Film Photocatalyst Research Articles

Effect of substrate conductivity on charge transfer and CO2 photoreduction in water vapor over silica-modified TiO2 films

Photocatalytic CO2 reduction is gaining popularity due to its ability to reduce accumulated CO2 in the atmosphere using a green approach. On a variety of substrates, the development of practical photocatalyst films has been attempted; however, the effect of the substrate on the charge transfer and catalytic activity has received less attention in the research. Herein, the effect of three different substrates including titanium (Ti), indium tin oxide coated on polyethylene terephthalate (ITO-PET), and PET on the charge transfer and activity in the photocatalytic CO2 reduction of two noble-metal free catalysts were studied by density functional theory calculation (DFT), as well as optical and photo-electrochemical analyses. We showed that the transfer of charge carriers between the substrate and the overlying catalyst varies significantly between substrates and has a substantial effect on the photocatalytic activity in the CO2 reduction reaction. This work presents a practical and straightforward approach to enhancing the activity of the photocatalytic films for the CO2 reduction in the water vapor.

Novel nanocomposite thin films for efficient degradation of Rhodamine B and Rhodamine 6G under visible light irradiation: Reaction Mechanism and Pathway studies

The present investigation aims to synthesize the novel nanocomposite thin film and utilize the material to remove emerging dyes efficiently (i.e., Rhodamine B (R-B) and Rhodamine 6G (R-6G)), in an aqueous solution using LED visible light and UV-A light. A facile synthetic route was adopted to obtain the TiO<sub>2</sub>-supported bentonite and <i>in situ</i> decorated with Au nanoparticles (NPs) thin film. The advanced analytical techniques characterizes the materials. The laboratory scale reactor was utilized for efficient degradation of R-B and R-6G using thin film catalysts. The percentage removal of R-B was 54.13% (visible light) and 76.26% (UV-A light) and the R-6G, was removed 60.37% (visible light) and 84.68% (UV-A light) at the initial pollutant concentration of 0.5 mg/L and at pH 6.0 using the thin film photocatalyst. The parametric studies demonstrated the insights of degradation mechanisms in photocatalytic operations. A significant mineralization of these dyes is achieved, and the repeated use in reactor operations indicated the catalysts

Investigation on ZnO nanorod array based ZnO/SnSe and ZnO/CdSe thin film heterostructures for photocatalytic degradation of methylene blue

ZnO/SnSe and ZnO/CdSe thin film photocatalysts were prepared by two steps via hydrothermal and thermal evaporation method for the photocatalytic degradation of methylene Blue (MB). UV/Vis spectrometer, XRD, SEM, EDX and PL were used to study the structural,morphological and optical characteristics of the deposited thin films. ZnO nanorods, ZnO/SnSe and ZnO/CdSe heterostructures were tested for the photocatalytic degradation of MB. Among these ZnO/SnSe heterostructure yielded a better performance as a photocatalyst. With the ZnO/SnSe thin film photocatalyst owing to its high charge separation efficiency, the best photocatalytic efficiency of 88% was attained in 150 min. This study confirms an improved photocatalytic efficiency of, ZnO/SnSe and ZnO/CdSe thin film heterostructures compared to ZnO nanorod arrays.

Quantitative assessment and optimization of bi-functional membrane for remediation of Cr(VI) from wastewater

This paper explores the innovative approach of using a green route synthesized cost-effective bi-functional to eliminate toxic hexavalent chromium commonly found in tannery wastewater by using an integrated application of membrane and photocatalyst. Contaminated wastewater is firstly passed through bi-functional ultrafiltration membranes to retain hexavalent chromium and further reducing the toxicity of rejected water having high concentrations of Cr(VI) by photocatalytic reduction into Cr(III) in the presence of sunlight using the same membrane as photocatalyst film. Conditions governing the separation process such as solution pH, nanoparticle loading in polymer matrix, and concentration of Cr(VI) have been optimized to maximize the % rejection and photocatalytic reduction to Cr(III). The purpose of this work was to optimize the process condition through the use of the response surface method (RSM) that governs the process. RSM analysis concludes that excellent rejection of 91.58% and reduction of 87.02% is possible at the predicted pH (5.55), particle loading (2.14%) and Cr(VI) concentration (25 mg/L).

