Surface Of TiO2 Film Research Articles

Adsorption and Cation-Exchange Behavior of Zinc Sulfide on Mesoporous TiO2 Film and Its Applications to Solar Cells.

Zinc sulfide (ZnS) was deposited onto the surface of mesoporous TiO2 film by a typical successive ionic layer adsorption and reaction (SILAR) process. By inducing a spontaneous cation exchange between ZnS and a target cation (Pb2+, Cu2+, Ag+, or Bi3+) dissolved in a chemical bath when they are in contact, it was demonstrated successfully that white translucent ZnS on the substrate could be changed to new brown-colored metal chalcogenides and the amount of ZnS deposited originally by different conditions could be compared in a qualitative way with the degree of color change. By utilizing this simple but effective process, the evolution of a well-known ZnS passivation layer prepared from different chemical baths in quantum dot (QD)-sensitized solar cells could be tracked visually by checking the degree of color change of TiO2/ZnS electrodes after the induced specific cation exchange. When applied to representative CdS QD-sensitized solar cells, it was revealed clearly how the different degrees and rates of ZnS deposition could affect the overall power conversion efficiency while finding an optimized passivation layer over TiO2/CdS electrode. An acetate anion-coupled Zn2+ source was observed to give a much faster deposition of a ZnS passivation layer than a nitrate anion one because of its higher pH-induced more-favorable adsorption of Zn2+ on the surface of TiO2. As another useful application of the ZnS-based cation exchange, as-deposited ZnS was used as a template for preparing a more complex metal chalcogenide onto a mesoporous TiO2 film. The ZnS-derived Sb2S3-sensitized electrode showed a promising initial result of over 1.0% overall power conversion efficiency with a very thin ZrO2 passivation layer between TiO2 and Sb2S3.

A novel BSA immobilizing manner on modified titanium surface ameliorates osteoblast performance

Surface modification of medical and dental devices, to improve their biocorrosion resistance and biocompatibility, can be achieved with the multidisciplinary field of biomaterials. Nanostructured titanium dioxide (TiO2) has been employed as surface modifier of titanium-based biomaterials because it can prevent the failure of the devices due to wear mechanisms. Moreover, this oxide surface is mostly terminated by hydroxyl groups (-OH) that can be directly functionalized with biomolecules to improve the biocompatibility of these devices. We explored the influence of 3-aminopropyltrimethoxysilane (APTMS) molecules as spacers in bovine serum albumin (BSA) protein immobilization on the physically hydroxylated surfaces of rutile phase TiO2 films grown by reactive Radio Frequency (RF) magnetron sputtering. X-ray Photoelectron Spectroscopy (XPS) was used to examine the adsorption of BSA and APTMS on the hydroxylated surface of TiO2 thin films. For biological tests, BSA was directly immobilized on the film surface and on the APTMS monolayer. Biological analysis found better osteoblast performance considering gene markers related to cell adhesion after interacting directly with the surface modified by the immobilization of BSA, especially on the surface where this protein was immobilized by APTMS. Additionally, we addressed the relevance of this biointerfaces on extracellular matrix remodeling by zymography analysis. Altogether, our data provides new insights about the cellular and molecular mechanisms covering the improved osteoblastic response of the proposed surface modification.

The effect of group-substitution on the sensitization properties of alkynylrhenium(I) tricarbonyl diimine complexes adsorbed to TiO2(101) film surface: a theoretical study.

