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.     

Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO₂) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τ_FWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO₂/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO₂ NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.     

Electrochemical synthesis and in situ spectroelectrochemistry of conducting polymer nanocomposites. I. polyaniline/TiO2, polyaniline/ZnO,and polyaniline/TiO2+ZnO

The polyaniline (PAn), polyaniline/titanium dioxide (PAn/TiO₂), polyaniline/zinc oxide (PAn/ZnO), and a novel conducting polymer nanocomposites, polyaniline/titanium dioxide + zinc oxide (PAn/TiO₂+ZnO), were synthesized by in situ electropolymerization and potential cycling on gold electrode. The PAn and nanocomposite films were characterized by cyclic voltammetry, Fourier transform infra‐red (FTIR) spectroscopy, in situ resistivity measurements, in situ UV–Visible, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The differences between cathodic and anodic peaks of three redox couples were obtained for PAn and polymeric nanocomposite films. During cathodic and anodic scans, the shift of potential was observed for polymer nanocomposite films. The characteristic FTIR peaks of PAn were found to shift to lower wavelengthsin polymer nanocomposite films. These observed effects have been attributed to interaction of TiO₂, ZnO, and TiO₂+ZnO particles with PAn molecular chains. Significant differences from in situ resistivity of PAn and nanocomposite films were obtained. The resistance of PAn/TiO₂, PAn/ZnO, and PAn/TiO₂+ZnO films were found to be smaller than the PAn film. The in situ UV–Visible spectra for Pan and polymer nanocomposite films were studied. The results show the intermediate spectroscopic properties between PAn and polymer nanocomposite films. The morphological analyses of PAn and nanocomposite films have been investigated. The nanocomposites SEM and TEM micrographs suggest that the inorganic semiconductor particles were incorporated in organic conducting polymer, which consequently modifies the morphology of the films significantly. POLYM. COMPOS., 35:351–363, 2014. © 2013 Society of Plastics Engineers     

Ag-TiO2多孔薄膜及其非紫外光辐照下的超亲水特性

采用溶胶凝胶法，以钛酸丁酯为前驱体、硝酸银络合物为银源、聚乙二醇2000（PEG2000）作为结构导向剂，制备超亲水多孔Ag-TiO₂复合薄膜。用X射线衍射仪、X射线光电子能谱仪、扫描电镜、原子力显微镜表征薄膜晶相结构、化学成分以及表面形貌。根据静态水接触角、动态润湿时间、超亲水长效稳定性综合评价不同Ag含量及PEG2000添加量薄膜的超亲水性能。研究发现，掺杂Ag与PEG2000对薄膜在非紫外光下的超亲水特性具有协同作用，掺杂Ag明显提高薄膜动态润湿速度及可见光响应，表面粗糙多孔结构有利于避光条件下的长效超亲水特性。Ag含量10%、PEG2000掺杂量5%的Ag-TiO₂复合薄膜在自然光条件下已具备优良的超亲水性能；水滴0.2 s内即可在表面完全铺展到0°；避光条件下保存，超亲水时效性可达到30 d以上。在可见光活化下即可强化超亲水性能，具有良好的防雾效果。     

Enhanced photochromism of heteropolyacid/polyvinylpyrolidone composite film by TiO2 doping

Novel composite film was synthesized by TiO₂ doping into phosphomolybdic acid (PMoA)/polyvinylpyrrolidone (PVP) system. The influence of TiO₂ doping on its microstructure and photochromic properties was investigated via atomic force microscopy, transmission electron microscope, Fourier transform infrared spectroscopy (FT‐IR), ultraviolet–visible spectra, and X‐ray photoelectron spectroscopy (XPS). After TiO₂ doping, the surface of TiO₂/PMoA/PVP composite film changed to rough from smooth, and the particle size significantly increased. The FT‐IR results verified that the basic structure of PMoA and PVP were not destroyed in the composite films. The non‐bonded interaction between the acid and polymer was strengthened by TiO₂ doping. Irradiated with UV light, composite films changed from colorless to blue. The TiO₂/PMoA/PVP composite film exhibited a strong photochromic effect and faster bleaching reaction than that of PMoA/PVP film. XPS results indicated that the amount of PMoA in photo‐reductive reaction was increased after TiO₂ doping, which resulted in the photochromic efficiencies enhanced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41583.     

Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification

Graphene oxide-particle composite films with filtration function have been successfully synthesized by a two-step method. First, graphene oxide–TiO₂ composite sheets are prepared, which can form stable dispersion in water. Then, by assembling these composite sheets, graphene oxide–TiO₂ films are obtained. In these as-prepared films, dilated space and channels are desirably formed by introducing nanoparticles between these carbon sheets, making them promising separation membranes. We used these films as filtration membranes to remove dye molecules (methyl orange and rhodamine B) from water. The results show that apart from the adsorption capacities of these dyes, these graphene oxide–TiO₂ films can also capture additional amount of dye molecules, indicating their potential applications in water purification areas.     

Morphological and thermal properties of photodegradable biocomposite films

Biocomposites containing ultraviolet (UV) radiation absorbing inorganic nanofillers are of great interest in food packaging applications. The biodegradable polylactide (PLA) composite films were prepared by solvent casting method by incorporating 1 wt % of titanium dioxide (TiO₂) and Ag‐TiO₂ (silver nanoparticles decorated TiO₂) nanoparticles to impart the photodegradable properties. The films were exposed to UV radiation for different time periods and morphology of the composite films before and after UV exposure were investigated. The results showed that homogenous filler distribution was achieved in the case of Ag‐TiO₂ nanoparticles. The thermal properties and thermomechanical stability of the composite film containing Ag‐TiO₂ nanoparticles were found to be much higher than those of neat PLA and PLA/TiO₂ composite films. The scanning electron microscopy and X‐ray diffraction studies revealed that the photodegradability of PLA matrix was significantly improved in the presence of Ag‐TiO₂ nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Superhydrophilic Transparent Titania Films by Supersonic Aerosol Deposition

Photocatalytic and hydrophilic TiO₂ thin‐film applications include water purification, cancer therapy, solar energy conversion, self‐cleaning devices, and antifogging windows. We demonstrate superhydrophilicity of aerosol‐deposition (AD) TiO₂ films on a glass substrate without use of a carrier solvent, thereby removing the possibility of impurity contamination. AD films exhibit high visible light transmittance (greater than 80%) and superhydrophilicity (0° contact angle) with even minimal UV‐light irradiation exposure. This AD method represents a significant step toward the realization of economically viable, functional thin films for the aforementioned applications.     

Hybrid polyaniline–TiO2 nanocomposite Langmuir–Blodgett thin films: Self‐assembly and their characterization

Polyaniline (PANi)–titanium dioxide (TiO₂) nanocomposite materials were prepared by chemical polymerization of aniline doped with TiO₂ nanoparticles. Surface pressure–area (π‐A) isotherms of these nanocomposites show phase transformations in the monolayer during compression process. Multiple isotherms indicate that the monolayer of the nanocomposite material can retain its configuration during compression‐expansion cycles. Langmuir–Blodgett thin films of PANi–TiO₂ nanocomposite were deposited on the quartz and indium tin oxide coated conducting glass substrates. Fourier transfer infrared spectroscopy and UV–visible spectroscopy study indicates the presence of TiO₂ in PANi, whereas X‐ray Diffraction study confirmed the anatase phase of TiO₂ and particle size (～nm) of PANi–TiO₂. The morphology of Langmuir–Blodgett films of these nanocomposites was also characterized by atomic force microscopy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41386.     

