Photocatalytic Activity Of TiO2 Coatings Research Articles

Photocatalytic and antibacterial activity properties of Ti surface treated by femtosecond laser–a prospective solution to peri-implant disease

Laser texturing seems to be a promising technique for reducing bacterial adhesion on titanium implant surfaces. This work aims to demonstrate the possibility of obtaining a functionally orientated surface of titanium implant elements with a specific architecture with specific bacteriological and photocatalytic properties. Femtosecond laser-generated surface structures, such as laser-induced periodic surface structures (LIPSS, wrinkles), grooves, and spikes on titanium, have been characterised by XRD, Raman spectroscopy, and scanning electron microscopy (SEM). The photocatalytic activity of the titanium surfaces produced was tested based on the degradation effect of methylene blue (MB). The correlation between the photocatalytic activity of TiO2 coatings and their morphology and structure has been analysed. Features related to the size, shape, and distribution of the roughness patterns were found to influence the adhesion of the bacterial strain on different surfaces. On the laser-structurised surface, the adhesion of Escherichia coli bacteria were reduced by 80% compared to an untreated reference surface.

Towards a Better Understanding of the Back-Side Illumination Mode on Photocatalytic Metal–Organic Chemical Vapour Deposition Coatings Used for Treating Wastewater Polluted by Pesticides

Pesticides are emerging contaminants that pose various risks to human health and aquatic ecosystems. In this work, diuron was considered as a contaminant model to investigate the influence of the back-side illumination mode (BSI) on the photocatalytic activity of TiO2 coatings grown on Pyrex plates by metal–organic chemical vapour deposition (MOCVD). A photoreactor working in recirculation mode was irradiated at 365 nm with ultraviolet A (UVA) light-emitting diodes in BSI. The degradation of diuron and its transformation products was analysed by high-performance liquid chromatography, ion chromatography, and total organic carbon analysis. The coatings were characterised by X-ray diffraction analysis and scanning electron microscopy. Five coatings containing 3, 7, 10, 12 and 27 mg of TiO2 exhibited different morphology, crystallinity, thickness and photocatalytic activities. The morphology and crystallinity of the coatings had no significant influence on their photocatalytic activity, unlike their mass and thickness. TiO2 contents less than 10 mg limit the photocatalytic activity, whereas those greater than 15 mg are inefficient in the BSI because of their thickness. The maximum efficiency was achieved for coatings of thickness 1.8 and 2 µm with TiO2 contents of 10 and 12 mg, revealing that the photocatalyst thickness controls the photocatalytic efficiency in the BSI.

Visible-light-induced antibacterial activity of carbon and nitrogen co-doped rutile TiO2 films

The visible-light-responsive photocatalytic activity of TiO2 coatings offers a promising route for the antibacterial functionalization of Ti implants. In this study, carbon and nitrogen co-doped single-phase rutile TiO2 films were fabricated on Ti substrates via a two-step thermal oxidation process involving subsequent treatments with N2–1% CO and N2–1% O2. Under optimized treatment conditions, the single-phase rutile TiO2 films exhibited antibacterial activity against Escherichia coli under visible-light irradiation (λ > 400 nm) at 15 mW∙cm–2 for 15 min. The TiO2 films exhibited a double-layered structure comprising an inner layer (containing carbon and nitrogen) on the Ti substrate side and an outer layer (without carbon or nitrogen) on the topmost surface. The excitation of electrons and holes generated by dissolved carbon and nitrogen in the inner layer of the TiO2 films contributed to visible-light responsiveness. The bonding strength between the TiO2 film and Ti substrate exceeded 60 MPa. The cytotoxicity against the mouse osteoblast-like cell (MC3T3-E1) of the TiO2 film was comparable to that of well plates, under visible light and in the dark. This study demonstrates the visible-light-responsive antibacterial activity of a single-phase rutile TiO2 film on Ti. Further, the TiO2 film exhibited excellent bonding strength with the Ti substrate, indicating its high potential as an antibacterial active coating in combination with visible-light irradiation for Ti implants.

Photocatalytic Activity of TiO2 Coatings Obtained at Room Temperature on a Polymethyl Methacrylate Substrate.

