TiO2 Nanosheet Films Research Articles

Novel Fe2O3/{101}TiO2 nanosheet array films with stable hydrophobicity and enhanced photoelectrochemical performance

Single crystal TiO2 nanosheet (TNS) arrays with coexposed {101} and {001} facets were synthesized on FTO conductive glass directly, thorn-like Fe2O3 were deposited on the {101} surface of TNS by a chemical bath deposition method. Taking advantage of different energy band positions of {101} and {001} facets, the higher band offset value between Fe2O3 and {101} facets was achieved, which would accelerate the photoexcited electrons and holes separation between Fe2O3 and {101} facets of TNS and enhance photoelectrochemical properties. Furthermore, without modification by low energy chemicals, such novel Fe2O3/TNS heterostructure electrodes exhibited stability hydrophobicity. After UV irradiation for 240 min, the contact angle of the Fe2O3/TNS (80min) films retained hydrophobicity (134.8°), which is approximately 7.1 times higher than that of bare TNS films. The optimal composite photoelectrode exhibited the highest transient photocurrent intensity (48 μA), which is about 4.4 times superior over the bare TNS. The superior photoelectrochemical properties and stability hydrophobicity were attributed to the suitable band edge positions and hydrophobic thorn-like α-Fe2O3.

The effect of nanostructure dimensionality on the photoelectrochemical properties of derived TiO2 films

Studying the effect of nanoscale morphology on the photoelectrochemical performance of semiconductor electrodes has been in the forefront of research for over a decade, there are still major inconsistencies and controversies in the literature. Here we aimed to resolve some of these issues, by the controlled preparation of TiO2 photoelectrodes from nanoparticles, nanorods, and nanosheets, where the nano dimension of the 0D, 1D, and 2D structures was kept similar (about 10 nm). XRD, Raman spectroscopy, XPS and UPS were employed to confirm that the chemical nature of the nanostructures is nearly identical, they only differ in their morphology. Photoelectrodes were prepared keeping the loading amount, surface area, or the film thickness identical, to deconvolute all trivial effects, and only scrutinize the role of morphology. TiO2 nanorod (NR) films exhibited the best photoelectrochemical performance in all comparisons, achieving ~4 mA cm−2 at 0.2 V vs. Ag/AgCl (under 100 mW cm−2, Xe-lamp illumination). In stark contrast, TiO2 nanosheet (NS) film showed the lowest performance owing to the small amount of active sites on the basal plane of the NSs and the insufficient charge carrier transport through the film. Overall, we have demonstrated that under carefully controlled conditions, it is possible to compare the PEC behavior of TiO2 photoelectrodes, and that the 1D nanostructures outperformed its 0D and 2D counterparts.

A facile hydrothermal synthesis and properties of TiO2 nanosheet array films

A facile hydrothermal procedure was adopted to prepare TiO2 nanosheet array film on Ti foil, with NaCl as a morphology control agent. SEM, EDS, XPS and XRD showed that the TiO2 nanosheets with uniform morphology were vertically grown on the surface of Ti foil, and the nanosheets were interlaced with each other. When the hydrothermal reaction was controlled at 140 °C for 6 h, TiO2 nanosheet array film with superhydrophilicity (water contact angle of 3°) was obtained. In addition, excellent flexibility of Ti foil with TiO2 nanosheet array films could be a promising material for flexible application.

The effect of bulk/surface defects ratio change on the photocatalysis of TiO2 nanosheet film

The photocatalysis behavior of TiO2 nanosheet array films was studied, in which the ratio of bulk/surface defects were adjusted by annealing at different temperature. Combining positron annihilation spectroscopy, EPR and XPS, we concluded that the bulk defects belonged to Ti3+ related vacancy defects. The results show that the separation efficiency of photogenerated electrons and holes could be significantly improved by optimizing the bulk/surface defects ratio of TiO2 nanosheet films, and in turn enhancing the photocatalysis behaviors.

Synthesis of Monodispersed TiO2 Nanosheets by Wet Chemical Method and their Applications in Dye-Sensitized Solar Cells

Anatase TiO2 nanosheets were prepared by wet chemical method in the presence of Tripropylamine as capping ligand. The obtained samples were characterized by Powder X-ray diffraction, Raman spectroscopy, Ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, Transmission electron microscopy and high-resolution transmission electron microscopy. The growth mechanism for the formation of TiO2 nanosheet has been investigated. The photovoltaic properties of anatase TiO2 nanosheets were investigated by assembling the TiO2 nanosheets as photoanodes in dye-sensitized solar cells (DSSCs). Experimentally, it shows that the anatase phase of TiO2 nanosheet films have conversion efficiency of 3.25%.

