posted on 2021-08-24, 08:04authored byFathi
S. Awad, Ayyob M. Bakry, Amr Awad Ibrahim, Andrew Lin, M. Samy El-Shall
In this study, the novel adsorbent
UIO-66-IT was synthesized to
extract mercury and phosphate ions from contaminated water. The synthetic
strategy involved the preparation of the metal–organic framework
(UIO-66-NH2) followed by post-synthetic modification using
the chelating ligand 2-imino-4-thiobiuret to form the UIO-66-IT adsorbent.
The structure and the morphology of the adsorbent were investigated
by a variety of analytical techniques including Fourier transform
infrared, X-ray diffraction, X-ray photoelectron spectroscopy, scanning
electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller
surface area measurements. The adsorption of mercury and phosphate
was optimized by studying the effect of pH, initial concentration,
contact time, dose, temperature, and competitive ions. The results
revealed exceptionally high adsorption capacities toward mercury and
phosphate ions of 580 and 178 mg/g, respectively, at pH = 5.5 and
an initial concentration of 1500 and 1000 mg/L. The adsorption isotherms
are in excellent agreement with the Langmuir isotherm model, indicating
the formation of a monolayer on the surface of UIO-66-IT. The kinetics
of adsorption fit well with the pseudo-second-order kinetics model,
which suggests the chemical adsorption of mercury ions via the nitrogen
and sulfur functional groups of the adsorbent and the physical adsorption
of phosphate anions by protonated functional groups on the surface
of the UIO-66-IT adsorbent. Selectivity studies showed removal efficiencies
of 98.9% Hg(II) from a solution containing a mixture of metal ions
at 25 mg/L. Regeneration studies showed that the adsorbent can be
recycled several times by using nitric acid for mercury removal and
sodium chloride for phosphate removal. Removal efficiencies were higher
than 99% for both regenerations. Due to the simple synthetic strategy
via cost-effective starting materials, unique chemical structure,
rapid adsorption kinetics, and high surface area, which lead to excellent
removal efficiency, stability, and excellent regeneration, UIO-66-IT
is introduced as a unique adsorbent for the selective removal of mercury
and phosphate ions to remediate polluted water.