Influence of pH on the synthesis of carbon spheres and the application of carbon sphere-based solid catalysts in esterification

Size uniformity is a key challenge in the preparation of hydrothermal carbon spheres and a prerequisite for size effect research and many applications of carbon spheres. To solve the scientific problem of low uniformity due to the slow carbonization in traditional preparation of glucose carbon spheres, we propose to add acid/base catalysts to accelerate nucleation, shorten the nucleation time, and improve the size uniformity of carbon spheres. The carbon spheres prepared under base conditions versus acid conditions have higher uniformity and smaller particle size (particle size = 503 nm). This result is due to the faster accumulation of aromatic clusters, shorter nucleation time, and larger number of carbon spheres in alkaline systems. The NaOH-HCSs-based solid acid catalyst as-prepared exhibits excellent catalytic activity, and the esterification rates of levulinic acid and n-butanol maximize to 96.36%.