September 30 2017 by Justin Harris

Hurricane Harvey and the other major storms that wreaked havoc in the US and Caribbean have impacted millions, and one major issue in dealing with the aftermath is the supply of clean water. The heavy winds and rain have knocked water treatment plants off-line, destroyed infrastructure, and the contaminated flood waters and sewage overflow have left locals without potable water. For this reason initial relief efforts include large shipments of clean bottled water and implementation of portable water filtration systems. In light of these crises water purification has been on the forefront of our minds; in particular (given our nanotechnology inclination) the significant advancements made in past year to use nanoparticles for the removal of oil from contaminated water.

THE IMPETUS OF NANOPARTICLES IN WATER PURIFICATION

In recent years, even before the 2017 hurricane season, the separation of oil from water has become increasingly important. New oil production techniques consume and pollute large quantities of water. For illustration, fracking generates 20 gallons of contaminated water for every gallon of crude oil obtained. Because of these demands, water management is one of the largest oilfield operational expenses. Likewise, oil spills and pipe ruptures cause massive environmental problems, and conventional cleaning methods have proven inefficient and environmentally risky. Recently, two new methods utilizing iron oxide nanoparticles have been published that offer novel solutions for purifying onshore and offshore water that has been polluted with oil.

ACCELERATED MAGNETIC SEPARATION OF OIL FROM WATER

Published in the Journal of Nanoparticle Research, researchers at the University of Texas at Austin use superparamagnetic iron oxide nanoparticles to separate oil from water.¹ The iron oxide nanoparticles are synthesized in a citrate solution with diameters of approximately 10 nm. They are then functionalized with primary amines which give them a positive charge. When mixed with a crude oil-in-water (or seawater) emulsion the positively charged magnetic nanoparticles attach to the negatively charged oil droplets.

This charge neutralization leads to aggregation of the iron oxide nanoparticles, coupled with coalescence of the oil droplets. After 2 hr mixing, the aggregates are easily removed with a magnet in under 5 min.

Traditional oil separation techniques only remove 95% of oil from polluted water; this technique removes >99%. The promise of this nanoparticle based water purification method could lead to compact separation designs that generate significantly less hazardous sludge, smaller costs, and less fresh water depletion in oil production. Also, due to the simple electrostatic interaction between the nanoparticles and oil, the aggregation is potentially reversible which would allow for recovery of the iron oxide nanoparticles and reuse.

NANOPARTICLE SPONGE FOR EFFICIENT OIL ADSORPTION

A second approach published in the Marine Pollution Bulletin by researchers at Northwest University in China utilizes iron oxide nanoparticles to create a magnetic sponge for the cleanup of oil spills in large bodies of water.² Standard oil sorbents are easily disturbed by severe weather conditions and are blown by ocean winds causing secondary pollution. Magnetic sponges can avoid these problems. By electrospinning iron oxide nanoparticles with polystyrene fibers a hydrophobic, oleophilic sponge is created that absorbs oil without absorbing water. Its low density allows it to float on water, and the iron oxide nanoparticles allow it to be retrieved via a magnet.

As shown below with a dyed oil (A), the sponge efficiently absorbs oil from water (B). The sponge is then attracted to a magnet (C), and easily removed to leave a pure water sample (D).

The magnetic nanoparticle sponge technology is a significant step forward for oil spill cleanup combining physical and chemical methods of oil separation, while also decreasing secondary pollution risks.

HELPING DISASTER RELIEF NOW

While these nanoparticle water purification methods are still being developed in labs around the globe they offer hope that one day soon better, more efficient, methods of water treatment will be available. When the next natural or man-made disasters strikes hopefully these nanotechnologies will provide improved tools to restore potable water supplies in a rapid and environmentally safe manner. In the meantime, however, please consider helping those devastated by the the recent hurricanes by donating to foundations that supply clean and safe water to the communities in need.

• Waves for Water - Caribbean Hurricane Relief Initiative
• LifeStraw - $20 Straw Could Provide Hurricane Victims With A Year Of Clean Water
• Oxfam - providing safe water, sanitation, and hygiene supplies to prevent diseases.