Generalized two-dimensional correlation infrared spectroscopy to reveal mechanisms of CO2 capture in nitrogen enriched biochar

In order to reveal mechanisms of CO2 adsorption-desorption on the nitrogen enriched biochar, the in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) was used to monitor the interfacial reaction between CO2 and nitrogen enriched biochar, and all spectral data sets of in situ DRIFTS was parsed by two-dimensional (2D) perturbation correlation. The results show that when the adsorption temperature is between 30 and 60 °C, the hydroxyl, primary amide, amines, azo compound NN, secondary amide groups and aliphatic CN/CO are all effective active sites to adsorb CO2; while the temperature rises to 120 °C, the CO2 adsorption capacity of secondary amide group shows a downward trend. After the adsorption of CO2, these active sites are mainly converted to CO groups (such as NCOOH, NCOO− and aldehyde groups), nitrogen atom-containing heterocyclic groups (pyridine-like groups), and NO groups (nitrate). Moreover, at 200 °C, the majority of hydroxyl and secondary amide groups as well as part of primary amide, amines and azo compound NN can be regenerated, while the aliphatic CN/CO groups are difficult to be regenerated.