Same area, better output: 3D rose-shaped multi-reflective hydrogel evaporator for salt-resistant seawater desalination and contaminant degradation

Abstract

High light-to-heat conversion efficiency and outstanding water purification performance are two essential parameters for sunlight-driven solar evaporation in real applications. With various limitations of the used photothermal materials, the traditional three dimensional (3D) evaporators could not achieve the high solar-vapour conversion efficiency and rapid salt mitigation ability simultaneously. Herein, a rose-shaped 3D hydrogel evaporator (RSE) has been designed by using g-C₃N₄ nanotube as a photothermal material integrated with polyvinyl alcohol (PVA)/chitosan hydrogel matrix. The RSE evaporator exhibits a broad light absorption capacity of 99 % and vertically aligned porous network for the effective heat confinement which prevents the thermal loss to the bottom water while permitting the steam to evaporate. The RSE evaporator can form a porous channel for faster water transport and allows the rapid dissolution of deposited salt to the bottom water, and prevents salt accumulation. Such a deliberately designed 3D evaporator exhibits excellent hydrophilicity (~ 0°), high solar-vapour conversion efficiency of 98 %, and a stable steam generation rate of 3 kg.m⁻².h⁻¹ under the solar irradiation of one sun. The addition of g-C₃N₄ nanotube as photothermal material also acts as a photocatalyst and restricts the contamination of organic contaminants by photocatalytic degradation to assure the purification ability of the evaporated distillate. Such an advantageously designed 3D RSE evaporator provides a promising method for the generation of fresh water from seawater and wastewater.