Disinfectant use has increased worldwide due to the COVID-19 pandemic. Quaternary ammonium compounds (QACs) are some of the most common disinfectants used for surface cleaning, as well as being used in everyday personal care products. QACs contain cations with the general formula NR₄⁺, where R corresponds any alkyl or aryl group. Those used as disinfectants have surfactant activity, namely with at least one long-chain alkyl group (R = C_nH_2n+1 with n ≥ 8). Increased QAC use leads to greater release of QACs to environmental systems. As such, understanding the interaction between QACs and environmental compounds is critical. One major class of environmental substances is mineral nanoparticles, which has been the focus of our studies.

We present preliminary data from our investigation into the impact of QACs upon mineral nanoparticle (NP) stability in solution, based upon the hypothesis that bilayer formation might impact the degree of NP aggregation. Hematite (a-Fe₂O₃) nanoparticles were exposed to QACs with varying alkyl group lengths: hexadecyltrimethylammonium chloride (denoted as Q-16), octyltrimethylammonium chloride (Q-8), and tetramethylammonium chloride (Q-1). We also exposed nanoparticles to benzalkonium chloride (BZC), a commonly used QAC containing a mixture of alkyl chain lengths. Along with controls (no QACs), three environmentally-relevant QAC concentrations were tested: for BZC, 1000 μg / L, 100 μg / L, 10 μg / L, and for Q-16, Q-8, and Q-1, 3.13 μM, 0.313 μM and 0.0313 μM. The Q-16 and BZC-exposed NPs were stabilized in solution at the two highest concentrations; Q-8 exposed NPs were stabilized at 3.13 μM only and Q-1 did not stabilize NPs at any concentration. We shall discuss our hypotheses on QAC stabilization of NPs in the context of characterization with scanning electron microscopy, dynamic light scattering, and Fourier transform infrared spectroscopy.

Trevor Sheckler

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