Film Photocatalyst Research Articles

Polyethylene glycol (PEG)-modified Ag/Ag2O/Ag3PO4/Bi2WO6 photocatalyst film with enhanced efficiency and stability under solar light

Bi2WO6 photocatalyst possesses great photocatalytic properties, modification with Ag, Ag2O, and Ag3PO4 further improve its photocatalytic activity. Photocatalyst utilized as suspended powders in wastewater treatment imposes restrictions for practical application. Therefore, the design and fabrication of photocatalyst film with high efficiency and stability are crucial for practical application. In this study, polyethylene glycol (PEG) modified AP-BWO (A: Ag, Ag2O; P: Ag3PO4; BWO: Bi2WO6) photocatalyst film coated on glass substrate was firstly synthesized with excellent photocatalytic activity and stability. Bi2WO6based films were modified with different PEG molecular weight, dosage and coating layers, followed by characteristic analysis (SEM, TEM, XPS, UVvis, PL, and photocurrent density) and photodegradation test. Photodegradation showed that 2-layered of 12 g L−1 PEG2000 modified AP-BWO film exhibited the highest photocatalytic activity. XPS and TEM indicated that PEG2000-AP-BWO film was fabricated successfully. SEM and UV–vis denoted the photocatalyst film showed small particle size and strong visible-light absorption. Furthermore, PL and photocurrent density confirmed its low recombination and fast charge separation of electronhole pairs. The photocatalytic films showed high activity and stability in both 10-cycle repeatability experiments and tandem-type photocatalytic recycle system. Therefore, PEG2000-AP-BWO film with enhanced photocatalytic performance and stability was a promising alternative for wastewater treatment.

The Role Played by Graphene Oxide in the Photodeposition and Surface‐Enhanced Raman Scattering Activity of Plasmonic Ag Nanoparticle Substrates

Layer‐by‐layer photocatalyst films made of TiO2 nanoparticles (TiO2NP) assembled with both poly(sodium 4‐styrenesulfonate) (PSS) and graphene oxide (GO) are used for the photodeposition of plasmonic Ag nanoparticles (AgNPs) and subsequently used in surface‐enhanced Raman scattering (SERS). Both photocatalyst films, TiO2NP/PSS and TiO2NP/GO, are capable of driving the formation of AgNP when they are wetted with a drop of AgNO3 diluted solution and submitted to UV irradiation (254 nm). The photodeposition of AgNP, as monitored by UV–vis spectroscopy, follows a first‐order kinetics process in both films and is slightly faster in the TiO2NP/PSS. In addition, scanning electron microscopy reveals that in the TiO2NP/PSS film, the photodeposited AgNPs are larger and isolated, whereas in the TiO2NP/GO film, they are smaller and highly interconnected. The SERS activity of the substrates is evaluated with rhodamine B. When samples are excited in resonance with rhodamine B absorption (514 nm), GO‐based substrates provide the largest enhancement because GO is able to quench the rhodamine B fluorescence, something that PSS is unable to do. Out of this condition (633 nm), the plasmonic effect of AgNP alone prevails regardless of the presence of GO.

Photocatalytic inactivation of marine microorganisms by a Ag/AgCl/ZnWO4 film under UV light

ZnWO4 was prepared by a hydrothermal method, and a Ag/AgCl/ZnWO4 composite photocatalyst with a high photogenerated electron–hole pair separation efficiency was prepared by ultrasonic-assisted precipitation-deposition photoreduction. The inactivation of microorganisms in seawater was carried out using ZnWO4 and Ag/AgCl/ZnWO4 films under ultraviolet light irradiation at 254 nm. The results showed that all of the composite samples had significantly enhanced activity compared to the original samples. After being loaded with the Ag/AgCl system, the inactivation time of the sample film with a loading of 40% for chlorella in seawater was 20 min, which was 42% (35 min) shorter than that of the ZnWO4 sample. In conclusion, Ag/AgCl improves the separation efficiency of photogenerated electron–hole pairs and contributes to the improvement in the photocatalytic performance. This is of great value for the preparation of photocatalyst films.

