可见光响应型Pt/GaP纳米粉体的光催化性质

利用水合肼液相还原法在纳米磷化镓(GaP)粉体表面沉积贵金属铂(Pt), 制备低Pt担载量Pt(0.80 wt%)/GaP和高Pt担载量Pt(4.2 wt%)/GaP纳米粉体样品. 在可见光照射条件下, 分别以GaP和Pt/GaP纳米粉体作为光催化剂, 对结晶紫水溶液进行光催化降解. 实验结果表明, GaP和Pt/GaP两种纳米粉体皆具有可见光响应光催化性能; Pt担载量对Pt/GaP纳米粉体的光催化性能有着较大的影响, 低Pt担载量Pt(0.80 wt%)/GaP纳米粉体的结晶紫光催化脱色率高于GaP纳米粉体, 而高Pt担载量Pt(4.2 wt%)/GaP粉体的结晶紫光催化脱色率则低于GaP纳米粉体.     

Synthesis of silver-integrated silica nanostructures using rice hulls and their electrochemical performance for supercapacitor application

We report the synthesis of silver-integrated silica nanostructures using rice hulls and silver chloride through a facile thermal combustion process. The formation of mesoporous silica nanomatrix embedded with silver nanoparticles (SiO₂:Ag 5 wt% and SiO₂:Ag 10 wt%) was confirmed by XRD, FTIR, EDX, BET, and TEM analysis. Also, the obtained results from the above studies revealed that the concentration of silver ions significantly increases the particle size and number of silver nanoparticles formed in the silica matrix. The electrochemical performance was studied using silver-integrated silica nanostructures as a working electrode in KOH electrolyte. The maximum specific capacitance of SiO₂:Ag 5 wt%- and SiO₂:Ag 10 wt%-coated electrode was found to be 517 and 580 F/g at current density of 1 A/g. It was also found that SiO₂:Ag 10 wt% electrode exhibit an excellent stability with the capacitance retention of 94% than SiO₂:Ag 5 wt% (capacitance retention of 85%) after 1000 cycles at a current density of 1 A/g. These results may be attributed to the inherent characteristic of more silver nanoparticles present in the silica nanomatrix in SiO₂:Ag 10 wt%. The intrinsic characteristic of rice hull-derived silica nanostructures such as high surface area and mesoporous structure along with the advantage of silver nanoparticles (conductivity) can facilitate the Faradic redox processes at electrode surface which are responsible for the supercapacitive behavior of the prepared silver-integrated silica nanostructures.

     

The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes

SnSe and silver (Ag) nanoparticles were sequentially deposited on TiO₂ nanotube (NT) by pulsed electrochemical deposition and polyol chemistry process, respectively. The morphological observation under scanning electron microscope (SEM) showed that the average size of SnSe was about 30 nm and the Ag was about 5 nm. Transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) examination indicated that Ag nanoparticles exhibited a well-defined crystallinity. However, SnSe nanoparticles were amorphous and they turned to crystalline after being annealed at 300 °C in the atmosphere. The photocatalytic behavior of SnSe/Ag-TiO₂ NT was evaluated by UV–vis diffuse reflectance spectra (DRS). The results showed that the deposition of SnSe and Ag nanoparticles increased light absorption intensity in the wavelength range of visible light, which implied that the SnSe/Ag-TiO₂ NT is a promising ternary hybrid material in photocatalysis.     

Annealing of polymer films with embedded silver nanoparticles: Effect on optical properties

The influence of annealing time and of the silver over polymer ratio on the optical properties of the silver nanoparticles embedded in a poly(vinyl alcohol) matrix has been analyzed by spectroscopic ellipsometry in the visible/near-infrared spectral domains. The complex refractive index shows a localized absorption near 420 nm which can be attributed to localized surface plasmons. An atomic force microscopy topographic analysis shows that the particles were nearly spherical with an average size less than 20 nm, as confirmed by optical transmission measurements with polarized light. The size of the particles and their number respectively decreased and increased as the annealing time of the film increased, yielding a plasmon absorption band whose intensity is correlated to the silver nanoparticles density, estimated from their nearest-neighbour distance.     

Green synthesis of stable silver nanoparticles by the main reduction component of green tea (Camellia sinensis L.)

