Enhanced surface accessibility and adsorption of Bacillus subtilis and Candida albicans on porous hierarchically ordered bio-based carbon materials

This work explores how pore structure and surface properties of bio-based carbon materials control the adsorption and immobilization of Bacillus subtilis and Candida albicans from aqueous suspension. Three carbons derived from apple wood: charcoal (CW), activated carbon (ACW), and reactivated carbon (RACW) - were systematically characterized by nitrogen adsorption, SEM, and FTIR spectroscopy. RACW exhibited the highest surface area (1750 m 2 g -1 ) and a hierarchical pore structure, resulting in microbial adsorption capacities up to three times greater than ACW, with a maximum of 4.65×10 8 CFU/g for C. albicans . Kinetic studies demonstrated rapid attainment of equilibrium (within 120 min), with the highest rates and capacities observed for RACW. SEM revealed that both bacteria and fungi were predominantly immobilized on the external surfaces and at the openings of large surface features, indicating that surface accessibility rather than microporosity governs adsorption efficiency. FTIR analysis confirmed the presence of characteristic biomolecular signatures after adsorption, consistent with non-covalent physical attachment of the microorganisms to the carbon surfaces. C. albicans consistently showed greater adsorption than B. subtilis on all carbons, reflecting differences in cell size and surface chemistry. These findings highlight the critical role of engineered porosity and external surface morphology in developing efficient carbon-based antimicrobial adsorbents, with practical implications for water purification and biomedical applications.