Synthesis and Characterization of Ternary α-Fe2O3/NiO/rGO Composite for High-Performance Supercapacitors.

Herein, pure α-Fe2O3, binary α-Fe2O3/NiO, and ternary α-Fe2O3/NiO/rGO composites were prepared by a hydrothermal method. The properties of the prepared materials were studied by powder X-ray diffraction, scanning electron microscopy, TEM, XPS, and Brunauer-Emmett-Teller techniques. The clusters of smaller α-Fe2O3 nanoparticles (∼30 nm) along with conducting NiO was freely covered by the rGO layer sheet, which offer a higher electrode-electrolyte interface for improved electrochemical performance. The ternary composite has shown a higher specific capacitance of 747 F g-1@ a current density of 1 A g-1 in a 6 M KOH solution, when compared with that of α-Fe2O3/rGO (610 F g-1@1 A g-1) and α-Fe2O3 (440 F g-1@1 A g-1) and the nanocomposite. Moreover, the ternary α-Fe2O3/NiO/rGO composite exhibited a 98% rate capability @ 10 A g-1. The exceptional electrochemical performance of ternary composites has been recognized as a result of their well-designed unique architecture, which provides a large surface area and synergistic effects among all three constituents. The asymmetric supercapacitor (ASC) device was assembled using the ternary α-Fe2O3/NiO/rGO composite as the anode electrode (positive) material and activated carbon as the cathode (negative) material. The ASC device has an energy density of 35.38 W h kg-1 at a power density of 558.6 W kg-1 and retains a 94.52% capacitance after 5000 cycles at a 1 A g-1 current density.

Environmental photochemistry with thiol- and silica-modified plasmonic nanocomposites: SERS sensing of municipal solid waste and tannery waste leachate from groundwater.

Mismanagement of obsolete solid waste generates a massive deteriorating effect on the environment. There is a high level of open trash disposal contaminating its neighboring water bodies. This despoliation trash causes an endangerment to the living environment. The waste management act is to hinder harmful effects on human beings, animals, plants, and their natural environment through the principles of waste prevention, waste processing, and waste disposal. Surface-enhanced Raman scattering (SERS) enhances the hazardous chemical sensing of environmental pollutants. To vigorously focus on the leaching of a couple of landfills in groundwater and surface water, an unusual combination of SERS-based poly vinyl thiol and silica-modified silver nanocomposites (PVT/SiO2@Ag NCs) was synthesized. The optical, crystalline, and structural properties of PVT/SiO2@Ag NCs were described with UV-visible spectroscopy (UV-Vis), X-ray diffractometer (XRD), transmission electron microscope (TEM), and energy-dispersive X-ray analysis (EDX). The surface plasmon resonance (SPR) is detected at 403 nm from the PVT/SiO2@Ag NPs. The average crystallite size of PVT/SiO2 @ Ag NCs is estimated using the Scherrer formula as 11 nm. The calculated specific surface area (SSA), strains, and dislocation densities demonstrate the improved mechanical properties of the substrate. The well-separated spherical shape of NPs is also observed, and the composition of silica and sulfur element in addition of Ag was confirmed by EDAX. Negatively charged SiO2 were bound strongly with the SH group and Ag NPs through electrostatic interaction mechanism as S-Ag-O-Si-O-Ag-S. SERS sensitivity is demonstrated by the prepared nanoparticles using an environmentally ignored leachate of municipal solid waste (MSW) and tannery waste (TW) landfill. PVT/SiO2@Ag NCs has detected the presence of innards of MSW leachate viz., aromatic hydrocarbon, phenols, phthalates, and pesticide from the groundwater. Furthermore, the TW leachate compositions of benzenes, hydrocarbons, amines, and chromium VI were analytically identified. Also, the leaching of TW leachate was confirmed in the water samples referred. Hence, this study provides a novel SERS sensor of PVT/SiO2@Ag NCs in the tile to detect and analyze environmentally ignored organic and inorganic compounds.

Hollow Gold Nanosphere Templated Synthesis of PEGylated Hollow Gold Nanostars and Use for SERS Detection of Amyloid Beta in Solution.

Hollow gold nanospheres (HGNs) have been used as the template for seed-mediated growth of multibranched hollow gold nanostars (HNS). The HGNs were synthesized via anerobic reduction of cobalt chloride to cobalt nanoparticles and then formation of a gold shell via galvanic replacement followed by the oxidation of the cobalt core. We obtained control of the inner core size of the HGNs by increasing the size of the sacrificial cobalt core and by varying the ratio of B(OH)3/BH4 using boric acid rather than 48 h aged borohydride. We synthesized the HNS by reducing Au3+ ions in the presence of Ag+ ions using ascorbic acid, creating a spiky morphology that varied with the Au3+/Ag+ ratio. A broadly tunable localized surface plasmon resonance was achieved through control of both the inner core and the spike length. Amyloid beta (Aß) was conjugated to the HNS by using a heterobifunctional PEG linker and identified by the vibrational modes associated with the conjugated ring phenylalanine side chain. A bicinchoninic acid assay was used to determine the concentration of Aß conjugated to HNS as 20 nM, which is below the level of Aß that negatively affects long-term potentiation. Both the core size and spike length were shown to affect the optical properties of the resulting nanostructures. This HGN templated method introduced a new parameter for enhancing the plasmonic properties of gold nanostars, namely, the addition of a hollow core. Hollow gold nanostars are highly desirable for a wide range of applications, including high sensitivity disease detection and monitoring.

Plasmonic silver nanospheres embedded ε-caprolactone/reduced graphite oxide nanolayers as active SERS substrates.

Label-free, sensitive, compatible and non-invasive nature of surface enhanced Raman spectroscopy (SERS) had substantially influenced various biological applications such as cell investigations, analysis of biomolecules such as DNA, RNA, proteins and detection of biomarkers for various diseases. This renders the engineering of bio-compatible, sensitive and efficient SERS substrates a necessity. In this study, the SERS activity of plasmonic silver nanospheres embedded ε-caprolactone/reduced graphite oxide nano layers (AGP) has been analyzed. The interactions of the nanolayers with nanospheres were evidenced by the broadening of the SPR band observed in UV-visible spectroscopy. Formation of AGP was further affirmed through X-ray diffraction patterns, X-ray photoelectron spectroscopy and the transmission electron microscopic images. Rhodamine 6G, a widely used SERS label for biological samples such as DNA and RNA sensing, protein screening, etc., was used here as the probing molecule to determine the efficiency of AGP as a SERS substrate. A low detection limit of 10-6 M was achieved with a calculated SERS enhancement factor of 1.2 × 108. The formation of 'hotspots' at the nanogaps between Ag nanospheres and the 'hot surfaces' on the nanolayers along with the efficient suppression of fluorescence, synergistically result in the enhanced Raman signals. This suggests the feasibility of developing AGP as a biocompatible, robust and efficient SERS substrate towards bio-sensing, molecule detection, etc.

Monodispersed Gold Nanoparticles as a Probe for the Detection of Hg2+ Ions in Water.

Gold nanoparticles were synthesized using Ananas comosus as reducing agent. UV-visible spectra show the surface plasmon resonance peak at 544 nm. TEM measurement shows that the formation of monodispersed spherical nanoparticles with average size of 7 nm. Crystalline nature of the nanoparticles was evident from TEM images and peaks in the XRD pattern. FTIR analysis provides the presence of biomolecules responsible for the reduction and capping of the prepared gold nanoparticles. A selective and sensitive method is proposed for detecting mercury based on the SPR change of gold nanoparticles. This mercury sensor based on surface plasmon optical sensor can be used in water analysis.