The competing effects of microbially derived polymeric and low molecular-weight substances on the dispersibility of CeO2 nanoparticles

Yuriko Nakano,Ayaka Takeda,Satoshi Utsunomiya,Asumi Ochiai,Kenta Ichiyoshi,Toshihiko Ohnuki,Michael F Hochella,Keisuke Kawamoto

doi:10.1038/s41598-018-21976-9

Abstract

To understand the competing effects of the components in extracellular substances (ES), polymeric substances (PS) and low-molecular-weight small substances (SS) <1 kDa derived from microorganisms, on the colloidal stability of cerium dioxide nanoparticles (CeNPs), we investigated their adsorption to sparingly soluble CeNPs at room temperature at pH 6.0. The ES was extracted from the fungus S. cerevisiae. The polypeptides and phosphates in all components preferentially adsorbed onto the CeNPs. The zeta potentials of ES + CeNPs, PS + CeNPs, and SS + CeNPs overlapped on the plot of PS itself, indicating the surface charge of the polymeric substances controls the zeta potentials. The sizes of the CeNP aggregates, 100–1300 nm, were constrained by the zeta potentials. The steric barrier derived from the polymers, even in SS, enhanced the CeNP dispersibility at pH 1.5–10. Consequently, the PS and SS had similar effects on modifying the CeNP surfaces. The adsorption of ES, which contains PS + SS, can suppress the aggregation of CeNPs over a wider pH range than that for PS only. The present study addresses the non-negligible effects of small-sized molecules derived from microbial activity on the migration of CeNP in aquatic environments, especially where bacterial consortia prevail.

Highlights

The cerium dioxide (CeO2, Fm3m) nanoparticle (CeNP) is a nanomaterial that is finding a wide variety of applications to a vast number of products involving fuel additives[1], fuel cell components[2], biomedical applications[3,4], combustion accelerators and abrasives[5,6], and specialized polishing agents[7]
The extracellular substances (ES) used in the present study contained 2–4 times higher concentrations of organic and inorganic species than the ES characterized in our previous study[29]
Adsorption experiments using ES (PS + SS), polymeric substances (PS) (>1 kDa), and SS (

Summary

Introduction

The cerium dioxide (CeO2, Fm3m) nanoparticle (CeNP) is a nanomaterial that is finding a wide variety of applications to a vast number of products involving fuel additives[1], fuel cell components[2], biomedical applications[3,4], combustion accelerators and abrasives[5,6], and specialized polishing agents[7]. In vitro and in vivo experiments with CeNPs have shown that this material can cause chronic toxicity to aquatic organisms[8], cell death to E. coli[9], increase of reactive oxygen species levels relevant to human lung cells[10], and decrease of glutathione levels in cultured human lung epithelial cells[11] Due to their small size, ~10 nm, the inhaled CeNPs can penetrate into the deep respiratory system[12] and potentially cause adverse health effects despite the existing study reported that CeNPs have low human toxicity[13]. Adeleye and Keller[37] carried out adsorption experiments of extracellular PS onto TiO2 nanoparticles This resulted in a reversal of the surface charge and enhanced particle stabilization. We aim to evaluate their competing effects on the adsorption processes onto CeNPs, changes in the CeNP surface properties, and the aggregation and sedimentation of CeNPs at various pHs

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Conclusion