Aneeya K. Samantara

Graphene-induced Pd nanodendrites: A high performance hybrid nanoelectrocatalyst

AbstractA facile and green approach has been developed for the in situ synthesis of hybrid nanomaterials based on dendrite-shaped Pd nanostructures supported on graphene (RG). The as-synthesized hybrid nanomaterials (RG-PdnDs) have been thoroughly characterized by high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy and electrochemical techniques. The mechanism of formation of such dendrite-shaped Pd nanostructures on the graphene support has been elucidated using TEM measurements. The RG induces the formation of, and plays a decisive role in shaping, the dendrite morphology of Pd nanostructures on its surface. Cyclic voltammetry and chronoamperometry techniques have been employed to evaluate the electrochemical performance of RG-PdnDs towards oxidation of methanol. The electrochemical (EC) activities of RG-PdnDs are compared with graphene-supported spherical-shaped Pd nanostructures, Pd nanodendrites alone and a commercial available Pd/C counterpart. The combined effect of the graphene support and the dendrite morphology of RG-PdnDs triggers the high electrocatalytic activity and results in robust tolerance to CO poisoning.

Sandwiched graphene with nitrogen, sulphur co-doped CQDs: an efficient metal-free material for energy storage and conversion applications

Here, a hybrid material composed of sandwiched reduced graphene oxide (rGO) and N,S co-doped carbon quantum dots (N,S-CQDs) was prepared following a facile synthetic route. This metal-free composite has demonstrated their dual performance as an electrode material for supercapacitors and fuel cell catalysts. It shows robust cyclic stability with high energy and power density without any binders. The enhanced activity of the composite can be ascribed to the CQDs present within the interlayer of the rGO which enhance the accessibility of the charged ions and increase the capacitance of the composite. In addition, the electrocatalytic activity of the composite has been assessed as a metal-free cathode catalyst towards the oxygen reduction reaction (ORR) for fuel cell applications. It shows better performance in terms of high reduction potential and high reduction current as compared to rGO. This can be ascribed to the significant contribution of electron rich heteroatom doped CQDs as well as the synergistic effect of both the CQDs and rGO for the electrocatalytic reduction of oxygen. The interesting dual performance of heteroatom doped CQDs and graphene hybrid composites hold potential for the development of energy storage and conversion devices.

Facile synthesis of Ag nanowire–rGO composites and their promising field emission performance

Crystalline, ultra long silver nanowires (Ag NWs), few-layered rGO (reduced graphene oxide) and their rGO–Ag NW nanocomposite have been synthesized using a polyol reflux technique under optimized experimental conditions. The field emission performance of the rGO–Ag NW nanocomposite, rGO and Ag NW emitters was investigated. The turn on field required to draw an emission current density of ∼1 μA cm−2 was found to be ∼5.00, 3.92 and 2.40 V μm−1 for the Ag NW, rGO and rGO–Ag NW nanocomposite emitters, respectively. The combined contribution of the sharp edges of the thin graphene sheets and high aspect ratio of the Ag nanowires, and their synergetic effect in the rGO–Ag NW nanocomposite, are responsible for the enhanced field emission behavior. First-principles density functional calculations show that the enhanced field emission may also be due to the overlapping of the electronic structures of the Ag NWs and rGO nanosheets.

Urea-Assisted Room Temperature Stabilized Metastable β-NiMoO4: Experimental and Theoretical Insights into its Unique Bifunctional Activity toward Oxygen Evolution and Supercapacitor

Room-temperature stabilization of metastable β-NiMoO4 is achieved through urea-assisted hydrothermal synthesis technique. Structural and morphological studies provided significant insights for the metastable phase. Furthermore, detailed electrochemical investigations showcased its activity toward energy storage and conversion, yielding intriguing results. Comparison with the stable polymorph, α-NiMoO4, has also been borne out to support the enhanced electrochemical activities of the as-obtained β-NiMoO4. A specific capacitance of ∼4188 F g-1 (at a current density of 5 A g-1) has been observed showing its exceptional faradic capacitance. We qualitatively and extensively demonstrate through the analysis of density of states (DOS) obtained from first-principles calculations that, enhanced DOS near top of the valence band and empty 4d orbital of Mo near Fermi level make β-NiMoO4 better energy storage and conversion material compared to α-NiMoO4. Likewise, from the oxygen evolution reaction experiment, it is found that the state of art current density of 10 mA cm-2 is achieved at overpotential of 300 mV, which is much lower than that of IrO2/C. First-principles calculations also confirm a lower overpotential of 350 mV for β-NiMoO4.