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Ag-decorated CuO NW@TiO2 heterojunction thin film for improved visible light photocatalysis

Herein, Ag-decorated CuO@TiO2 (CuO@TiO2-Ag) semiconductor heterojunctions are prepared using a porous CuO nanowire (NW) matrix for visible light photocatalysis applications. The CuO NW matrix is synthesized by wet-oxidation-based growth on a commercial Cu plate. Conformal coating of TiO2 on the CuO NW surfaces is successively achieved by atomic layer deposition, following which Ag nanoparticles (NPs) are deposited to synthesize a Ag-decorated CuO@TiO2 photocatalyst film. Microstructural and chemical analyses reveal uniform synthesis of a CuO@TiO2 heterojunction as well as a binding energy shift at the interface to form balanced Fermi energy, respectively. The performance of CuO@TiO2-Ag as a visible-light photocatalyst is evaluated under 20-W low-power visible-light LED illumination for the photodegradation of methylene blue. In addition, the effects of the TiO2 layer and the Ag NPs on the decomposition efficiency are investigated. To control the thickness of TiO2 and the dosage of Ag NPs, the photodegradation of CuO@TiO2-Ag is optimized at a rate of 0.0133 min−1, which is approximately 3 and 2.5 times higher than those of a bare CuO@TiO2 heterojunction and Ag-deposited CuO, respectively. The high decomposition efficiency achieved in this study results from the combined effects of the conformal core–shell heterojunction formed by atomic layer deposition and the well-distributed Ag NPs.

Ultrafast charge-transfer at interfaces between 2D graphitic carbon nitride thin film and carbon fiber towards enhanced photocatalytic hydrogen evolution

Homogeneous deposition of graphitic carbon nitride (g-C3N4) onto substrates on a large scale is of great interest in recyclable photocatalysis. However, g-C3N4 films prepared via conventional thermal condensation are thick and have problem of bad interface contacts with substrate, resulting in a poor photocatalytic performance. Herein, a thermal vapor condensation approach is developed for the growth of homogeneous g-C3N4 thin film on large area carbon fiber cloths (CFC). CFC serves as the template to guide g-C3N4 growth, resulting in a conformal thin overlayer of g-C3N4 on CFC surface. Moreover, a robust interaction between g-C3N4 and carbon fibers is achieved. A close stacking of g-C3N4 interlayers coupled with an efficient electron-withdrawing ability of carbon fiber expedites charge transfer and suppresses charge recombination. Consequently, the film exhibits an enhanced photocatalytic H2 evolution compared with g-C3N4 powder. A solid–gas bi-phase photocatalytic system is also constructed for manifesting remarkable superiority in gas evolution than solid–gas-liquid tri-phase system. Moreover, the sample is highly durable and recyclable, ensuring a robust, economical and environmentally friendly photocatalyst films.

Laser Ablation Nanoarchitectonics of Au-Cu Alloys Deposited on TiO2 Photocatalyst Films for Switchable Hydrogen Evolution from Formic Acid Dehydrogenation.

The regulation of H2 evolution from formic acid dehydrogenation using recyclable photocatalyst films is an essential approach for on-demand H2 production. We have successfully generated Au–Cu nanoalloys using a laser ablation method and deposited them on TiO2 photocatalyst films (AuxCu100–x/TiO2). The Au–Cu/TiO2 films were employed as photocatalysts for H2 production from formic acid dehydrogenation under light-emitting diode (LED) irradiation (365 nm). The highest H2 evolution rate for Au20Cu80/TiO2 is archived to 62,500 μmol h–1 g–1 per photocatalyst weight. The remarkable performance of Au20Cu80/TiO2 may account for the formation of Au-rich surfaces and the effect of Au alloying that enables Cu to sustain the metallic form on its surface. The metallic Au–Cu surface on TiO2 is vital to supply the photoexcited electrons of TiO2 to its surface for H2 evolution. The rate-determining step (RDS) is identified as the reaction of a surface-active species with protons. The results establish a practical preparation of metal alloy deposited on photocatalyst films using laser ablation to develop efficient photocatalysts.

