Inhibition Mechanisms of Zn Precipitation on Aluminum Oxide by Glyphosate: A 31P NMR and Zn EXAFS Study

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• 作者：Wei Li ; Yu-Jun Wang ; Mengqiang Zhu ; Ting-Ting Fan ; Dong-Mei Zhou ; Brian L. Phillips ; Donald L. Sparks
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：May 7, 2013
• 年：2013
• 卷：47
• 期：9
• 页码：4211-4219
• 全文大小：442K
• 年卷期：v.47,no.9(May 7, 2013)
• ISSN：1520-5851

文摘

In this research, the effects of glyphosate (GPS) on Zn sorption/precipitation on 纬-alumina were investigated using a batch technique, Zn K-edge EXAFS, and ³¹P NMR spectroscopy. The EXAFS analysis revealed that, in the absence of glyphosate, Zn adsorbed on the aluminum oxide surface mainly as bidentate mononuclear surface complexes at pH 5.5, whereas Zn鈥揂l layered double hydroxide (LDH) precipitates formed at pH 8.0. In the presence of glyphosate, the EXAFS spectra of Zn sorption samples at pH 5.5 and 8.0 were very similar, both of which demonstrated that Zn did not directly bind to the mineral surface but bonded with the carboxyl group of glyphosate. Formation of 纬-alumina-GPS-Zn ternary surface complexes was further suggested by ³¹P solid state NMR data which indicated the glyphosate binds to 纬-alumina via a phosphonate group, bridging the mineral surface and Zn. Additionally, we showed the sequence of additional glyphosate and Zn can influence the sorption mechanism. At pH 8, Zn鈥揂l LDH precipitates formed if Zn was added first, and no precipitates formed if glyphosate was added first or simultaneously with Zn. In contrast, at pH 5.5, only 纬-alumina-GPS-Zn ternary surface complexes formed regardless of whether glyphosate or Zn was added first or both were added simultaneously.