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.     

Improving the visible light photocatalytic activity of mesoporous TiO2 via the synergetic effects of B doping and Ag loading

B-doped together with Ag-loaded mesoporous TiO₂ (Ag/B–TiO₂) was prepared by a two-step hydrothermal method in the presence of boric acid, triblock copolymer surfactant, and silver nitrate, followed by heat treatment. The obtained samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption. It was revealed that all samples consist of highly crystalline anatase with mesoporous structure. For Ag/B–TiO₂, B was doped into TiO₂ matrix in the form of both interstitial B and substitutional B while Ag was deposited on the surface of B–TiO₂ in the form of metallic silver. Compared with the single B-doped or Ag-loaded TiO₂ one, mesoporous Ag/B–TiO₂ exhibits much higher visible light photocatalytic activity for the degradation of Rhodamine 6G, which can be ascribed to the synergistic effects of B doping and Ag loading by narrowing the band gap of the photocatalyst and preventing the fast recombination of the photogenerated charge carriers, respectively.     

The synthesis and kinetic growth of anisotropic silver particles loaded on TiO2 surface by photoelectrochemical reduction method

Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO₂ films by photoelectrochemical reduction of Ag⁺ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO₂ film after UV irradiation in AgNO₃ solution is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO₂ film was obtained with the AgNO₃ concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO₂ films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO₂ films. The maximum growth rate of silver particles loaded on TiO₂ films can be up to 0.353 nm min⁻¹ among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO₂ is 1.751 × 10⁻³ min⁻¹.     

Metal-on-oxide nanoparticles produced using laser ablation of microparticle aerosols

A continuous aerosol process has been studied for producing nanoparticles of oxides that were decorated with smaller metallic nanoparticles and are free of organic stabilizers. To produce the oxide carrier nanoparticles, an aerosol of 3–6 μm oxide particles was ablated using a pulsed excimer laser. The resulting oxide nanoparticle aerosol was then mixed with 1.5–2.0 μm metallic particles and this mixed aerosol was exposed to the laser for a second time. The metallic micron-sized particles were ablated during this second exposure, and the resulting nanoparticles deposited on the surface of the oxide nanoparticles producing an aerosol of 10–60 nm oxide nanoparticles that were decorated with smaller 1–5 nm metallic nanoparticles. The metal and oxide nanoparticle sizes were varied by changing the laser fluence and gas type in the aerosol. The flexibility of this approach was demonstrated by producing metal-decorated oxide nanoparticles using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag.     

Preparation and properties of nano-sized Ag and Ag2S particles in biopolymer matrix

Silver (Ag) and silver sulfide (Ag₂S) nanoparticles were synthesized in a sago starch matrix. The resulting nanocomposites were investigated using structural, optical and thermal methods. XRD spectra of the nanocomposites confirmed the presence of nanostructured silver (cubic phase) and silver sulfide (monoclinic phase) in the matrix. TEM micrographs showed that the nanoparticles are mostly spherical in shape. Analyzes of the optical properties of the silver nanocomposite aqueous dispersions/solutions of various concentrations were carried out. The results and the theoretical considerations suggested that at high concentrations there is a release of silver nanoparticles from the composite in the water environment. Further dilution produces homogeneous solution in which silver nanoparticles are capped with starch macromolecules. TGA analysis revealed reduced thermal stability of the nanocomposites with respect to pure starch matrix.     

Electrochemical deposition of silver nanoparticles on TiO2/FTO thin films

Silver nanoparticles were deposited on titanium oxide^IV (TiO₂) thin films supported on FTO (fluorine-doped tin oxide^IV) glass using a double pulse electrochemical deposition method. A systematic study of particle nucleation and growth is presented as a function of applied potential and time. Samples were analyzed by grazing-angle X-ray diffraction (GIXRD) technique and morphology was observed using Scanning Electron Microscopy and Energy Dispersive Spectroscopy device (SEM-EDS). Our results confirm the possibility of controlled electrochemical homogeneous deposition of metallic silver particles over TiO₂ surface, which exhibit a potential application in catalytic processes.     

