We report the growth and enhanced photoelectrochemcial (PEC) water-splitting reactivity of few-layer MoS2 nanosheets on TiO2 nanowires. TiO2 nanowires with lengths of ~1.5 ~ 2.0 μm and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 oC using hydrothermal methods with Ti(C4H9O)4. Few-layer MoS2 nanosheets with heights of ~250 ~ 300 nm are vertically grown on TiO2 nanowires at a moderate growth temperature of 300 oC using metalorganic chemical vapor deposition. The MoS2 nanosheets on TiO2 nanowires exhibit typical Raman and ultraviolet-visible light absorption spectra corresponding to few-layer thick MoS2. The PEC performance of the MoS2 nanosheet/TiO2 nanowire heterostructure is superior to that of bare TiO2 nanowires. MoS2/TiO2 heterostructure shows three times higher photocurrent than that of bare TiO2 nanowires at 0.6 V. The enhanced PEC photocurrent is attributed to improved light absorption of MoS2 nanosheets and efficient charge separation through the heterojunction. The photoelectrode of the MoS2/TiO2 heterostructure is stably sustained during on-off switching PEC cycle.

One-dimensional rutile TiO2 is an important inorganic compound with applicability in sensors, solar cells, and Li-based batteries. However, conventional synthesis methods for TiO2 nanowires are complicated and entail risks of environmental contamination. In this work, we report the growth of TiO2 nanowires on a Ti alloy powder (Ti-6wt%Al- 4wt%V, Ti64) using simple thermal oxidation under a limited supply of O2. The optimum condition for TiO2 nanowire synthesis is studied for variables including temperature, time, and pressure. TiO2 nanowires of ~5 μm in length and 100 nm in thickness are richly synthesized under the optimum condition with single-crystalline rutile phases. The formation of TiO2 nanowires is greatly influenced by synthesis temperature and pressure. The synthesized TiO2 nanowires are characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM).

TiO2 nanowires were grown by thermal oxidation of TiO powder in an oxygen and nitrogen gas environment at 1000 oC. The ratio of O2 to N2 in an ambient gas was changed to investigate the effect of the gas ratio on the growth of TiO2 nanowires. The oxidation process was carried out at different O2/N2 ratios of 0/100, 25/75, 50/50 and 100/0. No nanowires were formed at O2/N2 ratios of less than 25/75. When the O2/N2 ratio was 50/50, nanowires started to form. As the gas ratio increased to 100/0, the diameter and length of the nanowires increased. The X-ray diffraction pattern showed that the nanowires were TiO2 with a rutile crystallographic structure. In the XRD pattern, no peaks from the anatase and brookite structures of TiO2 were observed. The diameter of the nanowires decreased along the growth direction, and no catalytic particles were detected at the tips of the nanowires which suggests that the nanowires were grown with a vapor-solid growth mechanism.

We synthesized Fe-doped TiO2/α-Fe2O3 core-shell nanowires(NWs) by means of a co-electrospinning method anddemonstrated their magnetic properties. To investigate the structural, morphological, chemical, and magnetic properties of thesamples, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectronspectroscopy were used, as was a vibrating sample magnetometer. The morphology of the nanostructures obtained aftercalcination at 500oC exhibited core/shell NWs consisting of TiO2 in the core region and α-Fe2O3 in the shell region. In addition,the XPS results confirmed the formation of Fe-doped TiO2 by the doping effect of Fe3+ ions into the TiO2 lattice, which canaffect the ferromagnetic properties in the core region. For comparison, pure α-Fe2O3 NWs were also fabricated using anelectrospinning method. With regard to the magnetic properties, the Fe-doped TiO2/α-Fe2O3 core-shell NWs exhibited improvedsaturation magnetization(Ms) of approximately ~2.96emu/g, which is approximately 6.1 times larger than that of pure α-Fe2O3NWs. The performance enhancement can be explained by three main mechanisms: the doping effect of Fe ions into the TiO2lattice, the size effect of the Fe2O3 nanoparticles, and the structural effect of the core-shell nanostructures.

TiO2 nanowires were self-catalytically synthesized on bare Si(100) substrates using metallorganic chemical vapor deposition. The nanowire formation was critically affected by growth temperature. The TiO2 nanowires were grown at a high density on Si(100) at 510˚C, which is near the complete decomposition temperature (527˚C) of the Ti precursor (Ti(O-iPr)2(dpm)2). At 470˚C, only very thin (< 0.1μm) TiO2 film was formed because the Ti precursor was not completely decomposed. When growth temperature was increased to 550˚C and 670˚C, the nanowire formation was also significantly suppressed. A vaporsolid (V-S) growth mechanism excluding a liquid phase appeared to control the nanowire formation. The TiO2 nanowire growth seemed to be activated by carbon, which was supplied by decomposition of the Ti precursor. The TiO2 nanowire density was increased with increased growth pressure in the range of 1.2 to 10 torr. In addition, the nanowire formation was enhanced by using Au and Pt catalysts, which seem to act as catalysts for oxidation. The nanowires consisted of well-aligned ~20-30 nm size rutile and anatase nanocrystallines. This MOCVD synthesis technique is unique and efficient to self-catalytically grow TiO2 nanowires, which hold significant promise for various photocatalysis and solar cell applications.