Correlations and adsorption mechanisms of aromatic compounds on biochars produced from various biomass at 700 ℃

摘要

AbstractKnowledge of adsorption behavior of organic contaminants on high heat temperature treated biochars is essential for application of biochars as adsorbents in wastewater treatment and soil remediation. In this study, isotherms of 25 aromatic compounds adsorption on biochars pyrolyzed at 700 °C from biomass including wood chips, rice straw, bamboo chips, cellulose, lignin and chitin were investigated to establish correlations between adsorption behavior and physicochemical properties of biochars. Isotherms were well fitted by Polanyi theory-based Dubinin-Ashtakhov (DA) model with three parameters, i.e., adsorption capacity (Q0) and adsorption affinity (Eandb). Besides the negative correlation ofQ0with molecular maximum cross-sectional areas (σ) of organic compounds, positive correlations ofQ0with total pore volume (Vtotal) and average diameter of micropore (D) of biochars were observed, indicating that adsorption by biochars is captured by the pore-filling mechanism with molecular sieving effect in biochar pores. Linear solvation energy relationships (LSERs) of adsorption affinity (E) with solvatochromic parameters of organic compounds (i. e.,αmandπ∗) were established, suggesting that hydrophobic effect, π-π interaction and hydrogen-bonding interaction are the main forces responsible for adsorption. The regression coefficient (π1) and intercept (C) of obtained LSERs are correlated with biochar H/C andRmicro, respectively, implying that biochars with higher aromaticity and more micropores have stronger π-π bonding potential and hydrophobic effect potential with aromatic molecule, respectively. However, hydrogen-bonding potential of biochars for organic molecules is not changed significantly with properties of biochars. A negative correlation ofbwith biochar H/C is also obtained. These correlations could be used to predict the adsorption behavior of organic compounds on high heat temperature treated biochars from various biomass for the application of biochars as sorbents and for the estimating of environmental risks of organic compounds in the present of biochars.Graphical abstractDisplay OmittedHighlights•Correlations of adsorption with chemical and biochar properties were developed.•Adsorption is captured by the pore-filling mechanism with molecular sieving effect.•Biochars with higher aromaticity have stronger π-π bonding potential.•Hydrophobic effect is much significant in biochar micropores.•Hydrogen-bonding potential of different biochars are almost the same.Correlations of adsorption with physiochemical properties of aromatic compounds and biochars were developed for adsorption predicting and understanding the adsorption mechanisms.