Synthesis and characterization of nanostructured Ag on porous titania

In this work, porous titania was prepared on bulk Ti by chemical oxidation, and then nanostructured silver (Ag) was deposited on titania surface by ion beam sputtering. After annealing treatment, Ag/TiO₂ composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that a nano-porous titania layer with mean pore size of 150 nm and thickness of 1 μm was formed by chemical oxidation at 80 °C for 45 min. There were three Ag species (Ag (0), Ag (1+), and Ag (2+)) on composites surface after annealing treatment, and metallic Ag content achieved maximum value with annealing temperature of 500 °C in air. Ag showed high thermal stability being partly attributed to the inhibiting the diffusion of Ag by the underlying porous titania.     

Origin of ferromagnetism in iron implanted rutile single crystals

⁵⁷Fe doped titanium oxide monocrystals, prepared by ion implantation at different temperatures and subsequent thermal treatment, were characterized by conversion electron Mössbauer spectrometry, synchrotron radiation x-ray diffraction and superconducting quantum interference device magnetometry. After implantation at room temperature Fe is present in divalent state. Upon annealing in high vacuum Fe^2?+? is reduced to metallic Fe for the most part. After implantation at 623 K most iron is in metallic state. During annealing on air Fe is gradually oxidized from Fe^2?+? to Fe^3?+?. Depending on preparation conditions and thermal treatment the role of different nanosized secondary phases is discussed in terms of their influence on the magnetic properties of Fe:TiO₂. α-Fe nanoparticles are found to be responsible for ferromagnetism observed in TiO₂.     

Deposition of silver nanoparticles on carbon nanotube by chemical reduction method: Evaluation of surface,thermal and optical properties

Silver was stabilized on multi-walled carbon nanotubes (MWCNTs) by chemical-reduction technique using N,N-dimethylformamide (DMF) as a reducing agent. The influence of silver on the performance of carbon nanotubes (CNTs) was investigated by employing Fourier-transform infrared spectra (FTIR), Raman spectroscopy (RAS), thermal gravimetric analysis (TGA), zeta potential measurement, scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX), transmission electron microscopy (TEM), and reflectance spectroscopy (RS). FTIR as well as RS methods evidenced the synthesis procedure using chemical reduction method was successful. Performing TGA of the samples under oxygen atmosphere demonstrated that the silver nanoparticles (Ag NPs) generated on MWCNTs surface can decrease the thermal stability of the particles by the catalytic oxidation of CNTs. In contrary, the thermal stability of the MWCNTs has improved under nitrogen atmosphere. EDX results showed the presence of Ag, Au and Co on the surface of deposited sample. The synthesised silver multi-walled carbon nanotubes (Ag–MWCNTs) were found to have higher UV reflection activity compared with untreated particles. The Ag–CNTs can be used in producing anti-UV composites.     

Synthesis,characterization, and thermal stability of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>/CR-Ag multilayered nanostructures

The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO₂ particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO₂/TiO₂ particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C.     

Synthesis of Ag metallic nanoparticles by 120 keV Ag− ion implantation in TiO2 matrix

TiO₂ thin film synthesized by the RF sputtering method has been implanted by 120 keV Ag^? ion with different doses (3?×?10¹⁴, 1?×?10¹⁵, 3?×?10¹⁵, 1?×?10¹⁶ and 3?×?10¹⁶ ions/cm²). Further, these were characterized by Rutherford back Scattering, XRD, X-ray photoelectron spectroscopy (XPS), UV–visible and fluorescence spectroscopy. Here we reported that after implantation, localized surface Plasmon resonance has been observed for the fluence 3?×?10¹⁶ ions/cm², which was due to the formation of silver nanoparticles. Ag is in metallic form in the matrix of TiO₂, which is very interestingly as oxidation of Ag was reported after implantation. Also, we have observed the interaction between nanoparticles of Ag and TiO₂, which results in an increasing intensity in lower charge states (Ti³⁺) of Ti. This interaction is supported by XPS and fluorescence spectroscopy, which can help improve photo catalysis and antibacterial properties.     

