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VIS Light, Photocatalyst Deconstruct BPA

Photonics Spectra
Sep 2015
A hybrid photocatalyst that can break down bisphenol A (BPA) using visible light could eventually be used to help safely dispose of the widely used chemical. Because BPA doesn’t degrade easily, it can potentially cause harm to humans and the environment, including when it seeps into waterways.

Researchers affiliated with the University of Malaya, in Kuala Lumpur, Malaysia, and Leibniz University of Hannover in Germany, have developed a photocatalytic nanomaterial that could someday be used to treat water supplies. Their work is published in APL Materials (doi: 10.1063/1.4926454 [open access]).

BPA has been a key ingredient in the manufacture of polycarbonate plastic since the late 1950s. The ubiquitous plastic has been a practical solution for medical devices and many common consumables, including water bottles. BPA is also used in the epoxy resins that line water pipes and coat the interiors of many food and beverage cans.

There are public and scientific concerns about possible adverse health and environmental effects of BPA, and research addressing these concerns is ongoing. BPA can seep into food or beverages from containers made with the chemical, some research has shown. BPA could also have health effects on the brain, behavior and the prostate gland of fetuses, infants and children, according to the Mayo Clinic, a nonprofit medical practice and research group in Rochester, Minn.

A new photocatalytic nanomaterial can be used to treat water using visible light.
A new photocatalytic nanomaterial can be used to treat water using visible light. The hybrid photocatalyst was effective in degrading BPA, a widely used chemical.

The new nanomaterial breaks down BPA through photocatalytic oxidation, a process in which light activates an oxidizing chemical reaction. Researchers produced the substance by adding silver (Ag) and reduced graphene oxide (RGO) to titanium dioxide (TiO2) nanoparticles to improve the latter’s photocatalytic activity.

When the researchers mixed the hybrid nanoparticles with BPA solution under an artificial visible light source, they found that BPA oxidized and broke down much more effectively than it did without the catalyst present. They also noted that the RGO-Ag-TiO2 nanoparticles outperformed those where RGO or Ag alone were added to the TiO2.

The findings suggest that the modifications played a role in the enhanced catalytic activity under visible light.

When light is shone on a photocatalyst such as TiO2 nanoparticles, the energy can propel one of its electrons up to an excited state and create a charge distribution imbalance. There then exists an excess of negative charge at the higher energy electron band and an excess of positive charge at the lower-energy electron band (known as a “hole”) because the electron has left.

TiO2 can catalyze oxidation and reduction of materials around it in its unbalanced, excited state. In pure TiO2, however, it takes more energy to excite electrons from one level to another. The excited electron tends to quickly fall back down and recombine with the hole, giving the catalyst little time to induce a reaction. Also, pure TiO2 only displays photocatalytic properties under UV light.

To improve the photocatalytic properties of TiO2 nanoparticles, researchers first added Ag to their surfaces to enhance the charge separation. When light strikes TiO2 and excites one of its electrons, Ag draws the electron away so it can’t fall back down into the hole, and the hole can more readily assist in an oxidation reaction.

The Ag also shifted the wavelength of light necessary to activate the photocatalyst toward the visible light spectrum.

Like the Ag, the addition of RGO helped the hole to persist by accepting excited electrons from TiO2. It also reduced the nanoparticles’ bandgap, decreasing the amount of energy necessary to activate the photocatalyst.

The team hopes to use their findings to help break down BPA and other contaminants in water supplies.

“We strongly feel the developed nano-photocatalyst could be one of the nano-materials that can sustainably address said problem,” said project leader Dr. Saravanan Pichiah of the University of Malaya.


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