β-Cyclodextrin/Graphene Oxide Multilayer Composite Membrane: A Novel Sustainable Strategy for High-Efficiency Removal of Pharmaceuticals and Personal Care Products

Abstract

The efficient removal of pharmaceuticals and personal care products (PPCPs) from aqueous solutions using conventional adsorbents is hindered by low adsorption capacity, insufficient selectivity, poor regeneration performance, and limited stability. In this study, a multilayer β-CD/GO membrane was successfully prepared via layer-by-layer coating with β-cyclodextrin (β-CD) and graphene oxide (GO). The multilayer β-CD/GO membrane combines the host–guest complexation ability of β-CD with the abundant oxygen-containing functional groups of GO to enhance the targeted removal of PPCPs (CTD, SMZ, and DCF) from aqueous solutions. The prepared multilayer β-CD/GO membrane adsorbent overcomes the separation difficulties and poor regeneration performance of powdered adsorbents, and the multilayer structure can significantly enhance structural stability and increase the number of adsorption sites. Batch adsorption experiments showed that the optimal adsorption performance of the multilayer β-CD/GO membrane for PPCPs occurred at pH 4 and in the absence of coexisting ions. With increasing pH values in the range of 4–9, the adsorption capacities of CTD, SMZ, and DCF slightly decreased to 14.37, 13.69, and 13.01 mg/g, respectively, and the adsorption capacities decreased slowly to 4.88, 3.51, and 3.26 mg/g as the coexisting ion concentrations increased from 0 to 0.20 mol/L. The adsorption mechanism of the multilayer β-CD/GO membrane for PPCPs was systematically investigated through adsorption kinetics, isotherms, and thermodynamics. The adsorption processes of CTD, SMZ, and DCF by the multilayer β-CD/GO membrane were well described by both pseudo-first-order and pseudo-second-order kinetic models (R2 > 0.984), suggesting a hybrid adsorption mechanism involving both physisorption and chemisorption. The isotherm results indicated that the adsorption of CTD by the multilayer β-CD/GO membrane followed the Langmuir model (R2 = 0.923), whereas the adsorption of SMZ and DCF was better described by the Freundlich model (R2 = 0.984–0.988). The multilayer β-CD/GO membrane exhibited high adsorption capacities for CTD, SMZ, and DCF with maximum capacities of 35.56, 43.29, and 39.49 mg/g, respectively. Thermodynamic analyses indicated that the adsorption of PPCPs was exothermic ((Formula presented.) = −86.16 to −218.49 J/mol/K) and non-spontaneous ((Formula presented.) = 9.84–11.56, 9.50–12.54, and 10.09–14.46 kJ/mol). The multilayer β-CD/GO membrane maintained a removal efficiency of over 58.45–71.73% for CTD, SMZ, and DCF after five consecutive regeneration cycles, demonstrating high reusability for practical applications. The adsorption mechanisms of the multilayer β-CD/GO membrane include electrostatic interactions, hydrogen bonding, hydrophobic interactions, and π-π EDA interactions. This study offers a promising and environmentally friendly adsorbent for the efficient removal of PPCPs from aqueous solutions.