In-situ preparation and electrochromic properties of TiO2/PTPA-HTAN core-shell nanocomposite film

A new star-shaped structure conjugated microporous polymers, poly (2,8,14-tri[4-diphenyl-benzene]-hexaazatrinaphthylene) (PTPA-HATN), was designed and in-situ electrochemically polymerized on the surfaces of FTO electrodes with a directional alignment TiO₂ nanorod array to obtain TiO₂/PTPA-HATN core-shell nanocomposite films. Compared with the PTPA-HATN film, the TiO₂/PTPA-HATN composite film exhibits higher optical contrast and faster response time, with contrast of 57% at 783 nm, coloring time of 3.62 s and discoloring time of 2.55 s (43%, 4.63 s and 4.77 s for PTPA-HATN film, respectively). After 400 cycles, the contrast of nanocomposite film decreased by 28%, while the PTPA-HATN film basically lost its electrochromic properties. A simple three-layer EC prototype device based on TiO₂/PTPA-HATN nanocomposite film constructed with hydrogel electrolyte clearly shows color changes at different voltages. On the one hand, the formation of core-shell porous nanostructure of TiO₂/PTPA-HATN composite film provides a larger ion doping/de-doping interface, shortening the average diffusion length of ions. On the other hand, the large indented polymer-nanorods contact interface makes it difficult for the polymer to detach from the electrode, thus significantly improving the cyclic stability of the composite film.     

UV-degradation effect on optical and surface properties of polystyrene-TiO<Subscript>2</Subscript> nanocomposite film

Thin films of polystyrene and polystyrene-TiO₂ nanocomposite were prepared by spin coating from a polystyrene solution in which TiO₂ nanoparticles were dispersed by mechanical mixing. Thin films of polystyrene (PS) and polystyrene-TiO₂ nanocomposite were exposed to UV irradiation for varied time intervals. The effect of UV radiation on the optical properties, crystallinity, surface energy and degradation of PS-TiO₂ nano-composite has been studied. X-Ray diffraction analysis (XRD), UV-Vis and FTIR spectroscopy, Atomic Force Microscopy (AFM) and contact angle measurement were used to study the induced changes of the properties of the irradiated PS-TiO₂ nanocomposite. Optical band gaps and hydrophilicity in UV-irradiated samples were altered by destruction processes. The optical band gap values were found to reduce from 4.54 eV in pure PS to 4.45 eV for PS-TiO₂ nanocomposite prior to irradiation. This value is further reduced to 3.46 after UV irradiation for 45 h.     

Electrosynthesis,characterization and photoconducting performance of copolymer poly(terthiophene + sexithiophene + TiO<Subscript>2</Subscript>)/ITO composite material

In the present work, a new composite material poly(3T + 6T + TiO₂) was electrochemically synthesized. This composite material was synthesized in a solution of (CH2Cl2/TBAP) containing the monomers (terthiophene), (sexithiophene) and semiconductor (TiO₂) particles. The preparedsamples were characterized electrochemically by cyclic voltamperometry (CV) and spectrometry analysis by scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) absorption spectroscopy, energy dispersive X-ray spectroscopy (EDX) and fourier transform infrared spectroscopy (FTIR), respectively. The effect of TiO₂ concentration in the solution on dispersed microparticle entity and on the photocurrent response was investigated. The results showed that TiO₂ particles were dispersed and codeposited into the copolymer poly(3T + 6T + TiO₂) matrix, and titanium atom was confirmed by EDX spectra. From SEM images, the TiO₂ has a spherical shape and micrometer size. The FTIR spectrum indicated that titanium dioxide do not show a significant modification in terms of band shape and no interaction between polymers and TiO₂ particles. Furthermore, the results showed that the composite films with different amounts of TiO₂ exhibit good photocurrent properties which imply that these composites films can be used in various fields, such as photoelectrochemical applications as photovoltaic cells.     

