Photocatalytic Activity Of Films Research Articles

Efficiency of cathodic arc-grown N-doped TiO2 films for the photocatalytic reduction of Cr(VI) under UV-Vis irradiation

The photocatalytic activity of undoped and N-doped TiO2 anatase films with different thicknesses prepared by cathodic arc deposition on glass substrates is reported. After TiO2 deposition, the doping of the films was carried out by plasma immersion ion implantation in a nitrogen environment. The composition of the films was studied by x-ray photoelectron spectroscopy, the surface morphology was analyzed by atomic force microscopy and the crystalline structure was examined by x-ray diffraction. The thickness was determined by observing the film cross section with scanning electron microscopy. The transmittance of the films in the UV-Vis range was studied as well. The photocatalytic activity of the films was evaluated through the efficiency in the reduction of Cr(VI) in the presence of ethylenediaminetetraacetic acid under UV-Vis irradiation. N-doped films presented a higher photocatalytic efficiency than undoped films: Cr(VI) reduction after 5 h irradiation augmented from 58% (pure TiO2) to 85% (N-doped TiO2) for films of 300 nm thickness, and from 69% to 85% for films with a thickness of 440 nm. On the other hand, pure TiO2 films of 790 nm thickness were more efficient (99% of Cr(VI) reduction) but the effect of doping on the photocatalytic activity was negligible.

Phases evolution and photocatalytic activity of Cu2O films electrodeposited from a non-pH-adjusted solution.

A pure-phase Cu2O film photocatalyst was successfully prepared by the electrodeposition technique from a non-pH-adjusted solution. To investigate the phase evolution and photocatalytic activity of the film, the electrodeposition was conducted at different deposition temperatures. Photocatalytic activity of the films was evaluated from methylene blue (MB) dye degradation. The Cu2O phase initially appeared at room temperature and its fraction was found to increase with increasing the deposition temperature, while the impurity phase was successfully diminished. A pure Cu2O film with a narrow optical bandgap energy of 1.96 eV was obtained at 75°C. The multi-faceted crystals were found to form at 45°C and became a truncated octahedral structure that possessed {111} and {100} facets as deposition temperature further increased. A preferred orientation growth of {110} facet, which is known to possess a relatively high surface energy, was produced at 75°C. The performance of MB photodegradation enhanced gradually by increasing the deposition temperature. The increase of photocatalytic activity could be attributed to the rise of photoelectrochemical response and the decrease of resistance charge transfer because of narrowing bandgap energy, increasing Cu2O fraction, and growing a relatively high catalytic activity facet which had escalated redox reaction that decomposed MB at the photocatalyst-solution interface.

Photocatalytic and Antimicrobial Activity of TiO2 Films Deposited on Fiber-Cement Surfaces

In this study, TiO2 films were deposited via the doctor blade technique on fiber-cement surfaces. Two types of nanoparticles (TiO2-P25 from Degussa and TiO2-PC105 from Tronox) were used to produce films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images revealed films with homogeneous and nanoparticulated morphology. The TiO2 PC105 film presented a lower roughness parameter (RMS) in relation to that of the TiO2 P25-based film. Both films exhibited high hydrophilicity when exposed to UV-A radiation (contact angle θ < 6°). The photocatalytic activity of the films was evaluated by standardized methylene blue dye degradation assays under UV-A irradiation (1.0 mW/cm2). The TiO2-PC105 film showed a photonic efficiency of ξ = 0.1%, while for the films obtained with TiO2-P25, ξ = 0.08%. The cement surface modified with the PC105 film was evaluated for antimicrobial activity through the use of multiple pathogens commonly found in hospitals. A considerably high efficiency was measured with visible light. Growth inhibition rates of 99.0% ± 0.2, 99.1% ± 0.2, 99.1% ± 0.2, 97.5% ± 0.5, 98.0% ± 0.5 and 98.0% ± 0.5 were found for Staphylococcus aureus, Klebsiella sp., Escherichia coli, Rhizobium sp., Fusarium sp. and Penicillium sp., respectively. The results show the self-cleaning ability and their potential use for protection, by preventing contamination of the fiber-cement surface and opening new possibilities for the use of this building material.

