Titania Materials Research Articles

Synergistic effects of carbon doping and coating of TiO2 with exceptional photocurrent enhancement for high performance H2 production from water splitting

The “one pot” simultaneous carbon coating and doping of TiO2 materials by the hydrolysis of TiCl4 in fructose is reported. The synergistic effect of carbon doping and coating of TiO2 to significantly boost textural, optical and electronic properties and photocurrent of TiO2 for high performance visible light H2 production from water splitting has been comprehensively investigated. Carbon doping can significantly increase the thermal stability, thus inhibiting the phase transformation of the Titania material from anatase to rutile while carbon coating can suppress the grain aggregation of TiO2. The synergy of carbon doping and coating can not only ensure an enhanced narrowing effect of the electronic band gap of TiO2 thus extending the absorption of photocatalysts to the visible regions, but also promote dramatically the separation of electron-hole pairs. Owing to these synergistic effects, the carbon coated and doped TiO2 shows much superior photocatalytic activity for both degradation of organics and photocatalytic/photoelectrochemical (PEC) water splitting under simulated sunlight illumination. The photocatalytic activity of obtained materials can reach 5, 4 and 2 times higher than that of pristine TiO2, carbon doped TiO2 and carbon coated TiO2, respectively in the degradation of organic pollutants. The carbon coated and doped TiO2 materials exhibited more than 37 times and hundreds of times photocurrent enhancement under simulated sunlight and visible light, respectively compared to that of pristine TiO2. The present work providing new comprehensive understanding on carbon coating and doping effect could be very helpful for the development of advanced TiO2 materials for a large series of applications.

Thermal techniques as a tool for the direction of the preparation of photocatalytically efficient titania thin films and powders

Photocatalytically active titania thin films and powders were prepared via sol–gel route from TiCl4 precursor. Organic polymer hydroxypropyl cellulose was added into sol in order to increase active surface area. Thin films were deposited onto substrates using dip-coating technique. Thin films and xerogels were thermally treated in a muffle furnace to a different extent. Temperature of heat treatment was determined using thermogravimetry and differential scanning calorimetry, while X-ray diffraction was used to identify the formation of the anatase phase, eventual presence of other crystalline formations and the average particle size. The shape and size of the pores of the selected thin films were analyzed using SEM, while specific surface area of selected thermally treated xerogels was determined using Brunauer–Emmett–Teller (BET) surface area analysis. Measurements of photocatalytic efficiency of thin films and powders were performed by FT-IR spectroscopy; for thin films on the basis of diminishing C–H stretching vibrations of model fatty compound methyl stearate during irradiation with UVA light, while in the case of powders the oxidation of isopropanol into acetone was the model photocatalytic reaction. Obtained results confirm that different factors, such as particle size, porosity, thickness of thin film, the presence and type of crystalline titania modification have a substantial effect on photocatalytic efficiency of prepared titania materials.

The Photocatalytic Activity of Titania Coatings Produced by Electrochemical and Chemical Oxidation of Ti6Al4V Substrate, Estimated According to ISO 10678:2010The Photocatalytic Activity of Titania Coatings Produced by Electrochemical and Chemical Oxidation of Ti6Al4V Substrate, Estimated According to ISO 10678:2010.

The last twenty years have been a period of intense investigations of materials based on titanium dioxide, which have unique properties and functionalities, and which can be used in various areas of medicine. As a part of this issue, the results of our works for the assessment of the photocatalytic activity of titanium dioxide nanocoatings of different nanoarchitecture (nanoporous, nanotubular, nanosponge-like and nanofibrous examples), which were earlier checked in terms of their biocompatibility and usability for the modification of medical devices’ surfaces, are presented. The studied materials were produced on the surface of Ti6Al4V substrates using electrochemical and chemical oxidation methods. The activity of produced titania materials was studied on the base of the methylene blue (MB) degradation effect, in accordance to ISO 10678:2010. In our works, we have focused on the analysis of the correlation between the photocatalytic activity of nanoarchitecturally different TiO2 coatings, their morphology and structure. The obtained results prove that all studied coatings, both amorphous and amorphous containing crystalline domains, revealed photocatalytic activity in the photoinduced degradation of the organic pollution standard. This activity may be an additional advantage of medical device coatings, being adequate for use in sterilization processes applying UVA light.