A mechanical and modelling study of magnetron sputtered cerium-titanium oxide film coatings on Si (100)

Ce/Ti mixed metal oxide thin films have well known optoelectrical properties amongst several other physio-chemical properties. Changes in the structural and mechanical properties of magnetron sputtered Ce/Ti oxide thin films on Si (100) wafers with different Ce:Ti ratios are investigated experimentally and by modelling. X-ray Photoemission Spectroscopy (XPS) and X-ray diffraction (XRD) confirm the primary phases as trigonal Ce₂O₃ and rutile form of TiO₂ with SiO₂ present in all prepared materials. FESEM imaging delivers information based on the variation of grain size, the mixed Ce/Ti oxides providing much smaller grain sizes in the thin film/substrate composite. Nanoindentation analysis concludes that the pure cerium oxide film has the highest hardness value (20.1?GPa), while the addition of excess titanium oxide decreases the hardness of the film coatings. High temperature in-situ XRD (up to 1000?°C) results indicate high thermal phase stability for all materials studied. The film with Ce:Ti?=?68%:32% has a new additional minor oxide phase above 800?°C. Contact angle experiments suggest that the chemical composition of the surface is insignificant affecting the water contact angle. Results show a narrow band of 87.7–95.7° contact angle. The finite element modelling (FEM) modelling of Ce/Ti thin film coatings based on Si(100); Si(110); silica and steel substrates shows a variation in stress concentration.     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

Photocatalytic activity of Cr-doped TiO2 nanoparticles deposited on porous multicrystalline silicon films

This work deals with the deposition of Cr-doped TiO₂ thin films on porous silicon (PS) prepared from electrochemical anodization of multicrystalline (mc-Si) Si wafers. The effect of Cr doping on the properties of the TiO₂-Cr/PS/Si samples has been investigated by means of X-ray diffraction (XRD), atomic force microcopy (AFM), photoluminescence, lifetime, and laser beam-induced current (LBIC) measurements. The photocatalytic activity is carried out on TiO₂-Cr/PS/Si samples. It was found that the TiO₂-Cr/PS/mc-Si type structure degrades an organic pollutant (amido black) under ultraviolet (UV) light. A noticeable degradation of the pollutant is obtained for a Cr doping of 2 at. %. This result is discussed in light of LBIC and photoluminescence measurements.     

Synergetic Effects of Graphene Oxide and Clay on the Microstructure and Properties of HIPS/Graphene Oxide/Clay Nanocomposites

In this paper, double-network structure nanocomposite with improved mechanical and thermal properties were prepared using high-impact polystyrene as a matrix phase, clay and graphene oxide as effective reinforcing fillers through a facile solution intercalation method. The structure and morphology of nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, and the synergetic effects of clay and graphene oxide on the final properties were investigated using tensile, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA) analysis. Mechanical analysis showed that the combination of graphene oxide and clay exerted a favorable synergistic effect on the tensile modulus and the yield strength of the ternary composite that are greatly improved as compared with neat high-impact polystyrene, high-impact polystyrene/graphene oxide, and high-impact polystyrene/clay binary composites due to the double-network structure formation between the nanofillers as confirmed by the direct morphological observations using transmission electron microscopy and scanning electron microscopy analysis. The viscoelastic behavior showed that storage modulus of ternary composite significantly improvement over than that of the pure matrix, high-impact polystyrene/graphene oxide and high-impact polystyrene/clay while network structure made. TGA and DMTA measurements also demonstrated that thermal stability of high-impact polystyrene matrix modified by graphene oxide and clay slightly enhanced during the creation of dual network structure of graphene oxide and clay. Our data suggest a potential application for the combination of graphene oxide and clay in graphene-based composite materials.     