Enhanced photocatalytic activity of highly transparent superhydrophilic doped TiO2 thin films for improving the self-cleaning property of solar panel covers

Undoped and metal doped nanocrystalline TiO2 transparent thin films were synthesized on glass substrates via sol-gel/dip-coating method. TiO2 thin film coatings can be applied to the surfaces of solar panels to impart self-cleaning properties to them. The structural and optical properties of few nanometer-thick films were characterized by XRD, SEM, CA, AFM, XPS, and UV–Vis spectrophotometry techniques. The stoichiometric TiO2 films crystallized in anatase phase, with a particle size of ∼100 nm, which were uniformly distributed on the surface. The prepared films with a roughness of ∼1–5 nm, increased the hydrophilicity of the glass surface. Reducing the amount of Ti precursor (X) favored the improvement of film quality. To improve the photocatalytic activity of the TiO2 thin film, it was doped with Ni, Cd, Mo, Bi and Sr metal ions. The effect of metal doping on the photocatalytic activity of the films was investigated using the degradation process of methylene blue (MB) dye as the model contaminant. Among the prepared coatings, the Sr–TiO2 film showed the highest efficiency for MB degradation. It increased the dye degradation efficiency of the films under both UV and Vis lights. The kinetic investigations also showed that the degradation of MB by TiO2 and M − TiO2 films obeyed the pseudo-first order kinetics.

Effect of Ag loading content on morphology and photocatalytic activity of Ag-TiO2 nanoparticulate films prepared via simultaneous plasma-enhanced chemical and physical vapor deposition

Ag loading is known to enhance the photocatalytic performance of TiO2; however, the correlation between Ag and the resulting changes in TiO2 morphology and particle size is not well understood. A plasma-enhanced chemical vapor deposition (PECVD) and physical vapor deposition (PVD) were used to prepare Ag-TiO2 nanoparticulate thin films; the prepared films were annealed at 500 °C under N2 atmosphere. The Ag content was adjusted by the furnace temperature of the PVD system. Well-dispersed Ag nanoparticles on the surface of TiO2 nanoparticles were observed and analyzed using transmission electron microscopy (TEM). The morphology, particle size, and photocatalytic activity of the films were evidently affected by the Ag content. TEM images showed that the TiO2 nanoparticle size increased with increasing Ag content. Evaluation of the photocatalytic activity based on the degradation of methylene blue under ultraviolet (UV) light irradiation demonstrated that an Ag content of 2.2 wt% yielded the highest photocatalytic activity (5.5 times higher than that seen in a pristine TiO2 film). This fabrication method has advantages because it adds Ag in a more controlled manner compared to the liquid-phase methods. Furthermore, our fabrication method can provide a way to vary the Ag content while considering the relationship between the photocatalytic performance and the Ag content.

Enhanced photocatalytic activity of Mg-doped ZnO thin films prepared by sol–gel method

ABSTRACT Undoped ZnO and Mg-doped ZnO (MZO) thin films were synthesized by sol–gel dip-coating technique. The effect of Mg dopant on the structural, surface-morphological, and optical properties together with the photocatalytic activities of the films was studied. Morphological study shows that incorporation of Mg increases the porosity of the films. Structural investigation reveals that Mg doping declines the crystallinity of the films. The optical analysis demonstrates that the Urbach energy of the films increases due to Mg doping, suggesting the formation of localized energy states. Photocatalytic activities of the films were evaluated by studying the degradation of methylene blue under the ultraviolet light irradiation. MZO demonstrates better photocatalytic efficiency compared to ZnO films. The enhanced photocatalytic efficiency of MZO can be attributed to the charge trapping by localized states, and porosity-induced surface area enhancement due to Mg doping.