A series of dyes are designed by adding the different electron-donating (-CH3, -NH2, -OH) and electron-withdrawing groups (-Br, -Cl, -NO2) to the different ancillary ligands in the alkynylrhenium(I) tricarbonyl diimine complexes [Re(CO)3(N^N){C≡C-C6H4-CH=C(CN)(COOH)}], where N^N = 1,10-phenanthroline (phen)(1) and then investigated the sensitization properties of dyes linked to the TiO2(101) surface. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the electronic structure, frontier molecular orbitals, and absorption spectral properties. The effect of group-substitution on sensitization properties is obvious. When the dye molecules are combined with TiO2(101) surface, not only the absorptions of some sensitizers containing -CH3 or -OH groups have red shift but also the electrons can be directly injected into the TiO2 conduction band from the dye molecules compared with the parent molecular 1. The results indicate that the designed dyes containing electron-donating groups have smaller energy gaps, better light-harvesting efficiency, sufficient driving force, and higher charge transfer efficiency as appropriate dye sensitizers. We hope it can provide valuable hints so that we can design more efficient dye sensitizers in DSSCs.

Titanium 3d ferromagnetism with perpendicular anisotropy in defective anatase

Author(s): Stiller, M; N'Diaye, AT; Ohldag, H; Barzola-Quiquia, J; Esquinazi, PD; Amelal, T; Bundesmann, C; Spemann, D; Trautmann, M; Chasse, A; Hamed, HB; Adeagbo, WA; Hergert, W | Abstract: This work focuses on the generation of ferromagnetism at the surface of anatase TiO2 films by low-energy ion irradiation. Controlled Ar+-ion irradiation resulted in a thin (∼10) nm ferromagnetic surface layer. The intrinsic origin and robustness of the magnetic order has been characterized by x-ray magnetic circular dichroism at room temperature revealing that a Ti band is spin-polarized. These results, together with density functional theory calculations, indicate that Ti vacancy-interstitial pairs are responsible for the magnetic order. Superconducting quantum interference device measurements show the existence of a perpendicular magnetic anisotropy and a low remanent magnetization. Magnetic force microscopy reveals that this low remanence is due to oppositely aligned magnetic domains with magnetization vectors normal to the main surface. The weak domain-wall pinning, the magnetic anisotropy, together with the simplicity of the preparation method, open up interesting possibilities for future applications. As an example, single domain patterns of ∼1μm width and several μm length can be easily prepared.

A kinetic/thermodynamic study of transparent co-adsorbents and colored dye molecules in visible light based on microgravimetric quartz-crystal microbalance on porous TiO2films for dye-sensitized solar cells

In this study, a quartz crystal microbalance (QCM) in situ method is used to study the kinetic and thermodynamic processes of the adsorption of ruthenium-based dyes (N719, N3, N749), and the co-adsorbent chenodeoxycholic acid (CDCA) on the TiO2 film surface. The results of the kinetic studies show that the adsorption rate of N749 is slightly higher than the other two dyes, and the adsorption rate of CDCA is more sensitive to temperature change. The adsorption mechanism of the dye and CDCA on the surface of TiO2 can be reasonably inferred based on the result of the activation energy. The isotherm adsorption model studies show that the ratio of the number of surface molecules (296 K) is n(N719) : n(N3) : n(N749) : n(CDCA) = 0.69 : 1.48 : 0.50 : 1. The Keq value of CDCA is about two orders of magnitude smaller than that of all the dye molecules, which indicates that the adsorption strength of CDCA is much weaker than that of the dye molecules. Thermodynamic studies show that the adsorption reaction is an endothermic reaction. The ΔS is ΔS(N3 = 143.11 J mol-1) > ΔS(N719 = 112.72 J mol-1) > ΔS(N749 = 109.43 J mol-1) > ΔS(CDCA = 96.14 J mol-1). The Gibbs free energy ΔG is negative, and indicates that the adsorption reaction of the four molecules on the surface of the TiO2 film is spontaneous. The results of this paper show that the tedious and lengthy experimental process of the traditional method can be simplified by QCM. In addition, the development of this study provides a certain theoretical and experimental basis for future studies on the interaction mechanism between dyes and co-adsorbents.

