This study investigates the thermal deoxygenation of Graphene Oxide (GO) using high-resolution in situ X-ray based spectroscopies, including XPS, NEXAFS, and VB spectroscopy. The research aims to understand the evolution of oxygen functional groups and the electronic structure of GO during thermal reduction. The results show that edge-plane carboxyl groups are highly unstable, while carbonyl groups are more difficult to remove. At moderate temperatures (~400 °C), phenol groups are formed through the reaction of basal plane epoxide groups with adjacent hydroxyl groups. These phenol groups are predominant and survive even at 1000 °C. A drastic increase in the density of states (DOS) near the Fermi level is observed at 600 °C, indicating a progressive restoration of the aromatic structure in thermally reduced GO. The study also reveals that the thermal reduction process leads to the formation of smaller, more disordered structures, with the presence of phenolic groups being more stable than other oxygen functional groups. The results highlight the importance of understanding the thermal deoxygenation process for the development of graphene-based materials with improved electrical and mechanical properties. The findings suggest that thermal reduction at lower temperatures can be effective in restoring the aromatic structure of GO, which has significant implications for the application of graphene in electronics and other fields. The study provides a comprehensive understanding of the electronic structure and surface chemistry of GO during thermal reduction, which is essential for the development of efficient and sustainable methods for the synthesis of high-quality graphene.This study investigates the thermal deoxygenation of Graphene Oxide (GO) using high-resolution in situ X-ray based spectroscopies, including XPS, NEXAFS, and VB spectroscopy. The research aims to understand the evolution of oxygen functional groups and the electronic structure of GO during thermal reduction. The results show that edge-plane carboxyl groups are highly unstable, while carbonyl groups are more difficult to remove. At moderate temperatures (~400 °C), phenol groups are formed through the reaction of basal plane epoxide groups with adjacent hydroxyl groups. These phenol groups are predominant and survive even at 1000 °C. A drastic increase in the density of states (DOS) near the Fermi level is observed at 600 °C, indicating a progressive restoration of the aromatic structure in thermally reduced GO. The study also reveals that the thermal reduction process leads to the formation of smaller, more disordered structures, with the presence of phenolic groups being more stable than other oxygen functional groups. The results highlight the importance of understanding the thermal deoxygenation process for the development of graphene-based materials with improved electrical and mechanical properties. The findings suggest that thermal reduction at lower temperatures can be effective in restoring the aromatic structure of GO, which has significant implications for the application of graphene in electronics and other fields. The study provides a comprehensive understanding of the electronic structure and surface chemistry of GO during thermal reduction, which is essential for the development of efficient and sustainable methods for the synthesis of high-quality graphene.