Visible-Light-Driven Photoreduction of Industrial-Grade Graphene Oxide into Single-/Few-Layer Reduced Graphene Oxide Nanosheets: Structural Evolution and Enhanced Electrochemical Energy-Storage Performance

Abstract Graphene oxide (GO)-derived reduced graphene oxide (rGO) is an important two-dimensional carbon material for electrochemical energy storage, yet the controllable conversion of low-cost industrial-grade GO into high-quality rGO remains challenging because of its severe aggregation, multilayer stacking, and heterogeneous oxygen-containing functional groups, which usually require harsh reaction conditions and strong reducing agents. Herein, a mild visible-light-driven photoreduction strategy was exploited to convert industrial-grade GO into single-/few-layer rGO nanosheets under ambient temperature and pressure, using eosin Y as the photosensitizer and triethylamine as the sacrificial electron donor. Most importantly, the time-dependent structural evolution of industrial-grade GO during photoreduction was systematically revealed. Morphological and structural characterizations showed that visible-light irradiation progressively weakened interlayer interactions, promoted the delamination and flattening of stacked GO aggregates, and produced single-/few-layer rGO nanosheets. XRD, FTIR, XPS, Raman, and thermal analyses demonstrated a general decrease in oxygenated carbon species, defect reconstruction, and partial restoration of the sp2-conjugated carbon network. After 180 min, the C/O atomic ratio increased from 2.53 to 6.16 and the BET surface area increased from 325.87 to 472.40 m2 g–1, confirming substantial deoxygenation together with increased accessible surface area. The optimized rGO-3 sample delivered a specific capacitance of 370 F g–1 at 20 mV s–1 in 0.1 M KCl, which is competitive with previously reported rGO-based electrodes evaluated at the same scan rate. After 5000 galvanostatic charge–discharge cycles, rGO-3 retained 92.3% of its initial capacitance with a Coulombic efficiency of 99.4%. EIS measurements in ferro/ferricyanide-containing electrolyte and photocurrent measurements of the final washed rGO electrode further indicated faster interfacial electron transfer toward the redox probe and improved carrier-transport behavior, respectively. This work provides a green and controllable route for converting industrial-grade GO into single-/few-layer rGO nanosheets and clarifies the structural evolution underlying the enhanced electrochemical performance of photoreduced graphene materials.