Correlations And Mechanisms Of Typical Aromatic Compounds Adsorption On Bamboo Biochars

Biochars were expected as the potential environmental sorbents for organic contaminants due to the large surface area and fine microporosity. Biochars were added to soil in the potential applications of soil improvement and carbon sequestration could alternate the sorption behavior of organic pollutants by soil and their risks in soil environment. Knowledge of adsorption of organic pollutants by biochars and developing predictive models are essential not only for the assessment of their influences on environmental behavior of organic pollutants, but also for the application of biochars as low priced and highly effective sorbents. Adsorption of organic contaminants by biochars are mainly influenced by the properties of organic contaminants and biochars. Heat treatment temperature (HTT) of bichars is a key factor decides their properties. In this dissertation, sorption behaviors of organic contaminants, including polycyclic aromatic hydrocarbons, nitrobezenes, phenols, and anilines, by biochars produced at different HTTs were investigated. The mainly conclusion of this study are as follows:(1) Adsorption isotherms of organic contaminants by biochar produced at high HTTs (i.e.,700℃) were fitted well by the Polanyi-theory based Dubinin-Ashtakhov (DA) model. Correlations of adsorption capacity (Q0) of organic compounds with their molecule sizes and melting points, as well as correlations of adsorption affinity (E) with their solvatochromic parameters (i.e., π* and am), on the biochar, were developed and indicating that adsorption is captured by the pore filling mechanism and derived from the hydrophobic effects of organic compounds and the forming of π-π EDA and hydrogen bonding interactions of organic molecules with surface sites of the biochar. The effects of organic molecule sizes and melting points on adsorption capacity are ascribed to the molecular sieving effect and the packing efficiency of the organic molecules in the biochar pores, respectively. These correlations can be used to quantitatively estimate the adsorption of organic compounds on biochars from their commonly physiochemical properties including solvatochromic parameters, melting points and molecular cross-sectional area.(2) Besides isotherms of organic contaminants by biochar produced at high HTTs (i.e.,700 ℃), Dubinin-Ashtakhov (DA) model is also fitted well for isotherms of organic contaminants by biochar produced at other HTTs (e.g.,200,250,300,400, and 550℃). There is a multiple linear relationship of sorption capacity (Q0) with solubility in octanol and molecular cross-section area of organic compounds for a given biochar. Sorption capacity (Q0) of organic contaminants is dependent on their solubility in octanol and the partition mechanism for low temperature treated biochars (e.g.,200℃), but dependent on their molecular cross-section area and the pore filling mechanism for high temperature treated biochars (e.g.,700℃). This difference could be described by the (O+N)/C polarity of biochars. Besides hydrophobic effects, π-π EDA and hydrogen bonding interactions are responsible for adsorption due to the correlations of adsorption affinity (E and b) with their solvatochromic parameters (i.e., π* and am). These interactions are also dependent on H/C molar ratios of biochars. These correlations can be used to establish a predictive model for quantitatively estimating the adsorption from the commonly physiochemical properties of organic compounds, including solvatochromic parameters, solubility in octanol and molecular cross-sectional area, and biochar properties, such as the (O+N)/C polarity and H/C molar ratio.