A step forward towards the structural characterization of Na2Ti2O5·H2O nanotubes and their correlation with optical and electric transport properties

In this work we present the synthesis, structural, morphological, optical and electrochemical characterization of sodium titanate nanotubes (NaNT) obtained by hydrothermal means. According to our detailed structural study, we found that a Na₂Ti₂O₅·H₂O layered crystalline phase with [TiO₅] pyramidal square base coordination, utilized as a building block of the nanotubes, explains satisfactorily the experimental results. This is a very important aspect, since the bibliography does not always provide structural information about titanate nanotubes. With respect to the formation mechanism we highlight the crucial role of the post treatment washing in the final crystalline structure of the nanotubes. Simulated X-rays powder diffraction patterns (XRPD), based on real size nanotubes models, were refined with experimental data. Building blocks for the NaNT model were inferred from computational simulations, by means of Density Functional Theory. The obtained tube's model characteristic dimensions were also consistent with SAXS and TEM analysis. In addition, our SAXS analysis suggested that the presence of humidity in the cavities of titanate nanotubes is progressively lost at the 80–100 °C temperature range, in good agreement with thermogravimetric analysis. Electrochemical impedance spectroscopy analysis for dried samples in the temperature range, studied under cooling conditions, revealed a single ionic transport mechanism, probably associated to the in-between [TiO₅] layers ion transport. However, a secondary process was observed for non-dried samples, during heating conditions, that could be associated to the ionic transport along the water filled tube's cavity, consistent with SAXS analysis. In summary, this work shows an integral approach, through theory and experiment, in order to understand the effect of the structure on the physical and electronic properties of the system.     

Influence of the neutralization process on the preparation of titanate nanotubes by hydrothermal synthesis

The influence of the neutralization process after hydrothermal synthesis on the structure and morphology of titanate nanotubes was investigated by X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy. Well formed nanotubes were obtained during the hydrothermal treatment of anatase in highly alkaline conditions. Synthesis at 150 °C led to the formation of layered titanate structure with the general formula Na_2−x H _x Ti₂O₅·1.8 H₂O, where x depends on pH. The tubular morphology is not dependent on the Na⁺/H⁺ ion exchange reaction.     

Flash synthesis of Magnéli phase (TinO2n-1) nanoparticles by thermal plasma treatment of H2TiO3

A flash synthesis method of titanium suboxides (TSO) Ti_nO_2n-1 nanoparticles with Magnéli phases by thermal plasma using rutile-phase metatitanic acid (H₂TiO₃) as the raw material was proposed and investigated, comparing with common sintering hydrogenation process of H₂TiO₃. TSO powders with diverse colors were prepared and characterized by means of XRD, SEM and TEM. The results showed Magnéli phase nanoparticles with perfect spherical shape and particle size of 20–100 nm were rapidly synthesized by thermal plasma treatment under Ar and Ar/H₂ atmospheres. Typical Magnéli phases of Ti₅O₉ and Ti₄O₇ with peacock blue color were formed under argon atmosphere. An increase of hydrogen content in the atmosphere made nano-H₂TiO₃ efficiently reduced to form a different TSO phases with diverse colors of dark blue to blue black. Notably, parts of nanoparticles were of carbon shell/Magnéli phase core structure. The UV–visible absorptivity and electric conductivity of samples were tested and the results indicate that thermal plasma is an efficient way to improve the optical and conductive properties of materials. But the electric resistivity of nano Magnéli phase powders still keep 10⁵–10⁶ Ω^.cm.     

Synthesis of Heterogeneous Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> Nanostructured Anodes with Long-Term Cycle Stability

The 0D-1D Lithium titanate (Li₄Ti₅O₁₂) heterogeneous nanostructures were synthesized through the solvothermal reaction using lithium hydroxide monohydrate (Li(OH)·H₂O) and protonated trititanate (H₂Ti₃O₇) nanowires as the templates in an ethanol/water mixed solvent with subsequent heat treatment. A scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM) were used to reveal that the Li₄Ti₅O₁₂ powders had 0D-1D heterogeneous nanostructures with nanoparticles (0D) on the surface of wires (1D). The composition of the mixed solvents and the volume ratio of ethanol modulated the primary particle size of the Li₄Ti₅O₁₂ nanoparticles. The Li₄Ti₅O₁₂ heterogeneous nanostructures exhibited good capacity retention of 125 mAh/g after 500 cycles at 1C and a superior high-rate performance of 114 mAh/g at 20C.     

