Unveiling Adsorption Mechanisms of Emerging Pharmaceutical Contaminants on Graphene Oxide Via an Integrative Experimental–theoretical Approach

This study integrates batch adsorption experiments, post-adsorption XPS, and density functional theory (DFT) modeling to elucidate the uptake mechanisms of 17β-estradiol (E2), atorvastatin (ATV), diclofenac (DCF), and metformin (MET) on commercial, partially reduced graphene oxide (GO). The material exhibited low oxygen functionality (C/O ≈ 13) and pHₚzc ≈ 4.4. A nanometric GO sheet (~33.7 Å diameter; ~1827 Å2 accessible area) containing edge carboxyls and basal epoxides was constructed with an overall −1 charge, consistent with experimental characterization. Adsorption was rapid and followed pseudo-second-order kinetics. E2 and DCF were better described by the Langmuir model, with qmax values of 157 and 68.16 mg g−1, respectively. ATV and MET followed Freundlich behavior, with KF values of 30.73 and 3.96 and R2 values of 0.991 and 0.985, respectively. The Sips model provided the best fit for DCF (R2 = 0.994; qmax = 61.25 mg g−1), whereas the D–R model adequately described MET (R2 = 0.977), yielding a mean adsorption energy of 12.32 kJ mol−1. XPS and DFT linked selectivity (ATV ≈ E2 > DCF > MET) to π–π, hydrogen-bonding, polar, and electrostatic interactions. These results identify the C/O ratio and functional-group distribution as key parameters for tailoring GO-based adsorbents.