Microwave-assisted hydrothermal synthesis of carbon materials with tunable microstructure

Abstract

A facile microwave-assisted hydrothermal route has been developed for a synthesis of versatile carbon materials. The monosaccharide fructose aqueous solution was adopted as the starting material, and the pH of the solution was adjusted to be in acidic (pH 4), neutral (pH 7) and basic (pH 10.5) conditions. The pH buffered fructose solutions were treated at different temperatures by a microwave-assisted hydrothermal technique. As-prepared carbon materials displayed pH and temperature dependent multi-morphologies (porous, spherical or core-shell), which were determined by transmission and scanning electron microscopic analyses (TEM and SEM). And the hypothesis of dehydration mechanism of hydrothermal synthesis was analyzed by ultraviolet extinction and Fourier transform infrared spectroscopy. It was found that as compared with normal hydrothermal synthesis, microwave assistance could efficiently increase the production yield and improve the spherical geometry of the carbon particles in neutral condition. By changing the pH of the system, acidic pH induces aggregation of the spheres, while basic pH produces more trends toward core-shell or sponge-like porous structure. The study opens a novel route to the production of polytropic carbon materials and suggests a potential niche market established from the green synthesis.