Graphene oxide aerogel 'ink' at room temperature, and ordered structures by freeze casting

Abstract

A simple 'drop-by-drop' deposition method was invented to make graphene oxide (G-O) hydrogels at room temperature. Graphite oxide was synthesized at 5 degrees C for a low defect density in the carbon lattice, and was then dispersed in water to form "G-O(5)". This water dispersion was converted into a G-O(5) ink by adding L-ascorbic acid and the ink could then be deposited onto any substrate to prepare hydrogels using a dropper; using this gelation method, a stable hydrogel is formed within 1 hour at room temperature, without heating or high pressure. Hydrogels with desired patterns and sizes were readily deposited on various substrates. This method provides efficient control over the hydrogel and it was readily made into forms such as films, fibers, and aerogels. Freeze casting the hydrogel caused the G-O(5) sheets to assemble into a long-range lamellar structure, by controlling the growth pattern of the ice crystals that formed the lamellae when the hydrogel was frozen. The deposition of this G-O(5) ink at room temperature allows straightforward fabrication of G-O aerogels with ordered structures. (C) 2021 Elsevier Ltd. All rights reserved.