Two and four photon absorption and nonlinear refraction in undoped,chromium doped and copper doped ZnS quantum dots

The ZnS quantum dots (QDs) with Cr and Cu doping were synthesized by chemical co-precipitation method. The nanostructures of the prepared undoped and doped ZnS QDs were characterized by UV–vis spectroscopy, Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The sizes of QDs were found to be within 3–5 nm range. The nonlinear parameters viz. Two photon absorption coefficient (β₂), nonlinear refractive index (n₂), third order nonlinear susceptibility (χ³) at wavelength 532 nm and Four photon absorption coefficient (β₄) at wavelength 1064 nm have been calculated by Z-scan technique using nanosecond Nd:YAG laser in undoped, Cr doped and Cu doped ZnS QDs. Higher values of nonlinear parameters for doped ZnS infer that they are potential material for the development of photonics devices and sensor protection applications.     

Band-gap engineering of ZnSe quantum dots via a non-TOP green synthesis by use of organometallic selenium compound

Single-step green synthesis of ZnSe quantum dots (QDs) from 1,2,3-selenadiazole and zinc acetate resulted in formation of high-quality mono-disperse ZnSe with engineered band-gap. The present method is a non-TOP green route where oleic acid is used as a surfactant. The size quantization effect can be monitored by UV–visible spectroscopy which shows in the range 370–387 nm (3.20–3.35 eV), a blue shift of about 70–90 nm with respect bulk ZnSe. Photoluminescence measurement revealed band-gap emission at ∼390 nm (3.18 eV, Stokes shift of <10 nm with FWHM <30 nm). Broadened XRD pattern indicated formation of cubic ZnSe and the estimation of particle size from the line broadening at 〈1 1 1〉 matched well the TEM analysis.     

Synthesis and characterization of monodisperse copper nanoparticles using gum acacia

A simple method was put forward in this paper for preparing colloidal copper nanoparticles in aqueous solutions using copper sulfate, gum acacia and hydrazine hydrate as copper precursor, capping agents and reducing agents, respectively, without any inert gas. The formation of nanosized copper was confirmed by its characteristic surface plasmon absorption peak at 604 nm in UV–vis spectra. The transmission electron microscopic (TEM) and scanning electron microscope (SEM) images show that the as-synthesized copper fine spherical particles are distributed uniformly with a narrow distribution from 3 nm to 9 nm. The X-ray diffraction (XRD) and high resolution transmission electron microscopic (HRTEM) demonstrated that the obtained metallic nanoparticles are single crystalline copper nanoparticles. Fourier transform infra-red (FT-IR) spectroscopic data suggested that the copper nanoparticles are coated with gum acacia. The effects of the quantity of gum acacia on the particle size were investigated by the UV–vis spectra and TEM images. The growth process of the nanoparticles was monitored by the UV–vis spectra. The mechanism of the formation copper nanoparticles was discussed. The process raised in this study can be served as an excellent candidate for the preparation of copper nanoparticles in a large scale production.     

Ultrasound with low intensity assisted the synthesis of nanocrystalline TiO2 without calcination

A novel method has been developed for the preparation of nano-sized TiO₂ with anatase phase. Nanoparticles with diameter about 6 nm were prepared at a relatively low temperature (75 °C) and short time. The synthesis was carried out by the hydrolysis of titanium tetra-isopropoxide (TTIP) in the presence of water, ethanol, and dispersant under ultrasonic irradiation (500 kHz) at low intensity. The results show that variables such as water/ethanol ratio, irradiation time, and temperature have a great influence on the particle size and crystalline phases of TiO₂ nanoparticles. Characterization of the product was carried out by different techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV–vis spectroscopy.     

Electronic structure and optical properties of BaMoO4 powders

Barium molybdate (BaMoO₄) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 °C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm⁻¹, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO₄] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.     

In situ growth of CdSe/CdS quantum dots inside and outside of MWCNTs

The CdSe/CdS quantum dots were grown in situ inside and outside of the multiwalled carbon nanotubes in an innocuous solvent and at a lower temperature. The CdSe/CdS-CNTs nanoheterostructures were characterized by TEM, HRTEM, EDS, XPS and PL. The CdSe/CdS nanocrystals with diameters about 5 nm exhibit an improved PL emission.     

