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The use of green and sustainable biomass-derived compounds to obtain excellent electrochemical properties is important to address growing environmental and energy issues. In this paper, cheap and abundant watermelon peel was used as a raw material to successfully synthesize nitrogen-phosphorus double-doped bio-based porous carbon by a one-step carbonization method and explore it as a renewable carbon source for low-cost energy storage devices. The supercapacitor electrode exhibited a high specific capacity of 135.2 F/g at a current density of 1 A/g in a three-electrode system. A variety of characterization methods and electrochemical tests indicate that porous carbon prepared by this simple method has great potential as electrode materials for supercapacitors.

The carbon materials derived from discarded masks and lignin are used as adsorbent to remove two types of reactive dyes present in textile wastewater: anionic and cationic. This paper introduces the results of batch experiments where Congo red (CR) and Malachite green (MG) are removed from wastewater onto the carbon material. The relationship between adsorption time, initial concentration, temperature and pH value of reactive dyes was investigated by batch experiments. It is discovered that pH 5.0–7.0 leads to the maximum effectiveness of CR and MG removal. The equilibrium adsorption capacities of CR and MG are found to be 232.02 and 352.11 mg/g, respectively. The adsorption processes of CR and MG are consistent with the Freundlich and Langmuir adsorption models, respectively. The thermodynamic processing of the adsorption data reveals the exothermic properties of the adsorption of both dyes. The results show that the dye uptake processes follow secondary kinetics. The primary adsorption mechanisms of MG and CR dyes on sulfonated discarded masks and alkaline lignin (DMAL) include pore filling, electrostatic attraction, π-π interactions and the synergistic interactions between the sulphate and the dyes. The synthesized DMAL with high adsorption efficiency is promising as an effective recyclable adsorbent for adsorbing dyes, especially MG dyes, from wastewater.

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The lignosulfonate/polyaniline nanocomposite electrode material was made by polymerization of aniline with lignosulfonate as dispersant and structure-directing agent. Redox can convert the catechol/quinone groups on lignin, promoted by electron transfer of polyaniline.