Titania Support Research Articles

GO/TiO2 composites as a highly active photocatalyst for the degradation of methyl orange

Abstract

Disinfection of Water using Supported Titanium Dioxide Photocatalysts

TiO2 based photocatalyst has potential material for disinfection of harmful pathogens as well as removal of organic compounds. The formation of reactive oxygen species is a key part for overall process but aggregation and band gap constraint explore a new dimension to use of support for propounding its physicochemical properties. Therefore, the modification of TiO2 using various support alters photocatalytic action and promising ways of the mechanism based on nature of substrates and environments. In addition, the immobilization of nano dimension photocatalyst may reduce overall cost of operation and recovery of photocatalytic materials. In this perspective, extensive range of support materials as carbonaceous matters, clay, polymers, metal oxides have been studied by various researchers; that have been compiled in this review article. The properties of support were the key features for the assortment of appropriate supports for increase its efficiency as photocatalyst. In brief, overall TiO2 based photocatalyst supported on various substrates pave the ways toward new strategies for water disinfection.

Catalytic Dehydration of Ethanol over W/TiO2 Catalysts Having Different Phases of Titania Support

This study aims to investigate the catalytic behaviors on W/TiO2 catalysts having different phases of TiO2 towards catalytic dehydration of ethanol to higher value products including ethylene, diethyl ether, and acetaldehyde. In fact, TiO2 support with different crystalline phases can result in differences of physico-chemical properties of the catalyst. Therefore, the present work reports on the catalytic behaviors that were altered with different phases of TiO2 in catalytic ethanol dehydration to diethyl ether or ethylene as a major product. To prepare the catalysts, three different phases [anatase (A), rutile (R), and mixed phases (P25)] of TiO2 supports were impregnated with 10 wt% of tungsten (W). It was found that the W/TiO2-P25 catalyst revealed higher activity among other catalysts. At 300 °C, all catalysts can produce the diethyl ether yield of 24.1%, 22.8%, and 10.6% for W/TiO2-P25, W/TiO2-A, and W/TiO2-R catalysts, respectively. However, when the reaction temperature was increased to 400°C, ethylene is the major product. The W/TiO2-P25 and W/TiO2-A catalysts render the ethylene yield of 60.3% and 46.2%, respectively, whereas only 15.9% is obtained from W/TiO2-R catalyst. The most important parameter influencing their catalytic properties appears to be the proper pore structure, acidity, and distribution of W species. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Effects of impregnation sequence for Mo-modified V-based SCR catalyst on simultaneous Hg(0) oxidation and NO reduction

A series of molybdenum (Mo)-modified vanadium (V)-based selective catalytic reduction (SCR) catalyst samples were prepared by incipient impregnation method for the simultaneous removal of elemental mercury (Hg(0)) and nitrogen oxide (NO) under a simulated sub-bituminous coal combustion gas. The Hg(0) oxidation performances of the modified SCR catalysts significantly varied in terms of different formulations and impregnation sequences while NO reduction performance was quite stable. When Mo and tungsten (W) were sequentially doped onto titanium dioxide (TiO2) support followed by V, the modified SCR catalyst showed the best Hg(0) oxidation performance compared to those firstly doped with V onto TiO2 followed by Mo and W or V, Mo and W simultaneously doped onto TiO2. TEM, XPS and XANES results showed that the different impregnation sequences could result in the different particle sizes of MoO3 and the oxidation states of V and Mo speciation, which could lead to different Hg(0) oxidation performances.

