Graphitic sulfur functionalized carbon sheets as an efficient “turn-off” absorption probe for the optical sensing of mercury ions in aqueous solutions

Abstract

India is one of the world's largest producers of coconuts, with a turnover of 11 706 343 tonnes (11 521 459 long tons) in 2018 according to data reported by the Food and Agricultural Organization of the United States. The fleshy part (mesocarp) is either eaten or used to process oil, whereas the outer husk is usually removed and becomes waste. In this research work, a graphitic sulfur functionalized carbon sheet (g-SFCS) sample was prepared from Cocos nucifera (Coconut palm) by a chemical activation and thermal annealing process at 800 °C. X-Ray analysis confirmed the amorphous nature of the g-SFCS sample with increasing regularity of the crystalline structure. The BET specific surface area of the g-SFCS sample was found to be 659.41 m² g⁻¹ with a mesoporous structure. The XPS analysis revealed that the material obtained has a 90.44% carbon content. The material was then analyzed for its selectivity towards Hg²⁺ ions, and the UV spectroscopy results indicate the presence of a strong absorption peak at 237 nm in the absence of Hg²⁺. However, the presence of Hg²⁺ caused a significant reduction in the absorption intensity and a linear variation is seen with increasing concentration, with the LOD of 10.4 μM. The previous results clearly indicate that C. nucifera husks can be potentially applied as a precursor material for the preparation of highly efficient, low cost and eco-friendly g-SFCSs. This carbon material can act as a better adsorbent for adsorbing harmful and highly toxic heavy metals from water sources and make them suitable for use by humans and other living organisms.