Functionalized nanomaterials for biomass conversion

The valorization of the biomass is, nowadays, considered an eco-sustainable approach for the production of biofuels and added-value platform molecules. This research will focus on different types of functionalized silica or titania based materials applied both to the synthesis of added-value products (in particular GVL, HMF and pentandiols) and to the biodiesel production and its additives. As concern the nanomaterials, silica or titania materials were functionalized, by using several approaches, with organic (acid) frameworks or inorganic (Pd, Au, Ti) catalytic functions depending on the organic reaction in which they were applied. According to the principle of the circular chemistry, special attention was paid to the sustainability of the chemical processes, green working conditions, heterogeneous catalysis and use of wastes.

Solvothermal hydrodeoxygenation of hydroxymethylfurfural derived from biomass towards added value chemicals on Ni/TiO2 catalysts

Lignocellulosic biomass is one of the most abundant renewable source of commodity chemicals like hydroxymethylfurfural. Solvothermal hydrodeoxygenation of hydroxymethylfurfural towards value added chemicals was performed with a series of nickel based catalysts supported on different titania materials, ie. hydrothermally-prepared high aspect ratio and commercial TiO2 with different morphologies and crystallographic structures. The kind of titania strongly influenced the properties of the supported nickel nanoparticles, which allowed to tune the reaction selectivity towards specific products. Rutile-containing titania forced stronger Ni-Ti interaction, enhanced hydrogen adsorption, and formed larger Ni particles which resulted in high activity. Hydrothermally-prepared materials allowed to obtain selectively 2,5-bishydroxymethyltetrahydrofuran (biopolymer precursor) due a relatively small surface acidity and large Ni particles. By contrast, large surface area anatase with small nickel particles and small surface acidity allowed to selectively obtain 2,5-dimethylfuran (biofuel additive).

The geometry of free-standing titania nanotubes as a critical factor controlling their optical and photoelectrochemical performance

Titanium dioxide nanotubes are regarded as one of the most important functional materials and due to their unique electronic properties, chemical stability and photocorrosion resistance, they find applications in, for example, highly efficient photocatalysis or perovskite solar cells. Nevertheless, modification of TiO2 nanotubes is required to overcome their main drawback, i.e. large energy bandgap (>3.2 eV) limiting their ability to capture solar light. In this work, we report the changes in optical and photoelectrochemical properties of well-separated TiO2 nanotubes that are tuned by varying the geometry of the material. The ordered tubular titania is formed via anodization in the presence of fluoride ions in diethylene glycol at elevated temperature. Length, inner diameter, wall thickness, and separation distance are described in function of synthesis parameters such as applied voltage and duration. The morphology and optical properties are characterized by means of scanning electron microscopy and UV–Vis spectroscopy techniques, respectively, while cyclic voltammetry, linear voltammetry and chronoamperometry are used to determine electrochemical/photoelectrochemical activity in different light conditions. The obtained results suggest a link between specific surface area, the width of the band-gap, and photoactivity, each of which could be individually optimised via anodization conditions. Moreover, the behaviour of the Mott-Schottky plot before and after 3 min of irradiation is studied indicating the positive shift of the flat band position and an increase in donor density values for all the obtained materials. The Mott-Schottky analysis was correlated with the linear voltammetry scans suggesting the important role of surface trapped holes. Presented in here results significantly supplement the current state-of-art regarding separated TiO2 nanotubes that are considered as not fully investigated and unappreciated class of titania materials which due to the exposure of inner and outer wall can be used for further modifications.

Exotic Nanostructured Titania Supports for Deep Hydrodesulfurization Catalysts: Are They Better Than the Conventional Ones?

