Photocatalytic Films Research Articles

Exploring the synergistic interactions of TiO2, rGO, and g-C3N4 catalyst admixtures in a polystyrene nanocomposite photocatalytic film for wastewater treatment: Unary, binary and ternary systems

Reduced graphene oxide (rGO) as well as graphitic carbon nitride (g-C3N4) were synthesised and blended along with TiO2 at specific ratios in polystyrene photocatalytic films to find out the optimum efficiency. The prepared photocatalysts were characterised by scanning electron microscopy (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR) and contact angle analyser. The SEM, XRD, and FTIR analysis indicated that the nanoparticles were evenly distributed on the surface of the polystyrene film. The stability of the polymer film with respect to possible leaching of the embedded catalyst particles was evaluated by ICP-OES analysis. The photocatalytic activity of the admixture was evaluated using remazol turquoise blue dye as a model organic pollutant, and it was found that the photocatalytic ternary admixtures displayed much higher photocatalytic activity (˜99%) than the unary (˜89%) or binary (˜94%) mixtures indicating the synergistic effect of these catalysts. The effect of catalyst ratio, immobilisation, pH, initial dye concentration, irradiated light source, the presence of H2O2 and reusability of the film were also evaluated. The degradation of the dye is confirmed by TOC analysis (40% reduction), and HPLC/MS was used to identify the final degraded compounds.

TEM analysis of photocatalytic TiO2 thin films deposited on polymer substrates by low-temperature ICP-PECVD

Abstract TiO2 thin films were deposited on polymer substrates (polyethylene terephthalate and polystyrene) at low substrate temperature (

Reusable floating polymer nanocomposite photocatalyst for the efficient treatment of dye wastewaters under scaled‐up conditions in batch and recirculation modes

AbstractBACKGROUNDIn the last decade, research on floating photocatalysts has increased rapidly with polymer substrates being a popular choice. However, most of the published work is on very small volumes and there is very little work on scale‐up of such systems.RESULTSPolystyrene–titanium dioxide nanocomposite floating films were prepared using a facile solvent casting method and tested for the photocatalytic degradation of four different dyes under UV irradiation. The prepared film was characterised by Fourier‐transform infrared (FTIR), scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP‐OES) and profilometry. Scale‐up studies were done in batch mode under optimised conditions, and for the larger reactor volume, the effect of recirculation was studied. Complete decolourisation of the model dye (Remazol Turquoise Blue) was observed within 80 min in the scaled‐up batch process. In the recirculation mode, for a much larger volume of the dye solution, around 75% decolourisation in 6 h was observed. The reusability of the photocatalytic film was tested, and the results promise a minimum decolourisation efficiency of around 70%. Finally, total organic carbon (TOC) and liquid chromatography mass spectrometry (LC‐MS) analysis were used to assess the degradation of the dye. The maximum TOC reduction observed was around 25% possibly due to the complex nature of the dye used in this study. The intermediate products of degradation were identified, and a tentative mechanism is suggested.CONCLUSIONThis work demonstrates the recirculation aspects of the photocatalytic reactor under the scaled‐up conditions for a complex dye. The prepared film showed excellent stability with satisfactory wastewater decontamination under UV irradiation even after repeated use. © 2019 Society of Chemical Industry

CdS branched TiO2: Rods-on-rods nanoarrays for efficient photoelectrochemical (PEC) and self-bias photocatalytic (PC) hydrogen production

