Study of energy transfer from capping agents to intrinsic vacancies/defects in passivated ZnS nanoparticles

The study of energy transfer mechanism from different capping agents to intrinsic luminescent vacancy centres of zinc sulphide (ZnS) has been reported in the present work. Nanoparticles of capped and uncapped ZnS are prepared by co-precipitation reaction. These nanoparticles are sterically stabilized using organic polymers—poly vinyl pyrrolidone, 2-mercaptoethanol and thioglycerol. Monodispersed nanoparticles were observed under TEM for both capped and uncapped ZnS nanopowders. However, for uncapped ZnS nanopowders, tendency for formation of nanorod like structure exists. Size of ZnS crystallites was calculated from X-ray diffraction pattern. The primary crystallite size estimated from X-ray diffraction pattern is 1.95–2.20 nm for capped nanostructures and 2.2 nm for uncapped nanostructures. FTIR spectra were conducted to confirm capping. Zeta potential measurements have been done to check the stability of dispersed nanoparticles. Band gap measurement was done by UV–visible spectrophotometer. Excitation and emission spectra are also performed in order to compare optical properties in various samples. Increase in emission intensity and band gap has been observed by adding different capping agents in comparison to uncapped ZnS nanoparticles. The results show that in capped ZnS nanoparticles the mechanism of energy transfer from capping layer to photoluminescent vacancy centres is more pronounced.     

One-step synthesis and antibacterial property of water-soluble silver nanoparticles by CGJ bio-template

In this article, a new synthetic method of nanoparticles with fresh Chinese gooseberry juice (CGJ) as bio-template was developed. One-step synthesis of highly water-soluble silver nanoparticles at room temperature without using any harmful reducing agents and special capping agent was fulfilled with this method. In the process, the products were obtained by adding AgNO₃ to CGJ, which was used as reducing agent, capping agent, and the bio-template. The products of silver nanoparticles with diameter of 10–30 nm have strong water solubility and excellent antibiotic function. With the same concentration 0.047 μg mL⁻¹, the antibacterial effect of water-soluble silver particles by fresh CGJ was 53%, whereas only 27% for silver nanoparticles synthesized using the template method of fresh onion inner squama coat (OISC). The excellent water solubility of the products would enable them have better applications in the bio-medical field. The synthetic method would also have potential application in preparing other highly water-soluble particles, because of its simple apparatus, high yield, mild conditions, and facile operation.     

Study of nano-CdS prepared in methanolic solution and polymer electrolyte matrix

This present paper reports the study of cadmium sulphide (CdS) nanoparticles prepared under controlled condition in methanolic solution and also in polyethylene oxide polymer electrolyte matrix. The sulphurations of the cadmium salts were done in situ by a sodium sulphide solution. The concentration of the precursors has been controlled as detailed in the paper. All the preparation and characterization were carried out at room temperature. The nanoparticles were characterized by UV/Vis spectra in the range of 600 to 250 nm. The absence of bulk/micron size particles was noted in either of the system. The absorption edge near 510 nm indicates the presence of bulk CdS, whereas the presence of nanometer-sized particles is also reflected in low wavelength region. The sizes of the particles as well as particle distribution have been estimated using X-ray diffraction and scanning electron microscopy, respectively. A comparison in the spectra has been done for the sample prepared in either of the matrices. The particle size distribution in the polymeric matrix has been found to be more in comparison to that in the methanolic suspension. The polymer is reported to work as a binder, but not as a capping agent.     

Formation of CdS nanoparticles using starch as capping agent

CdS nanoparticles have been synthesized using starch as capping agent in aqueous solution. The morphology and crystalline structure of such samples were measured by high-resolution transmission electron microscopy and X-ray diffraction, respectively. The average grain size of the nanoparticles determined by these techniques was of the order of 5 nm. Photoluminescence of CdS nanoparticles shows a strong emission peak below to the band gap bulk semiconductor attributed to center trap states, also the broadening peak was interpreted in terms of electron-phonon interaction.     

Preparation,characterization and electroluminescence studies of copper doped zinc sulfide nanocrystals

Copper doped zinc sulfide nanoparticles were prepared by chemical precipitation method. The size of the particles was varied by changing the concentration of capping agent. The XRD studies indicate that most of the samples are cubic in nature. The broadening of peaks tends to increase with increasing capping agent concentration showing decrease in particle size. The crystalline size computed using Scherrer formula is found to be in range of 3–10 nm. Absorption spectra show absorption edge in UV region. The edge was found to shift towards shorter wavelength as the capping agent concentration is increased. This indicates increased effective band gap and hence reduced particle size. The nanoparticle size has been estimated in the range 5–10 nm using effective mass approximation model. For electroluminescence (EL) study of ZnS:Cu nanocrystals, the EL cells were prepared by placing ZnS:Cu nanoparticles between SnO₂ coated conducting glass plate and aluminum foil. Alternating voltage of various frequencies was applied and EL brightness (B) at different voltages (V) was measured and reported in this paper.     

