Interaction mechanisms of POSS-based adsorbents with VOCs, CO₂, CH₄, and H₂O: theoretical insights and prediction method

The dual nature of Polyhedral Oligomeric Silsesquioxane (POSS), with its cage framework and substituent groups, enables diverse interactions with liquid and gaseous pollutants. While Quantum Mechanical (QM) methods have been used for simpler POSS variants, evaluating all possible combinations of cages and substituents remains impractical. This study aims to fill the knowledge gap on how the polarity of liquid pollutants and the structural features of POSS influence the efficiency of separating Volatile Organic Compounds (VOCs) from aqueous streams in wastewater treatment processes. Using a comprehensive dataset on liquid-liquid adsorption selectivities, we developed a predictive model for estimating VOC-VOC and VOC-water partition coefficients across 1.424 × 10⁷ POSS variants, achieving accuracy comparable to expensive QM methods. This model enables users to design novel POSS molecules tailored for wastewater treatment or VOC recovery quickly and efficiently. We explored adsorption mechanisms for CO₂, H₂O, and CH₄, focusing on interactions between the cage and adsorbates, as well as between substituents and adsorbates. Our findings highlight that substituents are crucial for gas adsorption, with their electrostatic properties being a significant factor. While all substituents exhibited strong CO₂/CH₄ selectivity, this selectivity diminishes in the presence of H₂O. Additionally, gaseous pollutants are only effectively encapsulated when the POSS cage size exceeds T₁₀. This work provides a framework for designing optimized POSS materials for specific separation applications, facilitating the efficient selection of structures for targeted gas and liquid capture.