Titanium dioxide (TiO2) coatings have a wide range of applications. Anatase exhibits hydrophilic, antimicrobial, and photocatalytic properties for the degradation of organic pollutants or water splitting. The main challenge is to obtain durable anatase nanoparticle coatings on plastic substrates by using straightforward approaches. In the present study, we revealed the preparation of a transparent TiO2 coating on polymethylmethacrylate (PMMA), widely used for organic optical fibres as well as other polymer substrates such as polypropylene (PP), polystyrene (PS), and polycarbonate (PC). The films were spin-coated at room temperature without annealing; therefore, our approach can be used for thermo-sensitive substrates. The deposition was successful due to the use of stripped ultra-small (<4 nm) TiO2 particles. Coatings were studied for the photocatalytic degradation of organic pollutants such as MB, methyl orange (MO), and rhodamine B (RB) under UV light. The TiO2 coating on PMMA degraded over 80% of RB in 300 min under a 365 nm, 100 W mercury lamp, showing a degradation rate constant of 6 × 10−3 min−1. The coatings were stable and showed no significant decrease in degradation activity even after five cycles.

Role of phase content on the photocatalytic performance of TiO2 coatings deposited by suspension plasma spray

In this work, suspension plasma spraying (SPS) with different hydrogen (H2) flow rates was employed to produce TiO2 coatings with various phase contents, oxygen contents, and roughnesses. To eliminate the role of the morphology and oxygen content on the photocatalytic activity, all coatings were polished to reach the same roughness followed by heat-treatment at 550 °C in air for 48 h. Then coatings were analyzed by X-ray diffractometer (XRD), confocal laser microscope, scanning electron microscope (SEM), UV–visible spectrometer, Raman microscope, and thermogravimetric analyzer. The XRD data indicated that the percentage of anatase decreased as function of H2 flow rates, and almost 46% of anatase transformed to rutile during SPS process at the highest H2 flow rate. Moreover, the photocatalytic performance was evaluated by monitoring the degradation of methylene blue under visible light irradiation, and the results indicated that anatase phase positively enhances the photocatalytic activity of TiO2 coatings.

Photocatalytic Activity of TiO2 Coatings Fabricated on Al2O3 by Mechanical Coating Technique

The titanium coatings were prepared on Al2O3 balls by mechanical coating technique (MCT), and then the coatings were oxidized to titanium oxides(TiO2) films at 300–600 °C. The effects of different milling time and oxidation temperature on thickness of films were studied. The composition and microstructure of the films were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that the thickest coatings with an average thickness of 20 µm were obtained at the milling time of 15 h. In addition, with the increase of the oxidation temperature, the oxidation of the film is increased. When the milling time is 15 h, the oxidation temperature is 500 °C, and the addition of photocatalyst is 1 g/mL. The films have the best photocatalytic performance when the degradation rate of methyl orange solution reaches the maximum value of 74.9 %, and the films have a good reusability.

Enhanced photocatalytic activity of titania coatings fabricated at relatively low oxidation temperature with sulfate-acid-bath pretreatment

With the purpose of enhancing the photocatalytic activity of titania (TiO2) coatings with low cost, a method of sulfuric-acid-bath pretreatment followed by simple oxidation in air has been proposed to fabricate TiO2 coatings. The effect of oxidation temperature on the crystal structure, surface morphologies and photocatalytic activity of TiO2 coatings was investigated, to figure out the suitable oxidation temperature. XRD and Raman’s results show that the phase transformation of TiO2 starts at 773 K. The surface morphologies of TiO2 coatings clearly show the porous-like structure at lower than 873 K. With raising the temperature, the photocatalytic activity of TiO2 coatings firstly increases, then decreases, and reaches the highest at relatively low oxidation temperature of 773 K.

Uniform coating of TiO2 nanoparticles using biotemplates for photocatalytic wastewater treatment

Immobilization of TiO2 particles over substrates like glass can facilitate the separation after photocatalytic runs. Photocatalytic activity of TiO2 coatings is related to its morphology, crystallography, optical properties and adherence of the coating. Biotemplates, including animal-based and herbal-based templates are inexpensive, biocompatible and abundant and can control the quality of TiO2 coating. In this study the effects of biotemplates such as agar, gelatin, and starch on the physiochemical properties of TiO2 coatings were investigated. Synthesized coatings were characterized by XRD, BET, FESEM, TEM, FTIR, EDX, and UV-Vis DRS analyses. The results showed that using biotemplates reduces the TiO2 crystallite size. Template-free TiO2 had 30 nm crystallite size, but using templates like agar decreased the size to 18 nm. Moreover, the addition of biotemplates decreased the thickness of TiO2 coatings compared to template free coating. And the use of biotemplates also limits the pore size distribution and increases BET surface area. According to EDX, TiO2 coating with agar indicated a uniform Ti distribution and crack-free homogenous morphology. TEM analysis of agar-templated TiO2 film showed a uniform morphology of TiO2 particles with average particle size of 20 nm. The UV-Vis DRS also confirmed a reduction in the band gap of TiO2 after the introduction of biotemplates. The study of the photocatalytic performance of samples showed that agar-templated TiO2 coating was able to remove 62.4% of methylene blue, while the coatings synthesized with gelatin and starch were just able to remove 42.77% and 35%, respectively. The TiO2 coating with agar was studied at different pH values and different initial methylene blue concentrations as well. The stability test of agar-templated TiO2 coating after four runs indicated just 5% of activity lost.

