Mesoporous Rutile TiO2 Research Articles

Electrocatalytic methane conversion to high value chemicals at ambient conditions

A key catalytic challenge in the electro-conversion of methane (CH4) is to partially oxidize CH4 to liquid products under ambient environment. This paper describes the electrocatalytic activity of mesoporous rutile titanium dioxide (r-TiO2) nanorods (NRs) and Pt loaded mesoporous rutile TiO2 nanohybrids (Pt/r-TiO2) NRs prepared with the one step hydrothermal approach. The usefulness of this technique is to encapsulate Pt nanoparticles (NPs) and utilize this material in the liquid-phase oxidation of CH4. This electrocatalytic reaction of CH4 with Na2CO3 electrolyte was examined over highly active Pt/r-TiO2 NRs catalysts consisting of pure rutile phase TiO2 having enough loading amount (10 wt%) of metallic Pt NPs. The surface modification of r-TiO2 with Pt NPs promotes the activation of CH4 and •OH that can support to generate methyl radical (•CH3). Afterwards CH3OH (50 µmol/g catalyst⋅h) and C2H5OH (36 µmol/mg catalyst⋅h) including small amount of propanol products are formed along with H2 gas (0.1 ± 0.02 vol%) using Pt/r-TiO2 at 1.5 V vs. Ag/AgCl electrode. High-resolution transmission electron microscopy proves the existence of 4 to 8 nm spherical-shaped Pt NPs on r-TiO2 NRs. This research work should act as a template for the study and design of metal loaded mesoporous metal oxide nanohybrid catalysts for the C − H bond activation to liquid products.

Mesoporous rutile TiO2: Synthesis, characterization and photocatalytic performance studies

Pure rutile phase of TiO2(R-TiO2) nanocrystals were synthesized through a low temperature sol-gel synthesis route by tuning the chemical process. This modified process directly resulted in nano spindle structures of rutile TiO2 at the instant of solvent evaporation and which further found exhibiting stabilized growth upon an increase in calcination temperatures as evidenced by XRD and HR-TEM studies. BET surface area measurement revealed the presence of mesoporosity with a highest surface area of 127.25 m2/g for the 300 °C calcinated sample. Photo-luminescence studies revealed the presence of intra-band levels at 2.90 eV and 2.68 eV. XPS studies on the highly porous R-TiO2 reveals the presence of Ti3+ ions, which may arise from the missing of oxygen or self-doping. Highly porous 300ᵒC R-TiO2 exhibited in the flat-band potential of -0.39 V as the normalized value for NHE electrode and resulted in the photocatalytic reduction hierarchy of MB > RhB > MO.

Hierarchical Branched Mesoporous TiO2-SnO2 Nanocomposites with Well-Defined n-n Heterojunctions for Highly Efficient Ethanol Sensing.

The direct assembly of functional nanoparticles into a highly crystalline mesoporous semiconductor with oriented configurations is challenging but of significance. Herein, an evaporation induced oriented co‐assembly strategy is reported to incorporate SnO2 nanocrystals (NCs) into a 3D branched mesoporous TiO2 framework by using poly(ethylene oxide)‐block‐polystyrene (PEO‐b‐PS) as the template, SnO2 NCs as the direct tin source, and titanium butoxide (TBOT) as the titania precursor. Owing to the combined properties of ultrasmall particle size (3–5 nm), excellent dispersibility and presence of abundant hydroxyl groups, SnO2 NCs can easily interact with PEO block of the template through hydrogen bonding and co‐assemble with hydrolyzed TBOT to form a novel hierarchical branched mesoporous structure (SHMT). After calcination, the obtained composites exhibit a unique 3D flower‐like structure, which consists of numerous mesoporous rutile TiO2 branches with uniform cylindrical mesopores (≈9 nm). More importantly, the SnO2 NCs are homogeneously distributed in the mesoporous TiO2 matrix, forming numerous n–n heterojunctions. Due to the unique textual structures, the SHMT‐based gas sensors show excellent gas sensing performance with fast response/recovery dynamics, high sensitivity, and selectivity toward ethanol.

