Titania Nanocrystals Research Articles

Elasticity of Cross-Linked Titania Nanocrystal Assemblies Probed by AFM-Bulge Tests.

In order to enable advanced technological applications of nanocrystal composites, e.g., as functional coatings and layers in flexible optics and electronics, it is necessary to understand and control their mechanical properties. The objective of this study was to show how the elasticity of such composites depends on the nanocrystals’ dimensionality. To this end, thin films of titania nanodots (TNDs; diameter: ~3–7 nm), nanorods (TNRs; diameter: ~3.4 nm; length: ~29 nm), and nanoplates (TNPs; thickness: ~6 nm; edge length: ~34 nm) were assembled via layer-by-layer spin-coating. 1,12-dodecanedioic acid (12DAC) was added to cross-link the nanocrystals and to enable regular film deposition. The optical attenuation coefficients of the films were determined by ultraviolet/visible (UV/vis) absorbance measurements, revealing much lower values than those known for titania films prepared via chemical vapor deposition (CVD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed a homogeneous coverage of the substrates on the µm-scale but a highly disordered arrangement of nanocrystals on the nm-scale. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of the 12DAC cross-linker after film fabrication. After transferring the films onto silicon substrates featuring circular apertures (diameter: 32–111 µm), freestanding membranes (thickness: 20–42 nm) were obtained and subjected to atomic force microscopy bulge tests (AFM-bulge tests). These measurements revealed increasing elastic moduli with increasing dimensionality of the nanocrystals, i.e., 2.57 ± 0.18 GPa for the TND films, 5.22 ± 0.39 GPa for the TNR films, and 7.21 ± 1.04 GPa for the TNP films.

Origin of Photocatalytic Activity in Ti4+/Ti3+ Core–Shell Titanium Oxide Nanocrystals

Colored titanium dioxide (TiO2) nanocrystals have been studied intensively in recent years due to their substantial solar-driven photocatalytic activities. Because of the scarcity of information co...

In-situ synthesis of self Ti3+ doped TiO2/RGO nanocomposites as efficient photocatalyst to remove organic dyes from wastewater under direct sunlight irradiation

Reduced graphene oxide modified titania nanocomposite is successfully synthesized using an inorganic precursor of titania and graphite through a controlled hydrolysis method. Modified Hummers’ method is adopted to synthesize the graphene oxide. XRD analysis indicates that the synthesized anatase titania nanocrystals have crystallite size within the range of 3–10 nm. Microstructural and Raman study confirms the TiO2 nanocrystals are closely packed and in interfacial contacts with graphene oxide sheets respectively. It has been observed that small percentage of graphene oxide loading (5 wt%) on TiO2, some extent influences the textural properties; like, crystallite size, specific surface area, pore volume, etc. The low intense photoluminescence spectra of the nanocomposite reveal slower rate of radiative recombination of the charge carriers. UV-Vis absorption and DRS-spectra illustrates a red shift in absorption peak and a reduced band gap in the nanocomposite, respectively. The existence of Ti3+ and oxygen vacancies into lattice is observed from the XPS analysis. Electrical conductivity in the nanocomposite is found to be higher compared to reference TiO2, as evident from the CIS analysis. Therefore, the combination of reduced graphene oxide and titania in the nanocomposites significantly increases the adsorption aptitude towards organic pollutants (e.g. dyes) which is related to their typical surface properties. Moreover, the incorporation of graphene oxide in the nanocomposites exerts a significant combined effect on the charge transfer dynamics and adsorption, which together provide them with better photocatalytic activity toward rhodamine B and other organic dyes in aqueous solution.

An evaluation of fluorinated titanium oxide nanocrystals with UV exposure treatment for oxygen vacancy control

Abstract The oxygen vacancy properties of densified titanium oxide (TiO2) nanocrystals (NCs) with different surface ligand states were evaluated. Fluorous ligand modification resulting in the high densification of NCs and the effect of residual ligands on the surface of the NCs using ultraviolet (UV)-exposure treatment were investigated. After synthesizing the TiO2 NCs at 80 °C, their modification proceeded using 2,2,2-trifluoroacetic acid as the fluorous ligand. NC thin films were formed using spin-casting, after which the UV-exposure treatment was performed. According to the analytical results of crystalline size, surface, optical properties, and surface ligand states of the TiO2 NCs, the ligands on the NCs were decomposed by the UV-exposure treatment under various atmospheres and the flatness of the NC thin films was found to be controlled by the fluorous ligand modification. Thus, the recombination effect of the oxygen vacancies could be controlled by the fluorous ligand modification and UV-exposure treatment.