Synthesis and characterization of Ag/PVA nanorods by chemical reduction method

Silver (Ag) nanorods with the average length of 280 nm and diameters of around 25 nm were synthesized by a simple reduction process of silver nitrate in the presence of polyvinyl alcohol (PVA) and investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission-electron microscopy (TEM) and UV–vis spectrum. It was found out that both temperature and reaction time are the important factors in determining the morphology and aspect ratios of nanorods. TEM images showed the prepared Ag nanorods have a face centered shape (fcc) with fivefold symmetry consisting of multiply twinned face centered cubes as revealed in the cross-section observations. The fivefold axis, i.e. the growth direction, normally goes along the (1 1 1) zone axis direction of the basic fcc Ag-structure. Preferred crystallographic orientation along the (1 1 1), (2 0 0) or (2 2 0) crystallographic planes and the crystallite size of the Ag nanorods are briefly analyzed.     

Temperature dependent structural and optical properties of tin oxide nanoparticles

Nanocrystalline tin oxide (SnO₂) powders were synthesized through wet chemical route using tin metal as precursor. The morphology and optical properties, as well as the effect of sintering on the structural attributes of SnO₂ particles were analyzed using Transmission electron microscopy (TEM), UV–visible spectrophotometry (UV–vis) and X-ray diffraction (XRD), respectively. The data revealed that the lattice strain plays a significant role in determining the structural properties of sintered nanoparticles. The particle size was found to be 5.8 nm, 19.1 nm and 21.7 nm for samples sintered at 300 °C, 500 °C, and 700 °C, respectively. Also, the band gaps were substantially reduced from 4.1 eV to 3.8 eV with increasing sintering temperatures. The results elucidated that the structural and optical properties of the SnO₂ nanoparticles can be easily modulated by altering sintering temperature during de novo synthesis.     

Photocatalytic degradation of ciprofloxacin drug in water using ZnO nanoparticles

We report the synthesis of nanostructure ZnO semiconductor with ～2.1 nm diameter using a chemical precipitation method. The resulting nanoparticles were characterized by X-ray diffraction analysis (XRD), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties were investigated by UV–vis and fluorescence techniques. The absorption spectra exhibit a sharp absorption edge at ～334 nm corresponding to band gap of ～3.7 eV. The fluorescence spectra displayed a near-band-edge ultraviolet excitonic emission at ～410 nm and a green emission peak at ～525 nm, due to a transition of a photo-generated electron from the conduction band to a deeply trapped hole. The photocatalytic activity of the prepared ZnO nanoparticles has been investigated for the degradation of ciprofloxacin drug under UV light irradiation in aqueous solutions of different pH values. The results showed that the photocatalytic degradation process is effective at pH 7 and 10, but it is rather slow at pH 4. Higher degradation efficiency (～50%) of the drug was observed at pH 10 after 60 min. Photodegradation of the drug follows a pseudo-first-order kinetics.     

Synthesis,biocompatibility and luminescence properties of quantum dots conjugated with amino acid-functionalized β-cyclodextrin

A series of CdSe and CdSe/CdS quantum dots (QDs) labeled with amino acid-modified β-cyclodextrin (β-CD) was prepared by a simple ultrasonic method. These amino acid-modified β-CD-coated QDs are very soluble and stable in biological buffer. They also have high colloidal stability and strong optical emission properties that are similar to those of untreated tri-n-octylphosphine oxide (TOPO)-coated QDs. The quantum yields (QYs) of these amino acid-modified β-CD-coated CdSe and CdSe/CdS QDs in biological buffer were found to be very high. In particular, the QYs of the positively charged l-His-β-CD-coated CdSe/CdS QDs were as high as 33.5±1.8%. In addition, the fluorescence lifetime of these QDs was also very long in PBS solutions as determined by frequency domain spectroscopy. For example, the lifetime of l-His-β-CD-coated CdSe/CdS QDs was 8.6 ns. The in vitro cytotoxicity of these QDs in ECV-304, SH-SY5Y and HeLa cells was found to be lower. l-His-β-CD-coated CdSe/CdS QDs were the least cytotoxic (IC₅₀ 95.6±3.2 mg mL^?1 in ECV-304 cells after 48 h). The flow cytometry results show that the positively charged amino acid led to a considerable increase in biocompatibility of QDs. This may be attributed to the presence of an amino acid-modified β-CD outer layer, which enhanced the biocompatibility.     

Intercalation of papain enzyme into hydrotalcite type layered double hydroxide

Intercalation of proteolytic enzyme papain into hydrotalcite type LDH structure was achieved by controlled co-precipitation at pH=9.0 in the presence of papain. Characterization of the MgAl–papain–LDH phase was carried out using X-ray powder diffraction (XRD), elemental analysis, infrared spectroscopy (IR) and thermogravimetry (TG). According to XRD, papain was successfully intercalated. The d-value for the basal spacing of MgAl–papain–LDH was found at ～5.3 nm. Consequently, original papain (hydrodynamic diameter ～7.2 nm) attains a compressed conformation during intercalation.Formation of MgAl–papain–LDH was confirmed by elemental analysis and transmission electron microscopy (TEM). Under SEM, MgAl–papain–LDH phases appear as nanothin platelets which are intergrown to flower-like aggregates. Steric size and activity of the enzyme was retained after deintercalation from MgAl–LDH framework, as was evidenced by light scattering and UV/vis measurements. Thus, papain is not denatured during intercalation, and LDH is a suitable host structure which can provide a time-controlled release of the biomolecule.     