Photocatalytic methylene blue degradation on multilayer transparent TiO2 coatings

This paper presents the influence of coating thickness on the photocatalytic activity of TiO2 coatings. Methylene blue decomposition under UV light was tested. Transparent anatase TiO2 thin films were prepared by the sol-gel method using alcoholic solutions. Thin films were deposited on a borosilicate glass substrate by the multiple dip-coating technique across a much wider range than is typically described in literature, specifically, from 1 to 12 dip-coating cycles. The degradation of MB dissolvent in water was measured by UV-Vis spectroscopy. The structure, morphology and optical properties of thin film coatings were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The crystalline structure of TiO2 films was identified as the anatase phase, consisting of uniform spherical particles from 25 to 32 nm depending on the number of dip-coatings cycles. Decreasing roughness and optical band gaps were also observed in the produced oxide films with increasing numbers of dip-coating cycles. The reaction rate of discoloration of the dye solution by photocatalytic degradation is strongly related to the thickness of the layer, the number of layers and its morphology. The thicker the oxide layer, the faster the reaction; however, this relationship is not linear. In addition, in this article, a methylene blue discoloration reaction model was proposed which takes into account stoichiometry, reagent electric charge balance and the REDOX type of reaction.

Plasma electrolytic titanium oxide applied for pathogenic bacteria inactivation

ABSTRACTPhotocatalysis over TiO2 substrates is widely used in effluent treatment specially for organic compounds and for inactivation of pathogenic microorganisms. In the present work, TiO2 coatings were synthesized by plasma electrolytic oxidation (PEO) and its pathogenic bacteria inhibitory photoactivity was investigated. The photocatalytic activity of TiO2 coatings was investigated for the inactivation of Staphylococcus aureus and Salmonella bongori and the results were correlated with pore diameter and crystallite size. It was observed that both morphology and microstructure have an important role in the antibacterial photoactivity. The results show the larger the crystallite size and pore diameter the greater the photoactivity of the material. Porous materials that have a smaller pore diameter than the microorganism to be inactivated have low photoactivity. On the other hand, films that have pores with a diameter of the order or larger than the size of the microorganism to be inactivated present greater photocatalytic activity, once its pores allow the entrance and internal adsorption of the microorganisms, leading to the rupture of the cell membrane. Thus, in order to not sub-utilize the photocatalysts surface area, TiO2 coatings for using in microorganism inactivation must be synthesized with pore diameter bigger than the size of the microorganism.

The role of thermal annealing in controlling morphology, crystal structure and adherence of dip coated TiO2 film on glass and its photocatalytic activity

In this paper, sol–gel technique with dip coating was used to prepare photocatalytic TiO2 coatings on glass plates. Effect of different calcination temperatures of 400, 500, 600 and 700 °C on the photocatalytic activity of TiO2 coatings was investigated in de-colorization of methylene blue under UV-A irradiations in a batch reactor. The highest methylene blue degradation was achieved by the coating calcined at 500 °C. Lower and higher calcination temperatures had lower activity in degradation of methylene blue. The TiO2 coating calcined at 500 °C removed almost 90% of initial methylene blue while other coatings barley removed 30% of dye after 400 min of UV irradiations. XRD, FESEM, FTIR, EDX and TEM showed that the calcination temperature had a great influence on crystalline structure of TiO2 coatings. The coating calcined at 400 °C indicated mixed phase of anatase and rutile but with increasing the calcination temperature to 500 °C, crystalline phase transformed from mixed phase to pure phase of anatase. The TiO2 crystallites were small and highly dispersed in 500 °C calcined coating compared to other calcination temperatures. The sample calcined at 500 °C had a uniform morphology with smooth coating of small nanoparticles without any crack. Adhesion of TiO2 coatings on glass plates was investigated by atomic absorption of treated wastewater and sonication weight loss of TiO2 coatings. The amount of Ti leached from studied coatings was negligible and the 500 °C calcined coating showed the lowest weight loss after sonication. The effect of pH of wastewater, initial concentration of methylene blue and number of TiO2 coated glass plates was evaluated in decolorization of methylene blue using the TiO2 coating calcined at 500 °C.

