Insights on the Molecular Mechanism for the Recalcitrance of Biochars: Interactive Effects of Carbon and Silicon Components

Abstract

Few studies have investigated the effects of structural heterogeneity (particularly the interactions of silicon and carbon) on the mechanisms for the recalcitrance of biochar. In this study, the molecular mechanisms for the recalcitrance of biochars derived from rice straw at 300, 500, and 700 °C (named RS300, RS500, and RS700, respectively) were elucidated. Short-term (24 h) and long-term (240 h) oxidation kinetics experiments were conducted under different concentrations of H2O2 to distinguish the stable carbon pools in the biochars. We discovered that the stabilities of the biochars were influenced not only by their aromaticity but also through possible protection by silicon encapsulation, which is regulated by pyrolysis temperatures. The aromatic components and recalcitrance of the biochars increased with increasing pyrolysis temperatures. The morphologies of the carbon forms in all of the biochars were also greatly associated with those of silica. Silica-encapsulation protection only occurred for RS500, not for RS300 and RS700. In RS300, carbon and silica were both amorphous, and they were easily decomposed by H2O2. The separation of crystalline silica from condensed aromatic carbon in RS700 eliminated the protective role of silicon on carbon. The effect of the biochar particle size on the stability of the biochar was greatly influenced by C-Si interactions and by the oxidation intensities. A novel silicon-and-carbon-coupled framework model was proposed to guide biochar carbon sequestration.

Phytolith‐rich biochar: A potential Si fertilizer in desilicated soils

“…High surface area biochars are known to adsorb efficiently heavy metals (Beesley & Marmiroli, 2011;Houben et al, 2013;Reddy & Lee, 2014;Yang et al, 2016;Zhang et al, 2013), Al Qian et al, 2016), and other inorganic ions (Beesley & Marmiroli, 2011;Chan & Xu, 2009;Dai et al, 2016;Raveendran, Ganesh, & Khilar, 1995;Wang, Xiao, et al, 2018), because of their large internal porosity (Chia et al, 2015). Last, but not least, it is worth noting that a mutual protection occurs between C and PhSi in biochar (Guo & Chen, 2014;Xiao et al, 2014), suggesting the potential of biochar for C sequestration. This protection is, however, dependent on pyrolytic temperature as it is enhanced at low pyrolytic temperatures (Xiao et al, 2014;Figures 4 and 5).…”

Effect of H2O2 concentrations on copper removal using the modified hydrothermal biochar

“…On the other hand, Fang et al (2014) claimed that persistent free radicals (PFRs) were contained on biochar surface and could produce carboxylic groups when H 2 O 2 was added. However, carbon loss was also very obvious with the increase of H 2 O 2 concentrations (Guo and Chen, 2014), which could mainly be due to aromatic carbons decomposed by H 2 O 2 (Heard and Senftle, 1984). Kumar (2011) reported that the decomposition of aromatic carbons by H 2 O 2 was comprised of two different products: (i) aliphatic carboxylic acids; (ii) CO 2 and H 2 O.…”

Facile synthesis of corncob biochar via in-house modified pyrolysis for removal of methylene blue in wastewater

“…The biochar was considered mesoporous structure [10]. The adsorption average pore diameter was estimated as 1.58 nm by BET technique [19,40]. These results can be [41].…”