Sodium-activated bentonite as a dual-function clay platform for amikacin adsorption, pH-responsive release, and antibacterial activity

Antibiotic contamination of aquatic environments is a recognized driver of antimicrobial resistance, and amikacin — a clinically important aminoglycoside — poses dual concerns: environmental persistence and systemic toxicity that limits its clinical use, underscoring the need for materials capable of both sequestering it from wastewater and delivering it locally in a controlled manner. This study aimed to evaluate sodium-activated bentonite (SB), prepared from locally sourced Iraqi bentonite, as a dual-function platform for amikacin adsorption, pH-responsive release, and antibacterial activity. An amikacin-loaded composite (AMK-SB) was prepared and characterized by FESEM-EDS, XRD, FTIR, TGA, and nitrogen adsorption–desorption analysis. Batch adsorption experiments investigated the effects of adsorbent dose, contact time, pH, and temperature, followed by kinetic, isotherm, and thermodynamic modeling. pH-responsive release was evaluated at pH 3.0–9.0, and Korsmeyer–Peppas fitting was applied only to release profiles that provided sufficient data within the valid early-release range. Antibacterial activity, matrix effects in simulated hospital effluent, and regeneration over four cycles were also assessed. Sodium activation increased BET surface area from 16.9 to 27.7 m ² g⁻ ¹ and pore volume from 0.0623 to 0.0872 cm ³ g⁻ ¹ ; amikacin loading (∼6.7 wt%) partially reduced these values, consistent with drug deposition in interlayer spaces and pores. Adsorption followed pseudo-second-order kinetics (R ² = 0.9983–0.9997) and the Langmuir isotherm (R ² = 0.9737–0.9916), with qmax of 63.29–81.55 mg g⁻ ¹ over 25–60°C. The process was spontaneous and exothermic (ΔG° = -26.99 to -28.79 kJ mol⁻ ¹ ; ΔH° = -11.65 kJ mol⁻ ¹ ). Under the selected operating conditions, amikacin removal remained high, generally within the ∼88–90% range depending on the experimental endpoint. Antibacterial activity was retained against S. aureus, E. coli , and P. aeruginosa (inhibition zones: 30, 29, and 26 mm). Release was pH-dependent, approaching 100% at pH 3.0 but only ∼38% at pH 9.0 after 180 min. The material retained ∼85% adsorption capacity after four regeneration cycles. These findings establish AMK-SB as a low-cost, recyclable clay platform integrating antibiotic adsorption from aqueous media with pH-responsive release and preserved antibacterial activity, offering potential applications in both environmental remediation and localized antimicrobial delivery at acidic infection sites.