The earth represents around 71% of water. An ACCAB made of 97% of this water is in the oceans, leaving us only 3% in the form of fresh water – and a large part of it is frozen in the form of glaciers. This leaves only 0.3% of this fresh water on the surface in lakes, swamps, springs and our main sources of drinking water, rivers and streams.
Despite the famous blue appearance of our space planet, the thirsty extraterrestrials would be disappointed. Drinking water is actually quite rare.
As if it did not seem already disturbing, the little water we have is also threatened by climate change, urbanization, pollution and a world population which continues to develop. More than 2 billion people live in regions where their only source of drinking water is contaminated. Pathogenic microbes in water can cause cholera, diarrhea, dysentery, polio and typhoid, which could be fatal in areas without access to vaccines or medical treatments.
Desalination of seawater is a possible solution, and an approach implies absorbing water of porous materials which evaporates when heated by solar energy. The problem with most existing solar energy evaporators is that they are difficult to evolve for larger populations. The performance decreases with the size, because less water vapor can escape materials with tiny pores and thick limits, but there is a way to overcome this.
Feel salted
Researcher XI Shen of Polytechnic University of Hong Kong wanted to find a way to improve these types of systems. He and his team have now created an aerogel which is much more effective in turning fresh water than the previous desalination methods.
“The key factors determining the evaporation performance of porous evaporators include the location of heat, water transport and steam transport,” said Shen in a study recently published in ACS Energy Letters. “Significant progress has been made in the structural design of evaporators to achieve a very effective thermal location and transport of water.”
Solar radiation is the only energy used to evaporate water, which is why many attempts have been made to develop what are called photothermal materials. When sunlight strikes these types of materials, they absorb light and convert it into thermal energy, which can be used to accelerate evaporation. Photothermal materials can be made of substances, including polymers, metals, alloys, ceramics or cements. Hydrogels have been used to succeed in decontaminating and dentying water before, but these are polymers designed to keep water, which negatively affects efficiency and stability, as opposed to aerogels, which are made of polymers that hold the air. This is why Shen and his team decided to create a photoothermic aeroge.