Photocatalytic activity of (sulfur,nitrogen)-codoped mesoporous TiO<Subscript>2</Subscript> thin films

Nitrogen and sulfur co-doped mesoporous TiO₂ thin films were fabricated using thiourea as a doping resource by the combination of the sol–gel and evaporation-induced self-assembly (EISA) processes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and UV–vis spectra were performed to characterize the as-synthesized mesoporous TiO₂ materials. The XPS result shows that O–Ti–N and O–Ti–S bonds in the (S, N)-codoped mesoporous TiO₂ were formed. The resultant mesoporous (S, N)-codoped TiO₂ exhibited anatase framework with a high porosity and a narrow pore distribution. After being illuminated for 3 h, methyl orange (MO) could be degraded completely by the co-doped sample under the ultraviolet irradiation, whereas mesoporous TiO₂ film without doping could only degrade 60% MO. After being illuminated by visible light, the water contact angles of the mesoporous co-doped TiO₂ samples decreased slightly, but the pure TiO₂ mesoporous film exhibited no change in the hydrophilicity.     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Direct spectroelectrochemistry of peroxidases immobilised on mesoporous metal oxide electrodes: Towards reagentless hydrogen peroxide sensing

In this paper, we employ two peroxidases (horseradish peroxidase, HRP and cytochrome c peroxidase, CcP) to demonstrate their ability to retain their redox and biological functions after their immobilisation on mesoporous TiO₂ and SnO₂ electrodes. We will also demonstrate the use of HRP immobilised on the metal oxide electrodes for the development of reagentless optical and electrochemical biosensors for the detection of hydrogen peroxide (H₂O₂) with low detection limit of 0.04 and 1 μM, respectively.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

How room-humidity during the coating affects the structural,optical and photocatalytic properties of TiO<Subscript>2</Subscript> films

TiO₂ thin films were obtained on glass slide substrates by the sol–gel technique. The substrates were coated by the immersion-removal method, at a constant withdrawal speed. The TiO₂ precursor solution and the substrate were maintained in a closed box with a controlled relative humidity (RH) during the removal of the substrate. The RH was varied in the 30–90% range in steps of 20%. The films were dried and after that sintered in an open atmosphere. The effect of the RH was studied on the structural, optical and photocatalytic properties. The films are polycrystalline with an anatase phase and show a high optical transmission in the UV–Vis range. The photocatalytic activity was evaluated by the photobleaching of methylene blue in an aqueous solution. The best photocatalytic activity was obtained for the films with 90% RH, this fact is mainly attributed to the highest porosity value obtained for these films.     

Titania nanocomposite films derived by modified sol-gel process for photovoltaic application

Titania nanocomposite films were fabricated by spin-coating from sol-gel derived pastes of TiO₂ powder in titanium isopropoxide sol. The thin films were characterized for structural, optical and hydrophilic properties and evaluated as electrodes in a photoelectrochemical cell. Addition of TiO₂ powder increased film thickness, reduced transmittance, water contact angle and electrochemical impedance, and promoted photocurrent generation. Increasing Triton X-100 surfactant loading in the composite slurry influenced film texture and transmittance, and the resultant films exhibited a lower photocurrent yield but were more hydrophilic to favor charge transfer at the electrode/electrolyte interface. The aggregation of TiO₂ particles of different sizes in the composite film facilitates light-scattering and electron transport to enhance quantum efficiency. The addition of Triton X-100 surfactant influences the distribution of scattering centers to increase transparency.     

Effects of peak current density on the structure and property of PbO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> nanocomposite electrodes prepared by pulse electrodeposition

PbO₂–CeO₂ nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO₂ nanoparticles with different peak current density. The content of CeO₂ nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO₂–CeO₂ nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO₂–CeO₂ nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO₂–CeO₂ nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO₂–CeO₂ nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO₂ content in the composite electrodes.     

Interlaced polyaniline/carbon nanotube nanocomposite co-electrodeposited on TiO<Subscript>2</Subscript> nanotubes/Ti for high-performance supercapacitors

A series of PANI-CNTs/TiO₂ nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO₂ nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO₂ nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO₂ nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO₂ nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO₂ nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm^?2 with 90% retention after 1000 cycles) compared to the PANI/TiO₂ nanotubes/Ti (70 mF cm^?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm^?2, indicating its great potential for supercapacitor applications.

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Graphical abstract Interlaced polyaniline/carbon nanotube nanocomposite electrodeposited on TiO₂ nanotubes/Ti

     

Effects of duty cycle on the preparation and property of PbO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> nanocomposite electrodes

PbO₂-CeO₂ nanocomposite electrodes were prepared by pulse electrodeposition in the lead nitrate solution containing CeO₂ nanoparticles with different duty cycles. The effects of duty cycle on the morphology and phase structure were investigated by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the decrease of duty cycle can reduce the grain size of PbO₂-CeO₂ nanocomposite electrodes and make the electrodes more compact. The CeO₂ content in composite electrodes increases with the decrease of duty cycle. The steady-state polarization curves and accelerated life tests demonstrate that the oxygen evolution overpotential and service life of PbO₂-CeO₂ nanocomposite electrodes increase with the decrease of duty cycle. The service life of PbO₂-CeO₂ nanocomposite electrodes prepared with 25 % duty cycle reaches 218 h which is 1.8 times longer than that of PbO₂-CeO₂ nanocomposite electrodes prepared by direct electrodeposition. The bulk electrolysis shows that the degradation of malachite green (MG) on the PbO₂-CeO₂ nanocomposite electrodes is the pseudo-first-order reaction and the MG and chemical oxygen demand (COD) removal efficiency on PbO₂-CeO₂ nanocomposite electrodes increases with the decrease of duty cycle, which can be attributed to the higher oxygen evolution overpotentials, electrochemical active surface area, and CeO₂ content in the composite electrodes.     