Surface status and size influences of nickel nanoparticles on sulfur compound adsorption

Metallic nickel nanoparticles were incorporated on mesoporous silica to remove sulfur compounds in diesel selectively. In the first method, nickel nanoparticles were formed on mesoporous silica SBA-15 by impregnation and subsequent reduction of nickel nitrate. The sulfur adsorption capacity was strongly dependent on the nickel loading and the average nickel particle size. In the second method, nickel nanoparticles were synthesized in solution in the presence of a capping agent and then incorporated in mesoporous silica MCF by sonication. Although these particles maintain their sizes on the MCF surface after heat treatment, capping agent remaining on the Ni particle surface might interfere the adsorption of sulfur compounds.     

Core–shell nanostructures and nanocomposites of Ag@TiO2: effect of capping agent and shell thickness on the optical properties

Two different shell-forming reagents viz. titanium isopropoxide and titanium hydroxyacylate, have been employed to obtain core–shell nanostructures of Ag@TiO₂. However, nanocomposites were formed when the shell-forming agent, titanium isopropoxide, was added before breaking the micelles. Titanium hydroxyacylate has been used for the first time as a shell-forming agent which resulted in uniform core–shell structures of Ag@TiO₂ with core diameter ranging from 10 to 40 nm and a shell thickness of 10–50 nm. The low rate of hydrolysis of titanium hydroxyacylate than titanium isopropoxide (used in other methods) appears to be responsible for the uniform shell thickness. The presence of capping agent (2-mercaptoethanol) disrupts the formation of a uniform shell structure of Ag@TiO₂. HRTEM, IR, and XPS studies of Ag@TiO₂ synthesized using capping agent show the formation of Ag₂S coated with an amorphous layer of TiO₂. A red shift of 25 and 10 nm was observed in the surface plasmon band of silver for Ag@TiO₂ core–shell structures (compared with that of silver nanoparticles) synthesized using titanium hydroxyacylate and titanium isopropoxide, respectively. The presence of capping agent (2-mercaptoethanol) masks the surface plasmon peak. Photoluminescence studies show an increase in the emission intensity for the core–shell structures when compared to that of TiO₂ nanoparticles.     

From silver nanoparticles to nanostructures through matrix chemistry

Direct in situ reduction of silver ions by a biopolymer such as agar, without any other reducing nor capping agent is shown in this article to lead either to nanoparticles (typically 12(2) nm in an optimized case) or to more complex nanostructures depending on the reaction conditions used. This approach takes advantage of the porous polymer lattice acting as a template and leads to hybrid Ag–Agar materials with long-term synergic stability. Silver acts as an antibacterial agent for agar whereas the biopolymer prevents agglomeration of the inorganic nanoparticles leading to a stable nanocomposite formed by a thermoreversible biopolymer from which silver nanoparticles can eventually be recovered.     

Surface modification of ZnO nanocrystals

Nano-crystalline ZnO particles were synthesized using alcoholic solutions of zinc acetate dihydrate through a colloidal process. Five types of capping agents: 3-aminopropyl trimethoxysilane (Am), tetraethyl orthosilicate (TEOS), mercaptosuccinic acid (Ms), 3-mercaptopropyl trimethoxysilane (Mp) and polyvinylpyrrolidone (Pv) were added at the first ZnO precipitation time (first PPT) to limit the particle growth. The first three capping agents effectively capped the ZnO nanoparticles and limited the growth of the particles, while the last two capping agents caused agglomeration or larger clusters in the solutions. Particles synthesized were in the size range of 10-30 nm after capping, and grew to 60 and 100 nm in 3 and 6 weeks, respectively, during storage at ambient conditions. Refluxing time was found to only affect the first PPT time. Washing by ethanol and slow drying were very important in converting Zn(OH)₂ into ZnO. XRD analyses revealed single phase ZnO Wurtzite crystal structure. Photoluminescence (PL) spectra showed high-intensity in UV emission and very low intensity in the visible emission, which indicates a good surface morphology of the ZnO nanoparticles with little surface defects. Optical absorption spectra showed a blue shift by the capped ZnO due to the quantum confinement effect by the single crystal size of 5-6 nm as analysed by TEM. Capping effectiveness of each agent is discussed through possible capping mechanism and chemical reaction of each capping agent. This synthesis process is a low cost, high purity, easy to control method using only bio-compatible materials.     

