Continuous Hydrothermal Synthesis of Nickel Ferrite Nanoparticles Using a Central Collision-Type Micromixer : Effects of Temperature, Residence Time, Metal Salt Molality, and NaOH Addition on Conversion, Particle Size, and Crystal Phase
Continuous Hydrothermal Synthesis of Nickel Ferrite Nanoparticles Using a Central Collision-Type Micromixer : Effects of Temperature, Residence Time, Metal Salt Molality, and NaOH Addition on Conversion, Particle Size, and Crystal Phase
复制标题
使用中心碰撞型微混合器连续水热合成镍铁氧体纳米颗粒：温度、停留时间、金属盐摩尔浓度和 NaOH 添加对转化率、粒径和晶相的影响
DOI：
10.1021/ie200036m
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发表时间：
2011
影响因子：
4.2
通讯作者：
陶究
中科院分区：
文献类型：
--
作者：
Koyo Norinaga;Ryota Sato;and Jun-ichiro Hayashi;陶究
采用中心碰撞式微混合器，以Fe（NO3）3和Ni（NO3）2为原料，进行了连续水热合成铁酸镍纳米粒子的研究。温度、停留时间和硝酸盐质量摩尔浓度分别在573-673 K、0.02-2.00 s和0.05-0.50 mol/kg范围内变化。采用ICP光谱、EDX光谱、TEM和XRD研究了温度、停留时间、硝酸盐摩尔浓度和NaOH加入量对转化率、Ni/Fe摩尔比、颗粒尺寸和晶相的影响。在没有NaOH的情况下，Ni转化率在高达623 K的温度下小于2%，并且在673 K下急剧增加到约50%，而Fe转化率在所有温度下均大于94%。在转化率方面，在高达623 K的温度下，Ni/Fe摩尔比小于0.01，并且不产生稳定的镍铁氧体。相反，在673 K，Ni/Fe摩尔比急剧增加到0.2以上，可以得到稳定的镍铁氧体。随着在673 K停留时间的增加，Ni转化率和Ni/Fe比增加，晶格常数从8.35降至8.34 μ m。这些结果表明，反应初期产物的结构与γ-Fe_2O_3相似，可认为是缺Ni的NiFe_2O_4，而反应后期产物的结构与NiFe_2O_4相近。此外，随着温度的升高，0.05 mol/kg时平均粒径从5.2 nm略微增加到7.4 nm，而0.50 mol/kg时平均粒径从5.8 nm显著增加到12.3 nm，尽管在最短停留时间0.02 s时Fe转化率>97%。在使用NaOH的情况下，在673 K下产生小于5.0 nm且化学计量Ni/Fe摩尔比为0.5的较小纳米颗粒。在此基础上，讨论了镍铁氧体合成过程中的形核和长大机制。
Continuous hydrothermal synthesis of nickel ferrite nanoparticles from Fe(NO3)3and Ni(NO3)2was performed using a central collision-type micromixer developed for rapid heating of a starting solution to the reaction temperature and homogeneous nucleation. Temperature, residence time, and nitrate molality were varied in the ranges 573–673 K, 0.02–2.00 s, and 0.05–0.50 mol/kg, respectively. The effects of temperature, residence time, nitrate molality, and NaOH addition on conversion, Ni/Fe molar ratio, particle size, and crystal phase were examined using ICP spectroscopy, EDX spectroscopy, TEM, and XRD. In the cases without NaOH, the Ni conversion was less than 2% at temperatures up to 623 K and increased dramatically to around 50% at 673 K, whereas the Fe conversion was more than 94% at all temperatures. In terms of conversion, the Ni/Fe molar ratio was less than 0.01 at temperatures up to 623 K, and stable nickel ferrite was not produced. By contrast, at 673 K, the Ni/Fe molar ratio increased sharply to more than 0.2, and stable nickel ferrite could be obtained. With increasing residence time at 673 K, the Ni conversion and Ni/Fe ratio increased, and the lattice parameter decreased from 8.35 to 8.34 Å. These results indicate that the products at an early stage of the reaction are similar in structure to γ-Fe2O3and can be considered as a Ni-deficient NiFe2O4whereas the products at a later stage have a structure close to that of NiFe2O4. In addition, the average particle size increased slightly from 5.2 to 7.4 nm at 0.05 mol/kg and increased markedly from 5.8 to 12.3 nm at 0.50 mol/kg with increasing temperature despite the high Fe conversion of >97% at the shortest residence time of 0.02 s. In the cases with NaOH, smaller nanoparticles of less than 5.0 nm with a stoichiometric Ni/Fe molar ratio of 0.5 were produced at 673 K. On the basis of these results, the mechanisms of nucleation and growth in the nickel ferrite synthesis are discussed.