Tuning the Electronic Conductivity in Hydrothermally Grown Rutile TiO₂ Nanowires: Effect of Heat Treatment in Different Environments

Surface Oxygen Vacancies of Rutile Nanorods Accelerate Biomineralization

Titanium dioxide (TiO₂) materials have been widely used in biomedical applications of bone tissue engineering. However, the mechanism underlying the induced biomineralization onto the TiO₂ surface still remains elusive. In this study, we demonstrated that the surface oxygen vacancy defects of rutile nanorods could be gradually eliminated by the regularly used annealing treatment, which restrained the heterogeneous nucleation of hydroxyapatite (HA) onto rutile nanorods in simulated body fluids (SBFs). Moreover, we also observed that the surface oxygen vacancies upregulated the mineralization of human mesenchymal stromal cells (hMSCs) on rutile TiO₂ nanorod substrates. This work therefore emphasized the importance of subtle changes of surface oxygen vacancy defective features of oxidic biomaterials during the regularly used annealing treatment on their bioactive performances and provided new insights into the fundamental understanding of interactions of materials with the biological environment.

Correlation between the TiO2 encapsulation layer on Pt and its electrochemical behavior

Supported metal catalysts with partial encapsulation resulting from strong metal-support interactions show distinctive structural features which strongly affect their functionalities. Yet, challenges in systematic synthesis and in-depth characterization for such systems limit the present understanding of structure-property relationships. Herein, the synthesis and characterization of two Pt/TiO2 models are conducted by a simple change of the synthesis order, while keeping all other parameters constant. They differ in containing either bare or encapsulated Pt nanoparticles. The presence of an extremely thin and inhomogeneous TiO2 layer is clearly demonstrated on 2-3 nm sized Pt nanoparticles by combination of imaging, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy performed in a transmission electron microscope. The two Pt/TiO2 systems exhibit differences in morphology and local structure which can be correlated with their electrochemical activity and stability using cyclic voltammetry experiments. Beyond enhanced particle stability, we report an increase in H+ intercalation on titania and reduced Pt activity due to partial encapsulation by TiO2. Finally, the growth of an encapsulation layer as a result of cyclic voltammetry measurements is discussed. These results shed light on the in-depth structure-property relationship of catalysts with strong metal-support interactions which leads to enhanced functional materials for electrochromic devices and energy applications.

Rutile TiO2 Nanoparticles Encapsulated in a Zeolitic Imidazolate Framework-Derived Hierarchical Carbon Framework with Engineered Dielectricity as an Excellent Microwave Absorber

Aiming to solve the poor response of titanium dioxide (TiO₂) in the microwave frequency, versatile series of N-doped carbon (NC) components are employed to improve the conductivity and polarization strength of TiO₂-based composites. The bimetallic zeolitic imidazolate framework-derived TiO₂@NC complex (TNC-3) exhibits hierarchical microstructures and large-scale hetero-interfaces, whereas the pyrolysis composite of metal-polydopamine-coated TiO₂ (TNC-4) possesses the vesicle-like NC shell and bulk TiO₂ core. Thus, the optimal reflection loss and efficient absorption bandwidth of TNC-3 realize -44.0 dB at 3.0 mm and 5.4 GHz at only 2.0 mm of coating thickness, respectively. Nevertheless, the corresponding attenuation ability of TNC-4 is separately -24.3 dB and 4.8 GHz with a thickness of 5.0 and 2.0 mm, respectively. Importantly, the conduction and polarization loss can be enhanced by the large-scale interfacial contacts between nanoscale rutile nanoparticles and hierarchical graphitized carbon. Meanwhile, the superior performance of TNC-3 stems from the large proportion of pyridinic N and pyrrolic N, which provides asymmetric lone pairs to strengthen the dipole rotation. These results are of great value in constructing semiconductor-based complexes by carbon-coating engineering as functional materials.

Hydrothermally Grown TiO2 Nanorod Array Memristors with Volatile States

In the present study, the memristive characteristics of hydrothermally grown TiO₂ nanorod arrays, particularly, the difference in the retention time of the resistance state, are investigated in dependence of the array growth temperature. A volatile behavior is observed and related to a redistribution of oxygen vacancies over time. It is shown that the retention time increases for increasing array growth temperatures from several seconds up to 20 min. The relaxation behavior is also seen in the current-voltage characteristics, which do not show the common unipolar, bipolar, or complementary switching behavior. Instead, the temporal evolution depends on the duration of the applied voltage and on the nanowire growth temperature. Therefore, electronic measurements are combined with scanning electron and scanning transmission electron microscopy, so that the amount of oxygen defect-rich grain boundaries in the upper part of the nanowires can be linked to the differences in the current-voltage behavior and retention time.

Biomimetic Sensitive Elements for 2,4,6-Trinitrotoluene Tested on Multi-Layered Sensors

In spite of technological progress, most of the current techniques for 2,4,6-trinitrotoluene (TNT) detection are time consuming due to laborious sensor preparation. Thereby, the aim of this work was to enlarge the knowledge for preparing sensitive elements for TNT with the aid of molecular imprinting; a known technique used to deliver biomimetic materials. The study first depicts the auto-assembly mechanism of (TNT) with functional diamino-silanes (i.e., N-(2-aminoethyl)-3-aminopropyl methyl dimethoxysilane), via “double” Meisenheimer complexes. This mechanism is being described herein for the first time and applied further to obtain molecularly imprinted polymer (MIP) films for TNT recognition. For testing the potential application of films as chemical sensor elements, typical rebinding assays of TNT in a liquid state and the rebinding of TNT in a vapor state, using multilayered sensor chips composed of quartz-chromium (Cr)-gold (Au)-titanium oxide (TiO2), were employed. Batch rebinding experiments have shown that thinner films were more efficient on retaining TNT molecules in the first five min, with a specificity of about 1.90. The quartz-Cr-Au-TiO2-MIP capacitive sensors, tested in vapor state, registered short response times (less than 25 s), low sensitivity to humidity and high specificity for TNT.

One-Step Acidic Hydrothermal Preparation of Dendritic Rutile TiO₂ Nanorods for Photocatalytic Performance

Three-dimensional and dendritic rutile TiO₂ nanorods were successfully fabricated on a Ti foil surface using a one-step acidic hydrothermal method. The TiO₂ nanorods were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical contact angle testing. The results showed that the nanorods with diameters of 100⁻500 nm and lengths of 100 nm to 1 μm were obtained on the Ti foil surface. The length and density of the TiO₂ nanorods were perfect at the conditions of HCl concentration 0.5 mol/L, temperature 220 °C, and reaction time 12 h. The TiO₂ nanorods formed parallel to the consumption of Ti and grew along the (110) direction having a tetragonal rutile crystal. The morphology of the nanorods possessed a three-dimensional structure. The contact angle of the nanorods was only 13 ± 3.1°. Meanwhile, the photocatalytic activities of the TiO₂ nanorods were carried out using ultraviolet fluorescence spectrophotometry for the methyl orange detection, and the degradation was found to be about 71.00% ± 2.43%. Thus, TiO₂ nanorods can be developed by a one-step acidic hydrothermal method using Ti foil simultaneously as the substrate with a TiO₂ source; the TiO₂ nanorods exhibited photocatalytic performance while being environment-friendly.

Superior solar-to-hydrogen energy conversion efficiency by visible light-driven hydrogen production via highly reduced Ti2+/Ti3+ states in a blue titanium dioxide photocatalyst

A catalytic hydrogen production system was developed with TiO₂ that contains Ti³⁺/Ti²⁺ reduced states which act as both visible and IR light harvesting components as well as the catalytic site.