Propranolol adsorption onto multiwalled carbon nanotubes modified by green synthesis: pH, kinetic, and equilibrium studies

This research investigated the adsorption of propranolol (PROP) by functionalized green carbon nanotubes (MWCNT-B), assessing the influence of pH, in addition to kinetic, equilibrium, and thermodynamic studies and reuse of the material. For this purpose, speciation of PROP and the point of zero charge (pH_PZC) of MWCNT-B were performed, indicating a pKa of 9.67 and pH_PZC of 3.31. The adsorption tests at different pH values revealed that in the range of pH 3 to 9, there is no significant variation in PROP uptake, despite this, at pH 11, the removal decreases. Regarding PROP adsorption, the equilibrium time ranged from 30 to 90 min, and the PFO model best represented the kinetic data. The Langmuir model was more predictive in representing isotherms (R² > 0.95), and the adsorption process was spontaneous and favorable (ΔG < - 20 kJ mol^-1) and indicated exothermic behavior (ΔH = - 33 kJ mol^-1) for PROP removal. In addition, the material showed satisfactory thermal regeneration results and can be reused for four cycles. The results suggest that MWCNT-B is an attractive adsorbent and exhibits effective removal of propranolol from aqueous matrices.