Mechanistic aspects of nitrogen-heterocyclic compound adsorption on bamboo charcoal.

Adsorption of three nitrogen-heterocyclic compounds (NHCs), pyridine, indole, and quinoline, on a new porous carbonaceous adsorbent, bamboo charcoal (BC), is investigated. Different structures and surface properties of BC are created by HNO 3 and NaOH treatment as well as by microwave (MW) radiation. HNO 3 treatment decreases surface area, micropore volume, and surface hydrophobicity, whereas NaOH treatment increases surface area and micropore volume. MW treatment dramatically increases hydrophobicity and fraction of aromatic structure. Adsorption isotherms of NHCs are nonlinear and better fitted by Freundlich model (FM) compared with Langmuir model (LM) and Polanyi–Manes model (PMM). The maximum adsorption capacities for pyridine, indole, and quinoline reach 42.92, 93.24, and 91.74   mg   g −1 , respectively, at an initial concentration of 200   mg   L −1 . Surface area, hydrophobicicty, and electrostatic and π – π electron-donor–acceptor (EDA) interactions are accountable for NHC adsorption. A model relating NHC adsorption (log K ) and adsorbent–adsorbate physicochemical properties is developed to measure the relative contribution of these interactions giving the sequence of surface area   >   hydrophobic interaction   >   electrostatic interaction   >   π – π EDA interaction.