Selective removal of acetaminophen in urine with activated carbons from rice (Oryza sativa) and coffee (Coffea arabica) husk: Effect of activating agent, activation temperature and analysis of physical-chemical interactions

Abstract

In this work, activated carbons prepared from rice husk (RH) and coffee husk (CH), using NaOH or ZnCl2 as activating agents, were evaluated for the removal of acetaminophen (ACE) in both distilled water and synthetic urine. The activated carbon prepared from RH and activated with NaOH showed the best results in both matrices, which was attributed to the high external surface area and the microporosity developed in the activation process. The influence of the activation temperature (500–800 °C) in the preparation of the activated carbons from RH was also tested. As temperature raised to 800 °C, surface and microporous areas further increased to 1004 and 869 m2 g−1, respectively. Consequently, the material obtained at 800 °C (RH-NaOH-800) allowed a better ACE removal, which showed to be more efficient compared with a commercial activated carbon. The developed material did not experience a detrimental effect by the urine components (more than 95% of ACE was removed in both cases). Furthermore, the adsorption process showed a well-fit to the Redlich-Peterson isotherm. β values of approximately 1, indicated that the process resembles Langmuir, and suggests a homogeneous adsorption process. Kinetics analysis showed a better fit for the pseudo-second-order model, while the intra-particle diffusion model showed that the adsorption of ACE occurs both at the surface and within the material pores. According to thermodynamic results, the process occurred by physisorption in an endothermic and spontaneous way. Also, the adsorption mechanism showed that ACE is adsorbed on RH-NaOH-800 by hydrogen bonds and π-π interactions.