New hydrogel materials for improving solar water evaporation, desalination and wastewater treatment: A review

Ongoing to the modern societies and global economic developments, the water is recognized as one of the main concerns of humankind, particularly with the continuous decrease of the freshwater supply. Solar energy, which is abundant and available in many areas, can solve the problem of long-term energy and freshwater reduction in the whole world. Researchers do their best to solve this problem in different ways. Currently, many studies have used solar energy to improve the efficiency of evaporation, solar desalination, and wastewater treatment since it is the basis for freshwater. One of the new ways applied to achieve this is named “hydrogel”, which has various structures. Hydrogel, as a novel light-absorbing material, is an effective technique to enhance photothermal solar efficiency conversion by decreasing the heat loss in the heat transfer process due to the heat localization on the air-water interface. Moreover, hydrogel has many pores structures with excellent water transport from the bottom to the water-air interface. Hydrogels are floatable, durable, anti-fouling, and suitable recycling materials, which are energetically favorable for harvesting and amplifying the steam generation. Furthermore, over the past three years, they have revolutionized solar water vaporization with an evaporation efficiency of 95% and the evaporation rate of 4 kg/(m². hr), which cannot be achieved by other materials.