Photocatalytic degradation of triclosan by oxygen defected CuO thin film

CuO thin films with oxygen defects (oxygen vacancy and oxygen excess) were prepared by sputter deposition from stochiometric CuO target. Presence of Oxygen defects was confirmed by X-ray photoelectron spectroscopy. Effect of oxygen vacancy and excess on the photocatalytic activity (Triclosan (TS) degradation) of CuO thin films under sunlight irradiation was investigated. Generation of oxygen vacancy (lower than optimum concentration) and excess considerably improved the thin film photocatalytic activity. In original work, the photocatalytic activity of the samples with oxygen vacancy was compared to the ones with oxygen excess. Moreover, the durability of the samples (oxygen vacancy and excess) after several cycles was investigated. The samples with oxygen excess showed better photocatalytic activity; though, the durability of samples with oxygen vacancy was significantly superior to the ones with oxygen excess after 5 cycles.

Optical characterization of photocatalytic copper doped thin films of anodized titanium

Titanium oxide is used in a myriad of applications such as in capacitors, insulation paints among others. It is a prime candidate for water splitting due to its photocatalytic properties. In this work, undoped TiO2 thin films were prepared by anodizing titanium foils cut into pieces measuring 60 mm by 20 mm. The specimens were anodized in an electrolyte consisting of 0.5 M H2SO4 and 0.075% wt HF at room temperature. The anodizing voltages ranged from 50 V to 100 V. Anion doping of copper in as anodized TiO2 was done electrochemically. The as anodized Ti foils were dipped in a 1 M Cu2SO4 solution. All samples were annealed at 450 °C for 3 h. Near-normal total reflectance was measured on as anodized and copper pigmented samples in the solar (300–2500 nm) wavelength range. Spectrophotometric reflectance data was analyzed to obtain the absorption coefficient and using the same to determine the band gap of the films. It was noted that the films exhibited reduced solar integrated reflectance for TiO2 samples prepared at lower anodic voltages of 50, 60 and 70 V. The copper pigmented, and annealed, TiO2 samples exhibited both direct and indirect energy band gaps in the ranges, 3.38–3.86 and 2.50–2.74, respectively. Further, annealing and copper doping of the films lead to increased absorption. The photocatalytic activity of the films was assessed by measuring the rate of degradation of 10ppm methylene blue in UV light source. Copper doped TiO2 exhibited enhanced photocatalytic performance in compared to pure TiO2. An increase in the anodization voltage caused subsequent increase in photocatalytic activity of films with 70 V as the optimum voltage above which photo degradation of methylene blue decreased.

Enhancement of the photocatalytic activity of N-doped TiO2 nanograss array films by low-temperature sulfur doping

Moderate in-situ chemical oxidation of Ti meshes was used to prepare nitrogen-doped (N-doped) anatase TiO2 nano-grass array films with urea as the nitrogen source. Further sulfur doping through immersion of the films in a thiourea solution at a relatively low temperature of 353 K was subsequently performed to enhance the visible-light-driven photocatalytic activity of the films. SEM images confirmed that the loose microstructure of the nanograss arrays became compact after N-doping or N, S co-doping. N-doping and N, S co-doping decreased the band gap values of the TiO2 films and increased the effective visible light utilization. XPS analysis revealed that nitrogen mainly existed in interstitial form. Subsequent sulfur ions appeared as S6+, S4+, and S2−, with S6+ and S4+ replacing Ti4+, and S2− replacing O2−, respectively. With an increase in the urea treatment time, the sulfur ions were oxidized, achieving higher valence states. S6+ substitution resulted in a charge imbalance, which could only be neutralized by hydroxide ions. The imbalance made it easier for water that had settled on the TiO2 films to chemically dissociate, and thereby generating hydroxyl radicals. OH• radicals as well as Ο2•−radicals played a significant role in the degradation of RhB dye. The RhB decolorization activity achieved by the N, S co-doped samples was 48 times that of the undoped samples.