(Keynote) Water-Oxidation By Polyoxometalate-Complexed Manganese-Oxide Nanocrystals: Visible-Light Driven Photoelectrocatalysis through Hierarchical Assembly

Building on our use of polyoxometalate (POM) cluster-anions as ligands for gold-nanoparticle catalysts and building blocks [1], we show how POMs can serve as covalently attached ligands for reactive metal-oxide nanocrystals, providing soluble and isolable assemblies uniquely positioned between molecular macroanions and traditional colloids. For example, covalently coordinated redox-active POMs, serving as ligands for individual anatase titanium-dioxide nanocrystals [2], control hydrogen formation by rationally tuning rates of visible-light driven electron injection into the TiO2 cores, while soluble POM complexes of alpha-Fe2O3 (see Figure) serve as oxidatively and hydrolytically stable catalysts for visible-light driven water oxidation [3]. We now report the synthesis and characterization of POM complexed 3-nm manganese oxide nanocrystals that serve as building blocks for the assembly of water-soluble 200-nm cubic nanostructures. Notably, the hierarchical assembly of these cubic structures, each comprised of more than 50,000 of the manganese-oxide-core POM complexes, induces a shift of UV-vis absorbance into the visible. This results in enhanced visible-light semiconductor properties, whose utility is demonstrated through photoelectrocatalytic water-oxidation. [1] (a) Zhang, M.; Hao, J.; Neyman, A; Wang, Y.; Weinstock, I. A. Inorg. Chem., 2017, 56, 2400-2408 (Front cover); (b) Wang, Y.; Raula, M.; Wang, Y.; Zeiri, O.; Chakraborty, S.; Gan-Or, G.; Gadot, E.; Weinstock, I. A. Ang. Chem. Int. Ed. 2017,56, 7083-7087; (c) Wang, Y.; Zeiri, O.; Raula, M.; Le Ouay, B.; Stellacci, F.; Weinstock, I. A. Nature Nanotech. 2017, 12, 170-176. [2] M. Raula, G. Gan-Or, M. Saganovich, O. Zeiri, Y. Wang, M. R. Chierotti, R. Gobetto, I. A. Weinstock, Angew. Chem. Int. Ed. 2015, 54, 12416 –12421 (“Hot paper”). [3] Chakraborty, B.; Gan-Or, G.; Raula, M.; Gadot, E.; Weinstock, I. A., Nature Comm., 2018, 9, 4896. Figure 1

Synergistic effect of {101} crystal facet and bulk/surface oxygen vacancy ratio on the photocatalytic hydrogen production of TiO2

Anatase titanium dioxide (TiO2) nanocrystals with different percentages (up to 95%) of exposed {101} facet and different concentration ratios of bulk single-electron-trapped oxygen vacancies (SETOVs) to surface oxygen vacancies (SOVs) were prepared by alcohol-thermal method with nanotube titanic acid as the precursor in combination with solid-state reduction by NaBH4. The as-prepared TiO2 nanocrystals were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and ultraviolet–visible light spectrometry. The effects of the percentage of crystal facets and the concentration ratio of bulk SETOVs/SOVs on the photocatalytic hydrogen production rate of TiO2 nanocrystals were investigated with positron annihilation lifetime spectroscopy as well as photocurrent test. Findings indicate that the percentage of the exposed {101} facets of the as-prepared TiO2 nanocrystals and their concentration ratios of bulk SETOVs/SOVs can be well tuned by properly adjusting the amount of NaBH4 and the reduction reaction time as well. Increasing percentage of the {101} facet of anatase TiO2 nanocrystals contributes to improving their photocatalytic hydrogen production activity, because the {101} facets of the anatase TiO2 nanocrystals possess enriched electrons and can act as the reduction sites to enhance the reduction reaction of H+ affording H2 in the sacrifice system of splitting water. Both the bulk SETOVs and SOVs contribute to the improvement of the light absorption while SOVs can facilitate the separation of photogenerated charges, thereby adding to the photocatalytic activity. However, the bulk SETOVs and excessive SOVs are also the combination centers of photogenerated charges, which means it is essential to maintain a suitable concentration ratio of the bulk SETOVs/SOVs so as to enhance the light absorption and achieve the best separation efficiency of photogenerated charges and achieve the best photocatalytic activity for hydrogen production. Particularly, when anatase TiO2 nanocrystal with a high percentage (95%) of exposed {101} facet is reduced by NaBH4 at a mass ratio of 2: 1 for 20 min, the resultant reduced H-TiO2 nanocrystal (denoted as H-TiO2-R20(2:1)) provides the highest photocatalytic hydrogen productive rate. Furthermore, the combination of 0.5% Pt/H-TiO2-R20(2:1) with 0.5% Pt/WO3 can split water to simultaneously produce H2 and O2, showing promising potential for splitting water affording hydrogen and oxygen.

