Graphite Whiskers Derived from Waste Coffee Grounds Treated at High Temperature.

Graphite whiskers (GWs) are obtained from coffee grounds (CGs) treated at 2500 °C for 1 h in the presence of Ar gas at 1 atm. The majority of the GWs formed inside the CGs shell are rod-like with a conical tip with diameter and length in the range between 1 to 3 µm and 4 to 10 µm, respectively. At first, the carbon layer might be grown in a turbostratic manner, and then progressively graphitized at higher temperature. The strong G' peak intensity might be induced by the disclination of graphitized carbon layers.

Enhanced Antifouling Feed Spacer Made from a Carbon Nanotube-Polypropylene Nanocomposite.

Spacers are widely used in membrane technologies to reduce fouling and concentration polarization. Fouling can start from the spacer surface and grow, thereby reducing flux, selectivity, and operation lifetime. Fluorescein isothiocyanate labeled bovine serum albumin was used for fouling studies and observed during cross-flow filtration operation for up to 144 h. Here, we mixed carbon nanotubes (CNTs) and polypropylene (PP) to make a spacer with better antifouling than plain PP spacers. The fouling process was observed by scanning electron microscopy and monitored in situ by fluorescence microscopy. Molecular dynamics simulations show that bovine serum albumin has a lower interaction energy with the nanocomposite CNTs/PP spacer than with the plain PP. The findings are relevant for the development of spacers to improve the operation lifetime of membranes in filtration technologies.

Nitrogen self-doped activated carbons via the direct activation of Samanea saman leaves for high energy density supercapacitors.

In this study, nitrogen self-doped activated carbons (ACs) obtained via the direct activation of Samanea saman green leaves (SSLs) for high energy density supercapacitors were investigated. The SSL-derived direct-activated carbons (hereinafter referred to SD-ACs) were synthesized by impregnating sodium hydroxide as an activating agent and heating up to 720 °C without a hydrothermal carbonization or pyrolysis step. The optimum condition was investigated by varying the weight ratio of raw SSLs to NaOH. Surpassing the ACs derived from the two-step convention method, SD-ACs showed superior properties, including a higher surface area (2930 m2 g-1), total pore volume (1.37 cm3 g-1) and nitrogen content (4.6 at%). Moreover, SD-ACs exhibited enhanced electrochemical properties with specific gravimetric and volumetric capacitances of 179 F g-1 and 88 F cm-3 in an organic electrolyte, respectively, a high capacitance retention of approximately 87% at a current density of 0.5 A g-1 and excellent cycling stability of 97.5% after 3000 cycles at a current density of 5 A g-1. Moreover, the potential window of the supercapacitor cell was extended to 3.5 V with a significantly enhanced energy density of up to 79 W h kg-1. These results demonstrate that the direct activation of nitrogen-enriched SSLs offers advantages in terms of simplicity, low-cost and sustainable synthetic route to achieve nitrogen self-doped ACs for high energy density supercapacitors, which exhibit superior properties to that of ACs prepared via the conventional method.

Preparation and electrochemical performance of nitrogen-enriched activated carbon derived from silkworm pupae waste.

In this study, nitrogen-enriched activated carbon from silkworm pupae waste (P-AC) was successfully prepared and its electrochemical performances in aqueous and organic electrolytes were investigated. Silkworm pupae waste is beneficial because it is a nitrogen-enriched, inexpensive, and locally available material. The preparation process includes hydrothermal treatment of the silkworm pupae waste at 200 °C, and chemical activation using zinc chloride at activation temperatures of 700, 800 and 900 °C (P700, P800, and P900, respectively). The nitrogen content in the P-ACs was approximately 3.8-6.4 at%, decreasing with activation temperature, while the surface area was approximately 1062-1267 m2 g-1, increasing with activation temperature. Compared to a commercial AC, the P-ACs show higher nitrogen content but lower surface area. Furthermore, the P800 exhibited superior specific capacitance (154.6 and 91.6 F g-1 in aqueous and organic electrolytes) compared to a commercial AC despite possessing smaller surface area. The high nitrogen content enhanced the pseudocapacitance and improved the electrical conductivity of the P-ACs. These properties were confirmed by relatively low series and charge transfer resistances, a capacity retention higher than 88% at a current density of 0.5 A g-1 and excellent cycling stability demonstrated by maintaining 97.6% of its capacitance after 3000 cycles. These results demonstrate that silkworm pupae waste is a viable source of nitrogen-enriched AC for application in supercapacitors.