Carbon-modified graphite flakes prepared by hydrothermal carbonization to achieve superhydrophilicity

To improve the wettability and dispersion of graphite flakes in aqueous solvents without introducing impurities that could contaminate the graphite, the carbon-coated graphite flake (CGF) composite powders were fabricated using chitosan as a raw material by one-step hydrothermal carbonization. The effects of different types of saccharides (glucose, starch and chitosan), graphite/chitosan mass ratio, solution pH, amount of polyvinyl pyrrolidone (PVP), hydrothermal period and hydrothermal temperature on the preparation of CGF were investigated. The hydrothermal temperature of 190°C, hydrothermal period of 12h, dispersion pH of 7, graphite/chitosan mass ratio of 4 and PVP addition of 2 wt% were the most optimal preparation condition for the hydrothermal preparation of CGF. The water contact angle (WCA) of the prepared CGF was rapidly reduced from 49.1° to nearly 0° in about 1.2 s, exhibiting a superhydrophilicity. This behavior is attributed to the introduction of hydrophilic functional groups, and the absence of introduced impurities ensures that they can be used in applications requiring high purity graphite. Moreover, the bond between the carbon coating and the graphite was strong enough that it did not detach after 10 min of agitation in water. Thus, hydrothermal carbonized coatings prepared using chitosan as a raw material has great potential for improving the wettability and dispersion of graphite flakes in aqueous solvents. This approach provides an effective strategy for producing superhydrophilic graphite flakes without introducing impurities, thus expanding their potential use in more advanced high-tech applications.