Macroscopic and Mechanically Robust Hollow Carbon Spheres with Superior Oil Adsorption and Light-to-Heat Evaporation Properties

Hollow carbon spheres (HCSs) represent a special class of functional materials, to which intense interest has been paid in the fields of materials science and chemistry. A major problem with these materials is the lack of sufficient particle engineering and mechanical strength for practical applications and the difficulty of up-scaling. Herein, we report a general, template-free, phase-separation approach, in which the liquid-liquid phase-inversion process and a gas-foaming process are coupled for the first time, for fast and continuous processing of uniform HCSs. The obtained HCSs have particle sizes on the millimeter scale, and a hierarchical structure with an interpenetrating, open-porous, carbon shell and huge external voids, therefore permitting rapid transport of molecules into, throughout, and out of the hollow structure. By evenly dispersing the CNTs in the precursor solution, CNT-reinforced HCSs can be achieved with significantly enhanced mechanical strength, hydrophobicity, and electronic and thermal properties. The resulting CNT-reinforced HCSs offer a viable route to remove the engine oil from water in a fixed-bed system. Moreover, these floatable HCSs can receive and convert sunlight to heat at the water-air interface, resulting in a great enhancement in solar evaporation rate compared to conventional bulk heating schemes.