Titania Nanocrystals Research Articles

Changes in the titanium oxide optical properties during crystallization

Crystallization of amorphous titanium oxide films synthesized by magnetron sputtering was carried out at temperatures of 700, 800, and 900oC in an oxygen atmosphere. The refractive index of the films increases during crystallization with a time constant that depends on temperature, which made it possible to determine the activation energy of the crystallization process on the order of 0.6 eV. The growth kinetics model for the titanium oxide nanocrystals, which is used in this work, showed that the indicated activation energy corresponds to the diffusion energy of oxygen vacancies. This process is decisive for the growth of titanium oxide nanocrystals upon annealing in an oxygen atmosphere. The study of photoluminescence has shown that crystallization leads to a change in the ratio of intensities of different emission bands. The bands that are associated with the oxygen vacancy are extinguished. A decrease in the concentration of these vacancies in films leads to an increase in their resistance and stabilization of the films in time. Keywords: titanium oxide films, crystallization, refractive index, photoluminescence.

Unraveling the Effect of Cation Types on Electrochromic Properties of Titanium Dioxide Nanocrystals

Electrochromic (EC) devices have been regarded as promising candidates for energy-saving smart windows, next-generation displays, and wearable electronics. Monovalent ions such as H + - and Li + -based electrolytes are the benchmark insertion ions for EC devices but have serious limitations such as high cost, instability, and difficulty to handle. Seeking multivalent electrolytes is an effective alternative way to prepare high-performance EC devices; unfortunately, the related reports are currently limited to tungsten oxide EC materials. Herein, for the first time, we investigate the EC properties driven by different valence cationic (i.e., Li + , Zn 2+ , and Al 3+ ) electrolytes in the titanium dioxide system. It is found that the initial optical modulation ranges of TiO 2 nanocrystal (NC) films in Li + , Zn 2+ , and Al 3+ electrolytes are 76.8%, 77.4%, and 77.3%, respectively. After 250 cycles, the optical contrast of these films in Zn 2+ electrolyte decreased by only 2.3%, much lower than that in benchmark Li + electrolyte of 10.1% and Al 3+ electrolyte of 59.1%. Density functional theory calculation indicates that the potential barriers of Li + , Zn 2+ , and Al 3+ in TiO 2 are 0.59, 0.55, and 0.74 eV, respectively, which makes TiO 2 NCs show good EC properties in Zn 2+ electrolytes. This work unravels the effect of different valence cations on the electrochromic properties of titanium dioxide NCs, which may provide some new directions for the development of excellent EC devices with long-term stability and durability.

One-pot microwave synthesis of Pd modified titanium dioxide nanocrystals for 3D aerogel monoliths with efficient visible-light photocatalytic activity in a heated gas flow reactor

We present a one-pot microwave synthesis of Pd modified titanium dioxide nanocrystals for macroscopic aerogel monoliths, which are efficient visible-light photocatalysts for methanol oxidation in a heated gas flow reactor.

TiO2 nanocrystal rods on titanium microwires: growth, vacuum annealing, and photoelectrochemical oxygen evolution

Titania nanocrystal rods grown hydrothermally onto titanium microwire are mechanically robust and photoelectrochemically active.

Highly Ordered Inverse Opal Structures Synthesized from Shape-Controlled Nanocrystal Building Blocks.

Three-dimensional ordered porous materials known as inverse opal films (IOFs) were synthesized using nanocrystals with precisely defined morphologies. Comprehensive theoretical and experimental studies of the volume fraction ratio and electrostatic interactions between nanocrystals and polystyrene templating particles enabled the formation of highly ordered crack-free photonic structures. The synthetic strategy was first demonstrated using titanium dioxide (TiO2 ) nanocrystals of different shapes and then generalized to assemble nanocrystals of other functional materials, such as indium tin oxide and zinc-doped ferrite. Tunable photocatalytic activity of the TiO2 IOFs, modulated through the choice of the shape of TiO2 nanocrystals in conjunction with selecting desired macroscopic features of the IOF, was further explored. In particular, enhanced activity is observed for crack-free, highly ordered IOFs whose photonic properties can improve light absorption via the slow light effect. This study opens new opportunities in designing multi-length-scale porous nanoarchitectures having enhanced performance in a variety of applications.

