Effects of Activation Conditions on the Characteristics, Adsorption Capacity, and Energy Sorage of Carbon Aerogel from Watermelon Rind

Abstract In this work, a watermelon rind‐derived carbon aerogel (WRCA) was synthesized via a facile and green procedure including hydrothermal combined freeze‐drying and pyrolysis technique. The influences of pyrolysis conditions on the characteristics, adsorption capacity, and energy storage of the produced WRCA were thoroughly investigated under two distinctive pyrolysis conditions in N₂ and CO₂ media to obtain the corresponding WRCA‐N and WRCA‐C products, respectively, at different temperatures (600, 700, and 800 °C). As a result, WRCA‐N samples exhibited notable hydrophobicity with a wetting angle of 127°, showing excellent concordance with the adsorbent field. Furthermore, the maximum adsorption capacity of used coconut oil, hexane, butanol, and chloroform for WRCA‐N pyrolyzed at 800 °C (WRCA‐N800) reached 70.521, 53.506, 58.102, and 59.913 g/g, respectively, whilst the adsorption process also followed the pseudo‐first‐order kinetic model. On the other hand, WRCA‐C held up considerable hydrophilic traits and cannot be used to adsorb organic matters. Nonetheless, WRCA‐C activated at 600 °C (WRCA‐C600) indicated the best physicochemical properties and energy storage capacity with better specific capacitance (190 F/g) compared to WRCA‐N600 (31.40 F/g), thanks to its large specific surface area, high porosity (91.27 %), and higher hetero‐element O content (9.79%) than other samples. Additionally, the electrochemical characteristics of WRCA‐C600 electrode were alternatively confirmed using the 2‐electrode supercapacitor model, demonstrating a high energy density (26.38 Wh/kg) and power density (2374.50 W/kg). The obtained results demonstrate the promising applications of carbon aerogel synthesized from the watermelon rind in the adsorption and energy storage sectors.