Adsorption Behavior of SARS-CoV-2 S1-RBD Protein on Na+/Ca2+-Saturated Montmorillonites.

SARS-CoV-2, known for its high transmissibility, spreads via aerosols, enabling long-term environmental persistence. Mineral particles, a key aerosol component, may interact with the virus, yet research remains limited. This study investigated the adsorption of SARS-CoV-2's receptor-binding domain (RBD) protein onto Na+- and Ca2+-montmorillonite (NaM, CaM) at pH 5 and 9 and ionic strengths of 1 mM and 10 mM. Results showed NaM adsorbed RBD faster and more efficiently than CaM. Higher ionic strength delayed adsorption equilibrium. Adsorption was lower at pH 5 than pH 9, suggesting contributions beyond electrostatic forces (e.g., hydrophobic interactions, hydrogen bonding). Theoretical calculations confirmed experiments and revealed Ca2+-mediated bridging between RBD and CaM. This work clarifies viral adsorption mechanisms on clay minerals, aiding environmental risk assessment of virus-mineral interactions.