Porous polydopamine nanospheres with yolk shell-like structure to effectively remove methylene blue, bisphenol A, and tetracycline from wastewaters

Abstract

Nanoadsorbents have been widely utilized in wastewater treatment but still face the challenges of single-adsorption objects, difficulty of recycling, and low adsorption capacity. Wastewaters with complex contaminants urgently need recyclable nanoadsorbents with the ability to adsorb a variety of pollutants. In this work, porous PDA nanoadsorbents with yolk shell-like structures (YS-SiO₂@PDA) were successfully synthesized by acidic hydrothermal etching after coating PDA on monodisperse SiO₂ nanospheres. The resultant yolk shell-like nanospheres with high porosity and specific surface area (S_bet = 157.7 m² g⁻¹) were highly pH-dependent and rich in negative charge at pH less than 3.5 and can achieve effective adsorption of cationic dyes (methylene blue, MB), EDCs (bisphenol A, BPA), and antibiotics (tetracycline, TC) and the maximum adsorption capacity reached 365.4 mg g⁻¹, 85.5 mg g⁻¹, and 108.6 mg g⁻¹, respectively. The YS-SiO₂@PDA nanospheres can achieve removal efficiencies of 91.6%, 95.3%, and 94.1%, respectively, for the above three pollutants within 1 h and can still maintain excellent removal efficiency after five adsorption–desorption cycles using an acidic ethanol solution as the regenerating agent. YS-SiO₂@PDA nanospheres with excellent reusability can effectively adsorb a variety of pollutants through electrostatic attraction and π–π stacking due to abundant catechol, amine, and benzene ring structures on PDA and are expected to become excellent nanoadsorbents for practical water treatment.