Multi-shelled hollow porous carbon nanospheres-based evaporator for highly efficient solar-driven desalination

Carbon-based materials stand out as photothermal materials for interfacial solar evaporation due to their high solar absorptance, chemical stability, adjustable structure, ease of preparation, and low cost compared to other candidate materials. Development of multifunctional carbon-based materials that can endow the fabricated evaporators with reduced energy loss and evaporation enthalpy is highly demanded to achieve extraordinary evaporation rates. Herein, high-solar-absorptivity multi-shelled hollow porous carbon nanospheres are fabricated and incorporated with an insulating hydrogel bottom layer into an integrated solar evaporator. It achieves a fast photothermal response and a remarkably high solar evaporation rate of 2.4 kg m⁻² h⁻¹ under one sun. Multiphysics simulation indicates that the porous multi-shelled hollow structure enables sufficient and effective interactions between water and the hydrophilic carbon surfaces, thus producing more intermediate water (IW) and lowering the evaporation enthalpy. The solar-driven water evaporation in the evaporator is probed by in-situ low-field nuclear magnetic resonance relaxation time measurements, based on which conversion of free water (FW) into IW during solar evaporation is proposed. The molecular dynamics simulations reveal that the evolution of FW clusters into IW is facilitated on the carbon surface, thus replenishing the evaporated IW and maintaining continuous high evaporation rates. The demonstrated solar evaporator exemplifies the effectiveness of structural and thermal management in enhancing solar-driven desalination.