Abstract

This work explores how the ultrasonic exfoliation history of graphene oxide (GO), modulated via probe sonication time, impacts its structural features and thermal reduction behavior. GO dispersions subjected to sonication for 15, 105, and 180 min were synthesized via a modified Eigler method and characterized using UV–Vis, FTIR, XPS, DLS, and in-situ Thermo-Raman spectroscopy. Spectroscopic analyses confirmed that low- temperature sonication preserved the sp2 carbon framework and overall oxidation degree, while inducing gradual changes in lateral size and defect density. XPS data revealed that moderate sonication (105 min) provided the highest (C–C +C– –C)/OFGs index, indicating an optimal balance between ultrasonic exfoliation efficiency and structural retention. Thermogravimetric analysis (TGA) under N₂ atmosphere was carried out to evaluate the thermal stability and quantify the progressive removal of oxygen functional groups during heating. In-situ Thermo-Raman analysis revealed that the onset temperature of graphitic reordering decreased with increasing sonication time, shifting from ~530 ◦C for the GO-15 min sample to ~480 ◦C for the GO-180 min sample, highlighting a correlation between lateral size, defect landscape, and thermal activation. The evolution of ID/IG, I2D/IG, and FWHM indices demonstrated distinct reorganization pathways: larger GO sheets exhibited more coherent graphitization at higher temperatures, while smaller, defective sheets transitioned earlier but with less structural recovery. Complementary ex-situ FTIR analysis revealed a progressive removal of oxygen functional groups with increasing temperature, with hydroxyl and carbonyl species showing a marked attenuation, while epoxy groups exhibited comparatively higher thermal stability, evidencing distinct deoxygenation pathways. In parallel, X-ray diffraction (XRD) measurements showed the evolution of the (002) reflection from ~11◦ toward higher diffraction angles upon thermal treatment, consistent with interlayer contraction driven by the elimination of intercalated oxygen species and partial structural restacking. Altogether, this study bridges a critical gap by directly linking sonication time with GO's chemical state, size distribution, and vibrational response under thermal treatment. The findings provide a robust framework to understand how lateral size and defect density govern phonon dynamics and reordering kinetics during thermal reduction. Conducted entirely under ambient air conditions, this approach offers a scalable and tunable route for producing reduced GO with tailored properties for sensing, electronic, and coating applications.