Preparation of tunable silicon q-dots through ultrasound

Silicon quantum dots (QDs) have been prepared through ultrasound treatments of light-emitting porous silicon layers (PSL) electrochemically etched from a p⁺ type crystalline silicon (c-Si). The sonication treatments allowed separating the porous fraction from the bulk of c-Si as well as to mechanically reduce their dimensions. The ultrasounds processes have been carried out in two different organic solvents (toluene and tetrahydrofuran), and allowed obtaining silicon QDs emitting light in the blue–green part of the visible spectrum (estimated QDs diameter around 5 nm). Moreover, by adding the proper chemicals in the solvents, such as alkenes, or simply paraffin oil, we have stabilized the QDs achieving surface modification and observed an effect on size reduction. Photoluminescence spectra of the QDs, TEM images and a preliminary micro-FTIR investigation of functionalised QDs will be presented in this paper.     

Synthesis,characterization and photoluminescence of ZnO:Cd rosette-like nanostructures using solution process

Well crystalline undoped and Cd-doped ZnO rosette-like structures were successfully synthesized at low temperature (80 °C) via solution process technique during 30 min. Zinc nitrate, cadmium nitrate, sodium hydroxide and hexamine were used as starting materials. The morphology and microstructure were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. X-ray diffraction indicated that the structure has a single phase with wurtzite structure. FESEM indicated that rosette like structures have been formed. This rosette consists of nanorods with length 210 and 460 nm and diameter 50 and 74 nm for undoped and Cd doped ZnO, respectively. HRTEM showed a decrease in the lattice parameter after the Cd doping. EDX showed that the amount of Cd incorporated into ZnO is 6.4 wt.%. Photoluminescence measurements taken on both doped and undoped samples showed that, in the Cd-doped ZnO nanostructures, the band-edge UV emission is blue shifted and the broad green emission intensity decreased.     

Microwave synthesis of nitrogen doped Ti4O7 for photocatalytic applications

The nitrogen (N) doped Ti₄O₇ photocatalyst was prepared from urea as a nitrogen source by a microwave method. The resulting photocatalyst was characterized by X-ray diffraction (XRD), Field Emission Scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) and UV–vis spectroscopy (UV–Vis). 0.1 M N doped Ti₄O₇ photocatalyst exhibited methylene blue decomposition efficiency of 100% which was prepared by microwave treatment for above 30 min. Rate constant was found to be 0.028910 min⁻¹ in the first order kinetic.     

Effects of morphology on photocatalytic performance of Zinc oxide nanostructures synthesized by rapid microwave irradiation methods

In this study, two different chemical solution methods were used to synthesize Zinc oxide nanostructures via a simple and fast microwave assisted method. Afterwards, the photocatalytic performances of the produced ZnO powders were investigated using methylene blue (MB) photodegradation with UV lamp irradiation. The obtained ZnO nanostructures showed spherical and flower-like morphologies. The average crystallite size of the flower-like and spherical nanostructures were determined to be about 55 nm and 28 nm, respectively. X-ray diffraction (XRD), scanning electronic microscopy (SEM), Brunauer–Emmett–Teller (BET), room temperature photoluminescence (RT-PL) and UV–vis analysis were used for characterization of the synthesized ZnO powders. Using BET N₂-adsorption technique, the specific surface area of the flower-like and spherical ZnO nanostructures were found to be 22.9 m²/gr and 98 m²/gr, respectively. Both morphologies show similar band gap values. Finally, our results depict that the efficiency of photocatalytic performance in the Zinc oxide nanostructures with spherical morphology is greater than that found in the flower-like Zinc oxide nanostructures as well as bulk ZnO.     

Rapid sonochemical synthesis of irregular nanolaminar-like Bi2WO6 as efficient visible-light-active photocatalysts

Irregular Bi₂WO₆ nanolaminars have been successfully synthesized via a rapid sonochemical approach using bismuth nitrate and tungstic acid as precursors in an aqueous solution. The characteristics of them were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption, pore value, PL spectroscopy and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). These irregular nanolaminars are of geometric shapes of orthorhombic Bi₂WO₆ with their basal plane being (0 0 1). They possess high crystallinity, lager surface area and pore value, which means fewer traps and stronger photocatalytic activity. The growth mechanism of such special nanolaminar was related to the sonochemical synthesis route, which played a key role in the formation of Bi₂WO₆ nanolaminar. Simultaneously, it was found that the formation of Bi₂WO₆ nanolaminar is a time dependent process. The Bi₂WO₆ nanolaminar has higher photocatalytic activity than bulk Bi₂WO₆ nanoparticle obtained by refluxing method for rhodamine B (Rh.B) degradation under visible light irradiation (λ > 400 nm).     

