Engineering microporous humins derived from glucosamine for CO2 adsorption

In comparison to the thriving lignocellulosic biomass, the research on humins derived from marine biomass has not been thoroughly investigated. By choosing glucosamine (GlcN) as a model, the transformation process from raw material to solution intermediates until humins solid was demonstrated for the first time. The key intermediates were successfully captured and identified to be pyrazine dimers, such as 1-[5-(2,3,4-Trihydroxybutyl)-2-pyrazinyl]-1,2,3,4-butanetetrol and 1-[5-(3,4-dihydroxy-1-buten-1-yl)-2-pyrazinyl]-1,2,3,4-butanetetrol, which are formed through ring-opening of GlcN. By means of HPLC-MS/MS, FT-IR, XPS, elemental analyses and SEM characterizations, three elementary reactions were revealed including etherification reaction of pyrazine dimers and HMF, aldol condensation of LA, and thermal oxidation. At early stage, pyrazine dimers are linked by etherification. HMF could be linked through etherification as well, with LA reacted with the CHO group of HMF by aldol condensation. At the later stage, the thermal oxidation deepens, resulting in the enhancement of C=O. Moreover, GlcN-derived humins were engineered into porous carbon materials with excellent CO₂ adsorption capacity up to 5.60 mmol/g, whereas the CO₂ uptake was well correlated with the volume of micropores below 0.82 nm.