Nanostructured carbon nanotube/TiO2 composite coatings using electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) has been used to combine multi-walled carbon nanotubes of diameter in the range 20–30 nm and commercially available TiO₂ nanoparticles (23 nm particle size) in composite films. Laminate coatings with up to four layers were produced by sequential EPD, while composite coatings were obtained by electrophoretic co-deposition of carbon nanotubes and TiO₂ nanoparticles, respectively. Scanning electron microscopy was used to characterize the resultant microstructures. The mechanism of EPD of carbon nanotube/TiO₂ nanoparticle composites is discussed.     

Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process

This paper aims to study fabrication and characterization of silver/titanium oxide composite nanoparticle through sonochemical process in the presence of ethylene glycol with alkaline solution. By using ultrasonic irradiation of a mixture of silver nitrate, the dispersed TiO₂ nanoparticle in ethylene glycol associated with aqueous solution of sodium oxide yields Ag/TiO₂ composite nanoparticle with shell/core-type geometry. The powder X-ray diffraction (XRD) of the Ag/TiO₂ composites showed additional diffraction peaks corresponding to the face-centered cubic (fcc) structure of silver crystallization phase, apart from the signals from the cores of TiO₂. Transmission electron microscopy (TEM) images of Ag/TiO₂ composites, which average particle size is roughly 80 nm, reveal that the titanium oxide coated by Ag nanoparticle with a grain size of about 2–5 nm. Additionally, the formation of silver nanoparticles on TiO₂ was monitored by ultraviolet visible light spectrophotometer (UV–Vis). As measured the optical absorption spectra of as-synthesized Ag nanoparticle varying with time, the mechanism of surface formatting silver shell on the cores of TiO₂ could be explored by autocatalytic reaction; the conversion of Ag particle from silver ion is 98% for the reaction time of 1000 s; and the activity energy of synthesizing Ag nanoparticles on TiO₂ is 40 kJ/mol at temperature ranging from 5 to 25 °C. Hopefully, this preliminary investigation could be used for mass production of composite nanoparticles assisted by ultrasonic chemistry in the future.     

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.     

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.     

Second-order optical nonlinearity of surface-capped CdS nanoparticles and effect of surface modification

Surface-capped CdS nanoparticles (5 nm mean diameter) with hexametaphosphate and CTAB (hexadecyltrimethyl-ammonium bromide) in chloroform were prepared by colloidal chemistry and phase transfer method. The second-order nonlinear optical response was measured by incoherent hyper-Rayleigh scattering (HRS) technique. Results show that the surface-capped CdS nanoparticles have a large first-order hyperpolarizability β value of 1.30×10⁻²⁶ esu per particle. Surface capping molecule modification was performed by adding pyridine to a chloroform sol of the surface-capped CdS nanoparticles where pyridine can be bound to the CdS nanoparticle surface through Cd–N chemical bonds. A reduction in HRS signal intensity was observed when increasing pyridine concentration. This is explained in terms of a two-level model approximation derived from molecular chromophores, when considering the influence of the formation of Cd–N coordinating bonds on the charge-transfer transition energy of surface molecule-like scatterers of Cd–S polar bonds.     

Improving the electrical catalytic activity of Pt/TiO<Subscript>2</Subscript> nanocomposites by a combination of electrospinning and microwave irradiation

One of the greatest challenges in preparing TiO₂-based oxygen electrodes for PEM fuel cells is increasing the electrical catalytic activity of Pt nanoparticle/TiO₂ composites by improving the dispersion of Pt. This article describes a new way for improving the dispersion of Pt nanoparticles by depositing them on TiO₂ fibers and using microwave irradiation. The Pt nanoparticles used in this experiment is about 5 nm in diameter and the diameter of TiO₂ fibers could be controlled ranging from 30 to 60 nm and Pt nanoparticles still keep their size when the deposition amount is increased on the surface of TiO₂ fibers. The Pt nanoparticles were highly dispersed without agglomeration even at a weight percentage of composites as high as 40%. The position of Pt nanoparticles located in the fiber and the composition of Pt/TiO₂, which had great influence on the electric conductivity and electrical catalytic activity of the composite, could be easily controlled.     

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.     

Synthesis and characterization of bamboo-like CdS/TiO<Subscript>2</Subscript> nanotubes composites with enhanced visible-light photocatalytic activity

In order to efficiently use the visible light in the photocatalytic reaction, a novel bamboo-like CdS/TiO₂ nanotubes composite was prepared by a facile chemical reduction method, in which CdS nanoparticles located in the TiO₂ nanotubes. The composition and structure of this nanocomposite were characterized by TEM, HRTEM, XRD, XPS, FTIR and UV-vis spectroscopy. This CdS/TiO₂ nanotubes composite exhibited much higher visible-light photocatalytic activity for the degradation of methylene blue than pure TiO₂ nanotubes and CdS nanoparticles, and the highest photodegradation efficiency after 6 h irradiation can reach 84.5%. It is inferred that the unique structure of CdS/TiO₂ nanotubes composites acts an important role for the improvement of their photocatalytic activity.     

