Moisture-Promoted, Defect-Rich UiO-67/TiO2 Nanotube Heterojunctions for ppb-Level H2S Detection under Ambient Conditions.

In this paper, a facile method was proposed to load CeO2 nanoparticles (NPs) on anodic TiO2 nanotube (NT) arrays, which leads to a formation of CeO2/TiO2 heterojunctions. Highly ordered anatase phase TiO2 NT arrays were fabricated by using anodic oxidation method, then these individual TiO2 NTs were used as tiny “nano-containers” to load a small amount of Ce(NO3)3 solutions. The loaded anodic TiO2 NTs were baked and heated to a high temperature of 450 °C, under which the Ce(NO3)3 would be thermally decomposed inside those nano-containers. After the thermal decomposition of Ce(NO3)3, cubic crystal CeO2 NPs were obtained and successfully loaded into the anodic TiO2 NT arrays. The prepared CeO2/TiO2 heterojunction structures were characterized by a variety of analytical technologies, including XRD, SEM, and Raman spectra. This study provides a facile approach to prepare CeO2/TiO2 films, which could be very useful for environmental and energy-related areas.

Exhaled breath is considered an important source of samples and a reservoir of biomarkers, especially for disease diagnosis. In this study, we developed an ultrasensitive point-of-care gas sensor for the analysis of hydrogen sulfide (H2S), which is a typical biomarker for periodontitis. A high-performance metal oxide semiconductor (MOS)-based chemiresistive H2S sensor was developed by integrating Fe-doped MoO3-x onto TiO2 nanotube arrays. The substitution of Fe atoms into MoO3-x not only induced oxygen vacancies, but also generated defect levels in the MoO3-x/TiO2 heterostructure, thus synergistically activating the gas sensing reaction at room temperature under ambient light. The resulting gas sensor exhibited ultrahigh sensitivity, fast response/recovery ability, and wide-range response to H2S concentrations up to 400 ppm. Furthermore, the sensing device maintained more than 95% of its original response at 70% relative humidity. With a subparts-per-billion limit of detection (the LOD for H2S was 0.34 ppb), the present sensor represents the most sensitive H2S chemiresistor reported to date for room-temperature, real-time monitoring of H2S concentration changes in the breath of healthy subjects, as well as for distinguishing breath samples of periodontitis patients and healthy individuals. This study utilizes the synergistic action of defects to provide an effective route for developing MOS-based ultrasensitive H2S sensors for periodontitis diagnosis.

We have employed a simple process of anodizing Ti foils to prepare TiO2 nanotube arrays which show enhanced electrochemical properties for applications as Li-ion battery electrode materials. The lengths and pore diameters of TiO2 nanotubes can be finely tuned by varying voltage, electrolyte composition, or anodization time. The as-prepared nanotubes are amorphous and can be converted into anatase nanotubes with heat treatment at 480 degrees C. Rutile crystallites emerge in the anatase nanotube when the annealing temperature is increased to 580 degrees C, resulting in TiO2 nanotubes of mixed phases. The morphological features of nanotubes remain unchanged after annealing. Li-ion insertion performance has been studied for amorphous and crystalline TiO2 nanotube arrays. Amorphous nanotubes with a length of 3.0 microm and an outer diameter of 125 nm deliver a capacity of 91.2 microA h cm(-2) at a current density of 400 microA cm(-2), while those with a length of 25 microm and an outer diameter of 158 nm display a capacity of 533 microA h cm-2. When the 3-microm long nanotubes become crystalline, they deliver lower capacities: the anatase nanotubes and nanotubes of mixed phases show capacities of 53.8 microA h cm-2 and 63.1 microA h cm(-2), respectively at the same current density. The amorphous nanotubes show excellent capacity retention ability over 50 cycles. The cycled nanotubes show little change in morphology compared to the nanotubes before electrochemical cycling. All the TiO2 nanotubes demonstrate higher capacities than amorphous TiO2 compact layer reported in literature. The amorphous TiO2 nanotubes with a length of 1.9 microm exhibit a capacity five times higher than that of TiO2 compact layer even when the nanotube array is cycled at a current density 80 times higher than that for the compact layer. These results suggest that anodic TiO2 nanotube arrays are promising electrode materials for rechargeable Li-ion batteries.

