Sudip Nath

Ligand-stabilized metal nanoparticles in organic solvent

This critical review reports the fundamental behavior of metal nanoparticles in different organic solvents, i.e., metal organosol. An overview on metal organosol and then their smart synthetic approaches, characterization, and potential applications in the fields of catalysis and spectroscopy with special emphasis on SERS are embodied. Aspects of organosol fabrication, stabilization, morphology control, growth mechanisms, and physical properties as mono- and bimetallic nanoparticles are discussed. The article inspires the repetitive usage of metal nanoparticles as stable deliverable organic and molecular compounds.

Ab initio SCF study of maximum hardness and maximum molecular valency principles

Ab initio SCF calculations using the 6-31G** basis set have been performed on a number of molecules in order to test the validity of maximum hardness and maximum molecular valency principles. It has been observed that the former is valid under a variety of bonding situations, while the latter breaks down in the case of highly ionic molecules.

Linear Assembly of Gold Nanoparticle Clusters via Centrifugation

Centrifugation is widely used in the synthesis and handling of solution-phase nanoparticles to improve their purity and to change the composition of the solvent. Herein, we couple the optical properties of citrate-stabilized gold nanoparticles and silica encapsulation to investigate how centrifugation impacts the formation of stabilized nanoparticle clusters in solution without the use of linker molecules or asymmetric functionalization. Gold nanoparticles preconcentrated using a high (9,400) g force result in linear assemblies of gold cores that are spaced by approximately 1-4 nm within Au(n)@SiO(2) structures (n = number of gold nanoparticle cores per silica shell) with approximately 30% monomers, 30% dimers, 20% trimers, and 10% 4-7mers. In comparison, nanoparticles preconcentrated using (stirred) ultrafiltration and low (23) g force centrifugation have statistically identical cluster distributions (90% monomers, 9% dimers, and 1% trimers) whereas nanoparticles that are not preconcentrated always exhibit 100% monomers using the same silica coating procedure. We hypothesize that under high g force, the electrical double layer surrounding the gold nanoparticles is slightly polarized thereby increasing the attraction between nanoparticles and the formation of stable clusters. The conductivity of the solution plays an important role in this stabilization. This novel demonstration of linear cluster formation of gold nanoparticles using centrifugation suggests that this commonly used preparative tool can both positively or negatively impact the fundamental properties of these materials and their use in various applications.

Hardness dynamics in a chemical reaction

Temporal evolution of local and global hardness during a chemical reaction modelled as a collision process between a nitrogen atom and a proton has been studied within a quantum fluid density functional framework. Variation of local hardness is similar to that of charge density. Time dependence of global hardness seems to be governed by a dynamic variant of the maximum hardness principle.

Silver organosol: synthesis, characterization and localized surface plasmon resonance study

In this article a simple and reproducible technique for the synthesis of a silver organosol is reported from a specific silver precursor, solid silver acetate. Molten hexadecylamine acts as a solvent for silver acetate and imparts stability to the evolved nanoparticles. The amine-capped organosol shows unique stability as neither agglomeration nor oxidation takes place over one year. The synthesised silver particles have been characterised by UV-visible, TEM, XRD, XPS, FTIR and thermogravimetric studies. The hexadecylamine-stabilised silver organosol was employed to examine the altered optical properties in different solvent systems and with different ligands by accounting for the changes in the localised surface plasmon resonance (LSPR) spectrum. It was observed that the position of the surface plasmon band of silver nanoparticles is greatly affected by the solvents and ligands under consideration. The quantitative alteration of the LSPR spectrum involving encapsulated nanoparticles in a dielectric ligand shell has been rationalised from Mie theory. It has also been shown that cationic and anionic surfactants of different chain lengths induce changes in the optical properties of silver nanoparticles whereas, zwitterionic amino acid molecules reflect insignificant changes in the LSPR spectrum. The max of the LSPR gradually shifts to red with the increase in chain length of both the cationic and anionic surfactants, indicating specific binding of the surfactant molecules around silver nanoparticles. Finally the affinity of the synthesised silver nanoparticles for amine molecules has been accounted for by taking the HSAB principle into consideration.

Hardness and bond index profiles of hydrogen-bonded complexes with single-minimum and double-minimum potentials

Abstract The dissociation reaction, H 3 N · HF → H 3 N + HF and the proton-transfer reaction (F-H · Cl) − → (F· H-Cl) − have been studied at the HF//6-31G ∗∗ level in order to understand the progress of these reactions in terms of global and local reactivity parameters. Both the reactions are found to obey the maximum hardness principle. The potential energy curve for the proton transfer reaction passes through a transition state wherein the hardness is at a minimum. In this reaction bond index profiles of the bonds being broken and formed intersect at the point corresponding to the maximum in the potential energy curve. Condensed Fukui functions have been calculated at different stages of dissociation of H 3 N · HF. Variation of reactivity of a particular site towards electrophilic, nucleophilic or radical attack is properly reflected in these values.

Solution phase evolution of AuSe nanoalloys in Triton X-100 under UV-photoactivation

A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium.

Density functional calculation of a characteristic atomic radius

A quadratic Euler-Lagrange equation has been solved self-consistently for defining two types of radii for atoms which match closely with experimental covalent radii. The calculated radii values are either better than or comparable to any hitherto known calculated radii values. Excellent correlations have been observed between these radii values and other physical properties like softness, ionisation potential, electronegativity etc. in the vertical groups of the periodic table and the trends are found to match with that predicted by experimental covalent radii.

Gold Organosol as a Real-Time Optical Sensor for Monitoring Solvent Refractive Index and Chain Length:

Metallic particles in the nanometer size regime display many interesting physical properties that are significantly different from their bulk. Noble metal nanoparticles such as Cu, Ag, and Au exhibit a strong absorption band in the visible region. This absorption band results when the incident photon frequency is resonant with the collective oscillation of the conduction band electrons and is known as the localized surface plasmon resonance (LSPR).1 It is now well-established that the peak wavelength, lmax, of an LSPR spectrum is dependent upon the size, shape, and interparticle spacing of the nanoparticle as well as its own dielectric properties and those of its local environment, including the substrate, solvent, and adsorbates.2–4 Noble metal nanoparticles dispersed in organic solvent systems have proven to be an efficient tool to register the impacts of the solvents arising from bulk solution effects.5 In this experiment, we have chosen gold nanoparticles as the spectroscopic reporter group since the solvents introduced in the medium leave their direct impression on the optical properties of the gold particles. In recent years, the accurate determination of refractive index has witnessed increased scientific interest in view of its various applications in chemical6 and biological7 sensors. The measurements of the refractive index of the bulk liquid solutions are important in many industrial processes including industrial process monitoring and research applications such as chemical separation detectors, etc. It has now been seen that evanescent wave techniques such as surface plasmon resonance (SPR) spectroscopy can detect very low levels of chemical and bi-

Electronegativity and hardness profiles of a chemical process: Comparison between quantum fluid density functional theory andab initio SCF method

Temporal evolution of electronegativity and hardness associated with a collision process between a Be atom and a proton has been studied within a quantum fluid density functional framework. In the presence of a third collisional partner to take away excess energy, this collision may lead to a chemical reaction producing a BeH+ molecule. For comparisonab initio SCF level calculation (with 6–31G** basis set) on BeH+ molecule with different geometries have been performed. Electronegativity equalization and maximum hardness principles are analyzed.