Growth of Ag and Au Nanoparticles on Reduced and Oxidized Rutile TiO2(110) Surfaces

The nucleation and growth of Au and Ag nanoparticles on rutile TiO₂(110)–(1 × 1) surfaces in different oxidation states is studied by means of photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). Au and Ag nanoparticles were found to bind much more strongly to oxidized TiO₂(110) model supports than to reduced TiO₂(110) surfaces, as directly revealed by STM. Detailed PES studies addressing small Au and Ag particles complete this picture and show that the PES core level spectra acquired on Au/TiO₂(110) and Ag/TiO₂(110) can be best described by fitting with two binding energy (BE) components. Particularly for coverages in the sub-monolayer regime and for depositions at low temperatures (100 K) the PES core level spectra must be fitted with at least two BE components. The higher BE component is attributed to atoms at the interface between the metal clusters and the TiO₂(110) support. For Au/TiO₂(110), the two BE components were evident in the core level spectra for higher coverage than for Ag/TiO₂(110), consistent with different growth modes for Au (initially 2D) and Ag (3D) on TiO₂(110). Finally, strong evidence for charge transfer from Ag nanoparticles to the TiO₂(110) support is presented, whereas the charge transfer between Au nanoparticles and the TiO₂(110) support is very small.     

BisGMA/TiO2 Organic-Inorganic Hybrid Nanocomposite

BisGMA (Bisphenol-A-glycidyldimethacrylate) resin had been modified by incorporating TiO₂ nanoparticles (0.5–2% by weight). An ultrasonic mixing process was used to disperse the particles into the resin system prior to casting and curing test specimens. TEM investigation showed that the particles were nano size (5–60 nm) and dispersed throughout the entire volume of the resin. In dynamic mechanical analysis, nanophase resin showed increase in storage modulus and glass transition temperature from neat resin system. Thermogravimetric analysis revealed better thermal stability. Flexural loading, T _g and flexural modulus of the nanocomposites were enhanced as the particle volume fraction was enhanced and than decreased.     

A Cost-Effective Method of Aerosolizing Dry Powdered Nanoparticles

The ability to produce nanoscale aerosols from dry powdered material is needed for studies of the toxicity and environmental transformation and fate of manufactured nanoparticles. Wet aerosol generation methods can alter particle chemistry, while dry methods often cannot produce truly nanoscale aerosols. We have developed a cost-effective dry dispersion technique for manufactured nanoparticles and have demonstrated its use with C₆₀ fullerene, TiO₂, and CeO₂. The system disperses dry powders to create aerosols with mode diameters below 100 nm. Average mode and median diameters for each of the tested manufactured nanoparticles are 91 and 107 nm for C₆₀, 65 and 77 nm for TiO₂, and 40 and 43 nm for CeO₂. All aerosols exhibit right-skewed unimodal distributions and irregular morphology. Aerosol mass concentrations produced by the dispersion system vary linearly with the mass of nanomaterial loaded into it and are of a magnitude appropriate for inhalation nanotoxicology studies. This work demonstrates the ability of a simple device to produce nanoscale aerosols from powdered engineered nanoparticles.

Copyright 2013 American Association for Aerosol Research     

Direct synthesis of nano titania on highly-ordered mesoporous SBA-15 framework for enhancing adsorption and photocatalytic activity

This paper reports the synthesis of TiO₂-containing mesoporous catalysts for effectively enhancing the adsorption and photocatalytic activity. The factors that affect the photocatalytic activity of catalyst composites, including types of silica support, TiO₂ content, calcination temperature, and catalyst mass, were examined in this study. The samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and surface area analysis. The experimental results showed that incorporating TiO₂ nanoparticles into silica gel or SBA-15 frameworks could enhance the photodegradation rate more effectively than pure TiO₂. The TiO₂/SBA-15 sample displayed much higher adsorption and photocatalytic activity levels than did TiO₂/silica-gel. The pore volume and pore size of TiO₂/SBA-15 were as high as 1.317 cm³/g and 7.51 nm, respectively, which exceeded those of TiO₂/silica-gel (0.437 cm³/g and 3.68 nm, respectively). The rate constants of photocatalysis were determined. The photodegradation rate of the catalyst increased with decreasing TiO₂ content and increasing calcination temperature. The proposed method of preparing mesoporous photocatalysts is simple and suitable for mass production.     

