Adsorption of Extracellular Polymeric Substances Derived from S. cerevisiae to Ceria Nanoparticles and the Effects on Their Colloidal Stability
Hochella, Michael F. Jr.
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In order to understand the adsorption preferences of extracellular polymeric substances (EPS) components derived from fungus Saccharomyces cerevisiae on sparingly soluble CeO2 nanoparticles (CeNPs), the adsorption experiments of the EPS including organic matter with low molecular weight have been performed at pH 6.0 at room temperature (25 ± 1 °C). The subsequent effects of the coating on the dispersibility of CeNPs was systematically measured as a function of time and ionic strength ranging from 1 to 1000 mmol L−1. Among the EPS and other components, orthophosphate and saccharides preferentially adsorb onto CeNPs, and proteins are the only major N-compounds adsorbing onto the CeNP surfaces. Adsorption of orthophosphate resulted in a dramatic decrease in ζ potential to −40 mV at pH > 5, whereas the EPS adsorption suppressed the deviation of ζ potential within a narrow range (−20–+20 mV) at pHs ranging from 3 to 11. Critical aggregation concentrations (CAC) of an electrolyte (NaCl), inorganic orthophosphate, and EPS solutions are 0.01, 0.14, and 0.25 mol L−1, respectively, indicating that the EPS adsorption suppresses aggregation of CeNPs by the electrostatic repulsive forces derived from the adsorbed orthophosphate and the steric barrier formed by organic matter on the nanoparticle surfaces. Therefore, the EPS derived from fungus S. cerevisiae can potentially enhance colloidal dispersibility of CeNPs at circumneutral pH.