Green synthesis of blue-fluorescent carbon nanospheres from the pith of tapioca (Manihot esculenta) stem for Fe(III) detection Ambika Madhusoodanan Nima 1 , Philomina Amritha 1 , Vidhya Lalan 1 , and Ganesanpotti Subodh 1, * 1 Department of Physics, University of Kerala, Thiruvananthapuram, Kerala 695581, India Received: 29 May 2020 Accepted: 14 October 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020 ABSTRACT Blue-light emitting fluorescent carbon nanospheres (CNs) were synthesized from the biological precursor, the pith of tapioca (Manihot esculenta) stem, by simple and facile hydrothermal carbonization method. The extracted CNs were amorphous, having an average dimension of 23.6 nm and are surface-func- tionalized with hydroxyl, carbonyl, carboxyl, and ether groups. The hydrophilic functional groups provide the uniform dispersed nature and stability to the CNs in the aqueous medium. Moreover, these groups act as charge trapping centers and result in an enhanced blue fluorescence with a high quantum yield of 19%, which is relatively high compared to those reported for CNs derived from other biological precursors. The luminescence quenching of these functionalized CNs was highly selective to the Fe(III) ions. The static quenching mechanism involved in the system is employed for Fe(III) detection in the aqueous medium, and the limit of detection obtained is 26.5 lM. 1 Introduction Carbon, a unique, multifaceted element that can make strong bonds with itself, results in a range of structures with a wide variety of physicochemical properties. Hence, in the last four decades, most of the research works have highlighted the develop- ment of novel carbon nanostructures, mainly including graphene, fullerenes, carbon fibers, multi- walled, and single-walled carbon nanotubes, amor- phous carbons, carbon quantum dots etc. and their modifications [1]. Among these, Carbon Dots (CDs) or carbon-based quantum dots are quasi-spherical luminescent particles having a size less than 10 nm, which was first derived during the purification of single-walled carbon nanotubes in 2004 [2, 3]. The characteristic properties of CDs such as photo-sta- bility, water-solubility, chemical inertness, tunable surface moieties, and unique photoluminescence properties make them an attractive candidate in luminescence related research fields such as catalysis [4], light-emitting diodes [5], drug delivery [6–9], fluorescence imaging and bio-sensing [10–12]. The Address correspondence to E-mail: gsubodh@gmail.com https://doi.org/10.1007/s10854-020-04689-6 J Mater Sci: Mater Electron