Efficient photocatalytic elimination of Temephos pesticide using ZnO nanoflowers

Temephos (Tem) is a widely used pesticide to control mosquito’s proliferation in tropical countries. This pesticide is put in stagnant water bodies where mosquitoes reproduce, killing larvae effectively. Recently, Tem has been identified as a DNA damaging agent; despite, people use it unmoderated in water reservoirs for personal consumption. Thus, Tem has become a hazard for human health and needs urgent attention. In order to reduce the risk of toxicity in those water sources we propose the use of nanostructured zinc oxide (ZnO) photocatalyst films to degrade this toxic compound. ZnO films with nanoflower morphology were prepared using a simple spray pyrolysis method. The band gap was 3.2 eV but a large number of natural defects present in the films allowed the absorption of visible light. The photocatalytic degradation ability of ZnO nanoflowers removed the toxic Tem under the illumination of a solar simulator. The UV–vis spectroscopy and High-Performance Liquid Chromatography analysis of Tem at regular intervals during photocatalysis confirmed the degradation of Tem, along with its transformation products or metabolites from water, reducing seven times the Tem half-life time in water. Total organic carbon measurements also indicated the mineralization of the compound.

Graphene Quantum Dots Doped PVDF(TBT)/PVP(TBT) Fiber Film with Enhanced Photocatalytic Performance

We report the fabrication of polyvinylidene fluoride (tetrabutyl titanate)/polyvinyl pyrrolidone ((tetrabutyl titanate))-graphene quantum dots [PVDF(TBT)/PVP(TBT)-GQDs] film photocatalyst with enhanced photocatalytic performance. The polyvinylidene fluoride (tetrabutyl titanate)/polyvinyl pyrrolidone ((tetrabutyl titanate)) [PVDF(TBT)/PVP(TBT)] film was first prepared with a dual-electrospinning method and then followed by attaching graphene quantum dots (GQDs) to the surface of the composite film through a hydrothermal method. Later, part of the PVP in the composite film was dissolved by a hydrothermal method. As a result, a PVDF(TBT)/PVP(TBT)-GQDs film photocatalyst with a larger specific surface area was achieved. The photocatalytic degradation behavior of the PVDF(TBT)/PVP(TBT)-GQDs film photocatalyst was examined by using Rhodamine B as the target contaminant. The PVDF(TBT)/PVP(TBT)-GQDs photocatalyst showed a higher photocatalytic efficiency than PVDF(TBT)-H2O, PVDF(TBT)/PVP(TBT)-H2O, and PVDF(TBT)-GQDs, respectively. The enhanced photocatalytic efficiency can be attributed to the broader optical response range of the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst, which makes it useful as an effective photocatalyst under white light irradiation.

Synthesis and analysis of metallic Zn phase rich ZnO oxide films for the photocatalytic water treatment technologies

In this study ZnO based photocatalyst films were deposited using magnetron sputtering with in-situ control of the physical vapor phase composition. Precise monitoring and control of Zinc, Argon and oxygen content in plasma phase allowed to identify small range of parameters which led to the formation of samples in the intermediate zone between metallic Zn and stoichiometric ZnO. Photocatalytic tests have demonstrated that in such samples metallic zinc up to some extent improves the photocatalytic efficiency of ZnO oxide. The relationship between magnetron sputtering process parameters and film properties are provided and their influence to the photocatalytic activity of the films is discussed.

Immobilization of AgCl@TiO2 on the woven wire mesh: Sunlight-responsive environmental photocatalyst with high durability

The immobilized AgCl@TiO2 photocatalytic thin films were fabricated via electrophoretic deposition method. Affordability, scalability, and high chemical stability are some valuable characteristics making woven stainless steel wire mesh a suitable substrate for fabrication of photocatalyst film. The photocatalytic degradation efficiency of the thin film was investigated by removing hard-degradable methamphetamine under natural solar light. The AgCl@TiO2 photocatalyst with AgCl content of about 5% showed the most photocatalytic degradation efficiency. Using Mott-Schottky plots, the flat band potential of prepared photocatalysts was estimated. The flat band potential showed that the conduction band of AgCl@TiO2 is a better candidate for production of superoxide radicals than TiO2. A film thickness of 1629 nm yields optimal photodegradation efficiency. A series of ten sequential cycles for photodegradation of methamphetamine was conducted using thin film which caused neither significant destruction on photocatalytic substrate nor any considerable reduction in efficiency whatsoever. The AgCl@TiO2 thin film-induced mineralization of methamphetamine was reported to be approximately around 91 percent. The photoelectrochemical performance of TiO2 and AgCl@TiO2 thin film was evaluated by LSV technique under solar light and results show thatafter incorporation of AgCl, the photocurrent density corresponding to the oxygen evolution reaction significantly increased to 1.8 mA cm−2 at 1.23 V vs RHE.

