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Graphene and its derivatives are widely used in various fields due to their unique two-dimensional lamellar structure. This study aims to synthesize ultra-large graphene oxide (GO) sheets from natural flake graphite and investigate the factors influencing their size. Using a two-intercalation method based on the modified Hummers' method, we address the challenge of intercalating large-diameter graphene oxide by employing a secondary intercalation technique. Three different approaches were explored to control the size of the produced GO sheets. The results revealed that the completeness of the expansion graphite structure after initial intercalation significantly influenced the final GO sheet size, with more complete expansion leading to larger sheets. Optimal processing conditions were identified, involving soaking natural flake graphite in a mixed solution (H2SO4:H2O2 = 4:1), followed by drying at 60 °C for 24 h. Under these conditions, ultra-large GO sheets were predominantly monolayer with an average size of 220.99 μm and a maximum size of 438 μm. These monolayer GO sheets can be chemically reduced to graphene, making them promising for applications in transparent conductive films, optoelectronic devices, and aligned graphene composites.

• Structural response of ULD shield tunnel during construction of cross passage by mechanical technology is revealed. • Critical shifts in instability mechanism of ULD shield tunnel with lateral opening are discovered. • Constraining effects of SRG for disturbance during the mechanical construction of cross passages are highlighted. • Impact of SRG thickness on instability mechanism of reinforced ULD shield tunnel with lateral opening is analyzed. Construction of cross passages by mechanical methods represents an emerging construction technique with numerous advantages. However, cutting through segments of ultra-large diameter (ULD) shield tunnels poses significant safety risks, and the instability mechanism of those structures with lateral openings remains unclear. Based on China's first ULD shield tunnel project that adopted the mechanical method for construction of cross passages, refined three-dimensional finite element models were created with ABAQUS. The models considered material and geometric non-linearity and were employed for comprehensive analyses of construction disturbance responses, instability mechanisms of segments, and reinforcement measures. The findings reveal that (1) mechanical construction of cross passages leads to a 24.84 % to 58.57 % increase in structural convergence deformation and a significant stress concentration; (2) The C-shaped ring and the semi-split rings no longer behave consistently in terms of force and deformation after the opening is formed. Additionally, there are significant shifts in the instability characteristics under localized surcharge loads of the segmental lining, resulting in a 30 % decrease in instability start load; (3) After adopting the reinforcement measure of steel ring girders (SRG), the instability process of the structure with opening is similar to that of the initial structure. The loss in instability start load, caused by mechanical construction, has been reduced by 34.4 % ∼ 84.4 %. However, increasing SRG thickness beyond 40 mm has a limited impact on reinforcement efficacy. This study offers theoretical and practical insights for similar engineering projects, positively contributing to project safety. [ABSTRACT FROM AUTHOR]