Simple Growth of Faceted Au–ZnO Hetero-nanostructures on Silicon Substrates (Nanowires and Triangular Nanoflakes): A Shape and Defect Driven Enhanced Photocatalytic Performance under Visible Light

A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au-ZnO hetero-nanostructures (HNs) either with nanowires (NWs) or with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. This work reports on the use of these nanostructures on substrates for photodegradation of rhodamine B (RhB) dyes and phenol under the visible light illumination. The photoluminescence measurements showed a substantial enhancement in the ratio of defect emission to band-edge emission for TNF (ratio ≈ 7) compared to NW structures (ratio ≤ 0.4), attributed to the presence of more oxygen defects in TNF sample. The TNF structures showed 1 order of magnitude enhancement in photocurrent density and an order of magnitude less charge-transfer resistance (R(ct)) compared to NWs resulting high-performance photocatalytic activity. The TNFs show enhanced photocatalytic performance compared to NWs. The observed rate constant for RhB degradation with TNF samples is 0.0305 min(-1), which is ≈5.3 times higher compared to NWs case with 0.0058 min(-1). A comparison has been made with bulk ZnO powders and ZnO nanostructures without Au to deduce the effect of plasmonic nanoparticles (Au) and the shape of ZnO in photocatalytic performance. The results reveal the enhanced photocatalytic capability for the triangular nanoflakes of ZnO toward RhB degradation with good reusability that can be attracted for practical applications.

A Bioinspired Approach for Shaping Au Nanostructures: The Role of Biomolecule Structures in Shape Evolution

A new approach for shaping Au nanostructures by tuning the molecular structure of biomolecules has been explored. Different molecules, such as catechol, rutin, and quercetin, which have structural similarity to the catechol ring, were used to induce Au nanostructures under similar conditions. The as-synthesized nanostructures are characterized by using TEM, XPS, XRD, and UV/Vis spectral measurements. The growth mechanism for the formation of these noble metal shapes and the role of the molecular structure of the stabilizing/reducing agent were investigated by using TEM and UV/Vis spectral measurements. The structure and functional groups of the reducing/stabilizing agent play a vital role in the shape evolution of nanostructures. The electrocatalytic activity of different nanostructures in the reduction of oxygen was investigated and was found to be shape-dependent.

Good's buffer derived highly emissive carbon quantum dots: excellent biocompatible anticancer drug carrier

Here, a facile one-step approach has been developed for the synthesis of carbon quantum dots (CQDs) from Goods buffer. The as-synthesized CQDs emit a bright greenish blue coloured fluorescence after exposure to a 365 nm UV-lamp illumination. The bright fluorescence nature of the CQDs has proven them to be excellent probes for cellular imaging. The CQDs are highly biocompatible in nature, which has been validated by an MTT assay test. The in vitro MTT assay demonstrates a more than 95% survival rate when HEK293 (human embryonic kidney) and H357 (human oral squamous carcinoma) cells were treated with CQDs. The low cytotoxicity of Goods buffer derived CQDs opens the door to biomedical applications. The anticancer drug doxorubicin (DOX) was successfully loaded on the CQDs and their delivery efficiency to the target cells via in vitro treatment of cancerous cells was explored. The CQDs supported DOX showed a higher killing rate of the cancer cells compared to bare DOX due to its ease of internalization and efficient pH-triggered release inside the cells.

Photoelectrocatalytic oxidation of NADH by visible light driven plasmonic nanocomposites

Here, we report the efficient photoelectrocatalytic oxidation of NADH by plasmonic nanocomposites driven by visible light. The reduction in the recombination of photogenerated holes and electrons expedite the electrocatalytic oxidation process, which substantially decreases the overpotential and increases the oxidation current.

Highly Active 2D Layered MoS 2 - rGO Hybrids for Energy Conversion and Storage Applications

The development of efficient materials for the generation and storage of renewable energy is now an urgent task for future energy demand. In this report, molybdenum disulphide hollow sphere (MoS2-HS) and its reduced graphene oxide hybrid (rGO/MoS2-S) have been synthesized and explored for energy generation and storage applications. The surface morphology, crystallinity and elemental composition of the as-synthesized materials have been thoroughly analysed. Inspired by the fascinating morphology of the MoS2-HS and rGO/MoS2-S materials, the electrochemical performance towards hydrogen evolution and supercapacitor has been demonstrated. The rGO/MoS2-S shows enhanced gravimetric capacitance values (318 ± 14 Fg−1) with higher specific energy/power outputs (44.1 ± 2.1 Whkg−1 and 159.16 ± 7.0 Wkg−1) and better cyclic performances (82 ± 0.95% even after 5000 cycles). Further, a prototype of the supercapacitor in a coin cell configuration has been fabricated and demonstrated towards powering a LED. The unique balance of exposed edge site and electrical conductivity of rGO/MoS2-S shows remarkably superior HER performances with lower onset over potential (0.16 ± 0.05 V), lower Tafel slope (75 ± 4 mVdec−1), higher exchange current density (0.072 ± 0.023 mAcm−2) and higher TOF (1.47 ± 0.085 s−1) values. The dual performance of the rGO/MoS2-S substantiates the promising application for hydrogen generation and supercapacitor application of interest.

A facile approach for the synthesis of copper(II) myristate strips and their electrochemical activity towards the oxygen reduction reaction

The usage of an inexpensive and non-noble metal-based material as the electrocatalyst in the oxygen reduction reaction has gained great attention for fuel cell application. In this report, a facile approach has been developed for the synthesis of copper myristate strips. The as-synthesized material has demonstrated its electrocatalytic activity towards oxygen reduction reaction. This study opens up a new scope for the use of straight chain copper complexes as electrocatalysts. The interesting performance of the copper myristate strips holds promising application in energy conversion devices.