Asymmetric Janus monolithic biocomposites via silica stratification in cellulose diacetate films for enhanced adsorption

This study presents a waste-to-interface strategy for engineering high-performance Janus monolithic adsorbents through a circular biorefinery pathway utilizing coffee and rice residues. We demonstrate that a critical loading of 20 wt.% biogenic submicron silica into a coffee-derived cellulose diacetate matrix triggers a definitive gravity-induced stratification, transforming a traditional isotropic film into a sophisticated asymmetric architecture. This Janus transition yields a superhydrophilic interface (contact angle < 5°) and significantly enhances surface porosity, effectively bypassing the diffusion barriers that typically limit homogeneous biocomposites. Methylene Blue adsorption trials reveal that this 20 wt.% threshold achieves rapid adsorption kinetics (p < 0.05) by maximizing active-site accessibility. In contrast to conventional powder adsorbents, these monolithic films enable zero-energy manual recovery, entirely eliminating the need for energy-intensive post-treatement separation. By bridging the gap between multi-feedstock valorization and anisotropic materials science, this work provides a scalable blueprint for sustainable, high-flux water remediation.