Highly Ordered Inverse Opal Structures Synthesized from Shape‐Controlled Nanocrystal Building Blocks

AbstractThree‐dimensional ordered porous materials known as inverse opal films (IOFs) were synthesized using nanocrystals with precisely defined morphologies. Comprehensive theoretical and experimental studies of the volume fraction ratio and electrostatic interactions between nanocrystals and polystyrene templating particles enabled the formation of highly ordered crack‐free photonic structures. The synthetic strategy was first demonstrated using titanium dioxide (TiO2) nanocrystals of different shapes and then generalized to assemble nanocrystals of other functional materials, such as indium tin oxide and zinc‐doped ferrite. Tunable photocatalytic activity of the TiO2 IOFs, modulated through the choice of the shape of TiO2 nanocrystals in conjunction with selecting desired macroscopic features of the IOF, was further explored. In particular, enhanced activity is observed for crack‐free, highly ordered IOFs whose photonic properties can improve light absorption via the slow light effect. This study opens new opportunities in designing multi‐length‐scale porous nanoarchitectures having enhanced performance in a variety of applications.

Bi and Al co-doped anatase titania for photosensitized degradation of Rhodamine B under visible-light irradiation

Although TiO2 is a wide band gap semiconductor, it demonstrates photodegradation activity under visible light irradiation after dye sensitization. Compared with esterification between the surface hydroxyl group of TiO2 and the carboxylic group of dyes, electrostatic interaction between TiO2 and dye shows better photosensitized performance. In this work, Bi/Al co-doping anatase titania (Ti1-xBi2x/3Al2x/3O2 (0 ≤ x ≤ 0.3)) is designed to enhance the electrostatic interaction. The effect of Al ions is to enhance the solubility of Bi3+ into titania nanocrystals. A new band gap is generated after high concentration of Bi element doping, which not only promotes the absorption of visible light, but also improves the utilization of photogenerated carriers. Based on the results of transmission electron microscopy, light absorption, photodegradation activity and density functional theory calculations, it is found that bismuth dopant is the electron capture site. It first accumulates electrons through photocatalytic degradation reaction to enhance electrostatic adsorption between the catalyst and the positively charged dye molecules, and finally realizes high-efficiency photosensitization degradation of Rhodamine B. In addition, the sensitized titania has excellent photodegradation recyclability.

Rapid synthesis of TiO2 nanocrystal in aqueous solution at room temperature

In the presented work, we develop an original simple, green, and rapid protocol to prepare anatase titanium dioxide (TiO2) nanocrystal in aqueous solution at room temperature. The secret of this chemical process is the use of ammonium persulfate ((NH4)2S2O8) as initiator in the presence of titanium butoxide (Ti(C4H9O)4) as precursor. The reaction was conducted at room temperature which make this protocol very useful and efficient. The high crystallinity of the obtained TiO2 nanocrystal was confirmed by X-ray diffraction and high-resolution microscopy, both size and shape were observed by transmission electron microscopy. The average particle size of TiO2 nanocrystal was found to be 7 nm with quasi-spherical shape. X-ray photoelectron spectroscopy technique was performed to confirm the purity of the final product and the oxidation state of titanium. The optical property of the as-prepared TiO2 nanocrystal was studied using UV-visible spectroscopy. The thermal stability was measured using differential thermal analysis combined with thermogravimetric analysis. The decrease of TiO2 nanocrystal size affects well the absorption spectrum of TiO2 (UV absorption peak shift from 340 to 325 nm) and therefore affects their photocatalytic activity. This chemical process offers many advantages compared to previous works especially the soft synthesis condition (room temperature, reaction occurs instantly and the aqueous medium) which make it a very promising fast wet chemical process.

