The magnetic Fe 3 O 4 @SiO 2 −chitosan (MFSC) with an extremely high adsorption capacity of 336.7 mg g −1 toward toxic Cr(VI) was synthesized successfully by a simple cross-link method. The physicochemical properties of the Fe 3 O 4 , Fe 3 O 4 @SiO 2 , and MFSC were characterized comparatively via X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, N 2 adsorption−desorption, X-ray photoelectron spectroscopy analysis, and vibrating sample magnetometer. Their adsorption processes are well-fitted by the pseudo-second-order kinetic model; their equilibrium isotherms are better matched with the Langmuir isotherm. Further recycling experiments of MFSC show that its adsorption capacity of 78.6 mg g −1 still remains 81.7% of the original value (96.2 mg g −1 ), even after five times reuse. The interference adsorption experiments show that MFSC has stronger affinity for Cr(VI) in the solution containing Cr(VI), Cd(II), Cu(II), Zn(II), and Ni(II). The high adsorption capacity, good selectivity, and easy separation of MFSC clearly indicate that it is a potential recyclable adsorbent for Cr(VI) removal from wastewater.

No abstract

No abstract

No abstract

The rare-earth elements (La, Ce, and Y)modified SiO 2 films for effective Cr(VI) removal from electroplating effluent were synthesized by a convenient sol−gel method successfully. X-ray diffraction, Fourier transform infrared spectra (FT-IR), scanning electron microscope, energy-dispersive system, and X-ray photoelectron spectroscopy (XPS) were applied to characterize their physicochemical properties. The adsorption isotherms showed that the adsorption capacity of SiO 2 modified by La 3+ (64.43 mg g −1 ) is the best, followed by Ce 3+ (53.45 mg g −1 ) and Y 3+ (47.83 mg g −1 ) because of the different ion-exchange capacities of La/Ce/Y−(OH), whereas that of SiO 2 film without modification is only 38.54 mg g −1 . Their adsorption processes could be well depicted by the pseudo-second-order kinetic model. The thermodynamics study showed that the adsorption process of the La/SiO 2 film is spontaneous. The adsorption mechanism includes the ion exchange and electrostatic effect. Furthermore, the conversion of Cr(VI) to Cr(III) during the in situ reduction process was verified by both macro (optical photographs) and micro (FT-IR and XPS) levels. Importantly, the La/SiO 2 film showed high adsorption selectivity and high removal efficiency of 97.4% toward Cr(VI) from initial concentration of 41.7 mg L −1 to residual concentration of 1.1 mg L −1 in the real electroplating effluent, indicating its potential industrial value for pretreatment of heavy metal wastewater.