Dimensional TiO2 Research Articles

From 1D chain to 3D network: A theoretical study on TiO2 low dimensional structures.

We have performed a systematic study on a series of low dimensional TiO2 nanostructures under density functional theory methods. The geometries, stabilities, growth mechanism, and electronic structures of 1D chain, 2D ring, 2D ring array, and 3D network of TiO2 nanostructures are analyzed. Based on the Ti2O4 building unit, a series of 1D TiO2 nano chains and rings can be built. Furthermore, 2D ring array and 3D network nanostructures can be constructed from 1D chains and rings. Among non-periodic TiO2 chain and ring structures, one series of ring structures is found to be more stable. The geometry model of the 2D ring arrays and 3D network structures in this work has provided a theoretical understanding on the structure information in experiments. Based on these semiconductive low dimensional structures, moreover, it can help to understand and design new hierarchical TiO2 nanostructure in the future.

Double-Wall TiO2 Nanotubes for Dye-Sensitized Solar Cells: A Study of Growth Mechanism

One–dimensional TiO2 nanotubes (TNTs) are promising semiconductor photoanodes for dye–sensitized solar cells (DSSCs) due to their rapid electron transportation property, however, the lack of high surface area restricts their application. Double–walled TiO2 nanotubes (DWTNTs) were synthesized to compensate for the smaller surface area of single–walled TiO2 nanotubes (SWTNTs) and the comprehensive growth mechanism of DWTNTs is clearly demonstrated in this study. The evolution of pores and pits in three dimensions causes the formation of DWTNTs. After optimizing the thickness of DWTNTs, the DSSC with DWTNTs on the flexible Ti substrate showed a higher power conversion efficiency (η) of 6.85%, as compared to that of the cell with SWTNTs (4.63%), owing to a significant increase in the short–circuit photocurrent density (J SC) caused by the higher surface area for dye adsorption for the former case. Electrochemical impedance spectroscopy (EIS), incident photon–to–electron conversion efficiency (IPCE) curves, and UV–vis absorption spectra were conducted to sustain the explanations.

Facile non-hydrolytic solvothermal synthesis of one dimensional TiO2 nanorods for efficient dye-sensitized solar cells

One dimensional rod shaped TiO2 nanostructures were successfully synthesized by a simple non-aqueous, alcoholysis based solvothermal process. Anatase TiO2 nanorods (TiO2 NRs) exhibited a surface area of 109.79m2/g with particle length and diameter of ~30–50nm and ~10–15nm (from SEM data), respectively. The photovoltaic performance of TiO2 nanorods based electrode was investigated in the dye-sensitized solar cell (DSSC). The device based on TiO2 NRs electrode exhibited an excellent short-circuit current density (Jsc) of 17.75mAcm−2 and an open-circuit voltage (Voc) of 0.75V under 1Sun AM 1.5G solar light. Due to high dye loading, good light harvesting and fast electron transport, the optimal conversion efficiency (9.21%) of the DSSC fabricated from TiO2 NRs was significantly higher than that of the commercial DP-25 TiO2 nanoparticles based cell (6.43%).

Characteristics of the Dye-Sensitized Solar Cells Using TiO₂ Nanotubes Treated with TiCl₄.

The replacement of oxide semiconducting TiO2 nano particles with one dimensional TiO2 nanotubes (TNTs) has been used for improving the electron transport in the dye-sensitized solar cells (DSSCs). Although use of one dimensional structure provides the enhanced photoelectrical performance, it tends to reduce the adsorption of dye on the TiO2 surface due to decrease of surface area. To overcome this problem, we investigate the effects of TiCl4 treatment on DSSCs which were constructed with composite films made of TiO2 nanoparticles and TNTs. To find optimum condition of TNTs concentration in TiO2 composites film, series of DSSCs with different TNTs concentration were made. In this optimum condition (DSSCs with 10 wt% of TNT), the effects of post treatment are compared for different TiCl4 concentrations. The results show that the DSSCs using a TiCl4 (90 mM) post treatment shows a maximum conversion efficiency of 7.83% due to effective electron transport and enhanced adsorption of dye on TiO2 surface.

