Investigation of solid-liquid interfacial chemistry using nonlinear optical molecular probing method.

摘要

Solid-liquid interfacial chemistry studies adsorption and chemical reaction of molecules/ions in a very thin ( ∼ 20--50 A) interfacial region. Difficulties arise from the nature of the liquid phase and the equilibrium of solute molecules with the liquid phase and the interface. We overcome the difficulties using nonlinear optical molecular probing (NOMP) method---an innovative method that allows us to determine chemical processes at solid-liquid interfaces under real chemical conditions.;Nonlinear optical molecular probes are certain organic molecules that have nonlinear optical response a thousand to million times stronger than those of commonly used small organic molecules such as CH3CN and ions such as Cl-- and Na+. Therefore, their presence at a solid-liquid interface can easily be detected using second harmonic generation (SHG). The adsorption parameters of other chemical species present at the interface (e.g., organic molecules serving as corrosion inhibitors) can be extracted by investigating their co-adsorption behavior in the presence of properly chosen nonlinear optical molecular probes. Today, with over 1000 nonlinear optical molecular probes available, one can always find an appropriate molecular probe to suit the chemical requirements of a particular interfacial system.;We have investigated several important issues using the NOMP method. These include the competitive adsorption of ions with different charges and sizes, the density distribution of silanol (SiOH) groups at silica surfaces, and the adsorption and reaction mechanism of small organic molecules at solid-liquid interfaces.