Fast preparation of carbon spheres from enzymatic hydrolysis lignin: Effects of hydrothermal carbonization conditions.

This study explores the effect of carbon sphere preparation conditions on the morphology of the carbon spheres and the micropore development by fast potassium hydroxide activation via microwave heating. Enzymatic hydrolysis lignin is used as the precursor for carbon sphere preparation via environmentally friendly hydrothermal carbonization. The effects of various carbonization temperatures, carbonization times and reaction concentrations on the physical morphology of the carbon sphere surfaces are investigated. The Brunauer-Emmett-Teller surface area, yield and scanning electron microscopic images are used to characterize the carbon spheres. High carbonization temperatures and times result in large particle sizes, high sphericity, uniform size, and high dispersity of the carbon spheres. The best carbon spheres are obtained at 270 °C for 7 hours with a reaction concentration of 0.06 g ml-1 and a particle size of 3-6 µm. After activation, the Brunauer-Emmett-Teller surface area of the activated carbon spheres increases from 248 m2 g-1 to 1278 m2 g-1. Carbon spheres activated by treatment with fast potassium hydroxide and microwave heating can develop micropores that enhance the adsorptive capacity for small molecules, such as gases. Enzymatic hydrolysis lignin-derived carbon spheres formed via hydrothermal carbonization should be potentially sustainable materials applicable in energy and environmental fields.