Process-Oriented Engineering of Dye Adsorption: Controlling Diffusion and Surface Kinetics through Hierarchical Porosity in Pickering Emulsion-Derived Polymer Microspheres

Efficient removal of organic pollutants from water requires adsorbents with optimized transport pathways and accessible adsorption sites. While adsorption capacity is often linked to surface chemistry, the role of pore architecture in governing diffusion and adsorption kinetics remains insufficiently understood. This work investigates how hierarchical porosity controls dye adsorption in polymer microspheres synthesized by Pickering emulsion polymerization. Poly(methacrylic acid)-based microspheres with systematically varied pore architectures were prepared by modifying the crosslinking chemistry and porogen content, yielding distinct micro- and nanoporous structures. Methylene blue adsorption was monitored by UV–Vis spectroscopy and analyzed using a dual-process model separating diffusion-controlled transport from surface-controlled adsorption kinetics. Correlation analysis established quantitative relationships between transport and structural parameters. Adsorption behavior was strongly dependent on internal pore architecture. Hierarchical micro- and nanoporous networks promoted diffusion-assisted transport and enhanced dye penetration into the particle interior, wehreas progressive pore narrowing shifted adsorption toward a surface-controlled regime with reduced diffusion accessibility. Strong correlations between diffusion coefficients, kinetic constants, particle dimensions, and pore sizes demonstrate that pore architecture governs the transition between diffusion- and kinetics-controlled adsorption. The proposed model successfully captured the adsorption behavior across all particle types and provided mechanistic insight into the interplay between mass transport and adsorption. This findings demonstrate that adsorption performance can be engineered through controlled morphological design of polymer microspheres. Hierarchical porosity acts as a key parameter regulating the balance between diffusion and surface adsorption kinetics, providing a practical framework for developing advanced adsorbents for water purification and dye removal applications.