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.
ABSTRACT
Highly monodispersed silica nanoparticles (SiNPs) were synthesised using a fluorinated surfactant, HOCH2CH(CF3)CO2H, and its efficiency was compared with efficiencies of five other surfactants. The size of the SiNPs (â¼50-200 nm) was controlled by controlling the surfactant amount. The short alkyl-chain fluoro surfactant was found to be more efficient at producing monodispersed SiNPs than its long alkyl-chain fluoro or non-fluorinated surfactant counterparts.
ABSTRACT
Mesoporous silica nanospheres (MSNs-AH) with a Schiff-base ligand were synthesized using a snap-top strategy and post-synthetic grafting strategy for metal ion adsorption. The mesoporous MSNs-AH with the Schiff-base ligand were used for the adsorption of metal ions from artificial wastewater and artificial seawater. The adsorption characteristics of the functionalized adsorbents for various metal ions were tested for different adsorption times (1~48 h) in artificial wastewater and artificial seawater. In the case of artificial wastewater, the functionalized adsorbents had no preferential selectivity for metal ions except for Na+ ions, even though the MSNs-AH adsorbent adsorbed most of the metal ions investigated in this work, including Li+, Co2+, Ca2+, Fe3+, Mn2+, Mg2+, Al3+, Zn2+, and Ni2+. In the case of artificial seawater, however, the MSN absorbent showed high selectivity for Li+ ions.
