Effect of TiO2 nanoparticles on the antibacterial and physical properties of polyethylene-based film

TiO₂ nanoparticles and their application in packaging systems have attracted a lot of attention because of its antimicrobial activity. In this work, effect of TiO₂ nanoparticles on the antibacterial and physical properties of polyethylene (PE)-based film was investigated. Results indicated that the antibacterial activity of TiO₂-incorporated PE films should be due to the killing effect property of TiO₂ nanoparticles against microorganisms. The TiO₂-incorporated PE film exhibited more effective antibacterial activity for Staphylococcus aureus. The antibacterial activity to inactivate Escherichia coli or S. aureus was improved by UV irradiation. The inhibition ratio of TiO₂-incorporated PE films sample irradiated for 60 min by UV light was improved significantly, which were 89.3% for E. coli and 95.2% for S. aureus, respectively, compared to that of TiO₂-PE film without UV irradiation. The analysis of physical properties revealed that TiO₂ nanoparticles increased the tensile strength and elongation at break of PE-based film. The climate resistance of nano-TiO₂ films is greatly enhanced, compared to that of the blank PE film. Water vapor transmission increased from 18.1 to 24.6 g/m²·24 h with the incorporation of TiO₂ nanoparticles. Results revealed that PE based film incorporating with TiO₂ nanoparticles have a good potential to be used as active food packaging system.     

Adsorptive removal and oxidation of organic pollutants from water using a novel membrane

To develop an effective method to remove and mineralize trace organic pollutants, a series of composite functional membranes containing immobilized ACF (activated carbon fibre) powder (<300 mesh) and Ce³⁺-TiO₂, a combination of adsorbent and photo-catalyst on terylene (PET) filter cloth, was prepared by using a sol–gel and dip coating method. As high as 93% BPA (bisphenol A) pollutant can be separated successfully by adsorption onto the membrane in a series of batch adsorption tests, 40% removal was achieved in dynamic filtration/adsorption test, which also removed 98% koalinite suspended solids at the same time. The measured adsorption of BPA corresponds to 37.0, 70.6 and 62.2 mg (BPA)/g(ACF) for three membranes A, B and C, where the weight ratio of ACF to ACF + TiO₂ was 29.9%, 17.6% and 11.3% respectively in batch adsorption tests (50 ml solution) and 25.48 mg (BPA)/g(ACF) for membrane A after 2 h adsorption in 200 ml solution. After dynamic filtration, the total adsorption capacity was 81.0 mg (BPA)/g(ACF) for membrane A. It is noteworthy that membrane adsorption can be regenerated by UV/Fenton treatment. Order of BPA adsorption quantity is 1st > 2nd > 3rd time use for membrane C, due to loss of ACF resulted from the supersonic treatment before oxidative regeneration. Introducing TEOS in the preparation of sol–gel solution and subsequent coating to form composite membrane, improved membrane adsorption stability in UV/Fenton regeneration treatment.     

Application of TiO2/perlite photocatalysis for degradation of ammonia in wastewater

The purpose of this study was removal of ammonia by a new photocatalytic process from synthetic wastewater under UV irradiation. TiO₂ was used as the photocatalyst and immobilized on perlite granules as a supporter. The prepared catalysts were characterized by SEM and FTIR analysis showed that TiO₂/perlite catalyst has mesoporous structures and uniform coating of TiO₂ on support. Also, the optimum efficiency of photocatalytical degradation of ammonia was obtained at pH 11 for UV intensity irradiation with 125 W lamp. About 68% degradation of ammonia in wastewater was achieved after 180 min of irradiation by using the optimized reaction conditions.     