Novel synthesis and antimicrobial studies of nanoscale titania particles

In the present investigation, a novel strategy of continuous microwave assisted flow synthesis (CMFS) has been adopted in comparison to traditional synthesis procedures (sol-gel and chemical precipitation method) for the quick production of TiO₂ nanoparticles with very fine particle properties. The X-ray powder diffraction analysis (XRPD) and transmission electron microscopy (TEM) were two techniques used for analysing the properties related to structure and particle morphology of the resultant samples. It was observed that the particles formed by using continuous flow route were less agglomerated, and particle size (~ 6?nm) was smaller in comparison with others obtained using sol-gel (~ 9?nm) and chemical precipitation method (~ 15?nm). X-ray diffraction impressions established the generation of Anatase phase with preferential [101] dimension. Zeta potential computations were taken to inspect the colloidal stability of nanoparticles. Antimicrobial nature of TiO₂ nano-samples was analyzed by using various bacterial and fungal strains. The nanostructured TiO₂ particles confirmed outstanding uniformity with respect to chemical and structure. This new ceramic substance with strong antimicrobial activity promised magnificent potential in bone tissue engineering.     

Plasmonic Effects of Infiltrated Silver Nanoparticles Inside TiO2 Film: Enhanced Photovoltaic Performance in DSSCs

The plasmonic effects of infiltrated silver (Ag) nanoparticles, with different contents, inside a nanostructured TiO₂ film on the photovoltaic performance of dye‐sensitized solar cells (DSSCs) are explored. The synthesized Ag nanoparticles are immobilized onto deposited TiO₂ nanoparticles by a new strategy using 3‐mercaptopropionic acid (MPA), a bifunctional linker molecule. Transmission electron microscope (TEM) images show that monodispersed Ag and polydispersed TiO₂ nanoparticles have an average diameter of 12 ± 3 nm and 5 ± 1 nm, respectively. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis reveals that Ag nanoparticles were successfully functionalized and capped with MPA. Optical studies on the MPA‐capped Ag nanoparticles inside TiO₂ film show an increase in the total absorbance of the electrode. Moreover, EIS measurements confirm that MPA‐capped Ag nanoparticles inhibit the charge recombination and improve the stability of nanoparticles in I₃^?/I^? electrolyte. The DSSC assembled with optimal content of MPA‐capped Ag nanoparticles demonstrated an enhanced power conversion efficiency (8.82% ± 0.07%) compared with the pure TiO₂ (7.30% ± 0.05%). The increase in cell efficiency was attributed to the enhanced dye light absorption in strength and spectral range due to the surface plasmon resonance of MPA‐capped Ag nanoparticles in the photoanode.     

Photocatalytic H2 Production from Ethanol–Water Mixtures Over Pt/TiO2 and Au/TiO2 Photocatalysts: A Comparative Study

Pt/TiO₂ (Pt loadings 0–4 wt%) and Au/TiO₂ (Au loadings 0–4 wt%) photocatalysts were synthesized, characterized and tested for H₂ production from ethanol–water mixtures (80 vol% ethanol, 20 vol% H₂O) under UV excitation. Average metal nanoparticle sizes determined by TEM were 1–3 nm for Pt in the Pt/TiO₂ photocatalysts and 5–7 nm for Au in the Au/TiO₂ photocatalysts. Au/TiO₂ showed an intense localized surface plasmon resonance feature at ~570 nm, typical for metallic Au nanoparticles of diameter ~5 nm supported on TiO₂. X-ray photoelectron spectroscopy and X-ray diffraction analyses established that Pt and Au were present in metallic form on the TiO₂ support. X-ray fluorescence revealed close accord between nominal and actual Pt and Au loadings. The Au/TiO₂ and Pt/TiO₂ photocatalysts both displayed very high activities for H₂ production under UV irradiation, with the Au/TiO₂ samples affording slightly superior rates of H₂ production at most metal loadings. The 2 wt% Au/TiO₂ and 1 wt% Pt/TiO₂ photocatalysts showed the highest H₂ production rates (32–34 mmol g^?1 h^?1). Photoluminescence studies confirmed that Pt and Au nanoparticles positively enhance the photocatalytic properties of P25 TiO₂ for H₂ production by acting as electron acceptors and thereby suppressing electron–hole pair recombination in TiO₂.     