Изменение оптических свойств оксида титана при кристаллизации

Crystallization of amorphous titanium oxide films synthesized by magnetron sputtering was carried out at temperatures of 700, 800, and 900 oC in an oxygen atmosphere. The refractive index of the films increases during crystallization with a time constant that depends on temperature, which made it possible to determine the activation energy of the crystallization process on the order of 0.6 eV. The growth kinetics model for the titanium oxide nanocrystals, which is used in this work, showed that the indicated activation energy corresponds to the diffusion energy of oxygen vacancies. This process is decisive for the growth of titanium oxide nanocrystals upon annealing in an oxygen atmosphere. The study of photoluminescence has shown that crystallization leads to a change in the ratio of intensities of different emission bands. The bands that are associated with the oxygen vacancy are extinguished. A decrease in the concentration of these vacancies in films leads to an increase in their resistance and stabilization of the films in time.

Trap-Assisted Charge Storage in Titania Nanocrystals toward Optoelectronic Nonvolatile Memory.

Transistor-based memories are of particular significance in the pursuit of next-generation nonvolatile memories. The charge storage medium in a transistor-based memory is pivotal to the device performance. In this report, nitrogen doping titania nanocrystals (N-TiO2 NCs) synthesized through a low-temperature nonhydrolytic method are used as the charge storage medium in a graphene transistor-based memory. The decoration of the N-TiO2 NCs enables the device to perform as an ultraviolet (UV) light-programmable nonvolatile optoelectronic memory. Multilevel nonvolatile information recording can be realized through accurate control of the incident light dose, which is ascribed to the vast and firm hole trapping abilities of the N-TiO2 NCs induced by the N dopant. Accordingly, a positive gate voltage can be used to erase the programmed state by promoting the recombination of stored holes in N-TiO2 NCs. This study manifests the importance of trap engineering for information storage and provides an alternative path toward nonvolatile optoelectronic memory.

Free-standing hybrid films comprising of ultra-dispersed titania nanocrystals and hierarchical conductive network for excellent high rate performance of lithium storage

The construction of advanced electrode materials is key to the field of energy storage. Herein, a free-standing anatase titania (TiO2) nanocrystal/carbon nanotube (CNT) film is reported using a simple and scalable sol-gel method, followed by calcination. This unique free-standing film comprises ultra-small TiO2 nanocrystals (∼ 5.9 nm) and super-aligned CNTs, with ultra-dispersed TiO2 nanocrystals on the surfaces of the CNTs. On the one hand, these TiO2 nanocrystals can significantly decrease the diffusion distance of the charges and on the other hand, the cross-linked CNTs can act as a three-dimensional (3D) conductive network, allowing the fast transport of electrons. In addition, the film is free-standing, without requiring electrode fabrication and additional conductive agents and binders. Owing to these above synergistic effects, the film is directly used as an anode in Li-ion batteries, and delivers a high discharge capacity of ∼ 105 mAh·g−1 at high rate of 60 C (1 C = 170 mA·g−1) and excellent cycling performance over 2,500 cycles at 30 C. These results indicate that the free-standing anatase TiO2 nanocrystal/CNT film affords a superior performance among the various TiO2 materials and can be a promising anode material for fast-charging Li-ion batteries. Moreover, the TiO2/CNT film exhibits an areal capacity of up to 2.4 mAh·cm−2, confirming the possibility of its practical use.

Visible photocatalysis of Cr(VI) at g/L level in Si/N-TiO2 nanocrystals synthesized by one-step co-hydrolysis method

This paper focuses on a novel one-step co-hydrolysis synthesis strategy of silicon modified N-doped titanium dioxide nanocrystals and its application in the visible light photocatalysis of chromium at g L−1 level in wastewater. Titanium(IV) bis(ammonium lactato)dihydroxide (TALH) has been adopted firstly as both Ti and N sources for synthesis of N-doped TiO2 microspheres (N-TiO2). Si modified N-TiO2 was fabricated by adding γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH560) before hydrolysis of TALH. The adsorption and co-hydrolysis of silane molecules significantly inhibit the growth of N-TiO2 crystals, and further promote appropriate cross-linking of particles through silanol (hydrolysate) intermolecular force or potential Si-O-Si bond by the polycondensation reaction to form nano-sized Si/N-TiO2. Interestingly, the introduction of silicon turns the negative charge surface of N-TiO2 into positive charge one through the Si-O-N-Ti/Si-N-O-Ti bond, and improves the adsorption of Cr(VI). Systematic characterization and photocatalytic test documented that abundant adsorption pores, large amount of oxygen vacancies and transport channels jointly accelerate the reduction of Cr(VI) on Si/N-TiO2 nanocrystals surface. Up to 98.7% (30 min for 0.2 g L−1) and 53.2% (120 min for 1.0 g L−1) removal efficiency, importantly, confirmed that the Si/N-TiO2 nanocrystals was competitive for the treatment of highly [Cr(VI)] containing wastewater.