Effect of Chemical and Physical Properties of Titanium Oxide Support Surface during Nitrogen Monoxide Reduction by Carbon Monoxide in Presence Water over Titanium Oxide Supported Platinum Catalyst

With the goal of developing a method for utilizing reactive nitrogen species emitted from combustion processes as raw materials for the synthesis of useful compounds, we investigated the selective conversion of NOx to NH3 by means of the NO–CO–H2O reaction over Pt/TiO2 catalysts. High NH3 selectivity was obtained for high-specific-surface-area catalysts. Catalytic activity tests revealed that the activities of catalysts depended on the crystal structure of the support. Comparing CO conversion between NO–CO–H2O reaction and CO–H2O reaction, which could play a role of H-supply reaction, Pt/TiO2 exhibited higher CO conversion for the NO–CO–H2O reaction than that for CO–H2O reaction except for high-surface-area anatase TiO2-supported catalyst around 200 °C. We focused on how the chemical and physical properties of the catalyst surface. Specifically, we carried out temperature-programmed desorption of CO2, which revealed that the CO2 formed during the NO–CO–H2O reaction had no effect on the difference in activity. Carbonaceous surface species and NHx species were observed on the surface of Pt/TiO2 catalyst during NO–CO–H2O reaction by diffused reflectance infrared Fourier transform spectroscopy, and difference in formate formation on anatase-TiO2 supported Pt catalyst was confirmed compared to rutile-TiO2 supported Pt catalyst. We supposed that the difference in activity between anatase and rutile TiO2 was caused by behavior of formate formation.

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.

Review on bimetallic-deposited TiO2: preparation methods, charge carrier transfer pathways and photocatalytic applications

Plasmonic metal structure that can host size-tunable optical properties and tailored catalytic surface active sites elicits peculiar functionalities upon integrating with semiconductors. In the case of metal–semiconductor composites, formation of Schottky barrier height and surface plasmon resonance (SPR) effect stimulated by the metallic dispersion cooperatively separates the charge carriers and alters the optical response to longer wavelength region, respectively, which are of paramount importance in the light-induced redox reactions. From the view point of attaining maximum synergy, bimetallic deposition over the titania support has impelled interest due to the supportive interactions arising from metal–metal and metal–TiO2 heterojunctions. In this review article, bimetallic systems constituting mainly Cu, Ni, Au, Ag, Pd and Pt over the titania surface are discussed under the light of preparative methods, their distribution, electronic interactions between the metals and with the titania support, charge carrier transfer pathways, structural stability and optimized content towards achieving maximum efficiency in various applications such as pollutant degradation, CO2 reduction, H2 evolution reaction (HER) and in the functional group conversion of few organic compounds. The role of each metal in the bimetallic system and the effects arising from structure–morphology features of titania are considered to furnish insightful discussion into this exquisite heterojunction. The bimetallic deposition over the other emerged semiconductors are briefly surmised to attest the versatility of this strategy and its reliability from several prospects are brought to the fore to provide the room for developing efficient bimetallic–semiconductor heterostructures.

Modification of O and CO binding on Pt nanoparticles due to electronic and structural effects of titania supports.

Metal oxide supports often play an active part in heterogeneous catalysis by moderating both the structure and the electronic properties of the metallic catalyst particle. In order to provide some fundamental understanding on these effects, we present here a density functional theory (DFT) investigation of the binding of O and CO on Pt nanoparticles supported on titania (anatase) surfaces. These systems are complex, and in order to develop realistic models, here, we needed to perform DFT calculations with up to ∼1000 atoms. By performing full geometry relaxations at each stage, we avoid any effects of "frozen geometry" approximations. In terms of the interaction of the Pt nanoparticles with the support, we find that the surface deformation of the anatase support contributes greatly to the adsorption of each nanoparticle, especially for the anatase (001) facet. We attempt to separate geometric and electronic effects and find a larger contribution to ligand binding energy arising from the former. Overall, we show an average weakening (compared to the isolated nanoparticle) of ∼0.1 eV across atop, bridge and hollow binding sites on supported Pt55 for O and CO, and a preservation of site preference. Stronger effects are seen for O on Pt13, which is heavily deformed by anatase supports. In order to rationalize our results and examine methods for faster characterization of metal catalysts, we make use of electronic descriptors, including the d-band center and an electronic density based descriptor. We expect that the approach followed in this study could be applied to study other supported metal catalysts.