Cu/Cu2O nanoparticles modified Ti3C2 MXene with in-situ formed TiO2-X for detection of hydrogen peroxide

Hydrogen peroxide (H₂O₂) is frequently used in various chemical reactions, the food industry, environmental protection, and the medical and biological fields. Cost-effective, simple, and quick detection technologies with great sensitivity are highly desired. The emerging two-dimensional MXene is favorable in the sensing field due to its outstanding conductivity, stability, and large surface area. Moreover, the in-situ generated TiO_2-X on Ti₃C₂ MXene has been proven an excellent biosensor material due to its biocompatibility. Herein, we decorated Cu/Cu₂O nanoparticles onto Ti₃C₂ MXene with in-situ generated TiO_2-X nanoparticles, forming heterojunction through a simple one-step hydrothermal process. The Cu/Cu₂O/TiO_2-X/Ti₃C₂ (Cu/Cu₂O/TT) exhibits good electrochemical sensing capability toward H₂O₂, with a linear range up to 28.328 mM, a sensitivity of 312 μA mM^?1 cm^?2, and a detection limit (LOD) of 0.42 μΜ. The synergistic interactions between Cu/Cu₂O nanoparticles and TiO_2-X/Ti₃C₂ heterojunction not only improved electron transfer and electrocatalytic activity, but also facilitated the mobility of targeting molecules on the catalyst due to the abundance of exposed catalytic sites. Therefore, compared to TiO_2-X/Ti₃C₂, Cu/Cu₂O/TT has a lower LOD, faster reaction, and five times the sensitivity. Additionally, the outstanding photoelectrochemical (PEC) sensing performance is demonstrated of Cu/Cu₂O/TT for H₂O₂ detection, displaying a low LOD, long-term stability, repeatability, and selectivity. This report may expand the application of MXene-based materials as electrochemical sensors.     

Experimental study on CO2 hydrate formation in the presence of TiO2, SiO2, MWNTs nanoparticles

ABSTRACT

A series of experiments on CO₂ hydrate formation were carried out in the presence of titanium dioxide (TiO₂), silicon dioxide (SiO₂), multi-walled carbon nanotubes (MWNTs) nanoparticles. The effects of these nanoparticles on induction time, final gas consumption, and gas storage capacity have been investigated at the temperature of 274.15 K and the initial pressure of 5.0 MPa.g. The induction time of CO₂ hydrate formation was remarkably shortened to 12.5 min in the presence of 0.005 wt% MWNTs nanoparticles. The high thermal conductivity and heat capacity of MWNTs nanoparticles presented better heat transfer, and large surface area provided more suitable sites for heterogeneous nucleation of CO₂ hydrate.     

A highly active bi-crystalline photocatalyst consisting of TiO2 (B) nanotube and anatase particle for producing H2 gas from neat ethanol

Sodium titanate nanotubes (NaTNTs) are converted into monoclinic TiO₂ (B) nanotubes by rinsing with 0.10 M HCl followed by drying at 573 K. As calcination temperature is increased to 673 K, these TiO₂ (B) nanotubes start to transform into anatase nanoparticles producing a bi-crystalline mixture consisting of TiO₂ (B) nanotubes and anatase nanoparticles. The primary particle size of the anatase particles was estimated to be around 10 nm using Scherrer equation. After being promoted with 1% Pt, this bi-crystalline material becomes a very active photocatalyst producing 20% more H₂ gas than 1% Pt/Degussa P-25 TiO₂ in the photocatalytic dehydrogenation of neat ethanol after 2 h of UV light irradiation.     

Highly selective Pd/titanate nanotube catalysts for the double-bond migration reaction

Pd(II) and Pd(0) catalysts supported onto titanate nanotubes (H₂Ti₃O₇) were prepared by an ion-exchange technique. The catalysts are characterised by narrow size distribution of metal nanoparticles on the external surface of the nanotubes. Pd(II) catalysts show high selectivity toward double-bond migration reaction versus hydrogenation in linear olefins. The catalytic activity exhibits a volcano-type dependence on the metal loading, with the maximum activity observed at ca. 8 wt%. The Pd(II) was shown to be rapidly reduced to Pd(0) by appropriate choice of solvent. Prereduced Pd(0) catalysts were found to be less active toward double-bond migration and more selective toward hydrogenation. The DBM reaction was faster in protic solvents, such as methanol or ethanol.     

