Doxycycline Adsorptive Interaction with Mesoporous MCM-41: Kinetic and Isotherm Modelling with Thermodynamics

Antibiotics are bio-accumulating and persistent. its inappropriate disposal can affect human health and aquatic fauna. Development of antimicrobial resistance has been announced as one of the top ten threats to global health in 2019. In this study, Doxycycline adsorption on to MCM-41 (not reported earlier) was studied. Adsorbent dose (m), Doxycycline solution pH, adsorption time (t) and temperature (T) were considered as process parameters, and %Doxycycline removal and adsorption capacity were measured as responses of the adsorption. Parameters (m, pH and t) interaction, modelling and optimization for %Doxycycline removal and adsorption capacity was performed using Box Behnken Design. Based on this, a suitable model equation and adsorption mechanism was suggested. At optimized parameters, kinetics and adsorption rate controlling mechanism was studied. Further, various isotherm models (Freundlich, Langmuir and Redlich-Peterson) were studied to represent the adsorption equilibrium experimental data. the optimum process parameters were found to be pH = 7.3, m = 0.02 g/L and t = 20 min. At optimized parameters, very high %Doxycycline removal of 99% with 2425 mg/g adsorption capacity was observed (max 835.5 mg/g adsorption capacity for Doxycycline is reported in literature). Thermodynamics study revealed enthalpy (ΔH°) = 23.02 kJ/mol confirming DCL physisorption on MCM-41.