The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films

Hybrid nanocomposite films of titanium dioxide (TiO₂) in polyimide (PI) from 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) and 4,4′-oxydiphthalic anhydride (ODPA) have been successfully fabricated by an in situ sol-gel process. These nanocomposite films exhibit fair good optical transparency up to 40 wt% of TiO₂ content. X-ray diffraction spectroscopy shows three sharp peaks in pure BAO-ODPA PI. It results from the intermolecular regularity. However, the intermolecular regularity in the hybrid film is disrupted by the introduction of TiO₂ nanoparticles with no sharp peak in XRD spectra. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm the formation of TiO₂ particles in PI matrix. The surface Ti content is much lower than the theoretical bulk content in all hybrid films. The ratio of the former to the latter increases with the TiO₂ content and levels off at TiO₂ wt%≥20. Transmission electron microscope (TEM) images show that the TiO₂ phase is well dispersed in the polymer matrix. The size of the TiO₂ phase increases from 10 to 40 nm when the TiO₂ content is 5-30 wt%, respectively.     

Influence of Metal (Au, Ag) Micro-Grid on the Photocatalytic Activity of TiO2 Film

In this paper, we prepared TiO₂ thin film with the surface modified by a connected Au micro-grid via a microsphere lithography strategy, and the modified films show higher photocatalytic activity than the pure TiO₂ film. The photocatalytic activity improved as Au loading increased, obtaining the best performance at a certain loading amount, and then decreased at higher loading amount. This behavior, not observed in TiO₂ films modified with Ag micro-grid, can be attributed to the relationship between the energetic positions and the metal clusters size.     

Efficient preparation of hybrid nanocomposite coatings based on poly(vinyl alcohol) and silane coupling agent modified TiO2 nanoparticles

In the present investigation, at first, the surface of titanium dioxide (TiO₂) nanoparticles was modified with γ-aminopropyltriethoxy silane as a coupling agent. Then a new kind of poly(vinyl alcohol)/titanium dioxide (PVA/TiO₂) nanocomposites coating with different modified TiO₂ loading were prepared under ultrasonic irradiation process. Finally, these nanocomposites coating were used for fabrication of PVA/TiO₂ films via solution casting method. The resulting nanocomposites were fully characterized by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), thermogravimetric analysis/derivative thermal gravimetric (TGA/DTG), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The TEM and SEM results indicated that the surface modified nanoparticles were dispersed homogeneously in PVA matrix on nanoscale and based on obtained results a possible mechanism was proposed for ultrasonic induced nanocomposite fabrication. TGA confirmed that the heat stability of the nanocomposite was improved. UV–vis spectroscopy was employed to evaluate the absorbance and transmittance behavior of the PVA/TiO₂ nanocomposite films in the wavelength range of 200–800 nm. The results showed that this type of films could be used as a coating to shield against UV light.     

Thickness effect in the photocatalytic activity of TiO2 thin films derived from sol-gel process

TiO₂ films in various thicknesses were prepared by sol-gel method, and their photocatalytic activities in the decomposition of gaseous 2-propanol were evaluated. It was found that the photocatalytic activities of transparent TiO₂ films increase with the increase of film thickness: The photocatalytic activity of TiO₂ films in 670 nm-thickness was 3.7 times that of films in 70 nm-thickness. We proposed that the higher photocatalytic activities for the thicker TiO₂ films originate from the greater amount of photogenerated electron and hole pairs, which are transferred from the inside to the surface of TiO₂ films. We also provided some experimental evidences supporting this mechanism.     

