Removal of metoprolol by adsorption onto activated carbon prepared from a food by-product

Two activated carbons were prepared by chemical impregnation of bean peels using phosphoric and sulphuric acids, respectively, and tested for the removal of metoprolol from water. Retention capacities of 107.5 and 90 mg/g were achieved for phosphoric and sulphuric acids activated carbons, respectively. These values were by far much higher than 2.98 mg/g, the retention capacity corresponding to raw been peels. The phosphoric acid activated carbon showed the best retention of metoprolol and therefore it was considered to investigate the effects of operating parameters like the adsorbent dosage, the initial concentration, the solution pH, the ionic strength and the temperature. The adsorbent was characterized by pH(pzc), thermogravimetric analyses, infrared spectrum and Brunauer-Emmett-Teller analysis. The results of batch metoprolol adsorption onto phosphoric acid activated carbon showed that the optimal solid-liquid ratio was 2 g/L for which the maximum adsorption capacity was 107.5 mg of metoprolol/g of activated carbon, corresponding to a percentage retention efficiency of 98%. The kinetic data showed relatively fast metoprolol sorption onto the phosphoric acid activated carbon, reaching equilibrium in 5 min with initial concentrations lower than 150 mg/L. The results indicated that the adsorption kinetics was well described by the pseudo-second-order model. The adsorption data were best fitted by Langmuir adsorption isotherm model and were also used to calculate thermodynamic parameters like Gibbs free energy, enthalpy and entropy variations.