Synthesis and thermal properties of ZnAl layered double hydroxide by urea hydrolysis

• ZnAl-LDHs (with Zn/Al = 0.25 to 8) were synthesized by the urea method.
• Pure LDH phase was obtained for Zn/Al ratios of 1:2, 1:1 and 2:1.
• Zn/Al = 2 is an optimal choice to prepare pure and high crystalline LDH.
• The formation mechanism of the ZnAl-LDH by the urea method was discussed.

The synthetic zinc aluminum layered double hydroxide (LDH) with Zn/Al molar ratios of 0.25–8 was synthesized by the urea method. The structure, composition and morphological properties were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). Pure layered double hydroxide phase was obtained when the Zn/Al ratios are 0.5, 1 and 2. The lower (0.25 and 0.33) and higher (3, 4, 6 and 8) initial Zn/Al molar ratios resulted in the formation of ZnAl–CO3-LDH with AlOOH and Zn4(CO3)(OH)6·nH2O, respectively. The thermal properties of these LDHs were studied by the thermogravimetric and differential thermal analysis (TG–DTA). The XRD patterns of the calcined products at 900 °C showed that the LDHs prepared at different Zn/Al molar ratios can be used as good precursors for preparing mixed oxide or spinel.

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