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.     

Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

Polyimide/titania (PI/TiO₂) nanocomposite films have been successfully fabricated through the in situ formation of TiO₂ within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)₄] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO₂ hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO₂ nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.     

Chemical modification of TiO2 nanoparticles as an effective way for encapsulation in polyacrylic shell via emulsion polymerization

Encapsulation of inorganic nanoparticles by polymers is one of the interesting research topics that lead to the synthesis of nanocomposites. These nanocomposite materials comprise the properties of both organic polymer and inorganic nanoparticles. Here, hybrid latex particles with core–shell nanostructure were prepared via semi-batch emulsion polymerization. Copolymers of (methyl methacrylate-butyl acrylate) and (dimethylaminoethyl methacrylate-butyl acrylate-acrylic acid) were formed as the inner and outer layers, respectively on the surface of modified TiO₂ nanoparticles as the core. In order to create compatibility between inorganic and polymeric phases, modification of TiO₂ nanoparticles was performed with glycidyl methacrylate with an optimized procedure for the first time and then emulsion polymerization was carried out. The products of each step were fully characterized. The results of dynamic light scattering, TEM and SEM analyses proved the formation of encapsulated hybrid latex particles. DLS and SEM data revealed that the sizes of nanocomposite particles vary between 85 and 120 nm for 0–5 wt% of the modified TiO₂ nanoparticles. Physico-mechanical properties of the obtained nanocomposite films were studied by DMTA. It was found that using only 3 wt% of modified TiO₂ improved those properties of resulting films remarkably.     

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%).     

Structural,electrical and optical properties of molybdenum-doped TiO2 thin films

Molybdenum doped TiO₂ (MTO) thin films were prepared by radio frequency (RF) magnetron sputtering at room temperature and followed by a heat treatment in a reductive atmosphere containing 90% N₂ and 10% H₂. XRD and FESEM were employed to evaluate the microstructure of the MTO films, revealing that the addition of molybdenum enhances the crystallization and increases the grain size of TiO₂ films. The optimal electrical properties of the MTO films were obtained with 3 wt% Mo doping, producing a resistivity of 1.1×10^?3 Ω cm, a carrier density of 9.7×10²⁰ cm^?3 and a mobility of 5.9 cm²/Vs. The refractive index and extinction coefficient of MTO films were also measured as a function of film porosity. The optical band gap of the MTO films ranged from 3.28 to 3.36 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.14 eV was attributed to the Burstein–Moss effect.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Characterization of single crystalline a-TiO2 films on MgAl2O4(100) substrates by MOCVD

Anatase phase TiO₂ (a-TiO₂) films have been deposited on MgAl₂O₄(100) substrates at the substrate temperatures of 500–650 °C by the metal organic chemical vapor deposition (MOCVD) method using tetrakis-dimethylamino titanium (TDMAT) as the organometallic (OM) source. The structural analyses indicated that the TiO₂ film prepared at 600 °C had the best single crystalline quality with no twins. The out-of-plane and in-plane epitaxial relationships of the film were a-TiO₂(001)||MgAl₂O₄(100) and TiO₂[100]||MgAl₂O₄[100], respectively. A uniform and compact surface with stoichiometric composition was also obtained for the 600 °C-deposited sample. The average transmittance of all the TiO₂ films in the visible range exceeded 91% and the optical band gap of the films varied from 3.31 to 3.41 eV.     

Photocatalytic and adsorptive treatment of 2,4-dinitrophenol using a TiO2 film covering activated carbon surface