On the thermal growth and properties of doped TiO2 and In2O3 elongated nanostructures and nanoplates

In this work, the driving forces behind the growth mechanisms of In2O3 and TiO2 micro- and nano-structures grown by an evaporation–solidification method are discussed. Effective or limited doping incorporation and its influence on the growth and morphology of the low dimensional structures are also assessed. A dislocation driven growth mechanism is proposed for indium oxide, indium tin oxide (ITO) and zinc doped indium oxide (IZO) nanowires. This growth mechanism is extended to the growth of IZO nano-plates. On the other hand, different low dimensional TiO2 morphologies, mainly nanowires, needles, and bidimensional leaf-like nanostructures, have been obtained by an anisotropic induced growth. By introducing Cr in the precursor mixture, needles are formed showing stepped lateral faces related to oxygen defect stoichiometry areas as observed by EDS mapping.

Construction of Self-Supported Three–Dimensional TiO2 Sheeted Networks with Enhanced Photocatalytic Activity

The degradation of toxic gases and liquids using a catalyst and solar energy is an ideal method, compared with landfill and combustion methods. The search for active semiconductor photocatalysts that efficiently decompose contaminations under light irradiation remains one of the most challenging tasks for solar-energy utilization. In this work, free–supporting three-dimensional (3D) nanosheeted hierarchical porous tungsten, titanium, and tin oxide networks were obtained by a facile Lewis acid catalytic binary template route. These networks possess large macroscopic scale (millimeter–sized) and hierarchical macro/mesoporous nanostructure with high surface area and large pore volume. Photocatalytic degradation of Azo dyes demonstrated that the nanosheets-constructed hierarchical porous networks have high photocatalytic activity and stability. The present synthetic route can serve as the new design concept for functional 3D layered porous nanostructures.

The effect of light-scattering layer on the performance of dye-sensitized solar cell assembled using TiO2 double-layered films as photoanodes

Dye-sensitized solar cells (DSSCs) are fabricated based on double-layered films of TiO2 nanospheres and TiO2 nanorod arrays (NRAs). TiO2 nanospheres, including TiO2 hollow spheres (HSs) and TiO2 solid spheres (SSs), were served as light-scattering layers on TiO2 NRAs as composite photoanodes. The as-prepared TiO2 NRAs, TiO2 HSs and TiO2 SSs have been characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photoelectric properties of DSSCs were investigated by UV–vis reflectance spectra, current–voltage curves and electrochemical impedance spectroscopy. Owing to the synergic effects of the TiO2 HSs (SSs) and NRAs, including large specific surface area of HSs (SSs) as light-scattering layer for effective dye adsorption and harvesting light and rapid electron transport in one dimensional TiO2 NRAs, the optimal energy conversion efficiency of DSSCs with as-prepared double-layered films as nanocomposite photoanode (5.40%) were far higher than the ones using single-layered NRAs films (1.56%).

A stable bimetallic Au–Ag/TiO2 nanopaper for aerobic oxidation of benzyl alcohol

Well-dispersed small Au-Ag bimetallic nanoparticles (sub-3 nm) on one dimensional TiO2 nanobelts were synthesized by a facile successive photodeposition-galvanic replacement method. Based on these Au-Ag/TiO2-NB nanostructures, a porous paper-like monolithic catalyst was fabricated and exhibited synergistically enhanced activity and stability for catalyzing aerobic oxidation of benzyl alcohol.

Fabrication of TiO2 nanotube–nanocube array composite electrode for dye-sensitized solar cells

One dimensional TiO2 nanotube structure recently plays an important role in the application of dye sensitized solar cells (DSSCs) due to its faster electron transport. The fabrication of photoanode using the TiO2 nanotube structures mixed with the TiO2 nanoparticles was investigated to enhance the photovoltaic efficiency of DSSCs by increasing the surface area of electrode. In this work, self-organized and vertically-oriented TiO2 nanotube arrays (TNAs) covered with uniformly distributed TiO2 nanocubes (TNCs) were fabricated in a simple one-step anodization process. The X-ray diffraction patterns reveal that both TNAs and TNCs are in anatase phase. The scanning electron microscopy analysis demonstrates that the wall thickness and inner diameter of hexagonal close-packed TiO2 nanotubes from chemically polished Ti foils are 10–15 and 100–120nm, respectively, and the particle size of TNCs is 60–75nm. The DSSC fabricated by the mixed morphological TNAs with TNCs shows an enhanced photoconversion efficiency of ~63% than that of TNAs alone, due to the increase of both dye adsorption and electron transportation rate.

