WASHINGTON: Scientists have created tiny spheres that can catch and destroy bisphenol A (BPA), a synthetic chemical used to make plastics that often contaminates water. BPA is commonly used to coat the insides of food cans, bottle tops and water supply lines, and was once a component of baby bottles. While BPA that seeps into food and drink is considered safe in low doses, prolonged exposure is suspected of affecting the health of children and contributing to high blood pressure.
Scientists at Rice University in the US have developed something akin to the Venus' flytrap of particles for water remediation.
The micron-sized spheres resemble tiny flower-like collections of titanium dioxidepetals.
The supple petals provide plenty of surface area for researchers to anchor cyclodextrin -- a benign sugar-based molecule often used in food and drugs.
It has a two-faced structure, with a hydrophobic (water-avoiding) cavity and a hydrophilic (water-attracting) outer surface.
BPA is hydrophobic and naturally attracted to the cavity. Once trapped, reactive oxygen species (ROS) produced by the spheres degrades BPA into harmless chemicals.
In the lab, the researchers determined that 200 milligrams of the spheres per litre of contaminated water degraded 90 per cent of BPA in an hour, a process that would take more than twice as long with unenhanced titanium dioxide.
"Most of the processes reported in the literature involve nanoparticles," said Danning Zhang, a graduate student at Rice University.
"The size of the particles is less than 100 nanometers. Because of their very small size, they're very difficult to recover from suspension in water," said Zhang, lead author of the study published in the journal Environmental Science & Technology.
While a 100-nanometer particle is 1,000 times smaller than a human hair, the enhanced titanium dioxide is between 3 and 5 microns, only about 20 times smaller than the same hair.
"That means we can use low-pressure microfiltration with a membrane to get these particles back for reuse. It saves a lot of energy," Zhang said.
Since ROS also wears down cyclodextrin, the spheres begin to lose their trapping ability after about 400 hours of continued ultraviolet exposure, Zhang said. However, once recovered, they can be easily recharged.
"This new material helps overcome two significant technological barriers for photocatalytic water treatment," said Pedro Alvarez, from Rice University.