A gel full of porous holes, inspired by the dried core of the loofah fruit, can clean contaminated water by absorbing and releasing it, powered only by the heat of the sun. It could be used to provide clean water in regions without a reliable electricity supply.
Xiaohui Xu at Princeton University and her colleagues call their material a loofah-inspired solar absorber gel. It is hydrophilic when cool, meaning it readily absorbs water, but becomes hydrophobic when warmed by the heat of the sun and begins to release water. Because the gel only absorbs water and not contaminants such as oils, metals and microplastics, the released water is purified.
The researchers created the new hydrogel by adding ethylene glycol – a substance often used in the manufacture of polyester fibres – during the manufacturing process, creating porous holes similar to those found in a loofah. One gram of the gel can hold 50 milliliters of water, and it becomes hydrophobic at a temperature of 31°C (89°F), expelling 70 per cent of its absorbed water in 5 minutes.
Xu says that the material could be used alone to clean water in low-income countries, by absorbing water from polluted sources and then being placed in the sun to warm up and begin the process of releasing clean water – as long as the sunshine is strong enough to get it to the necessary temperature.
“We are developing a device to hold the materials. The manufacturing process is not difficult, all the reaction occurs at room temperature, no complicated equipment is required. It could be made in large scale,” she says. “We are working on designing a device for continuous water purification and we plan to try the new device next month. It won’t take long to put to use.”