Average Size Of Nanocrystals Research Articles

High impact of thiol capped ZnS nanocrystals on the degradation of single and binary aqueous solutions of industrial azo dyes under sunlight

Sulfur zinc (ZnS) nanocrystals were prepared using an aqueous colloidal route with thioglycolic acid (TGA) as a stabilizer. These ZnS-TGA nanocrystals were used as a low-cost and environmental friendly alternative for the photodegradation of methylene blue (MB) and methyl orange (MO) from aqueous solutions using sunlight irradiation. Structural and optical properties of nanocrystals were determined via X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopic, UV–Visible and photoluminescence spectroscopy. Results showed a blue shift of absorbance band and higher energy band gap values than bulk ZnS materials, which was in agreement with the quantum confinement effect. X-ray diffraction confirmed the formation of cubic phase of ZnS-TGA containing also a slight wurtzite phase. Calculated average size of ZnS nanocrystals by the Debye Scherrer relation was 3.5 nm. Characterization results showed the fixation of TGA on ZnS-NCs via sulphur and carboxylic functionalities on catalyst surface. Photoluminescence spectra obtained under excitation wavelength at 325 nm showed three emission bands (416, 441 and 484 nm), which were mainly related to band edge and defect-activated emissions. The photocatalytic activity of ZnS-TGA nanocrystals under sunlight irradiation to degrade tested MB and MO dyes and their mixture in aqueous solutions was evaluated. High dye degradation efficiency was achieved at a very short time (27 min) and this performance was attributed to the negative surface charge, surface area, surface defects and high dispersion of ZnS-TGA nanocrystals on the aquatic medium. Overall, this study demonstrates that these nanocrystals could be employed as low-cost nanocatalyst for the degradation of organic dyes in wastewater treatment.

In-situ synthesis of Co3O4 nanocrystal clusters on graphene as high-performance oxygen reduction reaction electrocatalysts

ABSTRACT The energy problem is closely related to the survival and development of human beings. Nowadays, the research of fuel cells is making rapid progress, but the bottleneck of the development of fuel cells is slow oxygen reduction reaction (ORR) of cathode. At present, it is difficult to develop a kind of oxygen reduction catalyst with high performance, low energy consumption and low pollution. Here, we synthesised Co3O4 nanocrystals loaded on a single graphene oxide layer via a convenient one-step hydrothermal method. According to the transmission electron microscopy characterisation tests, the average size of Co3O4 nanocrystals is 5 nm. Compared with the commercially available Pt/C catalyst, the obtained Co3O4/rGO catalyst demonstrates the same four-electron (4e−) oxygen reduction reaction, and the catalytic activity of ORR is significantly higher. This is due to the large surface area provided by the middle part of the composite catalyst Co3O4/rGO, which provides an effective mass transfer and electron transfer path for the catalyst.

High electrochemical performance of spinel Mn3O4 over Co3O4 nanocrystals

Manganese and Cobalt oxide (Mn3O4 and Co3O4) nanocrystals are prepared via a simple and low cost combustion synthesis. The structural studies using XRD, Raman Spectroscopy and Fourier Transform Infrared Spectroscopy reveal that, the formation of Mn3O4 in tetragonal structure with I41/amd (141) space group and Co3O4 in cubic structure with Fd3m (227) space group. The average crystallite size of nanocrystals are estimated using Debye Scherrer formula and found to be 14 and 22 nm for Mn3O4 and Co3O4, respectively. The SEM images of as-prepared Mn3O4 and Co3O4 nanocrystals show the irregular shape of grains and uniform spherical grains with an average grain size of 100 and 120 nm. The binding energy peaks of Manganese, Cobalt and Oxygen from EDS and XPS spectra show the chemical purity of the samples. The optical band gap of Mn3O4 and Co3O4 nanocrystals are 2.93 and 2.50 eV respectively. The magnetic properties of Mn3O4 and Co3O4 nanocrystals prove a strong ferromagnetic nature at 5 K temperature. The electrochemical investigations of the samples demonstrate that the Mn3O4 nanocrystals exhibited a high specific capacitance of 417 F g−1 at a current density of 0.5 A g−1 with almost 100% coloumbic efficiency after 600 cycles and good cyclic stability up to 10,000 cycles. The poor electrochemical behavior of spinel Co3O4 proves that Mn3O4 nanocrystals are good electrodes for electrochemical capacitors due to greater mass transport of electrolyte ions into the Mn3O4 electrode.