Growth mechanism and photocatalytic activity of chrysanthemum-like anatase TiO2 nanostructures

Chrysanthemum-like hierarchical anatase TiO₂ nanostructures self-assembled by nanorods have been successfully fabricated by a simple solvothermal route without using template materials or structure-directing additives. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectrometer system (Raman), UV–vis absorption spectroscopy (UV–vis) and N₂ adsorption–desorption measurement. The results indicate that synthesized chrysanthemum-like hierarchical anatase TiO₂ nanostructures have a spherical shape with an average diameter of 1.5 μm and they are composed of nanorods with a width of about 30 nm and a length of about 300 nm. The pore distribution of the sample exhibits two kinds of pores. Such mesoporous structure of the sample might be extremely useful in photocatalysis because they possess efficient transport pathways to the interior and supplies higher specific area for more pollutant molecules to be absorbed. In addition, the synthesized TiO₂ nanostructures show enhanced photocatalytic activity compared with commercial P25 for the degradation of RhB under UV light irradiation, which can be attributed to their special hierarchical structure and high light-harvesting capacity.     

Solar photocatalytic decolorization of dyes in solution with TiO2 film

Application of TiO₂ film to solar photocatalysis of organic dyes, including Methylene Blue (MB) (λ_max, 660 nm), RR195 (λ_max, 540 nm) and RY145 (λ_max, 420 nm), was investigated. It was found that after 6-h solar irradiation, the extent of color degradation of dyes using solar photocatalytic system without TiO₂ film was quite limited. The color removal percentage for MB, RR195, and RY145 was found to be 23.3, −9.3, and −20.7%, respectively, resulting from competitions between the photosensitizing reaction and formation of colored intermediates during solar irradiation. However, as TiO₂ film was applied, the color degradation capability of solar photocatalytic system was significantly improved, in spite of the fact that only approximately 7% of solar irradiation belongs to the UV region. The color removal percentage for MB, RR195, and RY145 was up to 93.6%, 85.3%, and 71.1%, respectively, after 6-h irradiation. We believed that in such a solar photocatalytic system immobilized with TiO₂ film, both the maximum absorbance wavelength of the dye and the adsorbability of the dye on TiO₂ film played significant roles on the rate and efficiency of color removal of the dye solutions. Moreover, the possible reaction mechanism was proposed. The solar photocatalytic process with immobilized TiO₂ film was found to follow the pseudo-first order reaction kinetics. Color removal rate of MB was almost twice of that of RY145. Accordingly, the photocatalytic degradation process using solar light as an irradiation source, and immobilized TiO₂ as a photocatalyst, showed potential application for the decolorization of wastewater.     

Sol–gel reverse micelle preparation and characterization of N-doped TiO2: Efficient photocatalytic degradation of methylene blue in water under visible light

A series of N-substituted titanium (IV) 2-ethyl-1,3-hexanediolate Ti(C₃₂H₆₈O₈) precursor were synthesized by the sol–gel reverse micelle (SGRM) method. The ethylene diaminetetraacetic acid (Na₂EDTA) has been used as a source of nitrogen n species. The obtained solids were calcined at 500 ?C for 1 h to obtain photoactive phases. The effect of nitrogen content (N/Ti = 0.025; 0.03; 0.05 atomic ratios) is examined. The materials were characterized by XRD, BET, TG/DTA and UV–vis reflectance spectroscopy (DRS). Photocatalytic decolourisation of methylen blue (MB) in aqueous solution was carried out using nano, doped TiO₂. Experimental results revealed that N/Ti = 0.05 atomic ratio N-doped TiO₂ required shorter irradiation time for complete decolourisation of MB than pure nano TiO₂ and commercial (Degussa P-25) TiO₂.     

