Synthesis and Controlled Release Characterization of Zinc-Aluminium-Layered Double Hydroxide-Chlorophenoxyacetates Nanohybrids

The massive use of agrochemicals, such as herbicides has led to the contamination of these chemicals in the environment especially surface and ground-water reservoir. One approach to solve this problem is to develop controlled release agrochemical, in which the chemical is embedded into a matrix/support system, and can be released in a controlled manner. This study aimed at the synthesis of new controlled release of herbicides, namely 2-chlorophenoxyacetate, 4-chlorophenoxy-acetate and 2,4,5-trichlorophenoxyacetate via intercalation of the chlorophenoxyherbicides into zinc-aluminium-layered double hydroxide by self-assembly and anion-exchange methods. Upon the successful intercalation of the herbicides, release profiles and the factors govern its release from their matrices into various aqueous media were determined. In this study, relatively phase-pure with well ordered layered nanohybrid materials were successfully synthesized by both methods at optimum condition. Expansion of basal spacing was observed from 8.9 Å in the zinc-aluminium-layered double hydroxide to 18.5, 20.1 and 26.2 Å, in zinc-aluminium-2-chlorophenoxyacetate, zinc-aluminium-4-chlorophe- noxyacetate and zinc-aluminium-2,4,5-trichlorophenoxyacetate nano- hybrids respectively, obtained from self-assembly method, compared to 19.6, 19.5 and 25.8 Å, respectively, in the nanohybrids synthesized by anion-exchange method. Controlled release study of the herbicides into the aqueous solutions of sodium carbonate, sodium sulfate and sodium chloride as well as in distilled water at pH = 3, 6.25 and 12 is in the order of: 2-chlorophenoxyacetate > 4-chlorophenoxyacetate > 2,4,5-trichloro-phenoxy acetate. Release of herbicides into the aqueous media is in the order of: sodium carbonate > sodium sulfate > sodium chloride and pH 12 > pH 3 > pH 6.25. The release profiles are best described by pseudo-second order kinetic model as shown by the regression values of about 1.0. The 4-chlorophenoxyacetates anion was selectively intercalated into zinc-aluminium-layered double hydroxide than 2,4,5-trichlorophenoxyacetate, with percentage anion of 35.5 and 21.0 %, for 4-chlorophenoxyacetates and 2,4,5-trichlorophenoxyacetate, respectively while 2,4,5-tri-chloro-phenoxyacetate was preferably intercalated compared to 2-chlorop-henoxyacetates with the percentage loading of 57.8 and 31.4 %, respectively, for the latter and the former. This study shows that the zinc-aluminium-layered double hydroxide can be used as a matrix for controlled release formulation of chlorophenoxyacetic acid herbicides. The release of chlorophenoxyherbicides from the matrix was found to be controlled by the concentration and the anion in the release aqueous solution as well as the pH of the release media

Surface properties transformation of multi-walled carbon nanotubes on reatment with various acids.

Multi-walled carbon nanotubes (MWCNTs) were treated with various acids namely nitric, citric, chromic and a mixture of nitric-sulphuric acids to introduce carboxylic acid functional groups on them. As a result of this treatment, carboxylic functional groups were found to exist as indicated by Fourier transformed infrared spectroscopy (FTIR) study. Breuneur-Emmet-Teller (BET) specific surface area of the resulting samples was found to be 98, 133, 167 and 247 m 3/g for the sample treated with a mixture of nitric and sulfuric, citric acid chromic acid and nitric acid respectively. Compared to the specific surface area of 1210 m 2/g for the starting MWCNTs, this is equivalent to percentage reduction of 91.8, 89.0, 86.2 and 79.6 % respectively. The crystallinity of the samples increased when nitric and a mixture of nitric and sulphuric acids were used for the treatment, but decreased when citric or chromic acid were used, as observed by X-ray diffraction (XRD) study. Except for the MWCNTs treated with nitric acid, diameter expansion was observed for all the samples

The effect of zinc to aluminium molar ratio on the formation of zinc-aluminium-4-chlorophenoxyacetate nanocomposite