Atomically Pt implanted nanoporous TiO2 film for photocatalytic degradation of trace organic pollutants in water

Trace organic pollutants in water can potentially and persistently impart destructive effects on human body and it is difficult to remove them by conventional treatment process owing to their low concentration. Herein, considering the importance and difficulty, a novel atomically Pt implanted nanoporous TiO2 film was prepared using a facile immersion and reduction method and confirmed by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), field-emission scanning electron microscope (FESEM), aberration-corrected high-angle annual dark-filed scanning transmission electron microscopy (HAADF-STEM), high resolution transmission electron microscopy (HRTEM), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The platinum single-atom photocatalyst exhibited considerable performance and good stability for vacuum ultraviolet (VUV) and ultraviolet (UV) photocatalytic degradation of ethenzamide, one of the typical trace organic pollutants in water, and the removal rate of ethenzamide reached 94.52% and 100% under VUV irradiation when residence time was only 0.5 min and its initial concentrations were 500 ppb and 100 ppb, respectively. The corresponding photocatalytic degradation ratios were 2.19 and 3.98 times those by pristine nanoporous TiO2 film, respectively and energy consumption was only 0.46 kW·h/m3, which was about 28% that by pristine nanoporous TiO2 film. 84.44% of ethenzamide was degraded under UV irradiation when the initial ethenzamide concentration was 500 ppb and residence time was 24 min. Mass transfer resistance coming from low concentration was effectively overcome owing to eddy diffusion accelerated by the nanopores on the surface of TiO2 film and molecular diffusion of trace pollutants promoted by Pt single atoms. The development of the platinum single-atom photocatalyst has great significance for highly efficient removal of trace organic pollutants in water.

Metalorganic-aerosol-deposited Au nanoparticles for the characterization of ultrathin films by surface-enhanced Raman spectroscopy

An alternative approach for ultrathin film characterization by means of Surface-Enhanced Raman Spectroscopy was realized and applied to the characterization of nanocrystalline TiO2 films. The vacuum-free metalorganic aerosol deposition (MAD) technique was used to grow gold nanoparticles onto the surface of thin TiO2 films. An averaged enhancement factor of 107, as well as the characterization of a 3 nm thin film, was accomplished. Since the thin film acts as a substrate itself, this technique can be used for the characterization of a variety of solid thin film materials. Furthermore, MAD-based nanoparticle growth can be of special interest for oxide films due to the high oxygen partial pressure and the constant oxygen flow during the deposition.

A Z-scheme ternary Bi2MoO6/Au/TiO2 photocatalytic films with high-efficient catalytic performance

TiO2 nanofiber film (TiO2 NFF) with visible light scattering ability was successfully synthesized by an ethylene glycol-assisted hydrothermal method, Au nanoparticles (Au NPs) were then deposited on the surface of TiO2 film using microwave-assisted chemical reduction process, and at last, Bi2MoO6/Au/TiO2 ternary photocatalytic film was successfully synthesized via a simple alcohol-thermal method using Au/TiO2 nanofilms as templates. The photocatalytic activities of as-fabricated samples were investigated by the oxidation of organic pollutants, like methylene blue (MB) and phenol, and the reduction of aqueous Cr(VI) under visible light. It shows that the Bi2MoO6/Au/TiO2 composite displays a much higher visible-light-responsive photocatalytic performance compared to pure TiO2, Au/TiO2 NFF, and Bi2MoO6/TiO2 complex. The improved visible light photoactivity could be ascribed to the excellent light scattering structure of TiO2 NFF, the surface plasmon resonance effect of Au NPs, and the highly effective separation of photogenerated electrons and holes through the Z-scheme Bi2MoO6/Au/TiO2 system, in which Au NPs plays a key role in transmitting charges in the photocatalytic process.

