Photocatalytic Films Research Articles

Dual-film optofluidic microreactor with enhanced light-harvesting for photocatalytic applications

Optofluidic microreactors are promising platform for photocatalytic reactions. However, the light transmission phenomenon is serious in optofluidic microreactors which makes a part of solar energy lose in surroundings. To resolve this problem, in this work, a novel dual-film optofluidic microreactor is proposed and fabricated by immobilizing TiO2 nanorod arrays on both the top and bottom internal wall of the microchamber. Such dual-film structure enables the transmitted light to be utilized by the bottom TiO2 film instead of being wasted, thus improving the light-harvesting capacity of optofluidic microreactor. Moreover, TiO2 nanorod arrays are employed as the photocatalytic film in this optofluidic microreactor to enlarge the specific surface area and facilitate the mass transfer. The photocatalytic performance and the kinetic properties of the dual-film optofluidic microreactor are evaluated by photocatalytic degradation of methylene blue. Results show that the proposed dual-film optofluidic microreactor yielded much higher degradation efficiency than the conventional one as a result of enhanced light-harvesting and improved mass transfer. In addition, the long-term testing proves that the durability of the dual-film optofluidic microreactor can be improved by operating it in a periodically rotated manner. In short, the TiO2 nanorod arrays-based dual-film optofluidic microreactor exhibits efficient light-harvesting and high durability and shows promising potential for photocatalytic applications.

Fabrication of Z-Scheme Fe2O3–MoS2–Cu2O Ternary Nanofilm with Significantly Enhanced Photoelectrocatalytic Performance

Ternary Fe2O3–MoS2–Cu2O nanocomposites were fabricated via electrodeposition and hydrothermal method. The as-prepared photocatalytic films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicated that MoS2 and Cu2O particles were successfully deposited onto the surface of Fe2O3 particles. MoS2 and Cu2O coloading achieved a synergetic effect on the improvement of the photoelectrochemical performance of Fe2O3 film. The highest photocurrent density was achieved on Fe2O3–MoS2–Cu2O film, which was 20, ∼5.5, and 2 times those of Fe2O3, Fe2O3–MoS2, and Fe2O3–Cu2O films, respectively. The excellent photoelectrocatalytic performance was attributed to the Z-scheme electron transfer mechanism, which results in the fast charge transfer and strong redox ability on the ternary composite. This work provides a promising Z-scheme ternary semiconductor for environmental purification and water oxidation.

Visible light active photocatalytic C-doped titanium dioxide films deposited via reactive pulsed DC magnetron co-sputtering: Properties and photocatalytic activity

Doping of TiO2 with carbon is known to be an efficient method of enhancing visible light photocatalytic activity. The present work describes the deposition of carbon-doped titania coatings deposited by reactive magnetron co-sputtering of Ti and C targets. Undoped titania coatings were produced under similar deposition conditions for comparison purposes. Following deposition, all coatings were annealed in air at 873 K for 30 min to develop the required crystalline structure; and then analysed with EDS, XRD, AFM, XPS and UV–visible spectrophotometry. A number of tests, including methylene blue and stearic acid decomposition tests, and photo-induced hydrophilicity measurements, were employed for the assessment of the photocatalytic properties of the C-doped and un-doped titanium dioxide coatings under UV and visible light irradiation. It was found that carbon-doped titania coatings significantly outperformed undoped titania when using both visible and UV irradiation. Similar trends were observed for other properties. While excessive carbon doping has been shown to have a negative effect on the photocatalytic properties of the titanium dioxide, overall, carbon doping via reactive co-sputtering has been confirmed as an efficient method of photocatalytic property enhancement. This is due to a narrowing of the bandgap and to extended lifetimes of the photo-generated charge carriers.

XANES study of vanadium and nitrogen dopants in photocatalytic TiO2 thin films.

We report an X-ray absorption near edge structure (XANES) study of vanadium (V) and nitrogen (N) dopants in anatase TiO2 thin films deposited by radio-frequency magnetron sputtering. Measurements at the Ti K and V K edges were combined with soft X-ray experiments at the Ti L2,3, O K and N K edges. Full potential ab initio spectral simulations of the V, O and N K-edges were carried out for different possible configurations of substitutional and interstitial dopant-related point defects in the anatase structure. The comparison between experiments and simulations demonstrates that V occupies substitutional cationic sites (replacing Ti) irrespective of the film structure and dopant concentration (up to 4.5 at%). On the other hand, N is found both in substitutional anionic sites (replacing O) and as N2 dimers within TiO2 interstices. The dopants' local structures are discussed with reference to the enhanced optical absorption and photocatalytic activity achieved by (co)doping.

