Silver nanoparticles, coupled with SERS, detect contaminants in water

Recognizing that organic contaminants in the air and in drinking water need to be detected at very low-level concentrations, researchers at the University of Notre Dame (Notre Dame, IN) used surface-enhanced Raman spectroscopy (SERS) to make use of silver nanoparticles to increase the sensitivity limit of chemical detection.

The researchers, led by Prashant V. Kamat, the John A. Zahm Professor of Science at the University of Notre Dame, have prepared a semiconductor-graphene-metal film that has distinct advantages: The absorption of organic molecules on the film’s graphene surface increases the local contaminant concentration adjacent to silver nanoparticles.

The researchers have investigated the use of graphene oxide films in which the semiconductor titanium dioxide (TiO₂) and metal nanoparticles are deposited on opposite sides of the graphene surface. “We are currently working toward the detection of environmental contaminants at even lower levels,” says Kamat. “Careful control of metal size and loading will be the key to optimize strips for testing water quality.”

Under UV illumination, the electrons from TiO₂ are captured by the graphene oxide film and shuttled across the film to reduce metal ions into metal nanoparticles. This electron-hopping process across the graphene oxide film allows the design of a side-separated semiconductor-metal nanoparticle architecture.

While the conducting properties of graphene sheets deposited on various substrates are well understood, Kamat's group has demonstrated that the transport of electrons is not limited to the 2D plane. Here, the hopping of electrons from one side of the graphene allows for the side-selective deposition of silver nanoparticles.

“Another potential application is in the area of photocatalytic generation of solar fuels," Kamat says. "For example, having semiconductor nanoparticles on one side of a graphene sheet and a metal catalyst on the other side, one can create a hybrid assembly that can selectively split water into oxygen and hydrogen.”

The work has been published in the Journal of Physical Chemistry Letters; for more information, please visit http://pubs.acs.org/doi/abs/10.1021/jz3004206.

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