Solvothermal fabrication of TiO2 nanosheet films on degradable Mg–Zn alloys

Anatase TiO2 nanosheet films were fabricated on Mg–Zn alloy substrates through a special solvothermal method, aiming to improve the corrosion resistance of degradable Mg–Zn alloy stents. In this novel synthesis process, absolute alcohol was used as solvent, and small amounts of hydrofluoric acid and NH4F aqueous solution were used to adjust the hydrolysis rate of titanium precursors and the crystal morphology of anatase TiO2, respectively. The NH4F played a key role in the growth of TiO2 nanosheets by supplying fluorine ions (F−). The anatase TiO2 films had a compact surface consisting of interleaving nanosheets with thickness of about 50 nm. In simulated body fluids, the corrosion current density (Icorr) of Mg–Zn alloy substrates decreased from 789.5 to 24.4 µA cm−2, after being coated with the TiO2 nanosheet films.

Enhancement of photocatalytic H2 evolution over TiO2 nano-sheet films by surface loading NiS nanoparticles

NiS/TiO2 nano-sheet films (NiS/TiO2 NSFs) photocatalysts were prepared by loading NiS nanoparticles as noble metal-free cocatalysts on the surface of TiO2 films through a solvothermal method. The prepared samples were characterized by XRD, SEM, EDS, UV–Vis absorption spectra and XPS analysis. The photocatalytic H2 evolution and photoluminescence spectroscopy (PL) experiments indicated that the NiS cocatalysts could efficiently promote the separation of photogenerated charge carriers in TiO2 and consequently enhance the H2 evolution activity. The hydrogen yield obtained from the optimal sample reached 4.31 μmol cm–2 at 3.0 h and the corresponding energy efficiency was about 0.26%, which was 21 times higher than that of pure TiO2 NSF. A possible photocatalytic mechanism of NiS cocatalyst on the improvement of the photocatalytic performance of TiO2 NSF was also proposed.

Lanthanum‐Doped TiO2 Nanosheet Film with Highly Reactive {001} Facets and Its Enhanced Photocatalytic Activity

AbstractLanthanum‐doped anatase TiO2 nanosheet films with exposed high‐reactivity {001} facets were synthesized directly on transparent conductive fluorine‐doped tin dioxide (FTO) substrates by a facile one‐pot solvothermal method. The surface morphological structure and crystal facets of the TiO2 nanosheets could be facilely controlled under appropriate conditions. The photocatalytic activities of the La‐doped TiO2 nanosheet films were evaluated for the degradation of methyl orange (MO) and methylene blue (MB). The results demonstrated that the photocatalytic activities of the La‐doped TiO2 nanosheet films are higher than those of the pure TiO2 film; this is ascribed mainly to the synergistic effect of the La doping and the high percentage of exposed {001} facets. A possible mechanism for the photocatalytic degradation of MO and MB has also been proposed.

Low-Cost Y-Doped TiO2 Nanosheets Film with Highly Reactive {001} Facets from CRT Waste and Enhanced Photocatalytic Removal of Cr(VI) and Methyl Orange

In this paper, efficiency recovery of rare earth elements from cathode ray tubes (CRT) waste. Moreover, recycled yttrium was also served as raw material to produce a low-cost Y-doped TiO2 nanosheets film with exposed {001} facets. An etching/dissolution growth mechanism was postulated by systematically investigating the influence of the reaction time. The synergistic effect of the Y dopant and the dominant {001} facets endows TiO2 nanosheets film with excellent activity in the photoremoval of Methyl Orange (MO) and Cr(VI). A possible mechanism of photoremoval of MO and Cr(VI) is proposed. This study not only contributes to recycling methods for CRT waste but also presents a new way to prepare low-cost sustainable photocatalytic materials using economically viable waste.

Plasmon enhanced photoelectrochemical sensing of mercury (II) ions in human serum based on Au@Ag nanorods modified TiO2 nanosheets film

Taking advantages of the monodisperse TiO2 nanosheets (NSs) with high active crystal face exposure and the tunable localized surface plasmon resonance (LSPR) properties of Au@Ag nanorods (NRs), this study demonstrated that TiO2 NSs film with trace amount of Au@Ag NRs modification possess a strong enhancement of photocurrent response, which was remarkably inhibited with the addition of mercury (II) ions (Hg2+). Based on the selective decrease of photocurrent with the addition of Hg2+, a simple photoelectrochemical (PEC) sensor has been assembled. The PEC sensor exhibits wide linear range (0.01–10nM), low detection limit (2.5pM), satisfying selectivity, reproducibility and acceptable stability for Hg2+ detection. The feasibility of this method for practical application in human serum has been evaluated and the result was satisfactory. This PEC sensing method would provide a potential application for Hg2+ detection in clinical diagnosis.

