Intercalation vs Adsorption Strategies of Myo-Inositol
Hexakisphosphate into Zn–Fe Layered Double Hydroxide: A Tiff
between Anion Exchange and Coprecipitation
Myo-inositol hexakisphosphates
(IHPs) or phytates are the most
abundant organic phosphates having the potential to serve as a phosphorus
reserve in soil. Understanding the fate of IHP interaction with soil
minerals tends to be crucial for its efficient storage and utilization
as a slow-release organic phosphate fertilizer. We have systematically
compared the effective intercalation strategy of a phytate onto Zn–Fe
layered double hydroxide (LDH) acting as storage/carrier material
through coprecipitation and anion exchange. Powder X-ray diffraction,
X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric
analysis, FTIR spectra, and molecular modeling demonstrated the formation
of phytate-intercalated Zn–Fe LDH through coprecipitation with
a maximum loading of 41.34% (w/w) in the pH range of ∼9–10
in a vertical alignment through monolayer formation. No intercalation
product was obtained from the anion exchange method, which was concluded
based on the absence of shifting in the XRD (003) peak. A change in
the zeta potential values from positive to negative and subsequent
increase in solution pH, with decreasing phytate concentration, are
suggestive of adsorption of IHP onto the LDH surface. The batch adsorption
data were best fitted with Langmuir isotherm equation and followed
the pseudo-second-order kinetic model. The maximum adsorption capacity
was found to be 45.87 mg g–1 at a temperature of
25 ± 0.5 °C and pH 5.63.