Preparation And Catalytic Performance Of Fe₃O₄ Magnetic Nanocomposites

In this paper,Au-Fe₃O₄,Cu-Fe₃O₄ and small-sized Fe₃O₄ magnetic nanoparticles were prepared by different methods.It is intended to prepare a recyclable and efficient catalyst for catalytic reduction of p-nitrophenol.First,the gold sol and Fe₃O₄ nanospheres were prepared,then Au-Fe₃O₄magnetic nanocatalyst was prepared by ultrasonically bonding Au and Fe₃O₄ using a chelating agent.The main results are as follows:（1）The catalytic performance of the catalyst can be significantly improved after soaking the catalyst in a sodium borohydride solution.The longer the soaking time,the more obvious the improvement of catalytic performance.This is the innovation and discovery in this article.（2）The samples with different Au loadings were prepared by changing the loading of Au,and the nanocatalyst was normally distributed with the increase of Au loading.When the Au loading is below 3mL,the Au nanoparticles on the surface of the Fe₃O₄ nanospheres are well dispersed and do not agglomerate.The more the Au loading,the better the catalytic performance.When the Au loading is above 3mL,the Au nanoparticles on the surface of the Fe₃O₄ nanospheres are severely agglomerated,causing the decrease of the catalytic rate.The optimum catalytic performance is achieved when the Au loading is 3 mL.The apparent rate constant k of the3mL-Au-Fe₃O₄ catalyst was 13.8208 min^-1.（3）The prepared Au-Fe₃O₄ catalyst has a saturation magnetization of 67 emu/g or more,and the catalyst can be quickly recovered by an external magnetic field.The3mL-Au-Fe₃O₄ catalyst was subjected to eight consecutive repeated catalytic tests,and no significant decrease in catalytic performance was observed,and the conversion rate was always higher than 98%.The catalyst exhibits good catalytic performance,recyclability and long service life.Second,we directly synthesized Cu-Fe₃O₄ magnetic nanocatalysts by hydrothermal method.The main results are as follows:（1）The loading of Cu in the Cu-Fe₃O₄ catalyst was successfully regulated by changing the amount of copper nitrate added during preparation.The introduction of Cu has successfully replaced the catalysis of Au,and even improved its catalytic performance.（2）The catalytic performance is proportional to the loading of Cu.The catalytic performance of Cu_1.0-Fe₃O₄ catalyst is the best.The apparent rate constant of Cu_1.0-Fe₃O₄ is k=57.7646 min^-1,which is four times higher than that of3mL-Au-Fe₃O₄ catalyst.（3）The saturation magnetization of the obtained Cu-Fe₃O₄ is reduced to some extent,and the lowest is only 28 emu/g,but it is still sufficient for effective magnetic separation recovery and reuse.And there is no significant reduction in catalytic performance after eight cycles of recycling,and the conversion rate is higher than98%.Third,we used thermal decomposition to prepare small-sized Fe₃O₄nanoparticles.The growth mechanism of small-sized ferroferric oxide nanoparticles were as follows:At the beginning,all the nanoparticles were nucleated and grown in turn.Next,the large-sized Fe₃O₄ nanoparticles are dissolved to promote the continued growth of the small-sized Fe₃O₄ nanoparticles.Finally,the size of all Fe₃O₄ nanoparticles are in the range of 10-20 nm,and the average particle size is stable around 13.5 nm.