Recently the use of medicinal plants potential in the production of nanoparticles has received serious attention. Here, the main component of Camellia sinensis L. (green tea) extract was detected by spectroscopy and the optimal conditions were determined for their performance in green synthesis of silver nanoparticles at room temperature. Epigallocatechin gallate was identified as the dominant component in the extract as determined by spectroscopy, and it was established that its oxidation was a function of the solution pH. Transmission electron microscopy, dynamic light scattering, and visible absorption spectroscopy (UV‐Vis) confirmed the reduction in silver ions to silver nanoparticles (Ag NPs). Controlling over Ag NPs shape and narrow size distribution was achieved with 10 ml green tea leaf extract solution and in different reaction pH. Spherical colloidal Ag NPs with well‐defined hydrodynamic diameters (with average hydrodynamic size of 27.9–50.2 nm) were produced. Silver nitrate concentrations used in this study were lower than that of reported in similar works, and synthesis efficiency was also higher. Nanoparticles were perfectly spherical and their uniformity, compared to similar studies, was much higher. These NPs showed higher degree of stability and were aqueously stable for >10 months in dark glasses at 4°C.Inspec keywords: hydrodynamics, nanoparticles, particle size, pH, visible spectra, ultraviolet spectra, reduction (chemical), transmission electron microscopy, silver, microorganisms, nanofabrication, colloids, biomedical materials, nanomedicine, drug delivery systemsOther keywords: transmission electron microscopy, dynamic light scattering, visible absorption spectroscopy, silver ions, narrow size distribution, silver nitrate concentrations, green synthesis, medicinal plants, solution pH, green tea leaf, hydrodynamic size, silver nanoparticles, Camellia sinensis L, drug delivery, reduction component, epigallocatechin gallate, UV‐visible spectra, hydrodynamic diameters, spherical colloidal Ag NPs, temperature 4.0 degC, Ag     

A Novel one-step synthesis of Ag-doped ZnO nanoparticles for high performance photo-catalytic applications

In this report, pure and silver (Ag) doped zinc oxide (ZnO) nanoparticles with various concentrations of silver (5 and 10 wt%) was successfully synthesized by a novel and one step microwave irradiation method. Powder X-ray diffraction results indicates that all of the as-synthesized samples including the highest Ag (10 wt%) doping have a hexagonal wurtzite type structure and average crystalline size was found to be 28, 21 and 16 nm for pure and Ag doped ZnO respectively. Spherical shaped morphology with an average diameter of around 32–13 nm was observed by Transmission electron microscope analysis. UV–Vis spectra revealed that, Ag doped samples exhibits a red shift in the absorption band edge with increasing Ag dopant concentration. The photocatalytic degradation of methyl violet (MV), phenol and rhodamine B (RHB) was investigated by using Ag-ZnO catalyst under UV light irradiation. The result showed that the photocatalytic property was significantly improved by Ag doping. The improved photocatalytic mechanism by Ag doping was also discussed. The samples were further characterized by photoluminescence spectra and Fourier Transform Infrared Spectra (FTIR) analysis.     

Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst

TiO₂ photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO₂ in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO₂ = 0.05 at%, N:TiO₂ = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%).     

Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.     

Optimisation of nitrate reductase enzyme activity to synthesise silver nanoparticles

Today, the synthesis of silver nanoparticles (Ag NPs) is very common since it has many applications in different areas. The synthesis of these nanoparticles is done by means of physical, chemical, or biological methods. However, due to its inexpensive and environmentally friendly features, the biological method is more preferable. In the present study, using nitrate reductase enzyme available in the Escherichia coli (E. coli) bacterium, the biosynthesis of Ag NPs was investigated. In addition, the activity of the nitrate reductase enzyme was optimised by changing its cultural conditions, and the effects of silver nitrate (AgNO₃) concentration and enzyme amount on nanoparticles synthesis were studied. Finally, the produced nanoparticles were studied using ultraviolet –visible (UV–Vis) spectrophotometer, dynamic light scattering technique, and transmission electron microscopy. UV–Visible spectrophotometric study showed the characteristic peak for Ag NPs at wavelength 405–420 nm for 1 mM metal precursor solution (AgNO₃) with 1, 5, 10, and 20 cc supernatant and 435 nm for 0.01M AgNO₃ with 20 cc supernatant. In this study, it was found that there is a direct relationship between the AgNO₃ concentration and the size of produced Ag NPs.Inspec keywords: enzymes, molecular biophysics, silver, nanoparticles, nanofabrication, microorganisms, cellular biophysics, silver compounds, ultraviolet spectra, visible spectra, light scattering, transmission electron microscopyOther keywords: nitrate reductase enzyme activity, optimisation, silver nanoparticle synthesis, Escherichia coli bacterium, E. coli bacterium, biosynthesis, ultraviolet‐visible spectrophotometer, UV‐vis spectrophotometer, dynamic light scattering technique, transmission electron microscopy, supernatant, metal precursor solution, AgNO₃ ‐Ag     

