| The magnesium resource is quite abundant in China. Brucite is a kind of mineral with the highest content of magnesium, and the reserve has been proved more than20million. However, the application of brucite is in the initial stage of development in our country. It is mainly used for export and low-value-added productions such as flue gas desulfurization. Thus, it is of great significance to research how to employ it to produce and process high-value-added and high-tech functional materials. Nano-structured magnesium hydroxide is a sort of fine and high-functional inorganic material. Great importance has been attached to it owing to its excellent characteristics such as optical properties, electromagnetic properties. From the point of comprehensive utilization, our group has developed a new technology to synthesize magnesium hydroxide nano-crystals, based on trans-crystallization of brucite directed by organic molecules. Superior to the traditional methods, our approach uses no acid or precipitant and no by-product resulting.p-toluenesulfonic acid and amino acid were applied as directing agents in our preliminary work. Direct transformation from irregular brucite to uniform magnesium hydroxide nanoplates was achieved in one step. On the basis, this paper selected organic acid and amine as directing agents. Research on the rule of brucite trans-crystallization was done in the aim of clarifying the control mechanism of organic molecules over brucite. The main contents and results are as follows:(1) Trans-crystallization of brucite with the aid of organic acid. Organic acids with different structures were employed in the hydrothermal process for the sake of exploring the discipline. It is found that the acid with phenyl could direct the transformation, while acid with naphthalene and chain organic acid have no effect. The solid product was analyzed by X-ray diffraction (XRD), infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TG/TGA). It is revealed that organic acid does not enter the final product. The law of transformation was investigated with the aid of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is demonstrated that trans-crystallization results are enhanced with the increase of acidity of organic acid.(2) Trans-crystallization of brucite in the presence of organic amine. Various kinds of amine with different structures were employed as directing agents with the aim of rule research. XRD, SEM, TEM, TG/TGA, FT-IR were used to analyze the product. As is indicated, amine with adjacent nitrogen displays best trans-crystallization effect. And organic amine did not combine into the final product through the above characterization. Control over reaction temperature and additive amount of organic amine are conductive to the realization of trans-crystallization.(3) Mechanism research. For organic acid, the key point lies on insertion of organic acid into brucite, and ion exchange process between organic acid and OH". Thus, those acids with stronger acidity present high transformation efficiency. The process is reversible, and mother liquor can be reused to trans-crystallization. For organic amine, the reason is attributed to the coordination between organic amine and Mg2+. As a result, amine with chelating binding sides presents higher transformation efficiency for a flexible chelating ligand generating.(4) Purity test of magnesium hydroxide nanoplates. Fe content of samples were analyzed by inductively coupled plasma emission spectral (ICP). It is revealed that purity is improved after the transformation process. For product induced by organic acid. Fe reduce91%. For organic amine, Fe reduce76%. The possible cause may be owing to the higher selectivity for ion exchange than coordination. |
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