Surface functional groups and degree of carbonization of selected chars from different processes and feedstock

Abstract

The knowledge of the structural and chemical properties of biochars is decisive for their application as technical products. For this reason, methods for the characterization of biochars that are generally applicable and allow quality control are highly desired. Several methods that have shown potential in other studies were used to investigate two activated carbons and seven biochars from different processes and feedstock. The chars were chosen to cover a wide range of chemical composition and structural properties as a hardness test for the analytical methods used in this study. Specific problems connected with the pretreatment of samples and drawbacks of some methods for some types of chars could be identified in an integrated consideration of the results from different methods. None of the spectroscopic methods was found to be suitable for the quality control of all types of chars. The most valuable results were obtained by chemical analysis that, however, required the complete determination of the main elements, including that of oxygen, and of inorganic components for adequate results. The combination of X-ray photoelectron spectroscopy (XPS) and FT-IR spectroscopy allows a rough characterization of surface functional groups, but cannot discriminate aliphatic and aromatic OH groups. FT-IR might be a suitable method for the quality control of biochars made at lower temperature. The results of Raman spectroscopy did not well correlate with the amount of sp2 hybridized carbon determined by XPS. A better correlation of XPS data was found with the electrical polarization determined by the method of spectral induced polarization that was used for the first time in conjunction with extensive analytical characterization.

Amine-Grafted Heterogeneous Catalysts from Waste for Diols Conversion into Cyclic Carbonates

“…Indeed, when lower pyrolysis temperatures (<400 °C) are applied for shorter time, a less aromatic char with higher amount of reactive C–C double bonds and oxygen groups is obtained. This results in higher H/C ratio and more carbonyl functionalities, that are lost when the temperature is above 350 °C. , The char obtained after the mild pyrolysis of potato starch (entry 1, Table ) showed lower carbon content (76.8 vs 82.8%) and higher H/C ratio (0.39 vs 0.5) than the one obtained using harsher pyrolysis conditions (entry 1, Table ); this corresponds to higher oxygen content and lower aromaticity of the former compared to the second, confirming the above mentioned behavior. When C-PS was subjected to the amination treatment with 1,6-DH, nitrogen content significantly increased (entry 1, Table ), attesting to the successful anchoring of the amine functionality on the char surface, through the formation of C–N covalent bonds and ammonium carboxylate interactions (see next paragraph).…”

Sugarcane bagasse-based biochar and its potential applications: a review

“…XPS, in addition, cannot distinguish between alcohols and phenols and necessitates the use of costly instrumentation. XPS and FT-IR spectroscopy enable a preliminary characterization of surface functional groups, yet they lack the ability to differentiate between aliphatic and aromatic OH groups [206]. Moreover, the outcomes from XPS can aid in illustrating and comprehending that the complexation between oxygenated groups and the metal constitutes a significant adsorption mechanism.…”

Unveiling the Potential of Corn Cob Biochar: Analysis of Microstructure and Composition with Emphasis on Interaction with NO2

“…Firstly, most biochar materials display basic properties owing to alkaline substances contained in the feedstock biomass [ 24 ]. Thus, alkaline sites present on the biochar surface, for example, alkali metal ions (potassium, sodium, calcium) or functional groups (hydroxyl groups) [ 26 ], are capable of interacting with acidic NO 2 molecules via chemical reactions. These interactions imply acid-base reactions, whereby the biochar’s base sites neutralize the acidic nature of NO 2 , enabling it to be adsorbed and eliminated from the atmosphere [ 27 ].…”