Manipulation of Electron Transfer between Pd and TiO2 for Improved Electrocatalytic Hydrogen Evolution Reaction Performance.

The urgent need of catalysts with improved performances toward the hydrogen evolution reaction (HER) is still one of the crucial issues for the water splitting electrocatalysis. Herein, we exhibit that the HER activity of the Pd nanocubes could be improved by selecting the appropriately shaped titania nanocrystals as support. In particular, we used Pd nanoparticles with (100)-facet exposed to show that the HER performance of Pd cubes can be improved in both acidic and alkaline electrolyte media when combined on the anatase TiO2 nanocrystals. Furthermore, we have also investigated the facet effect of TiO2 on the performance in detail, which indicated stronger catalytic activity when (001)-TiO2 was used rather than (mix 101/001)-TiO2 and (101)-TiO2. The electron-transfer-induced improvement of HER activity of Pd/TiO2 was assessed by electron energy loss spectroscopy (EELS). Thereafter, the combined support materials with suitable facet exposed can give an additional adjusting path to regulate the HER activities of Pd nanocatalysts, which henceforth can further contribute to a novel way for tuning other catalysts with good electrocatalytic properties.

Copper, silver, and titania nanoparticles do not release ions under anoxic conditions and release only minute ion levels under oxic conditions in water: Evidence for the low toxicity of nanoparticles

It is widely assumed that the discharge of nanoparticles into the environment may cause adverse effects on organisms. Nonetheless, so far most nanoparticles have demonstrated little to no observed hazards in multiple biological test systems. It is not until nanoparticles undergo transformations, e.g., release of metal ions, that most environmental toxicities are induced, yet the ionization of nanoparticles in natural oxic and anoxic conditions is poorly known. We hypothesized that in anaerobic conditions, where oxidation is absent or limited, metal nanoparticles should not release metal ions. We investigated the transformation of three commercially produced materials, i.e., copper nanoparticles, silver nanoparticles, and titania nanocrystals with an average particle size of 50 nm. The nanoparticles were subjected to different environmental conditions including oxic/anoxic suspension, incubation with natural organic matter, and pH gradient, then subsequently analyzed for zeta potential, hydrodynamic diameter, concentration of released metal ions, and generation of reactive oxygen species. Transmission electron microscopy was used to assess morphological changes. Under oxic conditions, results show that only 9.4 μg/mL of copper ions and 6.9 μg/mL of silver ions were released from nanoparticles, when continuously stirred over 48 h. These levels are low compared to levels found in natural media. Moreover, under anoxic conditions, an insignificant amount of copper ions of 0.9 μg/mL and silver ions, of 0.2 μg/mL, were released. For titania nanoparticle, less than 0.05 μg/mL ions were released under either oxic or anoxic conditions. Overall, our findings reveal the absence of ion release under anoxic conditions, and the very low levels of ion released under oxic conditions. As a consequence, the toxicity of Cu, Ag, and Ti nanoparticles should be very low in natural media.