Chemical Synthesis and Characterization of ZnO–TiO<Subscript>2</Subscript> Semiconductor Nanocomposites: Tentative Mechanism of Particle Formation

The compounds of ZnO–TiO₂ can combine the characteristics of the individual oxides which has allowed them to be used as photocatalysts in general, photodegradants in the degradation of dyes, photocatalytic oxidation of NO_x, antimicrobial, among other applications. In this study, ZnO–TiO₂ semiconductor nanocomposites were synthesized in a controlled way at low temperature. These samples of ZnO–TiO₂ were characterized using thermal analysis (TDA/TGA), IR and UV–Vis absorption spectroscopies, X-ray diffraction, and scanning electron microscopy. The primary particles showed a nanometric size (<?100 nm) and spheroidal morphology. All samples presented zincite as the main crystalline phase. When Ti⁴⁺ was added, the peaks of the diffractograms shifted slightly with respect to pure ZnO. This indicates the formation of a solid solution. Zn₂TiO₄ was observed in doped ZnO samples treated at 700 °C. The UV–Vis absorption spectra showed a band in the range between 350 and 425 nm, with a maximum around 375 nm (3.31 eV). With the addition of Ti⁴⁺, the nanocomposites showed a better absorbance in the visible range. Considering the nature of the synthesis process used, a mechanism was proposed to explanation of the formation of Nanocomposites.     

Photocatalytic Self-Cleaning of Wool Fibers Coated with Synthesized Nano-Sized Titanium Dioxide

Nano-sized TiO₂ was successfully synthesized and deposited onto wool fibers using the sol–gel process at ambient temperature. The prepared samples were characterized using several structural, textural, and morphological techniques. The electron micrographs show formation of TiO₂ nanoparticles 10–30 nm in size. The photocatalytic activity of TiO₂-coated wool fibers was investigated through the solid-phase self-cleaning of methylene blue (MB) under UV-vis irradiation by the diffuse reflectance spectroscopy (DRS) method. The fibers' structure is not altered upon light exposure. This preparation technique can also be applied to new fabrics to create self-cleaning and UV irradiation protection properties in them.     

Role of Nano‐ and Micron‐Sized Particles of TiO2 Additive on Microwave Dielectric Properties of Li2ZnTi3O8 – 4 wt% TiO2 Ceramics

Microwave dielectric ceramics with the composition of Li₂ZnTi₃O₈ – 4 wt% TiO₂ were synthesized by the conventional solid‐state reaction. 4 wt% TiO₂ powders with different particles size were added to the Li₂ZnTi₃O₈ ceramic. Then the ceramic samples were sintered at temperatures 1075°C, 1050°C, 1000°C, and 950°C for 4 h. The effect of the particles size of TiO₂ additive on the microwave dielectric properties of the ceramics has been investigated. In the study two categories of particles size of TiO₂ additive have been used; (i) Nanoparticle (50 nm), (ii) Micron sized (40, 5, 1 μm) powder. X‐ray showed that the TiO₂ additive has not solved in the LZT structure and has not almost undergone chemical reaction with the LZT ceramic. The results showed that the addition of TiO₂ nanoparticles to the LZT ceramics significantly improved the density and a dense and uniform microstructure and also abnormal grain growth were observed by SEM. The use of TiO₂ nanoparticle reduces porosity and leads to an increase in green density. The maximum density was found to be 98.5% of the theoretical density and the best relative permittivity of 28, quality factor of 68000 GHz and τ_f value of ?2 ppm/°C were obtained for the samples added with 4 wt% of the TiO₂ nanoparticles, sintered at 1050°C for 4 h.     