Rationally designing and constructing high-efficiency composite photocatalysts with advantaged structure play significant roles in efficient photoelectrochemical or photocatalytic solar energy conversion systems. In this work, contrasted to the typical CdS nanoparticles modified TiO2 nanomaterials, a novel rods-on-rods CdS branched TiO2 nanoarrays have been firstly synthesized by a simple in-situ growth strategy. The controllable surface-to-volume ratios of CdS nanorods, combining with their original intimate connection with TiO2 nanorods, not only enhance both the solar light scattering and absorption performance, but also effectively promote the separation and transportation of photogenerated charges. In addition, this structure ensures adequate exposure of CdS to the electrolyte, thus increasing the photooxidation reactive sites. In a typical photoelectrochemical water splitting system, the maximum photon-to-current conversion efficiency reaches 34% under 450 nm wavelength light irradiation, and the best applied bias photo to current conversion efficiency of the samples runs up to 1.5% under solar light irradiation. Interestingly, by using a ‘cocatalysts-separated-loading’ strategy, the novel CdS branched TiO2 nanoarrays films can be further employed as self-bias photocatalytic films, which also obtain an enhanced photocatalytic hydrogen production activity and stability.

Magnetic Field‐Assisted Control of Phase Composition and Texture in Photocatalytic Hematite Films

We report the influence of external magnetic fields applied parallel or perpendicular to the substrate during plasma chemical vapor deposition (PECVD) of hematite (α‐Fe2O3) nanostructures. Hematite films grown from iron precursors show pronounced changes in phase composition (pure hematite vs. coexistence of hematite and magnetite) and crystallographic textures depending upon whether PECVD is performed with or without the influence of external magnetic field. Static magnetic fields created by rod‐type (RTMs) or disk‐type magnets (DTMs) results in hematite films with anisotropic or equiaxed grains, respectively. Using RTMs, a superior photoelectrochemical (PEC) performance is obtained for hematite photoanodes synthesized under perpendicularly applied magnetic field (with respect to substrate), whereas parallel magnetic field results in the most efficient hematite photoanode in the case of DTM. The experimental data on microstructure and functional properties of hematite films show that application of magnetic fields has a significant effect on the crystallite size and texture with preferred growth and/or suppression of grains with specific texture in Fe2O3 films. Investigations on the water splitting properties of the hematite films in a photoelectrochemical reactor reveal that photocurrent values of hematite photoanodes are remarkably different for films deposited with (0.659 mA cm−2) or without (0.484 mA cm−2) external magnetic field.

High Defect Nanoscale ZnO Films with Polar Facets for Enhanced Photocatalytic Performance

The fabrication of highly efficient photocatalytic thin films has important consequences for self-cleaning, organic pollutant decomposition, and antimicrobial coatings for a variety of applications. Here, we developed a simple synthesis method to produce efficient, high-surface-area zinc oxide (ZnO) photocatalytic films using aerosol-assisted chemical vapor deposition. This approach used mixtures of methanol and acetic acid to promote preferential growth and exposure of polar facets, which favor photocatalytic activity. Interestingly, the initial enhanced efficiency of the films was correlated to structural defects, likely oxygen vacancies, as supported by photoluminescence spectroscopy results. Discussion over the influence of such defects on photocatalytic performance is described, and the need for strategies to develop high-surface-area materials containing stable defects is highlighted.

Effect of the deposition conditions on the properties of photocatalytic WO3 thin films prepared by mid-frequency magnetron sputtering

WO3 is a widely considered photocatalytic material for water purification. In this paper, nanocrystalline WO3 films were deposited on a glass slide by the mid-frequency reactive magnetron sputtering method. The aim is to determine the photocatalytic activities of the films, which are controlled by the process parameters (oxygen flow and substrate bias). The annealed films reveal a hexagonal structure and have some absorptivity in the visible region. The field emission scanning electron microscopy pattern shows that the films exhibit a uniform, smooth surface. The photocatalytic properties of the prepared films were evaluated by the photodecolorization of methylene blue. The films exhibit the best activity at an oxygen flow rate of 30 sccm and a substrate bias of −50 V. The reason is that this film can create more electron-hole pairs as a result of the greater absorption of visible light, which enhances the photocatalytic performance. Based on the results, a possible photocatalytic mechanism has been proposed.