Enhanced performance of dye-sensitized solar cells based on TiO2/MnTiO3/MgTiO3 composite photoanode

The TiO2/MnTiO3, TiO2/MgTiO3 and TiO2/MnTiO3/MgTiO3 composite photoanodes were prepared by immersing the TiO2 nanosheets film into the mixed solution of titanium tetrachloride and manganese chloride (or magnesium chloride), and followed by calcination treatment. The effects of MnTiO3 and MgTiO3 treatment on the photovoltaic performances of the dye-sensitized solar cells (DSSCs) were investigated. The MnTiO3 and MgTiO3 as coating layer on the surface of TiO2 can effectively promote the dye adsorption adhered to the photoanode film. The photoelectric conversion efficiency of the DSSC based on TiO2/MnTiO3 and TiO2/MgTiO3 photoanodes increased by 25.7% and 15.5% compared with that of pure TiO2-based DSSC, respectively. Furthermore, the DSSC based on the TiO2/MnTiO3/MgTiO3 photoanode exhibited the highest conversion efficiency of 6.39%, exceeding that of pure TiO2-based DSSC by a factor of 1.4. The highest efficiency observed for the DSSC based on this hybrid structure is attributed to the enhanced dye-absorption, fast electron transfer and the energy barrier formed by MnTiO3/MgTiO3 layer, which suppresses the charge recombination and increases the photocurrent. This investigation provides a new way for further improving the photoelectric conversion efficiency of the DSSCs.

Efficient Degradation of Methylene Blue over Two‐Dimensional Au/TiO2 Nanosheet Films with Overlapped Light Harvesting Nanostructures

Two‐dimensional TiO2 nanosheet films with visible light trapping nanostructures were successfully fabricated by alkali hydrothermal reaction using Ti sheet as precursor. Metallic Au nanoparticles (NPs) were then deposited on the surface of TiO2 film through a microwave‐assisted reduction process. The investigations reveal that the localized surface plasmon resonance (LSPR) of Au NPs is greatly enhanced by the overlapped light harvesting nanostructures between TiO2 film and Au NPs, resulting in an enhanced LSPR‐absorption with two peaks at 389 nm and 540 nm. The photocatalytic performance of the samples was evaluated by degradation of methylene blue (MB) as a model pollutant. The experimental results indicate that the photocatalytic performance of TiO2 is greatly promoted by a synergetic effect between the overlapped light harvesting nanostructures and the improved charge carrier separation processes. The MB degradation over the optimal sample is much faster than that of pure TiO2 film by a factor of 3.0 and 5.7 under UV light and UV + visible light irradiation, respectively. This study provides a simple strategy to develop film‐shaped plasmonic photocatalysts with high efficiency.

TiO2 nanosheets with highly exposed (001)-facets for enhanced photovoltaic performance of dye-sensitized solar cells

In this study, TiO2 nanosheets having highly exposed (001)-facets were synthesized and compared with the commercially available P25. The results indicate that the synthesized TiO2 nanosheets have a smaller specific surface area and yet with a higher dye-loading capacity. This gives a 26.7% enhancement in cell efficiency (η) when compared with the corresponding dye-sensitized solar cell (DSSC) made of P25. Abundant characterization data were obtained to understand the 001 surface activity of TiO2 nanosheets and their role on the device performance. Reasonable mechanism is proposed to explain the higher dye-loading capacity on the smaller specific surface area. Besides, according to the normalized photocurrent of TiO2 nanosheets, the longer wavelength region (600–800nm) contributes 52.9% of the integrated photocurrent density; this result further confirms their superior light scattering properties in the longer wavelength region. An optimal η of 8.77% is obtained for the DSSC with the TiO2 nanosheets film, as compared to that of the cell with the P25 film (6.92%).

Ultrathin Exfoliated TiO2 Nanosheets Modified with ZrO2 for Dye-Sensitized Solar Cells

In the present work, we use chemical exfoliation to fabricate ultrathin two-dimensional anatase TiO2 nanosheets (NSs) for application as photoanode materials in dye-sensitized solar cells. For the first time, colloidal Ti0.91O2 NSs are synthesized via chemical exfoliation of a layered precursor (HxTi2–x/4□x/4O4·H2O; □: vacancy, x = 0.7) through ion exchange with tetrabutylammonium (TBA+) cations. The as-prepared Ti0.91O2 NSs are well-dispersed and ultrathin with a lateral size of up to a few micrometers. Subsequent acid treatment induces colloidal Ti0.91O2 to reassemble and precipitate into a gelation form, followed by thermal annealing to convert the Ti0.91O2 gelation into anatase TiO2 nanosheets for applications as photoanode materials in DSSCs. Because of the enhanced light absorption and dye absorption resulting from the high surface area of ultrathin TiO2 nanosheets, the DSSC consisting of 8.8 μm thick TiO2 nanosheet film delivers the highest energy conversion efficiency of 4.76% and the largest shor...

