 thin film, diminished the field strength by about a factor of 4 to values less than or about equal to that measured for anatase TiO2. Heat treating some SnO2/TiO2 core/shell materials at 450 °C resulted in a crystalline rutile TiO2 shell that screened the field most effectively, more so even than rutile TiO2 alone. Taken together, the data indicate that injected electrons reside within the SnO2 core region.

Nanostructured Iridium Oxide: State of the Art

Iridium Oxide (IrO2) is a metal oxide with a rutile crystalline structure, analogous to the TiO2 rutile polymorph. Unlike other oxides of transition metals, IrO2 shows a metallic type conductivity and displays a low surface work function. IrO2 is also characterized by a high chemical stability. These highly desirable properties make IrO2 a rightful candidate for specific applications. Furthermore, IrO2 can be synthesized in the form of a wide variety of nanostructures ranging from nanopowder, nanosheets, nanotubes, nanorods, nanowires, and nanoporous thin films. IrO2 nanostructuration, which allows its attractive intrinsic properties to be enhanced, can therefore be exploited according to the pursued application. Indeed, IrO2 nanostructures have shown utility in fields that span from electrocatalysis, electrochromic devices, sensors, fuel cell and supercapacitors. After a brief description of the IrO2 structure and properties, the present review will describe the main employed synthetic methodologies that are followed to prepare selectively the various types of nanostructures, highlighting in each case the advantages brought by the nanostructuration illustrating their performances and applications.

Optical, structural and semiconducting properties of Mn doped TiO2 nanoparticles for cosmetic applications

Titanium dioxide (TiO2) nanoparticles, have been routinely used in cosmetic and sunscreen applications, due to their ability to absorb in the UV spectrum. Nevertheless, one of the main disadvantages has been the generation of reactive oxygen species (ROS), especially the hydroxyl radical, upon photoexcitation of titania. In this work, we investigate TiO2 nanoparticles doped with 0.6–0.7% manganese (Mn), based in the more stable rutile polymorph of titania. In particular, while the anatase crystal form has the ability to destroy almost any organic matter under UV illumination, rutile is less photoreactive, and with Mn doping its photoactivity is reduced further. In particular, we study its optical, structural and semiconducting properties via the Seebeck effect and show that the material displays p-type characteristics. This is very significant because it shifts the energy levels with respect to formation of hydroxyl free radicals. This ensures that for Mn doped p-type titania it is not energetically possible for the hole created in the valence band by photoexcitation to create an OH. free radical and this may explain its low photoreactivity. It also means that this material can act as a very effective scavenger for hydroxyl free radicals.

Synthesis and Characterization of Graphite Oxide Derived TiO2-Carbon Composites as Potential Electrocatalyst Supports

TiO2-C (carbon) hybrid materials are promising electrocatalyst supports because the presence of TiO2 results in enhanced stability. Use of new types of carbonaceous materials such as reduced graphene oxide instead of traditional active carbon provides certain benefits. Although the rutile polymorph of TiO2 seems to have the most beneficial properties in these hybrid materials, the anatase type is more frequent in TiO2-rGO composites, especially in graphite oxide (GO) derived ones, as GO has several properties which may interfere with rutile formation. To explore and evaluate these peculiarities and their influence on the composite formation, we compared TiO2-C systems formulated with GO and Black Pearls (BP) carbon. Various physicochemical methods, such as attenuated total reflection infrared (ATR-IR)-, solid state NMR-, Raman- and X-ray photoelectron spectroscopy, X-ray powder diffraction (XRD), electron microscopy, etc. were used to characterize the samples from the different stages of our multistep sol–gel synthesis. Our experiments demonstrated that utilization of GO is indeed feasible for composite preparation, although its sodium contamination has to be removed during the synthesis. On the other hand, high temperature treatment and/or solvothermal treatment during composite synthesis resulted in decomposition of the functional groups of the GO and the functional properties of the final product were similar in case of both composites. However, Pt/TiO2-GO derived sample showed higher oxygen reduction reaction activity than Pt/TiO2-BP derived one. Based on the decrease of electrochemical surface area, the stability order was the following: Pt/C (commercial) < Pt/TiO2-BP derived C < Pt/TiO2-GO derived C.

Titanium Dioxide in Commercial Sunscreens: the Morphological Characterization and the Quantification

<p class='IJASEITAbtract'>Due to nanotechnology's advancement, the application of nanomaterials in commercial products, including in sunscreens, has been increased rapidly. Physical sunscreens employ Titanium dioxide (TiO₂) or Zinc oxide (ZnO) nanoparticles as UV filter materials. Indonesian National Agency of Drug and Food Control regulates that TiO₂ rutile polymorph, size distribution ≥30 nm, and maximum concentration of 25% are criteria for physical sunscreen marketed in Indonesia. However, most of these products do not indicate the detailed inorganic material information in the product ingredients, resulting in the increasing concern of nanoparticle’s risk to human health and the environment. Therefore, the size, type of crystal structure, and amount of TiO2 or ZnO must be closely monitored. In this work, we investigated the morphological structure of TiO_2, including quantified its concentration in some commercial sunscreens marketed in Indonesia. TiO₂ was characterized using different characterization techniques. XRD analysis revealed that some studied sunscreens employed anatase TiO_2, which is not suggested to be added in a sunscreen product. HRTEM analysis proved that the sizes of materials in sample S1-S3 are below 50 nm, and silica-coated TiO₂ was observed in S4. Quantification of Titanium using GF-AAS yielded Ti's concentration in the range of 1400-7800 µg g^-1 (0.14-0.79%). To the best of our knowledge, this is the first study to report the physical properties and the concentration of TiO₂ nanoparticles (NPs) in commercial sunscreen marketed in Indonesia.