Structural and optical study of glutathione-capped Ag–In–S nanocrystals

Aqueous synthesis of glutathione-capped Ag–In–S nanocrystals (NCs) at various [Ag]:[In]:[S] molar ratios was performed under mild conditions. The average NC size is determined from X-ray diffraction data. Size-selective fractioning of the colloidal solutions is performed by repeated centrifuging with addition of 2-propanol. Based on the optical absorption and photoluminescence (PL) measurements, the dependence of the bandgap and the PL maximum position on the NC size and composition is analyzed. The analysis of the size-fractioned Ag–In–S NC Raman spectra shows that for small NCs the [Ag]/[In] ratio affects the Raman features only slightly and confirms the increase of [S]/[Ag] ratio with the decrease in NC size.

Optical and room-temperature ferromagnetic properties of Ni-doped CuO nanocrystals prepared via auto-combustion method

The pure and Ni-doped CuO nanocrystals were prepared via auto-combustion method and characterized by X-ray diffraction, scanning electron microscope, UV spectroscopy, and vibrating sample magnetometer method. The X-ray diffraction patterns of all samples revealed the monoclinic CuO nanocrystals with the nanocrystalline phase. XRD data revealed that the lattice constants of CuO nanocrystals were decreased with increasing Ni concentration which indicate that Ni2+ ions incorporated in CuO lattice. The average crystallite size of nanocrystals is intended by Scherer’s formula and found in the range of 21–24 nm. The variation of microstrain was investigated for pure and Ni-doped CuO samples. The SEM images exhibited that the prepared particles have spherical-like structure. The optical absorption spectra of the nanoparticles obtained using UV–Vis spectrophotometer show the blue-shift with increasing Ni doping. The optical band-gap energy increased with increasing Ni doping concentration due to the sp-d exchange interaction between d localized electrons of Ni. Magnetic measurement showed a ferromagnetic behavior at room temperature. Structural and magnetic properties are also discussed in detail.

Effect of pre-existing nuclei on microstructure and magnetic properties of high Bs FINEMET-like nanocrystalline alloys

The effect of conventional annealing and rapid annealing on the magnetic properties and microstructure of Fe78+2xSi7.2-xB13-xCu0.8Nb1 (x = 0, 1, 2) alloys is discussed systematically. The study was found that the existence of a large number of pre-existing nuclei in the amorphous phase of Fe82Si5.2B11Cu0.8Nb1 alloy can produce tiny nanocrystals and thus result in excellent soft magnetic properties. When the average nanocrystal size is 16 nm using rapid annealing, the best soft magnetic performance can be obtained, in which Bs reaches 1.80 T, Hc is 5 A/m, and μ is 20,000 at 1 kHz. The crystallization kinetics shows that as the Fe content increases, the incubation time of nucleation of the alloys decreases, and the nucleation is faster and easier. In addition, a large number of pre-existing crystal nuclei not only greatly reduces the nucleation activation energy of the alloy but also achieves grain refinement and excellent magnetic properties through grain competition growth.

Temperature-induced PbS quantum dots with tunable broadband wavelength grown by atomic layer deposition

Lead sulfide (PbS) quantum dots (QDs) were deposited onto silica substrates by atomic layer deposition (ALD). By controlling the number of growth cycles, the average size of the PbS nanocrystals (NCs) changed from approximately 6.3 to 95.4 nm. The crystalline phase of the PbS semiconductor materials was investigated via X-ray diffraction, and it was established that as the size of the NCs increased, the preferred growth orientation of the PbS films was (200). The obtained nanofilms were compact and continuous polycrystalline films with well-defined grain boundaries. To control the size of PbS QDs further, the temperature-induced characteristics of the ALD-fabricated PbS QD films were studied through annealing. Slow growth of the PbS QDs was observed for the nanofilms annealed at temperatures below 300 °C, whereas the QD size increased significantly at annealing temperatures above 300 °C. The broad near-infrared luminescence wavelength of the PbS nanofilms was tuned from 1000 to 1600 nm. Moreover, the photoluminescence lifetime of the annealed PbS QDs increased from 4.96 to 10.92 μs. The temperature-induced and size-controlled PbS QDs are ideal materials for application in wavelength-tunable optical devices.

Ternary CdS1–xSexnanocrystals formed in Cd‐doped As–Se–S films due to photoenhanced diffusion during micro‐Raman measurement

AbstractMicro‐Raman spectra of amorphous As–Se–S:Cd films prepared by thermal evaporation on silicon and silicate glass substrates measured at different laser power densities show the formation of CdS1–xSexnanocrystals in the As–Se–S:Cd film under laser beam illumination due to a photoinduced material transfer and photoenhanced diffusion in the laser spot area. The material transfer and the photoenhanced diffusion are caused by a non‐thermal interaction of light with the amorphous As–Se–S:Cd films. The chemical composition of the CdS1–xSexnanocrystals can be determined from the difference of the CdSe‐like and CdS‐like LO phonon wavenumbers in the Raman spectra. The photoluminescence peak energies are in agreement with the CdS1–xSexcomposition, with the average nanocrystal size being somewhat above the exciton Bohr radius.