Size-tuneable synthesis of nickel nanoparticles

A facile method is described for synthesising nickel nanoparticles via the thermal decomposition of an organometallic precursor in the presence of excess n-trioctylphosphine as a capping ligand. For the first time, alkylamines with different chain lengths were employed as size-limiting agents in this synthesis. A direct correlation is demonstrated between the size of the alkylamine ligands used and the mean diameter of the nickel nanoparticles obtained. The use of bulky oleylamine as a size-limiting agent over a reaction period of 30 min led to the growth of nickel nanoparticles with a mean diameter of 2.8 ± 0.9 nm. The employment of less bulky N,N-dimethylhexadecylamine groups led to the growth of nickel nanoparticles with a mean diameter of 4.4 ± 0.9 nm. By increasing the reaction time from 30 to 240 min, while employing oleylamine as the size-limiting agent, the mean diameter of the nickel nanoparticles was increased from 2.8 ± 0.9 to 5.1 ± 0.7 nm. Decreasing the amount of capping ligand present in the reaction system allowed further growth of the nickel nanoparticles to 17.8 ± 1.3 nm. The size, structure and morphology of the nanoparticles synthesised were characterised by transmission electron microscopy and powder X-ray diffraction; while magnetic measurements indicated that the particles were superparamagnetic in nature.     

Synthesis and characterization of disodium ethylenediaminetetraacetic acid capped and europium doped CdS nanoparticles

We present a novel two-step chemical synthesis route to produce of disodium ethylenediaminetetraacetic acid (EDTA) capped and europium doped CdS nanoparticles. First EDTA was applied to chelate with cadmium on the surface of cadmium-rich CdS nanoparticles and act as a capping agent. Further, the purified EDTA-capped particles were used to bind with Eu³⁺. The purified and redispersed particles were characterized by UV/vis absorption, photoluminescence, TEM and SEM. It was observed that Eu³⁺ on the nanoparticle surface significantly increased the band gap emission intensity of the CdS nanoparticles.     

Physicochemical properties and toxicological assessment of modified CdS nanoparticles

The synthesis procedure represents a key aspect in designing the physical and chemical properties of gold nanoparticles. The current study proposes a simple approach for gold nanoparticles synthesis using non-thermal plasma. The novelty of the setup consists in producing an in-liquid plasma discharge in argon bubbles that are externally generated in the solution exposed to treatment. Because plasma is the source of active species which are directly involved in gold reduction, no additional reducing agent was necessary. Collagen protein was used as capping agent. A plasma treatment of 10 min is sufficient for obtaining stable colloidal solutions with UV-Vis absorption maximum at 530 nm. Transmission electron microscopy images revealed preponderant spherical nanoparticles with dimensions in the range of 6–20 nm. The method of synthesis distinguishes by its good reproducibility, facility, efficiency, and ability to generate stable colloidal nanoparticles after several minutes of plasma exposure.     

Investigations of CdS and Ag-CdS nanoparticles by X-ray photoelectron spectroscopy

In the present report, CdS and Ag-CdS nanoparticles were synthesized using cysteine as a capping agent. Surface properties CdS and Ag-CdS nanoparticles were studied by X-ray photoelectron spectroscopy (XPS). XPS study of CdS nanoparticles was carried out as a function of pH and for a refluxed sample at pH 11.2. Effect of dopant concentration on surface properties of Ag-CdS nanoparticles was also studied for as prepared samples as well as for annealed sample at 2% doping. Effect of pH, dopant concentration, and effect of particle size on different sulfur species present in the system was studied. Features of Cd 3d, S 2p and Ag 3d core level have been discussed in detail.     

Non-linear optical properties of silver nanoparticles prepared by hydrogen reduction method

Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm⁻¹. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n₂) was measured to be in the order of 10⁻⁷ (cm²/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles.     

Synthesis of Linoleic Acid Capped Copper Nanoparticles and Their Fluorescence Study

Copper nanoparticles have been prepared through the reduction of cupric ions by ethanol with linoleic acid as a capping agent. The morphology and structure of these nanoparticles have been investigated using transmission electron microscopy. The X-diffraction study shows that the nanoparticles are crystalline and mainly composed of face-centered cubic (fcc) copper with a narrow size distribution having an average size of 5 nm. Fluorescence spectra of these copper nanoparticles have been analysed which show two emission peak at 450 nm and 625 nm corresponding to the large energy band and small energy band respectively, when illuminated at 250 nm of an optical source.     

