Synthesis and characterization of ZnS-based quantum dots to trace low concentration of ammonia

In the present work,a solution-based co-precipitation method has been adopted to synthesize pure and cobalt-doped ZnS quantum dots and characterized by XRD,SEM,TEM with EDX,FTIR and gas sensing properties.XRD analysis has shown a single phase of ZnS quantum dots having a zinc blend structure.TEM and XRD line broadening indicated that the aver-age crystallite size in the sample is in the range of 2 to 5 nm.SEM micrographs show spherical-shaped quantum dots.FTIR stud-ies show that cobalt has been successfully doped into the ZnS cubic lattice.EDX spectra have analyzed the elemental pres-ence in the samples and it is evident that the spectra confirmed the presence of cobalt (Co),zinc (Zn),oxygen (O),and sulphur(S) elements only and no other impurities are observed.The ZnS-based quantum dot sensors reveal high sensitivity towards 50 ppm of ammonia vapors at an operating temperature of 70 ℃.Hence,ZnS-based quantum dots can be a promising and quick traceable sensor towards ammonia sensing applications with good response and recovery time.     

A Comparative Study on the Photocatalytic Activity of Eucalyptus Leaf Assisted Green Synthesized ZnO and Chemically Synthesized ZnO towards the Degradation of Malachite Green Dye

Abstract

The photocatalytic activities of ZnO nanoparticles, synthesized by two methods, towards the degradation of Malachite green (MG) dye were studied and compared. Green synthesized ZnO nanoparticle was observed to be more effective in photodegradation and the effect of operating parameters such as catalyst loading, initial dye concentration and pH was investigated. Optimum condition was observed at catalyst load 0.24?g/L, initial dye concentration 20?ppm and pH nine which degrades 90% of the dye under 1?h of irradiation. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy and Fourier Transform Infrared spectroscopy(FTIR) were employed as characterization techniques for the samples.     

Study of the structure of degummed Antheraea assamensis (muga) silk fibre

The paper discusses a special type of silk (muga silk) produced by the moth Antheraea assamensis (Lepidoptera: Saturniidae), which is available in the north east region, particularly in Assam, India. The structure of the degummed muga silk fibre is characterised by spectroscopy and X‐ray diffraction. An attempt has been made to establish a correlation between the orientation of the protein of the fibre and the mechanical properties of the fibre. Inter‐conversion of the α‐ and β‐phases of proteins is very common, and in some cases, both the phases may be present. Since muga silk is a protein fibre, there is a strong possibility of exhibition of this inter‐conversion property. The results show that the structure of muga fibre is made up of four molecular chains contained in a primitive tetrahedral cell with an average cell edge a _o = b ₀ = 746 pm and c ₀ =738 pm (fibre axis) and lattice number 8. The space group of the α‐phase is P4₁, with screw axis 4₁. The α‐phase accounts for rigidity and crystallinity, while the β‐phase accounts for extensibility and the amorphous state of the fibre.     

Enhancement of field emission characteristics of carbon nanotubes on oxidation

Vertically aligned multi-walled carbon nanotubes (CNTs) were grown on p-type silicon wafer using thermal chemical vapor deposition process and subsequently treated with oxygen plasma for oxidation. It was observed that the electron field emission (EFE) characteristics are enhanced. It showed that the turn-on electric field (E(TOE)) of CNTs decreased from 0.67 (untreated) to 0.26 V/microm (oxygen treated). Raman spectra showed that the numbers of defects are increased, which are generated by oxygen-treatment, and absorbed molecules on the CNTs are responsible for the enhancement of EFE. Scanning electron microscopy and Transmission electron microscopy images were used to identify the quality and physical changes of the nanotube morphology and surfaces; revealing the evidence of enhancement in the field emission properties after oxygen-plasma treatment.     

Atomic vapor deposition approach to In2O3 thin films

In2O3 thin films were grown by atomic vapor deposition (AVD) on Si(100) and glass substrates from a tris-guanidinate complex of indium [In(N(i)Pr2guanid)3] under an oxygen atmosphere. The effects of the growth temperature on the structure, morphology and composition of In2O3 films were investigated. X-ray diffraction (XRD) measurements revealed that In2O3 films deposited in the temperature range 450-700 degreesC crystallised in the cubic phase. The film morphology, studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), was strongly dependent on the substrate temperature. Stoichiometric In2O3 films were formed under optimised processing conditions as was confirmed by X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), as well as by Rutherford backscattering spectrometry (RBS). Finally, optical properties were investigated by photoluminescence (PL) measurements, spectroscopic ellipsometry (SE) and optical absorption. In2O3 films grown on glass exhibited excellent transparency (approximately 90%) in the Visible (Vis) spectral region.     

