Heat-concentrating solar steam generation and salt extraction based on water-repellent germanium nanoparticles-coated oxidized copper foams

• Published in: Solar energy materials and solar cells Vol. 230; p. 111191
• Main Authors: Xu, Yisu, Qi, Zhifu, Luo, Zhouyang, Shen, Zhen, Li, Chenxi, Chen, Guo, Cai, Wenyi, Bao, Hua, Tu, Chang-Ching
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.09.2021; Elsevier BV
• Subjects: Cellulose; Coatings; Copper; Copper foams; Electromagnetic absorption; Evaporation; Evaporation rate; Foams; Germanium; Germanium nanoparticles; Heat concentration; Heat loss; Hydrophobicity; Immersion coating; Infrared absorption; Irradiance; Metal foams; Nanoparticles; Perfluoroalkyl & polyfluoroalkyl substances; Salt extraction; Salts; Sodium chloride; Solar steam generation; Steam generation; Thermal conductivity; Water reuse; Heat concentration; Germanium nanoparticles; Copper foams; Salt extraction; Solar steam generation
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2021.111191

We demonstrate solar steam generation with high evaporation rates and extraction of dry salts from solutions by using water-repellent germanium nanoparticles (GeNPs)-coated oxidized copper foams (CFs) as light absorbers and heat concentrators. The CF surface was first oxidized into black CuO, then dip-coated with colloidal GeNPs for enhancing infrared absorption, and lastly treated with perfluoroalkyl silane to render hydrophobicity. The CF can absorb more than 95% of the AM1.5G solar irradiance spectrum, for heating up a water-permeated cellulose paper underneath to generate steam which is then evacuated through the CF's interconnected pores. Furthermore, due to the CF's high thermal conductivity, the heat generated in the peripheral region can be efficiently concentrated to the center where the water evaporates. With the light-absorbing CF area about 7 times larger than the water-evaporating cellulose paper and the convective heat loss mitigated by an acrylic cover, under one sun solar irradiance, the CF temperature can reach 70 °C, resulting in an evaporation rate as high as 3.2 kg m−2 h−1. Moreover, when a NaCl solution is used for the heat-concentrating evaporation inside an enclosed system in which the water condensate is recycled, readily useful dry salts are formed and can be harvested from the hydrophobic CF surface, while the bulk solution is gradually desalinized. •While being clean and inexhaustible, one major issue of solar energy is its relatively low energy density. As a result, for solar steam generation, optical concentration is often employed to increase the evaporation rate. However, the optical concentrating systems are usually quite expensive.•We demonstrate heat-concentrating solar steam generation with high vapor temperature (70 °C) and high evaporation rate (3.2 kg m−2 h−1) by using water-repellent germanium nanoparticles (GeNPs)-coated oxidized copper foams (CFs) as light absorbers and heat concentrators.•The CF surface was first oxidized into black CuO, then dip-coated with colloidal GeNPs for enhancing infrared absorption, and lastly treated with perfluoroalkyl silane to render hydrophobicity. The CF can absorb more than 95% of the AM1.5G solar irradiance spectrum.•The major byproduct from coastal seawater desalination is the highly concentrated solution of salts. Traditionally, electrodialysis is used to extract salts from the brine, which however has high energy demands and requires the pre-treatment of feedwater.•As a green alternative to the electrodialysis method, we demonstrate the extraction of dry salts from NaCl solutions by using the water-repellent GeNPs-coated oxidized CFs.