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The adsorption of citric acid onto Ti[O.sub.2] anatase nanoparticles is examined at circumneutral and acidic pHs, where the analysis has focused on the surface chemistry of citric acid on Ti[O.sub.2], including measurements of surface coverage and speciation, and its impact on nanoparticle behavior. The results have shown that surface coverage is a function of pH and has decreased with increasing pH, whereas surface speciation has differed from the bulk solution and is time dependent.

The role of solvation in the photochemistry of adsorbates at solid interfaces and the impact of molecular oxygen, adsorbed water and relative humidity in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere are examined. The results have shown that the photolysis of adsorbed nitrate on mineral dust aerosol, as nitrate in organic films, have played a vital role in the chemistry of the atmosphere through renoxification.

The surface chemistry of calcite, the most common and stable phase of calcium carbonate, is studied by using infrared spectroscopy. The results reveal that carbonic acid might be an important, albeit short-lived, intermediate in the surface chemistry of calcium carbonate.

Citric acid plays an important role as a stabilizer in several nanomaterial syntheses and is a common organic acid found in nature. Here, the adsorption of citric acid onto TiO2 anatase nanoparticles with a particle diameter of ca. 4 nm is investigated at circumneutral and acidic pHs. This study focuses on both the details of the surface chemistry of citric acid on TiO2, including measurements of surface coverage and speciation, and its impact on nanoparticle behavior. Using macroscopic and molecular-based probes, citric acid adsorption and nanoparticle interactions are measured with quantitative solution phase adsorption measurements, attenuated total reflection-FTI R spectroscopy, dynamic light scattering techniques, and zeta-potential measurements as a function of solution pH. The results show that surface coverage is a function of pH and decreases with increasing pH. Surface speciation differs from the bulk solution and is time dependent. After equilibration, the fully deprotonated citrate ion is present on the surface regardless of the highly acidic solution pH indicating pKa values of surface adsorbed species are lower than those in solution. Nanoparticle interactions are also probed through measurements of aggregation and the data show that these interactions are complex and depend on the detailed interplay between bulk solution pH and surface chemistry. [ABSTRACT FROM AUTHOR]