Ag-Si Co-doped TiO2 photocatalyst synthesized via a nonaqueous method

Ag-Si/TiO2 photocatalysts were synthesized in a nonaqueous system at 140 degrees C, and then annealed at different temperatures. The obtained photocatalysts were characterized by XRD, TEM, BET, TG-DTA, XPS, as well as UV-vis DRS. The results showed that All Ag-Si/TiO2 held an anatase phase and high thermal stability and the phase transformation from anatase to rutile was retarded to about 900 degrees C. The Ag-Si/TiO2 particles were highly mono-dispersed and the particles size became smaller compared to TiO2. Additionally, UV-vis light absorption shifted to visible region after Ag doping. Si weaved into the matrix of TiO2, while Ag dispersed on the surface of TiO2 particles. The visible light photocatalytic activity was evaluated by Rhodamine B (RhB) degradation in an aqueous solution under visible light irradiation. It was found that the photccatalytic activities of the obtained Ag-Si/TiO2 samples were all higher than those of pure TiO2 and Ag/TiO2, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The enhanced visible photocatalytic activity may be attributed to the simultaneous effects of silver and silicon co-doping.     

A visible light-induced photocatalytic silver enhancement reaction for gravimetric biosensors

We have developed a novel microgravimetric immunosensor using a WO(3) nanoparticle-modified immunoassay and a silver enhancement reaction. When the nanoparticles in silver ion solution (i.e. AgNO(3)) are exposed to visible light, the silver ions are photocatalytically reduced and form a metallic silver coating on the nanoparticles. This silver coating consequently induces changes in the mass and light absorption spectrum. Although photocatalytic reduction reactions can be achieved using ultraviolet (UV) light and TiO(2) nanoparticles as described in our previous publication (Seo et al 2010 Nanotechnology 21 505502), the use of UV light in biosensing applications has drawbacks in that UV light can damage proteins. In addition, conventional quartz crystal substrates must be passivated to prevent undesirable silver ion reduction on their gold-coated sensing surfaces. We addressed these problems by adopting a visible light-induced photocatalytic silver enhancement method using WO(3) nanoparticles and lateral field excited (LFE) quartz crystals. As a proof-of-concept demonstration of the technique, streptavidin was adsorbed onto an LFE quartz crystal, and its mass was enhanced with biotinylated WO(3) nanoparticles, this being followed by a photocatalytic silver enhancement reaction. The mass change due to the enhancement was found to be > 30 times greater than the mass change obtained with the streptavidin alone.     

银粒子修饰下的介孔二氧化钛的制备及其光催化性能的研究

利用光还原的方法制备一系列不同银含量的改性介孔二氧化钛的颗粒。采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)、紫外一可见漫反射谱(DRS)和X射线能谱仪(EDX)等技术手段对制备的样品进行了表征。结果表明, 银纳米粒子被牢牢固定在二氧化钛表面, 并在银和二氧化钛界面形成肖特基势垒用以提高电子-空穴的分离。而从紫外可见漫反射光谱中看出, 银二氧化钛样品与未改性的二氧化钛样品相比显示出更高的红移。以亚甲基蓝(MB)为光降解模型, 银改性二氧化钛表现出较高的活性。     

Synthesis and characterization of Pt/BiOI nanoplate catalyst with enhanced activity under visible light irradiation

