Flow-induced transverse electrical potential across an assembly of gold nanoparticles

We report the generation of a potential difference, of the order of tens of millivolts, induced by the flow of polar liquids over an assembly of gold nanoparticles. The device consisted of two conducting glass plates, one of which contained the gold nanoparticle multilayer assembly. The potential generated is in transverse direction to the flow and is dependent on the nature of the flowing liquid. We propose a simple theoretical model to account qualitatively for the generation of the flow-induced transverse potential

Novel ZnO nanostructures over gold and silver nanoparticle assemblies

We report the growth of well-oriented nest (reticulum)-like and lotus flower-like submicron structures of ZnO, over gold and silver nanoparticle assemblies, respectively. The structures were grown by a convenient chemical bath deposition method in a nutrient solution made of zinc nitrate (Zn(NO3)2 · 6H2O) and methyl amine (CH3NH2) at low temperature. SEM, XRD, Raman, UV-Vis and fluorescence spectra were used to study the morphology, crystallinity and phase purity of the structures. The ZnO submicron structures were found to be in the hexagonal wurtzite phase

Visible fluorescence induced by the metal semiconductor transition in composites of carbon nanotubes with noble metal nanoparticles

We show that single-walled carbon nanotube (SWNT) bundles emit visible fluorescence in the presence of noble metal nanoparticles and nanorods in the solid state. Conductivity measurements with metallic nanotubes, isolated from pristine SWNTs, show that they become semiconducting in the presence of the metal nanoparticles. Nanoparticle binding increases the defects in the nanotube structures which is evident in the Raman spectra. The metal-semiconductor transition removes the nonradiative decay channels of the excited states enabling visible fluorescence. Nanotube structures are imaged using this emission with resolution below the classical limits

Employing Redox‐Active Additives for Enhanced Charge Polarization and Twofold Higher Energy Density in Supercapacitor

Abstract Remarkable improvement in the polarization and charge transport at the solid–solid electrode–electrolyte interface due to the incorporation of a redox‐active additive sodium molybdate (Na2MoO4) is demonstrated. The presence of the electrochemically active oxide center along with Na+ facilitates the hopping‐based charge transport of the ionic liquid leading to higher ionic conductivity and a twofold increase in specific capacitance (0.009 to 0.018 F cm−2). This drives a 200% increase in the energy density (0.76–1.7 µW h cm−2) and a 2.5 times improvement in the rate capability (10 000 mV s−1) of the solid‐state supercapacitor. Importantly, the power density, non‐Faradic nature, and cyclability remain unaltered, resulting in performance exceeding several solid‐state and liquid electrolyte‐based supercapacitors. Thus, the results established here through the use of redox‐active additive establish the robustness of the approach and practicality of the resulting device besides providing transformative opportunities in tuning the performance of solid‐state devices

Transverse electrokinetic effect: experiments and theory

We observe the transverse electrokinetic effect (TEK), namely, the generation of a transverse potential difference due to the flow of liquids over a surface on which self-assembled arrays of metallic nanoparticles are immobilized. This paper covers the recent experimental findings and improvements to the theoretical model described in ref 1 [Subramaniam, C.; Pradeep, T.; Chakrabarti, J. Phys. Rev. Lett. 2005, 95, 0164501], leading to a better understanding of the phenomenon. Issues critical for the comprehension and applicability of this effect as a potential flow sensor such as the need for a critical dipole moment, optimum surface coverage, nature of the flow rate dependence, and generalization of the phenomenon for several metallic nanostructures have been addressed in detail from both experimental and theoretical perspectives. This complete work stresses the uniqueness of this new phenomenon which could find applications in emerging areas of science, like microfluidics

On the formation of protected gold nanoparticles from AuCl<SUB>4</SUB><SUP>-</SUP> by the reduction using aromatic amines

Amines are used extensively as reductants and subsequent capping agents in the synthesis of metal nanoparticles, especially gold, due to its affinity to nitrogen. Taking 2-methyl aniline as an example, we show that metal reduction is followed by polymerization of the amine, while part of it covers the nanoparticle surface another fraction deposits in the solution. It is found that the oxidative polymerization of the amine goes in step with the formation of gold nanoparticles. The gold nanoparticles thus formed have a mean diameter of 20 nm. The polymerized amine encapsulates the gold nanoparticle forming a robust shell of about 5 nm thickness, making the gold core inert towards mineralizing agents such as chloroform, bromoform, sodium cyanide, benzylchloride, etc. which react with the naked gold nanoparticles. The deposited polymer is largely protonated, taking up protons from the medium during its formation. Similar results have been observed in the case of aniline also. The materials have been fully characterized by spectroscopy and microscopy

Room Temperature, Multiphasic Detection of Explosives, and Volatile Organic Compounds Using Thermodiffusion Driven Soret Colloids