Hierarchical TiO2–Si nanowire architecture with photoelectrochemical activity under visible light illumination

Bandgap engineering of TiO2 is a substantial strategy for efficient water splitting in the visible light range. Introducing dopants and hydrogenation have been found effective for that purpose. In this paper, we report the development of a hierarchical three dimensional TiO2–Si nanowire (NW)-based photoelectrochemical (PEC) anode with visible light photochemical activity. The TiO2 NWs were synthesized using a surface reaction-limited pulsed chemical vapor deposition method (SPCVD) with unbalanced TiCl4 and H2O precursors. Dangling Ti–Cl and Ti–OH groups inside TiO2 NW crystals were suggested to be the reason for band narrowing and visible light absorption. The NW structure with a large aspect ratio was formed via the oriented attachment mechanism, which offered a super-high surface area density. This in situ crystal decoration approach opens a new window to tailoring electrical properties of TiO2 for wider spectrum solar energy harvesting and conversion.

Thermal conduction effects impacting morphology during synthesis of columnar nanostructured TiO2 thin films

The aerosol chemical vapor deposition (ACVD) process allows for the synthesis of nanostructured films with well tuned morphologies that can be controlled based on the desired functionality and application. A robust understanding of the process parameters that result in desired features of the film is elucidated. One dimensional TiO2 nanostructured columns that have superior properties for solar energy harvesting and conversion applications were deposited on tin doped indium oxide (ITO) substrates. The sintering of the deposited particles was a key factor in the growth of the 1D structure with desired crystal planes. By ensuring that the sintering rate is faster than the arrival rate of deposited particles; a 1D columnar structure could be obtained. The sintering rate was controlled by the temperature and depositing particle size. As the columns grew in length, the increased thermal conduction resistance resulted in a drop in temperature and subsequently a slowing of the sintering process in upper regions of the film. This led to growth of branched structures rather than continued growth in a preferred direction. The growth of the branched structure could be overcome by enhancing the sintering rate by increasing the substrate temperature or reducing the depositing particle size (by lowering the feed rate of the precursor). The phenomenon was also confirmed by using different deposition substrates, such as FTO and glass. Dye sensitized solar cell performance efficiencies with different column lengths of 2 and 7 µm were determined to be 1.8 and 2.7% respectively.

Surface Modifications and Optoelectronic Characterization of TiO2‐Nanoparticles: Design of New Photo‐Electronic Materials

AbstractTiO2 nanoparticles are of great current interest for applications in photo‐electronic materials including light‐energy conversion, artificial photosynthetic systems as well as photocatalysis. The success of these applications relies on the exciton recombination dynamics and visible‐light sensitivity of the TiO2 nanomaterials. Thus, in order to develop the highly efficient photo‐electronic materials absorbing visible light, different low dimensional TiO2 nanostructures such as nanodiscs, nanofibers and nanochains were synthesized, and thereafter their surfaces were modified by incorporating with Sn‐porphyrins and heteropoly acid. The optoelectronic properties of the surface‐modified nanomaterials were investigated with regard to the optical properties and the surface exciton dynamics by using both steady‐state and ultrafast time‐resolved laser spectroscopic techniques including single nanoparticle photoluminescence technique. These results were correlated with the photo‐electronic properties including photocatalytic activities and solar cell efficiencies, indicating that the electron transfer mechanism in the modified nanostructures may be similar to the “Z‐scheme” of the plant photosynthetic system so that both photocatalytic activity and solar cell efficiencies were synergistically enhanced by using two color illumination.