Structural evolution of sol-gel SiO2 heated glasses containing silver particles

SiO₂ based glasses added with nanometric-silver particles have been prepared by the traditional sol-gel process, using the tetraethyl-orthosilicate alkoxide. The Ag particles were prepared using a new method described in this article, the method uses a cementation reaction between Ag ions and an iron electrode. The size of the particles, measured in the dried glass, was in the range of 100-200 nm. The observed structural changes depend on the annealing conditions, such as the annealing temperature, the amount of silver particles and the type of acid (HCl or HNO₃) used to catalyze the hydrolysis/condensation reactions during the sol-gel process. Samples prepared using both acids crystallized into the cristobalite phase after thermal annealing at 800 °C. The amount of SiO₂ crystallized depends on the amount of Ag present in the glass. Samples prepared from solutions catalyzed with HCl acid show the formation of nanometric Ag particles after thermal annealing at 500 °C, these small particles are not observed after similar treatments when HNO₃ is used as the catalytic acid. HCl and Ag₂O form AgCl which is reduced by residual carbon to form Ag ultrafine particles. The diffusion of the reduced Ag spices, which form these particles, is facilitated by the opened structure of the glasses added with Ag, as indicated by IR measurements.     

The investigation of oxidized silver nanoparticles prepared by thermal evaporation and radio-frequency sputtering of metallic silver under oxygen

The investigation of oxidized silver nanoparticles by the photoemission (XPS, UPS) and HRTEM methods was performed. The nanoparticles of oxidized silver were obtained in the vacuum chamber by two methods of synthesis: thermal evaporation of silver nanoparticles followed by transferring in convective gas flow and sputtering of oxidized clusters under the action of plasma. Both methods indicated that oxygen interaction with silver nanoparticles depends strongly on its size. It was shown that the chemical bonding of oxygen species stabilized on small particles differs from the oxygen species adsorbed on bulk silver surfaces (monocrystals, foils and large particles). The low charged oxygen with molecular type of bonding stabilizes on particles of size approximately 5 nm and smaller. Increasing particle size leads to the dissociation of molecular oxygen species and the formation of strongly charged oxygen composed of oxide nanoparticles like Ag₂O or AgO type. The presence of extended defects in the microdomain large nanoparticles facilitates the formation of Ag₂O or AgO layers covering metallic nanosilver.     

Elaboration and characterization of TiO2 nanoparticles incorporated in SiO2 host matrix

Nanometer-scale TiO₂ particles have been synthesized by sol-gel method. It was incorporated in a glass-based silica aerogel. The composite was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). The bulk glass presents a strong luminescence at wavelengths ranging from 750 to 950 nm. This PL was attributed to various non-bridging oxygen hole centers (NBOHCs) defects resulting from thermal treatment and crystallization of TiO₂ at the interface between titania nanoparticles and silica host matrix.     

Comparison of silver nanoparticles confined in nanoporous silica prepared by chemical synthesis and by ultra-short pulsed laser ablation in liquid

Hexagonally ordered mesoporous silica materials, MCM-41 and SBA-15, have been synthesized and loaded with Ag nanoparticles, utilizing both chemical synthesis and ultra-short pulsed laser ablation in liquid. In laser ablation, a silver target, immersed in aqueous suspension of ordered mesoporous silica SBA-15, was irradiated by ultra-short laser pulses to generate silver nanoparticles. For comparison, samples of similar silver contents were prepared either by incorporating silver into the SBA-15 during a hydrothermal synthesis or by introducing silver in MCM-41 by template ion-exchange. Samples were characterized by XRD, N₂ physisorption, TEM and UV–vis spectroscopy. All preparations contained significant amount of 5–50 nm size silver agglomerates on the outer surface of the silica particles. The laser ablation process did not cause significant destruction of the SBA-15 structure and metallic silver (Ag⁰) nanoparticles were mainly generated. It is demonstrated that by laser ablation in aqueous silica suspension smaller and more uniform metallic silver particles can be produced and loaded on the surface of the silica support than by synthesis procedures. Catalytic properties of the samples have been tested in the total oxidation of toluene. Because of its favorable Ag dispersity, the Ag/SBA-15 catalyst, generated by the laser ablation method, had better catalytic stability and, relative to its Ag load, higher activity than the conventional Ag/SBA-15 preparations.     