Plasma processing of nanomaterials: emerging technologies for sensing and energy applications

Plasma processing represents an attractive and versatile option for the fabrication of low-dimensional nanomaterials, whose chemical and physical properties can be conveniently tailored for the development of advanced technologies. In particular, Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) is an appealing route to multi-functional oxide nanoarchitectures under relatively mild conditions, owing to the unique features and activation mechanisms of non-equilibrium plasmas. In this context, the potential of plasma-assisted fabrication in advanced nanosystem development is discussed. After a brief introduction on the basic categories of plasma approaches, the perspectives of application to CVD processes are commented, reporting on the growth and characterization of Co3O4 nanomaterials as a case study. Besides examining the interrelations between the material properties and the synthesis conditions, special focus is given to their emerging applications as catalysts for photo-assisted hydrogen production and solid state gas sensors.     

Structural and optical properties of nanocrystalline WO<Subscript>3</Subscript> thin films

The nanocrystalline WO₃ thin films were deposited by r.f. magnetron sputtering on quartz and p- type Si (100) substrates at a constant power of 25 W and at three different sputtering pressures (0.05, 0.01 and 0.5 mbar) and post annealed at different temperatures. The deposited films were characterized by XRD, UV–VIS spectrophotometry, ellipsometry and atomic force microscopy (AFM). The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and post annealed at 573 and 673 K have the predominant orthorhombic phase, whereas at 0.1 mbar and 573, 673 K triclinic phase is predominant. When sputtering pressure is at 0.5 mbar the predominant phase is monoclinic when annealed at 473 K and triclinic at 673 K. The optical energy gap is influenced significantly by sputtering pressure and post annealing temperatures. The optical energy gap of the films deposited at higher sputtering pressures and post annealed at lower temperatures is high due to smaller crystallite sizes. The thickness of all deposited films at different conditions is around 200 nm.     

Fabrication of novel biofibers by coating silk fibroin with chitosan impregnated with silver nanoparticles

Nanoparticle based agents often applied as coatings on biomaterials have shown promise in delivering the improved sterility against variety of microbes. In the present study, silk fibers (SF) were coated with chitosan impregnated with silver nanoparticles (Ag–C–SF). These Ag–C–SF fibers were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray analysis, atomic force microscopy (AFM), Infra Red spectroscopy, Thermogravimetric Analysis and Microbiological assay techniques. AFM studies have confirmed the nano sized silver particles in chitosan solution; SEM pictures have exhibited the coating of chitosan along with silver nanoparticles on the silk fibroin. The modified fibers have also shown anti-microbial activity and improved thermal stability. The Ag–C–SF fibers may be explored as wound dressing and tendon reconstruction material in future.     

Preparation and characterization of rare earth orthoborates, LnBO3 (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO3:Gd, Tb, Eu by metathesis reaction: ESR of LaBO3:Gd and luminescence of LaBO3:Tb, Eu

Lanthanide orthoborates of composition LnBO₃ (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO₃:Gd, Tb, Eu have been prepared by metathesis reaction. This method provides a convenient route for the synthesis of orthoborates and its solid solutions at low temperatures. Powder X-ray diffraction and FT-IR spectroscopy were used to characterize these borates. Rare earth borates, (LnBO₃) are isomorphous with different forms of CaCO₃ depending on the radius of rare earth ion. LaBO₃, LaBO₃:Gd, Tb, Eu, PrBO₃, NdBO₃ crystallized in aragonite structure, SmBO₃ crystallized in H-form and TbBO₃, EuBO₃, GdBO₃, DyBO₃, YBO₃ crystallized in vaterite structure. The structural analysis of TbBO₃ was carried out. The morphology of these borates was obtained from Scanning electron microscopy. Spin-Hamiltonian parameters for Gd³⁺ are deduced from room temperature electron spin resonance spectrum of LaBO₃:Gd. The luminescence of LaBO₃:Tb, Eu gave characteristics peaks corresponding to Tb³⁺, Eu³⁺ respectively.     

Growth of epitaxial sodium-bismuth-titanate films by metal-organic chemical vapor phase deposition

The liquid-delivery spin metal-organic chemical vapor phase deposition method was used to grow epitaxial sodium-bismuth-titanate films of the system Bi₄Ti₃O₁₂ + xNa_0.5Bi_0.5TiO₃ on SrTiO₃(001) substrates. Na(thd), Ti(OⁱPr)₂(thd)₂ and Bi(thd)₃, solved in toluene, were applied as source materials. Depending on the substrate temperature and the Na/Bi ratio in the gas phase several structural phases of sodium-bismuth-titanate were detected. With increasing temperature and/or Na/Bi ratio, phase transitions from an Aurivillius phase with m = 3 to m = 4 via an interleaved state with m = 3.5, and, finally, to Na_0.5Bi_0.5TiO₃ with perovskite structure (m = ∞) were established. These phase transitions proceed at remarkably lower temperatures than in ceramics or bulk crystals for which they had been exclusively observed so far.