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Introduction
Water, which covers over 70% of the Earth's surface, gives our planet its characteristic blue appearance from space. However, this apparent abundance masks a critical scarcity of potable water. The vast majority of Earth's water is saline and unsuitable for consumption, and the compounding effects of climate change, population growth, and increasing pollution have intensified this problem in recent decades, leading to severe water shortages globally. Many regions, particularly in Africa and parts of Asia, lack access to clean water. A United Nations World Water Development Report [1] projects that by 2050, 748 million people will face drinking water scarcity.
The vast quantities of water in oceans, seas, and rivers are largely unusable for direct consumption due to salinity levels. Desalination and wastewater treatment offer potential solutions to mitigate these shortages and avert a global crisis. Techniques such as reverse osmosis [2, 3–4], electrocoagulation [5], membrane filtration [6, 7], thermal-based methods [8, 9], and hybrid thermal-membrane processes like membrane distillation [10, 11] have been developed for this purpose. However, these methods often suffer from limitations, including low efficiency, high costs, reliance on non-renewable energy sources, operational complexity, and the emission of greenhouse gases, particularly carbon dioxide [9, 12, 13]. These drawbacks impede the widespread and sustainable application of these techniques as long-term solutions to the global water crisis.
To effectively address the clean water shortage, we must draw inspiration from nature. The water cycle, a solar-powered process, naturally converts billions of liters of saline water into potable water daily, culminating in rainfall. In recent years, there has been a significant shift towards replacing conventional desalination techniques with greener, more environmentally friendly approaches that harness solar energy. Photothermal conversion, which utilizes light to generate heat, has emerged as a promising sustainable energy source for solar desalination. Researchers have explored diverse photothermal materials to produce clean drinking water from various sources, including wastewater, saline water [14, 15, 16, 17, 18–19], and even atmospheric moisture [20]. Direct solar steam generation (DSSG) systems, which employ nanocomposites with combined light-absorbing and heat-transfer capabilities to evaporate water and produce clean distillate, represent a particularly promising technology for mitigating water scarcity.
Reduced graphene oxide (rGO), with its high surface area, offers excellent adsorption capacity for water molecules, enhancing water molecules capture...