Recent Developments in Understanding Biochar’s Physical–Chemistry

Abstract

Biochar is a porous material obtained by biomass thermal degradation in oxygen-starved conditions. It is nowadays applied in many fields. For instance, it is used to synthesize new materials for environmental remediation, catalysis, animal feeding, adsorbent for smells, etc. In the last decades, biochar has been applied also to soils due to its beneficial effects on soil structure, pH, soil organic carbon content, and stability, and, therefore, soil fertility. In addition, this carbonaceous material shows high chemical stability. Once applied to soil it maintains its nature for centuries. Consequently, it can be considered a sink to store atmospheric carbon dioxide in soils, thereby mitigating the effects of global climatic changes. The literature contains plenty of papers dealing with biochar’s environmental effects. However, a discrepancy exists between studies dealing with biochar applications and those dealing with the physical-chemistry behind biochar behavior. On the one hand, the impression is that most of the papers where biochar is tested in soils are based on trial-and-error procedures. Sometimes these give positive results, sometimes not. Consequently, it appears that the scientific world is divided into two factions: either supporters or detractors. On the other hand, studies dealing with biochar’s physical-chemistry do not appear helpful in settling the factions’ problem. This review paper aims at collecting all the information on physical-chemistry of biochar and to use it to explain biochar’s role in different fields of application.

Biochar from Wood Chips and Corn Cobs for Adsorption of Thioflavin T and Erythrosine B

“…The T1 values reported in Figure 6 are consistent with the values of the physical pa- To evaluate the nature of biochar-water interactions, an innovative dynamic approach based on FFC NMR relaxometry was used [20] to measure the longitudinal relaxation times (T 1 ).…”

“…Surface functional moieties of BC and CC biochars and corresponding feedstock measured by FT-IR in the mid-infrared region are shown in Figure 4. It is clear that the FT-IR spectra of both biochars pyrolyzed at 500 • C compared to the feedstock material showed a substantial decrease in (i) O-H groups' vibrations (3400 cm −1 ) as a result of dehydration, and (ii) aliphatic C-H stretch vibrations (2925 cm −1 ) because of lignin demethoxylation and demethylation during pyrolysis [20]. However, the aromatic ν(C=C) band at 1586 cm −1 and C-H bending aromatic CH out-of-plane deformation at 876, and 820 cm −1 have significant intensities in both studied biochars (Figure 4).…”

“…Peaks at high binding energies 535.8 and 536.9 eV could be attributed to adsorbed water [45]. To evaluate the nature of biochar-water interactions, an innovative dynamic approach based on FFC NMR relaxometry was used [20] to measure the longitudinal relaxation times (T1).…”

“…However, higher production costs limit their industrial application on a large scale. Lately, biochars have become the major research topic for many scientific groups worldwide [20] and have been increasingly studied and used as soil amendments [21][22][23] and for carbon sequestration in soils [24,25]. Due to their adsorption properties (high carbon content, porosity, and surface area) biochars represent a promising sustainable material for the separation of contaminants from contaminated environments [20,26,27].…”

“…Lately, biochars have become the major research topic for many scientific groups worldwide [20] and have been increasingly studied and used as soil amendments [21][22][23] and for carbon sequestration in soils [24,25]. Due to their adsorption properties (high carbon content, porosity, and surface area) biochars represent a promising sustainable material for the separation of contaminants from contaminated environments [20,26,27]. According to a meta-analysis published by Alhashimi and Aktas [28], biochar as an adsorbent was found to have lower energy demand (6.1 MJ kg −1 vs. 97 MJ kg −1 ), lower global warming potential impact (−0.9 kg CO 2 eq kg −1 vs. 6.6 kg CO 2 eq kg −1 ), and lower environmental impacts than activated carbon.…”