Enhanced photoresponse and photocatalytic activities of graphene quantum dots sensitized Ag/TiO2 thin film

TiO₂ thin films were fabricated through hydrothermal method. Silver nanoparticles were loaded on TiO₂ thin films via photoreduction technique. Subsequently, the graphene quantum dots (GQDs) were spin‐coated on the Ag/TiO₂ nanocomposites thin films. The crystal structure, surface morphology and UV‐vis absorbance were tested by XRD, SEM and ultraviolet‐visible spectrophotometer. These results indicated that Ag nanoparticles and GQDs are anchored on the TiO₂ nanorods. Absorbance of Ag/TiO₂ and GQDs/Ag/TiO₂ nanocomposite thin films have been extended into the visible region. Visible‐light response of the samples were investigated by electrochemical workstation. The photoresponse of the sample can be enhanced by sensitization of the Ag nanoparticles and GQDs. The enhanced visible‐light response may be due to the surface plasmon resonance of silver nanoparticles and visible absorbance of GQDs. The highest photocatalytic activity has been observed in the 9‐GQDs/Ag/TiO₂ composite thin film. The efficient charge separation and transportation can be achieved by introducing the Ag nanoparticles and GQDs in the TiO₂ thin film.     

Hydrophilic modification of polypropylene microporous membranes by grafting TiO2 nanoparticles with acrylic acid groups on the surface

Hydrophilic microporous membranes were prepared based on polypropylene (PP) cast films blended with a commercial acrylic acid grafted polypropylene (PP-g-AA) via melt extrusion followed by grafting titanium dioxide (TiO₂) nanoparticles on its surface, annealing and stretching. ATR-FTIR, XPS and EDS analyses showed that the hydrophilic segments of an amphiphilic modifier (PP-g-AA) acted as surface functional groups on the film surface. The results indicated that the presence of the modifier was very important for grafting TiO₂ nanoparticles on the film surface. Compared to PP and PP/PP-g-AA blend films, the water contact angle decreased by a factor of 2.5 after grafting TiO₂ on the surface of the films, meanwhile the water vapor permeability of the microporous membranes prepared from those films increased by a factor of 1.5. All these results indicated that the hydrophilicity of the modified PP membranes was improved.     

Preparation of TiO2/carbon nanotubes photocatalysts: The influence of the method of oxidation of the carbon nanotubes on the photocatalytic activity of the nanocomposites

A method for the preparation of efficient TiO₂/multi-wall carbon nanotubes nanocomposite photocatalysts by precipitation of anatase TiO₂ nanoparticles onto differently oxidized carbon nanotubes is presented. The precursor compound titanium(IV) bromide was hydrolyzed producing pure anatase phase TiO₂ nanoparticles decorated on the surface of the oxidized carbon nanotubes. The oxidative treatment of the carbon nanotubes influenced the type, quantity and distribution of oxygen-containing functional groups, which had a significant influence on the electron transfer properties, i.e., the photocatalytic activity of the synthesized nanocomposites. The results of C.I. Reactive Orange 16 photodegradation in the presence of all the synthesized nanocomposites showed their better photocatalytic activity in comparison to the commercial photocatalyst Degussa P-25.     

Synthesis and dielectric properties of polyaniline/titanium dioxide nanocomposites

Two series of polyaniline–TiO₂ nanocomposite materials were prepared in base form by in situ polymerization of aniline with inorganic fillers using TiO₂ nanoparticles (P25) and TiO₂ colloids (Hombikat), respectively. The effect of particle sizes and contents of TiO₂ materials on their dielectric properties was evaluated. The as-synthesized polyaniline–TiO₂ nanocomposite materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermal analysis (DTA/TGA), and X-ray diffraction (XRD). Dielectric properties of polyaniline–TiO₂ nanocomposites in the form of films were measured at 1 KHz–1 MHz and a temperature range of 35–150 °C. Higher dielectric constants and dielectric losses of polyaniline–TiO₂ nanocomposites than those of neat PANI were found. PANI–TiO₂ nanocomposites derived from P25 exhibited higher dielectric constants and losses than those from Hombikat TiO₂ colloids. Electrical conductivity measurements indicate that the conductivity of nanocomposites is increased with TiO₂ content. The dielectric properties and conductivities are considered to be enhanced due to the addition of TiO₂, which might induce the formation of a more efficient network for charge transport in the base polyaniline matrix.     

