▎ 摘　　要

Reduced graphene oxide (rGO) is a representative commercialized graphene-related material that can be massproduced. However, the conventional thermal and chemical reduction methods require high temperatures and toxic reducing agents and consume energy and cause environmental pollution. Therefore, alternative ecofriendly methods that are less energy-intensive are required for their mass production. Herein, we propose a facile and eco-friendly reduction method that enables the mass production of rGO. Specifically, a custom-built focused ultrasound circulation system was used to reduce graphene oxide in a suspension without using toxic reagents. The sonicated rGO was reduced to a significant extent, and its carbon-to-oxygen atomic ratio (87.79%) and electrical conductance (9.15 mu S) were comparable to those of commercially available rGO. Raman spectroscopic analysis revealed that sonicated rGO gave a lower D-to-G band intensity ratio than commercial rGO reduced by heat treatment. This method can contribute to the active utilization of rGO in next-generation industrial products with lower environmental and energy impacts.