Bratindranath Mukherjee

A simple synthesis and characterization of CuS nanocrystals

Water-soluble CuS nanocrystals and nanorods were prepared by reacting copper acetate with thioacetamide in the presence of different surfactants and capping agents. The size of the nanocrystals varied from 3–20 nm depending on the reaction parameters such as concentration, temperature, solvent and the capping agents. The formation of nanocrystals was studied by using UV-visible absorption spectroscopy.

Nanopatterning by solid-state dewetting on reconstructed ceramic surfaces

We demonstrate ordered array formation of Au nanoparticles by controlled solid-state dewetting of a metal film on stepped alumina substrates. In situ transmission electron microscopy studies reveal that the dewetting process starts with nucleation of ordered dry regions on the substrate. The chemical potential difference between concave and convex surface regions induces anisotropic metal diffusion leading to the formation of nanowires in the valleys. The nanowires fragment due to Rayleigh instability forming arrays of metal nanoparticles on the substrate. The length scale of reconstruction relative to the starting film thickness is an important parameter in controlling the spatial order of the nanoparticles.

Highly photoactive heterostructures of PbO quantum dots on TiO2

We present a non-hydrolytic sol–gel combustion method for synthesizing nanocomposites of PbO quantum dots on anatase TiO2 with a high surface area. XRD, electron microscopy, DRS, cathodoluminescence and BET were employed for structural, microstructural and optical characterization of the composites. The photocatalytic activity of TiO2 and PbO/TiO2 was investigated and compared with Degussa P-25. The results indicate that the photocatalytic activity of quantum dot dispersed TiO2 is higher than that of bare TiO2 and much higher than that of commercial Degussa P-25. The origin of enhanced photoreactivity of the synthesized material can be assigned to a synergetic effect of high surface area, higher number of active sites and an engineered band structure in the heterostructure. The mechanisms for photocatalytic activity are discussed based on production of photogenerated reactive species. The knowledge gained through this report open up ideal synthesis routes for designing advanced functional heterostructures with engineered band structure and has important implications in solar energy based applications.

Functional nanoporous structures by partial sintering of nanorod assemblies

We present a general method for the synthesis of functional nanoporous structures by heat treating a loose compact of nanorods. Partial sintering of such a compact leads to spherodization of the nanorods and their fusion at the contact regions leading to an interconnected porous microstructure. The pore diameter can be controlled by changing the original nanorod diameter. We illustrate the generality of the method using TiO2, ZnO and hydroxyapatite as model systems; the method is applicable for any material that can be grown in the form of nanorods. The kinetics of the sintering process can be significantly enhanced in systems in which additional driving forces for mass transport arise from phase transitions proving an ultrafast pathway for producing biphasic porous structures. The possibility of producing hierarchical porous structures using fugitive sintering aids makes this process ideal for a variety of applications including catalysis, photoanodes for solar cells and scaffolds for biomedical applications.

Vacancy-mediated structural changes in Au–Cu nanoparticles

ABSTRACT We report the formation of new phases in bimetallic Au–Cu nanoparticles. These phases were observed in nanoparticle synthesised by adopting a three-step protocol in a single pot. Nanoparticles at 180°C for 1 h led to the formation of single-phase solid solution of Cu in Au. Subsequent heat treatment at 290°C for 2 h of these Au–Cu nanoparticles revealed three new phases. One of them relates to the modification of occupancy of Cu in an ordered AuCu tetragonal phase (tP4). This cell although retains tetragonal symmetry but displays metrical properties akin to that of a cube. The other two relates to vacancy ordering along <111> directions in the {111} planes of an ordered AuCu3 cubic phase (cP4). On the one hand, statistical occupancy of vacancy on Cu site in this cell leads to the reduction of cell size from ∼3.75 Å to ∼3.5 Å whereas ordering of vacant layer on the other hand gives rise to symmetry breaking. Former continues to display cubic symmetry whereas latter transforms to a trigonal cell.

Growth morphology and special diffraction characteristics of multifaceted gold nanoparticles

This paper deals with morphology of synthesized nano gold particles through seed based growth. Various types of morphologies have been observed. They primarily relate to decahedral and truncated tetrahedral shapes. Their relative abundance is dependent on temporal evolution of nanoparticles. These shapes are understood to have evolved from a seed having symmetry that is a supergroup of the point groups possessed by these nanoparticles. The usual pentagonal twinned morphologies observed under High Resolution Transmission Electron Microscopy have displayed two distinct types of interfaces. They have been attributed to cubic and icosahedral three-fold orientations. Such a discussion is lacking in literature. The five triangular faces of decahedral particles are essentially rotational twins resulting out of a common five-fold axis. Two special diffraction features for truncated tetrahedral particles have been observed. They refer to (i) triangular streaks around Braggs spots conforming to three fold symmetry of these particles and (ii) by observation of forbidden reflections of the type 1/3{422} and 2/3{422} along 〈422〉 directions. Latter has been understood in terms of intrinsic fault whereas former arises owing to shape transform of nanoparticles. The presence of faults has helped rationalize decrease of lattice parameter vis-à-vis that of standard FCC gold. The variation of intensities of these forbidden reflections seems to be arising out of density of such intrinsic faults in nano gold particles in addition to dynamical effects.

TEM and XPS studies on the faceted nanocrystals of Ce{sub 0.8}Zr{sub 0.2}O{sub 2}

article i nfo Faceted nanocrystals of Ce0.8Zr0.2O2 synthesised by co-precipitation method were characterised by X-ray diffrac- tion,high-resolutiontransmissionelectronmicroscopy,thermogravimetry-differentialscanningcalorimetryand X-ray photoelectron spectroscopy techniques. The nanocrystals were highly faceted and exhibited a cubic phase. X-ray photoelectron spectroscopy analyses confirmed the presence of vacancy related defects and revealed the presence of ~22% of Ce 3+ in the nanopowders. High-resolution transmission electron microscopy results con- firmed that the nanocrystal sizes are around 31 ± 5 nm and the obtained hexagonal cross-section shape is bound by hexagonal {111} and square {100} facets. The shape-controlled nanocrystals were synthesised without using any surfactants or complexing agents and retained their morphology beyond 800 °C. This is a simple and easy method for producing shape-controlled Ce0.8Zr0.2O2 nanoparticles which can be used for catalytic conver- sion and other related advanced technological areas.