Photocatalytic ozonation for a sustainable aquaculture: A long-term test in a seawater aquarium

A long-term test at a laboratory scale with a closed system (a coral reef aquarium) has been carried out to study the potentialities of photocatalytic ozonation and photocatalysis for the removal of noxious organic compounds in recirculating systems (aquaria and recirculating aquaculture systems) working with a minimum make up of new water. Attention has been focused not only on the depuration capabilities but also on possible negative phenomena, some of which could become apparent only at long times.After having tuned the system by setting appropriate operating conditions and procedures, positive results were obtained. In particular, it was observed that the alternation of photocatalytic ozonation with photocatalysis with definite cycle allowed to severely limit the presence of the organic compounds, which otherwise could accumulate in the system, and at the same time to control the formation of bromate, the ozonation side-product of main concern. In addition, the values of other parameters, which are important for water quality, remained at satisfactory values. It was also verified that the prepared photocatalytic films maintained a good photocatalytic activity even after several months of utilization in seawater.These results demonstrate that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of sustainable aquaculture.

Photocatalytic semiconductor thin films for hydrogen production and environmental applications

The semiconducting thin film materials are the main key elements in the fields of photonic, electronic and magnetic devices. The preparation of materials in the form of thin films allows easy incorporation into various through changing the properties of materials and reducing the size. The core benefits of thin film systems are cost reduction and efficiency of devices. They are widely used for the protection of surfaces, chemical resistance and to modify electrical and optical properties. The study on semiconducting thin films is rapidly growing due to their constructive applications in wireless communication, solar cells, semiconductor devices, integrated circuits, magneto-optic memories, light emitting diodes, multifunctional protective coatings, liquid crystal displays, and so on. This review explains about recent achievements in the photocatalytic nanostructured semiconducting thin films, their deposition, fabrication methodologies, controlling of film micro/nanostructures, physicochemical properties, photocatalytic mechanism and its photocatalytic applications in the fields of energy such as hydrogen generation, CO2 reduction to useful chemicals, and environmental remediation such as photodegradation of harmful bacteria and toxic chemicals.

Novel and versatile TiO2 thin films on PET for photocatalytic removal of contaminants of emerging concern from water

The current work presents new and versatile photocatalytic surfaces designed to remove contaminants of emerging concerns (CECs) from water. Photocatalytic thin films of titanium dioxide (TiO2) were deposited on a polyethylene terephthalate (PET) surface (PET-TiO2) and photosensitized by a natural and non-hazardous curcumin (turmeric). The TiO2 thin film was deposited in a single stage and solvent-free process, without thermal post treatment, using the high power impulse magnetron sputtering (HiPIMS) technique. The photocatalytic film was characterized by different techniques (SEM/EDS, STEM, AFM, UV–Vis spectroscopy, and wettability via water droplet contact angle). The photocatalytic activity was assessed by the degradation of two model CECs: the fungicide carbendazim (CBZ), used in different crops around the world (coffee, rice, fruits, etc.), and the anthropogenic pollution tracer caffeine (CAF). Removal of these model CECs of up to 39% were achieved under combined UV and visible irradiation under 7 h photocatalytic treatments. The degradation process was further studied by dissolved organic carbon analysis, with up to 80% removal, and acute ecotoxicity tests with Aliivibrio fischeri, indicating reduction of toxicity or non-change. The PET-TiO2 surfaces remained stable for 5 consecutive cycles of use, with similar kinetic rates. Finally, the species involved in photocatalytic reactions were investigated by the use of h+, HO and O2− trapping agents, both in the presence and absence of turmeric. The results indicated that the addition of the turmeric led to an increase in photogenerated O2− radicals due to a synergistic effect between the photocatalyst and photosensitizer. The results demonstrate the potential of the PET-TiO2 surfaces as a straightforward solution for the removal of CECs from waters, using a flexible, scalable, reusable and environmental friendly photocatalytic material.

