Sustainable development of ultrathin porous carbon nanosheets with highly accessible defects from biomass waste for high-performance capacitive desalination

Abstract

Biomass-derived defective porous carbons with numerous superiorities have received widespread attention in capacitive deionization (CDI). However, the effective synthesis of defective carbons with ultrathin layered nanosheets and hierarchically porous structures from biomass is still a great challenge. Herein, we developed a sustainable molten salt-assisted acid exfoliation strategy for the production of highly accessible defect-rich carbon nanosheets with hierarchical porosity. Notably, the proposed method has successfully overcome the necessary alkali and template use, avoiding environmental pollution and energy consumption. Furthermore, the adopted acetic acid and molten salt meet sustainable development demands. The acetic acid can effectively exfoliate the aggregative polymer to the apparent 2D layered structure by preferentially hydrolyzing lotus and break numerous C–O groups. The subsequent molten salt-assisted pyrolysis can further crush the carbon framework, resulting in ultrathin nanosheets with abundant edges and porous defects. This favorable ultrathin layered and hierarchical structure guarantees accessible rich-defect features, which can not only benefit ion storage, but also provide sufficient diffusion pathways for ion penetration, contributing to excellent performance for CDI. Consequently, C-A/S displays a superior salt removal capability of 30.1 mg g⁻¹ in 500 mg L⁻¹ NaCl solution at 1.2 V with an outstanding regeneration capacity. Additionally, the capacitive contribution analysis and density functional theory also clearly demonstrate that the ultrathin 2D structure can remarkably expose more defect sites and enhance their accessibility. This work not only provides an efficient and sustainable strategy to improve the ion-adsorption capability of carbons, but also realizes the green recycling of biomass waste in environmental remediation.