PNNL

Abstract

In order to understand the effects of extracellular polymeric substances (EPS) derived from microorganisms on the colloidal stability of nanoparticles in sub-surface environments, the adsorption experiment of EPS extracted from the fungus S. cerevisiae onto insoluble ceria nanoparticles (CeNPs) has been conducted at a pH of 6.0 at room temperature with cell/CeNPs ratios of 2.6×10-5 and 2.6×10-433 , which are within the range of the ratio (10-5 – 1) that is found in environment. Subsequently the dispersibility was analyzed as a function of time within 10 min to eliminate the deposition process and of ionic strength ranging from 1 to 1000 mmol L-1 using UV-Vis and dynamic light scattering (DLS) analysis. The EPS was mainly composed of ~70 mg L-1 of organic carbon, ~0.50 mmol L-1 of K+ , and ~0.16 mmol L-1 of total phosphorous including ~0.12 mmol L-1 of orthophosphate. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that the orthophosphate and saccharides preferentially adsorb onto CeNPs. Proteins are the only major N-compounds adsorbing onto the CeNP surfaces. Adsorption of inorganic orthophosphate resulted in a dramatic decrease in ? potential to -40 mV at pH > 5, whereas the EPS adsorption suppressed the deviation of zeta (?) potential within a narrow range (-20 - +20 mV) at a wide range of pH (3-11). Critical aggregation concentrations (CAC) of electrolyte in control, inorganic orthophosphate, and EPS solutions are 0.01, 0.14, and 0.25 mol L-1 , respectively. The CAC indicates that the EPS adsorption suppresses aggregation of CeNPs by the electrostatic repulsive forces derived from the adsorbed orthophosphate and the steric barrier formed by the organic matters on the surface of CeNPs. The present results, for the first time, suggest that the microbial EPS coating on nanoparticles, which form during the interaction between microorganisms and CeNPs, cause colloidal stabilization regardless of the surrounding geochemical conditions in the environment.