The coherence between TiO2 nanoparticles and microfibrillated cellulose in thin film for enhanced dispersal and photodegradation of dye

Microfibrillated cellulose (MFC) was used to enhance the dispersal and photocatalytic properties of TiO2 nanoparticles. With the small amount of MFC (0.1 wt.% or 0.3 wt.%), TEM images showed that particle agglomeration was greatly minimized due to the coherence between TiO2 nanoparticles and MFC. The surface area and pore volume of TiO2 nanoparticles was enhanced as proven in N2 adsorption-desorption analysis. Thermogravimetric and Fourier transform infrared spectra further confirmed the presence of MFC in TiO2/MFC coating solution. Using commercial adhesive, TiO2 and TiO2/MFC were spray coated on polyvinyl chloride sheet. The photocatalytic thin films were examined using scanning electron microscope with Energy dispersive X-ray analysis. The presence of MFC was not only helpful to enhance particle dispersal but also supportive to increase the hydrophilicity of the thin film. In comparison to TiO2 coating, the films were capable to adsorb 50% more methylene blue in 90 min. TiO2/MFC coatings removed 90% of methylene blue dye in 90 min under UV irradiation.

Evaluation of photocatalytic thin film pretreatment on anaerobic degradability of exopolymer extracted biosolids for biofuel generation

This study reports the result of sodium citrate induced exopolymer extraction on the photocatalytic thin film (TiO2) pretreatment efficiency of waste activated sludge (WAS). TiO2 is immobilized through DC spluttering method followed by annealing process. The exopolymer removal of 94.2% by sodium citrate (0.05 g/g SS) promotes better disintegration. This TiO2 thin film efficiently extricate the intracellular components of exopolymer extracted sludge at 50 min increasing the solubilization to 19.33%. As a result, the exopolymer extracted sludge shows high methane generation (0.24 gCOD/gCOD) than the other (pretreated sludge without exopolymer removal – 0.12 gCOD/gCOD and raw sludge without treatment – 0.075 gCOD/gCOD). The methane generated in sodium citrate induced TiO2 thin film pretreated sludge is 398.99 kWh. In cost analysis, it gives net cost of −57.46 USD/ton of sludge. In addition, the proposed method also accounts 51.3% of solid reduction.

Biomimetic Polyimide-Supported Cuprous Oxide Photocatalytic Film with Tunable Hydrophobicity, Improved Thermal Stability, and Photocatalytic Activity toward CO2 Reduction

Flexible and thermally stable polyimide (PI) films containing a hierarchical surface structure were synthesized as substrates to support visible-light active cuprous oxide for photocatalytic reduction of carbon dioxide for the first time. With the nanocasting technique, the surface structure on the leaves of Xanthosoma sagittifolium was successfully duplicated on PI films. Followed by the ion-exchange process and adequate thermal treatment, cuprous oxide nanoparticles were successfully immobilized on the artificial PI leaves and exhibited the capability to photoreduce carbon dioxide into carbon monoxide under visible-light illumination. With the selection of biomimetic structures and adjustment of fabrication parameters, the hydrophobicity and optical absorption edge of the photocatalytic film were tunable. An increase in hydrophobicity improved the yield of carbon monoxide. The introduction of a hierarchical structure on the surface and cuprous oxide within the matrix dramatically enhanced the thermal st...

Enhanced photocatalytic activity of AgVO<SUB align="right">3/TiO<SUB align="right">2 nanorod array composite film under visible light irradiation

The novel AgVO3/TiO2 nanorod array composite film (NACF) has been prepared by the hydrothermal and subsequent successive ionic layer adsorption methods. The photocatalytic films were characterised by the scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and UV-vis diffuse reflectance spectra (UV-vis DRS). The SEM result showed that AgVO3/TiO2 NACF exhibited a well nanorod array structure, and some AgVO3 nanocrystals were deposited on the TiO2 nanorods. The novel AgVO3/TiO2 NACF showed the enhanced visible photocatalytic activity for degradation of methyl orange (MO) compared with the pure TiO2 nanorod array film. The deposition of AgVO3 nanocrystals on the TiO2 nanorod array led to the improved visible light absorption of the composite film due to the narrow bandgap of AgVO3 (less than 2.5 eV). The contact of AgVO3 and TiO2 resulted in the formation of semiconductor heterostructure, which led to the enhanced separation of photogenerated carriers. The improved visible absorption and efficient separation of photogenerated electron-hole pairs should result in the higher visible activity of composite film compared with pure TiO2 nanorod array film.

