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Incorporating heteroatoms into graphene lattice results in enhanced electrical conductivity and electrochemically active sites and has significant importance in developing high-performance supercapacitors. In this study, sulfur and nitrogen co-doped graphene aerogel is synthesized via hydrothermal technique followed by a simple but effective freeze-thawing and ambient pressure drying process (referred to as SN-GA). The process requires low-cost raw materials and cost-effective equipment without the utilization of any special instrument that operates at ultra-low temperatures, under high pressure, or vacuum environment. Ammonium sulfate [(NH4)2SO4] and ethylenediamine are used as a source of sulfur and nitrogen and as a reducing agent. (NH4)2SO4 with different molarities (0, 12, 24, and 36 mM) are used to synthesize four different aerogel samples marked as GA, SN-GA1, SN-GA2, and SN-GA3. The electrode is prepared using an SN-GA2 sample, exhibiting an outstanding specific capacitance of 244 F g−1 at an applied current density of 1 A g−1 with almost 98.5% Coulomb efficiency. Furthermore, based on the SN-GA2 sample, the symmetrical supercapacitor is fabricated, displaying an energy density of 18.14 Wh kg−1 at a power density of 498.4 W kg−1. Hence, SN-GA2 renders a promising material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of ytterbium (Yb) (with concentration x = 0.01, 0.015, 0.02, 0.025 and 0.03) doped in to nickel cobalt ferrite (NCYFO: YbxNi0.5Co0.5Fe2-xO4) nanoparticles at temperature 500 °C with phase pure spinel using solution combustion technique. The phase purity and effect of doping on NCYFO complex oxide on structural, thermal, magnetic and dielectric properties have been determined by various characterization techniques. The FTIR data reveal that strong metal oxide linkages can be observed in the tetrahedral and octahedral sites at wavenumbers 460 to 410 cm−1 and 595 to 540 cm−1. The X-ray diffraction (XRD) studies confirmed the spinel structure. The crystallite sizes and lattice parameters were estimated to be in the range of 31 to 22 nm and 8.32 to 8.35 Å, respectively. The X-ray photoelectron spectroscopy (XPS) study confirmed that the increase in Yb concentration results in accumulation of Yb in the grain boundaries of NCYFO in the form of Yb2O3. The thermal stability of nanoparticles were investigated using TGA/DSC method. Transmission Electron microscopy (TEM) studies and Field emission scanning electron microscopy (FESEM) used to study the particle size distribution and elemental composition within the nanomaterial. In addition, the dielectric properties, such as, dielectric constant and dielectric loss were investigated for all the NCYFO nanomaterial. The saturation magnetization of the NCYFO is determined using vibrating sample magnetometer (VSM) analysis and is maximum for x = 0.03 (Ms = 97.56 emu/g) sample. The high magnetic behaviour and better dielectric properties of the NCYFO nanomaterials are suitable for electro-magnetic applications. [ABSTRACT FROM AUTHOR]

In this paper, a flexible graphene oxide-based antenna sensor is designed on the biodegradable substrate. It resonates at a frequency of 3.92 GHz. The flexible sensor is used in assessing water content in sandy loam subsoil near the Arabian Sea from the Western Ghats in India. The volumetric water content (VWC) of dry soil varies between approximately 0.06 VWC m3 m–3 to 0.7 VWC m3 m–3. The antenna sensor exhibits a linearity of 92.02% and a sensitivity of 402.6 MHz/VWC-(m3 m–3). The limit of detection (LOD) and limit of quantification (LOQ) of the antenna sensor are 0.75 VWC and 2.5 VWC m3 m–3. The sensor is beneficial for examining soil water to enhance crop productivity for precision agriculture. [ABSTRACT FROM AUTHOR]