Unwanted Humins─Promising Precursors for Ordered Mesoporous Carbons

Humins, which are intractable carbon byproducts formed during thermochemical conversion of carbohydrates, are considered to be undesirable because of their adverse effects on product yields, catalyst activity, stability, and recycling. Herein, we show that the alcohol-soluble fraction of humins can be used to directly synthesize ordered mesoporous carbons (OMCs) by the classical solvent evaporation-induced self-assembly (EISA) method without the use of aldehydes or metal ion cross-linkers. The key mechanistic feature of the self-assembly of alcohol (ethanol)-soluble humins is that ulmic acid-containing humins act to cross-link micelles according to condensation reactions occurring in humins formation. The prepared OMCs show well-defined two-dimensional (2D) hexagonal mesoporous structures having uniform pore sizes (3.5 to 4.8 nm), high surface areas (∼600 m2 g–1), and pore volumes (∼0.4 cm3 g–1). Using dyes as model pollutants, selective adsorption of OMCs for macromolecular organic pollutants was confirmed, thus the resulting OMC materials appear to have many technological applications. The method proposed for humins conversion to ordered materials may serve as a simple and green way to utilize undesirable and commonly generated humins in carbohydrate conversions, which should improve the sustainability of carbohydrate transformation schemes and broaden the scope of biomass-based or natural humic acid precursors.