Adsorption of ibuprofen from wastewater on NaAlg/MnSx adsorbents: Central composite design optimisation, equilibrium isotherms, kinetics, and thermodynamics

The presence of pharmaceuticals in water systems poses a threat to both aquatic and terrestrial life worldwide. Ibuprofen is a common emerging contaminant that has been consistently detected in various water systems, and its actual effects on the environment and public health are not well understood. The study addresses the removal of ibuprofen, an emerging pharmaceutical contaminant, from water systems using sodium alginate/manganese sulphide (NaAlg/MnS x ) bio-nanocomposite hydrogels. The adsorbents were synthesised and characterised through XRD, SEM, TEM, and zeta potential analyses. Batch adsorption experiments, optimised by response surface methodology (RSM), revealed high adsorption capacities of 77.08 and 103.76 mg/g for NaAlg/MnS_0.1g and NaAlg/MnS_0.2g hydrogel, respectively, under optimal conditions. Adsorption kinetics followed pseudo-second-order behaviour, with high correlation coefficients (R² > 0.98), and equilibrium data fitted best to the Sips and Langmuir isotherm models, indicating a combination of monolayer and heterogeneous adsorption. Thermodynamic studies revealed that the process was endothermic and spontaneous, with enhanced adsorption efficiency at higher temperatures. Both hydrogels achieved removal efficiencies greater than 87 % of ibuprofen from real wastewater samples, demonstrating their efficacy in complex matrices. Reusability assessments revealed that adsorbent efficiency exceeded 60 % after three cycles when regenerated with 0.1 M NaOH. The primary adsorption mechanisms involved hydrogen bonding, hydrophobic interactions, and electrostatic attraction. Comparative analysis highlighted the superior performance of NaAlg/MnS_0.2g relative to many hydrogel adsorbents reported in the literature. These findings demonstrate the high potential of NaAlg/MnS x bio-nanocomposite hydrogels for sustainable and efficient removal of pharmaceutical contaminants from water bodies.