Layered organic‐inorganic hybrid nanocomposite material containing 4‐chlorophenoxy acetate, (4CPA) intercalated into zinc‐aluminium‐layered double hydroxide (ZAL) was prepared by direct self‐assembly method for the formation of Zn‐Al‐4CPA nanocomposite (ZAC). Various Zn2+ to Al3+ molar ratios, R ranging from 1 to 6 were used in the preparation of the mother liquor with fixed concentration of 4CPA at 0.4 M. The pH of the solution was adjusted to 7.5 by slow addition of 2 M NaOH. Well‐ordered nanolayered organic‐inorganic hybrid nanocomposites with the expansion of basal spacing from 8.9 Å in the layered double hydroxide to 19.1–21.2 Å in the resulting nanocomposites were obtained. The FTIR spectra for the nanocomposites showed that the spectrum composed of spectral features of ZAL and 4CPA showing the successful intercalation of the organic moiety into the LDH interlayer. The BET surface area decreased as the XAl value increased while the percentage loading of 4CPA in the nanocomposites increased in the range of 38.9–44.7 % (w/w) as the XAl increased. This shows that the mole ratio of Zn2+ to Al3+, R in the mother liquor controlled the physicochemical properties of the resulting nanocomposite, Zn‐Al‐4CPA

Layered double hydroxide as carrier of herbicide, 2-methyl-4-chlorophenoxy acetic acid : physicochemical characterization and controlled release properties

A new organic-inorganic hybrid nanocomposite Zn-Al-MCPA layered double hydroxide was prepared by intercalation of 2-methyl-4-chlorophenoxy acetic acid (MCPA), into Zn-Al-layered double hydroxide (ZAL) at various concentration of MCPA ranging from 0.1 to 0.7. The pH of the formulation was kept constant at 7.5. Well-ordered hybrid nanocomposite was obtained with 0.4 M MCPA with an expansion of basal spacing from 8.9 Å in the ZAL s resemblance peaks of to 19.7 Å in the resulting nanocomposite. The FTIR spectra of the nanocomposite shows resemblance peaks of the MCPA and Zn-Al-layered double hydroxide indicates the inclusion of MCPA into the layered double hydroxide with loading of MCPA found to be 45% (w/w). The release of MCPA into various aqueous solution was found to be dependent on the anion in the aqueous solution, in the order of phosphate > sulphate > nitrate with the percentage release of 80%, 44% and 8%, respectively. This study shows that Zn-Al-layered double hydroxide can be used as a host carrier for herbicide, MCPA with controlled release capability

Physicochemical study of 3,4-dichlorophenoxyacetic acid intercalated into hydrotalcite-like compound by ion exchanged method

The intercalation of herbicide, 3,4-dicholorophenoxyacetic acid (3,4D), into zinc-aluminium-layered double hydroxide (LDH) for the formation of a new nanocomposite ZADX, was accomplished via anion exchange method. Due to the intercalation of 3,4D with LDH interlayer domain, basal spacing expanded from 8.9Å in the ZAL to 17.7-19.0 Å in the ZADX. The percentage loading of 3,4D in the ZADX is 51.4 % (w/w). The FTIR spectra of the nanocomposite shows resemblance peaks of the 3,4D and Zn-Al-layered double hydroxide indicating the inclusion of 3,4D into the layered double hydroxide. Surface area of the resulting nanocomposite increased from 1.3 to 7.14 m2g-1 with the nitrogen adsorption-desorption of type IV

Synthesis of dual herbicides-intercalated hydrotalcite-like nanohybrid compound with simultaneous controlled release property

A new monophasic nanohybrid containing two herbicides anions, 3,4-dichlorophenoxyacetate (3,4D) and 2-methyldichlorophenoxyacetate (MCPA), was successfully synthesized. The two anions were simultaneously intercalated into the inorganic interlayers of zinc-aluminium-layered double hydroxide (ZAL) for the formation of a nanohybrid, ZAL—MCPA—3,4D (ZAMDX) by anion exchange method. The properties of ZAL intercalated with single guest MCPA and 3,4D, as well as dual-guest nanocomposite were monitored using powder X-ray diffractometer (PXRD), and showed a basal spacing of 19.7, 19.0 and 19.2 Å, respectively. Direct-injection mass spectroscopy (DIMS) and Fourier transform infrared (FTIR) confirmed the dual intercalation of both anions into the interlayer regions of dual-guest nanocomposite. The release of MCPA and 3,4D from ZAMDX fitted a pseudo-second order model and possessed good controlled release properties. This release property exhibits the potential application of layered materials as a delivery system, as well as reservoirs, especially when multiple active agents are used simultaneously in the formation of an organic–inorganic host–guest nanohybrid

Ordered layered organic-inorganic of 4-chlorophenoxyacetate-zinc layered hydroxide nanohybrid