Visible light active IrO2/TiO2 films for oxygen evolution from photocatalytic water splitting in an optofluidic planar microreactor

An optofluidic planar microreactor has been fabricated, with the photocatalyst (IrO2/TiO2) film coated glass as a reactor plate and plain glass as a cover plate. A rectangular region was completely etched on plain glass and used as a spacer between reaction and cover plates to create a planar microreaction compartment. The water splitting activity to produce oxygen using sodium iodate as a sacrificial agent (electron acceptor) was tested in the fabricated planar microreactor under visible light illumination (with 400 W metal halide lamp). The effect of catalyst coating thickness and the reactant flowrate on the rate of oxygen production was studied in detail. An oxygen evolution rate of 3.99 mmol h−1 g−1 (1.84 μmol h−1 cm−2) was observed from the IrO2/TiO2 film of 3078 ± 362 nm thickness at an optimal flow rate of 0.3 mL min−1 in the presence of visible light. The stability study showed that the IrO2/TiO2 film was stable for at least 4 cycles, indicating the superior activity of the film firmly adhered to the glass substrate.

Preparation and performance evaluation of BiOI photocatalytic film

BiOI photocatalyst powder was prepared using the hydrothermal method. Using BiOI, PAN as the solute and DMF as the solvent, the mixed solution was stirred uniformly, and the photocatalytic film was prepared by an electrospinning machine. The microscopic morphology, pore size, and contact angle were characterised by scanning electron microscopy, N2 adsorption and desorption, and contact angle tests. The photocatalytic performance of the film at different calcination temperatures was explored. The results show that the film has the best photocatalytic performance under the heat treatment conditions of 280℃ and 6 h, and the degradation rate of MB to 10 mg/L is 94.3 %. Meanwhile, different cycles of experiments show that the film photocatalyst has good stability and strong mechanical properties. After four cycles of experiments, the film showed almost no damage and the degradation rate could still reach 93.6 %. The films showed good degradation potential of organic dye wastewater and have good application prospect.

Plasmonic coated spindle-shaped MIL-88A(Fe) ternary composites heterojunction for photocatalytic degradation of tetracycline: Mechanism studies and theoretical calculation

Ag/AgBr@MIL-88A(Fe)(ABM) was successfully prepared by in-situ growth method. ABM revealed a distinguished photocatalytic performance under simulated visible light source. The results endorsed that the optimized ABM-2 heterojunction photocatalytic degradation efficiency for tetracycline (95.1%) was 3.7 and 2.3 times in contrast with the original Ag/AgBr and MIL-88A(Fe), respectively. After four repetitions, ABM-2 exhibited satisfactory photocatalytic activity, with the degradation efficiency of tetracycline remaining approximately 83.0%. Combined with characterization and electrochemical analysis, it was proved that the interface between MIL-88A(Fe) and the plasmonic photo-catalyst film with a tight structure and uniform contact, which enabled ABM to have more reaction sites. Additionally, based on density functional theory (DFT), the band structures and state densities of three single-phase semiconductors were calculated by Perdew-Burke-Ernzerhof (PBE) formula, which confirmed Z-scheme electron transfer path. This work provided a new idea for designing surface heterojunction structure to prepare efficient and environmentally stable photo-catalysts.