In the present work, we compared the hydrodesulfurization (HDS) behavior of NiMo catalysts supported on titania-based nanomaterials (hydrogen titanate nanotubes and nanotubes decorated with anatase nanocrystals), with that of the reference NiMo/γ-alumina and NiMo/TiO2 samples. Supports and calcined catalysts were characterized by nitrogen physisorption, powder XRD, UV–Vis diffuse reflectance spectroscopy, Raman spectroscopy, temperature-programmed reduction, scanning electron microscopy and high resolution transmission electron microscopy (HRTEM). The sulfided catalysts were characterized by HRTEM and evaluated in the HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). In the hydrodesulfurization of DBT, all catalysts supported on nanostructured titania materials showed similar activity as the NiMo/Al2O3 reference. However, their selectivity towards the hydrogenation pathway of the reaction was significantly higher than that of the alumina-supported reference. In the hydrodesulfurization of 4,6-DMDBT, activities of the synthesized NiMo catalysts supported on titania-based nanomaterials were about 50% superior to that of the NiMo/Al2O3 reference. This is an interesting result, since the majority of the conventional NiMo or CoMo catalysts are significantly more active for the elimination of DBT than of the sterically-hindered 4,6-DMDBT. The presence of small titania anatase crystallites in the nanostructured supports had a slight positive effect on the catalytic activity of the NiMo catalysts in HDS of 4,6-DMDBT, and a more noticeable effect on an increase in their hydrogenation ability (production of larger amounts of methylcyclohexyltoluene in the products).

SYNTHESIS AND OPTICAL PROPERTY CHARACTERIZATION OF METAL ION AND HETERO ATOM DOPED TiO2 NANOCOMPOSITE FABRICATION FOR PHOTO CATALYSIS

The transition metal ions and heteroatoms such as iron cobalt and nickel modified titania were synthesized by insitu precipitation and hydrothermal technique. Prepared materials are further treated by thermal analysis towards crystalline phase formation. The particle size of prepared titania calculated from intense d-space values of prepared materials and it is found to be 22-23 nm. Raman spectra and the DR UV-Visible spectra of metal ion and nitrogen doped titania extends to the visible region (450-650 nm). Methylene blue (MB) dye degradation was performed to evaluate the photosensitivity property of the as prepared materials under sun light irradiation. Metal ion modified titania (0.01Fe- TiO2, 0.01CoTiO2 and 0.01Ni-TiO2) materials are showing complete degradation of MB. For the comparison purpose, the powder nanotitania samples are prepared and also coated on ITO (indium tin oxide) plates by electrodeposition method. XRD and DRS properties of coated titania were tested for electrode application.

Anomalous potential dependence of conducting property in black titania nanotube arrays for electrocatalytic chlorine evolution

Ru- and Ti-based oxide electrocatalysts have been intensively studied for chlorine evolution reactions since their synergistic effect was demonstrated in commercial dimensionally stable anodes. Basically, oxide materials intrinsically possess a semiconducting nature; therefore, tuning conducting properties is important in achieving high electrocatalytic activity. Here, black TiO2 nanotube arrays deposited with RuO2 by pulsed electrodeposition are investigated as a three-dimensional supporting electrode for chlorine and hydrogen evolution. RuO2-loaded black titania achieves high chlorine evolution activity (10 and 100 mA cm−2 at 1.090 and 1.125 V vs. SCE) with a faradaic efficiency of 95.25% while RuO2-loaded titania has no activity, though hydrogen evolution reaction performance is similar. This suggests that the type of titania support affects the conducting property at anodic potentials and chlorine evolution activity. This work provides new insights into the importance of black titania materials in enhancing the electrocatalytic activity of anodic reactions.

Modelling uranyl-ions sorption by nanostructured composite anatase-based materials

Influence of complex formation in solution on U sorption has been studied for mesoporous nanostructured anatase-based composites. Uranium sorption degree has been shown to correlate with the stability of the complexes in solution. A model for uranium sorption by titania materials has been suggested presuming two-stage sorption mechanism. It is assumed that initial binding of neutral and positively charged uranyl complexes to negatively charged hydroxyl groups occurs on the first stage, while decomposition of complex ion proceeds on the second stage with the UO2 being fixed on sorption sites. Prevailing uranium species in solution and kinetics of their ratios have been determined. Calculated rates of evolution of uranyl ion species distribution (therefore, rate and efficiency of the sorption) correlate well with complex stability in solution.