It has been revealed that the different morphologies of anodized TiO2 nanotubes, especially nanotube diameters, triggered different cell behaviors. However, the influence of TiO2 nanotubes with coexisting multi-size diameters on cell behaviors is seldom reported. In this work, coexisting four-diameter TiO2 nanotube samples, namely, one single substrate with the integration of four different nanotube diameters (60, 150, 250, and 350 nm), were prepared by repeated anodization. The boundaries between two different diameter regions show well-organized structure without obvious difference in height. The adhesion behaviors of MC3T3-E1 cells on the coexisting four-diameter TiO2 nanotube arrays were investigated. The results exhibit a significant difference of cell density between smaller diameters (60 and 150 nm) and larger diameters (250 and 350 nm) within 24 h incubation with the coexistence of different diameters, which is totally different from that on the single-diameter TiO2 nanotube arrays. The coexistence of four different diameters does not change greatly the cell morphologies compared with the single-diameter nanotubes. The findings in this work are expected to offer further understanding of the interaction between cells and materials.

Amorphous and crystalline MoO3 coatings are synthesized on anodic TiO2 nanotube arrays by electrodeposition, as a self-standing, binder-free anode material in Li-ion batteries for enhancing the Li-ion insertion performance. The amorphous MoO3 layer is uniform and conformal with a thickness of 10 nm, and is converted into crystalline nanoparticles via thermal treatment. Our results show that both the coated TiO2 nanotubes deliver much higher areal capacities than bare nanotubes or a dense crystalline α-MoO3 film, while the crystalline α-MoO3 coating greatly increases the areal capacity of TiO2 nanotubes compared to the amorphous. The results are obtained at 1340 μA h cm−2 initial capacity for nanotubes with a crystalline coating, 977 μA h cm−2 for those with an amorphous coating and 342 μA h cm−2 for the bare ones. The significant enhancement is due to a combination of MoO3 with high specific capacity and TiO2 nanotube arrays with large surface area allowing uniform MoO3 deposition and rapid ionic transfer. Crystalline α-MoO3 is better than amorphous MoO3 and the coating medium is discussed in terms of chemical state, crystal defects, capacitive contributions and the charge–discharge kinetics in coated TiO2 nanotube electrodes.

Synthesis and electrochemical properties of CeO2 nanoparticle modified TiO2 nanotube arrays

CdSe-sensitized TiO2 nanotube array film fabricated by ultrasonic-assisted electrochemical deposition and subsequently wrapped with TiO2 thin layer for the visible light photoelectrocatalysis

In the present study, ITO nanowires electrode within the anodized TiO2 nanotubes without using the polycarbonate membrane templates were attempted. The process begins with an anodized TiO2 nanotube arrays (TNA) and subsequent growth of indium‐tin‐oxide (ITO) nanowires into the TiO2 nanotube arrays via the electrophoretic process (EPD). The open‐end of TiO2 nanotubes were synthesized for the photoelectrode of DSSC. ITO nanowires were then grown into these TNA by EPD process. The composite of ITO/anodized TNA was employed as the working electrode for the assembly into DSSCs. The advantage of the present method is that the membrane templates in EPD process were not required. In addition, the ITO nanowires will surely not contact each other which might cause short circuit. The morphologies and the structures of ITO nanowires and TNA electrode were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Solution processed, vertically aligned, AZO nanocolumn array for chemiresistive sensor application with UV-enhanced sensitivity

Reduction in the band gap of anodic TiO2 nanotube arrays by H2 plasma treatment

TiO2 nanotube arrays treated with (NH4)2TiF6 dilute solution for better supercapacitive performances

Chapter 7 - Fabrication of chemiresistive gas sensor with carbon materials/polymers nanocomposites

Development of electrophoretically deposited hydroxyapatite coatings on anodized nanotubular TiO2 structures: Corrosion and sintering temperature

Intricate behaviors of gas phase CO2 photoreduction in high vacuum using Cu2O-loaded TiO2 nanotube arrays

One-dimensional nitrogen-doped carbon nanotube arrays fabricated by template carbonization over anodized TiO2 nanotube arrays