Effect of titania support on Fischer-Tropsch synthesis using cobalt, iron, and ruthenium catalysts in silicon-microchannel microreactor

Syngas conversion into hydrocarbons using Fischer Tropsch (F-T) Synthesis was carried out to investigate the effect of TiO2 support on catalytic performance using 12% by weight of metal -12Co-TiO2, 12Fe-TiO2 and 12Ru-TiO2 in silicon (Si) microchannel microreactor (50 μm wide x100 μm deep) at different reaction temperatures and 1 atm. A modified closed channel infiltration (mCCI) method was used for successful uniform coating of the sol-gel catalyst layer in the micro-channels of Si-microrecators. Temperature Program Reduction profiles with H2 showed interaction of TiO2 with each metal to be significantly different; TPR of Fe-TiO2 and Co-TiO2 indicated a significant strong metal (Co and Fe) support interaction (SMSI), while that of Ru-TiO2 suggested a weaker metal-support interaction. The XRD studies of the catalysts suggest that unlike Fe- and Co-TiO2, Ru-TiO2 consists of mixed anatase and rutile phases of TiO2. The absence of rutile phase in Co-TiO2 and Fe-TiO2 had a profound effect on F-T activity in the range of 150 °C to 300 °C for CO conversion and hydrocarbon selectivity at 1 atm and decreased the stability of these two catalysts. The overall stability and reactivity was in the order: 12%Ru-TiO2>> 12%Fe-TiO2 > 12%Co-TiO2. These results are distinctly different from our previous studies with silica sol-gel in microreactor where a reverse trend was observed.

Effect of metal nanoparticle size and titania crystallinity on the performance of Au/TiO2 catalysts for the promotion of carbon monoxide oxidation at cryogenic temperatures

The ability of Au/TiO2 catalysts to promote the oxidation of carbon monoxide at cryogenic temperatures was probed by using diffuse-reflectance infrared absorption spectroscopy (DRIFTS). The focus of this work was to identify correlations between the catalytic activity and both the nature of the titania support and the size of the Au nanoparticles (NPs). Two key intermediates were identified: an initial CO adsorbed on defect sites within the titania support with a 2175 cm−1 C–O stretching frequency signature, and a second species with a DRIFTS peak at 2163 cm−1 associated with the intermediate at Au–TiO2 interfacial sites that incorporates atomic oxygen to produce CO2. CO adsorption at the low temperatures associated with this process (120 K) appears to require defective sites, possibly titanate-type surface species: an amorphous (and NaOH-treated) support showed higher activity than crystalline titania. In addition, the catalytic activity peaks at an Au NP average size of about 3 nm, which, in turn, correlates with the population of the second CO intermediate mentioned above. The mechanism that explains this cryogenic oxidation reaction is different than that extensively reported for the room-temperature processes, but both appear to display similar dependence on Au NP diameter.

Ultra-fine size-controlled Pt (111) nanoparticles supported on mesoporous titania as an efficient photoelectrocatalyst for hydrogen evolution

Synthetic methods that allow tuning of well-defined Pt nanoparticles on metal-oxide support are much desirable in catalysis research. In this work, we report a synthetic strategy for tuning Pt nanoparticles (NPs) on titania support, which is widely used in the catalytic field. The Pt NPs size was varied from 1 to 5 nm with the variation of template concentration. The catalyst showed high metal dispersion (68–32%) as compared to 2% metal dispersion for the catalyst synthesized with the conventional method. The catalytic activity of the catalyst was demonstrated using photoelectrochemical hydrogen production in CO2 atmosphere in alkaline medium at potential ca. -0.9 V vs. Ag/AgCl. The photoelectrode gave photocurrents of −28.76 mA-cm−2 and -7.87 mA-cm−2 under UV and visible light irradiations, respectively. The catalyst showed the highest activity (−7.87 mA-cm−2) for hydrogen production amongst metal oxide based photoelectrodes under visible light. The variation of Pt metal loading on the mesoporous titania was studied. First principles based DFT calculations favored the bicarbonate dissociation route into formic acid with the conversion of bicarbonate into formate as the rate determining step. The adsorption energy of bicarbonate over the catalyst was calculated as −2.17 eV, whereas carbon dioxide showed adsorption energy of −1.34 eV.