Towards thermally stable aerogel photocatalysts: TiCl4-based sol-gel routes for the design of nanostructured silica-titania aerogel with high photocatalytic activity and outstanding thermal stability

Despite their excellent textural/structural properties, usage of aerogels in photocatalytic applications is critically limited by the necessity of high temperature annealing procedures to improve crystallinity, which lead to drastically decrease in surface area and the undesirable phase transformations. In this study, we report two novel straightforward TiCl4-based sol-gel routes for synthesis of SiO2/TiO2 nanocomposite and SiO2@TiO2 core-shell aerogels with exceptional photocatalytic performance even after annealing at temperatures as high as 1000 °C. While core-shell aerogels prepared by thermo-induced deposition method show higher and unprecedented thermal stability, epoxide-assisted gelation method offers greater control over phase composition, allowing preparation of highly photoactive anatase/rutile bicrystalline silica-titania nanocomposite aerogels. The improved structural properties achieved result in an increase of photocatalytic activity of silica-titania aerogels after high temperature annealing at 1000 °C. Such unusually high thermal stabilities outperform those shown by previously reported titania and silica-titania materials, representing significant advance on the design of thermally stable photocatalysts for applications that require the catalyst to undergo high temperature processing or endure extreme operating conditions.

Titanium Dioxide-Based Nanocomposites for Enhanced Gas-Phase Photodehydrogenation.

Light-driven processes can be regarded as a promising technology for chemical production within the bio-refinery concept, due to the very mild operative conditions and high selectivity of some reactions. In this work, we report copper oxide (CuO)-titanium dioxide (TiO2) nanocomposites to be efficient and selective photocatalysts for ethanol photodehydrogenation under gas phase conditions, affording 12-fold activity improvement compared to bare TiO2. In particular, the insertion method of the CuO co-catalyst in different TiO2 materials and its effects on the photocatalytic activity were studied. The most active CuO co-catalyst was observed to be highly dispersed on titania surface, and highly reducible. Moreover, such high dispersion was observed to passivate some surface sites where ethanol is strongly adsorbed, thus improving the activity. This kind of material can be obtained by the proper selection of loading technique for both co-catalysts, allowing a higher coverage of photocatalyst surface (complex-precipitation in the present work), and the choice of titania material itself. Loading copper on a high surface area titania was observed to afford a limited ethanol conversion, due to its intrinsically higher reactivity affording to a strong interaction with the co-catalyst.

Development of magnetically separable mesoporous N doped TiO2-SiO2 coated Fe3O4 nanomaterial as solar photocatalyst for environmental application

Present paper deals with the synthesis of visible light sensitive, easily separable mesoporous magnetic titania material having Fe3O4 in the core as solar photocatalyst. Core Fe3O4 was synthesized by two different methods for comparative evaluation. Top titania layer was found to be mesoporous thus providing more active sites. Synthesized materials were characterized by UV–vis, XPS, XRD, TEM and Raman. Core Fe3O4 prepared from Fe(II) and Fe(III) salts showed higher magnetic moment having nanosized particles. On the other hand, the hydrazine method resulted in the formation of tubular iron oxide having low magnetic moment. XRD and Raman spectra support the formation of porous anatase phase on the top and below SiO2 layer properly shielded magnetic core. The final magnetic moment of 7.8 emu in case of iron oxide obtained from Fe(II) and Fe(III) salts indicates that the magnetic separation by applying an external magnetic field is easy. Nitrogen doping of top titania layer increases the visible light absorption and photocatalytic efficiency. Comparative evaluation towards the photocatalytic decomposition of para-nitrophenol and methylene blue was carried out to observe the effect of N doping. The synthesized material is found to be stable and reusable for at least five times without any marked change in the catalytic activity and magnetic moment. Synergistic effect of mesoporosity, presence of oxygen vacancy and N doping on titania facilitates the higher rate of MB and p-NP degradation under visible light.