Preparation and characterization of TiO2 and polymer nanocomposite films with high refractive index

Novel nanocomposite films of TiO₂ nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol‐A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent‐resistance, good thermal stability, and mechanical properties were prepared by incorporating surface‐modified TiO₂ nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO₂ nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long‐chain alkyl amines. These TiO₂ nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free‐standing films were obtained by drying a mixture of TiO₂ nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO₂ nanoparticles of 3–6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO₂ nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films of TiO₂ and poly(bisphenol‐A and epichlorohydrin) was in the range of 1.58–1.81 at 589 nm, which linearly increased with the content of TiO₂ nanoparticles from 0 to 80 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Aging Studies on Food Packaging Films Containing β-Cyclodextrin-Grafted TiO2 Nanoparticles

Polymeric materials, such as polyvinyl alcohol (PVA) and ethylene–PVA copolymers (EVOH) are widely used in the food sector as packaging materials because of their excellent properties. TiO₂ nanoparticles (NPs) show photocatalytic activity; when added to the aforementioned polymers, on the one hand, they are expected to provide bactericidal capacity, whereas on the other hand, they could favor nanocomposite degradation. These types of nanoparticles can be derivatized with cyclodextrin macromolecules (CDs), which can act as food preservative carriers, increasing the packaging food protective properties. In this work, films containing β-Cyclodextrin (βCD)-grafted TiO₂ nanoparticles and PVA or EVOH were prepared. Regarding the photocatalytic activity of the nanoparticles and the possible environmental protection, accelerated aging tests for PVA, EVOH, and their composites with cyclodextrin-grafted TiO₂ nanoparticle (NP) films were performed by two methods, namely, stability chamber experiments at different conditions of temperature and relative humidity and UV light irradiation at different intensities. After analyzing the systems color changes (CIELAB) and Fourier transform infrared spectroscopy (FTIR) spectra, it was observed that the film degradation became more evident when increasing the temperature (25–80 °C) and relative humidity percentage (28–80%). There was no significant influence of the presence of CDs during the degradation process. When irradiating the films with UV light, the largest color variation was observed in the nanocomposite films, as expected. Moreover, the color change was more relevant with increasing NP percentages (1–5%) due to the high photocatalytic activity of TiO₂. In addition, films were characterized by FTIR spectroscopy and variation in the signal intensities was observed, suggesting the increase of the material degradation in the presence of TiO₂ NPs.     

Enhanced Solid‐Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)‐TiO2 Nanocomposite Film with Bismuth Oxyiodide

A new type of photodegradable poly(vinyl chloride)‐bismuth oxyiodide/TiO₂ (PVC‐BiOI/TiO₂) nanocomposite film was prepared by embedding a nano‐TiO₂ photocatalyst modified by BiOI into the commercial PVC plastic. The solid‐phase photocatalytic degradation behavior of the as‐prepared film was investigated in ambient air at room temperature under UV light irradiation, with the aid of UV‐Vis spectroscopy, weight loss monitoring, scanning electron microscopy, and FT‐IR spectroscopy. Compared to the PVC‐TiO₂ nanocomposite film, the PVC‐BiOI nanocomposite film and the pure PVC film, the PVC‐BiOI/TiO₂ nanocomposite film exhibited a higher photocatalytic degradation activity. The optimal mass ratio of BiOI to TiO₂ was found to be 0.75 %. The weight loss rate of the PVC‐BiOI/TiO₂ nanocomposite film reached 30.8 % after 336 h of irradiation, which is 1.5 times higher than that of the PVC‐TiO₂ nanocomposite film under identical conditions. The solid‐phase photocatalytic degradation mechanism of the nanocomposite films was briefly discussed.     