Single-step solvothermal synthesis of mesoporous anatase TiO<Subscript>2</Subscript>-reduced graphene oxide nanocomposites for the abatement of organic pollutants

In the present work, we have fabricated a novel mesoporous TiO₂–rGO nanocomposite by a facile one-step solvothermal method using titanic sulfate as the TiO₂ source. The as-prepared composites were characterized by transmission electron microscopy, X-ray diffraction; UV–Vis diffuse reflectance spectra, X-ray photoelectron spectroscopy and photoluminence spectra. In situ nucleation and anchoring of TiO₂ nanoparticles onto a graphene sheet is favorable fpr forming an intimate interfacial contact, and the chemically bonded TiO₂–rGO nanocomposites commendably enhanced their photocatalytic activity in the photodegradation of rhodamine B and phenol. The high photocatalytic activity of the as-synthesized nanocomposites are primarily ascribed to the mesoporous structure, efficient charge transportation and separation with enhanced visible light absorption, which come from the appealing nanoarchitecture, for instance, ultra-dispersed and ultra-small TiO₂ nanocrystals along with intimate and absolute interfacial contact between the TiO₂ nanocrystals and the graphene sheet.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

Enhancement of photocatalytic H<Subscript>2</Subscript> evolution over TiO<Subscript>2</Subscript> nano-sheet films by surface loading NiS nanoparticles

NiS/TiO₂ nano-sheet films (NiS/TiO₂ NSFs) photocatalysts were prepared by loading NiS nanoparticles as noble metal-free cocatalysts on the surface of TiO₂ films through a solvothermal method. The prepared samples were characterized by XRD, SEM, EDS, UV–Vis absorption spectra and XPS analysis. The photocatalytic H₂ evolution and photoluminescence spectroscopy (PL) experiments indicated that the NiS cocatalysts could efficiently promote the separation of photogenerated charge carriers in TiO₂ and consequently enhance the H₂ evolution activity. The hydrogen yield obtained from the optimal sample reached 4.31 μmol cm^–2 at 3.0 h and the corresponding energy efficiency was about 0.26%, which was 21 times higher than that of pure TiO₂ NSF. A possible photocatalytic mechanism of NiS cocatalyst on the improvement of the photocatalytic performance of TiO₂ NSF was also proposed.     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

Modification of TiO<Subscript>2</Subscript> electrode films in dye-sensitized solar cells with PMMA

Nanocrystalline porous TiO₂ electrodes for dye-sensitized solar cells (DSC) are modified by adding polymethyl methacrylate (PMMA). The result shows that large holes are formed in the TiO₂ films, and the short circuit photocurrent density and photoelectric conversion efficiency of DSCs are obviously enhanced compared with those without adding the PMMA. The relationship between the photoelectric conversion efficiency and the amount of PMMA is presented. In particular, the highest conversion efficiency was obtained with TiO₂ electrode films of adding 7.5 wt% PMMA, increasing the conversion efficiency by 27.5%.     

Preparation and characterization of poly(l-lactic acid)/TiO2 nanoparticle nanocomposite films with high transparency and efficient photodegradability

Poly(l-lactic acid)-TiO₂ nanoparticle nanocomposite films were prepared by incorporating surface modified TiO₂ nanoparticles into polymer matrices. In the process of preparing the nanocomposite films, severe aggregation of TiO₂ nanoparticles could be reduced by surface modification by using carboxylic acid and long-chain alkyl amine. As a result, the nanocomposite films with high transparency, similar to pure PLA films, were obtained without depending on the amount of added TiO₂ nanoparticles. A TEM micrograph of the nanocomposite films suggests that the TiO₂ nanoparticles of 3-6 nm in diameter were uniformly dispersed in polymer matrices. Photodegradation of PLA-TiO₂ nanoparticle nanocomposite films was also investigated. The results showed that nanocomposite films could be efficiently photodegraded by UV irradiation in comparison with pure PLA.     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.