Low-cost tangerine peel waste mediated production of Titanium Dioxide Nanocrystals: Synthesis and characterization

Nanocrystalline Titanium Dioxide is a promising nanomaterial with myriads of applications in diverse fields, from biotechnology to space science. Although several different methods have been proposed for the synthesis of such material, just a few have considered both the economic and environmental impact of the production protocols. In this study, based on previous works it is proposed a fast and low-cost green synthesis method of Titanium Dioxide Nanocrystals (TiO2-NCs). This method works by transforming a Titanium Dioxide (TiO2) precursor in TiO2-NCs, using two volumetric ratios of tangerine peels, an organic waste, as bio-mediator of chemical reactions. Nanocrystals produced with this alternative synthesis reduce the environmental impact by effectively using waste that would otherwise end up disposed in sanitary landfills. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis of the obtained TiO2, show nanocrystals with clear boundaries and diameters between 50–150 nm and the presence of nanocrystals agglomerations. The tendency to agglomeration was also confirmed by the dynamic light scattering (DLS) measurements. Energy-dispersive X-ray spectroscopy (EDX) measurements show the remaining traces of Calcium and Potassium from the tangerine extract. X-ray diffraction (XRD) patterns show that TiO2-NCs obtained are composed mainly by anatase crystalline phase (around 90 % anatase and 10 % rutile). UV–vis spectrophotometry shows absorbance characteristic peaks around 300 nm and 350 nm for the TiO2-NCs. Finally, the effects of increasing the volume of tangerine peels extract used in the synthesis were evaluated, showing that a relatively large concentration of phytochemicals is crucial for the growth and formation of TiO2-NCs.

A review on spectral converting nanomaterials as a photoanode layer in dye‐sensitized solar cells with implementation in energy storage devices

AbstractThe present review article aims at the application of rare‐earth‐based titanium dioxide nanocrystals as spectral converters in photovoltaic devices, with special focus on dye‐sensitized solar cells (DSSCs). Additionally, the implementation of DSSCs in energy storage, more importantly, DSSCs and lithium‐ion batteries (LIB) integrated devices are systematically described. The absorption in DSSCs is mainly confined to the visible solar spectrum, which is one of the main reasons behind its limited power conversion efficiency. This has led to shifting of research focus on broadening the light absorption range of DSSCs, which can further lead to enhancement in overall power conversion efficiency. TiO2, doped with rare‐earth (RE) ions, is often used as an electron transport layer (ETL) in DSSCs to overcome this absorption‐related issue. This article gives a detailed review of TiO2 doped with different RE ions, as an electron transport layer in DSSCs. More importantly, we have summarized all the recent important findings with the application of DSSCs in LIB and photocapacitors.

Titania:Graphdiyne nanocomposites for high-performance deep ultraviolet photodetectors based on mixed-phase MgZnO

Approachable graphdiyne (GDY), characterized by discrepancy hybridized carbon atoms of inhomogeneous π-bonding and carbon 2pz overlapping of orbitals, reveals versatility applications. Previously, interfaces high density between different structure materials induce the high response of photodetector, but the ratio of photocurrent to dark current is restricted for either limited materials properties or lattice mismatch when junctions formed. In this work, titania (TiO2) nanocrystals with a rational phase of anatase are encapsulated on GDY particles, further, the TiO2:GDY nanocomposites are synthesized. High specific surface area GDY, as a proper sustaining material optimizes the characters of TiO2 nanocrystals. Then TiO2:GDY nanocomposites cooperate with Mg0.3Zn0.7O (MZO) are mean to fabricate lateral bilayer ultraviolet photodetector. Because of the formed heterojunction between TiO2:GDY nanocomposites and MZO, the ultraviolet photodetector is highly sensitive to deep ultraviolet light, when optical band gap of MZO is as high as 3.8 eV. The responsivity of TiO2:GDY/MZO bilayer photodetector is also increased by more than one order of magnitude to 76 mA W−1 compares to the MZO device without TiO2:GDY nanocomposites while the photocurrent rejection is about three orders of magnitude from 254 nm to 365 nm. Meanwhile, signal-to-noise ratio is calculated as high as 1.5 × 105 in this work.

