Mesoporous TiO2 Nanotubes Research Articles

Surface engineering of mesoporous anatase titanium dioxide nanotubes for rapid spatial charge separation on horizontal-vertical dimensions and efficient solar-driven photocatalytic hydrogen evolution

The low charge separation efficiency and sunlight utilisation of traditional titanium dioxide (TiO2) nanoparticle photocatalysts greatly limit their applications. Herein, one-dimensional (1D) mesoporous anatase TiO2 nanotubes with engineered surface defects are fabricated using a combination of simple solvothermal synthesis and high-temperature surface hydrogenation strategy. The obtained mesoporous anatase TiO2 nanotubes with mesopores in the nanotube walls and a specific surface area of 110 m2 g−1 decrease the bandgap from 3.18 to 2.98 eV, enhancing the photoresponse to the visible-light region of the solar spectrum. The defective mesoporous anatase TiO2 nanotubes exhibited an excellent photocatalytic hydrogen evolution rate of 9.8 mmol h−1 g−1, which is approximately 2.5 times higher than that of the pristine anatase TiO2 nanotubes. This can be ascribed to the engineered surface defects and 1D mesoporous nanotube structure favouring efficient spatial charge separation on the horizontal–vertical dimensions, enabling visible-light absorption and exposing abundant surface active sites. This study provides a facile and feasible strategy for the fabrication of high-performance 1D mesostructured semiconductor oxide photocatalysts for efficient solar energy conversion.

Nitrogen-doped carbon encapsulated in mesoporous TiO2 nanotubes for fast capacitive sodium storage

Abstract Controllable synthesis of insertion-type anode materials with beneficial micro- and nanostructures is a promising approach for the synthesis of sodium-ion storage devices with high-reactivity and excellent electrochemical performance. In this study, we developed a sacrificial-templating route to synthesize TiO2@N-doped carbon nanotubes (TiO2@NC-NTs) with excellent electrochemical performance. The as-prepared mesoporous TiO2@NC-NTs with tiny nanocrystals of anatase TiO2 wrapped in N-doped carbon layers showed a well-defined tube structure with a large specific surface area of 198 m2 g−1 and a large pore size of ~5 nm. The TiO2@NC-NTs delivered high reversible capacities of 158 mA h g−1 at 2 C (1 C = 335 mA g−1) for 2200 cycles and 146 mA h g−1 at 5 C for 4000 cycles, as well as an ultrahigh rate capability of up to 40 C with a capacity of 98 mA h g−1. Even at a high current density of 10 C, a capacity of 138 mA h g−1 could be delivered over 10,000 cycles. Thus, the synthesis of mesoporous TiO2@NC-NTs was demonstrated to be an efficient approach for developing electrode materials with high sodium storage and long cycle life.

Dual-template synthesis of mesoporous TiO2 nanotubes with structure-enhanced functional photocatalytic performance

Mesoporous TiO2 nanotubes (m-TiO2-NTs) with outstanding photocatalytic performance have been successfully synthesized, for the first time, through a dual-template method. The dual-template method uses multi-walled carbon nanotube (CNT) as a hard template to control the morphology and cetyltrimethylammonium bromide (CTAB) as a soft template to form the mesoporous structure. The resulting m-TiO2-NTs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), nitrogen adsorption-desorption and X-ray photoelectron spectroscopy (XPS). Rhodamine B (RhB) and dibutyl phthalate (DBP) are used as model pollutants to evaluate the photocatalytic properties of the new materials. The m-TiO2-NTs possess a multiple channel tubular structure and have higher specific surface area than TiO2 nanoparticles (TiO2-NPs). These features result in significantly superior photocatalytic activity for photodegradation. Specifically, the reaction rate constant for the photodegradation of RhB is 9.8 times greater with m-TiO2-NTs than it is with TiO2-NPs. In the case of DBP, the rate constant is 7.7 times higher. Photocatalytic removal ratios of gaseous acetaldehyde (CH3CHO) and the generation of COx (CO + CO2) were detected to evaluate the decomposition ability of the materials, m-TiO2-NTs showed the best CH3CHO removal efficiency and the highest CO2 selectivity. The active species of photocatalytic process are found to be OH. In addition, the m-TiO2-NTs exhibit excellent thermal and photocatalytic stability even after six recycles. This work demonstrates a novel way to fabricate mesoporous TiO2 nanotubes that have multiple channel tubular structure and to apply them in environmental photocatalysis.

