| Cr(VI) and dyes are widely used in industrial applications, and it is well known that continuous discharge of Cr(VI) and dyes contaminated wastewater into the environment has provoked serious environmental concerns all over the world, adsorption is considered to be an efficient, simple and relatively low-cost approach for Cr(VI) and dyes removal. Compared with traditional materials, Fe3O4 magnetic nanoparticles as adsorbents have attracted considerable attention in the past several decades owing to their huge specic surface area and easily separation from wastewater with an external magnetic field. To enhance the stability, selectivity and adsorption performance of Fe3O4 magnetic nanoparticles as adsorbents, a facile, mild and reproducible chemical strategy, based on glutaraldehyde crosslinking reaction, was explored to modify Fe3O4 nanoparticles using polyethyleneimine (PEI) as stabilizer in present work. The magnetic nanoparticles covalently functionalized by PEI, denoted as Fe3O4@NH2@PEI, was prepared according to the glutaraldehyde crosslinking reaction between aldehydes in glutaraldehyde and amine groups in both PEI and Fe3O4 magnetic nanoparticles, showed strong adsorption affinity to Cr(VI), ARS and MO. Composition of the Fe3O4@NH2@PEI was measured by various techniques, such as TEM, SEM, XRD, FTIR, TGA, et al.The time-dependent adsorption experiments indicated that the adsorption of Cr(VI) onto Fe3O4@NH2@PEI could be finished within 10 min and the adsorption process was able to be described by the pseudo-second-order kinetics model. The studies on the adsorption of Cr(VI) revealed that the Langmuir adsorption isotherm with the adsorption capacity of 175.76 mg g-1 at 318 K could well fit the adsorption data. The calculated thermodynamic parameters (△G, AH, and AS) indicated that adsorption of Cr(VI) on Fe3O4@NH2@PEI was spontaneous and endothermic. Furthermore, the stability testing demonstrated that the used adsorbents could be regenerated effectively with 0.5 mol L-1 NaOH solution and no significant loss of adsorption capacity were observed after a run of 20 adsorption-desorption cycles, showing their highly stability in extremely acidic and alkaline solution. Most importantly, the obtained Fe3O4@NH2@PEI composite can effectively and selectively absorb Cr(VI) from complex industrial wastewater, indicating that Fe3O4@NH2@PEI could be used as a promising adsorbent for removal of Cr(VI) from real wastewater with high efficiency.A comprehensive understanding of adsorption behavior shows that the dyes adsorption process can be finished within 20 minutes and the pseudo-second-order kinetic model could well describe the adsorption process. The studies on Langmuir and Freundlich adsorption isotherm models revealed that the Langmuir adsorption model was applicable for the adsorption of ARS and MO onto Fe3O4@NH2@PEI composites, and the maximum adsorption capacity for ARS and MO reached 256 and 242 mg g-1 much higher than original magnetic nanoparticles. The adsorbent exerts selective adsorption characteristics for dyes, which can be used to separate anion dye over cationic dye from their solution mixture. Moreover, the adsorbent can keep the original adsorption ability after a run of 15 consecutive adsorption-desorption cycles, showing excellent mechanical strength. Considering all the advantages, this convenient adsorbent provides promising practical applications for the selective adsorption and separation of dyes from industrial effluents. |
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