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首页> 外文期刊>RSC Advances >Magnetically separable and reusable rGO/Fe3O4 nanocomposites for the selective liquid phase oxidation of cyclohexene to 1,2-cyclohexane diol
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Magnetically separable and reusable rGO/Fe3O4 nanocomposites for the selective liquid phase oxidation of cyclohexene to 1,2-cyclohexane diol

机译：磁性可分离和可重复使用的rGO / Fe3O4纳米复合材料，用于将环己烯选择性液相氧化为1,2-环己烷二醇

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A series of magnetically separable rGO/Fe _(3) O _(4) nanocomposites with various amounts of graphene oxide were successfully prepared by a simple ultrasonication assisted precipitation combined with a solvothermal method and their catalytic activity was evaluated for the selective liquid phase oxidation of cyclohexene using hydrogen peroxide as a green oxidant. The prepared materials were characterized using XRD, FTIR, FESEM, TEM, HRTEM, BET/BJH, XPS and VSM analysis. The presence of well crystallized Fe _(3) O _(4) as the active iron species was seen in the crystal studies of the nanocomposites. The electron microscopy analysis indicated the fine surface dispersion of spherical Fe _(3) O _(4) nanoparticles on the thin surface layers of partially-reduced graphene oxide (rGO) nanosheets. The decoration of Fe _(3) O _(4) nanospheres on thin rGO layers was clearly observable in all of the nanocomposites. The XPS analysis was performed to evaluate the chemical states of the elements present in the samples. The surface area of the nanocomposites was increased significantly by increasing the amount of GO and the pore structures were effectively tuned by the amount of rGO in the nanocomposites. The magnetic saturation values of the nanocomposites were found to be sufficient for their efficient magnetic separation. The catalytic activity results show that the cyclohexene conversion reached 75.3% with a highest 1,2-cyclohexane diol selectivity of 81% over 5% rGO incorporated nanocomposite using H _(2) O _(2) as the oxidant and acetonitrile as the solvent at 70 °C for 6 h. The reaction conditions were further optimized by changing the variables and a possible reaction mechanism was proposed. The enhanced catalytic activity of the nanocomposites for cyclohexene oxidation could be attributed to the fast accomplishment of the Fe ~(2+) /Fe ~(3+) redox cycle in the composites due the sacrificial role of rGO and its synergistic effect with Fe _(3) O _(4) , originating from the conjugated network of π-electrons in its surface structure. The rapid and easy separation of the magnetic nanocomposites from the reaction mixture using an external magnet makes the present catalysts highly efficient for the reaction. Moreover, the catalyst retained its activity for five repeated runs without any drastic drop in the reactant conversion and product selectivity.
机译：通过简单的超声辅助沉淀-溶剂热法成功制备了一系列具有多种氧化石墨烯的磁性可分离rGO / Fe _（3）O _（4）纳米复合材料，并评价了它们对选择性液相氧化的催化活性。过氧化氢作为绿色氧化剂制备环己烯使用XRD，FTIR，FESEM，TEM，HRTEM，BET / BJH，XPS和VSM分析对制备的材料进行表征。在纳米复合材料的晶体研究中可以看到结晶良好的Fe _（3）O _（4）作为活性铁的存在。电子显微镜分析表明球形Fe _（3）O _（4）纳米颗粒在部分还原的氧化石墨烯（rGO）纳米片的薄表面层上具有精细的表面分散性。 Fe_（3）O_（4）纳米球在薄rGO层上的装饰在所有纳米复合材料中均清晰可见。进行XPS分析以评估样品中存在的元素的化学状态。纳米复合材料的表面积通过增加GO的量而显着增加，并且通过纳米复合材料中rGO的量有效地调节了孔结构。发现纳米复合材料的磁饱和值足以用于它们的有效磁分离。催化活性结果表明，以H _（2）O _（2）为氧化剂，乙腈为溶剂，掺入5％rGO的纳米复合材料，环己烯转化率达到75.3％，最高1,1,2-环己烷二醇选择性为81％。在70°C下放置6小时。通过改变变量进一步优化了反应条件，并提出了可能的反应机理。纳米复合材料增强环己烯氧化的催化活性归因于rGO的牺牲作用及其与Fe _的协同作用，从而快速完成了复合物中Fe〜（2+）/ Fe〜（3+）的氧化还原循环。 （3）O _（4），起源于其表面结构中的π电子共轭网络。使用外部磁体从反应混合物中快速且容易地分离磁性纳米复合材料使得本发明的催化剂对反应非常有效。此外，该催化剂在重复运行五次后仍保持其活性，而反应物转化率和产物选择性没有任何急剧下降。

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