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.     

Electrophoretic deposition of TiO2 film on titanium foil for a flexible dye-sensitized solar cell

Electrophoretic deposition (EPD) method is employed to obtain mesoporous TiO₂ film on a titanium (Ti) foil; the film is then mechanically compressed and sintered at 350 °C before being subjected to dyeing. A comprehensive study was made on the mechanistic aspects of the EPD process. The dye-sensitized solar cell (DSSC) using the thus formed TiO₂ film rendered a power conversion efficiency (Eff.) of 6.5%. Effects of various compression pressures on the photovoltaic parameters and on other characteristic parameters of the pertinent DSSCs are studied. Electrochemical impedance spectroscopy (EIS) is applied for the first time, using a novel equivalent model, to study the impedance behavior of the DSSC with this type of TiO₂ film. We also obtain characteristic parameters of the TiO₂ photoanode by using EIS. The coordination number of the TiO₂ film, and the ratio of charge transfer resistances of electron recombination and electron transport are also obtained and analyzed. Moreover, we employ a multilayer approach and increase the film thickness to prepare TiO₂ films with the same coordination number and porosity; DSSCs using such TiO₂ films obtained from P90 and P25 rendered efficiencies of 6.5% and 5.24%, respectively. Scanning electron microscopy (SEM) micrographs are obtained to characterize the TiO₂ films formed by the EPD technique and laser-induced transient technique is used to estimate the electron lifetime in the TiO₂ films.     

Rutile TiO2-modified multi-wall carbon nanotubes in TiO2 film electrodes for dye-sensitized solar cells

The beneficial influence of incorporation of acid-treated and rutile TiO₂ (r-TiO₂)-modified multi-wall carbon nanotubes (MWNTs) in TiO₂ films on photocurrent–voltage characteristics of dye-sensitized solar cells (DSSCs) was studied. Two different routes were adopted for the modification of acid-treated MWNTs (a-MWNTs) with r-TiO₂. The films and MWNTs were characterized by electron microscopy, energy dispersive X-ray spectroscopy, XRD and Raman spectroscopy. In the case of incorporation of a-MWNTs with r-TiO₂ modification, short-circuit photocurrent (J _sc) of the pertinent DSSC increased by 35% compared with that of a cell with bare TiO₂ film. The open-circuit voltage remained almost the same for all cases. The enhanced J _sc is explained by the increased surface area of the film, enhanced cluster formation of TiO₂ particles around a-MWNTs, and improved interconnectivity of TiO₂ particles in the presence of a-MWNTs.     

Synthesis,physical properties,and characterization of starch‐based blend films by adding nano‐sized TiO2/poly(methyl metacrylate‐co‐acrylamide)

The purpose of this study was to improve the physical properties and to expand the application range of starch‐based blend films added nano‐sized TiO₂/poly(methyl methacrylate‐co‐acrylamide) (PMMA‐co‐AM). Starch‐based blend films were prepared by using corn starch, polyvinyl alcohol (PVA), nano‐sized PMMA‐co‐AM, nano‐sized TiO₂/PMMA‐co‐AM particles, and additives, i.e., glycerol (GL) and citric acid (CA). Nano‐sized PMMA‐co‐AM was synthesized by emulsion polymerization and TiO₂ nanoparticles were also prepared by using sol–gel method. Nano‐sized TiO₂/PMMA‐co‐AM particles were synthesized by wet milling for 48 h. The morphology and crystallinity of TiO₂, nano‐sized PMMA‐co‐AM and TiO₂/PMMA‐co‐AM particles were investigated by using the scanning electron microscope (SEM) and X‐ray diffractometer (XRD). In addition, the functional groups of the TiO₂/PMMA‐co‐AM particles were characterized by IR spectrophotometry (FTIR). The physical properties such as tensile strength (TS), elongation at break (%E), degree of swelling (DS), and solubility (S) of starch‐based films were evaluated. It was found that the adding of nano‐sized particles can greatly improve the physical properties of the prepared films. The photocatalytic degradability of starch/PVA/nano‐sized TiO₂/PMMA‐co‐AM composite films was evaluated using methylene blue (MB) and acetaldehyde (ATA) as photodegradation target under UV and visible light. The degree of decomposition (C/C₀) of MB and ATA for the films containing TiO₂ and CA was 0.506 and 0.088 under UV light irradiation and 0.586 (MB) and 0.631 (ATA) under visible light irradiation, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Production and characterization of nanocomposites based on poly(amide-imide) containing 4,4′-methylenebis(3-chloro-2,6-diethylaniline) using nano-TiO2 surface-coupled by 3-aminopropyltriethoxysilane