Carbon nitride and titania nanoparticles prepared using porous silica templates and photocatalytic activity

Abstract This work examined the band structure and photocatalytic activity of carbon nitride and titania nanoparticles prepared using porous silica templates with pore sizes of approximately 1 and 3 nm. The carbon nitride and titania specimens prepared in this manner exhibited absorption edge blue shifts compared to bulk samples, due to expansion of their band gap resulting from quantum size effects. The photocatalytic activity of these materials during hydrogen production from water was assessed, and the activity of carbon nitride prepared in the 1 nm pores was higher than that of the material made using 3 nm pores as well as that of the bulk carbon nitride. These results suggest that the expansion of the HOMO-LUMO energy gap contributed to increasing the catalytic performance. In contrast, the titania materials did not generate hydrogen. X-ray absorption fine structure analyses demonstrated that the titania in the silica templates had a distorted structure, which may have decreased its photocatalytic activity.

Size-dependent selectivity and activity of CO2 photoreduction over black nano-titanias grown on dendritic porous silica particles

Titania (TiO2) materials show great promising for photocatalytic CO2 reduction into solar fuels. However, the CO2 conversion efficiency of most TiO2-based photocatalysts is still low up to now, which mainly results from their low accessible active surface areas and weak light-absorption ability. Herein, we employed dendritic porous silica nanospheres (DPSNs) with high accessible internal surface as carriers to successfully fabricate a series of efficient and robust DPSNs@X% TiO2-x (X%: weight ratio of TiO2/DPSNs) composite photocatalysts with tunable sizes of black TiO2-x NPs. For CO2 photocatalytic selectivety and activity, only CO was generated for 1–3 nm of small TiO2-x NPs on DPSNs@X% TiO2-x (X% ≤ 20%), while both CO and CH4 were produced for 3–12 nm of larger TiO2-x NPs on DPSNs@X% TiO2-x (X% ≥ 40%). Noteworthily, DPSNs@80% TiO2-x showed ultrahigh CH4 production rate of 124.3 μmol g-TiO2-x−1 h−1, moderate CO production rate of 14.7 μmol g-TiO2-x−1 h−1 and high photocatalytic stability. The excellent photocatalytic performance should be attributed to be well-dispersed distribution, appropriate particle sizes, and suitable reduction degree of TiO2-x NPs on the pore surface of DPSNs@80% TiO2-x with high accessible specific surface area (208 m2 g−1). Furthermore, these characteristics lead to higher CO2 adsorption capacity, much lower recombination rate of photogenerated electrons and holes, and enhanced carrier transfer and separation in black TiO2-x, thus demonstrating dramatically high CO2 photoreduction activity. This study may open new perspectives for the design of the supported photocatalysts, in which the morphologies and structures of the carriers are the key parameters.

Titania surface chemistry and its influence on supported metal catalysts

This work characterized the surface chemistry of a number of different titania samples including four commercial anatase samples, an anatase sample that we synthesized, the pyrogenic titania samples P25 and P90, and a commercial rutile sample. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), were used to identified surface species that might interfere with the acid/base properties of the surface hydroxyls. All commercial anatase samples were contaminated by sulfur, which diminished their effectiveness as metal oxide supports for heterogeneous catalysis and has implications for their utility as photocatalysts. Hydrogen-bonded surface hydroxyls remained after calcination up to 400 °C for all anatase samples, in contrast to rutile and the pyrogenic titania materials P25 and P90, in which they were eliminated. Ru(0) catalysts on titania without hydrogen-bonded surface hydroxyls showed enhanced CO hydrogenolysis selectivity in the presence of water while Ru(0) catalysts on titania with hydrogen-bonded surface hydroxyls showed diminished selectivity in water, suggesting that surface hydrophilicity is important for this reaction. Heteroepitaxy between rutile RuO2 and rutile TiO2 is not essential for the creation of small evenly-spaced supported Ru(0) nanoparticles, which are important in many catalytic reactions.

Activity of Atomically Precise Titania Nanoparticles in CO Oxidation.