Antimicrobial properties of plasmonic metal decorated/doped titanium dioxide photocatalytic films

Antimicrobial properties of plasmonic metal decorated/doped titanium dioxide photocatalytic films

Self-organized nanocrack networks: a pathway to enlarge catalytic surface area in sputtered ceramic thin films, showcased for photocatalytic TiO2

Sputter deposited photocatalytic thin films offer high adherence and mechanical stability, but typically are outperformed in their photocatalytic properties by colloidal TiO2 nanostructures, which in turn typically suffer from problematic removal. Here we report on thermally controlled nanocrack formation as a feasible and batch applicable approach to enhance the photocatalytic performance of well adhering, reactively sputtered TiO2 thin films. Networks of nanoscopic cracks were induced into tailored columnar TiO2 thin films by thermal annealing. These deep trenches are separating small bundles of TiO2 columns, adding their flanks to the overall catalytically active surface area. The variation of thin film thickness reveals a critical layer thickness for initial nanocrack network formation, which was found to be about 400 nm in case of TiO2. The columnar morphology of the as deposited TiO2 layer with weak bonds between respective columns and with strong bonds to the substrate is of crucial importance for the formation of nanocrack networks. A beneficial effect of nanocracking on the photocatalytic performance was experimentally observed. It was correlated by a simple geometric model for explaining the positive impact of the crack induced enlargement of active surface area on photocatalytic efficiency. The presented method of nanocrack network formation is principally not limited to TiO2 and is therefore seen as a promising candidate for utilizing increased surface area by controlled crack formation in ceramic thin films in general.

Black ZnO/C nanocomposite photocatalytic films formed by one-step sol–gel technique

We developed a facile one-step sol–gel technique for fabrication of black zinc oxide/carbon (ZnO/C) nanocomposite films demonstrating an enhanced photocatalytic activity. Amorphous carbon covering ZnO grains inside the films was reduced from organic components of the zinc acetate based sol calcinated at 500 °C. The amount of carbon in the films can be controlled by varying the amount of zinc chloride added to the zinc acetate based sols. The surface layer of the films is composed by randomly oriented hexagon-shaped ZnO grains. Photoluminescence quenching indicating the suppression of electron-hole recombination in the prepared ZnO/C composites were observed. The recorded optical transmittance/reflectance spectra and the performed photocatalytic tests demonstrated that the synthesized ZnO/C nanocomposite is promising for photoinduced decomposition of organic compounds. Related peculiarities are discussed.

Preparation and characterization of photocatalytic TiO2 films on functionalized stainless steel

In this study, TiO2 was synthesized using controlled hydrolysis of TiCl4, followed by dialysis. We produced a transparent emulsion that was later dried into TiO2 powder. TiO2 photocatalyst films were deposited applying the technique of pulsed electrophoretic deposition, which decreased bubble formation caused by direct current. The substrates were bare stainless steel (SS) and stainless steel pre-functionalized in a conversion bath. Film surface morphology, crystallinity, elemental composition, and wettability were determined using XRD, SEM–EDAX, and contact angle measurements. The mechanical properties were determined by nano-indentation test. The adhesion was investigated using scratch test. The obtained results showed that the TiO2 film over a conversion layer had better adhesion and mechanical properties than TiO2 over bare SS. The optical characteristics of TiO2 films were tested using PL measurement. The photocatalytic decolourization of the amido black-10B dye was studied over TiO2 coating under UV and visible light irradiation. TiO2 film over a conversion layer without heat treatment exhibited the best photocatalytic activity as a result of its crystalline size and three-phase structure as well as the synergetic effect of TiO2 and Fe2O3.

