Nitrogen doped TiO2 nanoparticles decorated on graphene sheets for photocatalysis applications

Nitrogen doped TiO₂ nanoparticles decorated on graphene sheets are successfully synthesized by a low-temperature hydrothermal method. The resulting GR-N/TiO₂ composites are characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-Ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The optical properties are studied using UV–visible diffuse reflectance spectroscopy (DRS), which confirms that the spectral responses of the composite catalysts are extended to the visible-light region and show a significant reduction in band gap energy from 3.18 to 2.64 eV. Photoluminescence emission spectra verify that GR-N/TiO₂ composites possess better charge separation capability than pure TiO₂. The photocatalytic activity is tested by degradation of methyl orange (MO) dye under visible light irradiation. The results demonstrate that GR-N/TiO₂ composites can effectively photodegrade MO, showing an impressive photocatalytic enhancement over pure TiO₂. The dramatically enhanced activity of composite photocatalysts can be attributed to great adsorption of dyes, enhanced visible light absorption and efficient charge separation and transfer processes. This work may provide new insights into the design of novel composite photocatalysts system with efficient visible light activity.     

Effect of TiO2 nanoparticles on the surface morphology and performance of microporous PES membrane

PES-TiO₂ composite membranes were prepared via phase inversion by dispersing TiO₂ nanopaticles in PES casting solutions. The crystal structure, thermal stability, morphology, hydrophilicity, permeation performance, and mechanical properties of the composite membranes were characterized in detail. XRD, DSC and TGA results showed that the interaction existed between TiO₂ nanopaticles and PES and the thermal stability of the composite membrane had been improved by the addition of TiO₂ nanopaticles. As shown in the SEM images, the composite membrane had a top surface with high porosity at low loading amount of TiO₂, which was caused by the mass transfer acceleration in exposure time due to the addition of TiO₂ nanopaticles. At high loading amount of TiO₂, the skinlayer became much looser for a significant aggregation of TiO₂ nanopaticles, which could be observed in the composite membranes. EDX analysis also revealed that the nanoparticles distributed in membrane more uniformly at low loading amount. Dynamic contact angles indicated that the hydrophilicity of the composite membranes was enhanced by the addition of TiO₂ nanopaticles. The permeation properties of the composite membranes were significantly superior to the pure PES membrane and the mean pore size also increased with the addition amount of TiO₂ nanopaticles increased. When the TiO₂ content was 4%, the flux reached the maximum at 3711 L m⁻² h⁻¹, about 29.3% higher than that of the pure PES membrane. Mechanical test also revealed that the mechanical strength of composite membranes enhanced as the addition of TiO₂ nanopaticles.     

Morphology and natural wettability properties of sol-gel derived TiO2-SiO2 composite thin films

Previous studies suggest that granular interfaces induce a natural and persistent super-hydrophilicity in TiO₂-SiO₂ composite thin films deposited by sol-gel route. This effect enables to consider self-cleaning applications that do not require a permanent UV exposure, whereas such a permanent exposure is necessary for pure TiO₂ films. In this study, TiO₂-SiO₂ composite thin films have been deposited from a TiO₂ anatase crystalline suspension and different SiO₂ polymeric sols. Wettability studies show that a suitable control of the TiO₂-SiO₂ mixed sol formulations noticeably enhances persistence of the natural super-hydrophilicity in composite films. It is shown that, beside granular interface effects, modifications in the composite film morphologies can noticeably influence wettability properties.     

Facile Preparation and Excellent Ultraviolet Shielding Application of Polyurethane-TiO2 Composite Microcapsules

In this work, butyl stearate, isophorone diisocyanate, and glycerol are used to prepare reticulated polyurethane microcapsules using interfacial polymerization. In addition, anatase nano-TiO₂ is added to prepare TiO₂-polyurethane phase change microcapsules during the polymerization process. Polarized light microscope, scanning electron microscope, Fourier-transform infrared spectroscopy, thermogravimetric, differential scanning calorimeter, and other methods demonstrate the successful preparation of microcapsules, and microcapsules with different TiO₂ content have differences in morphology and performance. It is worth noting that the addition of TiO₂ enhances the thermal stability and mechanical strength of the prepared composite microcapsules. In addition, TiO₂ particles allow the microcapsules to have photocatalytic properties and ultraviolet shielding properties, and the prepared TiO₂-polyurethane composite capsules show good catalytic degradation properties for methyl orange solution. Moreover, the ultraviolet absorption performance of the TiO₂-polyurethane composite microcapsule coating is tested, and the results show that the strength of ultraviolet light is weakened after passing through the coating, indicating that the composite microcapsule can enhance the UV resistance of the coating. This work shows the preparation of multifunctional microcapsules and their potential applications in photocatalysis and UV resistance.     