In this work, the poly(amide-imide) (PAI) was synthesized from the polymerization reaction of 4,4′-methylenebis(3-chloro-2,6-diethyl trimellitimidobenzene) as a diacid with 4,4′-methylenebis(3-chloro-2,6-diethylaniline) under green condition using molten tetra-n-butylammonium bromide and triphenylphosphite. Ultrasonic technique was used for preparation of PAI/TiO₂ nanocomposites (PAI/TiO₂ NCs). For the improvement of TiO₂ nanoparticles (NPs) dispersion and enhancing interactions between NPs and polymeric matrix the surface of TiO₂ was successfully modified by silane coupling agent (3-aminopropyltriethoxysilane). The resulting NCs were characterized by FT-IR, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The TGA of the obtained NCs proves the enhancement in the thermal stability with an increase in the percentage of titania NPs. TEM and FE-SEM images showed that the NPs were uniformly dispersed in the polymer matrix. The shielding effect of nano TiO₂ under UV radiation was examined by UV–vis.     

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO<Subscript>2</Subscript> nanofibers in a TiO<Subscript>2</Subscript> film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO₂ nanofiber [TN] and Ag-doped TiO₂ nanofiber [ATN] have been extended to be included in TiO₂ films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO₂ photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO₂ films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.     

EIS analysis on low temperature fabrication of TiO2 porous films for dye-sensitized solar cells

A low temperature (<150 °C) fabrication method for preparation of TiO₂ porous films with high efficiency in dye-sensitized solar cells (DSSCs) has been developed. The Ti(IV) tetraisopropoxide (TTIP) was added to the paste of TiO₂ nanoparticles to interconnect the TiO₂ particles. The electrochemical impedance spectroscopy (EIS) technique was employed to quantify the charge transport resistance at the TiO₂/dye/electrolyte interface (R_ct2) and electron lifetime in the TiO₂ film (τ_e) under different molar ratios of TTIP/TiO₂ and also at various TiO₂ thicknesses. It was found that the R_ct2 decreased as the molar ratio increased from 0.02 to 0.08, however, it increased at a molar ratio of 0.2 due to the reduction in surface area for dye adsorption. In addition, the characteristic frequency peak shifted to lower frequency at a molar ratio of 0.08, indicating the longer electron lifetime. As for the thickness effect, TiO₂ film with a thickness around 17 μm achieved the best cell efficiency. EIS study also confirmed that, under illumination, the smallest R_ct2 was associated with a TiO₂ thickness of 17 μm, with the R_ct2 increased as the thickness of TiO₂ film increased. In the Bode plots, the characteristic frequency peaks shifted to higher frequency when the thickness of TiO₂ increased from 17.2 to 48.2 μm, indicating the electron recombination increases as the thickness of the TiO₂ electrode increases.Finally, to make better use of longer wavelength light, 30 wt% of larger TiO₂ particle (300 nm) was mixed with P25 TiO₂ as light scattering particles. It effectively increased the short-circuit current density and cell conversion efficiency from 7.44 to 8.80 mA cm⁻² and 3.75 to 4.20%, respectively.     

