Acid-Functionalized Nanoparticles for Pretreatment of Wheat Straw

Perfluoroalkylsulfonic (PFS) and alkylsulfonic (AS) acid-functionalized magnetic nanoparticles were synthesized, characterized, and then evaluated for their ability to hydrolyze hemicelluloses. The magnetic core was made of cobalt spinel ferrite and was coated with silica to protect it from oxidation. The silanol groups allowed surface chemical modification of the nanoparticles with the PFS and AS acid functionalities. Thermogravimetric analysis gave a total organic load of 12.6% and 32.5% (w/w) for AS and PFS nanoparticles, respectively. The surface sulfur content was calculated from XPS analysis as 1.37% and 1.93% for PFS and AS nanoparticles, respectively. Wheat straw samples were treated with the acid-functionalized nanoparticles at two different conditions: 80 ̊C for 24 h and 160 ̊C for 2 h. These experiments aimed to hydrolyze wheat straw hemicelluloses to soluble oligosaccharides. PFS nanoparticles solubilized significantly higher amounts of hemicelluloses (24.0% ± 1.1%) than their alkyl-sulfonic counterparts (9.1% ± 1.7%) at 80 ̊C, whereas the hydrothermolysis control solubilized 7.7% ± 0.8% of the original hemicelluloses in the sample. At 160 ̊C, PFS and AS nanoparticles gave significantly higher amounts of oligosaccharides (46.3% ± 0.4% and 45% ± 1.2%, respectively) than the control (35.0% ± 1.8%). The hemicelluloses conversion at 160 ̊C reached 66.3% ± 0.9% using PFS nanoparticles and 61.0% ± 1.2% using AS nanoparticles compared with the control experiment, which solubilized 50.9% ± 1.7% of hemicelluloses in the biomass.