Composition of Surface Groups and Adsorption Properties of Activated Carbons Derived from Different Bio-precursors

Abstract

Activated carbons (AC) are widely used in a variety of applications because of their controllable porosity and surface functionalities. In this work, AC were prepared from different hard woods through one- and two-step pyrolysis/activation for the adsorption of organic pollutants in water. Water vapor was used as the activating agent. The influence of the precursor and preparation methods on the properties of the resulting AC was evaluated through multiple techniques. Temperature-programmed oxidation (TPO) measured the reactivity toward oxygen of chars and AC, while temperature-programmed desorption coupled with mass spectrometry (TPD/MS) revealed functional groups on AC surface. Methylene blue adsorption tests evaluated the adsorption capacity of the prepared AC and the presence of mesopores. Depending on the oxidation reactivity of the char produced by pyrolysis, the resulting AC show different surface composition and adsorption performance. With the increasing char oxidation reactivity, the AC has higher degree of surface functionalization and enhanced adsorption toward methylene blue. In particular, Red Maple char is the more reactive one, followed by Birch and Ironwood. Thus, Red Maple AC prepared through the two-step process, exhibits lower activation yield, higher concentration of surface functionalities and improved methylene blue adsorption. TPO technique could predict the degree of surface functionalization and adsorption properties of the final AC.