The effects of activated carbon supports on the structure and properties of TiO2 nanoparticles prepared by a sol-gel method

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.     

Nanocomposites of magnetic cobalt nanoparticles and cellulose

Polymeric matrices with stabilized metallic nanoparticles constitute an important class of nanostructured materials, because polymer technology allows fabrication of components with various electronic, magnetic and mechanical properties. The porous cellulose matrix has been shown to be a useful support material for platinum, palladium, silver, copper and nickel nanoparticles. In the present study, nanosized cobalt particles with enhanced magnetic properties were made by chemical reduction within a microcrystalline cellulose (MCC) matrix. Two different chemical reducers, NaBH₄ and NaH₂PO₂, were used, and the so-formed nanoparticles were characterized with X-ray absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These experimental techniques were used to gain insight into the effect of different synthesis routes on structural properties of the nanoparticles. Magnetic properties of the nanoparticles were studied using a vibrating sample magnetometer. Particles made via the NaBH₄ reduction were amorphous Co-B or Co oxide composites with diminished ferromagnetic behaviour and particles made via the NaH₂PO₂ reduction were well-ordered ferromagnetic hcp cobalt nanocrystals.     

Photocatalytic performance of silver TiO2: Role of electronic energy levels

Nano-sized silver deposits on the surface of Degussa P25 TiO₂ (Ag-DP25) particles act as sites of electron accumulation where the reduction of adsorbed species takes place. Electrons can be transferred from Degussa P25 TiO₂ (DP25) to Ag particles because of the difference in the work functions of the two materials. The efficiency of the electron transfer depends on the size and the distribution of metal deposits. A significant photocatalytic oxidation enhancement by metal deposit will only be observed if the metal deposits play a more dominant role than just increasing the life time of charge carriers. The properties of metal deposits like, loaded amount, oxidation state of the deposit and its size will influence the performance. Further, a decrease in band-gap in DP25 and Ag-DP25 was observed due to the carbide ion substitution for the oxide ion in TiO₂. Such unintentional carbon incorporation is expected mostly in combustion synthesized materials. Silver metal deposits and unintentional incorporation of the carbon shows the beneficial effect by specific mechanism in the photocatalytic degradation of Congo Red (CR).     

Phase separation and partial devitrification in soda-lime silicate glasses

2 O-rich droplets dispersed throughout the SiO₂-rich matrix and nanoparticles of metallic silver. In exchanged specimens the joint effect of colloidal silver and electric field results in partial transformation of the amorphous droplets into crystalline Na₂O particles. Received: 11 February 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

Coarsening-resistant Ag nanoparticles stabilized on amorphous TiO<Subscript>x</Subscript> nanoparticles

Bare Ag nanoparticles (～10 nm) and Ag nanoparticles (1–20 nm) on the surfaces of larger TiO_x nanoparticles were prepared by laser ablation of microparticle aerosols (LAMA). The behaviors of the nanoparticles during high temperature annealing were then studied with ex situ and in situ transmission electron microscopy. For the ex situ heating experiments, Ag and Ag-on-TiO_x NPs were collected onto gold TEM grids and subjected to annealing treatments at 500 °C in argon, vacuum, and air. At this temperature, bare Ag NPs on carbon TEM supports coarsened rapidly in both air and argon atmospheres. In contrast, Ag-on-TiO_x NPs that were heated to 500 °C in flowing argon or in a vacuum did not coarsen significantly and were remarkably stable. Ag-on-TiO_x NPs that were heated to 500 °C in air, however, behaved quite differently. The TiO_x crystallized upon heating and a significant loss of Ag were observed from the surfaces of the TiO_x, likely due to sublimation. These results demonstrate that the surface defect structure and chemistry of the oxide support strongly influence the thermal stability of Ag NPs produced by LAMA.