Hollow carbon spheres, synthesis and applications - a review

Hollow carbon spheres (HCSs), also sometimes called carbon capsules, refer to hollow structured carbon particles of millimetre, micron or even nanometre size and correspondingly thin shells. These materials are presently attracting great attention due to their unique properties such as encapsulation ability, controllable permeability, surface functionality, high surface-to-volume ratios, and excellent chemical and thermal stabilities. In many aspects, carbon capsules are therefore superior to their polymer-or metal-based counterparts. In the present review, two main synthetic strategies, hard-templating and soft-templating routes, but also far more uncommon preparation ways are reported and concisely described. The main features of the resultant HCSs are also briefly given. Recent progress in the main application aspects of HCSs, such as adsorption, energy storage and catalysis, among others, is next discussed. Finally, an outlook of their prospects and challenges in terms of controlled synthesis and applications is presented.