Kinetically controlled low-temperature solution-processed mesoporous rutile TiO2 for high performance lithium-ion batteries

Solution-processed nanostructured mesoporous rutile phase titanium dioxides (TiO2) are a fascinating class of materials for energy applications owing to their remarkable properties, including thermal stability. The unique lattice structure of rutile TiO2 (R-TiO2) leads to multifaceted physicochemical properties, which influence its performances. We here report the preparation of mesoporous R-TiO2 via a simple and scalable solution process at a low temperature (<50°C). Kinetically controlled synthesis of mesoporous R-TiO2 with three-dimensional hierarchical sea-urchin-like morphology containing populous one-dimensional nanorods are prepared from the precipitates of our cocktail-like precursor solutions of TiCl4 and CH4N2S. The mesoporous R-TiO2 annealed at 300°C possessing a large surface area manifests excellent energy storage behavior, with a high capacity of 457mAhg−1 for the first discharge cycle, at a current density of 0.2 C in the potential range of 1–3V, as well as a high reversible charge–discharge capacity, high rate performance, and excellent cycling stability for lithium-ion batteries. We anticipate our straightforward wet-chemical method to advance the development of mesoporous TiO2 as a promising candidate for high-performance energy storage and other energy applications.

Construction of a porous core-shell homojunction for the photocatalytic degradation of antibiotics

The photocatalytic mineralization efficiency of antibiotics is primarily determined by the adsorption ability and photoactivity of the photocatalyst. In this work, we constructed a porous core-shell homojunction by growing amorphous TiO2 onto mesoporous rutile TiO2 crystals (MRCs) to simultaneously enhance the adsorption ability and photoactivity of the catalyst. Tetracycline hydrochloride (TCH) was chosen as a model agent of antibiotics. Scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption-desorption, and X-ray diffraction experiments were conducted to investigate the physical properties of the prepared samples. Surface photovoltage spectroscopy and X-ray photoelectron spectroscopy were applied to study the charge separation process. The results showed that amorphous TiO2 was homogeneously coated on the MRCs surface, thereby forming a 3D hierarchical porous core-shell morphology. The growth of amorphous TiO2 increased the surface area of the catalyst by 213% and the amount of TCH absorbed by up to 1760%. Moreover, a homojunction was formed at the interface of the MRC core and the amorphous TiO2 shell. The built-in electric field of the homojunction drove photogenerated holes (electrons) migrating from the core to the shell (shell to core) and thus enhanced the charge separation. TCH and the holes simultaneously concentrated in the amorphous TiO2 shell, thereby enhancing the mineralization of TCH.

High performance diesel oxidation catalysts using ultra-low Pt loading on titania nanowire array integrated cordierite honeycombs

High performance of an ultra-low Pt loading diesel oxidation catalyst can be achieved by using a combination of novel nano-array structured support, precise control of ultrafine active Pt particles, and an addition of H2 as a promoter into the exhausts. Highly stable mesoporous rutile TiO2 nano-array was uniformly grown on three-dimensional (3-D) cordierite honeycomb monoliths using a solvothermal synthesis. Atomic layer deposition was employed for precise dispersion of ultrafine Pt particles (0.95±0.24nm) on TiO2 nano-array with a Pt loading of 1.1g/ft3. Despite low Pt loading, the Pt/TiO2 nano-array catalyst shows impressive low-temperature oxidation reactivity, with the conversion of CO and total hydrocarbon (THC) reaching 50% at 224 and 285°C, respectively, in the clean diesel combustion (CDC) simulated exhaust conditions. The excellent activity is attributed to the unique nano-array structure that promotes gas-solid interaction and ultra-small Pt particle dispersion that increase surface Pt atoms. We also demonstrate that addition of more H2 into the exhaust can lower light-off temperature for CO and THC by up to ∼60°C and ∼30°C, respectively.

Solvothermal synthesis of hedgehog-like mesoporous rutile TiO 2 with improved lithium storage properties

Hedgehog-like mesoporous rutile TiO2 (HLR-TiO2) composed of well-defined nanoneedles is fabricated in a solvothermal system containing tetrabutyl titanate, hydrochloric acid aqueous solution and diethylene glycol with a proper volume ratio. A possible formation mechanism of the HLR-TiO2 is proposed on the basis of different experimental results and three different morphologies are obtained by changing the solvent with other conditions unchanged. Given its unique hierarchical mesoporous nanostructures, the HLR-TiO2 shows superior lithium storage properties with excellent discharge specific capacity of 243.3 mA h g−1 obtained after 100 cycles at a current rate of 1 C among the three samples, which is almost unparalleled to other rutile TiO2-based electrodes. In particular, a specific capacity of 80.2 mA h g−1 is still maintained after 2000 cycles even at a high current rate of 20 C, indicating that great potential of HLR-TiO2 as an electrode material for lithium-ion batteries (LIBs).

Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2: Bio-template assisted sol-gel synthesis and photocatalytic activity

Regenerated cellulose membrane was used as bio-template nanoreactor for the formation of rutile TiO2 mesoporous, as well as in-situ carbon dopant in acidified sol-gel system. The effects of calcination temperature on the physicochemical characteristic of core-shell nanostructured of bio-templated C-doped mesoporous TiO2 are highlighted in this study. By varying the calcination temperature, the thickness of the carbon shell coating on TiO2, crystallinity, surface area, and optical properties could be tuned as confirmed by HRTEM, nitrogen adsorption/desorption measurement, XRD and UV–vis-NIR spectroscopy. The results suggested that increment in the calcination temperature would lead to the band gap narrowing from 2.95 to 2.80eV and the thickness of carbon shell increased from 0.40 to 1.20nm. The x-ray photoelectron spectroscopy showed that the visible light absorption capability was mainly due to the incorporation of carbon dopant at interstitial position in the TiO2 to form OTiC or TiOC bond. In addition, the formation of the carbon core-shell nanostructured was due to carbonaceous layer grafted onto the surface of TiO2 via TiOC and TiOCO bonds. The result indicated that bio-templated C-doped core-shell mesoporous TiO2 prepared at 300°C exhibited the highest photocatalytic activity. It is worthy to note that, the calcination temperature provided a huge impact towards improving the physicochemical and photocatalytic properties of the prepared bio-templated C-doped core-shell mesoporous TiO2.

Enhanced photocatalytic hydrogen generation of mesoporous rutile TiO2 single crystal with wholly exposed {111} facets

The development of semiconductor photocatalysts with highly reactive facets exposed has great potential to improve their photocatalytic reactivity. We report the synthesis of mesoporous rutile TiO2 single crystals with tunable ratios of {110} and {111} facets through the seeded-template hydrothermal method. With increasing the amount of morphology controlling agent NaF, the facet ratio of {111} to {110} increases, and eventually the mesoporous rutile TiO2 single crystals with wholly exposed {111} reactive facets are obtained. The resultant faceted mesoporous single crystals exhibit a superior photocatalytic performance of hydrogen evolution to mesoporous single crystals with a large percentage of thermodynamically stable {110} facets, as well as the solid rutile single crystals.

Low-Temperature and Surfactant-Free Synthesis of Mesoporous TiO2 Sub-Micron Spheres for Efficient Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are one of the most promising next-generation solar cells due to their advantages over other counterparts. The photoanode of DSSCs has a great effect on the photovoltaic performance. Traditional photoanode includes a bottom nanoparticle layer and an upper scattering layer for better light capture in longer wavelength. Mesoporous nanostructures with size comparable to the wavelength of visible light are considered to be excellent light scattering centers by providing extra places for dye loading. Developing a green synthetic method is of great importance. Herein we report a facile and surfactant-free synthesis of mesoporous rutile TiO2 submicrometer-sized spheres at temperature as low as 70 °C. DSSCs based on photoanodes with an upper scattering layer composed of as-obtained mesoporous spheres on nanoparticle dense layer demonstrate an 18.0% improvement of power conversion efficiency. This simple approach may offer an energy-efficient and environmentally friendly alternative for DSSCs fabrication.

Hierarchical mesoporous rutile TiO2/C composite nanospheres as lithium-ion battery anode materials

Hierarchical mesoporous rutile TiO2 nanospheres were successfully synthesized via a simple low-temperature template-free method. The rutile TiO2 electrode showed poor electrochemical anodic performance in a lithium-ion battery. In order to improve the performance, conductive polyaniline was synthesized and coated on rutile TiO2 nanospheres via in-situ polymerization and chemical etching. After carbonization, the TiO2/C composite electrode showed more stable cyclability and a higher rate performance. Additionally, the amorphous carbon layer provided an effective pathway for charge transport, leading to a lower charge-transfer resistance and a higher lithium-ion diffusion coefficient compared to those of untreated rutile.

