Solar steam generation is a promising approach for water treatment, such as for desalination. This process involves harnessing energy from the sun to heat a material, which subsequently evaporates the water to be treated, leaving behind impurities. The steam then condenses, creating potable water. This is particularly appealing for addressing Sustainable Development Goal 6 from the United Nations, ‘Clean water and sanitation’, as solar treatment systems can be established in hard-to-reach communities, at point-of-use. Key to achieving this is ensuring a high light-to-water vapor conversion efficiency and low-cost materials.

Amongst the various material options, metals offer several benefits for use as the active photothermal material. However, many of the best performing candidates are based on noble metals – which make use of an enhanced plasmonic effect to improve conversion efficiency – and are therefore too expensive for widespread use. Now, a team from Shandong University report the synthesis and use of dealloyed nanoporous zinc films for efficient solar steam generation1.

The authors1 start with aluminum-rich Al-Zn alloys and then use NaOH to selectively dissolve aluminum, leaving behind a nanoporous, zinc-rich film (Fig. 1a). By varying the starting composition of the alloy, they control the ligament size (and therefore the porosity), creating an interconnected network of nanoporous channels, through which water can travel. The best performing film exhibits a high porosity of around 81%, good broadband optical absorption, and a high evaporation efficiency of 84.8% under one sun irradiation (Fig. 1b). Furthermore, desalination tests for water from the Yellow Sea in China show that salinity levels are below that required by the World Health Organization for drinking water. The authors attribute the performance of their porous zinc film to a fine ligament structure with rough surfaces enhancing light absorption, and to nanoporous channels promoting both water and vapor transport.

Fig. 1: Structure and photothermal performance of a nanoporous zinc thin films.
figure 1

a Scanning electron microscopy image of the nanometer-scale ligament structure of a dealloyed zinc film, b Photothermal evaporation efficiencies of two zinc films dealloyed from different starting compositions under different illumination conditions. Reprinted (adapted) with permission from ref. 1. Copyright 2024 American Chemical Society.

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Dealloyed nonporous materials have already found use in a number of energy-based applications, such as electrochemical energy conversion and storage. This work now demonstrates the potential that dealloying offers for producing cost effective and high-performance metal-based photothermal materials for solar-powered desalination.