Preparation of TiO2 Nanotube Supported Pd for the Hydrogenation of 4-carboxy-benzaldehyde

Mesoporous TiO2 nanotube (TNT) with high surface area was synthesized and used to support palladium. The as prepared Pd/TNT was characterized by different physico-chemical techniques, such as XRD, SEM, TEM, N2 physisorption, CO chemisorption and XPS. The catalytic behavior for the hydrogenation of 4-carboxy-benzaldehyde was evaluated and compared with that of a commercial Pd/C. It was observed that Pd species was highly dispersed on TNT at a nominal 0.5% loading, and mainly existed in a metallic state. In comparison with this commercial Pd/C, the Pd/TNT displayed a better catalytic performance for the conversion of 4-carboxy-benzaldehyde. At 0.6 MPa and 280 °C, the Pd/TNT tended to catalytically convert 4-carboxy-benzaldehyde into more stable benzoic acid via a decarbonylation process. A Pd/TNT with high palladium dispersion was successfully prepared by the wet incipient impregnation using a high surface area TiO2 nanotube support, and the fresh catalyst tended to catalytically convert 4-carboxy-benzaldehyde into more stable benzoic acid in the initial operation stage.

High rate lithium-sulfur batteries enabled by mesoporous TiO2 nanotubes prepared by electrospinning

Mesoporous titanium dioxide nanotubes (MTDNTs) were prepared by electrospinning and subsequent thermal treatment. The as-synthesized MTDNTs possess anatase mischcrystal structure, hollow texture morphology, and a relatively high specific surface area of 93.6m2g−1 with a pore volume of 0.2190cm−3g−1. The nanotube walls of MTDNTs act as a host for sulfur and the hollow structure is favorable for the fast transmission of Li+ ions. After sulfur was encapsulated into the pores of nanotube walls of MTDNTs, the MTDNTs/S composite electrode displays a relatively good cycling performance and especially excellent rate performance (about 610mAhg−1 at 8C). The retention capacity can be up to 74.2% when the discharge rate increases from 0.5C to 8.0C.

Hydrothermal synthesis of mesoporous TiO2 nanotubes and their adsorption affinity toward Basic Violet 2

Hydrothermal method was used to synthesize TiO2 nanotubes (TNTs), which are considered as a novel adsorbent with high surface area and adsorption capacity. Different methods including X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) analysis were used to investigate and identify synthesized TNTs. The adsorption capacity of TNTs was investigated with regard to removing Basic Violet 2 (BV2) as a model organic pollutant from aqueous solution. The mean outer, inner diameter and thickness of the TNTs were found to be approximately 9, 4 and 2.5 nm, respectively. BET–BJH method was used for measuring specific surface area and pore volume of the TNTs which turned out to be 200.38 m2 g−1 and 0.44 cm3 g−1, respectively. The results of the study indicated synthesized TNTs may be considered as efficient and effective adsorbent for removing BV2 (75.63%) from aqueous solution. The impact of the operational variables, i.e. initial BV2 concentration (2–20 mg L−1), dosage of adsorbent (0.01–0.6 g), and pH (2–8) in relation to the adsorption capacity of BV2 onto TNTs were investigated. The experimental results of the study were meticulously taken into consideration for discussing and analyzing the adsorption isotherms and kinetics. It was found that the collected experimental data regarding the kinetic and isotherm examinations were compatible and well-matched with the pseudo-first order kinetic model and Langmuir isotherm model (R2 = 0.9634).

