Photoinduced Superhydrophilicity Research Articles

Antireflective coating using a WO3–TiO2 nanoparticle photocatalytic composition for high efficiency thin-film Si photovoltaic modules

We propose a cost-effective, low-temperature antireflective coating for the outer glass substrates of 1.43m2 thin-film Si photovoltaic modules using a WO3–TiO2 nanoparticle photocatalyst. The coated nanoporous films provide the broadband antireflective effect, which results in the increased initial performances. Notably, the self-cleaning effect due to the photo-induced superhydrophilicity leads to a significantly reduced outdoor-exposed degradation. Therefore, the drastic energy output gain of 4.3% is achieved for a tandem photovoltaic module via a long-term outdoor field test.

High-permeability pluronic-based TiO2 hybrid photocatalytic membrane with hierarchical porosity: Fabrication, characterizations and performances

High-permeability Pluronic-based TiO2 hybrid photocatalytic membrane with hierarchical porosity has been fabricated via acid-catalyzed sol–gel method. Pluronic P-123 of different weight percentages was added to fine-tune the pore structure of the TiO2 sol and thus the resulting TiO2 layers. PVA was used as the pore fillers and binder. The sols were dip-coated layer-by-layer onto an alumina ceramic disc to fabricate hierarchically porous TiO2/alumina membrane with different porosity gradients. Physico-chemical and morphological characteristics of the membrane were investigated. Pluronic-based TiO2 photocatalytic membrane showed photo-induced super-hydrophilicity which is important for the accessibility of organic compound to the catalytic sites. The performances of the membrane were evaluated both in the batch photoreactor and continuous flow photoreactor operated in the dead-end filtration mode. In the batch photoreactor, the membrane was able to completely degrade rhodamine B despite the mass transfer limitation. The hierarchically porous Plu A membrane (which was coated with three different TiO2 layers of different pore structures) showed a high water permeability flux of 116Lm2h−1bar−1 with the corresponding intrinsic membrane resistance of 3.1×1012m−1. Plu A membrane also possessed excellent specific RhB removal of 2700mgm−2. The as-synthesized hybrid photocatalytic membrane showed a great potential for use in water and wastewater treatment owing to its fouling-control capability, high flux performances, good photocatalytic activity, and reusability.

Preparation of Hydroxyapatite-coated Anatase by Photoinduced Superhydrophilic Reaction of TiO2 for Water Purification

Abstract Hydroxyapatite coated on TiO2 for use as a photocatalyst for water purification was synthesized by using the superhydrophilicity of TiO2. The hydroxyapatite formed on TiO2 under UV irradiation with high crystallization in 1 h. The isoelectric point of the hydroxyapatite-coated TiO2 was shifted to acidic pH, and the aggregates formed in aqueous solution at pH 7 were smaller than those of anatase TiO2. Consequently, in water purification tests, the proposed photocatalyst effectively decomposed dimethyl sulfoxide and Methylene Blue in water.

Influence of catalyst on structural and morphological properties of TiO2 nanostructured films prepared by sol–gel on glass

Transparent TiO2 thin films have been prepared by the sol–gel method using titanium alkoxides as precursors. Thin films were deposited on glass supports by the dip-coating technique. The TiO2 layer acts as a self-cleaning coating generated from its photocatalysis and photoinduced superhydrophilicity. The crystalline structure of TiO2 films was dominantly identified as the anatase phase, consisted of uniform spherical particles of about 14–50nm in size, which strongly depends upon catalyst-type and heat treatment temperature. Increasing heat treating temperature can lead to an increase in crystalline size. The results indicated that the sample S.S (sample derived from sol containing sulfuric acid as catalyst) exhibits superhydrophilic nature and better photocatalytic activity, which can be attributed to its higher anatase content and lower crystalline size. Morphological studies, carried out using Atomic Force Microscopy (AFM), confirm the presence of crystalline phase with such a grain size and low surface roughness. Thus, the applied films exhibiting high photocatalytic activity, superhydrophilic behavior, and low surface roughness can be used as an efficient self-cleaning coating on glass and other optical applications.