Influence of iron doping on photocatalytic activity of TiO2 coatings formed on titanium by plasma electrolytic oxidation

This paper presents the results of our recent investigation focused on the preparation and possible photocatalytic application of iron doped TiO2 coatings formed by plasma electrolytic oxidation of high purity titanium in electrolyte containing FeSO4. The morphology, phase and elemental composition, and absorption band of the coatings were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The photocatalytic activity of coatings was evaluated by measuring the degradation of methyl orange under simulated sunlight conditions. It was found that the addition of iron precursor to electrolyte solution improves the photocatalytic properties of obtained coatings with respect to pure TiO2 coating. The incorporation of iron in TiO2 lattice was identified as the main factor affecting the increase of photocatalytic activity. The highest photocatalytic activity was observed when coatings were processed for 2 min with addition of 1 g/L FeSO4 to electrolyte.

Effect of Tb3+ doping on the photocatalytic activity of TiO2 coatings formed by plasma electrolytic oxidation of titanium

Tb doped TiO2 coatings are formed by plasma electrolytic oxidation (PEO) of titanium in water solution of 10 g/L Na3PO4⋅12H2O with addition of Tb4O7 powder. Surface morphology, chemical, and phase composition of obtained PEO coatings are investigated utilizing scanning electron microscopy equipped with energy dispersive x-ray spectroscopy and X-ray diffraction. Uniformly distributed Ti, O, P, and Tb are identified as the main constituents of the coatings. Diffraction patterns of obtained coatings show well pronounced reflections inherent to anatase phase of TiO2. Performed photoluminescence measurements indicate that incorporated Tb is in trivalent oxidation state. Photoluminescence emission spectra feature two overlapping regions: the first region is related to band of TiO2 host and the second region which features several emission bands is ascribed to f-f transitions of Tb3+ from excited level 5D4 to lower levels 7FJ (J = 3,4,5, and 6). The photocatalytic activity (PA) of Tb3+ doped TiO2 coatings is probed by measuring the photodegradation of methyl orange under simulated sunlight conditions, suggesting that the main factor affecting PA is concentration of Tb3+ ions incorporated into coatings. Tb3+ doped TiO2 coatings formed for short time have better PA than pure TiO2 coatings formed under the same conditions; the highest PA is observed for the coating formed after 1 min of PEO process. Presence of Tb3+ ions into TiO2 coatings in small concentration improves PA through effective suppression of electron/hole recombination.

Visible-light-driven oxygen vacancies and Ti3+ co-doped TiO2 coatings prepared by mechanical coating and carbon reduction

The photocatalytic activity of TiO2 coatings was improved through introducing the defects including Ti3+ and oxygen vacancy by means of mechanical coating followed by carbon reduction at elevated temperatures. The samples were characterized by XRD, SEM, XPS, EPR and UV–vis absorption spectrum. The XRD results showed that the phase transformation from TiO2 to Ti4O7 occurred when temperature was raised to 1173K holding for 0.5h. The XPS and EPR results confirmed that the defects including Ti3+ and oxygen vacancies in the surface and bulk of TiO2 coatings. Furthermore, the concentration of the bulk defects was increased with the increase of reduction temperature or holding time. The UV–vis absorption spectra revealed that the carbon reduction greatly enhanced visible light absorption due to the introduction of Ti3+ and oxygen vacancies. A moderate relative concentration ratio of bulk and surface defects including Ti3+ and oxygen vacancies favored to improve the photocatalytic activity.

