Ultrafast selective adsorption of pretreatment inhibitors from lignocellulosic hydrolysate with metal-organic frameworks: Performance and adsorption mechanisms

In this work, four metal-organic frameworks materials (MOFs, MIL-140A, MIL-140C, MIL-101(Fe) and NH2-MIL-101(Fe) were prepared, characterized and compared for the adsorptive removal of furfural and four phenolic inhibitors. MIL-140C demonstrated the best adsorption capability among the tested MOFs. Effects of pH, ionic strength, contact time, adsorbent dosage, temperature and sugars on adsorption of inhibitors on MIL-140C were systematically investigated. Inhibitors adsorption was ultrafast within minutes and kinetic data fitted pseudosecond-order model well. The Langmuir isotherm described the adsorption process satisfactorily with maximum adsorption capacities of 222.72, 240.38, 231.48, 207.04 and 60.79 mg/g for vanillin, syringaldehyde, ferulic acid, p-coumaric acid and furfural, respectively. Thermodynamic parameters disclosed that nature of the adsorption was exothermic and spontaneous under the experimental conditions. MIL-140C demonstrated exceptional adsorption selectivity towards inhibitors even with excessive amount of xylose and glucose, as well as excellent regeneration performance after five adsorption/desorption cycles. MIL-140C also exhibited satisfactory detoxification performance after treatment of real corn stover dilute acid hydrolysate. Furthermore, analysis of underlying adsorption mechanism showed that pi-pi interaction, hydrophobic interaction and hydrogen bonding/metal-coordination (depending on solution pH) were involved in the adsorption of tested phenolic inhibitors, while the pi-pi and hydrophobic interactions contributed to the furfural adsorption. The overall results revealed that MIL-140C could hold great promise in removing phenolic and furan inhibitors from lignocellulosic hydrolysate.