Synthesis of carbon nanoparticles from waste rice husk used for the optical sensing of metal ions

This work reports on a synthesis of carbon nanoparticles (CNPs) from waste rice husk by thermally-assisted carbonization in the presence of concentrated sulfuric acid. The fluorescent emmision characteristics of the CNPs, their quenching effects by metal ions and their use as a sensing material for Sn(II) ions were investigated. Results indicated that the yield of CNPs was optimized at a sulphuric acid concentration of 12 mol/L, heating temperature of 120 °C and heating time of 30 min. The sample showed a strong blue luminescence in water with a maximum emission at 439 nm. The fluorescence can be quenched by adding various metal ions by the formation of complexes between the metal ions and surface of the CNPs. Sn(II) ions had the most significant quenching effect on the fluorescence of the CNPs, which is concentration-dependent. The concentration dependent quenching was linearized with the Stern-Volmer equation, and showed a linear response up to a Sn(II) concentration of 6.13 mmol/L. The limit of detection for Sn(II) ions is 18.7 µmol/L with good repeatability.