Alginate/Graphite Oxide Hydrogel Beads as a Sustainable Solution for Diclofenac Elimination in Aqueous Systems

Diclofenac (DCF) is a widespread pharmaceutical pollutant in aquatic environments requiring efficient treatment strategies. This study evaluated alginate/graphite oxide (Alg/GrO) hydrogel beads as a sustainable solution for removing DCF from aqueous systems. Graphite oxide, synthesized via a modified Hummers method, was incorporated into an alginate matrix. One-Factor-at-a-Time (OFAT) experiments were conducted to screen operational parameters, establishing that DCF adsorption was favored at pH 6.0, 200 rpm stirring speed, and 180 min contact time. Holding these parameters constant, the effects of the initial DCF concentration and Alg/GrO dosage were modeled and optimized using a Central Composite Design (CCD) combined with Response Surface Methodology (RSM). Under optimal conditions (34.2 mg L−1 DCF and 2.55 g L−1 Alg/GrO containing 2 wt.% GrO), removal efficiencies exceeded 90%. Adsorption kinetics followed a pseudo-first-order model (R2 = 0.973), typical of physical adsorption, indicating that the adsorption rate depends on the number of available adsorption sites on the material surface. Equilibrium data best fit the Sips isotherm (R2 = 0.999), yielding a maximum capacity of 91.50 mg g−1 at 20 °C. Thermodynamic parameters confirmed a spontaneous (ΔG0 < 0) and exothermic adsorption process (ΔH0 = −17.05 kJ mol−1). Reusability tests demonstrated consistent performance across consecutive cycles. Overall, Alg/GrO hydrogel beads constitute an effective, sustainable, and reusable alternative for DCF removal.