Synthesis of Multiporous Carbons from the Water Caltrop Shell for High-Performance Supercapacitors

Abstract

In this study, an economic, sustainable, and green synthesis method of multiporous carbons from agricultural waste, water caltrop shell (denoted as WCS), was presented. To prepare the WCS biochar, the dried WCS was first carbonized to a microporous carbon with a surface area of around 230 m2 g–1 by using a top-lit-updraft method. Then, the microporous WCS biochar was directly mixed with an appropriate amount of ZnO nanoparticles and KOH as activating agents via a solvent-free physical blending route. After further activation at 900 °C, the resulted carbons possess both micropores and mesopores that were named as WCS multiporous carbons. The carbon yield of the prepared WCS multiporous carbons with high surface area in the range of 1175–1537 m2 g–1 is up to 50%. Furthermore, the micropore/mesopore surface area ratio can be simply tuned by controlling the ZnO content. For supercapacitor applications, the as-prepared WCS multiporous carbon electrodes showed high specific capacitance (128 F g–1 at 5 mV s–1) with a good retention rate at 500 mV s–1 scan rate (>60% compared to the capacitance at 5 mV s–1) and low Ohmic resistance in a 1.0 M LiClO4/PC electrolyte. In addition to the ZnO nanoparticles, CaCO3 nanoparticles with low environmental impact were also used to prepare the WCS multiporous carbons. The assembled supercapacitors also demonstrate high specific capacitance (102 F g–1 at 5 mV s–1) and good retention rate (∼70%).

Green synthesis of nitrogen-doped multiporous carbons for oxygen reduction reaction using water-caltrop shells and eggshell waste

“…A second activation process was then performed at a higher temperature in the range of 800-950 C to enhance the reaction of the added K 2 CO 3 with the carbon to form porous carbons with a large surface area and high porosity. 25,29 It is noted that while a higher temperature is benecial in increasing the surface area and pore volume of the resulting porous carbons, it decreases the nitrogen content and product yield. [26][27][28] Thus, in practice, an appropriate choice of the activation temperature is essential in optimizing the porous properties of the obtained N-MPCs.…”

“…2.1 Synthesis of N-MPCs via physical blending method WCSB (surface area >200 m 2 g À1 ) were purchased from FanC Recycling International Ltd., Taiwan. 25 To synthesize the N-MPCs, 8.0 g of the WCSB, 8.0 g K 2 CO 3 and 16.0 g of the eggshell waste were homogeneously ground and mixed in a blender (Lab Use Grinder, SRT-02, Fu-Lian Food Machinery) for 3 minutes. The resulting powder was sealed in a stainlesssteel container (150 mL), heated to a temperature of 750 C at a heating rate of 8 C min À1 for 2 h and then activated at higher temperatures in the range of 800-950 C for 3 h. Aer cooling to room temperature, the black powder was washed with water to remove the alkali salt and then immersed in 1.0 M HCl (aq) solution to remove the residual Ca(OH) 2 and other inorganic residues.…”

Liquid-Phase Removal of Methylene Blue as Organic Pollutant by Mesoporous Activated Carbon Prepared from Water Caltrop Husk Using Carbon Dioxide Activation

“…In addition, this surface area was comparable to other studies on WCH-AC. In the work by Hsu et al [33], the authors activated the microporous WCH biochar with ZnO and KOH at 900 • C, showing a BET surface area in the range of 1175-1537 m 2 /g. In the study by Kumar et al [34], the BET surface area and t-plot micropore volume of WCH-AC by H 3 PO 4 -activation were 782.89 m 2 /g and 0.134 cm 3 /g, respectively.…”

“…This agricultural residue is often discarded in farmlands, or sometimes reused as an organic fertilizer. Due to its lignocellulosic compositions, there are some studies on the reuse of WCH as a biosorbent for dye removal [28][29][30], and a precursor for producing carbon materials in recent years [31][32][33][34][35]. For example, Kumar et al [34] investigated the preparation of H 3 PO 4 -activated carbon from WCH and its removal performance of hexavalent chromium, showing a maximum adsorption capacity of 87.31 mg/g according to the Thomas model.…”

Synthesis of mesoporous carbon platelets of high surface area and large porosity from polymer blends‐calcium phosphate nanocomposites for high‐power supercapacitor

“…To reduce the ion-transport resistance for high-power supercapacitor, the synthesis of a mesoporous carbon with large pore size (>5.0 nm) and short channel length (<100 nm) is still required. [6][7][8] Typically, a complicated exo-synthetic method, including synthesis of the surfactant-free mesoporous silica as hard mold, multiple impregnation of the monomer-type carbon source, introduction of the catalytic sites and pyrolysis and silica removal, has been widely used. [9][10][11] Although some efficient synthesis method have been provided to reduce the synthetic procedures, using highly corrosive HF solution for silica remove to prepare the porous carbon from the carbonsilica nanocomposite is still a serious problem.…”