Specific features of luminescence quenching in a nematic liquid crystal doped with nanoparticles

The change in the intensity of the photoluminescence (PL) spectra of nematic liquid crystal (NLC) composites as a function of the concentration of CdSe/ZnS semiconductor quantum dots (QDs) and TiO₂ and ZrO₂ nanoparticles ~5 nm in diameter has been investigated. It is shown that the PL-quenching intensity in composites with CdSe/ZnS QDs exceeds that in composites with TiO₂ and ZrO₂ nanoparticles. The lowfrequency spectra of these composites with a concentration of 0.1 wt %, recorded in the range of 10²–10³ Hz, and the content of mobile ions in them have been investigated. It is found that the dielectric loss in the composite with CdSe/ZnS QDs is much higher and the content of mobile ions is larger by a factor of 3 than in the composites with TiO₂ and ZrO₂ nanoparticles. It is shown that an increase in the CdSe/ZnS QD concentration in NLC composites leads to an increase in the dielectric loss and a decrease in the PL intensity. Possible mechanisms of the interaction between NLC molecules and CdSe/ZnS QDs are discussed.     

Surface‐enhanced Raman scattering investigations on silver nanoparticles deposited on alumina and titania nanotubes: influence of the substrate material on surface‐enhanced Raman scattering activity of Ag nanoparticles

Silver nanoparticles deposited on various ‘inert’ porous materials (mainly Al₂O₃ and TiO₂) are often used as substrates for surface‐enhanced Raman scattering (SERS) measurements. In this study, we used the sputter deposition technique to cover tubular arrays of Al₂O₃ and TiO₂ with Ag nanoparticles. Raman spectra of pyridine (as a probe molecule) and of two selected dyes (5‐(4‐dimethylaminobenzylidene)rhodanine and 5‐(4‐(dimethylamino)benzylidene)‐3‐(3‐methoxypropyl)rhodanine) adsorbed on fabricated Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al substrates were measured. We found that the SERS spectra of pyridine adsorbed on Ag nanoparticles deposited on an Al₂O₃‐n/Al substrate are distinctly different from those measured for an Ag/TiO₂‐n/Ti composite. Similar effects were observed for dyes adsorbed on the surface of both composites. The spectral differences between two kinds of composites (Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al) are discussed in terms of (1) the modified electronic structure of the Ag nanoparticles due to their interaction with different substrate materials and (2) the different atomic topology of the metal particles thus deposited on the surfaces of the substrates. Composite samples were also studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Copyright © 2012 John Wiley & Sons, Ltd.     

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)     

Preparation and characterization of PES/TiO2 composite membranes

Polyethersulfone (PES)/TiO₂ composite membranes were prepared by phase inversion method with nano-TiO₂ as additive. The influence of TiO₂ on the morphologies and the performances of PES/TiO₂ membranes were investigated through the methods of SEM, XRD, TGA, contact angle goniometer, mechanical strength tests and filtration experiments. The results showed that the structure of membrane was not obviously affected by addition of TiO₂, and the performances such as hydrophilicity, thermal stability, mechanical strength and anti-fouling ability of membrane were enhanced through adding TiO₂ nanoparticles. At 0.5 wt.% TiO₂ content, the composite membrane has an excellent performance, however higher TiO₂ content (than 0.5 wt.%) resulted in defective pore structure of the membranes and decline of the performances, such as permeability and mechanical strength. TGA and mechanical strength analyses indicated good compatibility between polymers and TiO₂ nanoparticles.     

Synthesis and characterization of TiO2/Ag/polymer ternary nanoparticles via surface-initiated atom transfer radical polymerization

We report on the novel ternary hybrid materials consisting of semiconductor (TiO₂), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO₂-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF₃SO₃ precursor and a NaBH₄ aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO₂ nanoparticles and the in situ formation of Ag nanoparticles within the polymeric chains were confirmed using transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FT-IR spectroscopy also revealed the specific interaction of Ag nanoparticles with the CO groups of POEM brushes. This study presents a simple route for the in situ synthesis of both metal and polymer confined within the semiconductor, producing ternary hybrid inorganic-organic nanomaterials.     