Structural, optical properties and photocatalytic activity of Fe3+ doped TiO2 thin films deposited by sol-gel spin coating

Nanocrystalline TiO2: Fe3+ films were deposited using a simple spin coating technique. The effect of Fe3+ on spectroscopic features and photocatalytic activity of films were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), Energy dispersive X-ray (EDX), high-resolution transmission electron microscope (HR-TEM), Raman spectrometer, UV–Vis and fluorescence spectrophotometer. The XRD of all the TiO2: Fe3+ films exhibits a decrease in the crystallite size with an increase in Fe3+ concentration. The Fe3+ doped TiO2 nanocrystals exhibited a high specific surface area. The HR-TEM images of 1% and 7% Fe doped TiO2 thin films confirmed the average particle size is about 14 and 8 nm respectively. The Raman modes of vibrations present in the TiO2:Fe3+ films also confirms the formation of the anatase phase. The optical bandgap energy of titania decreases from 3.32 to 2.57 eV. The luminescent emission intensity of TiO2: Fe3+ films decreased compare to pure titania film. Moreover, the photocatalytic activity (PCA) of TiO2:x%Fe3+ (x = 0, 1, 3, 5, 7 and 10) catalysts were determined by the decomposition of methylene blue (MB) under irradiation of visible light. The observed results revealed that the optimized Fe3+ doped TiO2 film displayed high PCA. The enhancement of PCA of the films is due to the effect of Fe doping.

Structural, optical and photocatalysis properties of sol–gel deposited Al-doped ZnO thin films

Nanostructured ZnO and Al doped ZnO (AZO) thin films were deposited onto glass substrates by a simple sol–gel dip coating technique. The effect of Al dopant on the crystal structure, surface morphology, optical and electrical properties of films were studied using powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer, and four point probe technique respectively. The X-rays diffraction pattern showed the polycrystalline nature of pure and Al-doped ZnO thin films. The SEM images revealed that the films possess uniform distribution of identical nanoparticles throughout the surface and the grain dimension reduces with Al doping. The UV–visible transmission spectra showed that the Al substitution in ZnO leads to band gap narrowing together with a reduction in optical transmittance. The photocatalytic activity of these films was assessed through photocatalytic degradation kinetics of Methylene Blue (MB) dye and the degradation efficiency of the AZO films was compared with that of the ZnO films. The photocatalytic studies reveal that the AZO films exhibit better photocatalytic efficiency compared to the ZnO films. The enhanced photocatalytic activities of AZO thin films can be attributed to the charge trapping by Al dopant, enhanced surface area due to the decreased in grain size, and the band gap narrowing of AZO thin films.

BFO thin film on the stainless steel mesh by anodic EPD: A visible light photocatalyst for degradation of Rhodamin B

Bismuth ferrite thin film as an active visible light photocatalyst was synthesized by anodic electrophoretic deposition on the stainless steel mesh. The stability of suspension was studied in the presence of dispersant under different conditions through the sediment percentage measurements. The effect of various dispersants was also evaluated on the stabilization of BFO aqueous suspension. The films were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and magnetic force microscopy (MFM). Electrochemical impedance spectroscopy (EIS) was applied to evaluate the separation of photogenerated electron-hole by measured resistance and capacity of films under visible light irradiation. The visible light photocatalytic activity of thin films was investigated by degradation of Rhodamin B subjected to direct solar irradiation in a designed photocatalytic reactor. The film illustrated a better photocatalytic efficiency than slurry state. High efficiency in immobilized film can be attributed to the conductive substrate (stainless steel mesh) that makes better separation of photogenerated electrons and holes. In addition, the fractal dimension measurement indicated that films with high surface roughness improve the light adsorption capacity and leads to enhance the photocatalytic reaction rate. The photocatalytic activity of films was also investigated in the presence of some common anions in Rhodamin B solution. It can be highlighted that the thin film completely removed the dye from aqueous solution and COD reached to near zero.

Effect of sputtering parameters on the self-cleaning properties of amorphous titanium dioxide thin films

The aim of this work was to assess the effect of the direct current magnetron sputtering parameters on the photocatalytic activity and photoinduced wettability of amorphous TiO2 films. TiO2 films were deposited on glass using the direct current magnetron sputtering technique, without heating, at different total working pressures. Qualitative analysis using in situ X-ray photoelectron spectroscopy confirmed the TiO2 stoichiometry of the deposited films. Surface structure was studied as a function of working pressure using scanning electron microscopy. The hydrophilicity of the TiO2 surfaces was investigated macroscopically using measurements of the water contact angle. A threshold working pressure was observed, with a strong dependence on the film thickness. A super hydrophilic surface was observed after less than 1 h of UV irradiation. The photocatalytic activity of the films was evaluated under UV light through the degradation of methylene blue ( $$\lambda_{\hbox{max} } \approx 660\;{\text{nm}}$$ ). The effect of UV irradiation on the photocatalytic activity was rapid, strong, and dependent on film thickness and total working pressure. Fifty percent of organic compounds were photodegraded by films with a thickness of 60 nm deposited at 10 mTorr.

