Tuning surfactant packing parameter optimizes the stabilization of soil organic carbon by Organo-bentonite

This study demonstrates how the packing parameter (P) of cationic surfactants governs the efficacy of organo-bentonites in stabilizing soil organic carbon (SOC). A series of organo-bentonites, synthesized with single- and double-chain surfactants (C12-C18), were evaluated for their capacity to stabilize labile SOC. Higher P values promoted denser hydrophobic domains, primarily on the external surface of the bentonite, which enhanced the adsorption capacity for potassium fulvate (FA, the proxy for SOC). Didodecyldimethylammonium bromide-modified bentonite (DDAB-Bent), with the highest packing parameter (P = 0.5-0.6), achieved the highest FA equilibrium adsorption (428.93 mg/g). In soil incubation studies, DDAB-Bent reduced cumulative carbon mineralization by 40.18% compared to the control. In a 30-day pot experiment with Chinese cabbage, DDAB-Bent increased total SOC content by 35.42%, mineral-associated organic carbon (MAOC) by 51.76%, and plant biomass by 28%. Molecular dynamics simulations of the confined interlayer confirmed that higher P values lead to more compact surfactant aggregates and stronger FA adsorption. This study therefore validates the packing parameter as a key design tool for engineering organo-bentonites for enhanced SOC stabilization in agricultural soils.