Activation of Sibunit® carbon materials with nitrogen(II) oxide: study of physicochemical and adsorption properties of nitrogen-containing supports. Testing of the obtained adsorbents for the preparation of biocatalysts for low-temperature synthesis

Activation by etching the Sibunit® carbon material with nitrogen oxide (NO) allowed to obtain nitrogen-containing supports with a variable content of introduced nitrogen (N) from 2.3 at.% to 10.7 at.% (according to XPS data). Etching was carried out in a high-pressure reactor (from 15 to 29 bar) at elevated temperatures (180 and 230°C). The physicochemical and adsorption properties of the obtained nitrogen-containing carbon supports were studied. Thus, a study of the texture of the supports showed that with an increase in the nitrogen content, the specific surface area of the materials decreased from 470 m 2 /g to 65 m 2 /g, while the average pore diameter increased from 7.4 nm to 18.1 nm. From the analysis of the XPS spectra it followed that the introduced N atom was present in five forms: pyridine (fraction (α) of the state 0.47), pyrrole (α = 0.38), graphite N (α = 0.13), as well as in the O=N-C (α = 0.011) and C–NO 2 (α = 0.0077) groups. The obtained nitrogen-containing carbon materials were studied as adsorbents for the immobilization of the r Pichia /lip recombinant lipase. Using SAXS and SEM methods, it was shown that adsorbed lipase was capable of forming octamers and larger aggregates of complex structure (of 100 molecules). The fraction of single (non-aggregated) enzyme molecules increased (in 3.3 times) with an increase in nitrogen content (up to 11 at.%) in carbon material. Biocatalysts (BC) prepared by adsorptive immobilization of recombinant lipase r Pichia /lip were tested in the low temperature esterification n of heptanoic C 7 acid with butyl C 4 alcohol, occurring at 20±2°C in hexane. It was found that the introduction of nitrogen during a one-time post-activation of the Sibunit® with NO had a noticeable positive effect on the enzymatic activity and stability of the prepared BC. The optimal content of introduced nitrogen was about 7–10 at.%: the biocatalytic activity increased by 2–3 times (compared to the original Sibunit), and the conversion of heptanoic acid was 84% for 6 h at 20±2°C.