Effect of Long-Term Aging on Graphene Oxide and Its Recovery Characteristics Under Temperature Influence

The long-term performance of graphene oxide (GO) is often compromised by aging, which alters its morphology and physicochemical properties. This study investigates the recovery potential of aged GO (a-GO), stored for two years, through controlled thermal treatment. Heating from 20°C to 70°C induced notable structural and colloidal transformations, including partial unwrapping of folded sheets and heterogeneous redistribution of particle sizes, with populations as small as 13 nm emerging. Zeta potential measurements revealed a shift from − 7.5 mV to − 29 mV, indicating enhanced colloidal stability, while UV-Vis spectroscopy showed a red shift from 229 nm to 232 nm, suggesting partial restoration of sp² domains. AFM analysis confirmed the formation of smooth, flake-like structures with distinct thicknesses around 5, 13.2, and 17 nm. To evaluate functional recovery, we studied the interaction between thermally treated a-GO and L-cysteine (Cys), which resulted in a further red shift to 237 nm in the UV-Vis spectrum, confirming surface reactivity. These findings demonstrate that moderate thermal treatment can partially restore the structure and surface functionality of a-GO, supporting its reuse in biosensing and nanomedicine applications