3,4-Dichlorophenoxyacetate interleaved into anionic clay for controlled release formulation of a new environmentally friendly agrochemical
© Ghazali et al.; licensee Springer. 2013
Received: 9 April 2013
Accepted: 25 July 2013
Published: 23 August 2013
A new layered organic–inorganic nanohybrid material, zinc-aluminum-3,4-dicholorophenoxyacetate (N3,4-D) in which an agrochemical, 3,4-dichlorophenoxyacetic acid (3,4-D), is intercalated into zinc-aluminum-layered double hydroxide (ZAL), was synthesized by coprecipitation method. A well-ordered nanomaterial was formed with a percentage loading of 53.5% (w/w). Due to the inclusion of 3,4-D, basal spacing expanded from 8.9 Å in ZAL to 18.7 Å in N3,4-D. The Fourier transform infrared study shows that the absorption bands of the resulting nanohybrid composed of both the 3,4-D and ZAL further confirmed the intercalation episode. Thermal analysis shows that ZAL host enhances the thermal stability of 3,4-D. Controlled-release experiment shows that the release of 3,4-D in the aqueous media is in the order of phosphate > carbonate > sulfate > chloride. These studies demonstrate the successful intercalation of the 3,4-D and its controlled release property in various aqueous media.
In modern agriculture, various agrochemicals such as pesticides, herbicides, and plant regulators are widely used for effective pest management and ensuring optimum crop yield. Most herbicide formulations deliver the bulk of the active agents in an immediately available form that can be readily released to the environment . For highly soluble pesticides, these formulations may result in great pesticide losses shortly after application before the molecules have time to diffuse into soil aggregates and reach adsorption sites in soil colloids . This phenomenon leads to pesticide residues in the food chain, and this, in turn, has adverse effects in humans including carcinogenic, mutagenic, and teratogenic effects .
Contamination of pesticides through volatilization, leaching, runoff, and the persistence of agrochemicals in aqueous media has become a concerning environmental issue [4, 5]. In addition, agrochemicals are highly toxic to wildlife (especially mammals) and other organisms and can remain in the aquatic environment for a long time . Much effort was done focusing on ways to reduce the usage of excessive agrochemicals by the development of less hazardous formulations, such as controlled release formulations, in which only a part of the active ingredient is in an immediately available form and the bulk of the herbicide is sorbed in an inert support [1, 7]. This strategy is advantageous since it allows the gradual release of agrochemicals over time, besides preventing instant loss of agrochemicals through volatilization, leaching, and runoff . Moreover, it requires less energy and manpower than the conventional methods, leading to decreased nontarget effect and increased safety for agrochemical applicators [9, 10].
Clay has become one of the popular materials as a host of herbicides due to its unique properties such as high specific surface areas associated with their small particle size and ubiquitous occurrence in most soil and sediment environment [11–17]. One of the classes in the clay family is layered double hydroxide (LDH) or the so-called hydrotalcite-like compounds (HTs). This special material can be used as support in controlled-release formulations and has been proposed as the ideal solution to environmental problems caused by agrochemicals. LDHs or HTs are brucite-like layered materials with the general formula [MII1 − x MIII X (OH)2]x+(Am−)x/n·mH2O, where MII and MIII are divalent and trivalent cations, respectively, and Xn− is the interlayer anion, which balances the positive charge generated by the presence of MIII in the layers. The layer charge is determined by the molar ratio x = MIII/(MIII + MII) which can vary between 0.2 and 0.4 . LDHs have attracted the attention of the industry and academia because of their anion-exchange capability , low cost, ease of preparation, environmental compatibility (especially in agricultural application), and potential use in pharmaceuticals, detergents, and food additives .
In this study, the intercalation of 3,4-dichlorophenoxyacetic acid into the interlamellae of zinc-aluminum-layered double hydroxide (ZAL) was accomplished by a simple direct self-assembly method for the formation of a new organic–inorganic nanohybrid material. The physicochemical properties and the controlled release of the agrochemical were investigated and discussed.
All chemicals used in this synthesis were obtained from various chemical suppliers and used without further purification. Zinc nitrate (Zn(NO3)2·6H2O, 98%, ChemPurPiekary Slaskie, Poland) and aluminum nitrate (Al(NO3)3·9H2O, 98%, ChemPurPiekary Slaskie, Poland) were used as the sources of cations while 3,4-dichlorophenoxy acetic acid (C9H9ClO3, 95%, Sigma-Aldrich Corporation, St. Louis, MO, USA) was used as the starting material of the guest anion. All solutions were prepared using deionized water.