Anatase TiO2 decorated CuCr2O4 nanocomposite: A versatile photocatalyst under domestic LED light irradiation

The rutile and anatase polymorphs of TiO2 are the most extensively studied photocatalyst materials with the efficient absorption in the violet to near ultra violet region of the electromagnetic spectrum, which boost tremendous research endeavors in increasing the photocatalytic activity of TiO2 under visible light sources through rational modifications. Here, we report the astonishing performance of CuCr2O4(CCO)/anatase-TiO2 nanocomposite as a Fenton like catalyst with potential impact for sustainable design and environmental protection. All the materials were thoroughly characterized by several physico chemical techniques. CCO/TiO2 nanocomposite obtained by heat-treatment at 400 °C is found to exhibit high performance towards degradation of azo dyes like methylene blue (MB), rhodamine B (RhB) and methyl orange (MO), antibiotics like tetracycline hydrochloride and norfloxacine, and a promising Pt-free candidate for photoelectrocatalytic oxygen evolution reaction under domestic light emitting diode (LED) light irradiation. CCO/TiO2 shows high recycling activity and chemical stability. Under domestic visible LED light irradiation, the electrons are photoexcited from the conduction band of CCO to that of TiO2 resulting in enhanced charge separation eventually facilitating the catalytic performance of the nanocomposite. TiO2 plays two primordial roles, firstly, it acts as an electron receiver to improve the charge separation in the nanocomposite and secondly, it participates in the Fenton like reaction.

Chemical Modification of Polaronic States in Anatase TiO2(101).

Two polymorphs of TiO2, anatase and rutile, are employed in photocatalytic applications. It is broadly accepted that anatase is the more catalytically active and subsequently finds wider commercial use. In this work, we focus on the Ti3+ polaronic states of anatase TiO2(101), which lie at ∼1.0 eV binding energy and are known to increase catalytic performance. Using UV-photoemission and two-photon photoemission spectroscopies, we demonstrate the capability to tune the excited state resonance of polarons by controlling the chemical environment. Anatase TiO2(101) contains subsurface polarons which undergo sub-band-gap photoexcitation to states ∼2.0 eV above the Fermi level. Formic acid adsorption dramatically influences the polaronic states, increasing the binding energy by ∼0.3 eV. Moreover, the photoexcitation oscillator strength changes significantly, resonating with states ∼3.0 eV above the Fermi level. We show that this behavior is likely due to the surface migration of subsurface oxygen vacancies.

Extraction–Pyrolytic Method for TiO2 Polymorphs Production

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO2) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) for the production of nanocrystalline TiO2 powders. A titanium-containing precursor (extract) was prepared by liquid–liquid extraction using valeric acid C4H9COOH without diluent as an extractant. Simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC), as well as the Fourier-transform infrared (FTIR) spectroscopy were used to determine the temperature conditions to fabricate TiO2 powders free of organic impurities. The produced materials were also characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The results showed the possibility of the fabrication of storage-stable liquid titanium (IV)-containing precursor, which provided nanocrystalline TiO2 powders. It was established that the EPM permits the production of both monophase (anatase polymorph or rutile polymorph) and biphase (mixed anatase–rutile polymorphs), impurity-free nanocrystalline TiO2 powders. For comparison, TiO2 powders were also produced by the precipitation method. The results presented in this study could serve as a solid basis for further developing the EPM for the cheap and simple production of nanocrystalline TiO2-based materials in the form of doped nanocrystalline powders, thin films, and composite materials.

Phase evolution and optical properties of nanometric Mn-doped TiO2 pigments

This paper aims to evaluate the effects of calcination temperature and manganese doping on optical properties and phase evolution of Mn-doped TiO2 pigments. The powders were prepared by the polymeric precursor method at Mn contents of 0, 1, 2 and 3 % and calcined at 600, 700 and 800 °C. The results demonstrated that crystalline powders were produced in all conditions evaluated. It was further noted that the samples calcined at 600 °C were composed of rutile and anatase TiO2 polymorphs. However, the anatase phase was completely converted into rutile at temperatures above 700 °C. The particle size increased with increasing temperature. The same behavior was observed for the measured crystallite sizes. The Mn3+ ion charge was determined as the main valence for manganese ions in the TiO2 host. Oxygen vacancies are the probable crystal defects formed for charge balancing in the Mn-doped rutile structure. The results obtained for the powder with 3 % Mn and calcined at 800 °C demonstrated dopant cation segregation to form Mn2O3. It is important to emphasize that the absorbance values of the powders increase in the visible range when adding manganese compared to the absorbance values of pure TiO2. The band gap of the powders was reduced in accordance with the content of doping: from 3.04 eV (0 % Mn) to 2.05–2.20 eV (3 % Mn), with small differences depending on the calcination temperature. The increase in visible light absorbance led to a brown color in Mn-doped materials. Thus, the color intensity varied with the Mn content, ranging from light brown to dark brown powders. In conclusion, the temperature of 700 °C was established in this paper as the best condition to produce Mn-doped TiO2 pigments, based on the absence of anatase polymorph, small contents of residual carbon, and undetectable amounts of Mn2O3 due to segregation.