Preparation of dye sensitized solar cell by using supercritical carbon dioxide drying

Dye-sensitized solar cells (DSSC) derived from TiO₂ aerogel film electrodes were fabricated. TiO₂ aerogels were obtained by using sol–gel method and supercritical carbon dioxide (sc-CO₂) drying. First, TiO₂ wet gels were obtained by sol-gel method. Then, the solvents in the TiO₂ wet gels were replaced by acetone. The TiO₂ aerogels were obtained by using sc-CO₂ drying from the TiO₂ wet gels. The conditions of sc-CO₂ drying were at 313, 323 K and 7.8–15.5 MPa. The electrodes with TiO₂ aerogel films were obtained by deposition of the aerogels on glass substrates. The electrodes with TiO₂ aerogel films and a commercial particle film of various thickness were obtained by repetitive coatings and calcinations. The amount of dye adsorbed on the TiO₂ films with sc-CO₂ drying was higher than that of commercial particle film. The amount of dye adsorbed on the TiO₂ films increased with increasing surface area of the TiO₂ film. DSSCs were assembled by using the TiO₂ aerogel film electrodes and their current–voltage performance was measured. The power performance of DSSC made by supercritical drying was higher than that of commercial particles. The DSSC with the film electrode made at 313 K and 15.5 MPa showed the best power performance (J_sc = 7.30 mA/cm², V_oc = 772 mV, η = 3.28%).     

The size and dispersion effect of modified graphene oxide sheets on the photocatalytic H2 generation activity of TiO2 nanorods

Nano graphene oxide (NGO) was produced by further refluxing graphene oxide (GO) sheets in HNO₃, and carboxylic acid functionalized graphene oxide (GO–COOH) was obtained by a simple etherification reaction between GO and chloroacetic acid. The GO, GO–COOH and NGO sheets are combined with TiO₂ nanorods by a two-phase assembling method, and confirmed by transmission electronic microscopy. The GO–TiO₂, GO–COOH–TiO₂ and NGO–TiO₂ composites are used in a comparative study of photocatalytic H₂ generation activity under UV light irradiation. The H₂ generation rate of TiO₂ nanorods was slightly increased from 15 to 30 mL h⁻¹ g⁻¹ by replacing oleic acid ligands with hydrophilic dopamine, and significantly increased to 105 mL h⁻¹ g⁻¹ after combining with GO sheets. The further comparative study shows that GO–COOH–TiO₂ composite has higher H₂ generation rate of 180 mL h⁻¹ g⁻¹ than that of GO–TiO₂ and NGO–TiO₂ composites.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Preparation and characterization of CeO2–TiO2 support for Ru catalysts: Application in CWAO of p-hydroxybenzoic acid

The catalytic wet air oxidation of aqueous solutions of p-hydroxybenzoic acid has been carried out over CeO₂–TiO₂ supported ruthenium catalysts (Ru/Ce–Ti) at 140 °C and 50 bar of air. High activity of ruthenium supported catalysts was observed. It was found that the decrease of the molar ratio Ce/Ti from 3 to 1/3, improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Ti (1/3) > Ru/CeO₂ ≈ Ru/TiO₂ > Ru/TiO₂DT51. Characterization of samples was performed by means of N₂ adsorption–desorption, XRD, UV–visible, TPR, SEM and TEM.     

Dispersant-assisted low frequency electrophoretically deposited TiO2 nanoparticles in non-aqueous suspensions for gas sensing applications

The effect of dispersant on deposition mechanism of TiO₂ nanoparticles at 1 Hz under non-uniform AC fields was investigated. It was found that by adding Dolapix to suspension, deposition pattern is drastically changed enabling particles to enter the gap leaving the electrodes intact. Using low frequency AC electrophoretic deposition technique in the presence of dispersant, we succeeded in fabricating gas sensor in less than 2 min. Gas sensing measurements were performed in the temperature range of 450–550 °C. The results explained that the sensor has good stability in time and repeatability performance toward high response. The maximum sensitivity of about 180 for the TiO₂ nanoparticles sensor is observed with 47 ppm NO₂ gas and the response and recovery times is about 60–150 s. The optimum temperature of the gas sensor was obtained in 450 °C where sensor showed a linear trend up to 50 ppm of NO₂ gas. This sensing behavior in un-doped TiO₂ as NO₂ sensor can be mainly ascribed to the porous structure of the sensing film and its good contacts to the substrate and electrode assembly.     

