Sanjeev Kumar Ujjain

Morphology Controlled Synthesis of Nanoporous Co3O4 Nanostructures and Their Charge Storage Characteristics in Supercapacitors

Cubic spinel Co3O4 nanoparticles with spherical (0D) and hexagonal platelet (2D) morphologies were synthesized using a simple solvothermal method by tuning the reaction time. XRD and HRTEM analyses revealed pure phase with growth of Co3O4 particles along [111] and [110] directions. UV-vis studies showed two clear optical absorption peaks corresponding to two optical band gaps in the range of 400-500 nm and 700-800 nm, respectively, related to the ligand to metal charge transfer events (O(2-) → Co(2+,3+)). Under the electrochemical study in two electrode assembly system (Co3O4/KOH/Co3O4) without adding any large area support or a conductive filler, the hexagonal platelet Co3O4 particles exhibited comparatively better characteristics with high specific capacitance (476 F g(-1)), energy density 42.3 Wh kg(-1) and power density 1.56 kW kg(-1) at current density of 0.5 Ag(-1), that suited for potential applications in supercapacitors. The observed better electrochemical properties of the nanoporous Co3O4 particles is attributed to the layered platelet structural arrangement of the hexagonal platelet and the presence of exceptionally high numbers of regularly ordered pores.

Enhanced supercapacitor performance by incorporating nickel in manganese oxide

Nickel manganese mixed oxides (NiyMn1−yOx; 0 ≤ y ≤ 0.4) have been synthesized by in situ inclusion of nickel during the growth of manganese oxide (MnOx). The effect of nickel concentration in MnOx is investigated by cyclic voltammetry, current–voltage characteristics, scanning electron microscopy and N2 adsorption–desorption analysis. Variations in electronic conductivity and specific capacitance suggest that nickel concentration in the MnOx matrix significantly affects the supercapacitor electrode performance. At Ni/Mn ∼0.25, i.e. Ni0.2Mn0.8Ox, the material crystallizes into spinel NiMn2O4 as a prominent phase and exhibits a specific surface area (118 m2 g−1) with a granular morphology. Furthermore Ni0.2Mn0.8Ox exhibited low resistivity (2.07 × 104 Ohm cm) and consequently high specific capacitance ∼380 F g−1, endowing additional merits. The fabricated supercapacitor device (Ni0.2Mn0.8Ox//Ni0.2Mn0.8Ox) delivers 35 W h kg−1 energy density and 3.74 kW kg−1 power density with remarkably high capacitive retention ∼92% after 3000 galvanostatic charge–discharge cycles. These encouraging results show great potential in developing energy storage devices from manganese oxide based electrodes incorporating nickel in the lattice.

Nanoceria based electrochemical sensor for hydrogen peroxide detection

Oxidative stress is a condition when the concentration of free radicals and reactive molecular species rise above certain level in living systems. This condition not only perturbs the normal physiology of the system but also has been implicated in many diseases in humans and other animals. Hydrogen peroxide (H2O2) is known to be involved in induction of oxidative stress and has also been linked to a variety of ailments such as inflammation, rheumatoid arthritis, diabetes, and cancer in humans. It is one of the more stable reactive molecular species present in living systems. Because of its stability and links with various diseases, sensing the level of H2O2 can be of great help in diagnosing these diseases, thereby easing disease management and amelioration. Nanoceria is a potent candidate in free radical scavenging as well as sensing because of its unique redox properties. These properties have been exploited, in the reported work, to sense and quantify peroxide levels. Nanoceria has been synthesized using different capping agents: Hexamethylene-tetra-amine (HMTA) and fructose. CeO2-HMTA show rhombohedral and cubic 6.4 nm particles whereas CeO2-fructose are found to be spherical with average particle diameter size 5.8 nm. CeO2-HMTA, due to the better exposure of the active (200) and (220) planes relative to (111) plane, exhibits superior electrocatalytic activity toward H2O2 reduction. Amperometric responses were measured by increasing H2O2 concentration. The authors observed a sensitivity of 21.13 and 9.6 μA cm(-2) mM(-1) for CeO2-HMTA and CeO2-fructose, respectively. The response time of 4.8 and 6.5 s was observed for CeO2-HMTA and CeO2-fructose, respectively. The limit of detection is as low as 0.6 and 2.0 μM at S/N ratio 3 for CeO2-HMTA and CeO2-fructose, respectively. Ceria-HMTA was further tested for its antioxidant activity in an animal cell line in vitro and the results confirmed its activity.

Graphene nanoribbon wrapped cobalt manganite nanocubes for high performance all-solid-state flexible supercapacitors

Nanocubes of cobalt manganite, CoMn2O4, were grown in situ over graphene nanoribbons (GNRs) to form a CoMn2O4/GNR composite during hydrothermal processing. The proposed all-solid-state supercapacitor (SC), CoMn2O4/GNR//CoMn2O4/GNR, with a polymer gel electrolyte showed an excellent electrochemical performance. It can be reversibly cycled over a large potential range of 3 V, resulting from the synergism of the pseudocapacitive and electrical double layer capacitor (EDLC) materials. The pseudocapacitance arises from the binary redox couple of the different cations in CoMn2O4, which, in combination with the GNRs, endows a high performance and long term stability. The SC demonstrates a high energy density of 44.6 W h kg−1 and a power density of 11.3 kW kg−1 with a short diffusion coefficient (Da) of 1.02 × 10−7 cm2 s−1 and a relaxation time constant (τ) of 5.6 μs. It demonstrates ∼95% capacitive retention with a steady coulombic efficiency even after 12 000 charge/discharge cycles. Moreover, a steady performance of the cell with good capacitive behaviour, even in the harsh environment of different bending states, encourages its commercial use in portable electronics.

