Organonickel complex J-aggregation on interfacial evaporator promotes broadband absorption and salt rejection for efficient solar-powered desalination

Abstract

Solar steam generation (SSG) driven by environment-friendly and renewable energy is emerging as a promising technology for alleviating clean water scarcity. So far, developing solar-thermal conversion materials for solar interfacial absorbers to advance evaporation rate and efficiency is still a crucial challenge. Herein, the thienyl-substituted organonickel bis(dithiolene) complex (NiTh) with an intense second near-infrared (NIR-II) absorption of intervalence charge transfer transition was synthesized and systemically compared with the phenyl-based complex (NiPh). Based on the delocalization electron property of thiophene, NiTh behaves with low adiabatic and high reorganization energies, contributing to its nonradiative decay rate and photothermal conversion. Its J-aggregation on the foam fiber was fabricated as a solar-to-heating interfacial layer with broad absorption from visible to NIR-II regions and salt-resistance ability, resulting in excellent solar light-harvesting. Under one sun of irradiation, the NiTh-adsorbed foam with red-shifted absorption and higher photothermal conversion ability exhibits a faster solar energy-to-evaporation rate (1.99 ± 0.10 kg m⁻² h⁻¹) compared with the NiPh-adsorbed foam (1.83 ± 0.06 kg m⁻² h⁻¹), of which the blank foam is 0.48 ± 0.03 kg m⁻² h⁻¹. The evaporation rate of solar-driven seawater desalination based on NiTh@foam evaporator can reach up to 1.80 ± 0.05 kg m⁻² h⁻¹, and the efficiency is as high as 122.1 ± 3.1 % due to the additional energy harvesting in the side areas that absorb sunlight and the light-trapping effect inside the three-dimensional evaporator. For organic pollutant solution, clean condensed water with an evaporation rate of 2.03–2.17 kg m⁻² h⁻¹ can be obtained through the SSG operation based on NiTh@foam. This study promotes a strategy for designing small molecules with NIR-II absorption and further modification on porous foam surfaces to achieve high-efficitive solar-driven evaporation application.