Absorption boost of TiO2 nanotubes by doping with N and sensitization with CdS quantum dots

A process of obtaining N-doped TiO₂ nanotubes sensitized by CdS nanoparticles is presented, including detailed characterizations performed along the synthesis. Transparent TiO₂ films consisting of nanotubes, 2.5 µm long and of ~60 nm inner diameter, were obtained after anodization of a titanium film deposited onto FTO glass substrate. N-doping was achieved by annealing of TiO₂ film in ammonia. X-ray Photoelectron Spectroscopy measurements showed that nitrogen was substitutionally incorporated in the TiO₂ matrix, with the N:Ti concentration ratio of 1:100. The doping changed the optical properties of the material in such a way that the absorption edge was shifted from 380 nm to 507 nm, as observed from diffuse reflectance spectra. The influence of the microwave (MW) irradiation on the synthesized CdS quantum dots and their optical properties was investigated. It was shown that the diameter of CdS nanoparticles was increased due to releasing of S^2- ions from dimethyl sulfoxide (DMSO) as a consequence of the MW treatment. The (N)TiO₂ films were then used as substrates for matrix assisted pulsed laser deposition of the CdS quantum dots with DMSO as a matrix. The laser parameters for the deposition were optimized in order to preserve the nanotubular structure open, the latter being an important feature of this type of photoanode. The structure obtained under optimized conditions has an additional absorption edge shift, reaching 603 nm.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Self-cleaning ceramic tiles coated with Nb2O5-doped-TiO2 nanoparticles

In this work, 5 mol% Nb₂O₅-doped TiO₂ synthesized sol was sprayed on glazed ceramic tiles. The crystallization of TiO₂ nanoparticles occurs on the surface of the tiles after annealing at 600–900 °C, this innovative approach leads to a drastic decrease in the titania grain size as detected by SEM and XRD. The superhydrophilic and self-cleaning performance was evaluated by measuring the water contact angle under UV irradiation and by degradation of methylene blue according to ISO 10678 and JIS R1703-2. The results showed a high performance of doped samples at all temperatures tested, with a marked dependence on the anatase-to-rutile ratio and crystallite size. At 800 °C, the doped samples achieved water contact angle near to zero in just 15 min of UV irradiation, which confirms the high performance of the self-cleaning ceramic tiles.     

Preparation and photocatalytic activity of silver and TiO2 nanoparticles/montmorillonite composites

Ag–TiO₂/montmorillonite (Ag–TiO₂/MMT) was synthesized as photocatalyst using TiCl₄ hydrolysis to introduce nanosized TiO₂ into the interlayer space of the montmorillonite (MMT). Stable pillared TiO₂/MMT was obtained by calcination at 500 °C, then silver was loaded by reduction of silver nitrate. The physico–chemical properties of the photocatalyst were determined by X-ray diffraction (XRD), infrared spectroscopy (IR), atomic absorption spectrophotometer (AAS), nitrogen gas adsorption (BET method) and UV–Visible spectra. The photooxidation activity for methylene blue (M.B.) degradation was as follows: Ag–TiO₂/MMT > TiO₂/MMT > TiO₂(P25). Among them Ag–TiO₂/MMT had the highest photooxidation activity because of its larger specific surface caused by pillaring and loading of silver for improving its light absorption.     

A novel TiO2 − xNx/BN composite photocatalyst: Synthesis,characterization and enhanced photocatalytic activity for Rhodamine B degradation under visible light

A novel TiO_2 − xN_x/BN composite photocatalyst was prepared via a facile method using melamine–boron acid adducts (M·2B) and tetrabutyl titanate as reactants. The morphological results confirmed that nitrogen-doped TiO₂ nanoparticles were uniformly coated on the surface of porous BN fibers. A red shift of absorption edge from 400 nm (pure TiO₂) to 520 nm (TiO_2 − xN_x/BN composites) was observed in their UV–Vis light absorption spectra. The TiO_2 − xN_x/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) and the highest photocatalytic degradation efficiency reached 97.8% under visible light irradiation for 40 min. The mechanism of enhanced photocatalytic activity was finally proposed.     

