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Graphene quantum dots (GQDs), a novel type of zero-dimensional fluorescent materials, have gained considerable attention owing to their unique optical properties, size and quantum confinement. However, their high cost and low yield remain open challenges for practical applications. In this work, a low cost, green and renewable biomass resource is utilised for the high yield synthesis of GQDs via microwave treatment. The synthesis approach involves oxidative cutting of short range ordered carbon derived from pyrolysis of biomass waste. The GQDs are successfully synthesised with a high yield of over 84%, the highest value reported to date for biomass derived GQDs. As prepared GQDs are highly hydrophilic and exhibit unique excitation independent photoluminescence emission, attributed to their single-emission fluorescence centre. As prepared GQDs are further modified by simple hydrothermal treatment and exhibit pronounced optical properties with a high quantum yield of 0.23. These modified GQDs are used for the highly selective and sensitive sensing of ferric ions (Fe3+). A sensitive sensor is prepared for the selective detection of Fe3+ ions with a detection limit of as low as 2.5 × 10–6 M. The utilisation of renewable resource along with facile microwave treatment paves the way to sustainable, high yield and cost-effective synthesis of GQDs for practical applications.

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Summary The increasing plastic pollution and dwindling supply of fossil fuels have ignited research on the use of waste for generation of renewable energy and its reliable storage systems. This study investigates the feasibility of developing multiwall carbon nanotubes (MWCNTs) from flexible plastic packaging, as a prospective electrode material for the application in supercapacitors. The MWCNTs derived from flexible plastic packaging waste are functionalized using nitric acid to introduce oxygenated functional groups at their surfaces. Then, the MWCNTs are utilized as electrode material in supercapacitors, and their performance is compared with commercial MWCNTs. The results indicate that the as‐prepared MWCNTs exhibit superior capacitive performance as compared to commercial MWCNTs. Moreover, the functionalized MWCNTs demonstrate an improved capacitive performance among all the samples and display a double capacitance value as compared to commercial MWCNTs which is attributed to their higher electrochemical activity and faster charge transfer. These findings suggest that MWCNTs synthesized from flexible plastic packaging waste can be a superior alternate to the commercial MWCNTs. If developed at commercial scale, this will create a double‐win situation where plastic waste is reduced and cost‐effective high‐performance electrodes are developed for energy storage applications.