Characterizing and Designing Polycation−Clay Nanocomposites As a Basis for Imazapyr Controlled Release Formulations

Abstract

A novel controlled release formulation (CRF) of the herbicide imazapyr (IMP) was designed to reduce its leaching,which causes soil and water contamination. The anionic herbicide IMP was bound to polydiallyldimethylammonium-chloride (PDADMAC)-montmorillonite composites. PDADMAC adsorption reached a high loading of polymer, which resulted in charge reversal of the clay and promoted IMP binding. The composites were characterized by Fourier transform infrared, zeta potential, and X-ray diffraction measurements, indicating electrostatic interactions of the polycation with the surface, polycation intercalation in the clay and suggesting a configuration as loops and tails on the surface at high loadings. IMP binding to the composites is affected by polycation loading and flocculation. Upon adding high concentrations of IMP to a composite of 0.16 g/g, we obtained high herbicide loadings (66% active ingredient). IMP release from the CRFs applied on a thin layer of soil was substantially slower than its release from the commercial formulation (Arsenal). Accordingly, soil column bioassays indicated reduced herbicide leaching (nearly 2-fold) upon applying the CRFs while maintaining good herbicidal activity. The new PDADMAC-clay formulations are promising from the environmental and weed control management points of view.

Novel polymer/surfactant modified montmorillonite hybrids and the implications for the treatment of hydrophobic organic compounds in wastewaters

“…The basal spacing of Mt is about 1.45 nm, in accordance with that of a typical calcium montmorillonite. The PDADMA synthesized organo montmorillonites have slightly larger basal spacings comparing with that of the Mt, which means that the loaded PDADMA can further expand the layers of montmorillonite, in accordance with some previous results (Churchman 2002;Radian and Mishael, 2008;Shen et al, 2009). It also indicated a trans configuration of PDADMA on the siloxane surface (Radian and Mishael, 2008).…”

Effect of Humic Acid on Pyrene Removal from Water by Polycation-Clay Mineral Composites and Activated Carbon

“…This was explained in terms of aggregation caused by HA bridging between composites which decreased accessible surface area. 22 PVPcoS-MMT composites showed similar behavior; initial zeta potential of the composites ranged from −30 mV for 0.4 mmol/g loading (50% of CEC) reaching +30 mV for a loading of 200% of CEC (1.7 mmol polymer/g). As with PDADMAC-MMT composites the HA adsorption was complete for the positively charged composites (>0.65 mmol/g).…”

“…22,30 Charge neutralization was reached at a polymer loading of 0.3 mmol polymer/g clay, below the CEC, which was explained in terms of MMT surface screening by the highly charged polycation extending into the solution even at loadings lower than stochiometric neutralization. 22,30 The adsorption of HA to the negatively charged composite (prior to surface charge neutralization) was very low (<10%). At a polymer loading of 0.5 mmol/g PDADMAC, zeta potential was +27.5 mV and HA adsorption was complete.…”

“…PDADMAC spectrum showed characteristic peaks at 3460, 2800−3000, 2084, 1647, 1480, and 970−1000 cm −1 . 22 The band at 2084 cm −1 is attributed to the quaternary ammonium chloride bond; 35 this vibration showed a slight shift at the low concentration of HA and at higher HA concentration diminished significantly. We suggest that this behavior is a result of the formation of electrostatic interactions between the quaternary ammonium and the negatively charged HA.…”

“…We suggest that this behavior is a result of the formation of electrostatic interactions between the quaternary ammonium and the negatively charged HA. 22,36,37 PVPcoS showed distinctive peaks at 3050, 3000− 2800, 1950, 1450−1600, 1200−1210, 1000, and 800−680 cm −1 . The band at 1950 cm −1 corresponds to the charged ammonium on the pyridine; this vibration disappeared as well upon HA-polymer complexation.…”