Large-scale fabrication of upconversion/quantum dots photocatalyst film by a facile spin-coating method

Facile and large-scale preparation of upconversion photocatalyst films is promising for the degradation of volatile organic compounds (VOCs), major component of the landfill gas stench. Herein, a spin-assisted layer-by-layer coating method is explored to fabricate the upconversion photocatalyst film of polyethylene terephthalate (PET)/Tm/Yb-doped NaYF4 (TYN)/P25/(CdSe/CdS) QDs (PET/TYN/P25/QDs). The near-infrared light energy passes through the top QDs and P25 layers to excite TYN, and the strong upconversion emissions of UV (290, 346, and 362 ​nm) and visible (452 and 476 ​nm) light are produced and absorbed by P25/QDs for photocatalysis. In the photocatalytic degradation of gaseous toluene, the removal efficiency over the PET/TYN/P25/QDs film reaches 83% after 1 ​h of simulated sunlight irradiation, which is much higher than that (40%) of the PET/TYN/P25 film. This better photocatalytic activity is ascribed to the large absorption edge of the CdSe/CdS QDs and the efficient electron-hole pair separation in the QDs-P25 heterostructure.

Photocatalytic degradation kinetics of Orange G dye over ZnO and Ag/ZnO thin film catalysts

The degradation of water pollutants with photocatalysts is one of the most studied subjects in the past 20 years. Although considerable studies have been completed in this field, kinetic model studies are still a major inadequacy. In this study, ZnO and Ag/ZnO thin film photocatalysts were synthesized and SEM-EDS, XRD and chronoamperometric measurements were used the characterization of photocatalysts. The network kinetic model was applied the photocatalytic degradation of Orange G using ZnO and Ag/ZnO thin film photocatalysts. The photocatalytic degradation of Orange G was investigated under the different reaction medium (initial dye concentrations, temperature, light intensity). It was found that the network kinetic model is the most appropriate model for the degradation of Orange G dye on the ZnO and Ag/ZnO thin film photocatalysts. The calculated adsorption equilibrium (KB) constant and activation energy of ZnO thin film photocatalyst are 0.0191 and 21.76 kj/mol, respectively. Additionally, the calculated values for Ag/ZnO thin film photocatalyst are 0.035 and 18.32 kj/mol. The general rate equations were determined for each photocatalysts.

Surface-Polarity-Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays.

Photocatalytic overall water splitting has been recognized as a promising approach to convert solar energy into hydrogen. However, most of the photocatalysts suffer from low efficiencies mainly because of poor charge separation. Herein, taking a model semiconductor gallium nitride (GaN) as an example, we uncovered that photogenerated electrons and holes can be spatially separated to the nonpolar and polar surfaces of GaN nanorod arrays, which is presumably ascribed to the different surface band bending induced by the surface polarity. The photogenerated charge separation efficiency of GaN can be enhanced significantly from about 8 % to more than 80 % via co-exposing polar and nonpolar surfaces. Furthermore, spatially assembling reduction and oxidation cocatalysts on the nonpolar and polar surfaces remarkably boosts photocatalytic overall water splitting, with the quantum efficiency increased from 0.9 % for the film photocatalyst to 6.9 % for the nanorod arrays photocatalyst.

Bifunctional g-C3N4/WO3 Thin Films for Photocatalytic Water Purification

A bifunctional thin film photocatalyst consisting of graphitic carbon nitride on tungsten trioxide (g-C3N4/WO3) is introduced for the improvement of photocatalytic activity concerning hexavalent chromium reduction and methylene blue dye removal in water, compared to the bare, widely used WO3 semiconductor. A bilayered structure was formed, which is important for the enhancement of the charge carriers’ separation. The characterization of morphological, structural, optoelectronic, and vibrational properties of the photocatalysts permitted a better understanding of their photocatalytic activity for both dye degradation and Cr+6 elimination in water and the analysis of the photocatalytic kinetics permitted the determination of the corresponding pseudo-first-order reaction constants (k). Trapping experiments performed under UV illumination revealed that the main active species for the photocatalytic reduction of Cr+6 ions are electrons, whereas in the case of methylene blue azo-dye (MB) oxidation, the activation of the corresponding photocatalytic degradation comes via both holes and superoxide radicals.

