Karuna Kar Nanda

Bio: Karuna Kar Nanda is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Catalysis & Electrocatalyst. The author has an hindex of 39, co-authored 245 publications receiving 6273 citations. Previous affiliations of Karuna Kar Nanda include Institute of Physics, Bhubaneswar & National Institute for Materials Science.

Liquid-drop model for the size-dependent melting of low-dimensional systems

Abstract: Empirical relations are established between the cohesive energy, surface tension, and melting temperature of different bulk solids. An expression for the size-dependent melting for low-dimensional systems is derived on the basis of an analogy with the liquid-drop model and these empirical relations, and compared with other theoretical models as well as the available experimental data in the literature. The model is then extended to understand (i) the effect of substrate temperature on the size of the deposited cluster and (ii) the superheating of nanoparticles embedded in a matrix. It is argued that the exponential increase in particle size with the increase in deposition temperature can be understood by using the expression for the size-dependent melting of nanoparticles. Superheating is possible when nanoparticles with a lower surface energy are embedded in a matrix with a material of higher surface energy in which case the melting temperature depends on the amount of epitaxy between the nanoparticles and the embedding matrix. The predictions of the model show good agreement with the experimental results. A scaling for the size-dependent melting point suppression is also proposed.

Higher Surface Energy of Free Nanoparticles

Abstract: We present an accurate online method for the study of size-dependent evaporation of free nanoparticles allowing us to detect a size change of 0.1 nm. This method is applied to Ag nanoparticles. The linear relation between the onset temperature of evaporation and the inverse of the particle size verifies the Kelvin effect and predicts a surface energy of $7.2\text{ }\text{ }\mathrm{J}/{\mathrm{m}}^{2}$ for free Ag nanoparticles. The surface energy of nanoparticles is significantly higher as compared to that of the bulk and is essential for processes such as melting, coalescence, evaporation, growth, etc., of nanoparticles.

Green synthesis of biopolymer–silver nanoparticle nanocomposite: An optical sensor for ammonia detection

Abstract: Biopolymer used for the production of nanoparticles (NPs) has attracted increasing attention. In the presence article we use aqueous solution of polysaccharide Cyamopsis tetragonaloba commonly known as guar gum (GG), from plants. GG acts as reductive preparation of silver nanoparticles which are found to be <10 nm in size. The uniformity of the NPs size was measured by the SEM and TEM, while a face centered cubic structure of crystalline silver nanoparticles was characterized using powder X-ray diffraction technique. Aqueous ammonia sensing study of polymer/silver nanoparticles nanocomposite (GG/AgNPs NC) was performed by optical method based on surface plasmon resonance (SPR). The performances of optical sensor were investigated which provide the excellent result. The response time of 2-3 s and the detection limit of ammonia solution, 1 ppm were found at room temperature. Thus, in future this room temperature optical ammonia sensor can be used for clinical and medical diagnosis for detecting low ammonia level in biological fluids, such as plasma, sweat, saliva, cerebrospinal liquid or biological samples in general for various biomedical applications in human.

One-step, integrated fabrication of Co2P nanoparticles encapsulated N, P dual-doped CNTs for highly advanced total water splitting

Abstract: A one-step/one-pot strategy to synthesize phase pure Co2P nanoparticles encapsulated N, P dual-doped carbon nanotubes (denoted as Co2P/CNT) is developed. The method is free of toxic, pyrophoric alkylphosphine as the phosphorus source, does not involve the use of sophisticated instrumentation or expensive precursors and may be extended to other transition-metal phosphides. When the as prepared Co2P/CNTs are applied as an anode for OER in 1 M KOH, a current density of 10 mA/cm2 is achieved at an overpotential of 292 mV which is 36 mV less than that required for the state-of-art OER catalyst RuO2 with a small Tafel slope of ∼68 mV/decade. While applied as a cathode towards HER, Co2P/CNTs exhibit a current density of 10 mA/cm2 at an overpotential of 132 mV with a Tafel slope of 103 mV/dec that compares favourably with the state-of-the art HER catalyst, Pt/C. After 15 h of continuous electrolysis for both HER and OER, the electrode material preserves its structure along with its robust catalytic activity which points out to their excellent stability. A total alkaline water electrolyzer constructed by employing Co2P/CNT as catalyst on both anode and cathode delivered a current density of 10 mA/cm2 at around 1.53 V over an extended operational period rivalling the state-of-art combination of Pt/C and RuO2 and is among the best of the bi-functional total-water splitting electrocatalysts reported till date. This remarkable performance of Co2P/CNTs can be attributed to the intrinsic catalytic activity of Co2P nanoparticles fortified with heteroatom doped few layered graphene which results in enhanced electrical conductivity besides providing long-term stability.

Surface excitonic emission and quenching effects in ZnO nanowire/nanowall systems: Limiting effects on device potential

Abstract: We report ZnO nanowire/nanowall growth using a two-step vapor phase transport method on $a$-plane sapphire. X-ray diffraction and scanning electron microscopy data establish that the nanostructures are vertically well aligned with the $c$ axis normal to the substrate and have a very low rocking curve width. Photoluminescence data at low temperatures demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe a high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at $\ensuremath{\sim}3.366\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated nonradiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalization in the nanostructures with increased temperature, unlike the behavior in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects.

Biomolecular coronas provide the biological identity of nanosized materials

Abstract: The search for understanding the interactions of nanosized materials with living organisms is leading to the rapid development of key applications, including improved drug delivery by targeting nanoparticles, and resolution of the potential threat of nanotechnological devices to organisms and the environment. Unless they are specifically designed to avoid it, nanoparticles in contact with biological fluids are rapidly covered by a selected group of biomolecules to form a corona that interacts with biological systems. Here we review the basic concept of the nanoparticle corona and its structure and composition, and highlight how the properties of the corona may be linked to its biological impacts. We conclude with a critical assessment of the key problems that need to be resolved in the near future.

Optical properties of ZnO nanostructures.

Abstract: We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Anion-exchange membranes in electrochemical energy systems

Abstract: This article provides an up-to-date perspective on the use of anion-exchange membranes in fuel cells, electrolysers, redox flow batteries, reverse electrodialysis cells, and bioelectrochemical systems (e.g. microbial fuel cells). The aim is to highlight key concepts, misconceptions, the current state-of-the-art, technological and scientific limitations, and the future challenges (research priorities) related to the use of anion-exchange membranes in these energy technologies. All the references that the authors deemed relevant, and were available on the web by the manuscript submission date (30th April 2014), are included.