Facile fabrication of TiO 2 @TiO 2 transparent free‐standing film for photocatalysis

A transparent titanium dioxide (TiO 2 )@TiO 2 film with free-standing structure was synthesised by employing a cellulose paper as the template. By one-step hydrothermal method and subsequent thermal annealing, the fibre of cellulose paper was changed into porous TiO 2 core layer. The flower-like micro/nanostructure TiO 2 particle layer was intimately distributed on the porous TiO 2 core layer. The average diameter of the TiO 2 @TiO 2 fibre for the film was 11 μm. The size of spherical granular TiO 2 on the fibre surface was around 330 ± 130 nm. It was noted that the microtopography of fibre surface could be adjusted by tuning the hydrothermal temperature. The scanning electron microscopy and N 2 adsorption-desorption measurement results indicated that the prepared film possessed a large mass of mesopores and macropores. On the basis of the special microstructure, the TiO 2 @TiO 2 film exhibited high photocatalytic activity for methylene blue under ultraviolet irradiation. This work might provide a new insight for preparation of transparent photocatalytic film toward water purification.

Stability of the Cu2ZnSnS4/TiO2 photocatalytic thin films active under visible light irradiation

The study investigates the long term stability and photocatalytic activity (up to 72 h) of the Cu2ZnSnS4/TiO2 thin film heterostructures, under simulated solar radiation, at low irradiance values (34 W/m2), using phenol and imidacloprid (c = 10 ppm) as testing pollutants. High removal efficiencies correspond to both phenol (73%) and imidacloprid (57%) after 72 h of irradiation, while mineralization occurs slower, with efficiencies up to 42% for phenol, and less than 10% for imidacloprid, in agreement with the pollutant chemical structure.The stability of the photocatalysts in the aqueous pollutant solutions is investigated using VIS transmittance spectra, scanning electron microscopy, atomic force microscopy while photocatalyst leaching was evaluated based on surface composition analysis and atomic absorption spectroscopy. The processes affecting the photocatalyst surface and composition were discussed and the results were correlated with TiO2 layer morphology and porosity and pollutants' structure; promising results are outlined as low variation in the layers transmittance (after 72 h of testing: ΔT600 < 15% for imidacloprid, ΔT600 < 30% for phenol).The results recommend the use of Cu2ZnSnS4/TiO2 thin film photocatalyst for large-scale applications, involving organic pollutants removal from wastewaters, even at very low concentrations.

Bi2O3/TiO2 photocatalytic film coated on floated glass balls for efficient removal of organic pollutant

A novel photocatalytic reactor was designed for the photo-degradation of organic pollutants with floated glass balls on the solution surface, which were constantly rotated by the air pumping and coated with Bi2O3/TiO2 film. The uniform and stable Bi2O3/TiO2 film was prepared by the facile sol-gel method at the optimal conditions of Bi Bi2O3 content (1.0 mol%) and the three coating times with the film thickness of 210 nm. It was uniformly distributed and stably combined with the surface of the glass ball. Modification of Bi2O3 significantly improved the visible light absorption of TiO2 film and inhibited the photo-induced charges, promoting the photo-degradation activity. More importantly, the air pumping at the bottom of the reactor impelled the constant rotation of floated glass balls. It could realize the uniform aqueous membrane on the catalyst film to improve the efficient contact between catalyst and organics and to utilize the irradiation light efficiently, inhibiting the light shield effect of dyeing wastewater and facilitating the photo-degradation. Moreover, the Bi2O3/TiO2 photocatalytic film in this photocatalytic reactor exhibited high durability and prevented the leakage of catalyst, providing a potential for the practical applications in the future.

