Hydrothermal Synthesis and Characterization of Sulfur-Doped Carbon Microspheres

Sulfur-doped carbon microspheres (SCMSs) with mean size of about 4 pan were prepared successfully by a simple one-step sulfur-assisted hydrothermal carbonization (ASHTC) method. Soluble starch was used as carbon precursor and sublime sulfur as sulfur source. The as-prepared SCMSs were characterized systematically by means of SEM, TEM, XRD, N-2 absorption-desorption isotherms, FUR, XPS, and solid NMR. The existing forms of sulfur in SCMSs were also discussed. It was found that monodispersed SCMSs with high output could be obtained under high starch concentration (1.0 g.mL(-1)) and sulfur atoms could be introduced into carbon networks easily, indicating that the ASHTC is a powerful method for SCMS synthesis. For comparison, carbon microspheres (CMSs) were synthesized by conventional hydrothermal carbonization of starch in the absence of sulfur under the same hydrothermal conditions. Experimental results show that the as-synthesized SCMSs exhibit much higher specific surface area than that of CMSs. The reason of the increase of surface area of SCMSs may be due to the structural and chemical defects resulted from the sulfur doping. The chemical defects come from the -S-S-, -S-, -SO2- and -SO- groups, while the structural defects result from the substitution of graphite hexatomic-rings by thiophene five-membered rings in SCMSs.