Trimetallic NiMoW and CoMoW catalysts supported on SBA-15 modified with titania or zirconia for deep hydrodesulfurization

SBA-15, Ti-SBA-15 and Zr-SBA-15 were used to prepare trimetallic CoMoW and NiMoW catalysts in order to inquire into the effect of the support’s composition on the catalytic performance in deep hydrodesulfurization (HDS). Supports and catalysts were characterized by N2 physisorption, X-ray diffraction, temperature-programmed reduction, scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy. The catalytic activity was determined in the simultaneous HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene. The most important characteristics of the SBA-15 material were preserved in the titania and zirconia-containing supports and the trimetallic catalysts. The deposited metal oxide species (NiO, CoO, MoO3 and WO3) were well-dispersed. NiMoW catalysts were substantially more active in deep HDS than the corresponding CoMoW ones. Titania and zirconia addition to the supports resulted in higher HDS activity of NiMoW and CoMoW catalysts, being this effect larger for the Ni-promoted samples. The NiMoW/Zr-SBA-15 catalyst was the most active for the elimination of sulfur from both dibenzothiophene and 4,6-dimethyldibenzothiophene. Its activity was twice higher than that of the NiMoW/SBA-15 analog. This was attributed to the high dispersion of the deposited metal species in the sulfided NiMoW/Zr-SBA-15 sample. Regarding the catalysts’ selectivity, it depended more strongly on the promoter used than on the support’s chemical composition.

Polypyrrole- and polyaniline-supported TiO2 for removal of pollutants from water

In recent decades, the modification of titanium dioxide (TiO2) as a well-known photocatalyst with different strategies, such as morphological change, doping and supported substrate, has been investigated. The main goals of the modification process can be described as (a) enhancing titanium dioxide performance and (b) providing a situation that uses titanium dioxide under visible or sunlight radiation. Different types of materials have been used for titanium dioxide support, among them polymers; in particular, polypyrrole (PPy) and polyaniline (Pan), that seem to be very effective due to considerable chemical and environmental stability in the aqueous phase. Meanwhile, by combining PPy and Pan with titanium dioxide, the energy of the band gap of supported titanium dioxide may be reduced and the photocatalytic process can be carried out under visible light illumination. This review demonstrates different strategies (their mechanisms and drawbacks) for enhancing titanium dioxide performance. In the field of PPy- and Pan-supported titanium dioxide, photocatalysts present a comprehensive study on their synthesis and application for removal of dye and organic pollutants. The effects of various parameters on the photocatalytic performance of PPy/titanium dioxide and Pan/titanium dioxide are also demonstrated. The main mechanisms of organic contaminants’ photodegradation by PPy/titanium dioxide and Pan/titanium dioxide in water (via an aqueous solution) are also investigated.

Titania-supported iridium catalysts for dehydrogenative synthesis of benzimidazoles

In this review, development of supported catalysts for the dehydrogenative synthesis of benzimidazoles from primary alcohols and 1,2-phenylenediamine derivatives is briefly summarized. Among them, titania-supported iridium catalysts showed excellent activities under mild reaction conditions. Remarkably, the low-temperature activity of iridium catalyst was significantly affected by titania supports, and the reaction of 1,2-phenylenediamine and benzyl alcohol in the presence of rutile-supported catalysts proceeded smoothly at 100 °C to give 2-phenylbenzimidazole in high yields of up to 88%. On the other hand, catalysts supported on anatase generally showed poor activity at 100 °C. A significant relationship between CO uptake and the activity of titania-supported catalysts has been reported, indicating that well-reduced iridium species on rutile would be responsible for the predominant catalytic activity. The present results suggest the importance of the selection of suitable titania supports for the iridium catalysts.