Effective photodynamic therapy of polymer hydrogel on tumor cells prepared using methylene blue sensitized mesoporous titania nanocrystal

A novel hydrogel shell on cancer cells was prepared via in situ photopolymerization of polyethyleneglycol diacrylate (PEGDA) using methylene blue (MB) sensitized mesoporous titania nanocrystal for effective photodynamic therapy (PDT). TiO2 in this system served as an effective photosensitizer and initiator for the formation of hydrogel, also can protect the MB from being degraded into an inactive form. While MB was used as a significant photosensitive additive to improve the photochemistry effects of TiO2 and widen its optical response area to near infrared region (660–900 nm). The PEGDA hydrogel with peritumoral injectability shows competitive advantages, i.e. good biocompatibility and hydrophily, selective and minimally invasive delivery of TiO2@MB, maintaining a high PDT drug concentration for inducing tumor apoptosis, localized and sustainable release under 660 nm laser irradiation for reducing side effect. The hydrogel also could load chemo-therapy drugs, and serve as a versatile platform for multimode antitumor treatment.

A novel approach to the sol–gel synthesis of titanium dioxide-coated SBA-16 type silica mesoporous microspheres for water purification

The present work describes a novel synthesis approach for titanium dioxide coated SBA-16 type silica mesoporous microspheres. Anatase TiO2 coated SBA-16 type silica microspheres which have interesting photocatalytic properties offers the viability of the adsorption and photocatalytic degradation of dyes in water. SBA-16 type silica microspheres were synthesized by a sol–gel method with Pluronic F127 employed as a structure directing agent (template) and TEOS (tetraethyl orthosilicate) as the silica source. Surface modification of the SBA-16 type silica microspheres through titanium dioxide nanocrystals resulted in a titanium dioxide coated SBA-16 silica microsphere composite material. The prepared composite material was characterized by SEM, TEM, EDX, nitrogen adsorption-desorption analysis and Raman spectroscopy studies. The characterization results show that the material possesses relatively high surface area (223.48–233.08 m2/g), a periodically ordered porous nature, and anatase nanocrystalline titanium dioxide coating. Photocatalytic degradation tests show significant improvement in the photodegradation of crystal violet with increased titanium dioxide coating; further confirming the material's viability for photocatalytic degradation of light sensitive hazardous organic compounds in polluted waters.

Surface-bound sacrificial electron donors in promoting photocatalytic reduction on titania nanocrystals.

Titania nanocrystals have been investigated for fast color switching through photocatalytic reduction of dyes and hexacyanometalate pigments. Here we reveal that direct binding of sacrificial electron donors (SEDs) to the surface of titania nanocrystals can significantly promote the charge transfer rate by more efficiently scavenging photogenerated holes and releasing more photogenerated electrons for reduction reactions. Using diethylene glycol (DEG) as an example, we show that its binding to the nanoparticle surface, which can be achieved either during or after the nanoparticle formation, greatly enhances the photocatalytic reduction in comparison with the case where free DEG molecules are simply added as external SEDs.

Low-temperature synthesis of TIO2 nanocrystals for high performance electrochemical supercapacitors

Titanium dioxide (TiO2) nanocrystals in intermediate phase of amorphous and anatase has been successfully synthesized through a simple, low temperature peroxo sol gel approach. Transmission electron microscopy revealed that the TiO2 nanocrystals obtained have an average diameter of 8–133 nm. The effects of calcination temperature on the morphology and phase transformation were studied by annealing the samples at 200–800 °C. TiO2 nanocrystals annealed at 200 °C with diameter of 12 nm exhibited the highest specific capacitance of 146 F g−1 at current density of 0.2 A g−1 in 1 M KOH as the electrolyte. The high specific capacitance is attributed to the intermediate phase of amorphous and anatase structure which enhanced the redox active sites of the TiO2 nanocrystals. Using the TiO2 nanocrystals annealed at 200 °C and activated carbon as the anode and cathode electrodes, respectively, an asymmetrical supercapacitor was successfully prepared. The asymmetric supercapacitor demonstrated outstanding electrochemical performance with wide potential window of 1.45 V, high energy density (35.38 Wh kg−1) and power density (408.23 W kg−1) and excellent stability 80.4% capacitance retention after 3000 cycles, suggesting that it is an auspicious electrode material for supercapacitors.

