| Environmental pollution has become a serious global problem. Based on the advantages of adsorption method and nanaomaterials, a serial of nanocompounds are prepared to remedy the heavy metals contaminated water. The key contents include:preparation of magnetic nanocompound for the effective adsorption of Cu Zn and Cd in effluent; selective removal of Cr(VI) by stability-enhanced magnetic nanoparticles; selective adsorption of Pb and Zn from binary-metal solution; using of carbon nanotubes as immobilization materials to immobilize Pseudomonas aeruginosa for the reduction of Cr(VI). They are briefly as follows:(1) Magnetic porous compound was synthesized by dispersion polymerization method, and then polyethylenimine was modified onto its surface to obtain the adsorbent. The adsorbent was used to remove Cu, Zn and Cd in effluent. SEM and FTIR were applied to characterize its morphology and structure. Adsorption of heavy metal increased with the increasing of solution pH, and achieved adsorption equilibrium within10min. Kinetics study showed that the adsorption process was well fitted with pseudo-second-order model. The maximum adsorption capacity was Cu2+157.81mg/g, Zn2+138.84mg/g, Cd2+105.26mg/g based on Langmuir adsorption isotherms. The magnetic adsorbent showed different adsorption affinity towards heavy metal, which was Cu2+> Zn2+> Cd2+. Besides, the adsorbent had good stability, easy separation and could be used repeatedly, which provided an alternative for heavy metal wastewater remediation. What is more, other effective nanoadsorbent could be developed by modification of different functional composite onto magnetic porous powder (in chapter2).(2) The stability enhanced magnetic nanoparticle was prepared to selectively remove toxical Cr(VI). The Fe3O4was calcined to form magnetic nanoparticle with core-shell structure of Fe3O4@γ-Fe2O3, and then imine groups was grafted onto its surface to develop magnetic adsorbent. The adsorbent had a spheric shape with average diameter of100nm, its zero point of zeta potential was pH=11.4, dispersed in water evenly and could resist HCl and NaOH solution as high as1mol/L. The adsorbent was able to effectively remove anionic Cr(Ⅵ) in the pH range of2to3due to the large amount of protonated imine groups on its surface, and could be magnetically separated from liquid quickly. Adsorption equilibrium was reached within15min and independent of initial Cr(Ⅵ) concentration. The Cr(Ⅵ) maximum sorption capacity at a temperature range of35to15℃was74.07to83.33mg/g, which was obtained using the Langmuir adsorption isotherm. The calculated thermodynamic parameters (ΔG, ΔH, and ΔS) indicated that adsorption of Cr(Ⅵ) was spontaneous and exothermic in nature. Competition from coexisting ions (K+, Na+, Ca2+, Cu2+, Cl-, and NO3-) was found insignificant. The adsorbent had satisfying acid-alkali stability and could be regenerated by0.02mol/L NaOH solution. The results suggested the potential application of the PEI-modified magnetic nanoparticles in selective removal of Cr(Ⅵ) from wastewater (in chapter3).(3) A magnetic nanoadsorbent was prepared to selectively remove Pb and Zn from binary-metal ions. The nanoadsorbent was prepared by introducing imine groups onto the surface of stability enhanced magnetic nanoparticles and then characterized by TEM and FTIR. The tunable selectivity was achieved by adjusting the solution pH and adding EDTA chelator. It was found that when the solution condition was [EDTA]/[M2+]=0.7with pH of6, zinc was existed with the form Zn2+and lead was PbEDTA2-compound, the zinc was selectively removed by chelate interaction. When the solution condition was [EDTA]/[M2+]=0.7and pH of2, PbEDTA2-and PbHEDTA-was existed in binary metal solution, zinc existed stablely with the form of Zn2+, under this solution condition, the adsorbent selectively removed lead by electrostatic interaction. The lead and zinc loaded adsorbent could be regenerated by0.04mol/L NaOH and0.05mol/L HCl, respectively, and still possessed high adsorption capacity. The recovered metal ions could be concentrated and reused (in chapter4).(4) An immobilization technology based on polyvinyl alcohol (PVA), sodium alginate and multiwalled carbon nanotubes (MCNTs) was developed to immobilize Pseudomonas aeruginosa (Pa) for reduction of Cr(Ⅵ) to soluble Cr(Ⅲ). It was found that6%PVA,4%sodium alginate and0.4%MCNTs with4%Ca(NO3)2cross-linking agent (w/w) was the best option for forming beads with the average diameter of3mm. The immobilized Pa was subjected to freezing-thawing treatment to enhance its mechanical strength. MCNTs played a positive role in immobilization of chromium reductase. Compared with free cells, the immobilized Pa bead was able to resist higher toxicity of80mg/L Cr(VI), was convenient to operate for consecutive reduction of Cr(VI). The microbe immobilization technology provided an alternative for Cr(VI) wastewater treatment, and could be extended for other microorganism immobilization (in chapter5).(5) Magnetic nanocatalyst has immense potential in remediation contaminated environment. Therefore, magnetic mesoporous silica was developed. Its pore size was in the range of5-7nm with a narrow particle size distribution. The BET surface area was536.2m2/g and BJH pore volume was1.08cm3/g. The magnetic mesoporous silica was planned to immobilize Co to activate PMS to generate sulfate radical to remove dyes in water (in chapter6). |
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