Fabrication of PbS thin films composed of highly (200)-oriented nano-/micro-rods in deep eutectic solvent

PbS thin films composed of highly (200)-oriented shuttle-like nano-/micro-rods were successfully fabricated on glass substrates by the environment friendly ionothermal method at 140 °C in deep eutectic solvent (DES). The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), ultraviolet-visible (UV–vis) and photoluminescence (PL) spectra, respectively. The possible mechanism of the oriented growth of PbS nano-/micro-rods was discussed. The PbS thin films composed of shuttle-like nano-/micro-rods exhibited a large absorbance property in the wavelength range of 350–1100 nm, and moreover, the PL spectrum had a broad emission band centered at 490 nm. The shuttle-like PbS nano-/micro-rods-based thin films might have potential application in solar cells.     

Nanostructure materials for destruction of warfare agents and eco-toxins prepared by homogeneous hydrolysis with thioacetamide: Part 1—zinc oxide

Zinc sulphide (ZnS) nanoparticles were prepared by homogeneous hydrolysis of zinc sulphate and thioacetamide (TAA) at 80 °C. After annealing at temperature above 400 °C in oxygen atmosphere, zinc oxide (ZnO) nanoparticles were obtained. The ZnS and ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HRTEM), selected area electron diffraction (SAED), by BET and BJH methods used for surface area and porosity determination. The photocatalytic activity of the as-prepared ZnO samples was determined by the decomposition of Orange II in the aqueous solution under UV irradiation of 365 nm of wavelength.     

Green synthesis of nanocomposites consisting of silver and protease alpha chymotrypsin

The synergy of ultrasonication and the exposure to light radiation was found to be necessary in the formation of nanocomposites of silver and a protease alpha chymotrypsin. The reaction was carried out in aqueous medium and the process took just less than 35 min. Ultrasonication alone formed very negligible number of nanoparticles of <100 nm size whereas light alone produced enough number but the size of the particles was >100 nm.The effects of pH (in the range of 3–5, 9–10), ultrasonication time periods (0–30 min), ultrasonication intensity (33–83 W cm^?2), energy of light radiation (short UV, long UV and Fluorescent light) and time period of exposure (5–60 min) to different light radiations were studied.The formation of nanocomposites under these effects was followed by surface plasmon resonance (SPR) spectra, dynamic light scattering (DLS), transmission electron microscopy (TEM). Ag–chymotrypsin nanocomposites of sizes ranging from 13 to 72 nm were formed using the synergy of ultrasonication and exposure to short UV radiation. Results show that ultrasonication promoted nuclei formation, growth and reduction of polydispersity by Ostwald ripening.     

Photo-induced isomerization of poly 4′-(6-acryloxy) hexyloxy-4-methoxyazobenzene ultra-thin solid film prepared by Langmuir–Blodgett technique

The photo-induced response of an ultra thin polymeric film of poly 4′-(6-acryloxy) hexyloxy-4-methoxyazobenzene (P5) is investigated. A monolayer of P5 at a gas–water interface possesses a mean molecular area of 28.0 Å²/monomer-repeat. Multilayer films of P5 were prepared by horizontal deposition at a surface pressure of 25 mN/m². The uniformity of the transfer process is shown by UV–vis absorption spectra where a linear relationship between the absorption maxima and the number of transferred layer was observed. The average layer thickness of the transferred film determined by XRD measurements is 34.0 Å. This is longer than the length of the azobenzene side group. The transferred film shows a blue shift of the π–π¹ transition from 357 nm for the P5 in solution to 340 nm for the P5 in the film. This suggests the formation of H-aggregate with a head-to-head arrangement of the dipole within the film. The optical property of the transferred film is changed by the irradiation of the film with the UV light at 385 nm. An irreversible change in its molecular packing in the film is seen in the shift of the UV–vis absorption maxima and the change in morphology as observed by AFM. The film morphology changes from being a smooth film into an island-like surface when exposed to the UV irradiation. The layer structure in the film is destroyed. A mass transport is observed during the cis–trans thermal back isomerization process. This suggests that movement of the P5 took place in both the trans–cis isomerization process and the cis–trans back isomerization process. The first movement leads to a molecular expansion while the second, to a molecular contraction.