NOVELTY - A method (M1) of purifying oligomers, involves: a) providing an oligomer-containing solution; b) providing a carbonaceous material; and c) contacting the oligomer-containing solution with the carbonaceous material under conditions so that the carbonaceous material adsorbs at least one oligomer from the solution to purify the oligomers.    USE - For purifying oligomers from depolymerized biomass such as lignocellulosic biomass, where the oligomers are selected from lignin oligomers, hemicellulose oligomers, poly- beta -glucan fragments derived from cellulose, oligosaccharides, long chain poly- beta -glucans, glucose, cellobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, xylose, xylans, xyloglucans, mannans, mannose, galactose, rhamnose, arabinose, and/or arabinoxylans (claimed). The lignocellulosic biomass is used in the production of biofuels such as ethanol or butanol and other commodity chemicals.    ADVANTAGE - The improved carbon-based materials for adsorbing oligosaccharides during depolymerization, such as hydrolysis, of lignocellulose have an increased affinity and capacity for both long chain and short chain oligosaccharides, and functions at acidic pH values.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a method (M2) of isolating at least one monosaccharide from an oligomer-adsorbed carbonaceous material, involving: providing an oligomer-adsorbed carbonaceous material, where the oligomers adsorbed on the carbonaceous material are polysaccharides; contacting the oligomer-adsorbed carbonaceous material with an acid to hydrolyze at least a portion of the polysaccharides into monosaccharides; and isolating at least one of the monosaccharides produced in above step;    (2) a method (M3) of separating a mixture of oligomers, involving providing a mixture of oligomers, where the mixture comprises 5C oligomers and 6C oligomers; providing a mesoporous carbon material (MCM); and contacting the MCM with the mixture of oligomers under conditions so that the MCM adsorbs at least one 6C oligomer to separate the mixture of the oligomers; and    (3) an acid-functionalized mesoporous carbon material (MCM) comprising a phosphonic acid.