Synthesis,characterization and simulation of lithium titanate nanotubes for dye sensitized solar cells

In this work we present the comprehensive design of lithium titanate nanotubes (LiTNT) as semiconductors for DSSC photoanodes. The synthesis and characterization of Li_1.82Na_0.18Ti₃O₇.nH₂O nanotubes was performed and a prototype of cell using this material was assembled. The cell exhibited a 7.7% efficiency and a relatively high open circuit voltage, Voc?=?0.72?V. In comparison with previously obtained hydrogen titanate nanotubes (HTNT), improvements have been achieved, like better charge carriers’ lifetime and lower series resistance. In order to study this system, we carried out previous DFT simulations for this lithium titanate nanotubes through different model's complexity levels which were able to correctly predict its properties. Due to the improvements achieved this system would encourage further studies with the aim to explore its potential for solar cells applications.     

Preparation of K2Ti6O13 fibers by electrospinning for near-infrared reflectivity

Ceramic coatings have been widely used in industrial fields. K₂Ti₆O₁₃ fibers could be a potential coating material for low thermal conductivity, high mechanical strength and infrared reflectivity. The precursor fibers, using potassium acetate (CH₃COOK) and tetrabutyl titanate (TBOT) as potassium and titanium sources, were prepared by the electrospinning technique with the sol-gel method. To prepare K₂Ti₆O₁₃ fibers, the mole ratio of K/Ti was adjusted from 1:2 to 1:3. The transformation of other phases of potassium titanates was characterized by XRD patterns and Raman spectra. The effects of mole ratio of K/Ti on morphology of samples have been investigated. Well-crystallized fibers were prepared with single-crystal K₂Ti₆O₁₃ structure. The corresponding morphology and microstructure evolution were studied by SEM and TEM. The as-obtained K₂Ti₆O₁₃ fibers possessed the high near-infrared (NIR) reflectivity of 98%.     

Cost-effective Li4Ti5O12/C–S prepared by industrial H2TiO3 under a carbon reducing atmosphere as a superior anode for Li-ion batteries

Spinel-type Li₄Ti₅O₁₂ (LTO) is known as a “zero-strain” material due to its negligible structural change during the charge/discharge process. However, high production cost and poor electrical conductivity limit the wide application of spinel-type LTO. Herein, a novel preparation process was developed to prepare a Li₄Ti₅O₁₂/C–S composite using industrial H₂TiO₃ as the titanium source. In the calcination process under a carbon reducing atmosphere, SO₄^2? adsorbed on industrial H₂TiO₃ not only promotes the carbonization of glucose on the surface of LTO but also introduces S heteroatoms into the carbon coating layer in the form of C–S bonds through a series of reactions with glucose, which significantly improves the overall conductivity and the Li⁺ diffusion coefficient of the material. Therefore, the synthesized Li₄Ti₅O₁₂/C–S composite exhibits excellent rate performance and cycling stability, with a specific capacity of 135.88 mAh g^?1 even at 10C and a capacity decay rate of only 0.011% per cycle after 1000 cycles at 5C. This study delivers a novel method for the industrial production of LTO with both cost and performance advantages.     

Synthesis and photocatalytic properties of H2La2Ti3O10/TiO2 intercalated nanomaterial

H₂La₂Ti₃O₁₀/ TiO₂ intercalated nanomaterial was fabricated by successive intercalation reactions of H₂La₂Ti₃O₁₀ with n-C₆H₁₃NH₂/C₂H₅OH mixed solution and acid TiO₂ sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46 nm and a specific surface area of 31.58 m²·g⁻¹, which indicate the formation of a porous material. H₂La₂Ti₃O₁₀/TiO₂ shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity of TiO₂ intercalated material was superior to the unsupported one.     