Preparation of poly(methyl methacrylate)/titanium oxide composite particles via in‐situ emulsion polymerization

Poly(methyl methacrylate) (PMMA)/Titanium oxide (TiO₂) composite particles were prepared via in‐situ emulsion polymerization of MMA in the presence of TiO₂ particles. Before polymerization, the TiO₂ particles was modified by the silane coupling agent, which is crucial to ensure that PMMA reacts with TiO₂ via covalent bond bindings. The structure of the obtained PMMA/TiO₂ composite particles was characterized using Fourier transform infrared spectra (FTIR) and thermogravimetric analysis (TGA). The results indicate that there are covalent bond bindings between PMMA macromolecules and TiO₂ particles. Based on these facts, several factors affecting the resulting PMMA/TiO₂ composite system, such as the type of coupling agents, the mass ratio of the MMA to the modified TiO₂, the emulsifier concentration, and the initiator concentration, etc., were examined by the measurement of conversion of monomers, the gel content of polymers, the percentage of grafting, and the grafting efficiency, using gravity method or TGA method. As a result, the optimized recipe was achieved, and the percentage of grafting and the grafting efficiency could reach 216.86 and 96.64%, respectively. In addition, the obtained PMMA/TiO₂ composite particles were found to a stable colloidal dispersion in good solvent for PMMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4056–4063, 2006     

Preparation of submicron-sized porous titanium oxide particles by the swelling process

A method to prepare submicron-sized porous titanium oxide (TiO₂) particles is studied in this work. Polystyrene (PS) template particles were prepared by emulsifier-free emulsion polymerization. The polymer templates dispersed in the aqueous solution have been used for entrapping titanium(IV) isopropoxide (TTIP), by the swelling process in a suitable solvent mixture containing a swelling solvent (good solvent or poor solvent), a TiO₂ precursor (TTIP), and a chelating agent (AcAc), within the polymer templates, followed by hydrolysis/condensation reaction of TTIP confined in PS template particles by the addition of the chelating agent. The influence of various reaction parameters, such as mixtures of different weight ratios between the PS particles and desiccative TTIP, AcAc amounts, and the swelling solvent amounts and type, on the size, bulk, and composition of the particles was investigated. Porous TiO₂ particles have been prepared by thermal decomposition of the PS templates at 500 °C.     

Synthesis and anticorrosion performance of poly(2,3-dimethylaniline)–TiO2 composite

Poly(2,3-dimethylaniline)–TiO₂ composite (PTC) was prepared by oxidative polymerization of 2,3-dimethylaniline in phosphoric acid medium with ammonium persulphate as oxidant. The composite was characterized by Fourier transformation infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). TiO₂ particles, rather being simply blended or mixed up, are encapsulated or entrapped into the polymer core, resulting in some significant improvement in its anticorrosion properties. Suitable coating with PTC was formed on steel using epoxy resin, and its corrosion resistance behavior was studied by open circuit potential (OCP) and electrochemical impendence spectroscopy (EIS) in 3.5% NaCl solution and also compared with that of PANI and poly(2,3-dimethylaniline) (P(2,3-DMA)). It has been found out that the coating containing PTC has got higher corrosion resistance than that of PANI and P(2,3-DMA).     

Effect of molar ratio of TiO2/SiO2 on the properties of particles synthesized by flame spray pyrolysis

Titania (TiO₂)–silica (SiO₂) nanoparticles were synthesized from sprayed droplets of a mixture of TEOS and TTIP by flame spray pyrolysis (FSP). The effect of molar ratio between TEOS and TTIP in the mixture on the particle properties such as particle morphology, average particle diameter, specific surface area, crystal structure, etc., were determined using TEM, XRD, BET, and FT-IR. A UV-spectrometer was also used to measure the absorption spectrum and the band gap energy of the product particles. As the molar ratio of TEOS/TTIP increased by increasing TEOS concentration at the fixed TTIP concentration, the average particle diameter of the mixed oxide nanoparticles increased with maintaining uniform dispersion between TiO₂ and SiO₂, and crystal structure was transformed from anatase to amorphous. The band gap energy of the TiO₂–SiO₂ nanoparticles increased with respect to the increase of the molar ratio due to the decrease of width of UV-absorption spectrum. Photocatalytic activity of TiO₂–SiO₂ composite particles decreased with the concentration of TEOS.     