Development and properties of surfactant-free water-dispersible Cu2ZnSnS4 nanocrystals: a material for low-cost photovoltaics.

A simple, yet novel hydrothermal method has been developed to synthesize surfactant-free Cu2ZnSnS4 nanocrystal ink in water. The environmentally friendly, 2-4 nm ultrafine particles are stable in water for several weeks. Detailed X-ray diffraction (XRD) and high-resolution transmission electron microscopy revealed the formation of single-crystalline-kesterite-phase Cu2ZnSnS4. Elemental mapping by scanning electron microscopy/energy dispersive spectrometry corroborated the presence of all four elements in a stoichiometric ratio with minor sulfur deficiency. Finally, Raman spectroscopy ruled out the possible presence of impurities of ZnS, Cu2SnS3, SnS, SnS2, Cu(2-x)S, or Sn2S3, which often interfere with the XRD and optical spectra of Cu2ZnSnS4. X-ray photoelectron spectroscopic studies of the as-synthesized samples confirmed that the oxidation states of the four elements match those of the bulk sample. Optical absorption analyses of thin film and solution samples showed high absorption efficiency (>10(4) cm(-1)) across the visible and near-infrared spectral regions and a band gap E(g) of 1.75 eV for the as-synthesized sample. A non-ohmic asymmetric rectifying response was observed in the I-V measurement at room temperature. The nonlinearity was more pronounced for this p-type semiconductor when the resistance was measured against temperature in the range 180-400 K, which was detected in the hot-point probe measurement.

Cerium oxide nanoparticles prevent apoptosis in primary cortical culture by stabilizing mitochondrial membrane potential

Abstract Cerium oxide nanoparticles (CNPs) of spherical shape have unique antioxidant capacity primarily due to alternating + 3 and + 4 oxidation states and crystal defects. Several studies revealed the protective efficacies of CNPs in cells and tissues against the oxidative damage. However, its effect on mitochondrial functioning, downstream effectors of radical burst and apoptosis remains unknown. In this study, we investigated whether CNPs treatment could protect the primary cortical cells from loss of mitochondrial membrane potential (Δψm) and Δψm-dependent cell death. CNPs with spherical morphology and size range 7–10 nm were synthesized and utilized at a concentration of 25 nM on primary neuronal culture challenged with 50 μM of hydrogen peroxide (H2O2). We showed that optimal dose of CNPs minimized ROS content of the cells and also curbed related surge in cellular calcium flux. Importantly, CNPs treatment prevented apoptotic loss of cell viability. Reduction in the apoptosis could be successfully attributed to the maintenance of Δψm and restoration of major redox equivalents NADH/NAD+ ratio and cellular ATP. These findings, therefore, suggest possible route of CNPs protective efficacies in primary cortical culture.

A cyano-bridged copper(II)–copper(I) mixed-valence coordination polymer as a source of copper oxide nanoparticles with catalytic activity in C–N, C–O and C–S cross-coupling reactions

A cyano-bridged copper(II)–copper(I) mixed valence polymer, namely {[Cu4(CN)5(C5H5N)4]}n (1), was synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, differential scanning calorimetric analysis, and single crystal X-ray crystallography. Single crystal X-ray studies show that the coordination polymer 1 is linked by the cyanide anions with μ-1κN:2κC bridging modes to the copper centers, generating a two-dimensional (2D) layered network. The coordination polymer 1, upon pyrolyzing, yielded copper oxide nanoparticles, which have been characterized by TEM and powder X-ray diffraction. The catalytic properties of the resulting copper oxide nanoparticles have also been studied in C–N, C–O, and C–S cross-coupling reactions with aryl halides. The C–N, C–O and C–S coupling products were obtained in moderate to good yields (66–90%, 72–98%, and 50–86%), respectively.

Facile preparation of graphene nanoribbon/cobalt coordination polymer nanohybrid for non-enzymatic H2O2 sensing by dual transduction: electrochemical and fluorescence

A novel graphene nanoribbon (GNR)/cobalt coordination polymer (MCPs) composite (MCPs@GNR) is prepared by in situ reduction of graphene oxide nanoribbon (GONR) with simultaneous growth of MCPs nanoparticles on its surface. The morphology and structure are investigated by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy, X-ray diffraction and Raman spectroscopy. Results indicate that MCPs nanoparticles having dia. ∼6 nm are successfully deposited on GNR to form a hybrid conducting network. Analysis of the performance of the MCPs@GNR composite shows high non-enzymatic electrocatalytic activity for H2O2 reduction with a low limit of detection ∼60 nM at S/N = 3. The fluorescence of MCPs provides an optical feature which is also applied here for the detection of H2O2. The fluorescence quenching of MCPs@GNR can be achieved by addition of H2O2 which shows linearity over a range of increasing concentration of 10 μM to 150 μM.