Design and construction of an immobilized Z-scheme Fe2O3/CuFe2O4|Cu photocatalyst film for organic pollutant degradation with simultaneous hydrogen production

An immobilized Z-scheme Fe2O3/CuFe2O4|Cu photocatalyst composite film was prepared by using an incomplete solid-state chemical reaction method. In the designed composite film, the copper foil is used not only as a photocatalyst carrier, but also as a reactant to generate CuFe2O4. Based on the unique structure of the photocatalyst composite film, the electrons can be transferred to the other surface of the copper foil. Therefore, photocatalytic degradation and hydrogen production reactions can be carried out simultaneously on both sides of the copper foil. The structure and properties of the photocatalyst composite film were studied by various characterization techniques. Some factors such as calcination time and calcination temperature on the photocatalytic activity of the composite film in organic pollutant degradation and hydrogen production were investigated. The crystal violet degradation ratio and hydrogen production amount reached 88.22 % and 375.00 µmol/dm2, respectively, under simulated sunlight irradiation for 120 min. The cyclic experiments were carried out to investigate the stability and reusability of the composite film. The species and properties of the active species generated in the photocatalytic reaction were studied by trapping experiments and electron spin resonance. This study may provide an idea for large-scale photocatalytic treatment of wastewater and hydrogen production.

Facile fabrication of the Ag nanoparticles decorated graphitic carbon nitride photocatalyst film for indoor air purification under visible light

Visible light photocatalysis represents a promising procedure for indoor air purification. Here we developed the Ag nanoparticles decorated graphitic carbon nitride photocatalyst film supported on glass substrate. This photocatalyst film can effectively use visible light to degrade various volatile organic compounds which contain formaldehyde, acetaldehyde, ethylene, benzene, toluene, and p-xylene and deactivate Escherichia coli, Staphylococcus aureus, and Candida albicans. The decoration of Ag nanoparticles enhanced the visible-light-driven activity of graphitic carbon nitride because Ag nanoparticles strongly absorb visible light through the localized surface plasmon resonance effect and facilitate the efficient separation of charge carriers by forming Schottky barrier with the semiconductor. Photo-generated holes and superoxide radical anions, rather than hydroxyl radicals, are the major active species in the photocatalytic degradation of volatile organic compounds and deactivation of microorganisms. The application potential of the developed photocatalyst film for indoor air purification was demonstrated by the efficient removal of HCHO and TVOC under a simulated indoor environment and the favorable recyclability of the photocatalyst.

Construction of novel metal-free graphene oxide/graphitic carbon nitride nanohybrids on carbon cloth and efficient degradation of RhB under visible light irradiation

Photocatalytic technology has a wide range of application prospects, but due to the low degradation efficiency of photocatalytic materials at the present stage, difficult to recycle and other problems, seriously restricted its development, so it is urgent to prepare the efficient photocatalytic material. This article reports a novel metal-freephotocatalyst of the construction of graphene oxide (GO)/graphite-phase carbon nitride (g-C3N4) heterojunction on carbon cloth (CC). The GO/g-C3N4 /CC photocatalyst has excellent degradation rate of Rhodamine B (RhB) in the visible light. Due to the formation of a heterojunction between g-C3N4 and GO, the light absorption of the photocatalyst was improved and the rapid recombination of photocarriers was reduced. After 5 cycles, there was no significant reduction in photocatalytic activity. We designed a new type of multi-layer membrane filter photocatalytic reactor, RhB put into the device to simulate the flow of waste water and degrade. The results show that the filter film photocatalyst shows good photocatalytic activity of RhB degradation. The introduction of carbon cloth substrate solves the problems of separation and cycle life of this photocatalyst.

