Simultaneous removal of diclofenac, triclosan, and microplastics using graphene oxide-chitosan sponges

Abstract

The interconnected macroporous graphene oxide-chitosan (GO-CS) sponge endowed the ability to simultaneously remove diclofenac (DCF), triclosan (TCS), and polystyren microplastics (PS MPs). Compared to the adsorption capacity for a single pollutant, the adsorption capacity for TCS and PS MPs was slightly decreased, indicating the partial competition of adsorption sites; however, the major adsorption sites for each pollutant differed. Fourier transform infrared and X-ray photoelectron spectroscopy analyses revealed that the adsorption of the pollutants onto the GO-CS sponge was influenced by electrostatic interactions, hydrogen bonding, and π-π interactions. The GO-CS sponge effectively removed DCF, TCS, and PS MPs even in real water samples. While DCF removal decreased in effluent and river water due to elevated pH and ion competition, TCS and PS MPs removal remained stable, driven by hydrophobic and π-π interactions. Under the flow-through condition, the highest adsorption capacities for DCF (20.49 mg/g), TCF (18.15 mg/g), and PS MPs (6.43 mg/g) were observed at the lowest flow rate (1.52 mL/min). All the breakthrough curves for the adsorption of the pollutants were described well by the Clark model, indicating their favorable and multilayer adsorption. Further, the sponge maintained its morphology and adsorption capacity (> 90.4 %) after three cycles of adsorption/desorption. Additionally, the GO-CS sponge exerted no toxicity on Daphnia magna (48 h of exposure) and no growth inhibition effect on Pseudokirchneriella subcapitata (72 h of exposure). The sponge lost 54.28 % of its total weight after being buried in the soil for 35 days, verifying its biodegradability.