Photodegradation of o‐Cresol with Ag Deposited on TiO2 under Visible and UV Light Irradiation

This study investigated the effect of dosage of Ag on the characteristics of TiO₂, quantum yield, and temporal decomposition behavior of o‐cresol in an annular reactor under ultraviolet (UV) and visible light irradiation. In order to extend light absorption and minimize the rapid recombination during photoreaction, the Ag deposited on TiO₂ photocatalysts was prepared by a photodeposition process. The results of diffuse reflectance spectra (DRS) indicated that Ag deposited on TiO₂ promoted the optical absorption in the visible region and made it possible for it to be excited by visible light. The degradation rate of o‐cresol with 0.50 wt % Ag/TiO₂ under visible light irradiation was 2.0 times that with pure TiO₂.     

Influence of MWCTs and nanometal oxide/MWCTs hybrids on the thermal conduction of their acrylic-based nanocomposites

In this study, acrylic-based nanocomposites containing different contents of multi-walled carbon nanotubes (MWCNTs) and metal oxide nanoparticles (i.e., TiO₂, CuO and Fe₂O₃) were fabricated by solvent mixing method. The thermal conductivity of these samples was evaluated. The results indicated that the thermal conductivity of all fabricated samples was significantly improved even at small loading of MWCNTs. It was found that the thermal conductivity was enhanced by increase in MWCNTs content up to 5 wt%. Similarly, the metal oxide nanoparticles caused up to 75 % increment in thermal conductivity at 1.5 wt% of their loading in acrylic film. Contrary to expectations, the thermal conductivity of acrylic film was more increased by nanometal oxides (i.e., TiO₂, CuO and Fe₂O₃) than MWCNTs. The effect of hybridizing of nanometal oxide particles (1.5 wt%) and MWCNTs (1.5 wt%) on thermal conduction was investigated as well. It was found that hybridizing improved thermal conductivities by about 85, 94 and 97 % for Fe₂O₃, TiO₂ and CuO, respectively. Finally, the effects of TiO₂ pigment and CaCO₃ extender on the thermal conductivity of acrylic polymer and nano-TiO₂ acrylic composites were studied. It was found that TiO₂ could increase considerably thermal conduction of its acrylic films and acrylic nanocomposites.     

Approach to a pulse photoelectrocatalytic process for the degradation of organic pollutants

Ag–TiO₂ composite film was supported on indium–tin oxide glass (ITO) by a dip‐coating and subsequent photodeposition procedure. The composite film was employed as the photoanode for photoelectrocatalytic (PEC) degradation of Acid Orange II. The degradation efficiency for the PEC process on the Ag–TiO₂/ITO electrode with a 0.8 V anodic bias is significantly higher than that for a photocatalytic process on Ag–TiO₂/ITO film or for a PEC process on a neat TiO₂/ITO photoanode. A new PEC technology with a pulse anodic bias was also proposed in order to solve the problem of the loss of deposited Ag from the Ag–TiO₂/ITO. It was found that the PEC process with a 4.2 V pulse anodic bias could much more efficiently degrade Acid Orange II than that with a constant anodic bias of 0.8 V or 4.2 V. Moreover, when the duration of the open and close circuit time was identical, the treatment efficiency was observed to be optimal. Copyright © 2003 Society of Chemical Industry     

Electrospray Dense Suspensions of TiO2 Nanoparticles for Dye Sensitized Solar Cells

We report the feasibility of using electrospray to atomize dense suspension of nanoparticles with high solid concentrations. We demonstrate this principle through electrospraying dense suspensions of TiO₂ nanoparticles with 40 wt.% in ethylene glycol. A dye sensitized solar cell (DSSC) is fabricated by electrospray deposition and the power conversion efficiency up to 6.81% is demonstrated. This simple, one-step process can fabricate the active layer with uniform thickness and multiple length scales, including 25 nm TiO₂ nanoparticles, ～2 μm micro spherical particles, and ～20-μm-thick film. A judicious choice of drying temperature is important to ensure complete drying of suspension droplets while avoiding creation of hollow particles, because the hollow particles exhibit significantly lower carrier mobility and short circuit current. The very high solid concentration demonstrated in this work can potentially reduce the manufacturing cost of DSSC because less energy will be wasted on evaporating and/or recycling the organic solvent. In addition, because electrospray is compatible with roll-to-roll process and the yield is scalable through multiplexed electrosprays, the electrospray route is a promising and economically competitive approach for manufacturing DSSCs through spray deposition.

