2D Solid-State HETCOR 1H-13C NMR Experiments with Variable Cross Polarization Times as a Tool for a Better Understanding of the Chemistry of Cellulose-Based Pyrochars—A Tutorial

Abstract

The chemistry and nature of biochars are still far from being well understood. In the present work, solid-state 2D HETCOR 1H-13C NMR spectroscopy is introduced for an improved characterization of the aromatic network in biochars. To that end, a pyrochar obtained from the pyrolysis of cellulose at 350 °C for 1 h was used as an example. Variation of the contact time during cross polarization from 50 µs, to 200 µs and 1000 µs gave information about the protonation degree of the different C groups and their interactions. We demonstrated that carbohydrates did not survive the used pyrolysis conditions. Therefore, O-alkyl C was assigned to ethers. Phenols were not identified to a higher extent suggesting that furan and benzofuran-type units determine the O-functionality of the aromatic domains. The latter are directly connected to alkyl chains. Those features are expected to affect chemical but also physical properties of the biochar. Based on our results, we developed a new concept describing the nature of the aromatic network in the studied cellulose-based pyrochars. The latter contrasts common views about the chemical nature of biochar, possibly because pyrolysis temperatures > 350 °C are required for achieving advanced condensation of the aromatic domains.

Kraft Lignin Periodate Oxidation for Biobased Wood Panel Resins

“…To gain insights into the oxidative transformations of lignin, a 2D HETCOR NMR experiment was performed, as shown in Figure a,b. Further, the corresponding peak assignments are carried out by the following literature. , According to the 2D HETCOR, the peaks representing the aromatic carbon (δC/δH 110–122/6.3–6.9 ppm) are relatively reduced in intensity in the case of OL, which could be due to the low availability of protons for the cross-polarization of aromatic carbons . During the periodate oxidation, hydroxyl functional groups in the ligninare oxidized into carbonyl group.…”

Response of Water-Biochar Interactions to Physical and Biochemical Aging

“…A ramped 1 H-pulse from 100 to 50% of the full power was used during a contact time of 1 ms to reduce Hartmann-Hahn mismatches and 500 ms recycle delay between scans. A contact time of 1 ms is frequently used to obtain an efficient coupling between protons and 13 C atoms in environmental samples rich in aromatic rings, such as biochar, as a compromise for a good polarization for the different organic components (Courtier-Murias et al, 2014;Knicker et al, 2021). The obtained spectra were divided in six regions contributing to the total measured 13 C intensity and corresponding to the carbon atoms in the following functional groups: alkyl (0-45 ppm), N-alkyl/mehoxyl (45-60 ppm), O-alkyl (60-90 ppm), anomeric (90-110 ppm), aryl (110-140 ppm), heteroaromatic (140-160 ppm) and carboyl/amide (160-220 ppm) (Knicker, 2011a;Ludemann and Nimz, 1973).…”

The Thermo-Oxidative Behavior of Cotton Coated with an Intumescent Flame Retardant Glycine-Derived Polyamidoamine: A Multi-Technique Study

“…As shown in Figure 8, a comparison of the spectra recorded on COT and COT/M-GLY after the thermal treatments clearly indicated that the transformation of cotton by thermo-oxidative processes occurs at lower temperature for COT/M-GLY than for COT, in agreement with the above reported analyses, as well as with results reported in the literature for cotton treated with different flame retardants [19,20]. In fact, the spectrum of COT heated at 300 • C showed quite strong and sharp signals between 60 and 110 ppm arising from cellulose [19,21], the main component of cotton, together with broad peaks from aliphatic (0-60 ppm), aromatic and furanic (110-160 ppm), carboxyl (~167 ppm), and carbonyl (~198 and 205 ppm) groups in materials arising from the transformation of cellulose [22][23][24][25][26][27][28][29][30][31]. Indeed, upon heating in air, cellulose undergoes decomposition of the glycosidic units, dehydration, decarboxylation, and condensation polymerization reactions.…”