Encapsulation of Cyclotetramethylenetetranitramine (HMX) by Electrostatically Self‐Assembled Graphene Oxide for Desensitization

To improve the safety of cyclotetramethylenetetranitramine (HMX) particles, a novel strategy was developed for the fabrication of graphene oxide encapsulated HMX (HMX@GO) by electrostatic self‐assembly between graphene oxide and HMX particles. The prepared samples were characterized by optical microscopy, scanning electron microscopy, Raman spectroscopy, X‐ray photon spectroscopy, thermogravimetry, differential scanning calorimetry and water contact angle tests. The results revealed that GO sheets were coated densely and homogeneously on the HMX particles in a HMX@GO composite at a low GO content of about 0.23 wt %. Compared with that of raw HMX, the impact sensitivity of the HMX@GO composite decreased from 100 % to 30 %, and the 50 % probability of required ignition energy (E₅₀) in the electrostatic spark sensitivity test increased from 0.66 J for HMX to 1.12 J for the HMX@GO composite, suggesting that the electrostatically self‐assembled GO coating layer could obviously enhance the safety of HMX.     

Microwave photocatalysis II: novel continuous‐flow microwave photocatalytic experimental set‐up with titania‐coated mercury electrodeless discharge lamps

BACKGROUND: A continuous‐flow microwave photocatalytic reactor was set up consisting of a glass tube equipped with microwave powered mercury electrodeless discharge lamps (EDLs) coated with thin films of nanoporous titanium(IV) oxide. The effect of operational parameters on photocatalytic degradation of aqueous mono‐chloroacetic acid (MCAA) by a TiO₂/UV/MW process was investigated. RESULTS: Studies were carried out at a relatively high concentration of MCAA (0.1 mol L^?1), and revealed that reaction temperature and light intensity of the EDLs depend inversely on the flow rate, but that the 366 nm line intensity of EDL is directly proportional to the reaction temperature. The photodegradation of MCAA was enhanced by heating and significantly enhanced by air bubbling of the reaction mixture in the glass reservoir at laboratory temperature. The photocatalytic efficiency increased with the number of titania‐coated EDLs inserted in the glass tube reactor. CONCLUSIONS: It was found that the operational parameters (i.e. flow rate, reaction temperature, number of titania‐coated EDLs, and air bubbling) had important effects on degradation efficiency. The photocatalytic degradation of MCAA on thin films of titanium(IV) oxide in the continuous‐flow microwave photoreactor can be enhanced in the TiO₂/UV/MW system. Copyright © 2009 Society of Chemical Industry     

Synthesis and photocatalytic performance of PVA/TiO2/graphene‐MWCNT nanocomposites for dye removal

TiO₂/graphene‐MWCNT nanocomposite was prepared using solvothermal reaction for the effective distribution of TiO₂ nanoparticles on carbonaceous materials. TiO₂/graphene‐MWCNT nanocomposite was immobilized in poly(vinyl alcohol) (PVA) matrix for a convenient recovery after wastewater purification. MWCNT was incorporated in a nanocomposite not only to prevent the restacking of graphene but also to increase the electron transfer from TiO₂. The detailed characterization of the nanocomposite was performed using SEM, EDX, XRD, XPS, and FTIR. The photocatalytic performance of PVA/TiO₂/graphene‐MWCNT nanocomposite was investigated by UV spectroscopy on the basis of degradation of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite showed improved photocatalytic decomposition of more than 70% of residual dye left in case of using PVA/TiO₂/graphene nanocomposite due to the improved electron transfer and the higher adsorption of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite was suitable as a promising material for the recyclable photocatalytic wastewater purification system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40715.     

Preparation and blood compatibility of carbon/TiO2 nanocomposite

A carbon/TiO₂ nanocomposite, which consists of carbon film with various sp³C content and TiO₂ nanowire arrays, has been synthesized, in which the top surface of TiO₂ nanowire arrays prepared using hydrothermal method on fluorine-doped tin oxide glass were coated with carbon thin films. The carbon thin films with a higher, medium and lower sp³C content were deposited by pulsed magnetic filtered cathodic vacuum arc deposition, plasma-enhanced chemical vapor deposition and magnetron sputtering deposition, respectively. The surface morphology and structure of TiO₂ nanowire arrays were investigated by scanning electron microscopy, transmission electron microscope and X-ray diffraction. The sp³C content in carbon films was characterized using Raman spectroscopy. The blood compatibility of the samples including the TiO₂ nanowire arrays, carbon films and carbon/TiO₂ nanocomposite was assessed by tests of platelet adhesion in vitro. Results showed that the carbon/TiO₂ composite can effectively improve the anticoagulant function compared to the single materials. It is believed that the excellent blood compatibility of the carbon/TiO₂ nanocomposite is attributed to a joint function of surface properties adjusted by nanowire arrays and electronic structure of carbon thin films.     

