Physicochemical Characterization of Emerging Contaminants: A Conductance-Based Determination of Diffusion Coefficients for Butylparaben and Triclosan in Aqueous Solution

This work successfully demonstrates the application of fundamental electrochemical principles to derive critical physicochemical constants for complex organic molecules. The accurate characterization of mass transfer properties for micropollutants in aqueous systems is a fundamental challenge in applied physical science, bridging condensed matter physics with environmental engineering. This study presents a rigorous determination of the diffusion coefficients for two ubiquitous organic contaminants, Butylparaben and Triclosan, whose environmental persistence necessitates a precise understanding of their transport phenomena. We employ a robust and cost-effective electrolytic conductance method under infinite dilution conditions, systematically investigating the influence of temperature (305.15 K to 319.15 K) and concentration (0.0001 M to 0.0009 M) on both electrolytic and molar conductivity. The resulting data were modeled using both the Kohlrausch equation and a Modified Robinson–Stokes (MRS) quadratic model, with the MRS model demonstrating a superior fit (R² > 0.98) for extrapolating the limiting molar conductivity (Λ°). Using the derived Λ° values, the infinite dilution diffusion coefficients (D°) were calculated via the Nernst–Haskell equation, yielding values of 0.99 x 10⁻⁸ m²/s for Butylparaben and 0.98 x 10⁻⁸ m²/s for Triclosan at 303.15 K. Furthermore, the Nernst–Einstein and Stokes–Einstein equations were utilized to determine the self-diffusion coefficients and corresponding hydrodynamic radii (0.602 x 10⁻¹² m for Butylparaben and 0.740 x 10⁻¹² m for Triclosan), providing deeper insight into single-ion dynamics. The determined transport properties provide essential parameters for developing more accurate computational models of contaminant fate, contributing valuable data to both environmental science and the broader field of soft condensed matter physics.