Study on dynamic scaling of morphological evolution of TiO 2 film deposited with different O 2 /Ar flow ratio

With increasing O2/Ar flow ratio from 2/18 to 20/0, TiO2 films were deposited by the direct current pulsed magnetron sputtering technique. The influence of O2/Ar flow ratio on plasma properties was discussed, which controlled the growth behaviour of TiO2 film. The growth behaviour influenced the value of roughness exponent α of TiO2 film, which reflected the dynamic scaling of the morphological evolution of TiO2 film. Finally, the relation between the dynamic scaling of the morphological evolution of TiO2 film and O2/Ar flow ratio was discussed systematically. The results indicate that with the other parameters constant, the growth behaviour of TiO2 film is dominated by O2/Ar flow ratio. By increasing O2/Ar flow ratio from 2/18 up to 6/14, the growth behaviour of TiO2 film transforms from the shadowing effect controlling to diffuse effect controlling, which results in the density of island structure on TiO2 film surface decreases, the size of island structure on TiO2 film surface increases, and the roughness exponent α of film decreases. When O2/Ar flow ratio exceeds 6/14, the density of island structure on TiO2 film surface remains constant. In this situation, the crystallographic orientation effect controls the growth behaviour of TiO2 film, which increases roughness exponent α.

Kinetic model for color-center formation in TiO2 film using femtosecond laser irradiation

The authors investigate the formation of color centers (CC) using a femtosecond laser, which causes the darkening of TiO2 film surfaces and reduction of their electrical resistance under visible-light illumination. They propose a kinetic model to explain the CC formation from femtosecond laser irradiation. The kinetic model treats three components, which are conduction-band electrons, self-trapped excitons or polarons, and color centers. The CC formation coefficient is assumed to be expressed by the Arrhenius equation. The laser fluence dependence on the decrease of the electrical resistance is well explained by the kinetic model.

Oxidation, reduction, and inert gases plasma-modified defects in TiO2 as electron transport layer for planar perovskite solar cells

The bulk defects in the electron transport layers (ETLs) and the interface defects between the ETLs and the perovskite film are detrimental for charge transfer and transport from the perovskite film to the ETLs, which degrade the performance of the planar heterojunction perovskite solar cells (PSCs). Here, low temperature plasma technique with a few types of atmospheres including representative oxidation, reduction, and inert gases is proposed to modify the bulk and surface defects of TiO2 films. TiO2 film treated by CO2 plasma demonstrates a more low-density of defect state in both of surface and bulk than the as-fabricated one. Consequently, the efficiency of PSC is significantly improved from 16.47% of the PSC with the as-fabricated ETL to 18.10% of the PSC with the treated ETL. However, the He and H2 plasma treatments cause the increase in the oxygen-related defects on the surface of TiO2 film or/and in the TiO2 bulk. As a result, the He and H2 plasma-treated ETLs-based PSCs exhibit poor performance. This study highlights that, to tailor metal oxide ETLs for highly efficient PSCs, the plasma technique by the PECVD approach with suitable gas source should be well considered.

EFFECT OF METAL IONS ON PHOTOCATALYTIC PERFORMANCE OF TiO2 FILM PREPARED BY MICRO-ARC OXIDATION

The effect of different metal ions on the photocatalytic property of TiO2 film prepared by micro-arc oxidation was studied. Photocatalytic experiments showed that the impregnation of metal ions increased the photocatalytic efficiency of TiO2. The increase of transition element Fe[Formula: see text] and the rare earth element Dy[Formula: see text] is more obvious, and the optimum concentration is 0.1[Formula: see text]mol/L. The SEM results showed that there was no significant change on the surface of TiO2 film before and after metal ion immersion. The results of EDS surface scanning showed that Fe and Dy elements were uniformly distributed on the surface of TiO2 film after metal ion impregnation, and the deposition amounts were 0.81% and 3.39%, respectively. XRD results showed that a new phase was formed in Fe[Formula: see text]-impregnated TiO2, which could improve the photocatalytic efficiency.

