Sphere to Fight Water Pollutants
05, Oct 2018
Prelims level : Science & Technology – New Invention Mains level :
- Rice University researchers have enhanced micron-sized titanium dioxide particles to trap and destroy bisphenol A (BPA), a water contaminant with health implications.
- 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.
- The reactive oxygen species (ROS), hydroxyl radicals are bad for BPA. Inexpensive titanium dioxide releases ROS when triggered by ultraviolet light. But oxidating molecules fade quickly, BPA has to be close enough to attack.
- The spheres reveal themselves as flower-like collections of titanium dioxide petals. The supple petals provide plenty of surface area to anchor cyclodextrin molecules.
- Cyclodextrin is 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 also hydrophobic and naturally attracted to the cavity. Once trapped, 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 percent of BPA in an hour, a process that would take more than twice as long with unenhanced titanium dioxide.
- Cyclodextrin molecules on the surface trap BPA, which is then degraded by reactive oxygen species (ROS) produced by the light-activated particles.
- Most of the processes reported in the literature involve nanoparticles. The size of the particles is less than 100 nanometres. Because of their very small size, they’re very difficult to recover from suspension in water. The Rice particles are much larger. Where 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. Because ROS also wears down cyclodextrin, the spheres begin to lose their trapping ability after about 400 hours of continued ultraviolet exposure but once recovered, they can be easily recharged.
- This is an example of how advanced materials can help convert academic hypes into feasible processes that enhance water security.
- This new material helps overcome two significant technological barriers for photocatalytic water treatment. First, it enhances treatment efficiency by minimizing scavenging of ROS by non-target constituents in water. Here, the ROS are mainly used to destroy BPA.
- Second, it enables low-cost separation and reuse of the catalyst, contributing to lower treatment cost.