Highly Selective Removal of Pb(II) by a Pyridylpyrazole-β-ketoenol Receptor Covalently Bonded onto the Silica Surface

Efficient materials
capable of capturing toxic metals from water
are widely needed. Herein, a new pyridylpyrazole-β-ketoenol
receptor, X-ray diffraction analyzed, was covalently incorporated
into the silica surface to produce solid and recyclable adsorbent
particles. The new material, fully characterized, revealed extremely
efficient removal of toxic metals from water, with a selectivity order
of Pb­(II) > Zn­(II) > Cu­(II) > Cd­(II). The adsorption was
exceptionally
rapid at optimum pH and concentrations, showing Pb­(II) removal of
93 mg g–1 within 5 min and maximum Pb­(II) adsorption
of 110 mg g–1 after only 20 min. Sorption isotherms
agreed well with the Langmuir model suggesting a monolayer adsorption,
whereas kinetics agreed with the pseudo-second-order model suggesting
a chemisorption binding mechanism. Thermodynamics of adsorption were
fitted with an endothermic and spontaneous process. The material,
recyclable for at least five cycles, is therefore promising for the
cleanup of water polluted by toxic metals, especially lead.