Controllable One-Step Synthesis of Mixed-Phase TiO2 Nanocrystals with Equivalent Anatase/Rutile Ratio for Enhanced Photocatalytic Performance

In this study, the novel mixed-phase TiO2 nanocrystals (s-TiO2) with nearly equivalent anatase/rutile ratio were fabricated in the reagent of sec-butanol at the relatively low temperature of 80 °C by using a facile one-step condensing reflux method. The photocatalytic water splitting hydrogen production performance of s-TiO2 nanocrystals is close to that of commercial TiO2 (P25), and its photocatalytic degradation performance is about four times that of P25. The energy-level staggered interfaces and surface bridged hydroxyl groups significantly increased due to the anatase/rutile mixed-phase crystal structure and high specific surface area, which might generate the synergistic effect for the improvement of photocatalytic degradation.

Enhanced Diffuse Reflectance and Microstructure Properties of Hybrid Titanium Dioxide Nanocomposite Coating

In this research, we studied enhanced diffuse reflectance that can be achieved by excitations of multiple-scattering in a hybrid micro-structured titanium dioxide coating. Conventional approaches to obtain diffuse reflection structure rely heavily on exciting the scattering of randomly textured surface, whereas here, we reveal numerically and experimentally that, besides interface scattering, bulk scattering of ordered-disordered hybrid structure can be also employed to obtain highly efficient diffuse reflector. The diffuse reflectance over the measured wavelength region increases significantly with thickness, while angle and polarization-dependent specular reflections are suppressed. These results show the potential to be used as a highly efficient diffuse reflector or for applications in various advanced fields of photonics related to light extractions and diffusers.

Mesoporous TiO2 Nanocrystals/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium-Sulfur Batteries

Rechargeable lithium-sulfur (Li-S) batteries are promising in high-energy storage due to the large specific energy density of about 2600 W h kg(-1). However, the low conductivity of sulfur and discharge products as well as polysulfide-shuttle effect between the cathode and anode hamper applications of Li-S batteries. Herein, we describe a novel and efficient S host material consisting of mesoporous TiO2 nanocrystals (NCs) fabricated in situ on reduced graphene oxide (rGO) for Li-S batteries. The TiO2@rGO hybrid can be loaded with 72 wt % sulfur. The strong chemisorption ability of the TiO2 NCs toward polysulfide combined with high electrical conductivity of rGO effectively localize the soluble polysulfide species within the cathode and facilitate electron and Li ions transport to/from the cathode materials. The sulfur-incorporated TiO2@rGO hybrid (S/TiO2@rGO) shows large capacities of 1116 and 917 mA h g(-1) at the current densities of 0.2 and 1 C (1 C = 1675 mA g(-1)) after 100 cycles, respectively. When the current density is increased 20 times from 0.2 to 4 C, 60% capacity is retained, thereby demonstrating good cycling stability and rate capability. The synergistic effects of TiO2 NCs toward effective chemisorption of polysulfides and conductive rGO with high electron mobility make a promising application of S/TiO2@rGO hybrid in high-performance Li-S batteries.

Crystallographic Facet-Induced Toxicological Responses by Faceted Titanium Dioxide Nanocrystals

Toxicological responses of nanomaterials have been closely correlated to their physicochemical properties, and establishment of a property-activity relationship of nanomaterials is favorable for a deep understanding of the nanomaterials' toxicity mechanism, prospectively predicting nanomaterials' potential hazards and rationally designing safer nanomaterials. Faceted nanomaterials usually exhibit more versatile and effective performance than spherical nanomaterials due to their selectively exposed crystallographic facets with high densities of unsaturated atoms. These facets have high surface reactivity, capable of eliciting strong interactions with biological systems. Few studies paid attention to the toxic behaviors of faceted nanomaterials in terms of their distinctive facets. In the present study, the toxicological role of the crystallographic facets of TiO2 nanomaterials was investigated, and the precise property-activity relationship was exploited to clearly understand the toxicity of faceted nanomaterials. A series of faceted TiO2 nanocrystals with the morphology of truncated octahedral bipyramids were prepared to expose different percentages of {101} and {001} facets on the surface. Density functional theory calculation revealed that {101} facets could only molecularly absorb water molecules while {001} facets due to their surface-unsaturated Ti atoms could dissociate the absorbed water molecules to generate hydroxyl radicals. Biophysical assessments corroborated the increased production of hydroxyl radicals on the {001} facets compared to {101} facets, which endowed {001} facets with strong hemolytic activity and elicited severe toxicities. A series of increased oxidative stress toxicological responses, including cellular ROS production, heme oxygenase-1 expression, cellular GSH depletion, and mitochondrial dysfunctions, were triggered by faceted TiO2 nanocrystals with progressively increased {001} percentages, demonstrating the toxicological roles of {001} facets.