Achieving a label-free spectroscopic platform for multiphasic analytical detection in real-time, ambient conditions is extremely challenging due to the fundamental dichotomy between ultrahigh sensitivity and reliability of detection. Addressing these challenges, we demonstrate a versatile surface-enhanced Raman scattering (SERS) platform capable of multiphasic, reliable detection with ultrahigh sensitivity. The SERS platform is extremely sensitive and relies on vapor molecules present at the solid–vapor or liquid–vapor interface for reliable detection in ambient conditions (298 K, 1 atm). We observe that metal nanoparticles, subjected to a temperature gradient, migrate and self-assemble into precise nanoparticle assemblies, in a nanoscale analogue of Soret effect. The formation and monodispersity of these nanoparticles assemblies, termed Soret colloids (SCs), is kinetically controllable using the thermal gradient. Soret colloids exhibit excellent size uniformity (monodispersity index, MDI ∼ 0.8) and strong interplasmon coupling to generate uniform and intense electromagnetic hot-spots enabling multiphasic, reliable (relative standard deviation, RSD < 5%), instantaneous (<60 s), ambient (298 K, 1 atm) and spectroscopic detection through SERS. Thereby, we demonstrate SERS detection of analytes with a wide range of vapor pressures (10^–9–10^–1 atm) such as 2,4,6 trinitrotoluene (TNT) and volatile organic compounds (VOCs). Besides, extremely reliable (RSD< 5%), liquid-state SERS detection is also enabled with SCs over a broad concentration range (10^–16 – 10^–6 M) extending to single-molecular sensitivity. Besides fundamentally overcoming the trade-off between high sensitivity and reliability, the vapor-phase detection protocol and platform demonstrated here presents transformative opportunities for real-time detection of explosives, medical diagnostics by breath-analysis and pollution monitoring

Scalable Approach to Highly Efficient and Rapid Capacitive Deionization with CNT-Thread As Electrodes

A scalable route to highly efficient purification of water through capacitive deionization (CDI) is reported using CNT-thread as electrodes. Electro-sorption capacity (<i>q</i>_e) of 139 mg g^–1 and average salt-adsorption rate (ASAR) of 2.78 mg g^–1min^–1 achieved here is the highest among all known electrode materials and nonmembrane techniques, indicating efficient and rapid deionization. Such exceptional performance is achieved with feedstock concentrations (≤1000 ppm) where conventional techniques such as reverse osmosis and electrodialysis prove ineffective. Further, both cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) and anions (Cl^–, SO₄^2– and NO₃^–) are removed with equally high efficiency (∼80%). Synergism between electrical conductivity (∼25 S cm^–1), high specific surface area (∼900 m² g^–1), porosity (0.7 nm, 3 nm) and hydrophilicity (contact angle ∼25°) in CNT-thread electrode enable superior contact with water, rapid formation of extensive electrical double layer and consequently efficient deionization. The tunable capacitance of the device (0.4–120 mF) and its high specific capacitance (∼27.2 F g^–1) enable exceptional performance across a wide range of saline concentrations (50–1000 ppm). Facile regeneration of the electrode and reusability of the device is achieved for several cycles. The device demonstrated can desalinate water as it trickles down its surface because of gravity, thereby eliminating the requirement of any water pumping system. Finally, its portable adaptability is demonstrated by operating the device with an AA battery

Annular vertical cylindrical thermochemical storage system with innovative flow arrangements for improved heat dispatch towards space heating requirements

Thermochemical energy storage is a potential solution for low-temperature seasonal energy storage systems and for improving renewable solar thermal energy share in the global energy mix. Such systems can help in meeting the heating requirements in the Indian Himalayan region in an environment-friendly manner. A few studies have attempted to understand the performance of strontium bromide hexahydrate-monohydrate-based storage as a thermochemical energy storage medium. The present study evaluates the performance of the vertical cylindrical annular reactor configuration, considering innovative radial airflow configurations. A two-dimensional axisymmetric model has been developed to study the effect of the various geometrical and operating parameters. During the charging (dehydration) process, the outward flow configuration exhibits substantially higher exergy efficiency as against the inward flow counterpart, with the difference being more pronounced (∼6–8%) at lower aspect ratios (0.5–1.0). The flow work requirement is higher for the outward flow during the hydration (discharging process), resulting in better performance for the inward flow counterpart. Upon increasing the volumetric air flow rate, the pressure drop across the reactive bed is found to increase substantially, leading to lower exergy efficiencies for higher flow rates. During the hydration process, the exergy efficiency for the inward flow becomes almost constant (∼15%) for a relative humidity level exceeding 60%, whereas that for the outward flow gradually increases to reach ∼ 5% for an 80% relative humidity. The ratio of thermal energy stored to the flow work required is higher for the outward flow. The energy output to flow work ratio is about 35% higher for the inward flow for the aspect ratio of 4

Performance Evaluation of an Open Thermochemical Energy Storage System Integrated with Flat Plate Solar Collector

In this study, the performance of an open thermochemical energy storage (TCES) system integrated with a flat plate solar collector is evaluated using a simplified dynamic model for space heating applications, considering a charging phase during the summer daytime and a discharging phase during the winter night. For charging and discharging operations, the time-varying solar flux (DNI) and ambient conditions in Pune, India is used. Simplified energy balance equations for the reactive packed bed and the flat plate solar collector are developed and validated against the previous reported works. The effects of the energy density and the aspect ratio of the reactive packed bed on the performance of the TCES system are evaluated using a non-dimensional parameter , which is the ratio of thermal power extracted/stored to the power required to blow air through the reactive packed bed. An increase in reactive packed bed energy density by 16.66% is found to decrease the time-averaged value of by 63.97% and 48.06%, respectively, for charging and discharging phases. A four-fold increase of aspect ratio of the reactive packed bed is found to increase the time-averaged value of by 6.20 times and 6.35 times during the charging and discharging phases, respectively