Optical, Structural and Spectroscopic Characterization of ZnS Nanocrystals Embedded in KBr Single Crystal Matrix Grown by Czochralski Method

ZnS nanocrystals were embedded in a KBr single crystal matrix using the Czochralski growth technique. The X-ray diffraction, FT-IR and optical spectroscopy revealed the incorporation of ZnS nanocrystals. A blue shift of the absorption edge of the obtained samples has been observed, indicating the quantum confinement effect. The optical band-gap is estimated to be about 4.67 eV. Two excitonic peaks appeared at 300.4 nm and 271 nm. The average nanocrystal size was derived from the optical spectra. Annealing led to a shift in the absorption edge towards longer wavelengths and an increasing of the emissions intensity. Raman lines of the nanoparticles are broader and frequency-shifted compared to those of the bulk crystals. These results show that KBr is a good matrix-host of ZnS nanocrystals, and that the elaborated samples can be used for important technological applications.

CW laser‐initiated formation of nano‐Si crystals in glass‐metal nanostructures

AbstractLocal and controllable growth of nanocrystalline silicon (nano‐Si) in a commercial borosilicate glass is demonstrated. The nano‐Si was formed in the subsurface region of the glass via aluminothermic reaction in the course of the irradiation of a 2D array of aluminum nanodisks fabricated on the glass surface with CW low‐power 633 and 532 nm lasers. The thermoplasmonic nature of the nanodisks heating is demonstrated: at low incident intensity, the phenomenon takes place only if the plasmon resonance of the array and the laser wavelength is close enough. However, when the laser beam intensity at the sample surface exceeds 8 MW/cm2 mutual position of the plasmon resonance and the laser wavelength weakly influences the phenomenon. The nano‐Si formation is studied with Raman scattering technique, and the average size of the silicon nanocrystals is evaluated.

Ferromagnetic xyloglucan–Fe3O4 green nanocomposites: sonochemical synthesis, characterization and application in removal of methylene blue from water

In present study, novel magnetic nanocomposites based on an agro-based material, non-toxic and biocompatible xyloglucan (XG) with magnetic iron oxide (Fe3O4) were synthesized by a simple, safe and ecofriendly sonication method. The synthesized nanocomposites (XG–Fe3O4) were characterized by various analytical techniques such as powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM)-energy dispersive X-ray (EDX), transmission electron microscopy (TEM)–EDX analysis and selected-area electron diffraction (SAED). The average crystallite size of the nanocomposites as estimated by the Scherrer analysis were in the range of 17–20 nm and thus exhibited no significant difference in mean particle size on changing the ratios of Fe3O4 and Xyloglucan. The high resoloution (HR) TEM analysis revealed nanorod like shape of synthesized Fe3O4 nanoparticles. Lattice fringes of the individual crystallites were seen in the HRTEM image, indicative of their good crystallinity. The distance of 0.29 nm was found in between the lattice fringes that confirmed the cubic structure of nanoparticles. The FTIR spectrum of nanocomposite indicated the interaction of functional groups in XG with the Fe3O4 nanoparticles at the surface. The SEM analysis revealed the average crystal size of pure Fe3O4 nanocrystals to be 22.4 nm. The SAED analysis revealed that the nanocomposites (20 nm) were very close to behaving as superparamagnets at room temperature. A preliminary study on removal of methylene blue (MB) dye from aqueous solution indicated that the nanocomposite has potential to be used for photocatalytic and adsorptive removal of MB from aqueous solutions.

The dependence of morphology, structure, and photocatalytic activity of SnO2/rGO nanocomposites on hydrothermal temperature

In this work, we determined the morphological, structural, and photocatalytic properties of SnO2/rGO nanocomposites dependent on hydrothermal synthesis temperature. SnO2/rGO nanocomposites were synthesized with a hydrothermal method from SnCl4.5H2O, NaOH, and graphene oxide (GO) precursors at temperatures ranging from 100 to 200 °C. X-ray diffraction (XRD) analysis showed that the average particle size of SnO2 nanocrystals increased with hydrothermal temperature, although the tetragonal rutile crystalline structure of SnO2 did not change as the hydrothermal temperature increased. SnO2 nanoparticles and reduced graphene oxide (rGO) sheets were observed in all SnO2/rGO samples obtained with different hydrothermal temperatures. Raman spectra indicated that GO was successfully reduced to rGO, and that SnO2 nanocrystals formed during the hydrothermal process. At an excitation wavelength of 270 nm, the photoluminescence emission band of SnO2 nanocrystals increased in intensity with increasing hydrothermal temperature, while the emission intensity of the SnO2 defects decreased. The photocatalytic properties of the nanocomposites were significantly improved when the hydrothermal temperature was raised from 100 to 180 °C.

