Photo-switched biodegradable plastic that suppresses biodegradation under light irradiation via a g-C₃N₄...

Marine plastic pollution necessitates the development of biodegradable materials that maintain structural integrity during utilization while exhibiting rapid degradation upon disposal in marine environments. This study introduces a novel concept of photo-switchable biodegradable plastics that addresses this fundamental challenge through light-dependent biodegradation control. The approach employs photocatalytic antimicrobial activity to regulate bacterial degradation: under illumination conditions representative of typical use environments, antimicrobial photocatalysis inhibits plastic-degrading bacterial activity, whereas in dark marine environments, bacterial degradation proceeds unimpeded. The critical challenge was developing a photocatalyst that exhibits potent antimicrobial activity while avoiding degradation of the polymer matrix. Conventional photocatalysts such as TiO₂ generate highly oxidative hydroxyl radicals that simultaneously degrade both bacteria and polymers. This limitation was addressed by utilizing graphitic carbon nitride (g-C₃N₄), which demonstrates selective antimicrobial activity through alternative reactive oxygen species pathways. However, pristine g-C₃N₄ exhibits insufficient antimicrobial potency for practical applications; therefore, its performance was enhanced through thermal oxidation treatment while preserving its polymer-compatible oxidative properties. The resulting composite films comprising thermally-treated g-C₃N₄ and polycaprolactone demonstrated distinct photo-switching functionality: complete suppression of biodegradation under light irradiation, contrasted with normal degradation kinetics in dark conditions when exposed to marine bacteria (Alcanivorax xenomutans). This approach provides a viable strategy for materials that require stability during application while ensuring biodegradability in light-limited marine disposal environments.