Synthesis of 4-Chlorophenoxyacetate-Zinc-Aluminium-Layered Double Hydroxide Nanocomposite: Physico-Chemical and Controlled Release Properties

Layered organic–inorganic hybrid nanocomposite material was synthesised using 4-chlorophenoxyacetate (4CPA) as guest anion intercalated into the Zn–Al layered double hydroxide inorganic host by direct co-precipitation method at pH = 7.5 and Zn to Al molar ratio of 4. Both PXRD and FTIR results confirmed that the 4CPA was successfully intercalated into the Zn-Al-LDH interlayer. As a result, 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 20.1 Å in the resulting nanocomposite was observed. The FTIR spectrum of the nanocomposite (ZAC) showed that it composed spectral features of Zn-Al-LDH (ZAL) and 4CPA. The nanocomposites synthesized in this work are of mesoporous-type containing 39.8% (w/w) of 4CPA with mole fraction of Al³⁺ in the inorganic brucite-like layers (x_Al) of 0.224. The release studies showed a rapid release of the 4CPA for the first 600 min, and more sustained thereafter. The total amount of 4CPA released from the nanocomposite interlayer into the aqueous solution were 21%, 66%, and 72% in 0.0001, 0.00025, and 0.0005 M sodium carbonate, respectively. In distilled water, about 75, 35, and 57% of 4CPA could be released in 1000 min, when the pH of the release media was set at 3, 6.25, and 12, respectively. In comparison with a structurally similar organic moiety with one more chlorine atom at the 2-position of the aromatic ring, namely 2,4-dichlorophenoxyacetate (24D), the 4CPA showed a slower release rate. The slightly bulkier organic moiety of 24D together with the presence of chlorine atom at the 2-position presumably had contributed to its higher release rate, and it seems that these factors may be exploited for tuning the release rate of intercalated guest anions with similar properties. This study suggests that layered double hydroxide can be used as a carrier for an active agent and the chemical structure of the intercalated moiety can be used to tune the desired release kinetics of the beneficial agent.