Carbon dots from Manila tamarind for heavy metal ion removal and sensing through automatic classification.

Environmental remediation research has been focused on the detection and removal of heavy metal ions. In this work, Manila tamarind-derived simple and sustainable carbon dots (CDs) have been proposed for the optical detection/removal of heavy metal ions. Based on the distinct optical response of CDs toward Fe3+ and Zn2+/paraquat, an "on-off-on" strategy could be implemented for dual sensing of Fe3+/Zn+2 and Fe3+/paraquat systems. Higher concentrations of CDs revealed the facile removal of Fe3+ and Pb2+ through electron transfer mechanism and of Sn2+ possibly via electrostatic interaction. X-ray photoelectron spectroscopy (XPS) reveals the CD-induced reduction of Fe3+ and Pb2+ ions to Fe+2 and Pb0 states, respectively. The spectral and statistical features were analyzed for possible identification of 17 different metal ions through machine learning approaches. The demonstrated multifunctionality of the suggested carbon-based optical nanoprobes toward the heavy metal ion identification/removal and/or reduction can be applied in wastewater treatment and water quality assessment.