Candle soot derived carbon nanodot/polyaniline hybrid materials through controlled grafting of polyaniline chains for supercapacitors

A general approach for controlled grafting of polyaniline (PANI) chains from the surface of nano-structured carbon materials following a 'grafting from' strategy through oxidative polymerization of aniline is reported. Fluorescent spherical carbon nano-dots (CNDs) are obtained through HNO3 oxidation followed by size separation from an easily available and cheap source like candle soot. Oxidative polymerization of aniline under dilute acid conditions is conducted in the presence of CNDs tethered to the mono-amine group of N,N'-bis(4'-aminophenyl)-1,4-quinonediimine (APQD, in the emeraldine state) (CNDT), as the initiator. The appreciably lower oxidation potential of APQD compared to aniline directs the growth of PANI chains preferentially from these moieties acting as 'seeds'. Furthermore, the conditions are optimized to complete the entire polymerization within the duration of the induction period (IP) for the oxidative polymerization of aniline under similar conditions to ensure the grafting of PANI chains from the CND surface only. The attachment of APQD moieties to the CND surface and hence the formation of PANI chains are confirmed by using FTIR and XPS techniques. The covalently attached carbon nano-dot/polyaniline shows a remarkably higher specific capacitance of 972 F g(-1) with 90% retention after 2000 cycles, in comparison to only 482 F g(-1) for the non-covalently attached composite. The excellent electrochemical performance is attributed to the formation of the nano-structured composite material.