Spherical activated carbon as an enhanced support for TiO2/AC photocatalysts

Titanium dioxide nanoparticles prepared in situ by sol–gel method were supported on a spherical activated carbon to prepare TiO₂/AC hybrid photocatalysts for the oxidation of gaseous organic compounds. Additionally, a granular activated carbon was studied for comparison purposes. In both types of TiO₂/AC composites the effect of different variables (i.e., the thermal treatment conditions used during the preparation of these materials) and the UV-light wavelength used during photocatalytic oxidation were analyzed. The prepared materials were deeply characterized (by gas adsorption, TGA, XRD, SEM and photocatalytic propene oxidation). The obtained results show that the carbon support has an important effect on the properties of the deposited TiO₂ and, therefore, on the photocatalytic activity of the resulting TiO₂/AC composites. Thus, the hybrid materials prepared over the spherical activated carbon show better results than those prepared over the granular one; a good TiO₂ coverage with a high crystallinity of the deposited titanium dioxide, which just needs an air oxidation treatment at low-moderate temperature (350–375 °C) to present high photoactivity, without the need of additional inert atmosphere treatments. Additionally, these materials are more active at 365 nm than at 257.7 nm UV radiation, opening the possibility of using solar light for this application.     

Preparation of graphene film decorated TiO2 nano-tube array photoelectrode and its enhanced visible light photocatalytic mechanism

Graphene film decorated TiO₂ nano-tube array (GF/TiO₂ NTA) photoelectrodes were prepared through anodization, followed by electrodeposition strategy. Morphologies and structures of the resulting GF/TiO₂ NTA samples were characterized by scanning electrons microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. In addition, the optical and photoelectrochemical properties were investigated through UV–visible light diffuse reflection spectroscopy, photocurrent response and Mott–Schottky analysis. Furthermore, the photodecomposition performances were investigated through yield of hydroxyl radicals and photocatalytic (PC) degradation of methyl blue (MB) under visible light irradiation. It was found that GF/TiO₂ NTA photoelectrode exhibited intense light absorption both in UV light and visible region, higher transient photoinduced current of 0.107 mA cm⁻² and charge carrier concentration of 0.84 × 10¹⁹ cm⁻³, as well as effective PC performance of 65.9% for the degradation of MB. Furthermore, contribution of several reactive species to the PC efficiency of GF/TiO₂ NTA photoelectrode was distinguished. Moreover, the enhanced visible light PC mechanism was proposed and confirmed in detail.     

Improved hydrophilicity of zinc oxide-incorporated layer-by-layer polyelectrolyte film fabricated by dip coating method

ZnO nanoparticles suspended in poly(acrylic acid) (PAA) were deposited onto layer-by-layer (LBL) polyelectrolyte (PET) films fabricated from poly(allylamine hydrochloride) (PAH) and PAA by dip coating method. Effect of etching time and concentration of ZnO suspension on hydrophilicity of the LBL-PET films before and after UV irradiation was examined using water contact angle measurement. 2.0 M PAH/PAA solutions with a dipping speed of 3.0 cm/min provided stable LBL-PET films with thickness sufficient for HCl etching. Glass substrates with the etched LBL-PET film dipped into 0.2 wt.% ZnO suspension exhibited the contact angle of 10° after irradiated by UV for 60 min.     

Sintering of nanocrystalline Ta2O5 and ZrO2 films compared to that of TiO2 films

Thin (d = 60 nm/140 nm) nanocrystalline Ta₂O₅ and ZrO₂ films were deposited onto SiO₂ flakes, using a liquid route synthesis. Their sintering behaviour was characterized and compared to that of the corresponding powders and the known equivalent TiO₂ film in terms of grain size, grain growth and layer porosity. The effect of the substrate was noticeable on crystallisation process but not on grain growth. The sintering behaviour was actually dictated by the initial size and the packing of the precipitated grains related to the synthesis of the film.