Synthesis and characterization of phenoxy group herbicides intercalated into calcium-aluminium layered double hydroxide and its controlled release profile / Farah Liyana Bohari

Excessive use of commercial herbicides in agriculture can negatively impact the environment, leading to water pollution. The intercalation of herbicides, mainly 4-chlorophenoxyacetic acid (4-CPA) and 2-methyl- 4-chlorophenoxyacetic acid (MCPA) into the interlayer of calcium-aluminium layered double hydroxide (CAL) host was done to minimize the side effects by employing the controlled release profile. CAL host synthesis and the herbicide intercalation were achieved via co-precipitation method, resulting in CAL-4CPA and CAL-MCPA. The CAL host were prepared in six molar ratios (Ri) ranging from 1:1 to 1:6 using varying compositions of aluminium nitrate nonahydrate (Al(NO3)3·9H2O) and constant compositions of calcium nitrate tetrahydrate (Ca(NO3)2·6H2O), referred to as R1 to R6. The suitable ratio, R3 was selected for the intercalation process of 4-CPA and MCPA at various concentrations of 0.025 M, 0.05 M and 0.10 M. Later, 0.025 M was selected as the optimum concentration for the intercalation of 4-CPA and MCPA at varied pH values of 11, 12 and 13. The intercalation was supported by powder X-ray diffraction (PXRD) analysis, showing an expansion of the basal spacing from 8.60 Å to 12.11 Å and 19.90 Å for CAL-4CPA and CAL-MCPA, respectively. Moreover, the absence of nitrate peak at 1326 cm-1 for both intercalated compounds in the Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectra has proven the intercalation. This is in agreement with the lower nitrogen content in elemental analysis and displayed high thermal stability for CAL-4CPA and CAL-MCPA.