Formation of Nanocrystals in an Amorphous Phase of Multicomponent Systems

The effect of the concentration of alloying components on the crystallization of amorphous (Fe73Si13B9)1 – x – yNbxCuy and (Co70Si12B9)1 – x – yFexNby alloys has been studied by X-ray diffraction and transmission electron microscopy in a wide composition region. The formation of the bcc structures in both the alloy groups is shown to be substantially dependent on the alloying component concentrations. The bcc phase is found to form in the cobalt-based alloys in the concentration region, where it was not observed before. In the cobalt-based alloys, the bcc phase appears at a niobium concentration higher than 1 at % and the average bcc nanocrystal size varies from 40 nm (at 1 at % Nb) to 14 nm (at 5 at % Nb). In the Fe-based alloys, nanocrystals with the bcc lattice form at the copper concentrations of 0.45–1 at %, and the average nanocrystal size is dependent on the alloy composition and varies in the range 16–24 nm. The causes of the concentration dependence of the formation of nanostructures in these alloys are discussed.

Long-Term Stability of Optical Properties of Colloidal CdSe Nanocrystals in Polymer Matrices

Properties of CdSe nanocrystals (NCs) fabricated in aqueous solutions at relatively mild conditions in the presence of gelatine and stabilized in polymer (gelatine, gelatine + polyvinylpyrrolidone, polyvinyl alcohol) matrices are characterized by Raman, optical absorption and photoluminescence spectroscopies. The effect of heating of the reaction mixture on the average NC size is discussed.

Preparation of nano-glass ceramic in ZAS system without added nucleating agents

Transparent glass-ceramics in the ZnO-Al2O3-SiO2 (ZAS) system have great importance as optical glass-ceramics. Gahnite (ZnAl2O4) nanocrystals were used as a host for the various dopants which with increasing their amount, improving the performance of the product. In this research, without using theconventional nucleating agents, a transparent nano glass-ceramic including Gahnite nanocrystals was made. Precise temperature and time selection of nucleation and crystallization heat treatment were performed using XRD (X-ray diffraction), FESEM (Field Emission Scanning Electron Microscopy), Dilatometry, and differential thermal analysis (DTA). The average size of Gahnite nanocrystals was about 50 nm. The transparency of the nano glass-ceramic in the visible range was more than 60%.

The preparation and ozone-sensing performance of Co3O4 nanobricks

Co3O4 nanobricks were prepared using the method of the hydrothermal corrosion, in which CoSn(OH)6 was the precursor, and it was corroded by NaOH and transformed into Co3O4. The phase composition and morphology of the CoSn(OH)6 and the Co3O4 nanobricks prepared were examined by using XRD, SEM, and TEM. The Co3O4 nanobricks have a face-centered cubic structure with the average nanocrystals size of 10.2 nm. The sensor made by the Co3O4 nanobricks showed an ultra-sensitivity to ozone at low operating temperatures. It exhibited a fast rate of response and recovery, as well as a high stability and repeatability. The Co3O4 nanobricks can be a promising material for sensing ozone.

Swift heavy ion irradiation assisted Si nanoparticle formation in HfSiOx nano-composite thin films deposited by RF magnetron sputtering method

Silicon co-deposited HfOx thin films were prepared by RF magnetron sputtering method. The average size of Si co-deposited nanocomposites is around 10–12 nm. 100 MeV Ag ion irradiation induces the Si nano-crystal formation within the nanocomposite. The average grain size of the Si nano-crystals increases with the increase of ion fluence. The observed luminescence at 430 nm is due to oxygen related defect states and the luminescence at 530 nm may be attributed to the emission from Si nanoparticles. Red shift in emission wavelength indicates either the increase in the size of the nanoparticles or ion induced change in the dielectric constant of surrounding medium. The increase in the intensity of the luminescence peak at 440 nm indicates the creation of defect states by ion irradiation. Raman measurements further confirm the formation of Si NPs that are embedded in the composite medium.

Catalytic Performance of Nitrogen-Doped Activated Carbon Supported Pd Catalyst for Hydrodechlorination of 2,4-Dichlorophenol or Chloropentafluoroethane.

