| Ni-Fe-layered double hydroxides(N i-Fe-LDHs) and Fe3O4/Ni-Fe-LDHs composites were synthesized by hydrothermal and solventthermal methods, respectively. In order to supply the theoretical basis and practical significance on the removal of organic dyes, the effects of different process conditions on the structure, crystallinity, morphology, magnetic property, adsorption property and adsorption isotherms were studied.1. Ni-Fe-LDHs of different crystallinities and morphologies was synthesized by a hydrothermal process with varying the ratio of N i to Fe, the concentration of sodium citrate, reaction time and reaction temperature. The mechanism was discussed. Another layered Ni3(NO3)3(OH)4 was obtained on the preparation process of N i-Fe-LDHs. The experimental results showed that the ratio of N i to Fe and the concentration of sodium citrate had an important effect on the formation of N i-Fe-LDHs. The layered N i-Fe-LDHs with higher crystallinity was prepared when the ratio of N i to Fe was 2:1 and the concentration of sodium citrate was 0.25 mmol/L. N i-Fe-LDHs with worse crystallinity and magnetic property would get agglomerated with no sodium citrate or increasing the ratio of N i to Fe. Longer reaction time or higher reaction temperature were not in favor of the formation of well-crystallized N i-Fe-LDHs because of the formation of N i(OH)2.2. Fe3O4/Ni-Fe-LDHs composites were synthesized by solventthermal method and water bath method, respectively. The effects of the ratio of N i to Fe, the kinds and concentration of alkali and complexing agent, solvent and rection time on the preparation process and magnetic property of Fe3O4/Ni-Fe-LDHs were studied.Fe3O4/Ni-Fe-LDHs composites with higher crystallinity and magnetic property were prepared with urea as the alkali, methyl alcohol as solvent and sodium citrate as complexing agent. Urea providing OH- and sodium citrate complexing with Fe3+ could control the reaction speed to promote the preparation process of Fe3O4/Ni-Fe-LDHs composites. Fe3O4/Ni-Fe-LDHs composites showed lower crystallinity and magnetic property using NaOH(HMT) as alkali, water as solvent, or changing the kind of complexing agent(potassium sodium tartrate). Higher the ratio of N i to Fe, higher the crystallinity of Fe3O4/Ni-Fe-LDHs composites, but they were all layered flowering-structure.Fe3O4/Ni-Fe-LDHs composites with diffident reaction conditions had a lower coercivity, low remanence and paramagnetism. The content of Fe, crystallinity and different abilities of complexing agent could make different saturation magnetizations. Due to the strong complexing ability between N i3+ and HMT, Fe3O4/Ni-Fe-LDHs composites with higher saturation magnetization could be obtained with the ratio of N i to Fe being 2:1 and HMT as alkali. And Fe3O4/Ni-Fe-LDHs composites could also get a higher saturation magnetization with sodium citrate as complexing agent.3. Adsorption mechanism and isotherms of N i-Fe-LDHs, LDO and Fe3O4/Ni-Fe-LDHs composites on methyl orange and methylene blue were studied with varying the ratio of N i to Fe and composition conditions. Experimental results showed that the adsorption isotherms of three kinds of samples modeled well with the Freundlich equation and it was a multilayer adsorption process. But three kinds of samples had diffident adsorption mechanisms and adsorption effects on methyl orange and methylene blue. The adsorption process of N i-Fe-LDHs was mainly via ion exchange and LDO was via structure reconstruction, and they had a better adsorption effect of methylene blue. The adsorption effect of methyl orange and methylene blue was same for Fe3O4/Ni-Fe-LDHs composites due to layer spreading on the surface of Fe3O4 and having bigger specific surface. |
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