Regeneration performance tolerance of dye-sensitized solar cells based on continuous repeated electric erasure/re-sensitization

The reconstructing the photoanode after the dye-sensitized solar cells (DSC) was assembled can regenerate the DSC performance. In order to maximize the recycling of materials, extend the service life of DSC, and greatly reduce the cost of device, the tolerance of the regeneration cycle of DSC performance should be studied. This paper adopts the continuous repeated electric erasure/re-sensitization (EERS) dye molecules on surface of the TiO2 film to study the tolerance of the regeneration cycle of DSC performance. The effect of the multiple EERS process on DSC photoelectric properties, TiO2 surface states, electron transfer and transport properties are studied in depth. The result shows that after being erased and re-sensitized for the first two times, the performance parameters remain almost unchanged. However, Jsc declines, Voc declines slightly and FF is almost unchanged after the subsequent continuous operation with EERS. Finally, DSC efficiency remains around 90.98% after being erased and re-sensitized for six times. The major cause of efficiency decline is the declining Jsc and Voc caused by more defects on the TiO2 film surface due to EERS process. The research results predict that the DSC performance can be regenerated multiple times and service life of device can increase dramatically.

Fabrication of superhydrophobic TiO2 quadrangular nanorod film with self-cleaning, anti-icing properties

Abstract Superhydrophobic TiO2 quadrangular nanorod film was fabricated by hydrothermal reaction and stearic acid modification. X-ray diffractometer and Fourier transform infrared spectrometer were employed to characterize the surface crystal structures and chemical compositions of the superhydrophobic TiO2 film, respectively. The effects of the titanium source (titanium tetraisopropoxide (TTIP)) amount and reaction time on the morphology and wettability of the TiO2 film were studied by scanning electron microscope and contact angle meter. The results show that the diameter of the TiO2 quadrangular nanorods increases and then the water contact angle on modified TiO2 film decreases with the increase of the reaction time and TTIP amount. Moreover, when the TTIP amount is 0.3 mL and solvent is 30 mL, the wetted state of the superhydrophobic TiO2 film surface conforms to an improved Cassie model. Besides, the superhydrophobic TiO2 film shows good low adhesion, self-cleaning and anti-icing properties. Particularly, the anti-icing property decreases with the increase of the reaction time and TTIP amount.

Synthesis and photocatalytic properties of electrodeposited bismuth oxyiodide on rutile/anatase TiO2 heterostructure

Bismuth oxyiodide (BiOI) modified rutile/anatase TiO2 heterostructure was fabricated by a three-step process. Anatase TiO2 sheet was first formed on fluorine-doped tin oxide (FTO) glass substrate. Rutile TiO2 nanorods were then grown on anatase TiO2 sheet via a hydrothermal process. BiOI was finally coated on the surface of hierarchical TiO2 film using an electrochemical deposition method. Photocatalytic tests on degradation of methylene blue (MB) in water indicated that BiOI modified hierarchical TiO2 film possessed an excellent photocatalytic activity superior to those of the monophase anatase and rutile TiO2 films, commercial P25 film and hierarchical anatase/rutile TiO2 film. The enhanced photocatalytic performance was probably attributed to the synergetic effects of strong visible light absorption and formation of heterojunctions by the interfaces in the BiOI/rutile TiO2/anatase TiO2/FTO structure, which promoted efficient separation of photoinduced electron-hole pairs. In addition, the main active species during the degradation were confirmed to be hydroxyl radicals and superoxide radicals.

The in situ ligand exchange linker-assisted assembly of oil-soluble CdSe quantum dots to TiO2 films

Recently, the pre-synthesized oil-soluble quantum dots (QDs) have triggered great interests due to advantages of monodispersity, stability and easy synthesis. Aggregation of QDs is the reason for low loading and poor efficiency during the in situ ligand exchange linker-assisted assembly process of preparing photovoltaic devices. In this work, we modify TiO2 films with 4-mercaptobenzoic acid (MBA) as linkers and adjust modification time (MT) of MBA on the surface of TiO2 films. As the MT increases from 0 to 6 min, even 360 min, loading amount of QDs and photovoltaic performance improve first and then decrease. The results of line scan in cross-sectional view of photoanodes show that QDs uniformly distribute throughout the short-MT films thickness, while obvious aggregation occur in the surface of long-MT films. The best device with 3 min of MBA modification exhibits an optimal efficiency of 5.58%.