Photocatalytic NOx mitigation under relevant conditions using carbon nanotube-modified titania

Although a majority of photocatalysts exhibit improved NO conversion to NO2, the performance in the oxidation of NO2, the more toxic form of NOx, to nitrate remains a challenge; in addition, the performance of hybrid photocatalysts under practical conditions is unclear. This study demonstrates the use of carbon nanotube-TiO2 (CNT-TiO2) photocatalyst films for effective transformation of NOx into nitrates. Using the objective figure of merit for NOx abatement, DeNOx index, the catalyst performance in a laminar-flow reactor was evaluated under simulated conditions that are relevant in abating NOx. The conditions probed include relative humidity (RH), initial NOx concentration, reactor geometry (headspace distance), and state of the catalyst (fresh vs. recycled). Our results reveal CNT-TiO2 significantly outperforms P25 despite exhibiting comparable NO conversion at low RH. P25 experiences a 66% reduction in DeNOx at high RH compared to low RH while CNT-TiO2 only incurs a 27% reduction. For recycled photocatalysts, this disparity becomes even more pronounced; CNT-TiO2 experiences a 49% reduction in DeNOx at high RH, whereas P25 experiences a 134% reduction. In addition, mass transfer from the bulk airflow limits NO conversion when the reactor headspace is too large (>3 mm), due to limited diffusion of NOx to the photocatalyst surface. Our findings highlight the importance of headspace distance, a parameter that has mostly been overlooked in reactor design for photocatalytic oxidation of NOx, but which dictates the optimal catalyst configuration for flue gas treatment. The remarkable DeNOx activity of CNT-TiO2 over a wide range of RH levels is rationalized based on the ratio of physisorbed-to-chemisorbed water on the photocatalyst surface.

A strategy to improve the performance of TiO2 nanotube array film photocatalysts by magnetron-sputtered amorphous BiFeO3

Amorphous BiFeO3/TiO2 nanotube array thin films were prepared on indium tin oxide glass using an anodic oxidation technique coupled with magnetron sputtering. The morphology, structure, optical properties, photoelectrochemical properties, and photocatalytic activity of heterostructured nanotube array thin films with different morphologies of BiFeO3 were studied. HRTEM observations show the interface between amorphous BiFeO3 and anatase TiO2. The amorphous BiFeO3/TiO2 nanotube array thin films show enhanced visible-light absorption and outstanding separation and transfer of photoinduced charges. The BFO3-TNA sample shows excellent photocatalytic activity. By using it, 97.6% of chromium (VI) can be removed in 60 min under visible-light illumination. This work will provide a feasible route to further enhance the photocatalytic activities of visible-light responsive TiO2 nanotube array thin films as photocatalysts for rapidly removing chromium (VI) from water.

Ni Foam Supported TiO2 Nanorod Arrays with CdS Branches: Type II and Z‐Scheme Mechanisms Coexisted Monolithic Catalyst Film for Improved Photocatalytic H2 Production

TiO2 has garnered a flourish of interest in the field of energy storage and energy conversion. Herein, a new generation of 3D Ni foam supported in situ grown 1D TiO2 nanoarray (Ni/TiO2) is successfully prepared, through an easy solution‐phase hydrothermal process, and then CdS nanorods branched Ni/TiO2 nanoarrays are fabricated (Ni/TiO2@CdS). Their formation parameters and growth mechanism are carefully studied. Both Ni/TiO2 and Ni/TiO2@CdS monolithic catalysts exhibit advantaged photocatalytic (PC) and photoelectrocatalytic (PEC) water splitting properties compared with that of most previously reported TiO2‐based film photocatalysts. Mechanism investigation reveals that both type II and Z‐scheme charge transport mechanisms coexist in Ni/TiO2@CdS sample, and an additional Z‐scheme charge transfer effect accelerates the photogenerated charge separation and transport efficiency. This study may open a new avenue for the utilization of TiO2‐based film catalysts in a broader field of energy and environmental catalysis areas.