High-rate characteristics of novel anode Li4Ti5O12/polyacene materials for Li-ion secondary batteries

In recent years, spinel lithium titanate (Li₄Ti₅O₁₂) as a superior anode material for energy storage battery has attracted a great deal of attention because of the excellent Li-ion insertion and extraction reversibility. However, the high-rate characteristics of this material should be improved if it is used as an active material in large batteries. One effective way to achieve this is to prepare electrode materials coated with carbon. A Li₄Ti₅O₁₂/polyacene (PAS) composite were first prepared via an in situ carbonization of phenol-formaldehyde (PF) resin route to form carbon-based composite. The SEM showed that the Li₄Ti₅O₁₂ particles in the composite were more rounded and smaller than the pristine one. The PAS was uniformly dispersed between the Li₄Ti₅O₁₂ particles, which improved the electrical contact between the corresponding Li₄Ti₅O₁₂ particles, and hence the electronic conductivity of composite material. The electronic conductivity of Li₄Ti₅O₁₂/PAS composite is 10⁻¹ S cm⁻¹, which is much higher than 10⁻⁹ S cm⁻¹ of the pristine Li₄Ti₅O₁₂. High specific capacity, especially better high-rate performance was achieved with this Li₄Ti₅O₁₂/PAS electrode material. The initial specific capacity of the sample is 144 mAh/g at 3 C, and it is still 126.2 mAh/g after 200 cycles. By increasing the current density, the sample still maintains excellent cycle performance.     

Rationally designed CdS/Ti3C2 MXene electrocatalysts for efficient CO2 reduction in aqueous electrolyte

MXene-based catalysts have shown excellent activities in various electrocatalytic reactions due to the two-dimensional structure, good electrical conductivity and abundant surface functional groups. However, because of the competitive reactions in aqueous electrolytes, the application of MXene materials in CO₂ electroreduction still remains a challenge. Herein, a simple strategy was developed for the design of high efficient and stable CO₂ electroreduction catalysts in aqueous electrolyte. A series of MXene composite catalysts were successfully synthesized by densely coating sulfur vacancy-rich CdS nanoparticles on Ti₃C₂. The two-dimensional MXene skeleton with good conductivity delivers fast electron transfer, improves the electrolyte infiltration and increases the electrochemical surface area. CdS nanoparticles with abundant sulfur vacancies are attached on Ti₃C₂ MXene surface, providing active sites for CO₂ reduction. Faraday efficiency of the by-product hydrogen could be significantly reduced by minimizing the surface-exposed Ti of the catalyst. Benefited from these merits, the optimal CdS/Ti₃C₂ possesses fast CO₂ electroreduction reaction kinetics, exhibiting a high CO Faraday efficiency of 94% at -1.0 V vs. reversible hydrogen electrode. This work provides a feasible pathway for the design of MXene-based catalysts of CO₂ electroreduction.     

Fabrication of porous silicon nanowires by MACE method in HF/H2O2/AgNO3 system at room temperature

In this paper, the moderately and lightly doped porous silicon nanowires (PSiNWs) were fabricated by the ‘one-pot procedure’ metal-assisted chemical etching (MACE) method in the HF/H₂O₂/AgNO₃ system at room temperature. The effects of H₂O₂ concentration on the nanostructure of silicon nanowires (SiNWs) were investigated. The experimental results indicate that porous structure can be introduced by the addition of H₂O₂ and the pore structure could be controlled by adjusting the concentration of H₂O₂. The H₂O₂ species replaces Ag⁺ as the oxidant and the Ag nanoparticles work as catalyst during the etching. And the concentration of H₂O₂ influences the nucleation and motility of Ag particles, which leads to formation of different porous structure within the nanowires. A mechanism based on the lateral etching which is catalyzed by Ag particles under the motivation by H₂O₂ reduction is proposed to explain the PSiNWs formation.     

Microstructure effect on the electrochemical property of Li4Ti5O12 as an anode material for lithium-ion batteries

Porous (P-) and dense (D-) lithium titanate (Li₄Ti₅O₁₂) powders as an anode material for lithium-ion batteries have been synthesized by spray drying followed by solid-state calcination. Electrochemical testing results showed that the discharge capacities of P-Li₄Ti₅O₁₂ are 144 mAh/g, 128 mAh/g and 73 mAh/g at the discharging rate of 2C, 5C and 20C, respectively (cut-off voltages: 0.5-2.5 V). The corresponding values for D-Li₄Ti₅O₁₂ are 108 mAh/g, 25 mAh/g and 17 mAh/g. The higher capacity of the P-Li₄Ti₅O₁₂ at high charge/discharge rates was attributed to the shorter transport path of Li ions and higher electronic conductivity in the P-Li₄Ti₅O₁₂ as a result of its smaller primary particle size and higher surface area compared with those of the D-Li₄Ti₅O₁₂.     