Acid-assisted synthesis of dandelion-like rutile TiO2 and Li4Ti5O12 mesoporous spheres: towards an efficient lithium battery application

In this study, a new acid-assisted hydrothermal method was presented for the synthesis of dandelion-like mesoporous rutile TiO2 microspheres (MSPs) without using any template and surfactant. With this strategy, the spherical structure and pore size of the obtained TiO2 particles could be readily controlled just through varying the kind of acid (e.g., HNO3–TiO2 and HCl–TiO2 MSPs show different pore size distribution of 6 ± 2 nm and 12 ± 2 nm, respectively). Benefiting from the mesoporous structure, high specific surface area, and especially the high percentage of exposed (002) crystal facets, the samples of HNO3–TiO2 and HCl–TiO2 MSPs exhibit excellent electrochemical performance in lithium-ion batteries. For example, a high capacity of around 164.5 and 160.6 mA h g−1 at a rate of 0.1 C, and a reversible capacity of over 141.9 and 133.3 mA h g−1 after 100 cycles at a rate of 1 C were demonstrated respectively for the samples of HNO3–TiO2 and HCl–TiO2 MSPs (1 C = 168 mA h g−1). Moreover, another two kinds of mesoporous Li4Ti5O12 spheres (HNO3–Li4Ti5O12 and HCl–Li4Ti5O12 MSPs) were further prepared based on the above TiO2 precursors. Promisingly, they also showed a higher improved performance in lithium battery application, such as a high capacity of around 173.6 and 174 mA h g−1 at a rate of 0.1 C and a reversible capacity of over 161.9 mA h g−1 and 170.4 mA h g−1 after 100 cycles at a rate of 1 C (1 C = 175 mA h g−1).

Syntheses, Li Insertion, and Photoactivity of Mesoporous Crystalline TiO2

AbstractOrdered mesoporous rutile and anatase TiO2 samples are prepared using mesoporous silica SBA‐15 as template and freshly synthesized titanium nitrate and titanium chloride solutions as precursors. The rutile material formed from the nitrate solution is monocrystalline and contains minimal amounts of Si with a Si:Ti ratio of 0.031(4), whereas the anatase material formed from the chloride solution comprises nanocrystals and contains a higher content of Si with a Si:Ti ratio of 0.18(3). It is found that control of temperature and selection of Ti‐containing precursor play important roles in determining the crystal phase and crystallinity. A possible formation mechanism of porous crystalline TiO2 is suggested. Characterization of these porous materials is performed by XRD, HRTEM, and nitrogen adsorption/desorption. SBA‐15‐templated mesoporous rutile TiO2 exhibits a higher Li ion insertion capability than KIT‐6‐templated TiO2 due to its larger surface area. Likewise mesoporous anatase TiO2:SiO2 composite has a better photoactivity than bulk TiO2 or TiO2‐loaded SBA‐15 for bleaching methylene blue.

Synthesis and Li-Ion Insertion Properties of Highly Crystalline Mesoporous Rutile TiO2

Mesoporous TiO2 has attracted great attention as a promising Li insertion electrode material with improved cycling life, rate capability, and high power density. Up to date, mesoporous anatase TiO2 has been investigated for Li insertion. Recent studies have shown that nanosized rutile could be an excellent candidate for anode materials for higher Li insertion capacity and improved stability. However, synthesis of highly crystalline mesoporous rutile has met with limited success so far. There has been no report on Li insertion of mesoporous rutile TiO2. In this paper, we report a new low-temperature solution growth of TiO2 nanocrystals within an anionic surfactant matrix to produce highly crystalline mesoporous rutile and investigate Li insertion properties of the mesoporous crystalline rutile. X-ray diffraction (XRD) patterns and N2 sorption isotherms reveal that mesoporous structure in the highly crystalline mesoporous TiO2 directly results from the anionic surfactant templating effects with high surface area (245−300 m2/g) and tunable mesopore diameter ranging from 2.2 to 3.8 nm after calcination. Transmission electron microscopy (TEM) measurements show that framework of the highly crystalline mesoporous TiO2 are composed of aligned rutile nanorod building blocks grown along [001] direction. The new mesoporous crystalline rutile can accommodate more than 0.7 Li (Li0.7TiO2, 235 mA h g−1) during the first discharge at a C/5 rate between 1 and 3 V versus Li+/Li, with a reversible capacity of 0.55 Li (Li0.55TiO2, 185 mA h g−1). The mesoporous crystalline rutile shows excellent capacity retention with less than 10% capacity loss after more than 100 cycles. XRD and TEM characterization on the electrochemically lithiated sample show that the rutile nanorods were transformed into cubic rocksalt LiTiO2 nanorods, but the mesostructures remained stable after the phase transformation and cycling. Furthermore, the crystalline mesoporous rutile may also have good potential for other applications such as stable catalyst supports.