A Study of Low-Temperature CO Oxidation over Mesoporous CuO-TiO2 Nanotube Catalysts

Supported copper oxide nanoparticles have attracted considerable attention as active and non-precious catalysts for many catalytic oxidation reactions. Herein, mesoporous xCuO-TiO2 nanotube catalysts were fabricated, and their activity and kinetics toward CO oxidation were studied. The morphology and structure of the prepared catalysts were systematically studied using SEM, TEM, EDS, EDX, XRD, TGA, BET, XPS, H2-TPR, and Raman techniques. The BET surface area study revealed the effect of the large surface area of the mesoporous TiO2 nanotubes on promoting the catalytic activity of prepared catalysts. The results also revealed the existence of strong metal-support interactions in the CuO-TiO2 nanotube catalyst, as indicated by the up-shift of the E2g vibrational mode of TiO2 from 144 cm−1 to 145 cm−1 and the down-shift of the binding energy (BE) of Ti 2p3/2 from 458.3 eV to 458.1 eV. The active phase of the catalyst consists of fine CuO nanoparticles dispersed on a mesoporous anatase TiO2 nanotube support. The 50-CuO-TiO2 nanotube catalyst demonstrated the highest catalytic activity with 100% CO conversion at T100 = 155 °C and a reaction rate of 36 µmole s−1 g−1. Furthermore, the catalyst demonstrated excellent long-term stability with complete CO conversion that was stable for 60 h under a continuous stream. The enhanced catalytic activity is attributed to the interplay at the interface between the active CuO phase and the TiO2 nanotubes support.

TiO2 nanotubes and mesoporous silica as containers in self-healing epoxy coatings.

The potential of inorganic nanomaterials as reservoirs for healing agents is presented here. Mesoporous silica (SBA-15) and TiO2 nanotubes (TNTs) were synthesized. Both epoxy-encapsulated TiO2 nanotubes and amine-immobilized mesoporous silica were incorporated into epoxy and subsequently coated on a carbon steel substrate. The encapsulated TiO2 nanotubes was quantitatively estimated using a ‘dead pore ratio’ calculation. The morphology of the composite coating was studied in detail using transmission electron microscopic (TEM) analysis. The self-healing ability of the coating was monitored using electrochemical impedance spectroscopy (EIS); the coating recovered 57% of its anticorrosive property in 5 days. The self-healing of the scratch on the coating was monitored using Scanning Electron Microscopy (SEM). The results confirmed that the epoxy pre-polymer was slowly released into the crack. The released epoxy pre-polymer came into contact with the amine immobilized in mesoporous silica and cross-linked to heal the scratch.

Thoroughly mesoporous TiO2 nanotubes prepared by a foaming agent-assisted electrospun template for photocatalytic applications

A thoroughly mesoporous long TiO2 nanotube with intact morphology was firstly prepared using a foaming agent-assisted electrospun template method for photocatalytic applications.

Efficient water management of composite membranes operated in polymer electrolyte membrane fuel cells under low relative humidity

High performance and durable electrolyte membrane operated in polymer electrolyte membrane fuel cells (PEMFCs) under low relative humidity (RH) has been achieved by incorporating various diameter sizes of mesoporous hygroscopic TiO2 nanotubes (TNT) in a perfluorosulfonic acid (Nafion®) membrane. Porous TNTs with different tube diameters are synthesized by thermal annealing the electrospun polymer containing titanium precursor mat at 600°C under an air atmosphere. The diameter of the TNT is significantly controlled by changing the concentration of the precursor solution. Compared to a commercial membrane (Nafion, NRE-212), the Nafion-TNT-10 composite membrane operated under 100% RH at 80°C generates about 1.3 times higher current density at 0.6V, and 3.4 times higher maximum power density operated under dry conditions (18% RH at 80°C). In addition, the Nafion-TNT-10 composite membrane also exhibits stable and durable operation under dry conditions. The remarkably high performance of the Nafion-TNT-10 composite membrane is mainly attributed to the significant reduction of the ohmic resistance as well as the improvement of cathode catalyst utilization by incorporating TNTs, which greatly enhances the water retention and the water management capability through the membrane. Furthermore, Nafion–TNT membranes exhibit superior mechanical property.