Self-Cleaning and Photocatalytic Performance of TiO2 Coating Films Prepared by Peroxo Titanic Acid

Self-cleaning and photocatalytic TiO2 thin films were prepared by a facile sol-gel method followed by spin coating using peroxo titanic acid as a precursor. The as-prepared thin films were heated at low temperature(110 °C) and high temperature (400 °C). Thin films were characterized by X-ray diffraction(XRD), Field-emission scanning electron microscopy(FESEM), UVVisible spectroscopy and water contact angle measurement. XRD analysis confirms the low crystallinity of thin films prepared at low temperature, while crystalline anatase phase was found the for high temperature thin film. The photocatalytic activity of thin films was studied by the photocatalytic degradation of methylene blue dye solution. Self-cleaning and photocatalytic performance of both low and high temperature thin films were compared.

Solution precursor plasma spray process as an alternative rapid one-step route for the development of hierarchical ZnO films for improved photocatalytic degradation

The development of efficient photocatalytic hierarchical coral-like ZnO films via a relatively simple, efficient, rapid and single-step process is essential for industrial development. Herein, we report a novel method for directly synthesizing well-shaped ZnO nanorods (NRs) by Solution Precursor Plasma Spray (SPPS) process rather than conventional spherical/ellipsoidal particles. In the prepared ZnO-NRs films, the ZnO NRs display an average diameter of 190nm, and exhibit a preferential orientation growth along (002) plane compared to a reference ZnO films (called ZnO-P) containing spherical/ellipsoidal particles. ZnO-NRs films exhibit relative narrower bandgap (3.02eV) probably due to the apparent non-equilibrium heating-cooling process and to the use of hydrogen in the SPPS method. Such ZnO-NRs films are capable of a quasi-quantitative (99%) decomposition of the Orange II dye within 150min under Hg-Xe light irradiation, which is nearly 2.7 times of the reference sample ZnO-P (37% degradation). Besides, the ZnO-NRs films exhibit an excellent retention of performance (98.7% degradation in a second cycle). Moreover, these preliminary results demonstrate that SPPS process provides a promising alternative to conventional multi-step processes for the production of metal oxide photocatalytic films in practical applications.

Photocatalytic antimicrobial films on fluorinated contact lens polymers

Flat TiO2 thin films were dip coated on contact lens polymer substrates (fluorinated ethylene propylene copolymer, FEP) using a hybrid sol-gel and annealed for 12 h at ≤200 °C. The grain sizes were in the range 10–20 nm but extensive shrinkage cracking was present. The crystallinities of the films annealed at ≤150 °C increased with increasing temperature gradually but only to a limited extent, although the crystallinity at 200 °C was significant. Recrystallisation resulted in decreased transparency, increased reflectivity, and a red shift to lower band gap. The methylene blue (MB) degradation was in the order 25 °C < 200 °C < 100 °C < 150 °C, indicating that the photocatalytic performance was dominated by crystallinity and exposed surface area, the latter of which decreased at 200 °C owing to partial submergence in the softened polymeric substrate. The films indicated antimicrobial capacity since they exhibited a maximal level of S. aureus destruction (85%) following 5 h of UV irradiation. The films also appeared to be microstructurally stable following wash testing in contact lens washing solution.

Hexavalent chromium removal by multilayer membrane assisted by photocatalytic couple nanoparticle from both permeate and retentate

In this study, a novel photocatalytic thin film nanocomposite (TFC) membrane was prepared for removal of hexavalent chromium (Cr(VI)) from aqueous solution. In this regards, a TFC membrane was modified by a layer of chitosan as an adsorbent and then was coated with a layer of synthesized photocatalytic nanoscale zerovalent iron@titanium dioxide (nZVI@TiO2) nanoparticles via layer-by-layer (LBL) technology. Prepared membranes were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and contact angle analysis. The Cr(VI) removal efficiency of the membranes was evaluated by batch removal and dynamic filtration tests. The water flux was increased from 26.2 to 39.7l/m2h as a consequence of improved hydrophilicity which was approved by contact angle analysis. The modified TFC membrane has shown the significant removal of Cr(VI) in retentate as well as the permeate stream. Further, the Cr(VI) removal of retentate flow decreased with increasing pH and feed concentration whereas the Cr(VI) removal of permeate was enhanced with increasing initial feed concentration. Increasing the flux recovery from 62% (for neat TFC) to 87% (for modified TFC membrane) demonstrated that the modification of membrane improved the anti-fouling property of the modified membrane.