Carbon-Coated Mesoporous TiO2 Nanocrystals Grown on Graphene for Lithium-Ion Batteries

Graphene-based hybrids have been well studied as advanced catalysts and high-performance electrode materials. In this Article, we have fabricated a novel graphene@mesoporous TiO2 nanocrystals@carbon nanosheet by a simple one-step solvothermal method. We have found that titanocene dichloride can act as an extraordinary source with multiple roles for forming TiO2 nanocrystals, ultrathin carbon outer shells, and cross-linkers to binding TiO2 nanocrystals on graphene surface. Moreover, it also serves as a controlling agent to produce mesoporous structure on TiO2 nanocrystals. The loading-concentration of mesoporous TiO2 nanocrystals on graphene sheets can be well controlled by adjusting the initial content of titanocene dichloride. The as-obtained graphene@mTiO2@carbon nanosheets possess a uniform sandwich-like structure, highly crystalline mesoporous TiO2 nanocrystals, a high surface area of ∼209 m(2)/g, and a large pore volume of ∼0.68 cm(3) g(-1). When used as anodes for LIBs, the resultant nanosheets show a high reversible capacity (∼145 mAh/g), good rate capability, and long cycling life (capacity remains 110 mAh/g after 100 cycles at a current density of 0.2 A/g). We believe that our method represents a new path way to synthesize novel nanostructured graphene-based hybrids for future applications.

An insight into the role of oxygen vacancy in hydrogenated TiO₂ nanocrystals in the performance of dye-sensitized solar cells

Hydrogenated titanium dioxide (H-TiO2) nanocrystals were successfully prepared via annealing TiO2 in H2/N2 mixed gas flow at elevated temperatures ranging from 300 to 600 °C. Electron paramagnetic resonance (EPR) spectra were used to determine the produced oxygen vacancy in H-TiO2. Variations in temperature were studied to investigate the concentration change of oxygen vacancy in H-TiO2. The H-TiO2 nanocrystals prepared at different temperatures were employed into photoanodes sensitized by N719 dye and found to have exceptional effect on the solar-to-electric energy conversion efficiency (η). Photoanodes with H-TiO2 nanocrystals hydrogenated at 300 °C show the highest short-circuit current density (Jsc) of 18.92 mA cm(-2) and photoelectrical conversion efficiency of 7.76% under standard AM 1.5 global solar irradiation, indicating a 27 and 28% enhancement in Jsc and η, respectively, in comparison to those with TiO2. The enhancement is attributed to high donor density, narrow band gap and positive shift of flat band energy (Vfb) of H-TiO2 that promote the driving force for electron injection. Intensity-modulated photocurrent spectroscopy (IMPS) accompanied by intensity-modulated photovoltage spectroscopy (IMVS) and other analyses were applied to shed more light on the fundamental mechanisms inside the charge transfer and transport in these systems.

Green synthesis of anatase TiO(2) nanocrystals with diverse shapes and their exposed facets-dependent photoredox activity

The exposed facets of a crystal are known to be one of the key factors to its physical, chemical and electronic properties. Herein, we demonstrate the role of amines on the controlled synthesis of TiO2 nanocrystals (NCs) with diverse shapes and different exposed facets. The chemical, physical and electronic properties of the as-synthesized TiO2 NCs were evaluated and their photoredox activity was tested. It was found that the intrinsic photoredox activity of TiO2 NCs can be enhanced by controlling the chemical environment of the surface, i.e.; through morphology evolution. In particular, the rod shape TiO2 NCs with ∼25% of {101} and ∼75% of {100}/{010} exposed facets show 3.7 and 3.1 times higher photocatalytic activity than that of commercial Degussa P25 TiO2 toward the degradation of methyl orange and methylene blue, respectively. The higher activity of the rod shape TiO2 NCs is ascribed to the facetsphilic nature of the photogenerated carriers within the NCs. The photocatalytic activity of TiO2 NCs are found to be in the order of {101}+{100}/{010} (nanorods) > {101}+{001}+{100}/{010} (nanocuboids and nanocapsules) > {101} (nanoellipsoids) > {001} (nanosheets) providing the direct evidence of exposed facets-depended photocatalytic activity.