Direct immobilization and recovery of recombinant proteins from cell lysates by using EctP1-peptide as a short fusion tag for silica and titania supports

Immobilization of protein, compared to the use of free protein, offers improved stability, easy separation and continuous reusability. However, the classic routes for protein immobilization, based on non-specific adsorption, often negatively affect protein functionality. In this study, EctP1 peptide was explored as a novel short fusion tag for non-covalent adsorption on unmodified solid surfaces, silica and titania. A fusion of EctP1 with bovine carbonic anhydrase (BCA) was employed to investigate the optimal binding conditions that could diminish the nonspecific adsorption of Escherichia coli proteins. The stable binding of BCA-EctP1 on titania was observed in the pH range of 2–9, while the stable binding on silica was in the pH range 6–9. Moreover, the immobilized BCA-EctP1 on silica and titania particles showed enhanced thermal and storage stability and retained 95% of its residual activity after 5 uses. We further demonstrated the merits of the noncovalent immobilization of EctP1 fusion proteins to silica and titania in the recovery of the bound proteins. Interestingly, monomeric arginine showed better recovery yield of EctP1 fusion proteins (about 78–84%), compared to the recovery yield by the salts, NaCl and MgCl2 (about 30–51%). Using BCA and monomeric red fluorescent protein (mRFP) as model proteins, the EctP1 fusion proteins were released in a biologically active form with approximately 80% recovery and 93% purity. Our approach is a simple and reproducible technique for direct immobilization of recombinant proteins from E. coli lysates on solid supports, with the potential high-purity recovery of recombinant proteins.

CeOx/TiO2 (Rutile) Nanocomposites for the Low-Temperature Dehydrogenation of Ethanol to Acetaldehyde: A Diffuse Reflectance Infrared Fourier Transform Spectroscopy–Mass Spectrometry Study

Two nanocomposites of different layer thicknesses were synthesized by impregnation of a rutile titania support with a reduced ceria solution. An in situ diffuse reflectance infrared fourier-transfo...

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.

Comparative Study of Four TiO2-Based Photocatalysts to Degrade 2,4-D in a Semi-Passive System

In this study, the relative efficiency of four forms of supported titanium dioxide (TiO2) as a photocatalyst to degrade 2,4-dichlorophenoxyacetic acid (2,4-D) in Killex®, a commercially available herbicide was studied. Coated glass spheres, anodized plate, anodized mesh, and electro-photocatalysis using the anodized mesh were evaluated under an ultraviolet – light-emitting diode (UV-LED) light source at λ = 365 nm in a semi-passive mode. Energy consumption of the system was used to compare the efficiency of the photocatalysts. The results showed both photospheres and mesh consumed approximately 80 J/cm3 energy followed by electro-photocatalysis (112.2 J/cm3), and the anodized plate (114.5 J/cm3). Although electro-photocatalysis showed the fastest degradation rate (K = 5.04 mg L−1 h−1), its energy consumption was at the same level as the anodized plate with a lower degradation rate constant of 3.07 mg L−1 h−1. The results demonstrated that three-dimensional nanotubes of TiO2 surrounding the mesh provide superior degradation compared to one-dimensional arrays on the planar surface of the anodized plate. With limited broad-scale comparative studies between varieties of different TiO2 supports, this study provides a comparative analysis of relative degradation efficiencies between the four photocatalytic configurations.

Deciphering Charge Transfer and Electronic Polarization Effects at Gold Nanocatalysts on Reduced Titania Support

Gold nanoparticles supported on reduced TiO2 (110) surfaces are widely used as catalysts for oxidation reactions. Despite extensive studies, the role of oxygen vacancies in such systems remains elu...