Photoactive behavior of polyacrylonitrile fibers based on silver and zirconium co‐doped titania nanocomposites: Synthesis,characterization, and comparative study of solid‐phase photocatalytic self‐cleaning

Silver and zirconium co‐doped and mono‐doped titania nanocomposites were synthesized and deposited onto polyacrylonitrile fibers via sol–gel dip‐coating method. The resulted coated‐fibers were characterized by X‐ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diffuse reflectance spectroscopy, thermogravimetric analysis, and BET surface area measurement. Photocatalytic activity of the TiO₂‐coated and TiO₂‐doped coated fibers were determined by photomineralization of methylene blue and Eosin Y under UV–vis light. The progress of photodegradation of dyes was monitored by diffuse reflectance spectroscopy. The XRD results of samples indicate that the TiO₂, Ag‐TiO₂, Zr‐TiO₂, and Ag‐Zr‐TiO₂ consist of anatase phase. All samples demonstrated photo‐assisted self‐cleaning properties when exposed to UV–vis irradiation. Evaluated by decomposing dyes, photocatalytic activity of Ag–Zr co‐doped TiO₂ coated fiber was obviously higher than that of pure TiO₂ and mono‐doped TiO₂. Our results showed that the synergistic action between the silver and zirconium species in the Ag‐Zr TiO₂ nanocomposite is due to both the structural and electronic properties of the photoactive anatase phase. These results clearly indicate that modification of semiconductor photocatalyst by co‐doping process is an effective method for increasing the photocatalytic activity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Self-cleaning performance of sol–gel-derived TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> double-layer thin films

The self-cleaning properties of the TiO₂/SiO₂ double-layer films prepared by sol–gel method were investigated. Thin films were prepared by spin coating onto glass and then thermally treated at different temperatures, and characterized using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and UV–visible spectroscopy. The cross-sectional structure of the films was observed by FESEM. The surface roughness of the films was characterized by AFM. The root mean square surface roughness of the thin films was below 2 nm, which should enhance their optical transparency. The photo-induced hydrophilicity of the films was evaluated by water contact angle measurement in air. The photocatalytic activity of the films was studied by the photocatalytic degradation of methylene blue under UV light irradiations. The TiO₂/SiO₂ double-layer thin films are plausibly applicable to developing self-cleaning materials in various applications such as windows, solar panels, cement, and paints.     

Characterization and conductivity studies of nanocomposite films with polymer networks containing polyaniline‐alginate/titanium dioxide

Polyaniline nanocomposite films were chemically synthesized in the presence of alginate template by varying the concentration of TiO₂ in the composites. Characterization of the composite samples by FTIR, UV‐Vis spectra (UV), and X‐ray diffraction (XRD) indicates the formation of polyaniline‐alginate/titanium dioxide (PAT) composites. The morphology analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) also supports the formation of the composites. Temperature‐dependent DC conductivity of the polyaniline‐alginate (PA) and PAT composites was studied in the range of 300 ≤ T ≤ 500 K. UV‐Vis and FTIR spectral studies reveal that the alginate is a good template for the chemical interaction between polyaniline and TiO₂, which suggests that the micelles formed by the anilinium‐alginate cations containing TiO₂ are responsible for the transport properties of the PAT composites. POLYM. COMPOS., 31:1754–1761, 2010. © 2010 Society of Plastics Engineers.