ABSTRACT
A sago starch biopolymer with embedded silver nanoparticles has been studied as a material for the prevention of microbial growth. Approximately 8 nm in size, silver nanoparticles have been synthesized by reduction of the silver salt in aqueous solution in the presence of sago starch using sodium borohydride as a reducing agent. The obtained solutions were cast on glass plates to obtain thin supported silver-starch nanocomposite films. The morphology of the nanocomposites was investigated by scanning and transmission electron microscopy. UV-Vis absorption spectroscopy showed that during the film formation a part of the silver nanoparticles has been trapped in the water present in the sample, which enabled their partial oxidation into active Ag(+) species. The oxidation of the silver nanoparticles was confirmed by X-ray photoelectron spectroscopy. The antimicrobial activity tests have shown that the nanocomposite material can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.
Subject(s)
Anti-Bacterial Agents/pharmacology , Escherichia coli/drug effects , Nanocomposites , Silver/pharmacology , Staphylococcus aureus/drug effects , Starch/pharmacology , Anti-Bacterial Agents/chemistry , Borohydrides/chemistry , Candida albicans/drug effects , Candida albicans/physiology , Escherichia coli/physiology , Metal Nanoparticles/chemistry , Microscopy, Electron, Scanning , Microscopy, Electron, Transmission , Nanocomposites/chemistry , Photoelectron Spectroscopy , Silver/chemistry , Spectrum Analysis , Staphylococcus aureus/physiology , Starch/chemistry , Temperature , Water/chemistryABSTRACT
Adsorption of sulfide ions onto a surface of starch capped silver nanoparticles upon addition of thioacetamide was investigated. UV-vis absorption spectroscopy revealed that the adsorption of the sulfide ion on the surface of the silver nanoparticles induced damping as well as blue shift of the silver surface plasmon resonance band. Further increase in thioacetamide concentration led to shift of the resonance band toward higher wavelengths indicating the formation of the continuous Ag2S layer on the silver surface. Thus fabricated nanoparticles were investigated using electron microscopy techniques (TEM, HRTEM, and HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), which confirmed their core-shell structure.
Subject(s)
Biopolymers/chemistry , Nanoparticles/chemistry , Silver/chemistry , Starch/chemistry , Sulfur/chemistry , Adsorption , Microscopy, Electron, Transmission , Nanoparticles/ultrastructure , Spectrophotometry , Sulfides/chemistry , Surface Plasmon Resonance , Surface Properties , Thioacetamide/chemistry , X-Ray DiffractionABSTRACT
A synthetic procedure for the preparation of nanocomposite films of sago starch and CdS nanoparticles was introduced. The films were characterized using optical, structural, and thermal techniques. The formation of nanostructured CdS in the starch matrix was confirmed by a blue shift in the onset of absorption in the UV-VIS spectra of the nanocomposites. The average size of the nanoparticles varied from 3.6 to 5 nm, depending on the initial concentration of cadmium acetate during the nanocomposite preparation. Fluorescence measurements of the sago-CdS nanocomposite film showed broad emission in the orange-red part of the spectrum. DSC and TGA analyses revealed significant effects of CdS nanoparticles on the thermal properties of the starch matrix.
Subject(s)
Cadmium Compounds/chemistry , Nanocomposites/chemistry , Starch/chemistry , Sulfides/chemistry , Calorimetry, Differential Scanning , Microscopy, Electron , Nanocomposites/ultrastructure , Nanotechnology , Optics and Photonics , Thermogravimetry , Water , X-Ray DiffractionABSTRACT
Size-dependent optical properties of semiconductor nanocrystals are of great interest because of the myriad of phenomena stemming from them. The preparation of more complex colloidal shapes will facilitate the systematic study of shape-dependent phenomena. It is shown that a strategy to obtain systematically more complex nanocrystal structures is to exert a sequence of shape-directing steps during the colloidal growth. Using experiments based on multiple reagent injections we show how changes in the type of surfactant introduced during growth of CdSe nanocrystals promotes shape evolution. On this basis, we propose a means to achieve a further generation of shape design in nanometer-sized colloids by using a series of growth steps, each one building from the previous conditions of shape as well as surface-specific reactivity. To understand the shape formation and stability in nanocrystalline colloids, and particularly the importance of surface ligands, we introduce an analogy with the thermodynamics of droplets.
Subject(s)
Colloids/chemistry , Crystallization/methods , Models, Chemical , Models, Molecular , Nanotechnology/methods , Quantum Dots , Computer Simulation , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
The dynamics of exciton spin relaxation in CdSe nanorods of various sizes and shapes are measured by an ultrafast transient polarization grating technique. The measurement of the third-order transient grating (3-TG) signal utilizing linear cross-polarized pump pulses enables us to monitor the history of spin relaxation among the bright exciton states with a total angular momentum of F = +/-1. From the measured exciton spin relaxation dynamics, it is found that the effective mechanism of exciton spin relaxation is sensitive to the size of the nanorod. Most of the measured cross-polarized 3-TG signals show single-exponential spin relaxation dynamics, while biexponential spin relaxation dynamics are observed in the nanorod of the largest diameter. This analysis suggests that a direct exciton spin flip process between the bright exciton states with F = +/-1 is the dominant spin relaxation mechanism in small nanocrystals, and an indirect spin flip via the dark states with F = +/-2 contributes as the size of the nanocrystal increases. This idea is examined by simulations of 3-TG signals with a kinetic model for exciton spin relaxation considering the states in the exciton fine structure. Also, it is revealed that the rate of exciton spin relaxation has a strong correlation with the diameter, d, of the nanorod, scaled by the power law of 1/d4, rather than other shape parameters such as length, volume, or aspect ratio.
Subject(s)
Cadmium Compounds/chemistry , Nanostructures/chemistry , Selenium Compounds/chemistry , Particle Size , Quantum Dots , Sensitivity and Specificity , Spectrum Analysis , Spin Labels , Time FactorsABSTRACT
The rate of exciton spin relaxation (flips) between the bright exciton states (F = +/-1) of CdSe nanocrystals is reported as a function of shape, for dots and nanorods. The spin relaxation is measured using an ultrafast transient grating method with a crossed linearly polarization sequence. It is found that the spin relaxation rate depends on the radius, not length, of the nanocrystals. That observation is explained by deriving an expression for the electronic coupling matrix element that mixes the bright exciton states.
Subject(s)
Cadmium Compounds/chemistry , Models, Chemical , Models, Molecular , Nanostructures/chemistry , Quantum Dots , Sulfides/chemistry , Cadmium Compounds/radiation effects , Computer Simulation , Crystallization/methods , Light , Molecular Conformation , Nanostructures/radiation effects , Spin Labels , Sulfides/radiation effectsABSTRACT
The thermolysis reaction of a dual precursor system, comprising one that promotes a controlled nucleation event to produce a rod-shaped nanocrystal template, and the other introduced through a subsequent series of injections that maintain the reaction under kinetic drive, is shown to provide a means of controlling growth of CdSe nanorods with a pre-determined aspect ratio.
ABSTRACT
We report the preparation of CdS nanorods using a thiosemicarbazide complex of cadmium [Cd(NH2CSNHNH2)2Cl2]. The precursor was decomposed in tri-n-octylphosphine oxide (TOPO) at 280 degrees C to give TOPO capped CdS nanoparticles; nano-dimensional rods of the material are clearly visible in transmission electron microscopy (TEM); the particles have been further characterised by X-ray diffraction (XRD) and selected area electron diffraction (SAED) and optical measurements.
