Liquid Crystal Size Selection of Large-Size Graphene Oxide for Size-Dependent N-Doping and Oxygen Reduction Catalysis

Abstract

Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic liquid crystallinity. Many properties of GO-based materials, including electrical conductivity and mechanical properties, are limited by the small flake size of GO. Unfortunately, typical sonochemical exfoliation of GO from graphite generally leads to a broad size and shape distribution. Here, we introduce a facile size selection of large-size GO exploiting liquid crystallinity and investigate the size-dependent N-doping and oxygen reduction catalysis. In the biphasic GO dispersion where both isotropic and liquid crystalline phases are equilibrated, large-size GO flakes (>20 μm) are spontaneously concentrated within the liquid crystalline phase. N-Doping and reduction of the size-selected GO exhibit that N-dopant type is highly dependent on GO flake size. Large-size GO demonstrates quaternary dominant N-doping and the lowest onset potential (-0.08 V) for oxygen reduction catalysis, signifying that quaternary N-dopants serve as principal catalytic sites in N-doped graphene.

Sonication-free dispersion of large-area graphene oxide sheets using internal pressure from release of intercalated carbon dioxide

“…Thus additional processes are required to remove them (i.e., thermal annealing and acid treatment) [18]. Most of all, because sonication is unavoidably applied to exfoliate graphene sheets, even from intercalated and expanded graphite during the dispersion process, graphene sheets are easily broken into smaller pieces of sub-micron size [19][20][21]. This deteriorates the intrinsic properties of the graphene.…”

2D Material Liquid Crystals for Optoelectronics and Photonics

“…95 Lee et al introduce a method for facile size selection of large-size graphene oxide particles by exploiting liquid crystallinity. They show that in a biphasic graphene oxide dispersion where both isotropic and liquid crystalline phases are in equilibrium, large-size GO flakes (420 mm) are spontaneously concentrated within the liquid crystalline phase.…”

Liquid Crystalline Anisotropic Nanoparticles: From Metallic and Semiconducting Nanoparticles to Carbon Nanomaterials

“…Compared with other alignment media, very clean and high-quality NMR spectra were acquired with the GO molecules in solution because of their rigidity and high molecular weight. Lee et al used the liquid crystallinity of GO for size selection of large size GO and subsequently demonstrated size-dependent N-doping and oxygen reduction catalysis [124]. This work demonstrated that large GO may provide a better catalytic activity with controlled dopant structures.…”