Role of iron and chromium in the photocatalytic activity of titanium dioxide films on stainless steel

Photocatalytically active titanium dioxide films have been formed on stainless steel grids via sol–gel process followed by heat treatment in the temperature range of 450–550°C. During UV irradiation of the films in an aqueous solution of the Rhodamine B dye and in distilled water we have detected iron and chromium dissolution from uncoated grid regions and the deposition of iron and chromium compounds onto the titanium dioxide surface. The deposition rate of these compounds increases with annealing temperature, which leads to a decrease in the photocatalytic activity of the films.

Fabrication of Ta2O5 nanostructure films via electrochemical anodisation of tantalum

In this work, we report the electrochemical formation of Ta2O5 films with different morphology via one-step anodisation of tantalum foil in aqueous electrolytes consisting of H2SO4 and fluoride ion and small additions of ethylene glycol or glycerol. The morphology and structure were characterised by field emission scanning electron microscopy (SEM), X-ray diffraction and energy dispersive X-ray spectroscopy. SEM results show that under optimised electrochemical conditions in electrolytes containing H2SO4 and fluoride ion, Ta2O5 nanotube layers can be grown up to thickness of 2 μm. The addition of ethylene glycol or glycerol to this aqueous electrolyte resulted in the formation of irregular porous or compact films on the surface of tantalum. The photocatalytic activity of films was evaluated by measuring the degradation of methylene blue under UV irradiation. Ta2O5 nanotubes exhibited higher photocatalytic activity than did the other samples. The reason of this enhanced photocatalytic property can be attributed to high specific surface areas and the nanotube structures of this sample.

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of a pure Zn target in Ar/N2/O2 gas mixture was used to synthesize ZnOxNy thin films with nitrogen content and optical band-gap energy values ranging over 0–6.2at.% and 3.34–1.67eV, respectively. The fine control of the nitrogen content in the deposited ZnOxNy thin films composition was possible through the stabilization of the reactive HiPIMS discharge in the transition region, between the metallic and compound target sputtering modes. Various analytical techniques such as AFM, XPS, XRD, UV–Vis and Raman spectroscopy have been employed to characterize the properties of the deposited thin films. The photocatalytic activity, light excitation efficiency and life time of photo-generated charge carriers in the ZnOxNy films were investigated by photo-electrochemical and photo-current measurements during visible light on/off irradiation cycles. The as-deposited films showed poor visible-light photocatalytic activity and photo-current response. Post-deposition annealing of the films in nitrogen atmosphere resulted in a slight enhancement of crystalline order. However, the thermal treatment improved considerably the film photocatalytic activity and stability for water splitting under visible light irradiation. The optimum photo-current response and photocatalytic activity have been obtained for the annealed ZnOxNy films with a nitrogen content of 3.4at.% (photon-to-current efficiency up to 33% at λ=370nm and 0.5V biasing potential vs. Ag/AgCl). Increasing the nitrogen content above this value, in spite of lowering the energy band-gap, worsened the visible light photocatalytic activity of the films due to deterioration of the crystalline order.

