Adsorption Mechnisms Of Aromatic Compounds On Biochars Produced From Various Biomass At 700?

Preparation of biomass as biochar is an effective method to reduce CO2 emissions and mitigate climate change. Biochar produced at 600-700? have superior adsorption capability to organic contaminants because of their large specific surface area, fine microporosity and highly aromatic structure, which were expected as potential sorbents in soil remediation and wastewater treatment. Biochar entered the environment becomes part of the soil organic matter, thus affecting the environmental behavior, environmental fate and biological toxicity of organic contaminants in the environment by sorption.Therefore, exploring the underlying adsorption mechanism and establishing prediction model of organic contaminants on high heat temperature treated biochars is essential for selecting the appropriate biochar as sorbents and evaluating the environmental risks of organic contaminants in the present of biochar. Biochar made from different biomass are commonly with various structure and surface properties. Thus, different biochar has various adsorption behaviors for organic contaminants. In this study, adsorption behavior of 25 aromatic compounds on 5 biochars produced from different biomass including wood chips, rice straw, cellulose, lignin and chitin at 700? was investigated.The quantitative prediction model of aromatic contaminants adsorbed by high heat temperature treated biochar based on parameters of organic physicochemical properties and biochar properties was developed. The typical wood biochar (W700) was used as a representative to study the desorption process and mechanism of aromatic contaminants.(1) Correlations of DA model fitted adsorption capacity (Q0) and adsorption affinity (E and b) with structure and surface chemical properties of biochars were developed. Quantitative prediction model of aromatic contaminants adsorbed by high heat temperature treated biochars, based on physicochemical properties of both organic compounds and biochars, was established. Positive correlation of Q0 with total pore volume (Vtotal) and average diameter of micropore (D) of biochar was observed,indicating that adsorption by biochar was 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.,am and ?*) were established, suggesting that hydrophobic effect, ?-? interaction and hydrogen-bonding interaction are the main forces responsible for adsorption. The positive correlation of intercept C with biochar Rmicro indicates that hydrophobic effect on adsorption of aromatic molecules is much significant in biochar micropores than that on surface of mesopores or macropores. While the negative correlation of ?1 with biochar H/C indicates that biochar with higher aromaticity have stronger ?-? bonding potential with aromatic molecules. However, the hydrogen-bonding potential of biochar for organic molecules is not changed significantly with the properties of biochars,indicating that the ability of different types of biochar to form hydrogen bonds has little effect on the material properties. A negative correlation of b with biochar H/C is also obtained, suggesting that adsorption affinity b is also depending on biochar aromaticity.These correlations could be used to predict the adsorption behavior of aromatic contaminants on high heat temperature treated biochars.(2) Desorption hysteresis was not observed for 8 aromatic compounds, including 3 nitrobenzenes,3 anilines and 2 phenols from W700. It indicates that adsorption affinity(E) of aromatic compounds on W700, functional groups of organic compounds, ?-?interaction and hydrogen-bonding interaction are not responsible for desorption hysteresis. Since W700 has slit-shaped rigid pore structure, pore deformation of biochar pores is less likely to occur during adsorption process. Moreover, W700 contains few functional groups, so it is difficult for W700 to form stable chemical bonds with organic molecules. Thus, there is no hysteresis in the desorption of organic contaminants on the W700. The behavior of completely reversible desorption of organic contaminants from W700,on the one hand, increases the environmental health risks of organic contaminants in the environment. On the other hand, can elute organic contaminants adsorbed on biochar by desorption, which enhanced the regeneration and recycling of biochar as environmental sorbents.