Glyphosate-Hydrotalcite Interaction as Influenced by pH

Abstract

Abstract--Adsorption and the mechanism of adsorption of the herbicide glyphosate [N-(phosphonomethyl) glycine] by hydrotalcite (HT) and by hydrotalcite calcined at 500~ (HT500) was studied. The values of the Freundlich K constant of the adsorption isotherms and the distribution coefficients, Kd, depend on the pH of the adsorption system and vary between 55.54-9603 (K) and 36.82-6252 (Kd) for HT and between 10,106-23,242 (K) and 17,801-26,558 (Kd) for HT500. X-ray diffraction and infrared spectroscopy studies showed that glyphosate is not adsorbed into the interlayer of HT. The adsorption mechanisms are (1) electrostatic attraction between the surface of HT, charged positively below pH 12 according to its point of zero charge and the glyphosate anion, and (2) ligand exchange between the P-OH and/or C=O groups of the herbicide and the A1 and Mg atoms of the HT surface. The occurrence of one or both mechanisms depends on the pH of the adsorption system. These adsorption mechanisms and the amphoteric nature of glyphosate account for the variation in K and Kd values with respect to pH. Previous studies on adsorption of different organic anions by HT have only considered the mechanism of anion exchange as important.

Order and disorder among the layered double hydroxides: combined Rietveld and DIFFaX approach

“…3 shows the X-ray powder diffraction patterns of the Mg-Al-CO 2À 3 LDH obtained at 353 and 413 K, respectively. In complete contrast to literature reports (Bellotto et al, 1996;Drits & Bookin, 2001;Thomas et al, 2004;Radha et al, 2005;Martin et al, 1999;Tichit et al, 2002;Seida et al, 2002) and those patterns shown in Fig. 1, the X-ray powder diffraction patterns of both products show sharp Bragg reflections.…”

“…Such broadening arising from the random intergrowth of the 3R 1 and 2H 1 polytypes (as shown in Fig. 1) is commonly observed and reported by numerous authors (Martin et al, 1999;Tichit et al, 2002;Seida et al, 2002).…”

Changes in soil pH and addition of inorganic phosphate affect glyphosate adsorption in agricultural soil

“…Another factor to be considered is the difference in the size of the molecules. The glyphosate molecule is significantly larger than the phosphate molecule, and therefore, it requires more space than phosphate, thereby reducing the number of adsorption sites available to glyphosate in comparison with phosphate (Liu et al, 1999; Martin et al, 1999). Different clays show a specific affinity for glyphosate depending on their structures.…”

Comparison Study of PHBA-intercalated Mg/Al-LDH and PHBA-immobilized Mg/Al-LDH: Characterization and Application for [AuCl4]̄ Removal from Solution

“…The higher the pH value, the lower the removal of [AuCl 4 ]‾ by the materials. This was related to the pHpzc Mg/Al-LDH value reported by Martin et al (1999) was 12, so that at pH conditions 3 to 11, the positive charge level on Mg/Al-LDH tended to decrease, resulting in adsorption of [AuCl 4 ]‾ charged negative decreases [23]. [AuCl 4 ]‾ was dominant at pH lower than 4.5 and gradually changes to [Au(OH) 4 ]with the increasing pf pH [24][25][26].…”

“…This showed that the PHBA anion has interacted more in the PHBA intercalated Mg/Al-LDH hybrid material than in the PHBA-immobilized Mg /Al-LDH. In both materials was visible peaks peak at wave numbers around 1170 cm -1 estimated to be a vibration stretching C-O phenol group from PHBA [21][22][23].…”