Copyright 2013 American Association for Aerosol Research     

Synthesis,characterization and sintering of Li2TiO3 nanoparticles via low temperature solid-state reaction

Synthesis of fine Li₂TiO₃ powders via low-temperature solid-state reaction (LTSSR) was studied. Solid Li₂CO₃ and H₂TiO₃ were blended by planetary ball mill with deionized water as medium. Calcination of the milled powder at low temperature of 500 °C resulted in the formation of pure Li₂TiO₃ nanoparticles. Another Li₂TiO₃ powder was also prepared by the conventional solid-state reaction (SSR) and a good comparison between different routes was realized. The results show that the particle size of LTSSR powder is significantly decreased to 19.6 nm while the one obtained by SSR is 146.6 nm. Low temperature calcined powders have less agglomeration and higher sinterability, which can be sintered at lower temperature. Pebbles sintered from the LTSSR powders at 750 °C exhibit small grain size (650 nm), high relative density (85.1%) and satisfactory crush load (42.8 N), whereas the SSR pebbles can only be sintered above 950 °C with the relative density close to 80%. Besides, the LTSSR samples also have a higher conductivity at room temperature, indicating the lower tritium diffusion barrier in ceramics. It is confirmed that H₂TiO₃ rather than TiO₂ is more appropriate for the solid-state reaction to produce Li₂TiO₃ powders with nano-size particles and favorable properties.     

CO Oxidation Activity of Ag/TiO2 Catalysts Prepared via Oxalate Co-precipitation

Ag/TiO₂ catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) have been prepared by means of co-precipitation of Ag- and TiO-oxalates followed by temperature programmed oxidation (TPO). The catalysts were subjected to CO oxidation in a flow reactor at atmospheric pressure and temperatures up to 573 K. Best conversion performance was obtained in a CO/O₂ = 1:1 mixture over 10% Ag/TiO₂ for which the temperature of 50% CO conversion was T ₅₀ = 333 K. The initial reaction rates were determined in a circulation reactor at low conversions and apparent activation energies between 13 and 25 kJ/mol were found for all catalysts. Transmission electron microscopy shows a broad range of nano-sized Ag particles on TiO₂ (nearly pure anatase).     

Ultrasonic-assisted pH Swing Method for the Synthesis of Highly Efficient TiO2 Nano-size Photocatalysts

A new route for the preparation of nanocrystalline TiO₂ particles based on the pH swing method assisted by ultrasonic irradiation in the presence of a surfactant (Pluronic P-123) has been successfully achieved. The prepared TiO₂ catalysts were calcined from 400 to 800 °C and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infra-red spectroscopy (FTIR), gas adsorption measurements (BET) and thermogravimetirc measurements (TAG/DTA) analyses. Characterization results revealed that the enhancement in the particle size of TiO₂ by the pH swing method could be controlled by combining the pH swing with ultrasonic irradiation. Increasing the calcination temperatures led to an increase in both the particle and pore size, whereas the surface area and pore volume gradually decreased. A synergistic effect was observed in the combined process of pH swing with ultrasonication, yielding small TiO₂ particles as well as high surface area, pore volume, pore diameter, and crystalline anatase phase. The activity of the catalysts was investigated for the oxidation of 4-chlorophenol (4-CP). TiO₂ prepared with 15 times pH swing and calcined at 700 °C was found to show the highest rate for the oxidative degradation of 4-CP when compared to the TiO₂ sample prepared with just 1 time pH swing and to the commercial P-25 TiO₂ Degussa photocatalyst. Thus, a novel approach in controlling the various physico-chemical parameters of TiO₂ nanoparticles was developed.     