Effect of crystal structure on photoinduced superhydrophilicity of copper grafted TiO2 nanostructure thin film

In this work, copper grafted titanium dioxide (rutile and brookite) thin films were deposited on glass substrates using the dip-coating method. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to evaluate the surface morphology and properties of the film surfaces. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyser. The results indicate that copper grafted titanium dioxide brookite thin film showed higher hydrophilicity than copper grafted titania rutile thin film.

The photocatalytic inactivation effect of Ag–TiO2 on β-amyloid peptide (1–42)

Abstract Due to its low toxicity and excellent biocompatibility, titanium dioxide and its alloyed are widely used in biomedical applications. Furthermore, TiO2 can be excited by UV light to create charge carriers giving rise to photocatalytic redox reactions at its surface and photo-induced super-hydrophilicity. In this work, TiO2 films were modified with silver (Ag–TiO2) by the photocatalytic reduction of Ag+ from solution. The films and the adsorption of β-amyloid (1–42), were studied using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). These films were confirmed to contain mainly anatase crystallites and the photo-reduced Ag was predominantly Ag0 (>0%). Ag loading of the TiO2 markedly enhanced the Raman signal (ca. 15-fold), but caused significant changes to the protein spectrum indicating non-specific binding of β-amyloid side chain residues to the silver. The amide modes remained well-resolved and were used to estimate the conformational change induced in the protein by the silver. Raman analysis showed an increase in the intensity of the band at ∼1665 cm−1 assigned to the disordered conformation of the β-amyloid, suggesting that the adsorption to the silver sites induces conformational changes. Contaminated surfaces were exposed to UVB irradiation, caused further conformational changes in the β-amyloid, which mildly inhibited amyloid fibril formation, thought to be induced through a photocatalytic mechanism.

Photoinduced Superhydrophilicity: A Kinetic Study of Time Dependent Photoinduced Contact Angle Changes on TiO2 Surfaces

Transparent TiO(2) thin films were prepared on quartz substrates via a reverse micelle, sol-gel, spin-coating technique. The time dependence of the TiO(2) film photoinduced superhydrophilicity (PISH) was measured by goniometric observation of the contact angle, θ, of sessile water drops at the film surfaces. In these measurements, the TiO(2) substrate was illuminated by 315 nm light and drops were sequentially applied at a range of illumination times. Using a model for the wetting of heterogeneous surfaces derived by Israelachvili and Gee, these measurements were used to calculate the time dependence of f(2), the fractional surface coverage of the TiO(2) surface by adventitious contaminating organics (Israelachvili, J. N.; Gee, M. L. Contact angles on chemically heterogeneous surfaces. Langmuir 1989, 5, 288). Extending this model to include a Langmuir-Hinshelwood based kinetic analysis of f(2) as a function of time allowed for calculation of an expected value for θ immediately prior to illumination, that is, at illumination time t = 0. Such expected values of θ at t = 0 were calculated using two possible values of θ(1), the contact angle on a pristine unilluminated homogeneous TiO(2) surface: (i) θ(1) = 4° as suggested by, inter alia, Zubkov et al. (Zubkov, T.; Stahl, D.; Thompson, T. L.; Panayotov, D.; Diwald, O.; Yates, J. T. Ultraviolet Light-Induced Hydrophilicity Effect on TiO(2)(110)(1 × 1). Dominant Role of the Photooxidation of Adsorbed Hydrocarbons Causing Wetting by Water Droplets. J. Phys. Chem. B2005, 109, 15454); and (ii) where θ(1) = 25°, as suggested by Fujishima et al., representative of a more hydrophobic homogeneous TiO(2) surface that reconstructs upon exposure to ultraband gap illumination into a hydrophilic surface where θ(1) → 0° (Fujishima, A.; Zhang, X.; Tryk, D. A. TiO(2) photocatalysis and related surface phenomena Surf. Sci. Rep.2008, 63, 515). Analysis of data from our experiments and from selected literature sources demonstrates better agreement between these calculated and experimental values of θ at t = 0 when θ(1) is taken to be 4°, implying that an uncontaminated TiO(2) surface is inherently hydrophilic. The results of this study are discussed in the context of the current debate over the origin of the photoinduced superhydrophilic effect.