TiO2-coated alveolar clay foam as a photocatalyst for water detoxification

3D-clay foam support having alveolar open-cell structure of polyurethane sponge was produced by shape memory synthesis to enhance exposed surface area of TiO2 photocatalyst film for both light harvesting and liquid contact. The TiO2-coated alveolar clay foam photocatalysts were characterized in terms of compressive strength, mineral phase, light transmission ability and TiO2 film properties. The photocatalytic performances were evaluated as material and removal efficiencies of CHP solution under UV-A irradiation and TOC analysis. The material efficiency results of the photocatalysts coated with TiO2 films, synthesized by sol–gel method at various pHs, pointed out that the TiO2 film of pH 2 gave the highest CHP removal. It was also selected to repetitively operate in a recycle mode, and 94–96% of fresh CHP removal was retained in all the four runs.

Fullerene polymer film as a highly efficient photocatalyst for selective solar fuel production from CO2

ABSTRACTC60‐based polymeric systems have been constantly anticipated for sustainable solar energy conversion. Reported, herein is a C60 polymer film as visible light active photocatalyst for efficient and selective reduction of CO2 for the first time. The C60 polymer photocatalyst is synthesized via covalent coupling of C60 monomer units consisting of tetra substituted C60‐pyrene conjugates through spacer groups. The synthesized C60 polymer photocatalyst possesses an extended network of well‐defined repeating monomer units with good stability and visible light‐induced photocatalytic activity. The enhanced visible light harvesting ability of C60 polymer photocatalyst reasonably yields it with higher catalytic ability than its monomer unit. The C60 polymer film photocatalyst upon coupling with the biocatalyst carries out highly selective visible light driven reduction of CO2 to HCOOH (239.46 μmol). The tandem way of incorporating C60 into visible light active polymeric films for continuous use may be highly rewarding for their extended photocatalytic activity for solar fuel production from CO2. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48536.

Recent Advances in TiO2 Films Prepared by Sol-Gel Methods for Photocatalytic Degradation of Organic Pollutants and Antibacterial Activities

Photocatalysis has recently emerged as an advanced, green, and eco-friendly process for the treatment of wastewater and air, and antimicrobial disinfection applications. In this context, TiO2 nanostructures have been shown to be the prominent photocatalyst candidates due to their low cost, non-toxicity, and ease of fabrication. This review highlights the investigation and development of TiO2 photocatalyst film by sol-gel method with special emphasis on the photodecolorization of synthetic dyes and antibacterial activities. Furthermore, various synthesis methods for the preparation of TiO2 films and their advantages, as well as limitations, are summarized. Finally, recent advances in TiO2 films by sol-gel method for dye degradation and antibacterial activities, challenges, and future perspective are discussed.

Highly enhanced photoactivity of BiFeO3/Bi2WO6 composite films under visible light irradiation

In this research, the BiFeO3/Bi2WO6 composite photocatalysts were prepared via co-precipitation and hydrothermal methods. The as-prepared photocatalyst powders were coated on a glass substrate by a doctor blade method and calcined at a temperature of 500 °C for 1 h to produce films. Intimate contact between BiFeO3 and Bi2WO6 in the composite material, along with sufficient band edge energy offset, facilitates electron transfer from photoexcited BiFeO3 to Bi2WO6. This promotes charge recombination and thereby increasing the probability of reactive radical species generation which can degrade organic materials in the wastewater. Methyl orange (MO) was used as a model dye for testing the photocatalytic activity of all photocatalyst films under visible light irradiation. The obtained results show that the 0.6BiFeO3/0.4Bi2WO6 exhibited the best photodegradation efficiency, as compared to the other samples.

Visible light response ZnO–C3N4 thin film photocatalyst

Nanoflower-like ZnO–C3N4 thin film with a porous net structure was successfully synthesized by a simple chemical corrosion method. The prepared ZnO–C3N4 thin films presented remarkable photocatalytic activities for the degradation of methyl orange under visible light irradiation, and more than 90% methyl orange was removed from water by ZnO–C3N4 composite. Meanwhile, the ZnO–C3N4 composite presented an enhanced photocatalytic stability. The loading content of C3N4 had a great effect on the photocatalytic performance. Moreover, the photocatalytic activities were higher in acidic media than those in alkaline conditions. The adsorption of methyl orange was enhanced, and the recombination of photogenerated electrons and holes was suppressed with a suitable content of C3N4. However, too much loading content of C3N4 resulted in a poor dispersion of C3N4 as the aggregated C3N4 can behave as recombination centers. In addition, the prepared ZnO–C3N4 thin film can be used for the water splitting in water–methanol system under simulated solar light irradiation.

