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

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.