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The possibility of modulating the electromagnetic shielding mechanisms of graphene aerogels by varying the reduction state of graphene oxide was evaluated. Highly porous graphene aerogels were prepared by a modified hydrothermal treatment. Reduction state was varied through a subsequent thermal treatment under Ar-2/H-2 atmosphere at different temperatures: 400, 600 and 1000 degrees C. Thermal treatments reduced the amount of oxygenated functional groups without altering pore morphology and pore size as revealed by XRD, XPS, Raman and SEM image analysis. The resulting aerogels presented thus a very low density, in the range 8.5-5.6 mg/cm(3) and a conductivity in the range 10-80 S/m. Electromagnetic characterization was performed in the range 8-18 GHz in terms of power analysis and shielding efficiency. All samples transmitted less than 5% of incident power although an increase of the reflection mechanism was observed as the thermal treatment temperature was increased. (C) 2019 Elsevier Ltd. All rights reserved.