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A layered double hydroxide (LDH) composed of Ni 2+ and Fe 3+ with a Fe 3+ /(Ni 2+ + Fe 3+ ) ratio of 0.05, which is not commonly available, was successfully prepared by coprecipitation from an aqueous solution of glycerol containing nickel nitrate and iron nitrate. Precipitation using NaOH as a precipitating agent at room temperature or 120 °C under hydrothermal conditions gave products with micrometer-sized aggregates of nanometer-sized unshaped particles, while that using urea yielded LDHs with a foam-like porous architecture composed of platy particles with a size of 100–300 nm. The products were examined to remove Cr(VI) from an acidic (pH = 3) aqueous solution of K 2 Cr 2 O 7 by adsorption and photocatalytic reduction. The foam-like porous NiFe-LDH exhibited the highest adsorbed amount (122 mg g –1 ) and rate (0.017 g mg –1 min –1 ) in the dark and the highest rate (0.012 min –1 ) of photocatalytic Cr(VI) reduction among the NiFe-LDHs prepared in the present study, which can be explained as a positive effect of the foam-like porous architecture. These performances were superior to those of other reported LDHs, showing the importance of the composition and the particle morphology to boost the removal of Cr(VI).
Wijitwongwan et al. (Mon,) studied this question.