Synthesis of compressible and reusable chitin/O-gCN sponges for efficient removal of phthalate esters in water environments

Phthalate esters (PAEs) widely used as plasticizers in industrial products are a major threat to human health and water ecological security. In this work, chitin-based sponges doped with oxygen-modified graphitic carbon nitride (O-gCN) (ChCN) demonstrated adsorption-photocatalytic synergistic ability for the efficient removal of two typical PAEs, diethyl phthalate (DEP) and dibutyl phthalate (DBP). The addition of O-gCN increased the sponge mechanical strength from 0.629 to 1.39 MPa, enabling materials with interconnected pores, excellent compressibility, and mechanical durability. The saturated adsorption capacities of DEP and DBP reached 37.41-42.93 mg g-1 for ChCN sponges, wherein the driving forces were hydrophobic interactions, hydrogen bonding, and pi-pi interactions. Notably, O-gCN significantly improved PAE removal by simultaneously enhancing the adsorption and photocatalytic effect of ChCN sponges due to its high catalytic activity, leading to 100% removal of DEP and DBP within 2 h. The degradation pathway of DEP was confirmed to be de-esterification. Finally, filtration columns assembled with ChCN sponges showed 87.8-90.9% PAE removal from water under natural light, and the removal efficiency did not significantly change even after three reuses, indicating stable removal performance and good reusability with potential for practical applications. The sponges also possessed good biocompatibility and biodegradability, as demonstrated through algal toxicity experiments and biodegra-dation tests. Therefore, this research presents a convenient method for preparation of compressible and reusable sponge materials from renewable biomass for efficient PAE removal from aqueous environments and has revealed the underlying mechanisms of such removal by the adsorption-photocatalysis synergistic effect.