Scalable synthesis of three-dimensional interconnected mesoporous TiO2 nanotubes with ultra-large surface area

Mesoporous nanotubes represent a unique class of nanostructures with numerous applications including biomaterials, lithium ion battery anodes, and photocatalysts. Herein we describe for the first time a general, scalable, and reproducible approach for the production of 3D interconnected mesoporous TiO2 nanotubes with ultrahigh specific surface area and large pore volume by using a nanofibrous template of bacterial cellulose (BC). The obtained samples were characterized by Brunauer–Emmett–Teller (BET) surface area measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results demonstrated that TiO2 nanotubes sustained the 3D interconnected structure of pristine BC and exhibited an average diameter of 36nm and a mesoporous wall with a mean mesopore size of 3.2nm. The particular structure endows TiO2 nanotubes with ultra-large surface area (1629m2g−1) and high photocatalytic activity.

Broadband plasmon photocurrent generation from Au nanoparticles/ mesoporous TiO2 nanotube electrodes

There has been an increasing interest in plasmon-induced enhancement of solar cells and more recently in the direct generation of photocurrent using noble metal nanoparticles with their Localised Surface Plasmon Resonance (LSPR) in the visual part of the spectrum. In this paper we report broadband plasmon photocurrent generation using novel Au nanoparticle incorporated mesoporous TiO2 nanotube electrodes. Plasmonic induced photocurrent due to hot electrons is observed over a broad wavelength range (~500 to 1000nm). Incident photon-to-electron conversion efficiency (IPCE) measurements undertaken showed a maximum photocurrent enhancement of 200 fold around 700–730nm wavelength.

Electrochemical performance and biosensor application of TiO2 nanotube arrays with mesoporous structures constructed by chemical etching.

Novel mesoporous TiO2 nanotube arrays (TiO2 NTAs) were synthesized by an anodization method combined with chemical etching in HF solution, and the electrochemical performance was studied. Glucose oxidase (GOx) was immobilized on the mesoporous TiO2 NTAs to achieve an efficient biosensor for amperometric detection of glucose. The morphology, structure, component and electrochemical performance of mesoporous TiO2 NTAs were characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectrometry and an electrochemical workstation, respectively. The influence of the mesoporous structure on the electrochemical performance is discussed in detail by comparing the cyclic voltammograms and electrochemical impedance spectrum of TiO2 and mesoporous TiO2 NTAs in different conditions. High electrochemical active surface area and electron transfer rate play key roles in enhancing the electrochemical performance of mesoporous TiO2 NTAs. When used as the basis of a biosensor, the amperometric response of glucose on a GOx/TiO2-0.5 NTAs electrode is linearly proportion to the glucose concentration in the range from 0.1 to 6 mM with a sensitivity of 0.954 μA mM(-1) cm(-2), which is 14.3 times that of un-etched GOx/TiO2 NTAs.

Constructing a novel three-dimensional scaffold with mesoporous TiO2 nanotubes for potential bone tissue engineering.

Three-dimensional (3D) nanofibrous scaffolds for tissue engineering have been widely studied while 3D scaffolds made of nanotubes are rarely reported. Herein, we report a novel 3D porous network-structured scaffold built of mesoporous TiO2 nanotubes. The TiO2 nanotubes were synthesized using the template-assisted sol-gel method followed by calcination. Bacterial cellulose (BC) with 3D network structure was used as the template. TEM observation confirms the formation of tubular TiO2 nanotubes. The as-synthesized TiO2 nanotubes exhibit an average outer diameter of less than 100 nm and mesoporous walls consisting of aggregated TiO2 nanoparticles with a size of around 7 nm. SEM and TEM observations reveal that the TiO2 nanotube scaffold possesses 3D porous network structure and the surfaces of TiO2 nanotubes are rugged with nanotopography. Additionally, the scaffold built of mesoporous nanotubes with a mesopore size of 3.3 nm exhibits an extremely large surface area of 1629 m2 g-1. The capacity of the scaffold to support cell proliferation and osteogenic differentiation was evaluated using CCK-8 assay, alkaline phosphatase (ALP), and calcium content assay. The scaffold shows enhanced cell growth and proliferation and improved ALP activity and mineralization compared to the TCPS (tissue culture plate) control. Furthermore, the ALP activity of the scaffold is as high as a hydroxyapatite-coated nanofibrous scaffold. The enhanced proliferation and osteogenic differentiation of the TiO2 nanotube scaffold is ascribed to the outer surface roughness of TiO2 nanotubes, 3D porous network structure, mesopores, and large surface area.