Ordered layered organic‐inorganic nanostructure composed of zinc layered hydroxide‐4‐chlorophenoxy acetate (ZLH‐4CPA) was prepared by reaction of an organic anion, 4‐chlorophenoxy acetate (4CPA) with ZnO under aqueous environment. The concentration of 4CPA was found to be a controlling factor in determining the formation of phase pure, well ordered nanolayered hybrid material. At lower concentration of 4CPA (0.05 M), a mixed phase was observed in which ZnO co‐existed with the nanohybrid. At 0.01 M, a pure phase is obtained with high crystallinity but a well ordered nanolayered structure is lacking. A pure phase, well ordered nanolayered hybrid can be clearly observed at 0.2 M 4CPA. ZnO shows well defined grain structure of various sizes at nanometer scale range. Direct reaction between ZnO and 4CPA under aqueous environment resulted in the formation of 4CPA‐ZLH nanohybrid with flake‐like fibrous structure. On heating at 500° C for 5 h under atmospheric condition, the nanohybrid was transformed back to well defined grain structure, as previously observed for the starting materials, ZnO. This shows that the nanohybrid has “memory effect” property. Well ordered nanolayered hybrid with up to 5 harmonics, from which the average basal spacing of 19.03 Å of the material was deduced, showing long range order of the layer packing

Synthesis of a monophasic nanohybrid for a controlled release formulation of two active agents simultaneously.

A new monophasic nanohybrid containing two phenoxyherbicides anions, 4-(2,4-dichlorophenoxy)butyrate (DPBA) and 2-(3-chlorophenoxy)propionate (CPPA), was successfully synthesized. The two anions were simultaneously intercalated into the inorganic interlayers of zinc-aluminum-layered double hydroxide (ZAL) for the formation of a nanohybrid, ZAL-CPPA-DPBA (NCDX) by an anion-exchange method. Powder X-ray diffraction, direct-injection mass spectrometry and Fourier transform infrared spectroscopy studies confirmed the dual intercalation of both anions into the host interlayer regions. The well-ordered, layered nanohybrid was synthesized using 0.1. M solution of both anions. The basal spacing expanded from 8.9. Å in ZAL to 27.43. Å in the nanohybrid. The release of both anions from the nanohybrid into an aqueous solution of 0.001. M sodium carbonate was found to be governed by pseudo second-order kinetics. This release demonstrates the potential application of layered materials as reservoirs and delivery system, especially when multiple active agents are used simultaneously in the formation of an organic-inorganic host-guest nanohybrid with controlled-release properties

The effect of pH on the formation of host-guest type material: zinc-aluminium-layered double hydroxide-4-chlorophenoxy acetate nanocomposite

Layered organic-inorganic hybrid nanocomposite material containing 4-chlorophenoxy acetate (4-CPA) in an inorganic interlayer was prepared using 4-CPA as guest anion in Zn-Al layered double hydroxide inorganic host by direct precipitation method at various pHs. A well-ordered nanolayered organic-inorganic hybrid nanocomposite, with the expansion of the basal spacing from 8.9 Å in the layered double hydroxide to 19.5-20.1 Å were obtained. The nanocomposites show that they are of mesoporous-type with the percentage of 4-CPA intercalated of around 35-39% (w/w) and the Zn to Al molar ratio of 3.5-4.0. Generally, as the pH of the mother liquor increased, the Zn to Al molar ratio in the resulting nanocomposites is also increased, but the percentage of 4-CPA intercalated and the BET surface area, decreased. This shows that the pH of the mother liquor plays an important role in determining the resulting physicochemical properties of the synthesized materials

Synthesis of nanocomposite 2-methyl-4-chlorophenoxyacetic acid with layered double hydroxide : physicochemical characterization and controlled release properties

A new organic–inorganic hybrid nanocomposite Zn–Al-MCPA-layered double hydroxide (ZAM) was prepared by intercalation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) into Zn–Al-layered double hydroxide (ZAL) at various concentration of MCPA ranging from 0.1 to 0.7 M. The pH of the synthesis was kept constant at 7.5. Well-ordered hybrid nanocomposite was obtained with 0.4 M MCPA with an expansion of basal spacing from 8.9 Å in the ZAL to 19.7 Å in the resulting nanocomposite. The FTIR spectra of the nanocomposite show resemblance peaks of the MCPA and Zn–Al-layered double hydroxide indicating the inclusion of MCPA into the layered double hydroxide. The average particle size of ZAL and ZAM in this study was 115 and 128 nm, respectively. Percentage loading of MCPA was found to be 45.0 % (w/w), calculated based on the percentage of carbon in the sample. The release of MCPA into various aqueous solution was found to be dependent to the anion in the aqueous solution in the order of phosphate > sulfate > chloride with the percentage release of 80, 44, and 8 %, respectively. This study shows that Zn–Al-layered double hydroxide can be used as a host carrier for herbicide, MCPA, with controlled release capability