Protonated Titanate Nanotubes Research Articles

A new ion exchange behavior of protonated titanate nanotubes after deprotonation and the study on their morphology and optical properties

After the deprotonation of protonated titanate nanotubes (H2Ti3O7), we observed a novel ion exchange behavior on them. In the past literatures, protonated titanate nanotubes prepared via hydrothermal method have been reported with a poor exchangeability which may due to the chemical bonding of interlayer protons to nearby oxygen atoms. However, in this experiment under alkali environment (pH>10), protonated titanate nanotubes exhibited a vast ion exchange capacity toward [Co(NH3)6]2+. This interesting phenomenon is contrary to the past reports which found protonated titanate nanotubes hardly could be ionexchanged by objective cations. This paper proves the deprotonation process on H2Ti3O7 nanotubes sufficiently facilitates the diffusion of metal complex cations into protonated titanate nanotubes and significantly changes their ion exchange capacity. As a consequence of cabalt intercalting via ion exchange, the tube wall of H2Ti3O7 nanotubes is observed to get loosened. Additionally, the exciton concentrations corresponding to the nanotube surface states are discussed in the paper.

Polyethyleneimine functionalized protonated titanate nanotubes as superior carbon dioxide adsorbents

In this paper, protonated titanate nanotubes (PTNTs) were modified with polyethyleneimine (PEI) by wet impregnation method for CO2 adsorption. Their micro-morphology and structural properties were characterized by a range of analytical techniques, including XRD, TEM, SEM, N2 adsorption etc. Experimental results revealed that the functionalized PTNTs with 50wt.% PEI loaded exhibited a high CO2 adsorption capacity of 130.8mg/g-sorbent at 100°C. Only a minor loss of its capacity was observed after five consecutive adsorption–desorption runs. The PEI was existed both in the internal and external mesoporous pores of PTNTs via chemical combination between amino group and enriched protons, which accounted for their good thermal stability at elevated temperatures. The results present herein imply that the PEI modified PTNTs could be appealing materials for capturing CO2 from power plant flue gas.

Operando DRIFTS study of the role of hydroxyls groups in trichloroethylene photo-oxidation over titanate and TiO2 nanostructures

The aim of the present research was to gain further insight into the differences of the trichloroethylene photodegradation routes when using TiO2 (Degussa P25) and protonated titanate nanotubes (H2Ti3O7). These last materials have structural hydroxyls that, along with the surface OH groups present in both photocatalysts, could mediate in the mineralization of the pollutant. In order to obtain a realistic view, an operando Diffuse Infrared Fourier Transform Spectroscopy (DRIFTS) approach has been adopted for surface analysis during the photocatalytic oxidation. The study revealed that the mineralization yield of trichloroethylene on the titanate nanotubes calcined at 300°C was better than the one obtained with the benchmark photocatalyst Degussa P25. In particular, the synthesized nanotubes showed the selective removal of some specific hydroxyl groups, suggesting that their high density and, probably, the specific characteristics of their hydroxyl species can be responsible for the enhanced dechlorination photoactivity exhibited by these nanotubular structures.

Facile Preparation and Photoinduced Superhydrophilicity of Highly Ordered Sodium-Free Titanate Nanotube Films by Electrophoretic Deposition

Highly ordered sodium-free titanate nanotube films were one-step prepared on F-doped SnO2-coated (FTO) glass via an electrophoretic deposition method by using sodium titanate nanotubes as the precursor. It was found that the self-assembled formation of highly ordered sodium titanate nanotube films was accompanied with the effective removal of sodium ions in the nanotubes during the electrophoretic deposition process, resulting in the final formation of protonated titanate nanotube film. With increasing calcination temperature, the amorphous TiO2phase is formed by a dehydration process of the protonated titanate nanotubes at 300°C and further transforms into anatase TiO2when the calcination temperature is higher than 400°C. Compared with the as-prepared titanate nanotube film, the calcined titanate nanotube film (300–600°C) exhibits attractive photoinduced superhydrophilicity under UV-light irradiation. In particular, 500°C-calcined films show the best photoinduced superhydrophilicity, probably due to synergetic effects of enhanced crystallization, surface roughness, and ordered structures of the films.

