Influence of Molecular Structure and Adsorbent Properties on Sorption of Organic Compounds to a Temperature Series of Wood Chars

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• 作者：Charisma Lattao ; Xiaoyan Cao ; Jingdong Mao ; Klaus Schmidt-Rohr ; Joseph J. Pignatello
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：May 6, 2014
• 年：2014
• 卷：48
• 期：9
• 页码：4790-4798
• 全文大小：396K
• 年卷期：v.48,no.9(May 6, 2014)
• ISSN：1520-5851

文摘

Chars from wildfires and soil amendments (biochars) are strong adsorbents that can impact the fate of organic compounds in soil, yet the effects of solute and adsorbent properties on sorption are poorly understood. We studied sorption of benzene, naphthalene, and 1,4-dinitrobenzene from water to a series of wood chars made anaerobically at different heat treatment temperatures (HTT) from 300 to 700 掳C, and to graphite as a nonporous, unfunctionalized reference adsorbent. Peak suppression in the NMR spectrum by sorption of the paramagnetic relaxation probe TEMPO indicated that only a small fraction of char C atoms lie near sorption sites. Sorption intensity for all solutes maximized with the 500 掳C char, but failed to trend regularly with N₂ or CO₂ surface area, micropore volume, mesopore volume, H/C ratio, O/C ratio, aromatic fused ring size, or HTT. A model relating sorption intensity to a weighted sum of microporosity and mesoporosity was more successful. Sorption isotherm linearity declined progressively with carbonization of the char. Application of a thermodynamic model incorporating solvent鈥搘ater and char鈥揼raphite partition coefficients permitted for the first time quantification of steric (size exclusion in pores) and 蟺鈥撓€ electron donor鈥揳cceptor (EDA) free energy contributions, relative to benzene. Steric hindrance for naphthalene increases exponentially from 9 to 16 kJ/mol ( 1.6鈥?.9 log units of sorption coefficient) with the fraction of porosity in small micropores. 蟺鈥撓€ EDA interactions of dinitrobenzene contribute 鈭?7 to 鈭?9 kJ/mol (3鈥?.4 log units of sorption coefficient) to sorption on graphite, but less on chars. 蟺鈥撓€ EDA interaction of naphthalene on graphite is small (鈭? to 2 kJ/mol). The results show that sorption is a complex function of char properties and solute molecular structure, and not very predictable on the basis of readily determined char properties.