Hydrothermal Synthesis Of Functional Carbon Materials

Carbon microsphere(CMS) is a novel functional carbon material with excellent chemical and thermal stability, high thermal conductivity and regular spherical structure which is conducive to mass transferring of liquid reactant and product, and is widely applied in the fields of energy storage, catalyst support, fuel cell, drug delivery, and electrode materials of lithium ion battery.Although chemical vapor deposition, templating and other methods have been developed to prepare carbon microspheres ranging from nano-scale size to micron level with different structures, carbon microspheres of monodispersity, high purity and uniform size are still difficult to prepare. Besides, the high temperature and synthesis of appropriate template are needed in above mentioned methods, resulting in more complicated process, higher energy consumption and less surface functional groups of the product.In this work, carbon microspheres were synthesized by hydrothermal carbonization of renewable green resources hydroxypropyl starch and cyclodextrin at a lower carbonization temperature and mild reaction condition. Starch has a unique molecular structure and chemical property, and it is a natural polymer, a rich source of low price, swelling and gelatinizing after heating in water. In addition, the starch-based carbons contain many surface hydrophilic groups which make the surface modification easier, avoiding the difficulty in modification caused by the hydrophobic surface groups from the old synthesis approach. The raw materials and synthesis conditions were investigated to find a suitable synthesis route and reasonable explanation of the effects of various factors on the yield, shape and size distribution of carbon microspheres. The pore structures and surface chemical properties of obtained carbon samples were characterized by the isothermals of N2 adsorption, Raman spectrum, XRD, SEM, FT-IR and TGA.The results showed that carbon microspheres could be synthesized by using hydroxypropyl starch and cyclodextrin as precursors. The synthesis was as follows. The raw materials were firstly mixed with distilled water in mass ratio of 1:2, hydrothermal carbonized at no less than 170oC, then washed and extracted by ethanol, and finally dried at 85oC for 12h. Arginine could improve the yield of carbon samples while propylene oxide can inhibit the raw materials into carbon and reduce carbon yield. The suitable solution pH ranges from 3 to 7. The obtained carbon microspheres were smooth and monodisperse with particle size of about 10μm; The surface chemical groups of carbons were mainly hydroxyl, carbonyl and other hydrophilic groups, so, it was easy to modify and introduce some new groups on the prepared carbon microsphere. The surface area and pore volume of obtained carbon microspheres were less than 8m~2/g and 0.006cm~3/g, respectively. After high temperature carbonization, the porous carbon microsphere with 426m~2/g of specific surface area and 0.22cm~3/g of pore volume could be prepared.