Multifunctional composite multilayer coatings on glass with self-cleaning, hydrophilicity and heat-insulating properties

Multifunctional coated glass with self-cleaning, hydrophilicity and heat-insulating properties is prepared by reactive magnetron sputtering. A SiO2(top)/TiO2(under) double-layer structure is deposited on the outer surface of the glass to integrate self-cleaning and hydrophilicity functions. The inside of the glass is a similar six-layer coating that has heat-insulating function. Detailed optimization process for constructing the composite coatings on the glass is reported, and its efficacy is evaluated. TiO2 nanotubes sensitized with narrow-band-gap semiconductor drastically improve the photocatalytic activity. SiO2/sensitized TiO2 nanotube double-layer also exhibits excellent photo-induced super-hydrophilicity. The optical properties of each individual layer have been studied in order to achieve a balance between the heat-insulation performance and the visible-light transmittance of the heat-insulating multilayers. The spectra of the two-side composite coatings on the glass show that the color appearance can be tailored, which present potential applications in the architectural windows and automotive glazing.

Effects of Interface Defects on Charge Transfer and Photoinduced Properties of TiO2 Bilayer Films

By a combination of cold plasma treatment and sol–gel dip-coating technology, defective TiO2 bilayer films were successfully prepared, and then the defect was characterized by X-ray photoelectron spectroscopy and electron spin resonance. The photocatalytic activity and photoinduced superhydrophilicity of the films were evaluated by the photocatalytic degradation of organic dyes and water contact angle measurement in air, respectively. Compared to the conventional TiO2 film, the TiO2 bilayer films with defects provide much higher efficiency in photocatalysis and photoinduced hydrophilicity. Moreover, it is found that the introduction of defect sites at the interface of two TiO2 layers results in a significant improvement in the photonic efficiency due to the generation of electron trapping states. The defect sites can inhibit the recombination of electron–hole pairs and thereby increase the concentration of photogenerated carriers at the film surface, leading to an enhancement of quantum efficiency of TiO2 films under UV irradiation. Furthermore, the defects located at the interface between two TiO2 layers show higher stability as compared with that located at the outermost surface of TiO2 films. In addition, the fabrication of the interface defective TiO2 multilayer film is convenient and of low cost. The study demonstrates that this modified strategy is practical for promoting the photoinduced properties of TiO2 multilayer films.

Photoinduced superhydrophilicity of TiO2 thin film with hierarchical Cu doping

Hydrophilic Cu–TiO2 thin films with a gradient in the Cu concentration were prepared on glass by layer-by-layer dip-coating from TiO2 precursors. The effects of the Cu doping on the structure and properties of TiO2 self-cleaning thin films are discussed. The Cu gradient markedly affects the hydrophilicity of the films, with the water contact angle significantly reduced compared with those of the pure or uniformly doped TiO2 thin films. This enhanced hydrophilicity is explained by the more efficient absorption of the solar light and by the reduced recombination of photoexcited electrons and holes in the TiO2 films containing a gradient of Cu dopants.

Facile Preparation and Photoinduced Superhydrophilicity of Highly Ordered Sodium-Free Titanate Nanotube Films by Electrophoretic Deposition

Highly ordered sodium-free titanate nanotube films were one-step prepared on F-doped SnO2-coated (FTO) glass via an electrophoretic deposition method by using sodium titanate nanotubes as the precursor. It was found that the self-assembled formation of highly ordered sodium titanate nanotube films was accompanied with the effective removal of sodium ions in the nanotubes during the electrophoretic deposition process, resulting in the final formation of protonated titanate nanotube film. With increasing calcination temperature, the amorphous TiO2phase is formed by a dehydration process of the protonated titanate nanotubes at 300°C and further transforms into anatase TiO2when the calcination temperature is higher than 400°C. Compared with the as-prepared titanate nanotube film, the calcined titanate nanotube film (300–600°C) exhibits attractive photoinduced superhydrophilicity under UV-light irradiation. In particular, 500°C-calcined films show the best photoinduced superhydrophilicity, probably due to synergetic effects of enhanced crystallization, surface roughness, and ordered structures of the films.

ChemInform Abstract: Photodeposition of Metal Sulfide Quantum Dots on Titanium(IV) Dioxide and the Applications to Solar Energy Conversion

AbstractReview: 87 refs.

