Design of functional biocarbons for selective adsorption of 5-hydroxymethylfurfural from aqueous solutions

Abstract

A series of amino-functional biocarbons were synthesized via one-step and two-step, hydrothermal protocols from cellulose and characterized for application to adsorptive separation of 5-hydroxymethylfurfural (HMF), levulinic acid (LA), fructose (Fru) and formic acid (FA) from aqueous solutions. The additive tris(hydroxymethyl)aminomethane was found to be an effective additive for preparing amino-functional hydrothermal biocarbons (N-HC). Adsorption of HMF in aqueous solutions onto N-HC was highest (Qm≈166 mg/g) among the prepared adsorbents. In adsorption experiments using binary solute aqueous mixtures of (HMF - Fru), (HMF - LA) and (HMF-FA) species, N-HC exhibited maximum selectivities for HMF of 2.8, 12.3 and 3.9, respectively. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulations revealed that amino groups and pyrrolic nitrogen of the biocarbons showed strong interactions with the hydroxyl group of HMF and was responsible for an apparent adsorption induction period at contact times less than one hour in which there is competition between HMF and other solutes. Biocarbons could be regenerated with ethyl acetate, whereas adsorption capacity decreased after four cycles of reuse (140 mg/g). Amino functional biocarbons prepared by a one-step protocol are simple to prepare and allow for separation and recovery of product HMF in mixed product systems.