Engineers have developed an oil-catching sponge that could help recover contamination from offshore drilling.

Drilling and fracking for oil under the seabed produces 100 billion barrels of oil-contaminated wastewater each year by releasing tiny oil droplets into surrounding water.

Most efforts to remove oil from water focus on removing large oil slicks from industrial spills but these are not suitable for removing tiny droplets. Instead, scientists are looking for new ways to clean the water.

An international research team has now developed a sponge that removes over 90 per cent of oil microdroplets from wastewater within ten minutes.

When the sponge is used, the oil coats its surfaces like a thin film, via a process called adsorption. After use, the sponge can be treated with a solvent, which releases the oil. The oil can then be recycled, leaving the sponge ready to be used again.

To create the original sponge, the used ordinary polyurethane foams — similar to those found in couch cushions — to separate tiny droplets of oil from wastewater.

They then added tiny particles of a material known as nanocrystalline silicon to the foam surfaces. This meant they could better control the sponge’s surface area and surface chemistry, improving its ability to capture and retain oil droplets as a coating on the pores' surfaces – a concept known as critical surface energy.

“The critical surface energy concept comes from biofouling research, which tries to prevent microorganisms and creatures like barnacles from attaching to surfaces like ship hulls,” said project leader Dr Pavani Cherukupally.

“Normally, you want to keep critical surface energy in a certain range to prevent attachment, but in our case, we manipulated it to get droplets to cling on tight.

“It’s all about strategically selecting the characteristics of the pores and their surfaces. Commercial sponges already have tiny pores to capture tiny droplets: Polyurethane sponges are made from petrochemicals, so they have already had chemical groups which make them good at capturing droplets.

“The problem was that we had fewer chemical groups than what was needed to capture all the droplets. I therefore worked … to increase the number of chemical groups, and … to get the right amount of coating.”

Details of the latest work on the sponge are accessible here.