Molecular architecting of photothermal hydrogels reinforced by polar-porous C2NxO1-x for efficient solar water purification

Abstract

Solar-powered interfacial evaporation provides a sustainable and effective means of harvesting green energy to relieve the global water scarcity issues. While hydrogel evaporators are effective for purifying the contaminated or saline water, the use of hydrophobic carbon-based light-absorbers that compromises the hydratability and local heat exchange poses an impediment to the evaporation rates. Herein, we propose a concept of using heteroatoms-rich and porous C2NxO1-x as the light absorber for molecular design of hydrogel-based evaporators for solar-powered water purification. The synergy of abundant polar groups within C2NxO1-x and hydratable skeleton (chitosan and polyvinyl alcohol) enables the decline of water evaporation enthalpy and thus facilitates vapor generation. The hydrophilic C2NxO1-x that penetrates hydrogel network enlarges the pore aperture with improved pore interconnectivity, which allows for rapid water transport and sufficient water supply. Importantly, the converted energy was localized to sufficiently power the evaporation of water molecules present in polar pores of C2NxO1-x due to adequate heat exchange. The resultant photothermal hydrogel attains a high evaporation rate of ca. 2.9 kg m−2 h−1 with an ultrahigh ion removal efficiency (99.9 %) in both simulated seawater and complex ionic contaminants under one sun irradiation. This study offers a useful guideline of utilizing hydrophilic porous light-absorber to develop high-performance hydrogel for efficient solar-powered water purification.