Equilibrium, isotherm, kinetic and thermodynamic studies for removal of tetracycline antibiotics by adsorption onto hazelnut shell derived activated carbons from aqueous media

Hazelnut shell, an agricultural waste, was used to prepare activated carbons by phosphoric acid activation. Hazelnut shell derived activated carbon (HSAC) was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and N-2 adsorption/desorption isotherms, and was used as an adsorbent for the removal of three tetracycline (TC) antibiotics (tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)) from aqueous solution. Batch adsorption studies were carried out by varying the initial concentrations of TCs, pH of solution, ionic strength of solution, contact time and temperature. 20 min was required to attain equilibrium. There was no significant influence of ionic strength in a range from 0.0001 to 1 mol L-1 and pH in the range of 4-8 on the uptakes of TCs by the HSAC. The maximum adsorption capacities of the HSAC followed the sequence OTC (321.5 mg g(-1)) > CTC (313.5 mg g (-1)) > TC (302.9 mg g(-1)). The data fitted well with the pseudo-second-order kinetic and Langmuir models. The intraparticle diffusion model indicated that the adsorption of TCs on the HSAC was controlled by both intraparticle diffusion and external mass transfer. Under the test temperature and pressure, the thermodynamic constants revealed that the adsorption of TCs onto the HSAC was spontaneous and endothermic. The HSAC had relatively high potential for the removal of TCs from aqueous solution.