Lithium Ion Storage Characteristics of Mechanically Fractured Titanate Nanotubes

The effect of mechanical milling on the formation of short titanate nanotube and structural change induced is investigated. Mechanical milling produces the short nanotubes with the length of 30–160 nm. The lithium ion intercalation characteristics of the obtained short titanate nanotube were studied to verify the effect of the newly formed cross‐sections of nanotubes. It was found that the protonated titanate nanotubes maintained long shapes until 30 min of mechanical milling and were transformed into agglomerated nanosheets and finally anatase granules depending on the treatment duration. Through galvanostatic investigation, the nanotubes with milling of 15 min exhibited the highest discharge capacity of 336 mAh·g−1 in first cycle, 12.4% larger than pristine.

Hydrogenated titania: synergy of surface modification and morphology improvement for enhanced photocatalytic activity

Surface-hydrogenated anatase TiO(2) (TiO(2)-H) nanowire-microspheres were prepared by converting protonated titanate nanotube to TiO(2)-H under a hydrogen atmosphere. We show that TiO(2)-H nanowire-microspheres have Ti-H and O-H bonds on their surface and exhibit improved visible-light absorption and highly enhanced photocatalytic activity.

Lead titanate nanotubes synthesized via ion-exchange method: Characteristics and formation mechanism

A two-step method is presented for the synthesis of one dimensional lead titanate (PbTi 3O 7) nanotubes. Firstly, titanate nanotubes were prepared by an alkaline hydrothermal process with TiO 2 nanopowder as precursor, and then lead titanate nanotubes were formed through an ion-exchange reaction. We found that sodium titanate nanotubes have ion exchangeability with lead ions, while protonated titanate nanotubes have not. For the first time, we distinguished the difference between sodium titanate nanotubes and protonated titanate nanotubes in the ion-exchange process, which reveals a layer space effect of nanotubes in the ion-exchange reaction. In comparison with sodium titanate, the synthesized lead titanate nanotubes show a narrowed bandgap.

Preparation of Protonated Titanate Nanotube Films with an Extremely Large Wetting Contrast

ABSTRACTA facile anodic electrophoretic deposition (EPD) process has been developed to prepare thin uniform films consisting of titanate nanotubes (TNTs) that were synthesized by a hydrothermal approach. Such an EPD process offers easy control in the film thickness and the adhesion to the substrate was found to be strong. The chemical composition and structure of the products have been characterized by HRTEM, FESEM, XRD and TG/DTA. It was found that the functionalization of TNTs plays a key role on the electrolyte stability and the successful formation of a uniform TNT film with good adhesion. The as-prepared TNT films show exceptional superhydrophilic behavior with ultra-fast spreading, while it converts to superhydrophobicity yet with high adhesion after 1H,1H,2H,2H-perfluorooctyl-triethoxysilane modification. This study provides an interesting method to prepare films with extremely high wettability contrast that are useful for producing different kinds of functional materials.

ChemInform Abstract: Protonated Titanate Nanotubes as Solid Acid Catalyst.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Protonated Titanate Nanotubes as Solid Acid Catalyst

Protonated titanate nanotubes are demonstrated to function as a highly active solid Lewis acid catalyst even near room temperature. The high catalytic activity for the reaction can be attributed to the unique nanotube structure, which contains both Brønsted and Lewis acid sites.

Application of Magic-Angle Spinning NMR to Examine the Nature of Protons in Titanate Nanotubes

Systematic magic-angle spinning (MAS) 1H NMR studies of protonated titanate nanotubes (produced by alkaline hydrothermal treatment of TiO2 with NaOH) have revealed that there are several types of protons incorporated into their wall structure, including crystallographic water molecules and ion-exchangeable OH groups. Each type (a) has a characteristic chemical shift and (b) disappears at a different rate during annealing in air. The evolution of protons in titanate nanotubes during crystallographic and morphological transformation in the sequence H2Ti3O7·xH2O, H2Ti3O7, H2Ti6O13, TiO2(B), TiO2(anatase) during calcination, at temperatures from 140 to 500 °C, has been studied using MAS NMR and Raman spectroscopies together with thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The irreversible disappearance of ion-exchangeable OH groups has been observed, even under low temperature treatment.