Photocatalytic degradation of methylene blue with TiO2 nanoparticles prepared by a thermal decomposition process

The generation of TiO₂ nanoparticles by the thermal decomposition of titanium tetraisopropoxide (TTIP) was carried out experimentally using a tubular electric furnace at various synthesis temperatures (700-1300 °C) and TTIP heating temperatures (80-110 °C). The photocatalytic activity of the resulting TiO₂ nanoparticles was examined by measuring the rate of methylene blue decomposition. The TiO₂ nanoparticles were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) measurements and transmission electron microscopy (TEM). The crystallite size and crystallinity increased with increasing synthesis temperature and TTIP heating temperature. A TTIP heating temperature and synthesis temperature of 95 °C and 900 °C, respectively, were found to be the optimal synthesis conditions. The primary particle diameter obtained under optimum synthesis conditions was considerably smaller than the commercial photocatalyst (Degussa, P25). The specific surface areas were more than 134.4 m² g^− 1. Under the optimal conditions, the photocatalytic activity for methylene blue was higher than that of the commercial photocatalyst.     

Polyvinyl pyrrolidone aided preparation of TiO2 films used in flexible dye-sensitized solar cells

Polyvinyl pyrrolidone (PVP) is introduced to low temperature preparation of a good quality TiO₂ film used in flexible dye-sensitized solar cells (DSSCs). The samples are characterized by scanning electron microscopy and UV–vis absorption spectra, the photovoltaic performance of the DSSC is measured. It is found that PVP can improve the dispersion of TiO₂ particles and the adherence of TiO₂ particles to flexible substrate, as well as the adsorption of sensitized dye to TiO₂ film. Additionally, ultraviolet light irradiation can eliminate organics remained on the surface the TiO₂ film and improve the surface state of TiO₂ film. Under an optimal condition, a flexible DSSC using TiO₂ film doped PVP and UV irradiation treated achieves a light-to-electric energy conversion efficiency of 3.02% under irradiation with a simulate solar light intensity of 100 mW cm⁻².     

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.     

Microstructural and Optoelectronic Studies on Polyaniline: TiO2 Nanocomposites

Thin films of polyaniline (PANi) and PANi: titanium oxide (TiO₂) composites have been synthesized by sol–gel spin coating technique. The TiO₂ powder of particle size 50–60 nm was synthesized by the sol–gel technique and the polyaniline was synthesized by the chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and the four-probe method. The results were compared with corresponding data on pure polyaniline films. The intensity of diffraction peaks for PANi:TiO₂ composites is lower than that for TiO₂. The characteristic FTIR peaks of pure PANi are observed to shift to a higher wavenumber in PANi:TiO₂ composite, which is attributed to the interaction of TiO₂ particles with PANi molecular chains. The resistivity measurement shows that the molecular chain constitution of polyaniline is the most important carrier in the polyaniline: nano-TiO₂ composite.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

An efficient and low-cost TiO2 compact layer for performance improvement of dye-sensitized solar cells

A TiO₂ organic sol was synthesised for the preparation of a compact TiO₂ layer on fluorine-doped tin oxide (FTO) glass by a dip-coating technique. The resultant thin film was used for the fabrication of dye-sensitized solar cells (DSSCs). The compact layer typically has a thickness of ca. 110 nm as indicated by its SEM, and consists of anatase as confirmed by the XRD pattern. Compared with the traditional DSSCs without this compact layer, the solar energy-to-electricity conversion efficiency, short-circuit current and open-circuit potential of the DSSCs with the compact layer were improved by 33.3%, 20.3%, and 10.2%, respectively. This can be attributed to the merits brought by the compact layer. It can effectively improve adherence of TiO₂ to FTO surface, provide a larger TiO₂/FTO contact area, and reduce the electron recombination by blocking the direct contact between the redox electrolyte and the conductive FTO surface.     