Optical properties of poly(methyl methacrylate)–titania nanostructure thin films containing ellipsoid-shaped titania nanoparticles from ex-situ sol-gel method at low growth temperature

This paper reports on the linear and nonlinear optical responses of the PMMA-TiO₂ nanohybrid thin films which are synthesized by a flexible ex-situ sol-gel/polymerization process, assisted by spin coating and multi-step baking. Triethanolamine (TEOA) as surfactant and shape controller is used to modify the interface between PMMA and TiO₂, allowing a highly homogeneous dispersion of the ellipsoid-shaped TiO₂ nanoparticles. The resulting nanohybrid thin films have highly optical transparency as proved by the linear absorption photon-energy spectra and indicate an enhanced nonlinear optical (NLO) response as confirmed by the Z-scan technique using 800-nm, 120-femtosecond (fs) laser pulses, highlighting the potential of the nanocomposites for efficient optical devices.     

Preparation of TiO2-carbon surface composites with high photoactivity by supercritical pretreatment and sol-gel processing

TiO₂-carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol-gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol-gel method, the small nanosize TiO₂ particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti³⁺ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO₂ nanoparticles, baffles the agglomeration of TiO₂ nanoparticles and easily produces Ti³⁺ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO₂-carbon (TC) composites and pure TiO₂. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO₂ in comparison with TC and pure TiO₂, because their surface area are greater than that of TC and pure TiO₂.     

The electrical conductivity properties of polythiophene/TiO2 nanocomposites prepared in the presence of surfactants

A composite of polythiophene (PT) and nano-titanium dioxide (TiO₂), possessing core–shell structure, was synthesized via oxidative polymerization of thiophene using FeCl₃ in the presence of three different surfactants: anionic, cationic, and nonionic. The morphology of the obtained composite materials was investigated by SEM, proving the core–shell structure of the prepared nanocomposite. The formation and thermal stability of the PT onto TiO₂ nanoparticles were confirmed by FTIR and TGA analyses, respectively. XRD data show all of composite materials were amorphous structures. The electrical properties of the nanocomposites were investigated in the presence of surfactant materials, and the best semiconductor property was observed for PT/TiO₂-anionic system. This difference in the conductivity has been attributed to differences in the stability of the composites.     

Computational study on the structural and surface properties of amorphous hydroxylated TiO<Subscript>2</Subscript> spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO₂) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO₂ in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO₂ surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 ^o . The bulk system was developed using periodic boundary conditions. The TiO₂ nanoparticles were extracted by applying a spherical cut section in the bulk TiO₂ melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO₂ nanoparticles and bulk amorphous TiO₂, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO₂ nanoparticles are strongly size-dependent and different from those of the bulk TiO₂. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO₂ nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO₂ nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO₂ spherical nanoparticles is estimated to be around 8.1/nm ², which lies in the range of 8–16/nm ², found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.     

Surface-initiated atom transfer radical polymerization from TiO2 nanoparticles

Two kinds of hydrophilic polymers, poly(oxyethylene methacrylate) (POEM) and poly(styrene sulfonic acid) (PSSA), were grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. Chlorine modified TiO₂ nanoparticles (TiO₂-Cl), the ATRP initiators, were synthesized by the reaction of -OH in TiO₂ with 2-chloropropionyl chloride (CPC). FT-IR, UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the polymer chains were successfully grafted from the surface of TiO₂ nanoparticles. The hydrophilically modified TiO₂ nanoparticles have a better dispersion in alcohol than unmodified nanoparticles, as revealed by transmission electron microscopy (TEM). It was also found that the polymer grafting did not significantly alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction (XRD) patterns. Grafting amounts were 10% of the weight for both TiO₂-POEM and TiO₂-PSSA nanoparticles, as determined by thermogravimetric analysis (TGA).     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

Electrochemical properties of TiO2 nanoparticle/nanorod composite photoanode for dye-sensitized solar cells

A unique composite of TiO₂ nanoparticles (NPs) and nanorods (NRs) has been used to fabricate a photoelectrode for developing dye-sensitized solar cells (DSSCs) with higher sensitivity. The TiO₂ nanorods were synthesized using a mechanical process, in which electrospun TiO₂ nanofibers was grinded in a controlled way to obtain uniform size distribution. The characteristics of electron transport, recombination lifetime and charge collection were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). Photoelectrodes prepared with the composites of NRs and NPs showed significant improvements in electron transportation compared to only NP photoelectrodes, which would enhance the photovoltaic performance of DSSCs. IMPS and IMVS measurements show that fast electron transport and slightly decreased recombination lifetime resulted in the improvement of efficiency. The highest energy conversion efficiency obtained from the photoelectrodes fabricated with the as-prepared rutile TiO₂ nanofibers at 5 wt% NR content was up to 6.1% under AM1.5G solar illumination. The results demonstrate that the composite nanostructure can take advantage of both the fast electron transport of the nanorods and the high surface area of the nanoparticles.