Photooxidative properties of various BiVO4/TiO2 layered composite films and study of their photocatalytic mechanism in pollutant degradation

The pollution of the natural environment by organic pollutants has become a great issue since several decades. As a result, the removal of compounds by using photocatalytic processes under sunlight irradiation attracts a growing interest. In the present work, BiVO4/TiO2 photocatalysts were prepared in the form of films by simple wet chemical methods Various layered configurations of BiVO4/TiO2 film were studied and it was found that the best photocatalyst was composed of top-coated TiO2 layer onto a BiVO4 layer. Such composite exhibited better photodegradation ability toward organic pollutants than single components or top-coated BiVO4 onto TiO2 film. Indeed, the photooxidative mechanism involved oxidative radical species. Therefore the mechanism of photooxidative degradation depended on the layered configuration of the composite film. All the photocatalytic films were characterized by XRD, SEM, UV–vis spectroscopy and XPS in order to study the composition, the surface, and the energy band gap of the photocatalyst. The mechanism of photodegradation was investigated indirectly by using different charge scavengers in order to determine the main oxidative species.

Photocatalytic and Magnetic Porous Cellulose-Based Nanocomposite Films Prepared by a Green Method

The present work expands our previous studies related to cellulose processing with room-temperature ionic liquids and simultaneous integration of functional nanoparticles toward photocatalytically active and easily recyclable nanocomposite porous films based on a renewable matrix material. Porosity can be tuned by the selection of phase separation conditions for the films obtained from the casting solutions of cellulose in ionic liquids or their mixture with an organic co-solvent. TiO2 nanoparticles confer to the nanocomposite photocatalytic activity, while Fe3O4 nanoparticles make it magnetically active. The photocatalytic activity of the cellulose film containing 10 mg of TiO2 was 1 order of magnitude lower than that of the same amount of pure TiO2 nanopowder, due to the reduction of the active catalytic surface which can be reached by UV irradiation after embedment in the polymer matrix. However, this fixation in a solid polymer support allows facile recovery of the catalyst after use. The rate constan...

Reactive Magnetron Sputter Deposition of Bismuth Tungstate Coatings for Water Treatment Applications under Natural Sunlight

Bismuth complex oxides, in particular, bismuth tungstate, have recently attracted attention as promising photocatalytic materials for water treatment processes. In the present work, photocatalytic bismuth tungstate films were prepared by pulsed direct current (DC) reactive magnetron sputtering of Bi and W targets in an Ar/O2 atmosphere onto spherically-shaped glass beads. The uniform coverage of the substrate was enabled by the use of oscillating bowl placed underneath the magnetrons. The atomic ratio of Bi/W was varied through the variation of the power applied to the magnetrons. The deposited coatings were analyzed by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy and atomic force microscopy. The photocatalytic properties of the films were studied via the methylene blue (MB) degradation process under artificial (fluorescent light) and natural (sunlight) irradiation, and compared to the photocatalytic performance of titanium dioxide coatings deposited onto identical substrates. The results showed that the photocatalytic performance of bismuth tungstate and bismuth oxide-coated beads was superior to that exhibited by TiO2-coated beads. Overall, reactive magnetron co-sputtering has been shown to be a promising technique for deposition of narrow band gap bismuth-based semiconducting oxides onto irregularly-shaped substrates for potential use in water treatment applications.

Low temperature synthesis of few-layer titanate nanobelts on Ti mesh and the hot-water induced transformations to highly photocatalytic active titania nanorods

An efficient photocatalytic reactor to remove pollutants from either water or air relies on highly active photocatalytic thin films on appropriate substrates, which contribute to both light harvesting and pollutant molecules transfer. In this investigation, few-layer titanate nanobelts were deposited on metallic Ti mesh using hydrogen peroxide solution, which were then subjected to a subsequent hot water treatment to achieve crystallized titania nanorod arrays. The three-dimensional arrays of nanorods formed on Ti mesh (three layers overlapped) exhibited an exceptional high efficiency when utilized to assist photodegradation of rhodamine B in water under UV light illumination, which is 25 times that of P25 film, and even 1.3 times that of P25 nanoparticles in a slurry system. For photodegradation of phenol in water, the three-layer Ti mesh also exhibited a reaction rate constant 6.9 times that of P25 film. The reduced band gap, abundant surface hydroxyl groups, and mixed phase effects arising from the low temperature approach contribute to the high photocatalytic activity.