Carbon nanofiber-templated mesoporous TiO2 nanotubes as a high-capacity anode material for lithium-ion batteries

The present communication demonstrates the synthesis of uniform mesoporous TiO2 nanotubes via hydrolysis and condensation of tetrabutyl titanate (TBOT) using carbon nanofibers as templates followed by calcination under air. We further demonstrate the use of such TiO2 nanotubes as an anode material for rechargeable lithium-ion batteries (LIBs) with high discharge capacity, good rate capability and excellent cycling performance. They deliver a high discharge capacity of 209.6 mA h g−1 at a current density of 0.2 C in the voltage range 1.0–3.0 V. They can still deliver a discharge capacity of 108.1 and 88.8 mA h g−1 with 100 and 93.2% capacity retention after 500 charge–discharge cycles under current densities of 2 and 4 C, respectively.

Fabrication of large-diameter tube-like mesoporous TiO2 via homogeneous precipitation and photocatalytic decomposition of papermaking wastewater

Large-diameter tube-like mesoporous TiO2 nanotubes were synthesized via homogeneous precipitation from aqueous solutions containing titanium oxysulfate (TiOSO4) using urea. The cationic surfactant cetyltrimethylammonium bromide was used as a structure-directing agent. Prepared samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and N2 adsorption–desorption isotherms. Experimental results indicated that the samples exhibit tube-like structures with lengths of approximately 6μm to 8μm, large tube diameters of approximately 500nm to 600nm, and a wall thickness of approximately 450nm. TEM images and N2 adsorption–desorption isotherms showed that the tube walls of the samples have a uniform mesoporous structure. A possible mechanism for the formation of tube-like mesoporous TiO2 was proposed. The photocatalytic activities of the large-diameter tube-like mesoporous TiO2 were assessed via the photocatalytic decomposition of papermaking wastewater under ultraviolet light irradiation. The effects of different parameters such as UV light irradiation, catalyst dosage and solution pH on photocatalytic activities of tube-like mesoporous TiO2 were studied. The as-synthesized tube-like TiO2 showed higher photocatalytic activities than Degussa P25. MTS3 exhibited the highest photocatalytic activity. The chemical oxygen demand and chroma percent degradations of papermaking wastewater were approximately 73.0% and 99.5%, respectively, at MTS3 dosage of 1.0g/L and pH value of 3.0 after 12h of photodegradation.

Alumina decorated TiO2 nanotubes with ordered mesoporous walls as high sensitivity NOx gas sensors at room temperature

