TherGel: Thermosensitive hydrogels to recover drinking water from saline water

Almost two billion people live in countries with high water stress. In the coming decades, this situation will worsen, due to the increase in water demand and the impact of climate change, which is already being noted with a severe drought in the entire Mediterranean region in recent months. For this reason, it is vital to find new materials for water desalination to try to alleviate water scarcity. 

Thermosensitive hydrogels are polymers that can undergo controlled changes in their hydration depending on the temperature to which they are exposed. Due to their three-dimensional porous network, hydrogels can absorb a large amount of water without dissolving in it. Thermosensitive hydrogels can expel the water when they get warm (approximately above 32ºC), which generates water that is free from salts. For this reason, in recent years their efficiency in direct osmosis desalination systems has been researched and verified. Some researchers have achieved an evaporation efficiency of around 70% of the water absorbed by the hydrogel in only 10 minutes, to reach a rate of ∼26 KMH (kg/metres squared × hour) of clean water. This is enough to meet the daily water demand of an adult person. To boost its capacity to “expel water”, compounds are generally used that can absorb energy, such as conductive polymers. Conductive polymers are compounds that can respond to light and act as a photothermal absorbent. In addition, they can be used potentially as light, semiconductive materials in electrochemical applications, such as the semi-solid electrodes that are used in desalination technologies for brackish water or seawater.

In this context, the TherGel project is being developed. This project is led by the research group in Innovation in Materials and Molecular Engineering - Biomaterials for Regenerative Therapies (IMEM-BRT), at the Universitat Politècnica de Catalunya - BarcelonaTech (UPC). The aim of TherGel is to combine the properties of both materials in a conductive polymer hydrogel that could be used in water evaporation systems, as filtration membranes and as solid-state electrolytes that are active in electrochemical cells of capacitive deionisation of salt water.

The project is designed to develop a prototype of self-purification of water in homes, without the need for electricity consumption or pressure equipment, simply using the heat energy of the sun. The development of low-cost technologies for water purification is an important strategy to meet current and future water needs adapted to domestic consumption and framed within the Sustainable Development Goals (SDG 6 - Clean water and sanitation).