Hovenia dulcis crosslinked graphene oxide nanocomposite for simultaneous drug adsorption in synthetic and human urine: Standard adsorption studies, statistical physics approach, selectivity, and DFT atomic level insights

Pharmaceutical residues, particularly urinary analgesics and their metabolites, are emerging contaminants that pose potential environmental and health risks. This study reports the synthesis of a novel nanocomposite (GOHD) obtained by citric acid crosslinking of H. dulcis with PCT, and its application for adsorbing PhP and PCT from fresh synthetic and real human urine. The material was characterized using various characterization techniques, indicating the formation of a heterogeneous, mesoporous structure with the presence of different functional groups. Adsorption studies revealed that GOHD reached a maximum capacity of 204.82 mg g −1 at the lowest dosage (0.125 g L −1 ). PhP uptake was favored at pH 5.0, and the general-order model well described the kinetic data. Equilibrium analysis revealed that the Freundlich isotherm effectively described the data. At the same time, the M5 statistical physics model provided a deeper interpretation, indicating the presence of two to three adsorption layers with a parallel molecular arrangement ( n < 0.5). Thermodynamic parameters confirmed that the process was spontaneous, exothermic, and governed by weak interactions ( Δ G < 0, Δ H = −12.74 kJ mol −1 ). This is corroborated by the adsorption energy values, which confirm the occurrence of physisorption. In the binary system, GOHD showed high selectivity for PhP, increasing its removal to 80.98% ( q e = 100.73 mg g −1 ), while PCT removal decreased to 11.86% ( q e = 3.75 mg g −1 ), evidencing competitive adsorption. In human urine, PhP removal reached 14.29% ( q e = 29.39 mg g −1 ), whereas PCT adsorption was not observed. The adsorption energy obtained by DFT ( E ads = 49.3 kJ mol −1 ) corroborates the statistical physics energies for the first adsorption layer Δε₁ = 8.27–13.73 kJ mol −1 ), confirming stable, surface-confined adsorption dominated by strong physical interactions. DFT calculations revealed that PhP exhibits higher chemical softness (η = 1.64 eV), electrophilicity (ω = 4.36 eV), and a lower HOMO–LUMO gap (3.27 eV) than PCT, explaining its stronger affinity and preferential adsorption on GOHD. These findings demonstrate that GOHD is a promising, sustainable adsorbent for the adsorption of PhP. • Hovenia dulcis croslinked graphene oxide for drug adsorption in synthetic urine; • A maximum adsorption capacity of 204.82 mg g −1 for phenazopyridine (PhP); • The nanocomposite (GOHD) was selective for phenazopyridine.