Adsorption behavior of arsenic onto protonated titanate nanotubes prepared via hydrothermal method

A mesoporous material, titanate nanotubes (TNs) with different surface areas (197–312 m 2 g −1) and pore size diameters (2–6 nm) was synthesized by alkaline hydrothermal method. Their adsorption abilities to arsenic, the notoriously poisonous inorganic contaminant in groundwater were evaluated. Batch experiments showed that the adsorption of arsenate [As (V)] was more favored in acid solution, while the uptake of arsenite [As (III)] was preferred in alkaline solution. The maximum uptake of As (V) and As (III) calculated by Langmuir equation was 208 mg g −1 (pH 3.0) and 60 mg g −1 (pH 7.0) respectively achieved on TN (180-1) adsorbent (312 m 2 g −1, internal diameter, 5 nm), which was 33 and 10 times greater than those of nanosized titania particles (40–50 nm, 15 mg g −1). Silicate anions, phosphate and sulfate had little effect on arsenic adsorption onto TNs. In several real water samples, TNs still showed high uptake efficiency to arsenic at pH 7.0. More than 80% of As (III) and 95% of As (V) adsorbed on TNs could be desorbed with 1.0 M NaOH solution within 1 h. Comparison study indicated that all the tubular titanate materials exhibited great adsorption capacity to arsenic regardless their surface areas. Since the equipment required for TNs synthesis is simple and cheap, and alkali solutions are reusable, TNs can be regarded as an efficient, low-cost adsorbent for the removal of arsenic.

<I>In-Situ</I> Fourier Transform Infrared Spectroscopy Study on CO Oxidation Over Au/Titanate and Au/Titania Nanocatalysts

Surface charge state and surface hydroxyl coverage of the catalyst support were reported to have great impact on the CO catalytic oxidation activity. Protonic layered titanate nanotubes are featured with cation-vacancy defects and full surface Ti-OH group coverage, whereas titania nanoparticles are featured with anion-vacancy defects and partly Ti-OH surface group coverage. In order to explore the influence on the activity from these differences, Fourier transform infrared spectra study of CO adsorption and oxidation over the Au/titanate and Au/titania catalysts is performed and the results indicate that (i) both Au/titanate and Au/titania have strong adsorption for CO molecules, and (ii) the Au/titania sample has a higher reactive activity for CO oxidation than the Au/titanate sample. This phenomenon is reasonably explained combining with a traditional strong metal-support interaction theory known in CO catalytic oxidation reactions.

Solvothermal synthesis of N-doped TiO2 nanotubes for visible-light-responsive photocatalysis

Visible-light-responsive tubular N-doped TiO2 nanocrystallites were synthesized via an environment-conscious solvothermal treatment of protonated titanate nanotubes in an NH4Cl/ethanol/water solution.

Gold nanocatalysts supported on protonic titanate nanotubes and titania nanocrystals

Gold nanoparticles were first supported on protonic titanate nanotubes with the formation of Au/titanate nanocomposites. They were further transformed to Au/titania nanocomposites via an acetic acid treatment at 70 °C for 60 h. The porosity, crystal structure and morphology of those composites have been studied by X-ray diffraction (XRD), High-resolution transmission electron microscope (HRTEM), and low-temperature nitrogen adsorption. Catalytic tests for CO oxidation show that the Au/titanate nanocomposites had a promising activity with complete conversion of CO at 70 °C and that of Au/titania was at room temperature (25 °C). Both catalysts exhibited good thermal and long-term stabilities. The influence of the crystal vacancies and surface properties of the titanate and titania supports on the catalytic activities were evaluated.

