A 3D-macroporous pomelo peel foam based on anti-shrinkage properties of MnOx for solar water purification

The conversion of biomass waste into photothermal materials is a promising solution. However, the carbonization process always leads to structural collapse and blocks vapor diffusion channels of biomass-derived carbon materials, resulting in poor evaporation performance. Herein, by utilizing a cheap and abundant biowaste of pomelo peels (denoted PP) as a porous structure precursor, a 3D-macroporous evaporator (denoted MPP) was formed through a one-pot pyrolysis method in the presence of MnCO3 (filler agent). The pyrolysis of MnCO3 generated gas and MnOx anchored on the skeleton of PP, confining its shrinkage, in turn obtaining MPP with larger pore volume. As a result, the 3D-macroporous structure facilitates the fast water vapor diffusion and MnOx improves the photothermal conversion capability of the direct carbonized pomelo peel (denoted CPP). The surface temperature of MPP reaches 92.2 ℃ under one sun irradiation, which is ~ 10 ℃ higher than CPP. And the evaporation rate of MPP (1.43 kg m−2 h−1) increased significantly by 50% compared to that of CPP (0.95 kg m−2 h−1). Moreover, its performance can be further enhanced up to 1.805 kg m−2 h−1 by being fabricated into a hierarchical mimetic tree-like solar vapor system, due to the reduced heat loss from MPP to bulk water and enhanced thermal concentration at the MPP surface. Furthermore, this system performed the excellent self-desalting performance without salt crystals on the surface of the MPP even in 20% brine during 8 h desalination and showed the high removal efficiency of metallic ion and dye (over 99.9%) in wastewater disposal.