Alumina (Al2O3) decorated anatase TiO2 nanotubes with ordered mesoporous pore walls (Al2O3/meso-TiO2 nanotubes) are successfully synthesized through vacuum pressure induction technology, and then combined with the thermal decomposition of a mesoporous TiO2 sol precursor, inside the cylindrical nanochannels of an anodic aluminium oxide (AAO) template. The decorated Al2O3 was formed by in situ deposition via direct reaction of the strong acid sol precursor and the nanochannel wall of the AAO template. The resultant Al2O3/meso-TiO2 nanotubes are characterized in detail by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and N2 adsorption-desorption. The experimental results reveal that the Al2O3/meso-TiO2 nanotubes have a tubular structure with an average diameter of ∼200 nm and highly ordered mesopores in the tubular walls. The Al2O3 is distributed evenly on the anatase TiO2 nanotubes. Moreover, the Al2O3/meso-TiO2 nanotubes possess a large specific surface area (136 m(2) g(-1)) and narrow mesopore size distribution (∼10 nm). By using NO(x) as a probe molecule, the Al2O3/meso-TiO2 nanotube films exhibit better sensing performance than that of mesoporous TiO2 nanotubes, in terms of their high sensitivity, fast response-recovery time, and good stability in air at room temperature. The outstanding performance in the gas sensing ability of Al2O3/meso-TiO2 nanotubes is a result of their one-dimensional tubular and mesoporous nanostructures, advantageous for the adsorption and diffusion of NO(x) gas. In addition, the sensing response is greatly improved by virtue of the decorated Al2O3 on the surfaces of the TiO2 nanotubes, which acts as an energy barrier to suppress charge recombination. The structural properties of the Al2O3/meso-TiO2 nanotubes makes them a viable novel gas sensor material at room temperature.

Simultaneous copper ion removal and hydrogen production from water over a TiO2 nanotube photocatalyst

A one-dimensional (1-D) mesoporous TiO₂ nanotube (TiNT) was successfully synthesized via a hydrothermal-calcination process, and employed in simultaneous photocatalytic Cu(2+) removal and H₂ production. Under irradiation, Cu(2+) in the wide concentration range of 8-800 ppm, could be reduced rapidly, and the reduction was not severely impacted by co-existing inorganic ions in solution. Simultaneous with Cu(2+) reduction, noticeable H₂ was produced over the in-situ fabricated Cu incorporated TiNT (Cu-TiNT) photocatalyst, while H₂ evolution rate was controlled by the Cu(2+) reduction process, due to competition of electron capture between protons and Cu(2+). In addition, H₂ generation activity of Cu-TiNT depended on the initial Cu(2+)/Ti ratio, and could be depressed by co-existing ions in solution. Fast Cu(2+) reduction and remarkable H₂ evolution confirmed the feasibility of simultaneous Cu(2+) removal and H₂ production over a TiNT photocatalyst.

Synthesis of Mesoporous Anatase TiO<SUB>2</SUB> Nanotubes by a Hydrothermal Treatment and Their Use in Solid-State Dye-Sensitized Solar Cells

Mesoporous anatase TiO2 nanotubes (NTs) with the diameter of about 7 12 nm and the length of several hundred nanometers were synthesized by a hydrothermal method on commercial TiO2 particles in NaOH followed by HCI washing. The samples were characterized by X-ray diffraction (XRD), transmitting electron microscopy (TEM), and Brunauer-Emmet-Teller (BET) measurements. The hydrothermal treatment temperature at 130 degrees C was shown to affect not only the extent of particle-to-sheet conversion, and thus the resulting structures of the NTs, but also the anatase-to-rutile transformation. The surface area of the NTs was 200 m2g(-1). This value was much higher in comparison to TiO2 nanoparticles of 50 m2g(-1). It was also found that the NT photoelectrodes had a pronounced impact on the performance of solar cells as compared to nanoparticle ones. This was probably due to lead to a significantly higher specific dye loading and, for certain hydrothermal treatments, resulting in a doubling of the solar cell efficiency (in our case from 2.84% to 4.03% of AM 1.5 conditions).

Fabrication of Mesoporous Titanium Oxide Nanotubes Based on Layer-by-Layer Assembly

Titanium oxide (TiO2)/polyacrylic acid (PAA) composite nanotubes were firstly fabricated through the sol-gel process of titanium alkoxide in the inner pores of alumina template followed layer-by-layer assembly with polyacrylic acid (PAA). Mesoporous TiO2 nanotubes could be obtained after the removal of PAA component by calcination and etching of the template with concentrated sodium hydroxide aqueous solution. The surface area of as-prepared porous TiO2 nanotubes was measured as twice larger than that of the conventional TiO2 nanotubes and the pore diameter in the wall of the tubes is several nanometers. Such assembled mesoporous nanotubes can serve as carriers for catalysis release and biomolecules.