pH-Dependence of Pesticide Adsorption by Wheat-Residue-Derived Black Carbon

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• 作者：Yaning Yang ; Yuan Chun ; Guangyao Sheng ; and Minsheng Huang
• 刊名：Langmuir
• 出版年：2004
• 出版时间：August 3, 2004
• 年：2004
• 卷：20
• 期：16
• 页码：6736 - 6741
• 全文大小：98K
• 年卷期：v.20,no.16(August 3, 2004)
• ISSN：1520-5827

文摘

The potential of black carbon as an adsorbent for pesticides in soils may be strongly influenced by theproperties of the adsorbent and pesticides and by the environmental conditions. This study evaluated theeffect of pH on the adsorption of diuron, bromoxynil, and ametryne by a wheat (Triticum aestivum L.)residue derived black carbon (WC) as compared to a commercial activated carbon (AC). The pH driftmethod indicated that WC had a point of zero charge of 4.2, much lower than that of 7.8 for AC. The densityof oxygen-containing surface functional groups, measured by the Boehm titration, on WC was 5.4 timeshigher than that on AC, resulting in a pesticide adsorption by WC being 30-50% of that by AC, due tothe blockage of WC surface by the waters associated with the functional groups. A small decrease (5.5%/unit pH) in diuron adsorption by WC with increase in pH resulted from increased deprotonation of surfacefunctional groups at higher pH values. A much larger decrease (14-21%/unit pH) in bromoxynil adsorptionby WC with increase in pH resulted from the deprotonation of both the adsorbate and surface functionalgroups of the adsorbent. The deprotonation reduced the adsorptive interaction between bromoxynil andthe neutral carbon surface and increased the electrical repulsion between the negatively charged WCsurface and bromoxynil anions. Deprotonation of ametryne with increase in pH over the low pH rangeincreased its fraction of molecular form and thus adsorption on WC by 15%/unit pH. Further increase inpH resulted in a 20%/unit pH decrease in ametryne adsorption by WC due primarily to the developmentof a negative charge on the surface of WC. The pH-dependent adsorption of pesticides by black carbon maysignificantly influence their environmental fate in soils.