Abstract
Recently, the release of some metal ions to the environment has been observed to cause serious damages to human health and the environment. Herein, a chromium(VI)- and zinc(II)-selective adsorbent (CB18crown6/SBA-15) was successfully fabricated through the covalent attachment of 4′-carboxybenzo-18-crown-6 (CB18crown6) as a ligand on mesoporous silica support (SBA-15). The CB18crown6/SBA-15 adsorbent was characterized by Fourier-transform infrared (FTIR) spectrometry, X-ray diffraction (XRD), N2 adsorption–desorption, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). To evaluate its ability to selectively capture Cr(VI) and Zn(II), adsorption experiments were conducted. The influences of pH, initial concentration of metal ions, and coexisting metal ions on the adsorption process were examined. The CB18crown6/SBA-15 selectively adsorbed Cr(VI) at pH 2 and Zn(II) at pH 5, respectively, from the mixed aqueous solutions of chromium, zinc, lithium, cadmium, cobalt, strontium, and cesium ions. The data for the adsorption of Cr(VI) onto the CB18crown6/SBA-15 were well explained by the Langmuir adsorption isotherm. In addition, the recycling and reuse of CB18crown6/SBA-15 was successfully achieved, and 71 and 76% reuse efficiency of Cr(VI) and Zn(II), respectively, was obtained after five cycles. This study suggests that the use of the CB18crown6/SBA-15 can be a feasible approach for the selective remediation of Cr(VI) and Zn(II) contamination.
Highlights
When industrial water containing metal ions and heavy metal ions is released into nature, the contaminated water causes damages to various lifeforms, and eventually affects humans [1,2]
Santa Barbara Amorphous-15 (SBA-15) was prepared by a sol–gel reaction as described in our previous work, with optimized material ratios, as follows [23]: SBA-15 was synthesized using poly-block-poly-block-poly (P123) as a template and tetraethyl orthosilicate (TEOS) as a silica source
Fourier-transform infrared (FTIR) spectra were used to explore the changes in the functional group of SBA-15 after modifying
Summary
When industrial water containing metal ions and heavy metal ions is released into nature, the contaminated water causes damages to various lifeforms, and eventually affects humans [1,2]. Hong et al [19] reported the adsorption of Ag+ using mesoporous silica with crown ether moieties introduced by chemical reaction. These works mainly studied the adsorption behavior using a single solution of metal ions. Highly selective adsorption of Cr(VI) and Zn(II) in aqueous solutions with various metal ions using an adsorbent chemically modified with crown ether moieties on mesoporous silica with high surface area and uniform pore size have not yet been reported, to the best of our knowledge. We employed SBA-15 as a supporting material, for which carboxycontaining 4 -carboxybenzo-18-crown-6-ether (CB18crown6) was grafted onto the surface of the SBA-15-NH2 (amino-functionalized SBA-15) through a facile and robust covalent grafting approach. The selectivity of the CB18crown6/SBA-15 adsorbent towards Cr(VI) and Zn(II) ions was evaluated in the presence of coexisting metal ions of chromium, zinc, lithium, cadmium, cobalt, strontium, and cesium ions
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