Biomass‐derived porous carbon and colour‐tunable graphene quantum dots for high‐performance supercapacitor and selective probe for metal ion detection

The abundance of biomass waste and their alteration into carbon-based electrodes grants practical application of the same. The present work describes all-round utilization of orange peel waste for the synthesis of graphene quantum dots (GQDs) and carbon-based electrode fabricated via facile hydrothermal reaction. The supernatant liquid is used for Fe3+ ion sensing and the remnant material is used for synthesis of porous carbon for supercapacitor application. GQDs synthesised via hydrothermal and microwave technique showed dual emission in blue and green wavelength region. Presence of Fe3+ ions quenched the fluorescence of GQDs and the selectivity is studied using other metal ions. Concentration of Fe3+ is varied upto 2.0 mM and the corresponding photoluminescence intensity is observed in the range 85–195 unit, indicating the inverse proportionality relation between these parameters. Carbon obtained has a combination of meso/macro and microporous structure with surface area of 64.002 m2 g−1. Porous OC electrode is employed in three electrode system and is fabricated as coin-cell which delivered specific capacitance of 290.64 F g−1 and 146.9 F g−1, respectively. The asymmetrical supercapacitor delivered an efficiency of 86% after 10 000 charge-discharge cycle. The resultant material derived from this work is suitable for both energy and sensing application.