Transition- Metal-Free Piranha-Assisted One-Pot Oxidative Iodination of Graphene Oxide for Selective Turn-On Fluorescence Sensing of Cu2+ Ions.

Iodine-functionalized graphene oxide (i-FGO) was synthesized through a one-pot, transition-metal-free approach under ambient conditions. An optimized oxidation strategy was developed by replacing conventional H2SO₄ with a combined piranha solution, NaIO₄, and m-CPBA system to achieve efficient oxidation of the graphite framework. The method enabled simultaneous oxidation and iodine intercalation, producing enhanced functionalization and improved structural properties compared with the previously reported i-GO system. m-CPBA promoted the formation of abundant epoxide groups on the graphene basal planes, while the modified oxidation environment facilitated uniform functionalization throughout the carbon framework. Compared with our previously reported NaIO₄-based oxidation method, the optimized piranha-assisted strategy reduced NaIO₄ consumption by approximately 38% while maintaining effective oxidation and iodine functionalization. The incorporation of iodine and oxygen-containing functional groups was confirmed using P-XRD, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared (FT-IR) analyses. UV-visible absorption and photoluminescence studies revealed the distinctive optical properties of i-FGO and its sensitive fluorescence response toward Cu2+ ions, attributed to photo-induced electron transfer (PET) and intramolecular charge transfer (ICT) mechanisms. The developed i-FGO chemosensor exhibited excellent selectivity for Cu2+ ions in complex systems, with minimal interference from other competing metal ions, demonstrating its promising potential for selective, sensitive, and reliable fluorescence-based Cu2+ detection in environmental samples.