EFFECT OF ZnFe22O4 DOPING ON THE OPTICAL PROPERTIES OF TiO2 THIN FILMS

Amorphous TiO₂ thin films and ZnFe₂O₄ doped TiO₂ composite films were deposited by radio frequency magnetron sputtering. The effect of ZnFe₂O₄ doping on the optical properties of TiO₂ thin films was reported. Our results show that the absorption edge of TiO₂ thin films and composite films exhibits a blue shift with decreasing annealing temperature. The absorption edge of composite films has moved to visible spectrum range, and a very large red shift occurs in comparison with TiO₂ thin film. An enhanced photoluminescence in ZnFe₂O₄ doped anatase TiO₂ thin film at room temperature.     

Photocatalysis and wave-absorbing properties of polyaniline/TiO2 microbelts composite by in situ polymerization method

Polyaniline (PANI)/TiO₂ composite is prepared by in situ polymerization of polyaniline on the surface of TiO₂ template obtained by the sol-gel process via cotton template. The TiO₂ microbelts are prepared by sol-gel method using the absorbent cotton as template for the first time. Then the TiO₂ microtubules are used as template for the preparation of polyaniline/TiO₂ composites. The structure, morphology and properties of the composites are characterized with scanning electron microscope (SEM), IR, Net-wok Analyzer. A possible formation mechanism of TiO₂ microtubules and polyaniline/TiO₂ composites has been proposed. The effect of the mol ratio of polyaniline/TiO₂ on the microwave loss properties and photocatalysis properties of the composites is investigated.     

Photocatalytic disinfection of water with Ag–TiO2 nanocrystalline composite

A method of solution impregnation and calcination has been demonstrated for synthesizing nanoparticles of Ag–TiO₂ composite photocatalysts for use in the disinfection of water. Only a small proportion of the TiO₂ surface is covered by nano-islands of Ag corresponding to a loading of 4 wt.% of Ag; thus, most of the TiO₂ surface is available for photocatalytic function. Although the primary particles of both Ag and TiO₂ are in the 10- to 20-nm range, microscopic studies indicate that the primary particles of Ag are deposited on nano-agglomerates of 30- to 70-nm-sized TiO₂. It is seen that the relatively small loading of Ag has not caused any UV–vis spectral shift but has enhanced the rate of photocatalytic antibacterial action of TiO₂, presumably by electron trapping.     

Carrier transport and photoresponse for heterojunction diodes based on the reduced graphene oxide-based TiO2 composite and p-type Si

The present work reports the fabrication and detailed electrical properties of heterojunction diodes based on p-type Si and the reduced graphene oxide-based TiO₂ (TiO₂:RGO) composite. The enhanced dark conductivity was observed for TiO₂:RGO composite films. The improved electrical conductivity is considered to mainly come from the mobility enhancement. The TiO₂/p-type Si diode shows a poor rectifying behavior and low photoresponse. This is because of the dominance of electron traps in TiO₂. However, the TiO₂:RGO/p-type Si diode shows a good rectifying behavior and high photoresponse, which is attributed to high-mobility electron transport combined with the reduced number of electron traps.     

Effect of TiO2 crystalline composition on the dielectric properties of TiO2/P(VDF‐TrFE) composites

In order to study the effect of the TiO₂ particle crystalline composition (with different proportions of rutile and anatase crystals) on the dielectric properties of the composite, titanium dioxide (TiO₂) particles and TiO₂/poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] composites were synthesized by a reflux method and the solution route, respectively. The results indicated that the optimum TiO₂ particle crystalline composition is anatase content of 37% and rutile content of 63% for dielectric‐constant modifier applications. Furthermore, a dielectric constant of 25.7 with dielectric loss of 0.17 at 100 Hz at room temperature were obtained in the composite with 40 wt% TiO₂ particles. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanical performance of apatite/TiO2 composite coatings formed on Ti and NiTi shape memory alloy

To make metals bioactive for orthopaedic applications, apatite/TiO₂ composite coatings were formed on Ti and NiTi shape memory alloy (SMA) using a H₂O₂-oxidation and hot water aging technique and the subsequent accelerated biomimetic process. In the current investigation, nanoindentation, scratch testing and frictional testing were employed to assess mechanical properties and the adhesion of apatite/TiO₂ composite coatings formed on Ti and NiTi SMA. Nanoindentation testing conducted on cross-sections of composite coatings indicated that there was no significant difference in nanohardness and elastic modulus between apatite/TiO₂ composite coatings formed on Ti and NiTi SMA samples. The enhancement of the adhesion between the apatite layer and the metal substrates arose from the TiO₂ intermediate layer in the composite coating. The highest values of coating adhesion strength for Ti and NiTi SMA samples, as measured by scratch tests, were 22.58 N and 19.07 N, respectively. However, compared to corresponding Ti samples, NiTi SMA samples had better tribological properties.     