A series of Pt/BiOI nanoplate catalysts have been synthesized by a solution combination with photodeposited method at room temperature. The as-synthesized products have been investigated by photocatalytic reaction tests and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) emission spectroscopy, and UV–vis diffuse reflectance spectra (DRS). The results show that platinum has important role in promoting the photocatalytic performance of BiOI in degradation of acid orange II in an aqueous solution under visible light (λ > 420 nm) irradiation. The deposition of optimal amount of 0.2 wt% Pt brings about a two-time increase in the photocatalytic performance. The dispersed platinum nanoparticles over BiOI nanoplate could decrease the recombination rate of the e^?/h⁺ pairs, hence promoting the photocatalytic activity.     

Intensified photocatalytic degradation of 2, 4–dicholorophenoxyacetic acid using size-controlled silver nanoparticles: Effect of pre-synthesis extraction

In this study, ultrafine silver (Ag) nanoparticles were synthesised in Orthosiphon stamineus (OS) extract via facile electrochemical method. Different pre–synthesis extraction methods, namely ultrasonic assisted extraction hydro–distillation (UAE–HD) and classical aqueous extraction (AE) were used and compared. UAE–HD attained the highest total phenolic compounds at 8563.90 mg/kg. The Ag nanoparticles prepared via pre–synthesis extraction of UAE–HD (Ag_UAE-HD) and classical AE (Ag_AE) gave ultrafine sizes of 2 nm and 15 nm, respectively. It was suggested from the characterisation results that the phenolic compounds present in the OS extract had a significant role in the capping and stabilisation of Ag nanoparticles. Moreover, it was also demonstrated that the size of the Ag nanoparticles could simply be altered by varying the amount of total phenolic content (TPC) using different pre–synthesis extraction methods prior to the synthesis of Ag. Next, the photocatalytic activity of the Ag nanoparticles was tested towards the degradation of 2, 4–dicholorophenoxyacetic acid (2,4–D) herbicide. The synthesised Ag nanoparticles also showed outstanding photocatalytic activity with maximum degradation efficiency of up to 99.78% at pH 3, 0.01 g L⁻¹ of catalyst dosage and 10 mg L⁻¹ of 2, 4-D concentration. High amount of TPC contributed to the low energy band–gap (E_g) of Ag_UAE-HD catalyst and significantly inhibited the electron-hole recombination as well as enhanced the photocatalytic activity. The figures of merit based on electric energy consumption (E_EO) indicate that less energy was consumed during the degradation of 2,4–D in the presence of Ag_UAE-HD compared with other catalysts. Therefore, it could be concluded that Ag_UAE-HD is a promising material for high photocatalytic degradation efficiency of 2,4–D under optimal condition.     

Silver nanoparticles/montmorillonite composites prepared using nitrating reagent at water and glycerol

Three procedures (P) were applied to prepare silver nanoparticles on natural Ca-montmorillonite (MT). The intercalation of the montmorillonite with silver nitrate in aqueous solution (P1), the intercalation of the montmorillonite with silver nitrate in glycerol (P2) and the successive combination of both P1 and P2 methods resulted to P3 method. X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared (FTIR) spectroscopy and the molecular modeling were employed to characterize silver nanoparticles and montmorillonite nanocomposite. The P1 produced MT-1 composite with 2.3 wt% Ag and the partially collapsed layered structure. Nanoparticles of silver larger than 20 nm with a lot of planar defects were randomly distributed on the MT-1 surface; nanoparticles smaller than 20 nm were oriented to the montmorillonite substrate. The MT-2 composite from P2 contained only 1 wt% of Ag. The molecular simulation model of MT-2 showed the interlayer space with the exchangeable cations and metallic silver atoms arrangement within the glycerol bilayer. The P3 produced composite MT-3 that contained 2.4 wt% Ag. The nanoparticles > 20 nm size had a well-defined geometry, very small nanoparticles were amorphous. The modeled structure showed the exchangeable cations, Ag+ and Ag0 located close to the silicate layers and monolayer of glycerol molecules in the interlayer space.     

