Biomass supported magnesium-aluminium layered double hydroxide composites as sustainable adsorbents for doxycycline removal

In this study, a novel bio-based adsorbent was synthesized via the coprecipitation method by supporting magnesium–aluminium layered double hydroxide (MgAl-LDH) on waste cinnamon bark (CB), for the efficient removal of doxycycline (Dox) from aquatic environments. Due to LDH's layered structure, anion-exchange capacity, and synergistic interaction with CB, the composites were used to enhance the adsorption efficiency for Dox. The composites were produced using two different amounts CB (5 g and 2.5 g) with MgAL-LDH and various analyses such as SEM, FT-IR, XRD and BET/N 2 were used to characterize the resulting samples. Adsorption key parameters including adsorbent dosage, solution pH, contact time, initial concentration and temperature were investigated for doxycycline. The adsorption characters for CB conformed to Langmuir isotherm (R 2 = 0.99), while Dox adsorption for LDH (R 2 = 0.95), 2.5CB@LDH (R 2 = 0.97) and 5CB@LDH (R 2 = 0.99) fitted Freundlich isotherm. The maximum adsorption capacities (q max ) of CB, LDH, 2.5CB@LDH and 5CB@LDH were obtained as 34.97 mg g −1 , 43.10 mg g −1 , 108.68 mg g −1 and 114.90 mg g −1 , respectively. The adsorption kinetic data for all adsorbents were determined to fit best (R 2 = 0.99) with the pseudo second order kinetic model indicating chemisorption process. The 5CB@LDH composite reached equilibrium the fastest in 240 min and exhibited the highest equilibrium adsorption capacity (q t = 9.2 mg g −1 ) using a minimal adsorbent dosage of 0.1 g. Additionally, Dox removal efficiency of 5CB@LDH and 2.5CB@LDH composites remained above 85 % in wide pH range. The LDH-based composites showed reusability for Dox removal, especially with the 5CB@LDH exhibiting a removal rate of 92.1 % in the first cycle, which decreased to 56.3 % by the fifth cycle. Thermodynamic studies revealed that the Dox adsorption for LDH-based composites is an endothermic process and the highest adsorption capacity of 6.87 mg g −1 was obtained with the 5CB@LDH at 50 °C. The synthesized 5CB@LDH composite exhibited highly adsorption performance for doxycycline and shows great potential for application in future wastewater treatment processes. • Biowaste cinnamon bark was evaluated as a sustainable and renewable adsorbent for doxycycline removal. • MgAl-LDH decorated cinnamon bark composites were successfully synthesized via the coprecipitation method. • The highest maximum adsorption capacity of 114,90 mg g-1 was achieved with 5CB@LDH adsorbent. • The 5CB@LDH composite reached equilibrium the fastest in 240 min with a minimal adsorbent dosage of 0.1 g.