Dual-layer coatings combining biomimetic surface with chlorophyll/Fe modified water chestnut-shell biochar for antibacterial and protective applications

The rise of bacterial infections and biofilm-associated issues has increased the demand for multifunctional antibacterial coatings. In this study, we developed a biochar-based material that combines photothermal and photodynamic antibacterial properties. Biochar derived from water chestnut shells (WCSB) exhibits inherent photothermal behavior. After surface modification with a chlorophyll/Fe (Chl/Fe) complex, it also gains the ability to generate reactive oxygen species under 660 nm light. The resulting WCSB@Chl/Fe shows strong singlet oxygen and hydroxyl radical production and achieves a photothermal conversion efficiency of 45 % under 808 nm irradiation. The multifunctional WCSB@Chl/Fe was incorporated into a lotus-leaf-inspired polydimethylsiloxane (PDMS) bilayer coating via spray-coating techniques. The micro-nano surface patterning enhanced hydrophobicity and reduced bacterial adhesion, while the combined photothermal and photodynamic effects led to a 6-log reduction in S. aureus and E. coli populations after light activation. In addition to its antimicrobial efficacy, the coating also demonstrated improved corrosion resistance when applied to metal substrates. These findings highlight the potential of WCSB@Chl/Fe-based coatings as robust and sustainable solutions for biomedical devices and public health surfaces requiring both antibacterial protection and structural durability.