Preparation and Characterization of Low-Molecular-Weight Natural Rubber Latex via Photodegradation Catalyzed by Nano TiO₂.

Natural rubber is one of the most important renewable biopolymers used in many applications due to its special properties that cannot be easily mimicked by synthetic polymers. To sustain the existence of natural rubber in industries, modifications have been made to its chemical structure from time to time in order to obtain new properties and to enable it to be employed in new applications. The chemical structure of natural rubber can be modified by exposure to ultraviolet light to reduce its molecular weight. Under controlled conditions, the natural rubber chains will be broken by photodegradation to yield low-molecular-weight natural rubber. The aim of this work was to obtain what is known as liquid natural rubber via photodegradation, with titanium dioxide nanocrystals as the catalyst. Titanium dioxide, which was firstly synthesized using the sol–gel method, was confirmed to be in the form of an anatase, with a size of about 10 nm. In this work, the photodegradation was carried out in latex state and yielded low-molecular-weight natural rubber latex of less than 10,000 g/mol. The presence of hydroxyl and carbonyl groups on the liquid natural rubber (LNR) chains was observed, resulting from the breaking of the chains. Scanning electron microscopy of the NR latex particles showed that titanium dioxide nanocrystals were embedded on the latex surface, but then detached during the degradation reaction.

Enhanced up-conversion red light emission from rare earth titanium oxide nanocrystals with pyrochlore phase

A facile sol-gel method combined with the post-annealing process has been used to synthesize Yb3+/Er3+ co-doped TiO2 nanocrystals. It is found that the high Yb3+ concentrations can promote the formation of TiO2 nanocrystals with pyrochlore phase. An intense up-conversion (UC) red light emission (658 nm) has been achieved under 980 nm laser excitation, which is enhanced by 108 folds compared with the reference sample. Both the luminescence intensity and the red-to-green emission intensity ratio are dependent of the annealing temperature, which can be explained as the distribution of rare-earth ions and phase change of TiO2 nanocrystals.

Low-temperature solid-state reduction approach to highly reduced titanium oxide nanocrystals

Considerable attention has been paid to reduced transition metal nanomaterials because they exhibit attractive properties for practical applications in fuel cells, memory or thermoelectric devices, and photocatalysts. In particular, a series of oxygen-nonstoichiometric titanium oxides has advantages such as abundance of the elements, non-toxicity, corrosion resistance, and high electrical conductivity. However, the control of nanostructures is not straightforward because a high-temperature reductive condition is required for the synthesis of highly reduced metal oxides. Recently, it has been demonstrated that the novel low-temperature reduction technique can afford highly reduced titania nanoparticles with different particle sizes ranging from 20 to 300 nm diameter. This review article is focused on the synthesis of corundum-type Ti2O3 nanoparticles, the reaction mechanism, and the correlation between structure and physical properties.

Surface Characterization of TiO2 Polymorphic Nanocrystals through 1H-TD-NMR.

Nanocrystals (NCs) surface characterization is a fundamental step for understanding the physical and chemical phenomena involved at the nanoscale. Surface energy and chemistry depend on particle size and composition, and, in turn, determine the interaction of NCs with the surrounding environment, their properties and stability, and the feasibility of nanocomposites. This work aims at extracting more information on the surface of different titanium dioxide polymorphs using 1H-TD-NMR of water. Taking advantage of the interaction between water molecules and titanium dioxide NCs, it is possible to correlate the proton transverse relaxation times ( T2) as the function of the concentration and the specific surface area (δp· Cm) and use it as an indicator of the crystal phase. Examples of three different crystals phase, rutile, anatase, and brookite, have been finely characterized and their behavior in water solution have been studied with TD-NMR. The results show a linear correlation between relaxivity ( R2) and their concentration Cm. The resulting slopes, after normalization for the specific surface, represent the surface/water interaction and range from 1.28 g m-2 s-1 of 50 nm rutile nanocrystals to 0.52 for similar sized brookite. Even higher slopes (1.85) characterize smaller rutile NCs, in qualitative accordance with the trends of surface energy. Thanks to proton relaxation phenomena that occur at the NCs surface, it is possible to differentiate the crystal phase and the specific surface area of titanium dioxide polymorphs in water solution.