Mesoporous TiO<Subscript>2</Subscript> microspheres synthesized via a facile hydrothermal method for dye sensitized solar cell applications

Mesoporous TiO₂ microspheres were successfully synthesized by a facile hydrothermal process and the obtained product was sintered at 450 °C. The sintered TiO₂ powder was characterised by powder X-ray diffraction pattern and the result shows pure anatase phase with good crystalline nature. The morphological image of field emission scanning electron microscopy and high resolution transmission electron microscopy shows spherical shape and size of the particles is around 100 to 300 nm. The Brunauer–Emmett–Teller surface area of synthesized TiO₂ material was 56.32 m² g^?1 and average pore width of synthesized materials was 7.1 and 9.3 nm. Bimodal pore structure of TiO₂ microspheres has been very effective for electrolyte diffusion into photoanode in dye sensitized solar cells. The synthesized anatase TiO₂ microsphere based dye sensitized solar cells have high surface area with light scattering effect to enhance the photocurrent and conversion efficiency than the commercial P25 photoanode material. The power conversion efficiency of synthesized mesoporous TiO₂ microspheres and commercial P25 material is 4.2 and 2.7 % respectively. Therefore bimodal mesoporous anatase TiO₂ microsphere appears to be a promising and potential candidate for dye sensitized solar cells (DSSC) application.     

Preparation of calcined hydrotalcite/TiO2-Ag composite and enhanced photocatalytic properties

A series of calcined hydrotalcite/TiO₂-Ag (HTC/TiO₂-Ag) composites with different silver (Ag) contents were successfully prepared and investigated as a catalyst for the photodegradation of phenol using UV–vis light (λ>300 nm). The Ag nanoparticles were deposited on the surface of TiO₂ (TiO₂-Ag) through photodeposition method. The TiO₂-Ag nanoparticles were supported on hydrotalcite (HT) by the co-precipitation method at variable pH (HT/TiO₂-Ag), and then calcined at 500 °C to obtain the HTC/TiO₂-Ag composites. The composites were characterized by inductively coupled plasma mass spectrometry (ICP-MS), N₂ adsorption/desorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and diffuse reflectance spectra (DRS). Results show that there is an optimum silver ratio to obtain the highest photocatalytic performance in the HTC/TiO₂-Ag photocatalyst which is 2 wt%, and is assigned as HTC/TiO₂-Ag(2). The association of silver nanoparticles on TiO₂ enhanced photocatalytic activity of the bare semiconductor composite. Only 56% of phenol was photodegraded when photodegradation was performed with HTC/TiO₂, whereas ~100% was photodegraded using HTC/TiO₂-Ag(2). The data gathered from the photocatalytic degradation of phenol were successfully fitted to Langmuir-Hinshelwood model, and can be described by pseudo-first order kinetics. The results showed the HTC/TiO₂-Ag(2) as efficient photocatalyst, low cost, separable from solution by sedimentation, and reusable. The superior performance of HTC/TiO₂-Ag(2) composite photocatalyst may be attributed to the synergic catalytic effect between silver and TiO₂, dispersion of TiO₂-Ag(2) nanoparticles supported on calcined hydrotalcite, and the calcined hydrotalcite like photocatalyst.     

A Novel Precursor for Preparation of Silver Nanoparticles: Synthesis, Characterization and Crystal Structure of Ag(PPh3)2(2-pyCOO)

A novel silver complex, Ag(PPh₃)₂(2-pyCOO)·0.5H₂O·0.5C₂H₆O, was prepared from Ag(CH₃COO)(PPh₃)₂ and 2-pyridinecarboxylic acid and after characterization by elemental analysis, infrared, ¹H and ³¹P NMR spectroscopes, and X-ray crystallography, was used as a precursor for the preparation of silver nanoparticles. The silver nanoparticles were obtained by thermolysis of the silver complex at 350 °C in the presence of oleic acid as a surfactant. Resulting silver nanoparticles were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The formation of silver nanoparticles with an average size of 60 nm and spherical morphology was confirmed by SEM. Bulk silver particles were obtained instead of silver nanoparticles when thermolysis of the silver complex was carried out in the absence of oleic acid.