Synthesis and electronic behaviors of TiO2/carbon clusters/Cr2O3 composite materials

Nano-structured TiO₂/carbon clusters/Cr₂O₃ composite material has been successfully obtained by the microwave treatment of a TiO(acac)/Cr(acac)₃/epoxy resin complex. The compositions of the composite materials were determined using ICP, elemental analysis and surface characterization by SEM-EDX, TEM and XRD. ESR spectral examinations suggest the possibility of an electron transfer in the process of TiO₂ → carbon clusters → Cr₂O₃ with an oxidation site at TiO₂ particles and a reduction site at Cr₂O₃ particles. The preliminary experimental results show that the calcined materials could decompose methylene blue under visible-light irradiation.     

The electronic behaviors of TiO2/MnO2/carbon clusters composite materials obtained by the calcination of a TiO(acac)2/Mn(acac)3/epoxy resin complex

The calcination of a TiO(acac)₂/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere successfully produced nano-sized TiO₂/MnO₂/carbon clusters composite material. The surface characterizations of the resulting composites indicate that they are composed of nano-sized particles of TiO₂, MnO₂ and carbon clusters. ESR spectral examination suggests the possibility of an electron transfer in the process of MnO₂ → carbon clusters → TiO₂. The visible light-responsive oxidation–reduction function of the composite materials has also been confirmed.     

Enhanced photocatalytic activity of graphene–TiO2 composite under visible light irradiation

Novel graphene–TiO₂ (GR–TiO₂) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO₂ nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO₂ shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using graphene–TiO₂ composite catalysts in order to study the photocatalytic efficiency. The results showed that GR–TiO₂ composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO₂ under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant π-conjugation system and two-dimensional planar structure of graphene.     

The effect of particles size distribution on aesthetic and thermal performances of polydisperse TiO2 pigmented coatings: Comparison between numerical and experimental results

A new approach in designing pigmented coatings considering both visual and thermal concerns was introduced by authors in previous works. The objective was to design a pigmented coating with dark appearance which can stay cool while exposed to sunlight. This behavior can be achieved by coating a typical black substrate with a pigmented coating with controlled size and concentration of particles and coating thickness. In present work, the spectral behaviour of polydisperse TiO₂ pigmented coatings was studied. The radiative properties of polydisperse TiO₂ powders were evaluated and the radiative transfer in the pigmented coating was modelled using the radiation element method by ray emission model (REM²). The effects of particles size distribution on spectral reflectivity, optimization parameter, and color coordinates were discussed. The results of numerical calculation were validated by experimental reflectivity measurements of several TiO₂ pigmented coating samples made from two different TiO₂ powders with different size distributions of particles. The results show that our model can reasonably predict the spectral reflectivity of TiO₂ pigmented coating samples. Moreover, the results of optimized monodisperse TiO₂ pigmented coatings were again validated.     

Preparation and photoelectrochemical performance of Ag/graphene/TiO2 composite film

By dipping-lifting in sol-gel solution and reducing process, the graphene/TiO₂ composite film on the glass plate was first prepared. Then, the Ag/graphene/TiO₂ composite film was fabricated by interface reaction with AgNO₃ and N₂H₄·H₂O on the surface of graphene/TiO₂ composite film. The characterization results show that the uniform porous TiO₂ film is made up of the anatase crystal, and the Ag/graphene/TiO₂ composite film is constructed by doping or depositing graphene sheets and Ag nanoparticles on the surface of TiO₂ film. The photoelectrochemical measurement results indicate that the Ag/graphene/TiO₂ composite film has an excellent photoelectrochemical conversion property.     

Enhanced photocatalytic performance of ultrasound treated GO/TiO2 composite for photocatalytic degradation of salicylic acid under sunlight illumination

The current research work deals with the preparation of TiO₂ and GO/TiO₂ composite by simple, chemical, cost effective hydrothermal method. Graphene oxide (GO) is prepared by modified Hummer’s method. Dispersion of GO is achieved by an ultrasonic cleaning bath for 1 h. using a power of 200 W and at a frequency of 40 kHz. The prepared catalyst material is characterized by different characterization techniques. XRD study confirms the prepared material is polycrystalline in nature. The synthesized TiO₂ and GO/TiO₂ photocatalyst materials are used to study the photocatalytic degradation of salicylic acid under sunlight illumination. GO/TiO₂ composite shows superior photocatalytic activity than TiO₂. GO/TiO₂ composite shows 57% degradation of salicylic acid. Mineralization of salicylic acid is studied using chemical oxygen demand.     

