Size effects of graphene oxide nanosheets on the construction of three-dimensional graphene-based macrostructures as adsorbents

Abstract

Three different sizes of graphene oxide (GO) nanosheets (1, 5–8, and 20 μm) were used for the construction of three-dimensional graphene-based macrostructures (3D GBMs). It was found that the minimal concentration required to form a stable 3D GBM decreased when larger nanosheets were used, and the use of larger GO nanosheets led to the formation of more porous 3D GBMs. The adsorption capabilities of the 3D GBMs for methyl blue (MB), Cd²⁺, and diesel as representative pollutants were investigated using column filtration and immersion adsorption experiments. The 3D GBMs constructed from the largest GO nanosheets (20 μm) exhibited the fastest adsorption rate for MB (0.000467 g (mg min)⁻¹) and Cd²⁺ (0.000143 g (mg min)⁻¹) and the reduced 3D GBMs displayed the highest adsorption capacity for diesel (193 g g⁻¹). It is highly possible that the more porous 3D GBMs may provide more interspace and more active sites for pollutant adsorption. The effects of GO nanosheet size on the porous structure, surface properties, adsorption rate, and adsorption performance of 3D GBMs were elucidated for the first time. The size effect of GO nanosheets is to balance the consumed effective sites for the assembly of stable porous 3D GBMs and the residual active sites for pollutant management. Moreover, increasing the graphene nanosheet size was demonstrated to be a simple strategy to improve the adsorption performance of 3D GBMs. This study provides basic insight into the construction of a 3D GBM by regulating the graphene nanosheet size to produce highly effective graphene-based adsorbents for environmental applications.