Anatase titanium dioxide (TiO₂) in particle sizes of roughly 0.5–20 μm was prepared from amorphous TiO₂ in an aqueous H₂O₂ solution by heating at 90 °C for 9 h and directly deposited on a PET film. On the other hand, granular activated carbon (AC) particles in sizes of 1–2 mm in diameter were adhesively deposited on a PET film, and their surfaces were also coated with TiO₂. The resulting three preparations (TiO₂-, AC-, and TiO₂/AC-PET films) were set up in an annular-flow reactor to treat aqueous solutions of 2,4-dinitrophenol (DNP) in a batch-recirculation mode. The rate of DNP adsorption onto the TiO₂/AC-PET film without UV irradiation was almost the same as that onto the AC-PET film, indicating that the attraction of DNP to AC was not lowered in the presence of TiO₂ film. Observation of SEM photographs suggests that this result is attributed to the porous structure of the thin TiO₂ film covering AC particles. The rate of DNP removal by the TiO₂-AC PET film under UV irradiation was 2.9 times higher than that by the TiO₂-PET film under UV irradiation, and was 1.1 times higher than the rate of DNP adsorption onto the AC-PET film. The rate of DNP removal by the AC-PET film decreased by 40% after six runs, while that by the TiO₂/AC-PET film decreased by 22%. Durable experiments using the TiO₂/AC-PET and AC-PET films clarified that the lifetime of the TiO₂/AC-PET film is at least two times longer than that of the AC-PET film. This result suggests that DNP molecules are photocatalytically decomposed when passing through the porous TiO₂-PET film, which lessens a burden of DNP adsorption on AC. Moreover, the DNP treatments in the batch-recirculation flow system suggested that the TiO₂/AC-PET film saturated with DNP can be successfully regenerated at 60 °C.     

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.     

Effect of Pt or Pd doping on stability of TiO2 nanoparticle suspension in water

Stability of suspensions of TiO₂ nanoparticles synthesized by the flame aerosol reactor (FLAR) could be altered by doping TiO₂ nanoparticles with Pt, Pd, or Pt–Pd dopants. It was found that doping of TiO₂ with Pd or Pt could contribute to the control of the agglomeration of TiO₂ suspended in water. With the change of doping content, the isoelectric point (IEP) of stable TiO₂ suspension decreased gradually from 5 to 3.6 while the specific surface area was increased from 43.27 to 60.84 m²/g. With pH > 6.0, 2 wt% Pt–Pd/TiO₂ suspension exhibited the lowest agglomeration behavior. The plausible intrinsic structures of Pt, Pd, and Pt–Pd doped TiO₂ nanoparticles were proposed and discussed with respect to their IEP based on the DLVO theory.     

Synthesis of phase- and shape-controlled TiO2 nanoparticles via hydrothermal process

The TiO₂ nanoparticles with anatase (5.7–12.7 nm), rutile (5.4–8.8 nm), mixed (4.4–8.6 nm) phase were individually prepared using the hydrothermal method. The structure and shape of the particles could be controlled by careful alterations of the hydrothermal conditions. Herein, the TiO₂ nanoparticles were successfully synthesized by employing Ti-isopropoxide as the titanium source into hydrochloric acid solution at mild conditions. The crystal structures such as anatase, rutile and mixed phase of TiO₂ nanoparticles were determined by means of concentration of hydrochloride. Especially, we observed that the rutile TiO₂ crystallites were grown into one-dimensional nanostructures, especially, nanowires, with increasing reaction time. The mechanism of the crystallization of the nanoparticles and the growth habit of TiO₂-rutile structure were discussed.     

Supercritical CO2 based processing of amorphous fluoropolymer Teflon-AF: Surfactant-free dispersions and superhydrophobic films

We report the application of a modified RESS process to create and collect in high yield nanoparticles of an amorphous fluoropolymer, Teflon-AF1600. The nanoparticles with diameters ranging from 10 to 100 nm can be synthesized from polymer solutions in supercritical CO₂ at 300 bar and 60 °C. The nanoparticles are collected by formation of dry ice in a liquid nitrogen-cooled trap. Nanoparticles embedded in dry-ice can be dispersed in organic solvents (acetone, ethanol, and n-heptane) creating surfactant-free dispersions. When dispersed in water, the nanoparticles self-assemble at the air–water interface forming a mechanically robust, superhydrophobic film. The film can support large water droplets (up to volume 250 μL) without breaking and is impermeable to water. The films cast from dispersions as well as those lifted-off water surface, are highly porous and superhydrophobic in nature (water contact angle θ_adv = 162°). This work demonstrates the utility of supercritical fluids based processing of fluoropolymers.     

TiO2–SnO2 nanomaterials for gas sensing and photocatalysis

Nanopowders of TiO₂–SnO₂ over a full composition range extending from 100 mol% TiO₂ to 100 mol% SnO₂ are obtained by the sol–gel method from TTIP and SnCl₂·5H₂O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO₂ is 95 m²/g while that of SnO₂ amounts to 129 m²/g. The highest SSA of 156 m²/g is achieved at 20 mol% of TiO₂. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO₂–SnO₂ over the range of 0–80 mol% TiO₂ is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO₂) to 3.18 eV (100 mol% TiO₂).     

