Madhav Ghimire

Flower-shaped cobalt oxide nano-structures as an efficient, flexible and stable electrocatalyst for the oxygen evolution reaction

The industrial application of water splitting for oxygen evolution requires low cost, high performance and stable electrocatalysts which can operate at low overpotential. Here, we develop a high performance and stable electrocatalyst for the oxygen evolution reaction (OER) using earth abundant materials. A binder free approach for the synthesis of flower-shaped cobalt oxide (Co3O4) composed of nanosheets showed high OER catalytic activity. The Co3O4 electrode requires a low overpotential of 356 mV to achieve a current density of 10 mA cm−2 with a low onset potential of 284 mV. The electrode showed outstanding flexibility and stability. The catalytic activity of the Co3O4 electrode was very stable up to the 2000th cycle of the polarization study. The high catalytic activity and structural stability arise due to efficient and fast charge transportation through the nanosheets of Co3O4 which are in direct contact with the conducting nickel of the electrode. The porous structure of Co3O4 allows easy access of the electrolyte and escape of generated oxygen without damaging the structure. Collectively, the flower-shaped nanostructured Co3O4 electrode can be used as a flexible and high performance electrode for the OER in an industrial setup.

Eco‐Friendly and High Performance Supercapacitors for Elevated Temperature Applications Using Recycled Tea Leaves

Abstract Used tea leaves are utilized for preparation of carbon with high surface area and electrochemical properties. Surface area and pore size of tea leaves derived carbon are controlled by varying the amount of KOH as activating agent. The maximum surface area of 2532 m2 g−1 is observed, which is much higher than unactivated tea leaves (3.6 m2 g−1). It is observed that the size of the electrolyte ions has a profound effect on the energy storage capacity. The maximum specific capacitance of 292 F g−1 is observed in 3 m KOH electrolyte with outstanding cyclic stability, while the lowest specific capacitance of 246 F g−1 is obtained in 3 m LiOH electrolyte at 2 mV s−1. The tea leaves derived electrode shows almost 100% capacitance retention up to 5000 cycles of study. The symmetrical supercapacitor device shows a maximum specific capacitance of 0.64 F cm−2 at 1 mA cm−2 and about 95% of specific capacitance is retained after increasing current density to 12 mA cm−2, confirming the high rate stability of the device. An improvement over 35% in the charge storage capacity is seen when increasing device temperature from 10 to 80 °C. The study suggests that used tea leaves can be used for the fabrication of environment friendly high performance supercapacitor devices at a low cost.

Synthesis and magnetic study of magnetically hard-soft SrFe12-yAlyO19 - x Wt.% Ni0.5Zn0.5Fe2O4 nanocomposites

Pure phase exchange coupled nanocomposites of magnetically hard-soft oxides, (hard) SrFe12-yAlyO19 -(soft) x Wt.% Ni0.5Zn0.5Fe2O4 were prepared via one-pot autocombustion method. The hard-phase magnetic anisotropy was systematically varied via Al3+ doping and magnetic properties of the nanocomposites were assessed as a function of magnetic soft-phase content in the nanocomposite. As synthesized, ferrites were assessed for phase composition, crystallinity, and magnetic properties by using XRD and VSM respectively. Exchange coupling behavior was observed in nanocomposites for all soft phase content in the low field region up to 1200 Oe. Also, exchange coupling was observed to weaken with increase in Al3+ content in the hard phase of the composite. As a result of hard-soft exchange coupling, the saturation magnetization, reduced remanence, and Curie temperature were observed to be higher than those of pure SrFe12O19 hexaferrite. The present study is novel in its approach of tuning magnetic parameters of exch...

Magnetic stimulus responsive vancomycin drug delivery system based on chitosan microbeads embedded with magnetic nanoparticles

Local antibiotic delivery can overcome some of the shortcomings of systemic therapy, such as low local concentrations and delivery to avascular sites. A localized drug delivery system (DDS), ideally, could also use external stimuli to modulate the normal drug release profile from the DDS to provide efficacious drug administration and flexibility to healthcare providers. To achieve this objective, chitosan microbeads embedded with magnetic nanoparticles were loaded with the antibiotic vancomycin and stimulated by a high frequency alternating magnetic field. Three such stimulation sessions separated by 1.5 h were applied to each test sample. The chromatographic analysis of the supernatant from these stimulated samples showed more than approximately 200% higher release of vancomycin from the DDS after the stimulation periods compared to nonstimulated samples. A 16-day long term elution study was also conducted where the DDS was allowed to elute drug through normal diffusion over a period of 11 days and stimulated on day 12 and day 15, when vancomycin level had dropped below therapeutic levels. Magnetic stimulation boosted elution of test groups above minimum inhibitory concentration (MIC), as compared to control groups (with no stimulation) which remained below MIC. The drug release from test groups in the intervals where no stimulation was given showed similar elution behavior to control groups. These results indicate promising possibilities of controlled drug release using magnetic excitation from a biopolymer-based DDS.

Band-gap engineering of La1-xNdxAlO3（x = 0,0.25,0.50,0.75,1）perovskite using density functional theory：A modified Becke Johnson potential study

The structural, electronic, and magnetic properties of the Nd-doped Rare earth aluminate, La1−x Nd x AlO3 (x = 0% to 100%) alloys are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The effects of the Nd substitution in LaAlO3 are studied using the supercell calculations. The computed electronic structure with the modified Becke–Johnson (mBJ) potential based approximation indicates that the La1−x Nd x AlO3 alloys may possess half-metallic (HM) behaviors when doped with Nd of a finite density of states at the Fermi level (E F). The direct and indirect band gaps are studied each as a function of x which is the concentration of Nd-doped LaAlO3. The calculated magnetic moments in the La1−x Nd x AlO3 alloys are found to arise mainly from the Nd-4f state. A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at E F. The observed decrease of the band gap with the increase in the concentration of Nd doping in LaAlO3 is a suitable technique for harnessing useful spintronic and magnetic devices.

Chitosan microbeads with MNP on printed electrodes for electric stimulus responsive drug delivery

Over the last few decades, various drug delivery systems (DDS) have been fabricated to overcome limitations of direct drug administration like solubility, short circulation lifetime, low tissue specificity, etc. Several of these DDS are also capable of controlling the passive drug release profile in response to a stimulus. This work describes a novel stimuli responsive DDS that alters its normal elution profile to release a higher drug amount when electric pulses are provided as excitation. The DDS is in form of microbeads made from chitosan cross linked with polyethylene glycol dimethacrylate, containing magnetite nanoparticles and vancomycin as the drug of interest. Silver (Ag) Inter-Digitated Electrodes (IDE) on Polyimide films were printed using a material printer and placed on the DDS. Two separate stimuli, each of 30 s duration were applied to the DDS via the IDE. The stimulated groups showed vancomycin release increased by 75% and 51% after the first and second stimuli respectively, in comparison to samples that were not stimulated. This preliminary work shows promising mechanism of a multiple- stimuli responsive DDS.