Electrorheological response of swollen silicone gels containing barium titanate

We have investigated storage moduli of silicone gels containing barium titanate in the presence of dc electric fields. The gels containing barium titanate swollen by silicone oil showed a storage modulus reduction, i.e. negative electrorheological effect. Contrary, no negative electrorheological effect was observed in the unswollen gels and silicon gels without barium titanate. Swollen silicone gels and most of silicone/BaTiO₃ gels obeyed empirical quadratic dependence in electric field strength. Although an apparent phase separation was not observed in the swollen gel, microscopic phase separation may occur due to the difference in electric conductivity between particles (∼10⁻¹⁰ S/cm) and silicone oil (10⁻⁹ S/cm), as a result, the negative electrorheological effect appears. The effects of frequency, degree of swelling, and the field strength have been discussed.     

Tuning the electronic and thermal transport behaviors of metal-dispersed Ti2O3 composites derived by metal–insulator transition

Thermal management requires an understanding of the relations among the thermal energy transfer, electronic properties, and structures of thermoconductive materials. Here, we enhanced the metal–insulator transition (MIT)-induced effect on the thermal conductivities of microstructure-controlled Ti₂O₃ composites containing W as a thermal conductive filler at approximately 450 K. To change the electronic and thermal transport properties, we varied the particle radii of the conductive phases in the raw material. The change in the calculated electronic thermal conductivity relative to the electrical conductivity of the W_x(Ti₂O₃)_1?x composite was enhanced by compounding the material. When x was reduced from 50 vol% to 20 vol% and the W particle diameter was reduced from 150 μm to 5 μm, the variation in the estimated electronic thermal conductivity of the W_x(Ti₂O₃)_1?x composite was increased by a factor of 2.01. The total thermal conductivity was also changed by the MIT. At x = 50 vol% and a W particle diameter of 5 μm, the maximum thermal conductivity change was 6.34 times larger than that of pure Ti₂O₃. The detailed relation between the MIT-induced changes in thermal transport and the microstructure were elucidated in classical effective medium approximations.     

The structural and electrical comparison of Y2O3 and Ti-doped Y2O3 dielectrics

A Ti-doped Y₂O₃(Y₂Ti₂O₅) dielectric on polycrystalline silicon followed by rapid thermal annealing results in improved characteristics including a higher effective dielectric constant, higher breakdown electric field, lower electron trapping rate, and larger charge-to-breakdown when compared with Y₂O₃. The performance of high-k Y₂O₃ and Y₂Ti₂O₅ dielectrics were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), capacitance-voltage, and current density-voltage. Incorporating Ti into the Y₂O₃ dielectric imparts improvements in the structural and electrical performance of the material. The Y₂Ti₂O₅ dielectric with 800 °C annealing treatment has the best performance among all the samples tested.     

Gold nanoparticles mediate the assembly of manganese dioxide nanoparticles for H2O2 amperometric sensing

Aggregates of gold nanoparticles (AuNPs) that mediate the assembly of manganese dioxide nanoparticles (nano-MnO₂) for hydrogen peroxide (H₂O₂) amperometric sensing have been developed. The aggregates were prepared by directly mixing citric-capped AuNPs and poly(allylamine hydrochloride) (PAH)-capped nano-MnO₂ using an electrostatic self-assembly strategy. The prepared sensor exhibited excellent electrochemical behaviors and a wide linear range from 7.80 × 10⁻⁷ to 8.36 × 10⁻⁴ M with a detection limit of 4.68 × 10⁻⁸ M (S/N = 3) because of the synergistic influence of excellent catalytic ability of MnO₂ and good electrical conductivity of AuNPs. In addition, its applicability to practical samples for measuring H₂O₂ in toothpastes has obtained a satisfactory result. Due to the ease of preparation and excellent properties of the sensor, indicating the MnO₂-AuNP material may be a potential H₂O₂ sensor.