On the apparent visible-light and enhanced UV-light photocatalytic activity of nitrogen-doped TiO 2 thin films

Abstract Nitrogen-doped titania (N TiO2) thin films were synthesized using atmospheric-pressure chemical vapor deposition (APCVD) using ammonia, tert-butylamine or benzylamine as the nitrogen source. The influence of these precursors on the structural, morphological and optical absorption properties of the films was studied using X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and UV/Vis spectroscopy. The chemical state and location of the nitrogen species in the films was investigated using X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of films with similar structural properties was evaluated during degradation of stearic acid under UVA and visible light illumination. A previous study established a potential photosensitization mechanism involving surface N groups with binding energy of ∼400 eV, which would result in extrinsic enhanced UV activity of the N TiO2 films. Here, an empirical approach was adopted in order to establish correlation between structural features, nitrogen content and photocatalytic properties of these films. Within the thickness range considered, the photocatalytic activities of the undoped TiO2 films were consistent with their diffraction features (peak intensities and sharpness). Nevertheless, the activities of the N TiO2 films did not follow the same trend but it was consistent with their nitrogen content. Further evidence is provided on the participation of nitrogen species on the enhanced UV activity of N TiO2 films and the impact of surface N O groups such as N O Ti O (or O N Ti O) and bulk substitutional nitrogen groups is discussed. Discussion is also provided on the apparent visible light activity of the N TiO2 films.

Improved photocatalytic activity of cerium doped TiO2 films prepared by microarc oxidation

Cerium doped TiO2 films were synthesised by microarc oxidation (MAO) process on pure titanium. The suitable condition for MAO treatment were first investigated under various concentration of electrolytes, then the doping process was carried out in the suitable concentration of electrolytes with MAO. The characterisations of MAO-TiO2 and cerium doped MAO-TiO2 films were studied by means of scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The photocatalytic activity of the films was evaluated by decolourisation of methylene blue in aqueous solution as a model pollutant under sunlight irradiation simulation with homemade ultraviolet–visible spectroscopy. The results showed that the photocatalytic activity of MAO-TiO2 films first increased and then decreased with the concentration of electrolytes. Moreover, after doping, the cerium doped MAO-TiO2 films were of evidently improved photocatalytic activity than that of the MAO-TiO2 films.

Effect of temperature and concentration of precursors on morphology and photocatalytic activity of zinc oxide thin films prepared by hydrothermal route

Zinc oxide (ZnO) is an important semiconductive material due to its potential applications, such as conductive gas sensors, transparent conductive electrodes, solar cells, and photocatalysts. Photocatalytic activity can be exploited in the decomposition of hazardous pollutants from environment. In this study, we produced zinc oxide thin films on stainless steel plates by hydrothermal method varying the precursor concentration (from 0.029 M to 0.16 M) and the synthesis temperature (from 70 °C to 90 °C). Morphology of the synthesized films was examined using field-emission scanning electron microscopy (FESEM) and photocatalytic activity of the films was characterized using methylene blue decomposition tests. It was found that the morphology of the nanostructures was strongly affected by the precursor concentration and the temperature of the synthesis. At lower concentrations zinc oxide grew as thin needlelike nanorods of uniform length and shape and aligned perpendicular to the stainless steel substrate surface. At higher concentrations the shape of the rods transformed towards hexagon shaped units and further on towards flaky platelets. Temperature changes caused variations in the coating thickness and the orientation of the crystal units. It was also observed, that the photocatalytic activity of the prepared films was clearly dependent on the morphology of the surfaces.

Evaluation of the correlations between temperature, humidity, incident UV light and the photocatalytic activity of TiO2 films using a rationale approach

The effect of temperature, humidity and incident UV light on the photocatalytic activity of two TiO2 films with different microstructures (dense and mesoporous) was explored in terms of stearic acid degradation. Previous works reported in the literature suggest that the activity of TiO2 films does not only depend on single factors but also on interactions between them. Hence, the design of experiments (DoE) approach was used in this work to plan the experiments in a systematic way, simultaneously considering several variables. This approach provided an efficient working strategy to explore both individual and interaction effects on the photocatalytic activity of the films. The statistical evidence found here revealed that single factors temperature and mesoporous microstructure have the strongest positive effect on the efficiency of the films. In the case of temperature, this was explained by easier degradation and/or desorption of reaction intermediates. On the other hand, the positive effect of the mesoporous microstructure was correlated with its large surface area. An interaction factor between temperature and incident UV light also affects the activity of the films. Results suggest that this phenomenon depends of the degree of film hydration before the deposition of SA.