Preparation of photocatalytic thin films with composition dependent wetting properties and self-healing ability

This paper presents the preparation of a multifunctional coating with triplet photoreactive, superhydrophobic and intelligent self-healing properties. Beside the structural and morphological behaviors of the hybrid thin films consist of fluoropolymer matrix and Ag-TiO2 photocatalyst particles, the wetting properties were also studied by static (Θ) and dynamic water contact angle measurements. The photoactivity of layers was evidenced both at solid/gas (S/G) and solid liquid (S/L) interfaces. The surface roughness (Rq = 3.7 ± 0.9 μm to 15.2 ± 1.2 μm) and thus the wetting properties and apparent surface free energy values (γstot) of the layers were adjustable from superhydrophilic (Θ = 0°; γstot = 70.2 mJ m−2) to superhydrophobic properties (Θ = 150.9°; γstot = 13.1 mJ m−2). At S/G interface the photoactivity of the layers was increased with the Ag-TiO2 photocatalyst content, however, at S/L interface the photocatalytic properties were tailored by the wetting of the films: 90% of the apolar SUDAN IV dye was photodegraded, while the aqueous Methylene Blue dye was not decomposed due to the inadequate surface adsorption. Moreover, it was also presented that the ambient moister catalysed hydrolysis/self-condensation reaction of the hydrophobic dodecyltrichlorosilane (DDSiCl3) molecules resulted self-assembled micro-protrusions on the surface of low energy photoreactive film and this mechanism resulted self-healing superhydrophobic surfaces with photocatalytic properties.

Production and testing of novel photocatalytic TiO2 surface-exposed nanoparticle (TiO2-SEN) thin plastic films

Thin, flexible, surface-active, polystyrene-based, optically transparent films, embedded with a coating of commercially sourced titanium dioxide nanoparticles (Evonik P25), are made by coupling protonated TiO2 particles with an anionic phase transfer agent (tetraphenylborate), to create an ion-paired species that is drawn to a water/dichloromethane (DCM) interface to form a monolayer. The latter is subsequently embedded in a thin polystyrene (PS) film, typically 2.5 μm thick, by allowing the DCM to evaporate. The resulting clear TiO2 Surface-Exposed Nanoparticle (TiO2-SEN) thin plastic films are characterised using scanning electron microscopy (SEM) and found to have 25.3 ± 5.4 nm TiO2 nanoparticles exposed to the air on one side and PS on the other. The photocatalytic activity of these films is demonstrated using a number of different tests including: the photo-oxidation of 4-chlorophenol (4-CP) and methylene blue (MB) and the photoreduction of resazurin (Rz) and MB. In most of these tests the photoactivity of the film is more than double compared to that of a commercial photocatalytic film, Activ™.

Transparent Photocatalytic Thin Films on Flexible Polymer Substrates

Self-cleaning and/or photocatalytic films on polymer substrates have found numerous applications during the past decades. However, the common demand for high-temperature post synthesis treatment limits the application to temperature resistant substrates only. Herein, we prepared self-cleaning photocatalytic films on four thermosensitive polymeric substrates: polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), and acryl coated polyester (PES) fabric (D2) with poly(vinylidene fluoride) (PVDF) containing lacquer (D1). TiO2 was prepared via a low-temperature sol-gel process using titanium(IV) isopropoxide and zirconium(IV) butoxide as precursors with various loading levels of Zr; 0, 5, 10, and 20 mol.%, and deposited on the substrates by using a SiO2 binder in form of thin films (ca. 200 nm thick) via dip-coating. The films were characterized by SEM, hardness test, UV-Vis, photothermal beam deflection spectroscopy, and IR spectroscopy, while photocatalytic activity was measured by the fluorescence-based method of the terephthalic acid probe and wetting by contact angle measurements. Films containing 10 mol.% of Zr showed the best compromise regarding photocatalytic activity and mechanical stability while from substrates point of view PVC performed the best, followed by PMMA, D1, and D2. The beneficial role of SiO2 binder was not only guaranteeing excellent mechanical stability, but also to prevent the D1 polymer from deterioration; the latter was found to be labile to long-term solar-light exposure due to degradation of the top PVDF layer.