Immobilization of TiO2 into a poly methyl methacrylate (PMMA) as hybrid film for photocatalytic degradation of methylene blue

Abstract In this work, a simple and effective approach to prepare a poly methyl methacrylate – TiO2 (TiO2/PMMA) film photocatalyst, by cheap and low coast technique was presented. The characterization of the film by XRD, FTIR and Transmittance spectroscopy; confirmed that TiO2 has been well deposited on the surface of the polymer. The film prepared was subsequently used in photodegradation of Methylene Blue (MB) under artificial UV irradiation and showed a good prospect for the immobilization of TiO2 intended for the photodegradation of pollutants generally present in waters.

Tolerance to electron beams of TiO2 film photocatalyst

In orbit, contamination outgassed from spacecraft materials has been reported to degrade optical systems such as CCD cameras, lenses, mirrors, and optical filters mounted on a spacecraft. We focus on TiO2 photocatalyst to solve this contamination problem. TiO2 has the potential to decompose contaminants and suppress the deterioration of optical systems in orbit. However, the resistance of TiO2 itself to electrically charged particles, i.e., electrons in space, has not been clarified. The TiO2 films were irradiated with an electron beam (EB) with an energy of <480 eV in a vacuum. The irradiation dose was about 2.4 MGy. Chemical properties, surface morphology, and photocatalytic activity were compared before and after EB irradiation. Almost basic properties except surface roughness were unchanged, and the change of surface roughness was very small. These results indicate that TiO2 has sufficient resistance to an EB.

Dye degradation studies using immobilized pristine and waste polystyrene-TiO2/rGO/g-C3N4 nanocomposite photocatalytic film in a novel airlift reactor under solar light

Complex dyes are not completely removed in most wastewater treatment plants and thus released into nearby waterbodies posing problems to aquatic life and humans. In this study, a chemically synthesized nanocomposite photocatalyst containing TiO2, rGO and g-C3N4 immobilized in a polystyrene film is evaluated for the degradation of the Cu-phthalocyanine complex dye (Remazol Turquoise Blue, RTB) in a multiphase airlift reactor under sunlight. Both pristine and waste polystyrene were used in the synthesis of the film. The characterisation of the powder photocatalyst composite as well as the immobilized photocatalyst film is performed using particle size analyzer, SEM-EDX, BET, XRD, XPS, FTIR, and ICP-OES. The optimization of various parameters affecting the photocatalytic decolourization such as the g-C3N4 quantity in the composite catalyst, catalyst loading, the initial concentration of dye, use of waste polystyrene and catalyst reuse has been studied thoroughly. The photocatalytic treatment of RTB dye under optimum conditions for 90 min shows that the decolourization (60%) and degradation (51.43%) as measured by TOC analysis are quite similar. The possible breakdown compounds from the parent molecule after the photocatalytic operation are identified by HPLC-MS. In conclusion, the immobilized nano-composite photocatalyst incorporated into a multiphase airlift reactor, is a very promising system to improve the water quality by TOC reduction, before discharge to nearby natural water sources.

Development of an advanced hybrid process coupling TiO2 photocatalysis and zeolite-based adsorption for water and wastewater treatment

We present an advanced hybrid process coupling a fixed-bed photocatalysis reactor with the TiO2 photo-catalyst film coated on microstructured α-Al2O3 hollow fibers (AlHF) under UV exposure, with a second fixed-bed reactor where the zeolite-based adsorbent is fixed onto AlHF support for water and wastewater treatment. The physicochemical properties of both coated films were investigated by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). The sequential activity of the dual fixed bed reactor was overall evaluated by examining the degradation of 20 ppm Methylene Blue (MB), 1 ppm Iron and 0.04 ppm Arsenic solution as a general model of a complex aqueous solution containing not only an organic pollutant but also heavy metal and toxic cations. The results show that the proposed hybrid process by coupling two processes together could remove MB, Fe (II), and As (III) effectively, and the removal rates reached nearly 90%, 30%, and 70%, respectively, in 1 hour. These excellent results using the UV-TiO2/zeolite-based adsorbent combined process could be attributed to a synergistic effect between photocatalysis and adsorption process.