Nitrogen-doped activated carbon (N-AC) obtained through the thermal treatment of a mixture of HNO3-pretreated activated carbon (AC) and urea under N2 atmosphere at 600 °C was used as the carrier of Pd catalyst for both liquid-phase hydrodechlorination of 2,4-dichlorophenol (2,4-DCP) and gas-phase hydrodechlorination of chloropentafluoroethane (R-115). The effects of nitrogen doping on the dispersion and stability of Pd, atomic ratio of Pd/Pd2+ on the surface of the catalyzer, the catalyst’s hydrodechlorination activity, as well as the stability of N species in two different reaction systems were investigated. Our results suggest that, despite no improvement in the dispersion of Pd, nitrogen doping may significantly raise the atomic ratio of Pd/Pd2+ on the catalyst surface, with a value of 1.2 on Pd/AC but 2.2 on Pd/N-AC. Three types of N species, namely graphitic, pyridinic, and pyrrolic nitrogen, were observed on the surface of Pd/N-AC, and graphitic nitrogen was stable in both liquid-phase hydrodechlorination of 2,4-DCP and gas-phase hydrodechlorination of R-115, with pyridinic and pyrrolic nitrogen being unstable during gas-phase hydrodechlorination of R-115. As a result, the average size of Pd nanocrystals on Pd/N-AC was almost kept unchanged after liquid-phase hydrodechlorination of 2,4-DCP, whereas crystal growth of Pd was clearly observed on Pd/N-AC after gas-phase hydrodechlorination of R-115. The activity test revealed that Pd/N-AC exhibited a much better performance than Pd/AC in liquid-phase hydrodechlorination of 2,4-DCP, probably due to the enhanced stability of Pd exposed to the environment resulting from nitrogen doping as suggested by the higher atomic ratio of Pd/Pd2+ on the catalyst surface. In the gas-phase hydrodechlorination of R-115, however, a more rapid deactivation phenomenon occurred on Pd/N-AC than on Pd/AC despite a higher activity initially observed on Pd/N-AC, hinting that the stability of pyridinic and pyrrolic nitrogen plays an important role in the determination of catalytic performance of Pd/N-AC.

Growth of perovskite nanocrystals in poly-tetra fluoroethylene based microsystem: on-line and off-line measurements

Cesium lead halide perovskite nanocrystals are photoelectric nanomaterials that have potential applications in a variety of areas due to their excellent photoelectric and tunable photo luminescent properties. In this work, we investigate the synergetic effects of reaction temperature, reaction-capillary length and flow rate on the growth kinetics of perovskite nanocrystals in a PTFE-based microsystem and the photoluminescence characteristics of the perovskite nanocrystals both on-line and off-line. The on-line measurement finds that increasing the reaction temperature leads to the increase of the wavelength of the PL emission peak of the synthesized nanocrystals and reduces the average size of the perovskite nanocrystals synthesized in long reaction-capillaries. The intensity of the PL emission peak of the nanocrystals synthesized at different reaction temperatures decreases with the increase of the flow rate. The off-line measurement reveals that increasing the flow rate generally leads to the blueshift of the PL emission peaks and the decrease of the average size of the perovskite nanocrystals synthesized at the reaction temperature of 160 °C in the capillary length of 60 cm. Increasing temperature leads to the increase of the emission wavelength of the perovskite nanocrystals from 560 to 608 nm. The temperature dependence of the average size of the synthesized nanocrystals with the same synthesis conditions at different temperatures can be described by the Arrhenius relationship with an activation energy of 8.54 kJ mol−1. Five different cross-sections of the synthesized perovskite nanocrystals are observed, including rhombus, hexagon, rectangle, square and quadrangle with three of them being observed for the first time.

Site‐Resolved Cu2O Catalysis in the Oxidation of CO

AbstractThe identification of the contribution of different surface sites to the catalytic activity of a catalyst nanoparticle is one of the most challenging issues in the fundamental studies of heterogeneous catalysis. We herein demonstrate an effective strategy of using a series of uniform cubic Cu2O nanocrystals with different sizes to identify the intrinsic activity and contributions of face and edge sites in the catalysis of CO oxidation by a combination of reaction kinetics analysis and DFT calculations. Cu2O nanocrystals undergo in situ surface oxidation forming CuO thin films during CO oxidation. As the average size of the cubic Cu2O nanocrystals decreases from 1029 nm to 34 nm, the dominant active sites contributing to the catalytic activity switch from face sites to edge sites. These results reveal the interplay between the intrinsic catalytic activity and the density of individual types of surface sites on a catalyst nanoparticle in determining their contributions to the catalytic activity.