Effect of compressed TiO2 nanoparticle thin film thickness on the performance of dye-sensitized solar cells

In this study, dye-sensitized solar cells (DSSCs) were fabricated using nanocrystalline titanium dioxide (TiO₂) nanoparticles as photoanode. Photoanode thin films were prepared by doctor blading method with 420 kg/cm² of mechanical compression process and heat treatment in the air at 500°C for 30 min. The optimal thickness of the TiO₂ NP photoanode is 26.6 μm with an efficiency of 9.01% under AM 1.5G illumination at 100 mW/cm². The efficiency is around two times higher than that of conventional DSSCs with an uncompressed photoanode. The open-circuit voltage of DSSCs decreases as the thickness increases. One DSSC (sample D) has the highest conversion efficiency while it has the maximum short-circuit current density. The results indicate that the short-circuit current density is a compromise between two conflict factors: enlargement of the surface area by increasing photoanode thickness and extension of the electron diffusion length to the electrode as the thickness increases.     

Assessment of Novel Water-Borne Coatings Obtained from Composite Latex Particles and Reinforced with TiO2 Nanotubes

Novel, environmentally friendly waterborne coatings were obtained from the filmification of nanostructured latex particles reinforced with inorganic nanotubes. The latex used to form the coatings consists of core-shell particles with a shell functionalized with different amounts of acrylic acid (AA). This external polymer layer was doped, in some cases, with TiO₂ nanotubes at three different concentrations: 100, 500 and 1000 ppm. The composite particles were synthesized in two steps by semi-continuous emulsion polymerization at 75°C. A series of films was prepared by employing core-shell particles with different sizes, core cross-linking and shell functionalization. The coatings obtained were characterized by infrared spectroscopy (FTIR), tapping mode atomic force microscopy (TM-AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Drying rates and tests were also performed to further evaluate these films. It was observed that the addition of small amounts of TiO₂ nanotubes contributes to improve the application properties, mainly adhesion to metallic substrates and water impermeability. The resistance to thermal degradation was also strongly increased, as showed by the DSC and TGA analyses.     

Synthesis,structural characterization and properties of novel functional poly(ether imide)/titania nanocomposite thin films

In this study, the synthesis, morphology, and thermal properties of new poly(ether imide)/titania nanohybrid films were investigated. The novel diamine containing functional nitrile groups was prepared in two steps by the nucleophilic substitution reaction and it was fully characterized by different techniques. Reaction of this diamine with pyromellitic dianhydride and 4-aminobenzoic acid gave poly(ether imide) with carboxylic acid end groups. This acid functionalized poly(ether imide) was condense with different amount of TiO₂ nanoparticles to provide organic-inorganic bonding, and the flexible films of these hybrid were prepared. The obtained materials were characterized by Fourier transform-infrared spectroscopy, thermogravimetry analysis (TGA), differential scanning calorimetry, X-ray powder diffraction, UV–Vis spectroscopy, field emission-scanning electron microscopy, and transmission electron microscopy (TEM) techniques. TEM of the nanohybrid films with 12% of TiO₂ contents confirms well dispersion of nanoparticles in the polymer matrix. TGA data indicated that the thermal behavior of the hybrid materials was increased with an increasing the content of TiO₂ nanoparticles. The tensile stress–strain of the hybrids was investigated and the resulting nanocomposites showed good mechanical properties. The permeability and selectivity of the PEI/TiO₂ membranes as a function of the titania weight percentage were study and the results indicated that the permeabilities of CO₂ and N₂ increase with increasing the titania content.