Self-cleaning films of biopolymer polyhydroxybutyrate with different semiconductors incorporation: Development, characterization, and photocatalytic activity evaluation

Self-cleaning hydrophobic films were developed using polyhydroxybutyrate (PHB), enhanced with titanium dioxide (TiO₂), bismuth oxyiodide (BiOI), and a BiOI/α-Fe₂O₃ heterojunction. This is the first study to analyze the photoactivity of BiOI and BiOI/α-Fe₂O₃ immobilized into PHB. Alternative solvents for dissolving PHB were investigated. Additionally, formation methods such as casting in Petri dishes, as well as controlled thickness casting through non-solvent-induced phase separation (NIPS), and evaporation-induced phase separation (EIPS), were employed and compared. Despite differing morphologies, both NIPS and EIPS films exhibited similar photocatalytic activity, suggesting that only the catalyst on the external surface of the film is active. The highest pseudo first-order apparent kinetic constant (0.1468 ± 0.0015 min⁻¹ g⁻¹) was found in films with the lowest polymer and catalyst concentrations analyzed (5% $w_{\mathrm{PHB}}/w_{{\text{CHCl}}_3}$ and 3% $w_{{\mathrm{TiO}}_2}/w_{\mathrm{PHB}}$). A double-layer film preparation method was proposed to enhance photocatalytic activity, resulting in a 70% increase in the kinetic constant (0.2506 ± 0.0019 min⁻¹ g⁻¹). Double-layer composite films with BiOI and BiOI/α-Fe₂O₃ showed photocatalytic activity comparable to TiO₂ under UV–visible light. Furthermore, their photocatalytic activity under visible light was confirmed, unlike TiO₂, which exhibits a negligible kinetic constant in this wavelength range.