Abstract
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.
Highlights
Natural, engineered, and incidental nanoparticles are ubiquitous in all portions of the Earth system [1,2,3]
The Na+ concentration does not represent sodium release from the yeast, but the sodium initially added to the solution to adjust the ionic strength
Masaki and others have already reported that the dissolved organic matter in the extracellular polymeric substances (EPS) consists of various species as determined by HPLC [29]
Summary
Natural, engineered, and incidental nanoparticles are ubiquitous in all portions of the Earth system [1,2,3]. Naturally occurring nanoparticles include inorganic, organic substances, and mixed substances [4,5]. They can play a key role in the migration of radionuclides [4,6,7,8]. The mobility of nano-scale colloids in subsurface environments are often delicately dependent on their physico-chemical properties such as their size and shape, including surface topography, as well as surface charge, attached ligands, and aggregation state. In such processes, Environments 2017, 4, 48; doi:10.3390/environments4030048 www.mdpi.com/journal/environments
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