Photocatalytic Reduction of CO<sub>2</sub> on Au/TiO<sub>2</sub> Nanocomposite Film

Plasmonic Au decorated TiO2 nanosheet film was firstly prepared by the combination of a hydrothermal method and a microwave-assisted chemical reduction process. The prepared sample was characterized by scanning electron microscopy (SEM), UV-vis absorption spectrum (UV-vis) and photoluminescence spectrum (PL) respectively. Results show that Au nanoparticles with narrow distribution are uniformly loaded on the nanosheet surface, and the resulted composite nanostructure exhibits distinct surface plasmon absorption and quenched photoluminescence compared to pure TiO2 nanostructure. Photocatalytic tests show that Au decorated TiO2 exhibits enhanced photocatalytic activity for photocatalytic reduction of CO2 to methanol.

Plasmonic Ag deposited TiO2 nano-sheet film for enhanced photocatalytic hydrogen production by water splitting

TiO2 nano-sheet film (TiO2 NSF) was prepared by a hydrothermal method. Ag nanoparticles (NPs) were then deposited on the surface of TiO2 NSF (Ag/TiO2 NSF) under microwave-assisted chemical reduction. The prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible (UV–vis) absorption spectroscopy, x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, and Raman scattering spectroscopy. The results revealed that the Ag NPs were well dispersed on the anatase/rutile mixed-phase TiO2 nano-sheet surface with a metallic state. The visible light absorption and Raman scattering of TiO2 were enhanced by Ag NPs based on its surface plasmon resonance effect. Besides, Ag NPs could also effectively restrain the recombination of photogenerated electrons and holes. Photocatalytic water splitting was conducted on the films to obtain hydrogen, and the experimental results indicated that plasmonic Ag NPs could greatly enhance the photocatalytic activity of TiO2 due to the synergistic effect between electron transfer and surface plasmon resonance enhanced absorption. The hydrogen yield obtained from the optimal sample reached 8.1 μmol cm−2 and the corresponding energy efficiency was about 0.47%, which was 8.5 times higher than that of pure TiO2 film. Additionally, the formation mechanism of TiO2 nano-sheet film is preliminarily discussed.

Investigation on preparation and photocatalytic activity of TiO2 nanosheet film on Ti substrate

Titania nanosheet array film was prepared through direct oxidation of titanium substrate by H2O2 at 80°C in the presence of common inorganic salts. A subsequent heat treatment at 450°C transformed the amorphous thin film to anatase phase without destroying the morphology of nanosheets. The as-prepared TiO2 nanosheet film was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images of the samples indicated that the nanosheets grew nearly vertical to the surface of Ti substrate. The photocatalytic activity was evaluated by degradation of methylene blue under UV irradiation. Furthermore, photocurrent was also measured to investigate the separation efficiency of photogenerated electron and hole.

The effect of photoanode thickness on the performance of dye-sensitized solar cells containing TiO2 nanosheets with exposed reactive {001} facets

Abstract

Core/Shell PbSe/PbS QDs TiO2 Heterojunction Solar Cell

AbstractQuasi type‐II PbSe/PbS quantum dots (QDs) are employed in a solid state high efficiency QD/TiO2 heterojunction solar cell. The QDs are deposited using layer‐by‐layer deposition on a half‐micrometer‐thick anatase TiO2 nanosheet film with (001) exposed facets. Theoretical calculations show that the carriers in PbSe/PbS quasi type‐II QDs are delocalized over the entire core/shell structure, which results in better QD film conductivity compared to PbSe QDs. Moreover, PbS shell permits better stability and facile electron injection from the QDs to the TiO2 nanosheets. To complete the electrical circuit of the solar cell, a Au film is evaporated as a back contact on top of the QDs. This PbSe/PbS QD/TiO2 heterojunction solar cell produces a light to electric power conversion efficiency (η) of 4% with short circuit photocurrent (Jsc) of 17.3 mA/cm2. This report demonstrates highly efficient core/shell near infrared QDs in a QD/TiO2 heterojunction solar cell.

Fabrication, characterization, and photocatalytic activity of double-layer TiO2 nanosheet films

The double-layer TiO2 nanosheet films have been deposited on Si substrate by a liquid-phase deposition method using ZnO nanosheets as the template. The initial morphology of the ZnO nanosheet templates is maintained after the TiO2 deposition. The TiO2 nanosheets are uniformly distributed widely and grown perpendicularly to the substrate. The TiO2 nanosheets are of anatase phase with the outside thickness of ~220–380nm. The growth mechanism for the formation of TiO2 nanosheet films is investigated. Experimentally, it shows that the TiO2 nanosheet films have highly photocatalytic activities for the decomposition of azo dye C. I. reactive yellow 15.