Determining the size dependence in the absorption spectra of rutile nanoparticles

This paper discusses the optical absorption spectra of ensembles of titanium dioxide nanocrystals of size 2.0–3.5 nm, obtained by mechanically crushing microcrystalline rutile powder, followed by fractionation of an aqueous suspension of the material and stabilization of the lightest selected fractions in a gelatin matrix. It is established from an analysis of the electron-diffraction patterns that ensembles of rutile nanocrystals are formed. A size effect is found in the spectra of the absorption-efficiency factor of rutile nanocrystals with mean diameters 3.5–2.0 nm, the value of which was 0.2–0.5 eV, respectively.

Template- and surfactant-free synthesis of mesoporous TiO2 spheres with hollow core-shell structure for dye-sensitized solar cells

We have demonstrated a simple and effective hydrothermal route to synthesize titania mesoporous spheres with hollow core-shell structure. The synthesis is free of any surfactants or templates. The formation mechanism is investigated on the basis of the results of time-dependent experiments. The as-obtained mesoporous titania spheres with a specific surface area of 21.5 m2 g−1 and diameters of 1.2–2.3 μm are composed of anatase titania nanocrystals. The excellent light scattering property of mesoporous titania spheres with hollow core-shell structure is proved. A higher cell efficiency of 8.27% is achieved with mesoporous titania spheres with hollow core-shell structure as a light scattering layer, compared with a cell efficiency of 6.63% for the P25 film electrode with the similar thickness. The higher cell efficiency is attributed to the hollow core-shell structure scattering layer, resulting in excellent pore fitting for electrolyte diffusion, enhanced light scattering ability, and reduced charge recombination.

Synthesis and characterization of novel unsymmetrical phthalocyanine/TiO 2 composites and their evaluation as photocatalysts for degradation of 4-chlorophenol under visible light

We prepared novel unsymmetrical A$_{3}$B-type zinc and cobalt phthalocyanines bearing monocarboxylic acid groups on peripheral positions using statistical condensation method, especially designed to anchor on the TiO$_{2}$ semiconductor surface. The novel complexes were anchored on TiO$_{2}$ semiconductor to prepare effective dye sensitized photoactive composites as heterogeneous catalysts. The results indicated that modified TiO$_{2}$ nanocrystals possessed only the anatase phase and MPc-TiO$_{2}$ photocatalysts with loading amount of dye ca. 8.27 $\mu $mol/g TiO$_{2}$ exhibit strong visible light absorption. Photocatalytic degradation of 4-chlorophenol (4-CP) under illumination with visible light ($\lambda >$ 400 nm) was tested with the composites prepared. The degradation profile indicates that MPc-modified titania nanocrystals are superior to pristine titania under visible light in terms of photocatalytic effect. Photocatalytic reusability efficiency and the stability of photocatalyst composites were also investigated. Additionally, the effect of different substituent groups (such as aromatic vs. aliphatic, alkyl chain length) on photocatalytic efficiency was revealed and also compared to our previous works.

The electrical conductivity and energy band gap of ‘bunga belimbing buluh’/tio2 nanocrystals as hybrid solar cell

This research intends to explore the effect of thickness of inorganic titania nanocrystals (TiO2 NCs) materials and Averrhoe bilimbi’s flower towards the electrical conductivity. Averrhoe bilimbi’s flower or also known as ‘bunga belimbing buluh’ was used for the first time as a natural dye in hybrid solar cells. The performance of electrical conductivity can be improved in bilayer heterojunction hybrid solar cell (HCS). The TiO2 NCs was deposited on the ITO substrate using Electrochemistry method at room temperature. The dye extracted from Averrhoe bilimbi’s flower was deposited on the top of TiO2 NCs layered using the same method. The electrical conductivity can be recorded using Four Point Probe (FPP) under dark and light radiation (range of 0 Wm-2 to 200Wm-2). From the results, electrical conductivity was increased by the increment light intensity and suitable for further solar cell fabrications.

Low-temperature solution-phase route to sub-10 nm titanium oxide nanocrystals having super-enhanced photoreactivity

High-purity anatase nanocrystals were prepared by using a low-temperature surfactant-assisted solution-phase method.

“Pea-pod-like” nitrogen-doped hollow porous carbon cathode hosts decorated with polar titanium dioxide nanocrystals as efficient polysulfide reservoirs for advanced lithium–sulfur batteries

The peculiar “pea-pod-like” rod-TiO2@C/S cathodes deliver high capacity, superior rate capability and long-term cycle stability.