The Synthesis And Formation Mechanism Study Of Magnesium And Aluminum Carbonate Layered Double Hydroxide

Layered double hydroxides （LDHs）, members of a family oftwo-dimensional anionic clay with flexibility in composition, have founda wide variety of applications in industry, including as additives inpolymers, as precursors to magnetic materials, in biology and medicine,in catalysis, and in environmental remediation. A detailed understandingof the mechanism of the LDH formation should gain deep insight on thesynthetic methodologies of the material and further allow the propertiesof the resulting LDH to be tailored to specific applications.Herein, we report a systematic investigation of the formationmechanism of the typical MgAl-LDH by urea precipitation method froma magnesium and aluminum precursor salt solution. T he nucleation andgrowth of LDH crystallites were monitored by high resolutiontransmission electron microscopy （HRTEM） combined with selected-areaelectron diffraction （SAED）, X-ray diffraction （XRD）, fourier transforminfrared spectroscopy （FT-IR）, field emission scanning electronmicroscopy （FESEM）, X-ray photoelectron spectroscope （XPS）, CHN organic element analyzer, inductive coupled plasma emission spectrum（ICP-ES）. It is revealed that, at the first stage of the synthesis, amorphouscolloidal hydroxide aluminum is formed from the aluminum precursorsalt solution. Then, the amorphous hydroxides are transformed into thecrystallites of oxide-hydroxide aluminum boehmite γ-AlOOH,accompanying the continuous incorporation of surrounding Mg²⁺into thesheet of the lamellar γ-AlOOH, leading to the charge imbalance of thesheet, which destroys the hydrogen bonds existing between the sheets.Subsequently, the carbonate ions in the solution are intercalated into theinterlayer galleries by an electrostatic interaction for balancing the sheetcharge, resulting in an initial LDH phase with alveolate-like structure.Finally, the main layers stack to build a three-dimensional network withthe positive charge being balanced by the carbonate ions arranged in thehydrated interlayer galleries, and the integrated plate-like structure ofLDH is formed. Throughout the above-mentioned processes, theincorporation of magnesium ions into the sheet of the lamellar boehmitecan play a primary role for the formation of LDH crystallites.