High efficient pH-universal photo-Fenton degradation of antibiotics by amorphous FeSiB microspheres decorated TiO2 nanowire hybrid film

Immobilized reactors with catalyst films fixed in are widely used for photodegradation of water pollutants, in which the photocatalyst film is critical for the reactors’ performance. In this work, trace amount of amorphous FeSiB microspheres decorated TiO2 nanowires hybrid films were fabricated by the simple painting method, and they exhibit excellent photodegradability for antibiotic contaminants. The heterogenous photocatalytic films were characterized by microscopic, spectroscopic and photoelectrochemical techniques, and were demonstrated with great tetracycline degradation at universal pH conditions between 2 and 12. By optimizing the FeSiB content in the composite film, it was found that the film containing 1 wt% FeSiB exhibited the best performance with the tetracycline degradation efficiencies of 98.2% (pH = 2) and 85.5% (pH = 12) within 4 h. Furthermore, the FeSiB/TiO2 hybrid films exhibited a high degradation efficiency of > 80% after 3 recycling, and the enhanced reusability was attributed to the corrosion resistance of FeSiB microspheres wound by the TiO2 nanowires. This study combines the merits of FeSiB metallic glass and TiO2 nanowires to improve their degradation performance of antibiotics through building the Z-Scheme FeSiB-TiO2 heterojunction, which accelerated the separation of photogenerated electrons/holes on the photocatalyst films and the conversion between Fe2+ and Fe3+ in the photo-Fenton reactions.

Co-doped amorphous MoSx supported on CuO/CM (Cu mesh) with enhanced photocatalytic activity for ammonia synthesis

As one of the world's most significant industrial synthetic chemicals, ammonia has critical applications in many fields. Mo-based catalyst has an excellent effect on photocatalytic nitrogen fixation. Compared with crystalline molybdenum sulfide, low crystalline or amorphous molybdenum sulfide has rich unsaturated defects to improve the photocatalytic activity. Therefore, we used CuO/CM (Cu mesh) as the substrate and a simple electrochemical deposition method to load amorphous MoSx doped with different contents of Co on CuO/CM and successfully synthesized a thin film heterojunction photocatalyst. At the same time, we fabricated a gas-liquid-solid three-phase photocatalytic reactor to evaluate the catalytic activity of the catalyst. Compared with the powder catalyst reported in the literature, because the catalytic reaction of the three-phase gas-liquid-solid three-phase reactor occurs at the gas-liquid interface, the film catalyst can also absorb sufficient N2 in the gas phase while contacting the liquid proton source (water). It can effectively enhance photocatalytic nitrogen fixation efficiency. The constructed film photocatalyst showed good photocatalytic performance and stable structure under the 350 W simulated light source. While exploring the catalyst structure, the photocatalytic effect of the catalyst was evaluated. When the molar ratio of Mo and Co is 1:0.9, the photocatalyst efficiency shows the high photocatalysis at a rate of 1.062 mg·L−1 for 4 h. Compared with pure CuO / CM and MoSx / CuO / CM, the NH3 yield of the catalyst was increased by 7.86 and 7.52 times, respectively. In addition to N2, no other N sources were introduced during the reaction, which ensured the accuracy of the experimental results.

Photocatalytic degradation of amoxicillin and tetracycline by template synthesized nano-structured Ce3+@TiO2 thin film catalyst

Contamination of the aquatic environment with pharmaceutical compounds is a serious environmental concern. The present investigation aims to utilize the Ce3+/TiO2 thin film catalyst to remove of potential antibiotics (amoxicillin and tetracycline) using the less harmful UV-A radiations. Reduced cerium ion-doped TiO2 is obtained by a simple one-step facile template method using polyethylene glycol as the templating agent. The synthesized catalysts Ce3+@TiO2 (non-template) and Ce3+@TiO2(T) (template) were characterized by spectroscopic methods. The XPS reaffirms the reduced Ce3+ dispersed within the titania network, and the AFM showed the surface roughness of the thin films. Detailed physicochemical analyses were conducted to deduce the degradation mechanism, and repeated use of the thin film photocatalyst showed enhanced stability. Significant mineralization of the antibiotics indicates the potential applicability of the photocatalytic catalyst. Furthermore, the presence of Ce3+ significantly restricted the recombination of electron/hole pairs in the photo-excited TiO2 semiconductor and showed enhanced photocatalytic degradation of the antibiotics proceeded predominantly through the •OH.