Degradable quaternary ammonium salt-modified rice straw cellulose/chitosan composite aerogel for high-efficiency microplastic adsorption

Microplastic pollution poses a serious threat to aquatic ecological safety, and the development of efficient and sustainable removal materials is urgently needed. Inspired by the concept of "treating waste with waste," this study innovatively utilizes discarded rice straw (RSC) as substrate to capture or adsorb microplastics. To enhance the adsorption performance, 2,3-epoxypropyl trimethylammonium chloride (EPTMAC) was used to modify the cellulose originating from RSC, which combined with chitosan (CS) to create a novel quaternary ammonium salt-modified cellulose/chitosan composite aerogel (RSCECA). Verified by comprehensive characterization and DFT calculation, the resulting RSCECA achieves "binary synergistic" adsorption of polystyrene microplastics (PS) through electrostatic interactions, and p-π interactions, with an adsorption capacity of 389.65 mg/g, higher than chitosan aerogel (CSA) (303.19 mg/g) and cellulose-chitosan aerogel (RSCCA) (211.78 mg/g). The stability of RSCECA far exceeds that of CSA, maintaining adsorption efficiency above 80 % under different pH conditions (4-10) and temperatures (20-40 °C). It also demonstrates excellent adaptability in various salt environments, achieving PS removal rates above 82 % in river water, lake water, and tap water. After five consecutive adsorption cycles, the adsorption efficiency remains above 81 %. The adsorption process fits the pseudo-second-order kinetics well; while a theoretical maximum adsorption capacity of 729.9 mg/g is estimated according to Langmuir isotherm. Compared to previous reports, this material demonstrates excellent adsorption capacity and biodegradability. Therefore, the novel biodegradable composite aerogel developed in this work is promising for adsorption of microplastics owning to multi-functionality and synergistic effect.