Study On Preparation And Crystallization Morphology Of Magnesium, Cobalt And Nickel Compounds Via Wet Chemical Route

Magnesium, cobalt and nickel compounds such as Mg-Al-CO3 layered double hydroxides,β-Co(OH)2 andβ-Ni(OH)2 have unique layered structures. Therefore, they have aroused increasing attention from international and domestic related fields due to their existing and potential applications such as catalysts and catalytic supports, ion exchangers, adsorbents, flame retardant and battery materials and so on. In recent years, the preparation and applicants of layered double hydroxides,β-Co(OH)2 andβ-Ni(OH)2 have become the research highlights. In the paper, the crystallization morphology of layered double hydroxides,β-Co(OH)2 andβ-Ni(OH)2 has been studied via the wet chemical route (the urea hydrolysis route and the hydrothermal method), and the influences of various factors on the crystal structure, size and morphology have been systematically investigated.In current work, Mg-Al-CO3 layered double hydroxides were prepared by the urea hydrolysis route. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that hexagonal nanoplatelet Mg-Al-CO3 layered double hydroxides were successfully synthesized through adjusting the volume of ethylenediamine and the crystal size is controlled in the range of 50～100 nm. Under the condition that other experimental parameters are not changed, the crystal size is becoming smaller with increasing the volume of ethylenediamine and the reaction temperature, while the crystal size is becoming larger with the prolonged reaction time. Moreover, ethylenediamine not only inhibits impurity phases generated in the synthesis of Mg-Al-CO3 layered double hydroxides but also can effectively control the crystal size of Mg-Al-CO3 layered double hydroxides. In particular, a possible formation mechanism of hexagonal nanoplatelet Mg-Al-CO3 layered double hydroxides is proposed based on the coordination role of ethylenediamine and the crystal nucleation and growth process. The present work develops a simple and mild route to crystallize Mg-Al-CO3 layered double hydroxides with hexagonal nanoplatelet morphology, which is a key engineering step toward its potential size-dependent applications.Secondly,β-Co(OH)2 andβ-Ni(OH)2 were fabricated through the hydrothermal method. With the aid of XRD, FT-IR and SEM techniques, the crystal structure, size and morphology of all samples were analyzed. The results show that with ethylenediamine assisted, three-dimensional flower-likeβ-Co(OH)2 andβ-Ni(OH)2 were successfully synthesized. When other experimental conditions remain unchanged, flake-like and flower-likeβ-Co(OH)2 andβ-Ni(OH)2 are prepared by adding right amount of ethylenediamin or NaOH, while the crystal size ofβ-Co(OH)2 andβ-Ni(OH)2 is becoming smaller with higher concentrations of Co2+and Ni2+. Especially, ethylenediamine avoids forming ultrafine crystals in the synthesis ofβ-Co(OH)2 andβ-Ni(OH)2, so the samples with high crystallinity can be obtained. Moreover, ethylenediamine also protectsβ-Co(OH)2 from oxidation. Based on the coordination role of ethylenediamine and the crystal nucleation and growth process, possible formation mechanisms of flower-likeβ-Co(OH)2 andβ-Ni(OH)2 are put forward.