Modulating local oxygen microenvironments in floatable chitosan hydrogels for enhanced TiO2 photocatalytic degradation of dyes and antibiotics.

Polymer gas-barrier matrices overcome mass-transfer limitations in heterogeneous photocatalysis under hypoxic conditions. A floatable chitosan/TiO2-APTES (CSTA) composite hydrogel containing oxygen clusters was synthesized via alkali-induced precipitation and in situ oxygen generation. The crosslinking and dense hydrogen-bonding network of chitosan enabled concurrent generation and physical encapsulation of nascent oxygen at the solid-liquid interface. The resulting CSTA composite formed an internal oxygen reservoir that reduced the dependence of the reactive oxygen species (ROS) cascade on bulk dissolved oxygen (DO) fluctuations. The chitosan matrix sustained interfacial near-field oxygen delivery for over 12 days, maintaining an oxidative microenvironment under hypoxic conditions (<0.5 mg/L). This localized oxygenation functioned as an electron scavenger, suppressing charge-carrier recombination and yielding a 4.15-fold kinetic increase in pollutant degradation. The CSTA hydrogel retained 74-87% photocatalytic degradation efficiency over five consecutive cycles during the degradation of recalcitrant dyes and antibiotics. This design provides an efficient microscale gas-management strategy for continuous advanced oxidation processes in hypoxic conditions.