Title : Eco-friendly doxycycline adsorption using a dual-waste-derived cellulose/graphene oxide-iron oxide-nickel hydroxide nanocomposite: Kinetic, isotherm, and thermodynamic evaluation
Abstract:
To combine antibiotic remediation with waste valorization, a magnetically recoverable cellulose/graphene oxide–Fe?O?–Ni(OH)? nanocomposite (WCC/GO–Fe?O?–Ni(OH)?) was developed from discarded cloth and spent-battery graphite. The study investigated its structural properties, adsorption efficiency, and reusability. Comprehensive characterization using TEM/HRTEM–SAED, SEM–EDX, XRD, and FTIR verified a heterogeneous, hydroxyl-rich WCC/GO matrix incorporating crystalline Fe?O? and Ni(OH)? nanodomains. The composite exhibited an average particle size of 28.17 nm, while XRD analysis revealed coherent crystallite domains of approximately 27 nm. LC–MS/MS analysis confirmed rapid doxycycline (DOX) removal, achieving 94.92% within 5 min, equivalent to 99.33% of the removal attained after 60 min. Independent one-factor experiments demonstrated 98.06% removal at an adsorbent dosage of 0.25 g L?¹, whereas the maximum pH-dependent removal of 91.78% occurred at pH 5.5, with a pH?zc of approximately 3.6. Nonlinear kinetic modeling identified the pseudo-second-order model as the best-fitting model, with q? = 1.9068 mg g?¹, RMSE = 0.01183 mg g?¹, and AICc = −83.03. Equilibrium analysis identified the Langmuir model as the most physically reasonable common endpoint isotherm over the temperature range of 25–50 °C. At 25 °C, the calculated maximum adsorption capacity was 41.96 mg g?¹, closely agreeing with the experimental value of 41.04 mg g?¹. Thermodynamic analysis suggested favorable adsorption, with ΔG??? values ranging from −7.85 to −5.74 kJ mol?¹, ΔH??? of −34.11 kJ mol?¹, and ΔS??? of −88.55 J mol?¹ K?¹. The material maintained 90.00% removal efficiency after nine cycles, demonstrating its reusability. Overall, this dual-waste-derived nanocomposite shows promise as a rapid and reusable adsorbent for DOX remediation, potentially involving electrostatic attraction, hydrogen bonding, π–π interactions, metal coordination, and intraparticle redistribution.
Keywords: Doxycycline; graphene oxide; cellulose; magnetic adsorption; nickel hydroxide; adsorption thermodynamics; LC–MS/MS
