Phyllanthus emblica Seed-Derived Hierarchically Porous Carbon Materials for High-Performance Supercapacitor Applications.

The electrical double-layer supercapacitance performance of the nanoporous carbons prepared from the Phyllanthus emblica (Amala) seed by chemical activation using the potassium hydroxide (KOH) activator is reported. KOH activation was carried out at different temperatures (700-1000 °C) under nitrogen gas atmosphere, and in a three-electrode cell set-up the electrochemical measurements were performed in an aqueous 1 M sulfuric acid (H2SO4) solution. Because of the hierarchical pore structures with well-defined micro- and mesopores, Phyllanthus emblica seed-derived carbon materials exhibit high specific surface areas in the range of 1360 to 1946 m2 g-1, and the total pore volumes range from 0.664 to 1.328 cm3 g-1. The sample with the best surface area performed admirably as the supercapacitor electrode-material, achieving a high specific capacitance of 272 F g-1 at 1 A g-1. Furthermore, it sustained 60% capacitance at a high current density of 50 A g-1, followed by a remarkably long cycle-life of 98% after 10,000 subsequent charging/discharging cycles, demonstrating the electrode's excellent rate-capability. These results show that the Phyllanthus emblica seed would have significant possibilities as a sustainable carbon-source for the preparing high-surface-area activated-carbons desired in high-energy-storage supercapacitors.

High Surface Area Nanoporous Graphitic Carbon Materials Derived from Lapsi Seed with Enhanced Supercapacitance.

Nanoporous activated carbon materials derived from agro-wastes could be suitable low-cost electrode materials for high-rate performance electrochemical supercapacitors. Here we report high surface area nanoporous carbon materials derived from Lapsi seed agro-waste prepared by zinc chloride (ZnCl2) activation at 700 °C. Powder X-ray diffraction (pXRD) and Raman scattering confirmed the amorphous structure of the resulting carboniferous materials, which also incorporate oxygen-containing functional groups as confirmed by Fourier transform infrared (FTIR) spectroscopy. Scanning and transmission electron microscopy (SEM and TEM) analyses revealed the granular, nanoporous structures of the materials. High-resolution TEM (HR-TEM) confirmed a graphitic carbon structure containing interconnected mesopores. Surface areas and pore volumes of the materials were found, respectively, in the ranges from 931 to 2272 m2 g-1 and 0.998 to 2.845 cm3 g-1, and are thus superior to commercially available activated carbons. High surface areas, large pore volumes and interconnected mesopore structures of these Lapsi seed-derived nanoporous carbon materials lead to their excellent electrochemical supercapacitance performance in aqueous electrolyte (1 M H2SO4) with a maximum specific capacitance of 284 F g-1 at a current density of 1 A g-1. Furthermore, the electrodes showed high-rate capability sustaining 67.7% capacity retention even at high current density of 20 A g-1 with excellent cycle stability achieving 99% capacitance retention even after 10,000 charge-discharge cycles demonstrating the potential of Lapsi seed derived nanoporous carbons as suitable electrode materials in high-performance supercapacitor devices.

Development of nanoporous structure in carbons by chemical activation with zinc chloride.

Series of activated carbons (ACs) have been prepared from Lapsi (Choerospondias axillaris) seed powder (LSP) by chemical activation with zinc chloride (ZnCI2) and the effects of ZnCl2 impregnation ratio, carbonization time, and precursor sources on the structure and properties of ACs have been systematically investigated. Carbonization was carried out at 400 degrees C and the ratio of LSP and ZnCI2 was varied from LSP:ZnCl2 = 1:0.25 (AC-0.25), 1:0.50 (AC-0.50) 1:1 (AC-1), 1:2 (AC-2), and 1:4 (AC-4). The ACs were characterized by Fourier transform-infrared (FTIR) spectroscopy, Raman scattering, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Surface properties (effective surface areas, pore volumes, and pore size distributions) were studied by nitrogen adsorption-desorption measurements. The electrochemical and vapor sensing properties were investigated by cyclic voltammetry, and quartz crystal microbalance (QCM) method, respectively. All the ACs are amorphous materials containing oxygenated surface functional groups and having nanoporous (microporous and mesoporous) structures. We found that surface properties depend on the LSP:ZnCI2 ratio, carbonization time, and also on the precursor type. The effective surface area increased significantly with increasing LSP:ZnCI2 ratio from 1:0.25 to 1:0.5 and then remain apparently constant. However, total pore volume increased continuously with ZnCI2 ratio. Increase in the carbonization time above 4 h decreased both the surface area and pore volume. ACs prepared from bamboo and coconut shell showed better surface properties compared to AC prepared from sugarcane; surface area and pore volume of the former systems are nearly double of the later system. AC derived from LSP (AC-4) showed excellent electrochemical performance giving specific capacitance value of 328 F/g in 1 M H2SO4 solution demonstrating the potential use of this material for supercapacitor electrodes. Our ACs showed good capability of molecule sensing of toxic solvent vapors such as carbon tetrachloride and pyridine.

Nanoporous activated carbon derived from Lapsi (Choerospondias axillaris) seed stone for the removal of arsenic from water.

Activated carbons were prepared from Lapsi (Choerospondias axillaris) seed stone by zinc chloride (ZnCl2) activation at three different Lapsi seed powder (LSP):ZnCl2 ratios: 1:0.5 (AC-0.5), 1:1 (AC-1), and 1:2 (AC-2). The properties of these activated carbons (ACs), including effective surface areas, pore volumes, and pore size distributions were characterized from N2 adsorption-desorption isotherms. The ACs obtained were essentially nanoporous (including both micro- and mesoporous) with effective surface area ranging from 1167 to 1328 m2/g. Fourier-transform infrared (FTIR) spectroscopy showed the presence of functional groups on the surface of ACs. Scanning electron microscopy (SEM) images showed a high pore development in the ACs. X-ray diffraction (XRD) patterns showed that, in addition to the amorphous structure, ACs contains crystalline ZnO formed during the carbonization. Presence of amorphous carbon is further confirmed by Raman scattering, where we observed only D and G bands. Iron impregnated nanoporous AC has been found to be very effective for arsenic removal from ground water; amount of arsenic is decreased from ca. 200 ppb to 10 ppb. These experimental results indicate the potential use of Lapsi seed as a precursor material for the preparation of high surface area nanoporous activated carbons.