Production of phosphorus-containing activated carbons from coffee husk and application in adsorption processes

Abstract

The present research investigates the production of activated carbons from natural resources using methods of chemical activation and the use of these activated carbons for the adsorption of organic molecules in aqueous media. The lignocellulosic precursor used for the activated carbon preparation was coffee husk, which is an agricultural waste generated during coffee production in many regions of Brazil. The activation was achieved by the reaction between phosphoric acid (H3PO4) and the raw coffee husk. The materials were characterized by thermogravimetry, textural analysis, infrared spectroscopy, solidstate nuclear magnetic resonance and X-ray diffraction. From the analysis of the produced activated carbons, it was found that the H3PO4 : coffee husk weight ratio of 3:1 results in a phosphorus-containing material with a well-developed porosity; larger amounts of H3PO4 resulted in negligible increase in the specific surface area. The sample prepared with the 3:1 weight ratio was applied in liquid phase adsorption experiments, with studies of the kinetics of methlylene blue adsorption and the application of Langmuir and Freundlich theoretical models to the equilibrium adsorption isotherms.