Fabrication of TiO<sub>2</sub> Films on Glass Substrates by a Pulsed Dc Reactive Magnetron Sputtering

Due to its ability of photocatalysis and photoinduced superhydrophilicity, TiO2was paid significant attentions in recent years. In this study, TiO2films were deposited at room temperature and 300 °C by pulsed dc reactive magnetron sputtering. The gas pressure was varied in the range of 0.3-1.1 Pa by filling Ar/N2gas mixture with the ratio of 1:1. The surface morphologies, phase structure and optical property of the TiO2films were investigated. TiO2films with good crystalline quality containing mainly of anatase phase were obtained by deposition using gas pressure of 0.7 Pa at room temperature and gas pressure of 1.5 Pa at 300 °C.

Effect of nickel oxide seed layers on annealed-amorphous titanium oxide thin films prepared using plasma-enhanced chemical vapor deposition

The effect of a nickel oxide (NiO x) seed layer on the crystallization and photocatalytic activity of the sequentially plasma-enhanced chemical vapor deposited amorphous titanium oxide (TiO x) thin film processed by a post-annealing process was investigated. The evolution of the crystalline structures, chemical bond configurations, and surface/cross-sectional morphologies of the annealed TiO x films, with and without a NiO x seed layer, was examined using X-ray diffractometer, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscope measurements. Thermo- and photo-induced hydrophilicity was determined by measuring the contact angle of water droplet. Photocatalytic activity after UV light irradiation was evaluated from the decolorization of a methylene blue solution. The crystallization temperature of the TiO x film, deposited on a NiO x seed layer, was found to be lower than that of a pure TiO x film, further improving the thermo- and photo-induced surface super-hydrophilicity. The TiO x film deposited onto the NiO x seed layer, resulting in significant cluster boundaries, showed a rough surface morphology and proved to alleviate the anatase crystal growth by increasing the post-annealing temperature, which yielded a more active surface area and prohibited the recombination of photogenerated electrons and holes. The photocatalytic activity of the NiO x/TiO x system with such a textured surface therefore was enhanced and optimized through an adequate post-annealing process.

Adsorption and photocatalytic degradation of human serum albumin on TiO 2 and Ag–TiO 2 films

Titanium dioxide is a useful material in the biomedical field as it has excellent biocompatibility based on its non-toxicity and non-inflammatory properties. Furthermore, TiO 2 can be excited by UV light to create charge carriers giving rise to photocatalytic redox reactions at the surface and photo-induced super-hydrophilicity. These properties might be exploited for surface decontamination of medical devices and implants. With this in mind, titanium dioxide TiO 2 films were prepared on stainless steel substrates using magnetron sputtering. Silver loaded (Ag–TiO 2) films were prepared by the photocatalytic reduction of Ag + from solution. The adsorption of human serum albumin (HSA) was studied. Surface analysis methods used included X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and atomic force microscopy (AFM). The TiO 2 films were predominantly anatase crystal phase and the photoreduced Ag was present at greater than 90% of the silver content as Ag 0 on the surface. Ag loading of the TiO 2 markedly enhanced the Raman signal (ca. 15-fold), but caused significant changes to the spectrum indicating non-specific binding of protein side chain residues to the Ag. The amide I and III modes remained well-resolved and were used to estimate the conformational change induced by the Ag. Raman analysis showed an increase in the intensity of the band at ∼1665 cm −1 assigned to the disordered conformation, suggesting that the adsorption to the Ag sites induces conformational changes in the protein. UVB irradiation of the protein contaminated surfaces caused further changes in the protein conformation, consistent with denaturation and enhanced binding and oxidation, thought to be induced through a photocatalytic mechanism.

Photo-induced superhydrophilicity of nanocomposite TiO2-SiO2 thin film

In this work, TiO2 and TiO2-SiO2 thin films on glass substrates were prepared by the sol-gel dip coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. The super-hydrophilicity was assessed by water contact angle measurement. XRD measurements confirmed the presence of polycrystalline anatase and rutile phases in the films. The water contact angle measurements showed that addition of SiO2 has a significant effect on the super-hydrophilicity of TiO2 thin films, especially if they are stored in a dark place.