Structure, morphology and adsorption properties of titania shell immobilized onto cobalt ferrite nanoparticle core

A magnetic core-shell adsorbent was synthesized by immobilization of titanium dioxide nanoclusters on the cobalt ferrite nanoparticles. The synthesis was carried out using a modified Pechini sol-gel method with citric acid and ethylene glycol as chelating agents. The structure and morphology of reference TiO2, pristine CoFe2O4 and resulting nanocomposite CoFe2O4@TiO2 were thoroughly characterized using XRD, XRF, BET, SEM, IR spectroscopy and Mössbauer spectroscopy. The obtained spectral data indicate that a shift of electron density from titanium to oxygen atoms takes place. Antistructure modeling suggests that some titanium atoms are entered into the CoFe2O4 spinel structure resulting in defects of crystalline structure. In this way additional adsorption centers arise. The adsorption efficiency of the CoFe2O4@TiO2 nanocomposite was found to be more than twice as high as compared to TiO2 and CoFe2O4 alone. The observed synergistic effect is associated just with the formation of distorted titania nanocrystals. The obtained magnetic nanoadsorbent proved to be efficient in water purification from dichromate anions (83% removal) and Congo Red dye (61% removal).

Highly robust La1-xTixFeO3 dual catalyst with combined photocatalytic and photo-CWPO activity under visible light for 4-chlorophenol removal in water

A highly robust Ti-substituted LaFeO3 dual catalyst was synthesized via a facile Pechini sol-gel route using a dried amorphous sol-gel titania as titanium source and a final calcination at 800 °C that enabled solid-solid diffusion of titanium atoms within the perovskite network. Using an amorphous precursor instead of crystallized titania nanocrystals increased the Ti → La atomic substitution degree in the crystalline network from 5 at% to 11 at%, together with a strong increase in the catalytic activity. The partially substituted La1-xTixFeO3 catalyst with a 11 at% substitution degree allowed pure heterogeneous surface reactions to take place under pure visible light (λ > 420 nm), with an increase in the catalyst robustness by more than two orders of magnitude compared to the unmodified LaFeO3 counterpart, evidenced by the absence of any Fe release, the structural stability of the substituted catalyst and the absence of any loss of catalytic activity with test cycles. Further, the strategy of combining both photocatalysis and H2O2-mediated heterogeneous photo-Fenton advanced oxidation processes within one single heterogeneous catalyst allowed the dual La1-xTixFeO3 catalyst to simultaneously take advantage from the higher reaction rate of photo-Fenton and from the higher mineralization yield of photocatalysis in water treatment. As a result, the dual 11 at% Ti-substituted La1-xTixFeO3 catalyst clearly outperformed its unmodified LaFeO3 counterpart and led to a complete mineralization of the 4-chlorophenol substrate under pure visible light, with strongly enhanced H2O2 decomposition, 4-chlorophenol and TOC conversion rates. Finally, the activity of the La1-xTixFeO3 catalyst under visible light contributed significantly to its overall activity obtained using the full solar spectra.

True Photoreactivity Origin of Ti3+-Doped Anatase TiO2 Crystals with Respectively Dominated Exposed {001}, {101}, and {100} Facets.

Combining the advantages of reactive crystal facets and engineering defects is an encouraging way to address the inherent disadvantages of titanium dioxide (TiO2) nanocrystals. However, revealing the true photoreactivity origin for defective TiO2 with coexposed or predominant exposed anisotropic facets is still highly challenging. Here, the photoreactivity of TiO2 nanocrystals with respectively predominant exposed {001}, {101}, and {100} facets before and after Ti3+ doping under both ultraviolet and visible light was compared systematically. In detail, the photocatalytic H2 production for R-TiO2-001, R-TiO2-101, and R-TiO2-100 increased by a factor of 1.34, 2.65, and 3.39 under UV light and a factor of 8.90, 13.47, and 8.72 under visible light. By contrast, the photocatalytic degradation of methyl orange for R-TiO2-001, R-TiO2-101, and R-TiO2-100 increased by a factor of 3.18, 1.42, and 2.17 under UV light and a factor of 4.03, 2.85, and 1.58 under visible light, respectively. The true photocatalytic activity origin for the obtained photoreduction and photo-oxidation ability is attributed to the exposure of more active sites (under-coordinated 5-fold Ti atoms), the facilitated charge transfer among {001}, {101}, and {100} facets, and the Ti3+ energy state with variable doping levels to extend the visible light response. This work hopefully provides significant insights into the photoreactivity origin of defective TiO2 nanocrystals with anisotropic exposed facets.