Colloidal stability and aggregation behavior of CdS colloids in aquatic systems: Effects of macromolecules, cations, and pH

Bingcheng Liu; Chuling Guo; Changdong Ke; Kai Chen; Zhi Dang

doi:10.1016/j.scitotenv.2023.161814

Colloidal stability and aggregation behavior of CdS colloids in aquatic systems: Effects of macromolecules, cations, and pH

Sci Total Environ. 2023 Apr 15:869:161814. doi: 10.1016/j.scitotenv.2023.161814. Epub 2023 Jan 25.

Authors

Bingcheng Liu¹, Chuling Guo², Changdong Ke¹, Kai Chen¹, Zhi Dang¹

Affiliations

¹ School of Environment and Energy, South China University of Technology, Guangzhou 510006, PR China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, PR China.
² School of Environment and Energy, South China University of Technology, Guangzhou 510006, PR China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, PR China. Electronic address: clguo@scut.edu.cn.

PMID: 36708836
DOI: 10.1016/j.scitotenv.2023.161814

Abstract

Redox-dynamic environments such as river floodplains and paddy fields have been demonstrated to be important sources of CdS colloids. To date, the aggregation kinetics of CdS colloids had not yet been studied, and the structure and properties of macromolecules on the interaction between different macromolecules and CdS colloids, as well as the aggregation behavior of CdS colloids are unclear. This study investigated the colloidal stability of CdS colloids in model aqueous systems with various solution chemistry and representative of macromolecules. The results showed that increased electrolyte concentration destabilized CdS colloids by charge screening, with the cationic effect following Ca²⁺ > Mg²⁺ > K⁺ > Na⁺; Higher solution pH stabilized CdS colloids by raising the critical coagulation concentration from 33 to 56 mM NaCl. Electron microscopy and spectroscopy verified the strong interaction between macromolecules and CdS colloids, and macromolecule adsorbed on the surface of CdS to form a protective layer called "NOM corona". The interaction between macromolecules and CdS induced distinct aggregation behaviors in NaCl and CaCl₂ solutions. The steric repulsion generated by "NOM corona" significantly stabilized CdS colloids in NaCl solution, and the stabilizing order was consistent with the adsorbing capacity of macromolecules on CdS colloids, namely Bovine serum albumin (BSA) > sodium alginate (SA) > calf thymus DNA (DNA) > Suwannee River humic acid (HA). BSA and DNA also inhibited CdS colloids aggregation in the CaCl₂ solution due to the balance of steric hindrance, cation bridging, and electrostatic repulsion. For HA and SA, Ca²⁺ bridging and EDL compression contributed to their destabilization of CdS colloids in CaCl₂ solution. Macromolecules concentration affect corona formation that alter stability of CdS colloids. There results showed that the complex influences of solution chemistry and macromolecules on fate and transport of CdS colloids in environment. The findings will help to understand the potential risks of CdS colloids in environment.

Keywords: Cation bridging; CdS colloids; Electrostatic interaction; NOM corona; Steric hindrance.