Influence of carbon atmosphere on surface morphology and photocatalytic activity of TiO2 coatings by multi-heat treatment

Photocatalyst titanium dioxide (TiO2) coatings on alumina (Al2O3) balls had been prepared by mechanical coating technique with titanium (Ti) powder and multi-heat treatment (pretreatment-oxidation–reduction). The influence of carbon atmosphere during multi-heat treatment on the surface structure and photocatalytic activity of TiO2 coatings was investigated and characterized. Results show that thin coatings of TiO2 and Ti2CO form on the surface of Ti coatings during pretreatment in air or in carbon atmosphere, respectively. Due to the pretreatment, different surface morphologies of rutile TiO2 form on the surface of Ti coatings, during subsequent oxidation in air. Oxygen vacancies are generated in the lattice of rutile TiO2, during subsequent reduction in carbon atmosphere. The photocatalytic activity of the TiO2 coatings prepared by multi-heat treatment is effectively enhanced, compared with the TiO2 coatings prepared by solo-oxidation of Ti coatings. The visible light photocatalytic activity of TiO2 coatings treated in carbon atmosphere could be effectively enhanced by more than eight times. The photocatalytic activity under ultraviolet is more related with nano-fiber morphology, while the photocatalytic activity under visible light is related with the narrowed band gap.

Effect of hydrodynamics during sol–gel synthesis of TiO2 nanoparticles: From morphology to photocatalytic properties

In this study, the role of mixing hydrodynamics during the sol–gel synthesis of titania nanoparticles and the consequences on their photocatalytic properties were investigated. For the first time three different T-mixer geometries were tested. Alcoholic solutions of titanium tetra-isopropoxide and water were mixed in three different T-mixers with turbulence promoters and thus different mixing characteristics. The changes of nanoparticle sizes during the induction time of the sol–gel process were followed by dynamic light scattering and velocity and turbulence fields were simulated by Computational Fluid Dynamics (CFD) for the three T-mixer geometries. The results indicated that macro-mixing is crucial during the first step as it determines the nucleation rate and then the primary particle size. The micro-mixing has an influence on particle properties, especially on particle stability. Titanium dioxide nanoparticles synthesized by the sol–gel process were deposited on alumina supports. A homogeneous film of about 200nm was deposited in all cases. Degradation of Acid Orange 7 (AO7) was used to evaluate the photocatalytic activity of TiO2 coatings. No difference was observed between the photoactivity of synthesized TiO2. Total mineralization of the dye occurred after 24h irradiation.

Structure and photocatalytic activity of TiO2 coatings deposited by atmospheric plasma spraying

Titanium dioxide coatings were deposited by utilizing an atmospheric plasma spraying (APS) system, at different spray parameters like argon flow rate and arc current. The structure and crystallite size of the as-sprayed TiO2 coatings were characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The photo-catalytic efficiency was determined in an environmental test chamber and evaluated from the conversion rate of ethanol. The as-sprayed TiO2 coatings were photo-catalytically reactive for the degradation of ethanol and the photo-catalytic activity was influenced by spray conditions.

The effects of thermal spray technique and post-deposition treatment on the photocatalytic activity of TiO2 coatings

Abstract Titanium dioxide coatings were deposited by two thermal spray methods: high velocity oxygen fuel and atmospheric plasma spray. The coatings were characterized by XRD, SEM, Raman and UV–vis spectroscopy. The photocatalytic activities of the samples towards decomposition of methylene blue were also determined. As-prepared samples showed a very limited photocatalytic activity. In contrast, post-deposition oxidation of the samples in air resulted in significantly improved catalytic performance of the coatings. It appears that the oxidation state of titania played a critical role in photocatalytic activity given that partially reduced coatings resulted a very low activity. This conclusion was consistent with the observation of the Ti 8 O 15 phase in the as-prepared samples. However, when oxidized, parameters such as the anatase content became a dominant factor in catalytic performance of the samples. The coating sprayed by high velocity oxygen fuel resulted in much higher activity than the atmospheric plasma sprayed coating, which can be attributed to higher anatase content of the former.

Determination of the photocatalytic activity of TiO2 coatings on clay roofing tile substrates methylene blue as model pollutant

The photocatalytically active mesoporous coatings, based on titanium dioxide sols (Degussa), of the fired clay roofing tiles substrate were prepared by using poly(ethylene glycol) (PEG) M-600 and M-4000, as the structure directing agents. The coatings were deposited using spray technique followed by thermal treatment. Photocatalytic activity of the TiO2 coatings was evaluated by aqueous solution of methylene blue as model dye, deposited on the top of the coatings, after irradiation with UV light. The results were compared with the photocatalytic efficiency of some commercial self-cleaning products (clay roofing tiles, glass). The newly design coatings showed an interesting decolourisation performance (over 30 % after 24 h). It appeared that the procedure of photocatalytic activity determination, in the case of porous substrates, should be renewed by a preadsorption process.