Colloidal stability of hematite nanoparticles in the presence of a common quaternary ammonium compound at environmentally-relevant concentrations

• Published in: Environmental science. Nano 2023-12, Vol.1 (12), p.3476-3485
• Main Authors: Aruguete, Deborah M, Zhuang, Andy, Canonaco, Cameron, Sheckler, Trevor, Schmidt, Corryn, Borgohain, Rituraj
• Format: Article
• Language: English
• Subjects: Air-water interface; Ammonium; Ammonium compounds; Cations; Contact angle; Diameters; Ferric oxide; Haematite; Hematite; Interfaces; Iron oxides; Nanomaterials; Nanoparticles; Nanotechnology; Organic chemistry; Quaternary ammonium compounds; Quaternary ammonium salts; Soil water; Surface tension; Surfactants; Zeta potential
• ISSN: 2051-8153; 2051-8161
• DOI: 10.1039/d3en00544e

The fate and behavior of environmental nanomaterials can be strongly affected by organic molecules, including surfactants. Quaternary ammonium compounds (QACs) are cationic surfactants of increasing concern in the environment due to their massive everyday use and continuous release into water and soil. To examine QAC-NP interactions, ∼38 nm hematite (α-Fe 2 O 3 ) nanoparticle (NP) suspensions were mixed end-over-end with cetyltrimethylammonium chloride (CTAC), a commonly-used QAC, for 22 hours (23 °C) at environmentally-relevant concentrations of 0, 10, 100, and 1000 μg L −1 . Iron concentrations were measured to determine how many NPs remained in suspensions after mixing, along with characterization of the hydrodynamic diameter (Z-average) and zeta potential. Without CTAC, the NPs were destabilized by contact with air-water interfaces (AWIs) with [Fe] decreasing from 17.65 ± 3.26 mg L −1 to an [Fe] final of 6.33 ± 2.90 mg L −1 . However, at 100 and 1000 μg CTAC L −1 , the NPs were stabilized and NP loss reduced with [Fe] final values of 9.50 ± 1.20 mg L −1 and 11.69 ± 1.25 mg L −1 , respectively. Measurements of surface tension and contact angles on CTAC-exposed glass were performed to explore possible stabilization mechanisms. Results suggest that in systems with air-water interfaces such as unsaturated pores or turbulent waters, elevated QAC content might alter the environmental fate and transport of iron oxide and other positively-charged NPs. The stability of a model environmental nanomineral, colloidal hematite (α-Fe 2 O 3 ) nanoparticles, can be strongly affected by environmentally-relevant levels of quaternary ammonium surfactants, a surfactant present in ubiquitous daily-use household products.