Understanding the property evolution of atomically precise nanoparticles atom by atom along the size continuum is critical for selecting potential candidates to assemble nanomaterials with desired functionality, but it is very challenging experimentally especially for systems having mixtures of elements such as metal oxides. In this work, the capability to oxidize carbon monoxide has been measured experimentally for titania nanocluster anions of (TiO2 )n Om - (-3≤m≤3) across a broad size range in the gas phase. Stoichiometric (TiO2 )n O- exhibits superior oxidative activity over other clusters of (TiO2 )n Om - (m≠1) even when the cluster dimensions are scaled up to n=60, indicating that each atom still influences the chemical behavior of titania nanoparticles composed of ≈180 atoms. The fascinating result not only identifies a promising building block of Tin O2n+1 for devising new nanoscale titania materials with desirable oxidative activity, but also provides compelling molecular-level evidence for the Mars-van Krevelen mechanism of CO oxidation over titania supports.

Activity of Atomically Precise Titania Nanoparticles in CO Oxidation

AbstractUnderstanding the property evolution of atomically precise nanoparticles atom by atom along the size continuum is critical for selecting potential candidates to assemble nanomaterials with desired functionality, but it is very challenging experimentally especially for systems having mixtures of elements such as metal oxides. In this work, the capability to oxidize carbon monoxide has been measured experimentally for titania nanocluster anions of (TiO2)nOm− (−3≤m≤3) across a broad size range in the gas phase. Stoichiometric (TiO2)nO− exhibits superior oxidative activity over other clusters of (TiO2)nOm− (m≠1) even when the cluster dimensions are scaled up to n=60, indicating that each atom still influences the chemical behavior of titania nanoparticles composed of ≈180 atoms. The fascinating result not only identifies a promising building block of TinO2n+1 for devising new nanoscale titania materials with desirable oxidative activity, but also provides compelling molecular‐level evidence for the Mars–van Krevelen mechanism of CO oxidation over titania supports.

Characterisation and properties of visible light-active bismuth oxide-titania composite photocatalysts

Bismuth oxide – titanium dioxide composite materials were produced by pulsed DC reactive magnetron sputtering onto two types of commercially available titanium dioxide nanoparticles. The use of an oscillating bowl enabled deposition of bismuth oxide uniformly onto loose powders, in contrast to solid substrates typically used for the conventional magnetron sputtering processes. Variation of the deposition time allowed the production of composite materials with different amounts of bismuth oxide. The composite materials, as well as uncoated titania powders, were extensively analysed by a range of analytical techniques, including SEM/EDX, XRD, BET, XPS, TEM and UV–visible diffuse reflectance spectroscopy. Photocatalytic properties of the materials were assessed under simulated visible light irradiation via degradation of acetone and methanol through measurements of carbon dioxide evolution. Additionally, the composite materials were characterised with a newly developed technique of reversed double-beam photoacoustic spectroscopy in order to obtain information on the distribution of electron traps. Bismuth oxide was found in crystalline β-Bi2O3 form on both types of substrates without any additional heat treatment applied. Though the distribution of bismuth oxide on titanium dioxide was found to depend strongly on particle size and deposition time used, the composite materials exhibited significantly enhanced visible light photocatalytic activity compared to either of the commercial titania materials used as a substrate.

Double-layered hierarchical titanate and its attaching and splitting mechanism

Abstract Double-layered hierarchical titania materials exhibit outstanding properties. However, most hydrothermal synthesis methods of bilayer hierarchical titania materials are time-consuming and high alkali-consuming. In this study, a less alkali-consuming one-pot method was developed to synthesize bilayer hierarchical titanate, specifically, 1D nanoarray layer and 3D hierarchical layer. Morphologies of the composites can be manipulated by varying hydrothermal conditions and introducing titanate nuclei based on the attachment rule and splitting mechanism. More importantly, splitting phenomena were observed and confirmed in both nanosheet-to-nanowire transformation process and nanowire-to-nanotube transformation process. It was firstly confirmed that the driving force of the splitting process is the transformation from amorphous state titanate to crystalline state titanate.