Electrochemical Lithium Storage of Titanate and Titania Nanotubes and Nanorods

Layered protonated titanate nanotubes, synthesized via a hydrothermal reaction in alkaline solution, were calcined at different temperatures (200−500 °C) in air to achieve the products of various morphologies and crystal-phase compositions. The microstructure of obtained products was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption. The electrochemical lithium storage of these samples was studied by galvanostatic method and cyclic voltammetry. It is found that the protonated titanate nanotubes maintain layered structure below 300 °C and undergo phase transition to a mixture of anatase and TiO2(B) with anatase as the main phase between 300 and 500 °C. In addition, the hollow nanotube morphology still remains below 400 °C, but the tubes convert to solid nanorods during the calcination at 500 °C. It is found the nanotubes calcined at 300 and 400 °C have larger surface areas and exhibit relatively large reversible capacity and good reversibility (remain about 200 mA h/g after 80 cycles). Moreover, the electrochemical lithium storage is controlled by the pseudocapacitive effect, the mixed process of both the pseudocapacitive effect, and diffusion-limited reaction, and the diffusion-limited reaction depends on different microstructures of the resulting samples. The relationship among their phase composition, morphology, porous structure, and electrochemical properties is also discussed.

Hydrothermal synthesis of titanate nanotubes followed by electrodeposition process

Titanate nanotubes were synthesized by hydrothermal process using commercial titania nanoparticles. The experiments were carried out as a function of reaction time, temperature, and NaOH concentration. Furthermore, the titanate nanotube film was fabricated on the Si substrate using electrodeposition method with 60 V and at room temperature. The specimens were investigated by using various techniques such as field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman Spectroscopy, and Xray photoelectron spectroscopy (XPS). The formation of sodium titanate nanotubes was affected strongly by the variation in all parameters. The best conditions for the titanate nanotubes were found to be a reaction temperature of 150°C, 10 M NaOH concentration, and reaction time of 48 hr. Under the best conditions, the resulting titanate nanotubes did not contain any remains of starting material, namely P25 nanoparticles, and also the resulting nanotubes had very smooth morphology with a diameter of ∼10 nm and length extending up to several micrometers without presence of any bundlelike structures. The washing of sodium titanate nanotubes with HCl solution leads to conversion into protonic titanate nanotubes via ion exchange reaction. The subsequent sintering of the titanate nanotubes renders dehydration of interlayered OH groups, thereby leading to precipitation of anatase phase. The tubular structure also gets destroyed during phase change, beyond 375°C. The electrodeposited titanate film with 60 V for 10 min at room temperature was dense and uniform. In this work, we suggest that electrochemical deposition method of titanate nanotubes film can be used for its applications.

Syntheses, characterization and properties of novel nanostructures consisting of Ni/titanate and Ni/titania

Ni/titanate one-dimensional nanostructures and Ni/titania nanocrystal composites were produced by a facile synthetic procedure using protonic titanate nanotubes as the precursor templates. The formation mechanisms for the nanostructures were proposed. The nickel ions first enter into the titanate matrix through three approaches, ion-exchanges reaction with the interlayered hydrogen ions, capillary forces from the microcavities, and electrostatic adsorptions due to the negatively charged outer surface of the titanate nanotubes. The following metallic nickel nucleation and growth may have occurred for these three kinds of the nickel ions reduced under hydrogen gas flow at elevated temperatures. The supports' titanate nanotubes may phase transform into the anatase titania nanocrystals and further into the mixture of anatase and rutile titania along with the increases of temperature. The Ni/titanate nanocomposites demonstrate paramagnetic behaviors and the Ni/titania nanocrystals display typical ferromagnetic behaviors. The Ni/titania sample reduced at 550 °C containing 14.5% rutile has higher photocatalytic activities than the sample reduced at 350 °C containing pure anatase, which is ascribed to a synergistic effect between anatase and rutile. The ferromagnetic characteristics of the Ni/titania products make them available as magnetically separable photocatalysts, which can be separated and recovered quickly by applying an external magnetic field.