Chemiluminescent properties of polyurethane fluorophores containing red and blue chromophore moieties

Polyurethane copolymer fluorophores-containing perylene tetracarboxylic diimide and diphenyl anthracene units were prepared to examine the chemiluminescent properties. The UV-VIS spectrophotometric, photoluminescent and chemiluminescent characteristics were investigated for the monomeric and polymeric fluorophores. The sodium salicylate-catalyzed reaction of bis(2-carbopentyloxy-3,5,6-trichlorophenyl)oxalate with hydrogen peroxide provided a strong chemiluminescent light emission from red to blue color according to the mixing ratio of two chromophore units as analogous to the photoluminescent spectra. Although the chemiluminescent intensity was found to decay biexponentially as a function of measuring time, the chemiluminescent glow lasted for more than 24 h and was visible with the naked eye.     

Hydrothermal synthesis and photocatalytic properties of WO3 nanorods by using capping agent SnCl4·5H2O

Hexagonal tungsten trioxide (h-WO₃) nano-rods of different sizes are prepared via hydrothermal synthesis using a capping agent of SnCl₄·5H₂O. The size of the synthesized WO₃ nanoparticles can be controlled by changing concentration of the capping agent SnCl₄·5H₂O alone. We also investigate microstructures and optical properties of the WO₃ nanorods and propose a synthesis mechanism for the nanorods. The photocatalytic activities of the h-WO₃ nanorods are evaluated by degradation of Rhodamine-B (RhB), revealing that these nanorods exhibit excellent photocatalytic properties. The capping agent SnCl₄·5H₂O is found to be critical to governing sizes and properties of the h-WO₃ nanorods. Our results demonstrate that functional nano-crystallites with tunable size and morphology can be synthesized via a facile hydrothermal synthesis process by adjusting the concentration of capping agent alone. Such a facile hydrothermal synthesis process should be applicable to other types of nanomaterials and relevant to a wide range of applications.     

Poly(allylamine) Stabilized Iron Oxide Magnetic Nanoparticles

This paper describes a new method for the dispersing and surface-functionalization of metal oxide magnetic nanoparticles (10 nm) with poly(allylamine) (PAA). In this approach, Fe₃O₄ nanoparticles, prepared with diethanolamine (DEA) as the surface capping agent in diethyleneglycol (DEG) and methanol, are ligand exchanged with PAA. This method allows the dispersing of magnetic nanoparticles into individual or small clusters of 2–5 nanoparticles in aqueous solutions. The resulting nanoparticles are water soluble and stable for months. The PAA stabilized Fe₃O₄ nanoparticles are characterized by TEM, TGA, and FT-IR. The PAA-coated Fe₃O₄ nanoparticles will allow further chemical tailoring and engineering of their surfaces for biomedical applications.     

聚丙烯胺稳定铜纳米粒子的制备及其SERS活性研究

报道了聚丙烯胺稳定的球形和棒状铜纳米粒子的制备方法。在水溶液中空气条件下,通过水合肼还原二价铜离子到铜纳米粒子。聚丙烯胺的作用除稳定粒子防止聚集外,也可使粒子分散在水溶液中。该法的优点是在室温下,无需惰性气体保护,即可制备水溶液中分散的铜纳米粒子。紫外光谱和透射电镜监测了铜纳米粒子的生长过程。发现氢氧化钠的用量,聚丙烯胺浓度,反应时间等因素都影响到铜纳米粒子的组成,尺寸,形貌和聚集程度。氢氧化钠用量决定了制备粒子的组成成分是铜或氧化亚铜。所制备的球形铜纳米粒子表现出优良的表面增强拉曼散射活性。     

Understanding the role of hexadecyltrimethylammonium bromide in the preparation of selenium nanoparticles: a spectroscopic approach

In this work, we report the size tunable synthesis of selenium (Se) nanoparticles with an average particle size ~16 nm by using hydrazine hydrate as the reducing agent. The solution of selenium dioxide was taken as the precursor and hexadecyltrimethylammonium bromide (CTAB) a cationic surfactant, which helps in providing sufficient stabilization to the Se nanoparticles. The synthesized Se nanoparticles were characterized by the UV–vis, X-ray diffraction (XRD), and transmission electron microscopic techniques, which demonstrated high stability of Se nanoparticles in aqueous media. The particle sizes estimated from the band gap values using effective mass approximation (EMA) agreed fairly well with those calculated from the XRD measurements. The concentration effects of Se and CTAB on the particle size have also been examined. The capping ability of the CTAB has been quantitatively evaluated from FTIR studies.