Visible light photocatalytic degradation of thiophene using Ag–TiO2/multi-walled carbon nanotubes nanocomposite

Ag–TiO₂ nanocatalyst, supported on multi-walled carbon nanotubes, was synthesized successfully via a modified sol–gel method, and the prepared photocatalyst was used to remediate aqueous thiophene environmentally by photocatalytic oxidation under visible light. The prepared Ag–TiO₂/multi-walled carbon nanotubes nanocomposite photocatalyst was characterized through X-ray diffraction, Brunauer–Emmett–Teller (BET), transmission electron microscopy, and UV–vis spectra (UV–vis). The results showed that both Ag and TiO₂ nanoparticles were well-dispersed over the MWCNTs and formed a uniform nanocomposite. Ag doping can eliminate the recombination of electron–hole pairs in the catalyst, and the presence of MWCNTs in the TiO₂ composite can change surface properties to achieve sensitivity to visible light. The optimum mass ratio of MWCNT:TiO₂:Ag was 0.02:1.0:0.05, which resulted in the photocatalyst's experimental performance in oxidizing about 100% of the thiophene in a 600 mg/L solution within 30 min and with 1.4 g L⁻¹ amount of catalyst used.     

Dynamic mechanical analysis and broadband electromagnetic interference shielding characteristics of poly (vinyl alcohol)-poly (4-styrenesulfonic acid)-titanium dioxide nanoparticles based tertiary nanocomposites

ABSTRACT

Novel tertiary nanocomposite films comprising of poly (vinyl alcohol) (PVA), poly (4-styrenesulfonic acid) (PSSA) and titanium dioxide (TiO₂) nanoparticles (NP_S) were prepared using simple solvent casting method. The structural, thermal, morphological, thermo-mechanical and electromagnetic interference (EMI) shielding properties of PVA/PSSA/TiO₂ nanocomposite films were investigated. The EMI shielding effectiveness (SE) of PVA/PSSA/TiO₂ nanocomposite films in the X and Ku band was found to be 12 dB and 13 dB respectively at 25 wt% TiO₂ NPs loading. These results demonstrate the possible applications of PVA/PSSA/TiO₂ nanocomposite films as low cost, lightweight and flexible material for EMI shielding.     

Flexible TiO2 nanograss array film decorated with BiOI nanoflakes and its greatly boosted photocatalytic activity

A flexible TiO₂ nanograss array film on Ti wire mesh was prepared by a mild chemical reaction. To overcome its shortcoming of almost no absorption of visible light, successive ionic layer adsorption and reaction (SILAR) was executed to decorate the prepared TiO₂ film with BiOI. The results of XRD and SEM measurements showed that BiOI nanoflakes formed on the surface of TiO₂ film, and the loading amounts of BiOI nanoflakes increased with the increase in SILAR cycles. The XPS results confirmed the heterojunction formation of BiOI-TiO₂. The photocurrent measurement suggests that a moderate loading amount of BiOI nanoflakes is beneficial to improve the charge separation efficiency, which is ascribed to the heterojunction formation of BiOI-TiO₂. The BiOI-decorated TiO₂ film with SILAR cycles of seven showed the most excellent visible-light photocatalytic activity among all the samples. Compared with the bareTiO₂ nanograss array film, its visible-light photocatalytic activity increased by 11.7 times. The flexible BiOI-decorated TiO₂ nanograss array film with high photocatalytic activity shows great applications in air pollution and the pollution caused by offshore oil spills.     

Preparation of highly stable superhydrophobic TiO2 surfaces with completely suppressed photocatalytic activity

TiO₂ nanoparticles with a mean size of 20–30 nm were covered by ultrathin polydimethylsiloxane (PDMS) film, which shows hydrophobic properties. Surfaces consisting of the PDMS-coated TiO₂ particles showed water contact angles close to 170°. In contrast to the hydrophobic films consisting of organic molecules, which can be photocatalytically decomposed on TiO₂ in the presence of UV light, PDMS-coating on TiO₂ was highly stable. The PDMS-coating completely suppressed the photocatalytic activity of TiO₂. The unique properties of PDMS-coating can be exploited for UV protection layer and self-cleaning surfaces.     

