logo Pearson Lab, Department of Chemistry, Tufts University, Medford, MA 02155
  logo Shultz Laboratory for Water and Surface Analysis  


General Description

Interfaces can legitimately be called the final frontier for chemistry particularly those interfaces that are highly flexible liquids, glasses, and irregular solids. Yet picturing interactions at such interfaces is critical for understanding phenomenon ranging from the impact of human activities on the environment to macromolecular configuration and transport across cell membranes.
Our current focus is on water at any interface:

The first challenge in probing such interfaces is finding a technique that distinguishes molecules at the interface from the much larger concentration in the bulk phases on either side of the interface. Our primary probe is the nonlinear optical spectroscopy sum frequency generation, SFG. SFG combines a visible photon with an infrared photon to generate the sum of these two. Scanning the infrared frequency generates a vibrational spectrum of the surface. With the advent of increasingly reliable light sources, it is relatively easy to collect SFG spectra. Interpreting these spectra remains a challenge. Recently, we developed a methodology termed polarization angle null, PAN, greatly increasing the power of SFG.

Recently, we have applied SFG and PAN to generate the first molecular-level glimpse of the ice surface simultaneously providing a rich picture of this surface and demonstrating the power of the PAN methodology. We are currently pulling together the ice work with work with aqueous nanodrops to unlock the secrets of formation of clathrates. Clathrates consist of shells of water around hydrophobic molecules such as methane. It has been estimated that clathrates in the oceans contain more carbon than all the oil discovered on Earth. Global warming may render these clathrates unstable, presenting a run-away mechanism that could lead to incredibly high temperatures.

Our most applied work focuses on production of clean water. It has been suggested that shortage of clean water will be a global crisis far surpassing the oil crisis. Billions of people world wide currently lack access to safe drinking water. One of the initiatives aimed at generating safe water uses solar energy and semiconductor materials, specifically TiO2, to oxidize unsafe substances in the water. Semiconductors oxidize pollutants in the gas phase with near unit efficiency. Unfortunately, contact with condensed water greatly reduces this efficiency.

Our efforts are aimed at discovering the mechanism by which water quenches the oxidation reaction with the goal of modifying the basic substrate to avoid this quenching.

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