Preparation and characterization of polyaniline+TiO2 composite films

In this work, we have prepared electrochemically and studied a composite materials based on an organic conducting polymer, polyaniline (PANI), in which inorganic semiconductor titanium dioxide (TiO₂) particles were incorporated with different concentrations. The polyaniline/titanium dioxide composite material which had been deposited by cyclic voltammetry on substrates of indium tin oxide was then characterized. The cyclic voltammogram showed one redox couple characteristic of the oxidation and reduction states of the produced composite material. The impedance spectroscopy study showed that the resistance of the film increases with the TiO₂ cocntent incorporated in the polymer. The incorporation of TiO₂ in PANI covering the surfaces was confirmed by the scanning electron microscopy and the energy dispersive X-ray analysis. The morphological analysis of the film surfaces showed that the TiO₂ nanoparticle increased the roughness. These observations allow to consider a new approach to improve the physicochemical properties of the interface between the organic and inorganic material. The I–V characteristics of PANI+TiO₂ heterostructure diode showed the nonlinear nature of the I–V curve of PANI+TiO₂ heterostructure device.     

Microstructure and properties of a copper electrocontact material with a nanodispersed titanium dioxide additive

The influence of TiO₂ nanopowder additive on the microstructure, physicomechanical properties, and performance characteristics of a copper-based composite is studied. The properties of the composites are compared with those of pure copper compacts. The microstructure and state of the composite’s working surface after performance tests are examined. It is shown that, when the amount of TiO₂ grows, the hardness of the material rises and the arc quenching effect is enhanced.     

Ti:sapphire femtosecond laser direct micro-cutting and profiling of graphene

Zinc oxide and titanium dioxide composite thin films were prepared on Corning 7059 glass substrates by co-sputtering. The reactive gas-surroundings used was ultrahigh purity oxygen. To analyze the structural, optical and photocatalytic properties of the ZnO?CTiO₂ samples, X-ray diffraction (XRD), atomic force microscopy (AFM), optical absorption, Raman spectroscopy and methylene blue bleaching were carried out at room temperature. XRD patterns indicate the presence of TiO₂ (anatase and rutile phases), ZnO, ZnTiO₃, and Zn₂TiO₄ crystalline structures. AFM images allow the observation of non-homogeneous surface in the ZnO?CTiO₂ system, suggesting the separation of different crystalline phases in the composite. Raman studies exhibit different spectra in the films depending on the area analyzed, which can be interpreted as a result of the existence of well separated crystalline regions as seen in AFM images. The photocatalytic activity (PA) of TiO₂?CZnO?CZnTiO₃?CZn₂TiO₄ composite, as expected for adequate coupling semiconductors, is larger than PA of ZnO and TiO₂ oxides, used as references. A simple proposal about the probable alignment of the conduction band, the valence band, and the Fermi level is included.     

TiO2/carboxylate-rich porous carbon: A highly efficient visible-light-driven photocatalyst based on the ligand-to-metal charge transfer (LMCT) process

A novel visible-light-driven photocatalyst based on TiO₂/carboxylate-rich porous carbon composite (TiO₂/CRPC) was successfully synthesized by low temperature carbonization process in air. Sodium gluconate plays a crucial role in the formation of TiO₂/CRPC. Different functional groups of sodium gluconate play synergetic roles in the formation of TiO₂/CRPC. XRD and Raman spectra studies indicated that there are two different TiO₂ crystalline phases existing in TiO₂/CRPC, which are anatase and brookite, and the CRPC is amorphous. Via FT-IR and XPS spectra investigations, it was demonstrated that carboxylate group, the ligand-to-metal charge transfer (LMCT) forming functional group, was solidified into the CRPC and form the LMCT complex on TiO₂ surface through the fabrication of TiO₂/CRPC. Compared with the pure TiO₂, TiO₂/CRPC exhibit enhanced absorption in the UV and visible light region around 260–600 nm. The strong absorption in the visible light region gives TiO₂/CRPC advantages over pure TiO₂ for the degradation of organic pollutants. TiO₂/CRPC can activate O₂ in air under mild conditions and exhibit excellent visible-light-driven photocatalytic activities. However, TiO₂/C composite obtained by using glucose instead of sodium gluconate exhibits poor photocatalytic activity, which demonstrated that carboxylate–TiO₂ complexes are responsible for the prominent photocatalytic properties of TiO₂/CRPC under visible light irradiation.