Fabrication of broadband anti-reflective layers by mask-free etching TiO2 films.

We present a simple way to make TiO2 anti-reflective layers on top of silicon substrates. Surfaces of TiO2 films have been modified by radio frequency plasma with CF4 as an etchant. Mask-free etching process on the polycrystalline films leads to the formation of random sub-wavelength textures. The reflection of the etched samples are significantly suppressed in the wavelength range of 400~800 nm (2.9~4.6%, 3% compared with 34% on bare silicon at the wavelength of 600 nm). We have numerically simulated the optical properties of TiO2 layers using the finite-difference time-domain method. The anti-reflective effects are attributed to random roughness on TiO2 surfaces. The etching porcess increases the surface roughness, therefore, the gradient of refractive index between air and silicon substrate is reduced. As a result, the Fresnel reflection is supressed. Our results demonstrate an efficient way of anti-reflective coating for solar cells.

Graphene quantum dots decorated TiO2 mesoporous film as an efficient electron transport layer for high-performance perovskite solar cells

In mesoscopic perovskite solar cells, the electron transport layer plays an important role in charge extraction and determines the charge-transport property to attain a superior photovoltaic performance. Herein, we report a low-cost, solution-based deposition procedure of decorating graphene quantum dots on the surface of mesoporous TiO2 film, expecting that a more effective electron-transport channel can be formed for the enhancement of solar cell performance, finally, an impressive power conversion efficiency of 20.45% is achieved in the resulting optimized perovskite solar cell. Furthermore, the results of various spectroscopic characterizations including electronic impedance spectroscopy, steady-state and time-resolved photoluminescence spectrum elucidate that the introduction of GQDs on the surface of mesoporous TiO2 film not only enhance the electron extraction but also facilitate the charge transportation at interface between the perovskite and electron transport layer.

Boosting efficiency of planar heterojunction perovskite solar cells by a low temperature TiCl4 treatment

It is well known that electron transport layer (ETL) plays an indispensable role in the planar heterojunction perovskite solar cells (PSCs). TiO2 is widely used as an ETL material due to its excellent transport properties, however, the presence of defects in the TiO2 layer diminishes the power conversion efficiency (PCE) of the devices. Herein, we introduce a method of low-temperature TiCl4 treatment to deposit a TiOx layer on the surface of TiO2 film, which can effectively passivate trap states at the TiO2 surface. Moreover, the treating process is optimized to be 30[Formula: see text]min using a 40[Formula: see text]mM TiCl4 aqueous solution. Benefiting from this, we obtain the champion device with the highest PCE of 18.47%, which is mainly due to the reduction of surface defects and the deposition of the well-crystallized perovskite films. Besides, the modified PSCs exhibit an average PCE of 17.59%, which is much better than the control devices.

Different effects of Zn and Cu ions incorporated on TiO2 photoelectrodes on the back electron transfer in solar cells

ABSTRACTZinc and copper ions were incorporated on the surface of TiO2 films via a dipping process, and the resulting films were used as the photoelectrodes of dye-sensitized solar cells (DSSCs). The DSSC with Zn2+(30)-TiO2/FTO electrode, prepared by soaking bare TiO2/FTO in a zinc nitrate solution for 30 min, showed an improvement in power conversion efficiency, due to an enhancement in both open circuit voltage (Voc) and short circuit current (Jsc), compared to those of reference cell with bare TiO2/FTO. It was revealed that the Zn2+ incorporation on the TiO2 surface led to a retardation of the back electron transfer, inducing a prolonged electron lifetime of photo-injected electrons, and thereby increasing the Voc and Jsc. On the contrary, the back electron transfer was scarcely delayed in the device with Zn2+(30)-TiO2/FTO electrode.