P. Sreekumari Nair

Cadmium ethylxanthate: A novel single-source precursor for the preparation of CdS nanoparticles

CdS nanoparticles capped with tri-n-octylphosphine oxide (TOPO) have been synthesised by a single-source route using cadmium ethylxanthate as a precursor. The nanoparticles obtained show quantum size effects in the optical absorption spectra and the photoluminescence shows an emission maximum that is characteristically red shifted in relation to the band edge. The X-ray diffraction (XRD) pattern shows the material to be hexagonal with a calculated particle size (from the Scherrer equation) of 3.9 nm. The size of the particles is confirmed by the transmission electron microscope (TEM) image, which shows well-defined, spherical particles with an average size of 4.2 nm ± 10%.

Thermal decomposition of single source precursors and the shape evolution of CdS and CdSe nanocrystals

A systematic analysis of the thermal decomposition of various single-source precursors is reported with the aim of finding a correlation between the pattern of thermal decomposition and morphology of the nanocrystals resulting from the thermolysis of these precursors in a coordinating solvent. The precursors studied are cadmium complexes of N,N′-dioctylthiourea, N,N′-diocyclohexylthiourea, N,N′-diisopropylthiourea, N,N′-tetramethylthiourea, dithiobiurea, ethylxanthic acid, thiosemicarbazide, selenosemicarbazide. Cadmium complexes of thiosemicarbazide and selenosemicarbazide uniquely yield rod-shaped CdS and CdSe nanocrystals respectively while all other precursors yield spherical CdS nanoparticles. Nanorod formation without the aid of any external shape-directing agent is explained through analysis of the thermal decomposition patterns, as observed by thermogravimetric analysis, for the range of precursor molecules. It is suggested that the low activation energy for the semicarbazide precursor decomposition, compared to those that produce dot-shaped nanocrystals, provides conditions favourable for the growth of nanorods. Evidence supporting the idea that the semicarbazide precursors furthermore release a structure-directing agent during decomposition is provided by infrared spectra and elemental analysis. Hence it can be presumed that thiosemicarbazide and selenosemicarbazide ligands each act as both the source of sulfur and a shape-directing agent.

Preparation of CdS nanoparticles using the cadmium(II) complex of N,N′-bis(thiocarbamoyl)hydrazine as a simple single-source precursor

CdS nanoparticles have been synthesised by thermolysing Cd(SCNHNH2)2Cl2 in tri-n-octylphosphine oxide (TOPO) at 230°C. The optical properties and structural characteristics of the particles are reported.

Adsorption of sulfur onto a surface of silver nanoparticles stabilized with sago starch biopolymer.

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.

Cd(NH2CSNHNHCSNH2)Cl2: a new single-source precursor for the preparation of CdS nanoparticles

Abstract The complex of cadmium with dithiobiurea, [Cd(NH 2 CSNHNHCSNH 2 )Cl 2 ], has been used as a precursor for the synthesis of CdS nanoparticles. The precursor was decomposed in tri- n -octylphosphine oxide to give CdS nanoparticles that show quantum confinement effects with characteristic close to band edge luminescence. The broad diffraction in the XRD pattern and diffused diffraction rings of the SAED pattern are typical of nanometer-sized particles. The particle morphology was found to depend on the temperature of injection of the precursor. Transmission electron microscopy shows irregular non-spherical particles prepared by injection at 150 °C, whilst with injection at 240 °C the particles are formed as spherical aggregates of relatively uniform size (50 nm).

Characterization of polystyrene filled with HgS nanoparticles

A polystyrene (PS)–HgS nanocomposite has been synthesized by first preparing a copolymer of styrene and mercury–acrylamide (5% by weight) and further reaction of it with H2S in chloroform solution. The effect of the HgS nanoparticles on the physical properties of the composite has been studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature of the composite is 20 jC higher than that of polystyrene. The thermal stability of the composite is higher than that of polystyrene as evidenced by the shift of onset temperature of degradation by 12 jC as measured by TGA. D 2003 Elsevier B.V. All rights reserved.

The synthesis of HgS nanoparticles in polystyrene matrix

A composite of nanodimensional HgS and polystyrene has been prepared by reacting a solution of the copolymer formed from mercury acrylamide and styrene in chloroform solution with H2S. The product shows different colours depending on the amount of H2S used. The composite material has been characterised by UV, PL, TEM, and XRD techniques. The TEM images show particle sizes of less than 12 nm. The band gaps calculated from the optical spectra are higher than that for bulk material as expected for quantum confined materials.

A single-source route to CdS nanorods

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.

Biopolymer-protected CdSe nanoparticles.

A synthetic procedure for the encapsulation of cadmium selenide (CdSe) nanoparticles in a sago starch matrix is introduced. The nanocomposite was investigated using structural, spectroscopic, and thermal methods. TEM micrographs of the nanocomposite showed spherical CdSe particles of 4-5 nm in size coated with a biopolymer layer. The absorption edges of both the aqueous solution and the thin film of the CdSe-starch nanocomposite were shifted toward lower wavelengths in comparison to the value of the bulk semiconductor. Infrared measurements revealed that the interaction of CdSe nanoparticles and starch chains takes place via OH groups. Although the onset of the temperature of decomposition of CdSe-starch nanocomposite is lower than that of the pure matrix, thermogravimetric analysis also showed that introduction of CdSe nanoparticles significantly reduced starch degradation rate leading to high residual mass at the end of the degradation process.

Inhibition of Microbial Growth by Silver–Starch Nanocomposite Thin Films

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.