Natural water resources are depleting with the increasing population and economic growth. Thus, sustainable technologies using green energy need to be developed to provide a solution that does not contribute to climate change. By doing so, it is possible to contribute to the clean water and sanitation, and the affordable and clean energy sustainable development goals established by the United Nations.
Solar energy is a promising energy source to carry out water filtration. The majority of solar water filtration technologies rely on the evaporation of water and subsequent condensation to recover clean water. To accelerate this process, it is necessary to increase heat adsorption.This could be done by implementing an array of mirrors to concentrate sunlight. However, this would require a large investment in equipment and space.Fortunately, alternatives for heat concentration can be obtained with frontier materials.
Carbon materials have shown excellent heat conductivity and adsorption in carbon nanotubes (CNTs) and graphene. They can absorb up to 99% of the visible and mid-infrared irradiation from the sun. For solar water treatment, a porous film or foam of carbon nanomaterial is kept on the surface of the water source under solar irradiation. Heat is adsorbed in the carbon nanomaterials and transferred to the water source, promoting water evaporation that can permeate the porous film/foam. Later, water vapor can be condensed to obtain clean water. These types of frontier materials are capable of yielding a conversion efficiency up to 90%, meaning that 90% of the solar energy is used for water evaporation.
After evaporation, water needs to be condensed. Here, carbon nanomaterials can also enhance water condensation and harvesting. For example, by using a vertical array of CNTs that is hydrophilic on one end and hydrophobic on the other end, it is possible to attract water vapor then condense it and store it within the CNT array. In another use case, graphene grown on a copper substrate can be cooled to promote water condensation. Graphene can provide an enhanced hydrophobic surface allowing water droplets to easily roll down the surface and allow further condensation and water dripping.
By combining solar filtration and harvesting with frontier materials, it should be possible to create an energy efficient system to provide clean water. The system could be used in areas that are extremely dry, where the high temperatures could enhance water evaporation; and they can be used in humid areas where the condensation system can excel to provide clean water. Therefore, its implementation can be of interest to a wide population.
The frontier material-based solar water filtration system could be used for seawater as an alternative for natural water resources, and it can be used with wastewater to recycle water in an efficient manner. Another advantage is that it is possible to obtain zero liquid discharge, meaning that all the water can be evaporated and turned into clean water, while leaving a dry solid waste that can be further repurposed.
These breakthroughs make it possible to reach a future where clean energy can provide an efficient way to obtain and recycle water by using frontier materials such as carbon nanomaterials.
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