Flexible Photocatalytic Composite Film of ZnO-Microrods/Polypyrrole

Zinc oxide (ZnO)-based photoanodes with sunlight photocatalytic activity are widely used in dye-sensitized solar cells. Presently, most of such electrodes are inflexible due to the rigidness of ZnO and substrate, thus hindering their application in flexible electronics. Here, we report a flexible composite film of ZnO microrod arrays and polypyrrole (PPy) featuring significant flexibility, durability, and photocatalytic capability under visible light. In this composite film, the upper section of the ZnO microrods is coated with an approximately 400 nm thick PPy shell, and the lower section of the ZnO microrods is tightly embedded into an underlying PPy base layer, creating an integrated heterogeneous structure. The upper PPy coating shell serves as a photosensitizer for the ZnO-based photocatalysis, while the lower PPy base layer facilitates electron transport to the substrate and mechanically reinforces the ZnO microrod arrays. Under visible light, this facile structure achieves much higher photocatalytic efficiency in comparison to pure ZnO microrod arrays or PPy film, degrading methylene blue at a rate of 0.22%/min. This photocatalytic composite film may find promising applications in flexible solar cells to power stretchable and wearable electronics.

Role of the electrode morphology on the optimal thickness of BiVO4 anodes for photoelectrochemical water splitting cells

Photoelectrochemical (PEC) water splitting is one of the most promising technologies able to exploit renewable resources such as water and sunlight for the sustainable production of energy carriers (i.e. H2, solar fuels). Recently, it was demonstrated that the currents through a PEC water splitting cell present a maximum for a specific thickness of the photocatalytic anode film (J. Electroanal. Chem. 2017, 788, 61–65 ), which is related to the attenuation of the light in the semiconductor layer and to the applied bias potential. In this work, it is shown that this non-monotonic behavior is not only due to the trade-off between the absorption length of light and thickness of a photocatalyst (e.g. BiVO4) film, but mainly to the porous nature of the semiconducting material. A theoretical analysis of such behavior for an ideal compact medium shows a very broad maximum, in contrast to the experimental values that present steeper slopes both at low and large thicknesses (e.g. for films prepared by dip-coating method). There have been taken into account, subsequently, the loss of useful current at grain boundaries, due to an increased number of recombination centers, the reduction of specific area (less porosity) as the grains increase in size when increasing the number of dip-coatings, the possible non-uniform coverage of the substrate by the BiVO4 for a low number of coatings, and the partial blocking of pores with oxygen bubbles under operation. For each of these considerations, a normalized current plot in terms of the number of coatings has shown a remarkably good concordance to the experimental data.

Geopolymer-supported photocatalytic TiO2 film: Preparation and characterization

The article reports preparation and characteristics of TiO2 films deposited on geopolymer substrates via sol-gel dip coating process. Serious cracking takes place within TiO2 film derived from sol precursor with butyl titanate as titanium source and prepared by traditional dip-coating process on geopolymer substrates. It is found that the incorporation of 6% Polyvinylpyrrolidone, and the application of vacuum impregnation before withdrawing relieve cracking significantly, and the resulting TiO2 film exhibits mesoporous morphology. The TiO2 film annealed at 600°C is mainly composed of anatase phase, and exhibits highest photocatalytic activity evaluated by degrading methylene blue. Multilayer dip-coating promotes photocatalytic activity of the obtained TiO2 film in some extent, but decreases in photocatalytic efficiency and homogeneity are observed when the number of coating layers is over 3.

Novel pH-based photocatalyst activity indicator hydrogel film ( Hpaii )

Abstract A novel, hydrogel-supported photocatalyst activity indicator, Hpaii , is presented, based on an agar gel containing the pH indicator dye propyl red (PR), and the photoacid generator, diphenyliodonium nitrate (DPIN). The latter is broken down when the film is on an active photocatalytic film, and the acid released protonates the PR, turning the gel from a yellow colour to a red. Initially tested on a TiO 2 sol-gel film, the Hpaii is also shown to be effective in indicating the activity of several different commercially available photocatalytic surfaces, including: glass, tiles and paint. This is the first example of a water-based photocatalyst activity indicator ink based on monitoring a photocatalytic process via the change in pH induced in the indicator films, as revealed by the pH-indicator, propyl red.