Adsorption of diclofenac sodium from aqueous solutions on commercial activated carbons

The research presented in this paper aimed to evaluate the possibility of using commercial activated carbons currently used in water treatment plants (WG-12, ROW 08 Supra, F-300) to remove diclofenac sodium, a drug belonging to the group of non-steroidal anti-inflammatory drugs. The kinetics and statics of diclofenac adsorption from solutions of different pH and temperature were studied. The results were described by kinetics equations: pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion model. The highest correlation coefficients were obtained for Elovich (R-2 0.9937 - 0.9978) and pseudo-second-order models (R-2 0.9885 - 0.9935). The highest adsorption rate was observed for the activated carbon F-300 (k(2) = 0.0147 h(-1)), whereas its lowest values were found for ROW 08 Supra (k(2) = 0.0088 h(-1)). Adsorption statics was analyzed based on solutions with a concentration of 159-1272 mg/L, pH 6, 8, and 10, and temperatures of 20 degrees C, 30 degrees C, and 40 degrees C. Examinations of isotherms of adsorption on activated carbons WG-12, ROW 08 Supra, and F-300 revealed that the lower pH and the higher temperature in the analyzed range, the higher adsorption of the compound tested. The highest adsorption capacities q(m) were obtained after adsorption from the solution with pH = 6 and were 107.91 mg/g for F-300, 90.41 mg/g for ROW 08, and 88.97 mg/g for WG-12. The adsorption from the solution with pH 10 was much lower: 91.30 mg/g for F-300, 70.79 mg/g for ROW 08, and 58.54 mg/g for WG-12. Increasing the solution temperature from 293 K to 313 K caused an increase in the monolayer capacity from 88.97 to 115.29 mg/g for WG-12 carbon, from 90.41 to 145.45 mg/g for ROW 08 and from 107.91 to 147.88 mg/g for F-300 coal. Diclofenac sodium was best adsorbed on the activated carbon F-300, whereas the poorest adsorption was found for WG-12. The effect of chemical surface structure on the effectiveness of diclofenac sodium adsorption was also observed. The adsorption of sodium diclofenac results from the net force of electrostatic repulsion and attraction forces and hydrogen bonds (H-bonds) and electron donor-acceptor (p-p EDA) interactions. Based on the Langmuir R-L and Freundlich 1/n isothermal coefficients, it can be stated that diclofenac sodium adsorption is beneficial for all activated carbons. Among the models used (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) the study results are best described by Langmuir and Freundlich models.