Single-Hole Hollow Carbon Nanospheres via a Poly(ethylene glycol)-Assisted Emulsion-Templating Strategy for Intensified Liquid-Phase Adsorption

Single-hole hollow carbon nanospheres (HCH) possess unique properties that combine the advantages of a hollow cavity and an opening hole in the shell, making them very attractive in various applications. However, it is still a challenge to synthesize HCH via a facile and scalable route. Herein, we develop a poly(ethylene glycol) (PEG)-assisted emulsion-templating method to synthesize HCH, involving only a hydrothermal process and pyrolysis. In the emulsion system, the PEG molecules can be used as a reverse demulsifier to induce the formation of hollow structures with a closed shell (HCS, PEG-1000), a single hole in the shell (HCH, PEG-2000), and a bowl-like shell (HCB, PEG-4000). It is found that HCH exhibits higher adsorption capacities (2–4 times higher than those of HCS) and faster adsorption rates toward large molecules (e.g., Congo red), indicating the intensification of liquid-phase adsorption induced by the single-hole hollow structure, which can promote mass transfer and simultaneously enhance the adsorption capacity.