Influence of photo-induced superhydrophilicity of titanium dioxide nanoparticles on the anti-fouling performance of ultrafiltration membranes

Fouling is one of the most present prominent problems in almost all membrane processes. An increase in the membrane hydrophilicity is one of the effective ways to improve the membrane resistance to fouling. In this research, TiO 2 nanoparticles were deposited on the surface of composite ultrafiltration (UF) membrane, and then irradiated by ultraviolet (UV) light. The coating of the membrane surface with TiO 2 nanoparticles and radiation with (UV) light led to the considerable increase of hydrophilicity on the membrane surface. The deposition of TiO 2 nanoparticles was carried out through coordinance bonds with OH functional groups of the polymer on the membrane surface. The flux through a coated and (UV) light radiated membrane was increased to a large extent compared to a virgin membrane. In this research, the effect of different concentrations of TiO 2 nanoparticles in the presence and absence of (UV) irradiation was investigated, and the role of increasing of hydrophilicity on the anti-fouling property of membranes was studied. In order to characterize the membranes FTIR, XRD, SEM, water contact angle and cross-flow filtration were employed. This procedure is a useful technique for improvement of hydrophilicity to decrease (increase) fouling (anti-fouling performance) and enhance the permeation of membranes.

Photodeposition of metal sulfide quantum dots on titanium(iv) dioxide and the applications to solar energy conversion

Heteronanojunction systems consisting of narrow gap semiconductors represented by metal sulfides and TiO(2) are highly expected as visible-light-active photocatalysts and the key materials for various photoelectrochemical devices. The common central issue is increasing efficiency of the light-induced interfacial electron transfer from the metal sulfide quantum dots (QDs) to TiO(2). We have newly developed simple and versatile low-temperature photodeposition techniques for directly coupling metal sulfide QDs and TiO(2) by taking advantage of its photocatalysis and the photoinduced surface superhydrophilicity. This critical review summarizes the recent developments in the photodeposition techniques and their unique characteristics. Subsequently to the Introduction, a theoretical view of the interfacial electron transfer is presented to obtain the guidelines for the design of the heteronanojunction systems. Then, the itemized description is given for the photodepositions of several kinds of metal sulfides on TiO(2) followed by the summary of the features of the photodeposition technique. Finally, the applications of the resulting heteronanojunction systems to the photocatalysts and QD-sensitized solar cells are described, and the excellent performances are discussed by relating with the features of the photodeposition technique (87 references).

Visible light photocatalysts—N-doped TiO2 by sol–gel, enhanced with surface bound silver nanoparticle islands

Antimicrobial thin film photocatalysts consisting of N-doped titania have been prepared by sol–gel methods and further enhanced using silver nanoparticles formed in situ on the surface of the films. The films have been characterised using XRD, SEM, XPS, UV-Visible spectroscopy and functionally tested using measurements for the photoinduced superhydrophilicity, stearic acid destruction and anti-microbial measurements using both E. coli and an epidemic strain of MRSA, EMRSA-16. The N-doped TiO2 films were seen to have interstitially doped nitrogen with the N 1s peak appearing at 400.0 eV in the XPS and as such showed good photocatalytic activity under white light. The photoactivity was then further enhanced by silver nanoparticle formations on the surface. The highly active photocatalytic films were seen to be effective agents against both bacteria and stearic acid using a white light source that is commonly found in UK hospitals.

UV/Thermally Driven Rewritable Wettability Patterns on TiO2−PDMS Composite Films

Composite films of TiO2 and polydimethylsiloxane (PDMS) are prepared by a sol-gel method, cured with UV irradiation, and then treated in hot water to crystallize the TiO2 in the film. The presence of anatase TiO2 contributes to the photoinduced superhydrophilicity of the film under UV irradiation. Contact angle studies reveal that the TiO2-PDMS composite film recovers its original hydrophobic state. Hydrophobic-superhydrophilic patterns are successfully formed on the films. The wettability patterns can be erased by UV irradiation and thermal treatment. New wettability patterns can be reconstructed, demonstrating that the film exhibits rewritable wettability without the need for organic chemicals.