Long-term aging effects on structural and chemical characteristics of graphene oxide and their thermal recover

The long-term stability of graphene oxide (GO) is an important factor influencing its performance in technological and biomedical applications, as prolonged aging can lead to changes in morphology, surface chemistry, and colloidal behavior, potentially limiting its practical use. In this study, the physicochemical and morphological properties of freshly prepared GO were compared with those of material aged for 2 years (a-GO), and the effect of controlled thermal treatment on the partial reduction of agglomeration and modification of physicochemical properties was investigated. Dynamic light scattering (DLS) indicated that heating from 20 to 70 °C led to partial exfoliation and the emergency of additional particle size populations, while subsequent cooling to 20 °C suggested that these changes were largely retained. Zeta potential measurements indicated enhanced electrostatic stabilization, while UV–Vis spectroscopy showed a red shift consistent with structural modifications. Raman (ID/IG = 1.12 → 1.32; G band shift = 1594 → 1603 cm⁻¹) and FTIR results further support changes in sp² domains and rearrangement of oxygen-containing functional groups rather than complete structural recovery. Microscopic observations using scanning electron microscopy (SEM) and atomic force microscopy (AFM) further suggested structural reorganization of a-GO into smoother, flake-like morphologies. The interaction of a-GO with L-cysteine (L-Cys) was also examined to assess surface reactivity, where thermally treated a-GO exhibited a spectral shift, indicating possible interaction and modification of surface functional groups. Overall, the results suggest that moderate thermal treatment may partially mitigate the effects of long-term aging in graphene oxide, leading to improved colloidal behavior and suggesting possible potential for future applications in biosensing and nanomedicine․