Visible photocatalytic activity and photoelectrochemical behavior of TiO2 nanoparticles modified with metal porphyrins containing hydroxyl group

TiO₂ nanoparticles modified with 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin (HTPP), 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin zinc (ZnHTPP) and trans-dichloro-5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin tin (SnHTPP) were prepared in order to improve the visible photocatalytic activity of TiO₂ nanoparticles. The photocatalytic activity of the modified TiO₂ nanoparticles was investigated by carrying out the photodegradation of methyl orange in aqueous solution under visible light irradiation. The TiO₂ nanoparticles modified with SnHTPP show the highest visible photocatalytic activity with a degradation ratio of 86% of methyl orange after 180 min irradiation among three catalysts. This result indicates that the central metal ions in porphyrins can significantly influence the sensitization efficiency of porphyrins. In addition, the photoelectrochemical behavior of the modified TiO₂ nanoparticles was examined and related to their photocatalytic activity. Finally, the photocatalytic mechanism was discussed preliminarily.     

Effects of V and Zn codoping on the microstructures and photocatalytic activities of nanocrystalline TiO2 films

To enhance the photocatalytic activity of TiO₂, V and Zn co-doped TiO₂ films were synthesized by the sol–gel method. The experimental results indicated that the films were composed of round-like nano-particles or aggregates. V and Zn codoping could not only obviously increase the specific surface area of TiO₂ but also result in the narrowed band gap of TiO₂ sample. The photocatalytic activities of the TiO₂ films were evaluated by the photocatalytic decomposition of organic dyes in aqueous solution. Compared with un-doped TiO₂ film or single doped TiO₂ film, V and Zn co-doped TiO₂ film exhibited excellent photocatalytic activities under both UV light and visible light. The improvement mechanism by V and Zn codoping was also discussed.     

A novel deposition precipitation method for preparation of Ag-loaded titanium dioxide

Ag/TiO₂ photocatalysts were prepared by a novel deposition precipitation method. Formation of Ag nanoparticles on the surface of TiO₂ was confirmed by XRD, HRTEM and XPS. The photocatalytic activity of Ag/TiO₂ was tested with the photocatalytic degradation of methyl orange and found effectively enhanced. The optimum content of Ag for photocatalytic activity is about 2.0 wt%.     

Synthesis, characterization and photocatalytic properties of sol-gel TiO2 films

The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO₂ as a photocatalyst. Starting TiO₂ solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO₂ films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO₂ films were studied by means of atomic force microscopy (AFM). Structural properties of TiO₂ were identified by X-ray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO₂ films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model.The addition of PEG to the TiO₂ solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO₂. The TiO₂ film prepared with PEG is characterized by higher roughness parameters (R_a, R_max, R_q, R_z and Z_max), a lower amount of the rutile phase of TiO₂, a higher amount of the anatase phase of TiO₂ and a better photocatalytic activity compared to the TiO₂ film without the addition of PEG.     

Solid-phase photocatalytic degradation of polystyrene with modified nano-TiO2 catalyst

A novel photodegradable polystyrene-grafted-TiO₂ (PS-g-TiO₂) nanocomposite was prepared by embedding the grafted-TiO₂ into the commercial polystyrene. Solid-phase photocatalytic degradation of the PS-g-TiO₂ nanocomposite was carried out in ambient air at room temperature under ultraviolet lamp and/or sunlight irradiation. The properties of composite film were compared with those of the pure PS film by methods such as weight loss measurement, scanning electron microscope (SEM), gel permeation chromatogram (GPC), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, and UV-vis spectroscopy. The results show that the photo-induced degradation of PS-g-TiO₂ composite film is significantly higher than that of pure PS film. The weight loss of composite film reached 31.9%, average molecular weight (M_w) of composite film decreased by 53.1%, and the number average molecular weight (M_n) decreased by 73.2% after 396 h of UV-light irradiation. FT-IR analysis and weight loss indicated that the benzene rings in PS-matrix of composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the films is briefly discussed.