Photocatalytic hydrogen evolution over surface-modified titanate nanotubes by 5-aminosalicylic acid decorated with silver nanoparticles

The efficiency of titanate-nanotubes-based photocatalysts towards hydrogen production was studied in the presence of the sacrificial agent, 2-propanol. The highest hydrogen production rate (~120 μmol h⁻¹ g⁻¹) was observed over surface-modified titanate nanotubes by 5-amino salicylic acid decorated with nanometer-sized silver nanoparticles. The X-ray diffraction analysis, transmission electron microscopy, nitrogen adsorption–desorption isotherms, and diffuse reflection spectroscopy were applied to characterize the prepared photocatalytic materials. The better photocatalytic performance of inorganic–organic hybrid materials in comparison to the pristine titanate nanotubes is a consequence of their improved light-harvesting ability due to the formation of interfacial charge transfer (ICT) complex, as well as the presence of metallic silver nanoparticles that suppress the recombination of photo-generated charge carriers. The spin trapping EPR experiments under irradiation of prepared photocatalysts with either UV or visible light were used to monitor the appearance of hydroxyl radicals and superoxide radical anions. The generation of superoxide radical anions under visible light irradiation was detected for hybrid materials, but not for the pristine titanate nanotubes. These results are a consequence of enhanced promotion of electrons to the conduction band due to extended absorption in visible spectral range in hybrids and support the higher efficiency of hydrogen generation observed for surface-modified titanate nanotubes by 5-amino salicylic acid decorated with silver nanoparticles.     

Nanoscale silver cluster embedded in artificial heterogeneous matrix consisting of protein and sodium polyacrylate

Nanoscale silver cluster protected by sodium polyacrylate (PAA) was prepared through the reduction of aqueous silver nitrate solution containing PAA. PAA concentration was varied against a fixed concentration of silver nitrate to optimize the PAA to metal ratio, in which stable colloidal solution of silver nanoparticles of 7 ± 3 nm size could be obtained. These PAA-protected silver nanoparticles in clusters of nanoscale dimension (nanoclusters) were dispersed into the artificial heterogeneous matrix fabricated from aqueous solution of polyacrylate and protein (bovine serum albumin, BSA) by adjusting the pH in the acidic region. PAA-protected Ag-nanoparticle and Ag/PAA-BSA composites were characterized by UV-VIS spectroscopy and TEM.     

Weighting the influence of TiO2 anatase/brookite ratio in TiO2–Ag porous nanocomposites on visible photocatalytic performances

Nanocomposites based on TiO₂ aerogel and Ag nanoparticles have been successfully obtained through different synthesis methods and their specific surface areas have been determined by N₂ sorption (BET method). The photocatalytic potential for salicylic acid degradation has been evaluated. It was found that under visible light irradiation, all synthesized nanocomposites exhibit higher photocatalytic activity than the commercially available Aeroxide P25. By correlating the structural parameters with the photocatalytic performances, it has been found that the Ag nanoparticles and brookite phase presence alongside the anatase play important roles on the visible photocatalysts behavior. For the Ag containing samples with mixed anatase–brookite phases, it has been observed that the visible photocatalytic performance decreases with the increase in brookite crystalline phase content. On the other hand, the addition of Ag nanoparticles results, as expected, in a clear enhancement of the visible photocatalytic activity.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).     

Facile synthesis of Ag/AgX (X = Cl,Br) with enhanced visible-light-induced photocatalytic activity by ultrasonic spray pyrolysis method

Ag/AgX (X?=?Cl, Br) plasmonic photocatalysts were synthesized via a facile one-pot ultrasonic spray pyrolysis method, wherein no additional issues such as high pressure, surfactants and reducing agents were required. The structure, morphology, and optical property of the as-prepared photocatalysts was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet–visible light absorption spectra and total organic carbon (TOC). The results showed that Ag/AgX photocatalysts have excellent photocatalytic performance for the photodegradation of methyl orange (MO) and methylene blue (MB) pollutants under visible light illumination, and the photocatalytic activity maintains a high level after seven cycles. Metallic Ag⁰ particles nucleate on the surface of AgX uniformly through the thermal decomposition of residual AgNO₃ solution, which enhanced the interaction between Ag⁰ and AgX. The outstanding photocatalytic activity benefits from the small size and high dispersion of Ag⁰ nanoparticles and the enhanced interaction between Ag⁰ and AgX.