Preparation of oriented SiO32− doped TiO2 film and degradation of methylene blue under visible light irradiation

SiO₃^2? doped TiO₂ films with oriented nanoneedle and nanorectangle block structure has been firstly synthesized by hydrothermal synthesis method. The prepared samples are characterized, X-ray diffraction (XRD) results demonstrate that the SiO₃^2? doped TiO₂ films are rutile and brookite phases. The scanning electron microscope (SEM) analysis reveals that the quantity of O₂ affects the morphology of the SiO₃^2? doped TiO₂ films (SiTiA films prepared with unmodified substrate). The SiO₃^2? doped TiO₂ films (SiTiB films prepared with modified substrate) display two layers, one is porous structure, the other is nanoneedle structure. UV–vis, IR, transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) microscopy all prove that SiO₃^2? have been doped in the TiO₂ crystal structure. They have remarkable red shift and higher photocatalytic activity of degradation of methylene blue than P-25 under visible light (λ > 420 nm) irradiation. Besides, photocatalytic activity of the film is stable during 4 times recycling.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

Preparation and characterization of transparent indium- doped TiO2 films deposited by MOCVD

Titanium dioxide (TiO₂) films doped with different indium (In) concentrations have been prepared on SrTiO₃ (STO) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) analyses revealed the TiO₂ films doped with low In concentrations to be [001] oriented anatase phase and the films with high In concentrations to present polycrystalline structures. The 1.8% In-doped TiO₂ film exhibited the best electrical conductivity properties with the lowest resistivity of 8.68×10⁻² Ω cm, a Hall mobility of 10.9 cm² V⁻¹ s⁻¹ and a carrier concentration of 6.5×10¹⁸ cm⁻³. The films showed excellent transparency with average transmittances of over 85% in the visible range.     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

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.     

The effects of deposition temperature on structure and dielectric properties of Ba0.6Sr0.4TiO3 thin films produced by pulsed laser deposition

The effects of deposition temperature on orientation, surface morphology and dielectric properties of the thin films for Ba_0.6Sr_0.4TiO₃ thin films deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition were investigated. X-ray diffraction patterns revealed a (2 1 0) preferred orientation for all the films. With rising substrate temperature from 650 °C to 700 °C, the crystallinity and crystal grain size of the films increase, the relative dielectric constant increases, but the dielectric losses have not obvious difference. The film deposited at 350 °C and annealed at 700 °C has strongly improved roughness and dielectric permittivity compared with the film only deposited directly at 700 °C. Three distinct relaxation processes within tan(δ) were found for the Ba_xSr_1?xTiO₃ film: a broadened process of the film relaxation, an intermediate peak which originates from Maxwell–Wagner–Sillars polarization, and an extremely slow process ascribed to leak current. The complex dielectric permittivity and loss can be fitted by an improved Cole–Cole model corresponding to a stretched relaxation function.     

Transparent and high infrared reflection film having sandwich structure of SiO2/Al:ZnO/SiO2

New transparent and high infrared reflection films having the sandwich structure of SiO₂/Al:ZnO(AZO)/SiO₂ were deposited on the soda-lime silicate glass at room temperature by radio frequency (R.F.) magnetron sputtering. The optical and electrical properties of SiO₂ (110 nm)/AZO (860 nm)/SiO₂ (110 nm) sandwich films were compared with those of single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. The results show that these sandwich films exhibit high transmittance of over 85% in the visible light range (380–760 nm), and low reflection rate of below 4.5% in the wavelength range of 350–525 nm, which is not shown in the conventional single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. Further these sandwich films display a low sheet resistance of 20 Ω/sq by sheet resistance formula and high infrared reflection rate of above 80% in the wavelength range of 15–25 μm. In addition, the infrared reflection property of these sandwich films is determined mainly by the AZO film. The outer SiO₂ film can diminish the interference coloring and increase transparency; the inner SiO₂ film improves the adhesion of the coating to the glass substrate and prevents Ca²⁺ and Na⁺ in the glass substrate from entering the AZO film.