Synthesis of materials
The synthesis of Zn-Al-3,4D nanocomposites was performed by self-assembly method from a mixed aqueous solution of 0.1 M Zn(NO3)2·6H2O and 0.025 M Al(N03)3·9H2O at various concentrations of 3,4D ranging from 0.0035 to 0.5 M. NaOH (2 M) was then added to the mixture with vigorous stirring under nitrogen atmosphere at a constant pH of 7.5 ± 0.02. The precipitate was aged for 18 h in an oil bath shaker at 70°C, filtered, thoroughly washed, and dried in a vacuum oven at 70°C. The resulting nanocomposite was finely ground, kept in a sample bottle, and stored in a vacuum desiccator for further use and characterization. A similar procedure was performed for the preparation of ZAL except the addition of 3,4D.
Powder X-ray diffraction (PXRD) patterns were recorded on a Rigaku model Ultima IV powder λ diffractometer (Rigaku Corporation, Tokyo, Japan) using filtered Cu-Kα radiation (λ = 1.540562 Å) at 40 kV, 20 mA, and 2° min−1. Fourier transform infrared (FTIR) spectra were recorded using a PerkinElmer ×1,725 spectrophotometer (PerkinElmer, Waltham, MA, USA) in the range of 400 to 4,000 cm−1. Finely ground 1% samples in KBr powder were compressed to obtain a pellet, and the pellet was then used to obtain the IR spectra. Thermogravimetric and differential thermogravimetric analyses (TGA/DTG) were carried out using a Mettler Toledo TGA/SDTA851 thermogravimetric analyzer (Mettler Toledo Inc., Columbus, OH, USA) with a heating rate of 10°C min−1 between 35°C and 1,000°C, under a nitrogen flow rate of 50 ml min−1. The elemental analysis was performed using a CHNS analyzer (model CHNS-932, LECO Corporation, St. Joseph, MI, USA) together with inductively coupled plasma atomic emission spectrometry using a PerkinElmer spectrophotometer (model Optima 2000DV) under standard condition.
Results and discussion
Powder X-ray diffraction
Basal spacing and chemical composition of Zn/Al-LDH (LDH) and its nanohybrid (N3,4-D)
Mole fraction (xAl)
Aniona(% w/ w)
BET surface area (m2g−1)
BJH desorption pore volume (cm3g−1)
BET average pore diameter (Å)
The surface area and porosity of ZAL and N3,4-D obtained by the nitrogen adsorption-desorption method are given in Table 1. The successful intercalation has increased the Brunauer-Emmett-Teller (BET) surface area from 1.3 m2 g−1 in ZAL to 3.0 m2 g−1 in N3,4-D. The change in pore texture with larger width, as a result of the modification by the intercalation of 3,4-D into the ZAL interlayer, which is in agreement with the expansion of basal spacing from the resulting nanohybrid (Figure 1) is thought to be the reason.
Release profile of the 3,4-D into various aqueous solutions
The accumulated release of 3,4-D into various aqueous solutions containing phosphate, carbonate, sulfate, and chloride anions increased with contact time. The release of the 3,4-D from the nanohybrid was fast for the first 200 min, followed by a slower one subsequently before reaching the saturated release at approximately 300 and 500 min for PO43− and Cl− and CO32− and SO42−, respectively.
Saturated release of the anions is in the order of phosphate > carbonate > sulfate > chloride with percentages of saturated release of 75%, 40%, 27%, and 11%, respectively. The highest saturated release of 3,4-D in the PO43− aqueous solution is due to the high charge density of the anion (PO43−), whereas the lowest saturated release of 3,4-D was in the aqueous solution containing Cl−. This shows that the saturated release for the aqueous media toward the anion encapsulates in LDH agreed with the previous work by Miyata et al. . This result suggests that the charge density of the anion to be exchanged with 3,4-D plays a vital role in determining the saturated release of the 3,4-D from the nanohybrid into the aqueous media.
Rate constant, half time, and correlation coefficient ( r 2 ) value
Aqueous solution (0.005 M)
A herbicide compound, 3,4-D, was successfully intercalated into the layer of ZAL for the formation of a new organic–inorganic hybrid nanocomposite, N3,4-D, which shows a potential to be used as a controlled-release formulation in agrochemicals. The interlayer spacing of LDH increased from 8.9 to 18.72 Å in the N3,4-D due to the inclusion of 3,4-D into the Zn-Al-LDH interlayer space. Release of 3,4-D from the Zn-Al-layered inorganic host follows pseudo-second-order kinetic models with regression values of 0.959 to 1. This study suggests the possibility of zinc-aluminum-layered double hydroxide to be used as a carrier host for 3,4-D for the generation of environmentally friendly agrochemicals.
This research was funded by the Ministry of Higher Education Malaysia (MOHE) under the Fundamental Research Grant Scheme (FRGS) grant no. 600RMI/ST/FRGS/FST (194/2010).
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