Preparation And Properties Of Magnetic Nano-Fe₃O₄/LDH Composite Catalyst

Synthetic dyes are widely used in many fields of advanced technology,including various kinds of the textile,paper,leather tanning,food processing,plastics,cosmetics,rubber,printing and dye manufacturing industries.The total dye consumption in the textile industry worldwide is more than 10,000 tons each year and approximately 100tons of dyes is discharged into water streams.Dye wastewater has the characteristics of being resistant to discoloration,heavy toxicity and contain considerable amounts of organic matter which are refractory to removal.Such pollutants are refractory to be degraded by traditional treatment methods.As a kind of advanced oxidation method,heterogeneous Fenton catalysis has been widely used in the degradation of organic pollutants.To develop a novel Fenton catalysis which was efficient,environment-friendly and low-cost is an important research trend in the advanced treatment of dye wastewater.In this dissertation,Fe3O4 nanoparticle,which was prone to aggregate,was loaded on hydrotalcites with the adsorption property for anion dyes to prepare magnetic Fe3O4/LDH and Fe3O4/CuMgAl-LDH composite catalysts by in situ oxidation precipitation method.The representative methyl orange dye was selected as the substrate of simulative dye wastewater.The preparation of LDH,Fe₃O₄/LDH and Fe3O4/CuMgAl-LDH,its properties and comparative study of adsorption and degradation were investigated.The study is briefly summarized as follow:（1）A series of Mg-Al hydrotalcites（Mg/Al-LDH）with different Mg/Al ratios were synthesized through coprecipitation method.The basal spacing of the hydrotalcite became lager with the increase of the Mg/Al ratio.The crystallinity,thermal stability and adsorption capacity for methyl orange also increased with the increase of Mg/Al ratio.Mg-Al hydrotalcite showed the best adsorption capacity for methyl orange when the molar ratio of Mg/Al was 3,butα-Al（OH）3 is formed when the molar ratio of Mg/Al reached 1.The adsorption process of Mg-Al hydrotalcite to methyl orange was spontaneous and exothermic.The Mg-Al hydrotalcite has good adsorption capacity for methyl orange.And the adsorption process conformed to the pseudo-second-order kinetic and Langmuir isotherm adsorption model.The saturated adsorption capacity at25℃was 70.54 mg?g^-1.（2）Mg-A1 hydrotalcites were loaded with Fe₃O₄ nanoparticle to prepare magnetic composite catalysts（Fe3O4/LDH）by oxidation precipitation method.The crystal phase of the Fe₃O₄/LDH was simple and pure.Fe₃O₄ nanoparticles were uniform in size and well distributed on the surface of hydrotalcite with less aggregation.Fe3O4/LDH has good thermal stability and magnetic properties with the saturated magnetization of56.61 emu?g^-1,which could be easily separated and recycled by magnetism.The removal rate for methyl orange of Fe3O4/LDH increased at first and then reduce with the increase of the loading level of Fe₃O₄.The Fe₃O₄/LDH magnetic composite catalysts showed the best loading effect of Fe3O4 nanoparticle and the removal rate for methyl orange reached 96%when the mass ratio of Fe3O4/LDH was 2.（3）The adsorption-catalytic synergy among Fe₃O₄ and LDH improved the catalytic capacity for methyl orange of Fe3O4/LDH magnetic composite catalyst,which was much higher than that of the pure Fe₃O₄.The degradation of the methyl orange by Fe3O4/LDH composite catalyst followed pseudo-first-order reaction.The activation energy of this reaction was 30.39 kJ?mol^-1 in our experiment condition.Under the optimum conditions as follows:Fe₃O₄/LDH dosage 1 g/L,initial p H 3,reaction temperature 25℃and H2O2 dosage 30 mmol/L,the removal rate of 100 mg/l methyl orange solution reached 97%within 120 min.The catalyst showed good chemical stability and reusability with low dissolution rate of Fe.（4）A series of Cu-Mg-Al ternary hydrotalcites（CuMgAl-LDH）with different Cu content were prepared by coprecipitation method.The hydrotalcite showed lager basal spacing with the increase of Cu content.Taking Cu-Mg-Al ternary hydrotalcites as carriers,Fe₃O₄/CuMgAl-LDH composite catalyst were prepared by oxidation precipitation method.The Fe3O4 and the CuMgAl-LDH were linked via the bond of Cu-O-Fe.The introduction of Cu promoted the Fenton reaction.The catalytic capacity of Fe₃O₄/CuMgAl-LDH was higher than Fe₃O₄ and Fe₃O₄/MgAl-LDH.With the increase of Cu content,the degradation rate of methyl orange gradually increased,and the removal rate reached 99%.Fe3O4/CuMgAl-LDH composite catalyst showed good chemical stability.The final removal rates of methyl orange（95～98%）remain stable in4 cycles.The above results show that Mg-Al hydrotalcites have good adsorption capacity for representative methyl orange dyes,and the removal rate of methyl orange by Fe3O4/LDH and Fe3O4/CuMgAl composite catalysts loaded with Fe3O4 nanoparticle are both higher than 97%.The treatment effect is obviously better than the application of hydrotalcites as adsorbent in the field of dye wastewater.