(395c) Synthesis of Hierarchical Hydrotalcite-Derived Mgal-Ldos for CO2 Adsorption: the Effects of Anions and Structure-Directing Agents

Synthesis of Hierarchical Hydrotalcite-derived MgAl-LDOs for CO₂ Adsorption: the Effects of Anions and Structure-Directing Agents

Weiquan Cai^a,*, Pengpeng Shen^a, Jiaguo Yu^b and Mietek Jaroniec^c

^aSchool of Chemical Engineering, Wuhan University of Technology, Luoshi Road 205#, Wuhan 430070, P. R. China

^bState Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road 205#, Wuhan 430070, P. R. China

^cDepartment of Chemistry, Kent State University, Kent, Ohio, 44242, USA 

^*Corresponding author. E-mail address: caiwq@whut.edu.cn

Mg-Al layered double oxides (MgAl-LDOs), as one of LDOs, has a large number of Brǿnsted basic sites on their surface, and thus is considered as a promising candidate for CO₂ removal[1]. Herein, a series of hierarchical hydrotalcite-derived MgAl-LDOs with Mg/Al molar ratio of 2:1 were prepared by a simple hydrothermal method using chloride and nitrate as starting metal salts (SMS), respectively and urea as precipitating agent. Effects of structure-directing agents (SDAs) including Pluronic F127 and Na₂SO₄, and as mentioned SMS on the phase structures, morphologies, textural properties and adsorption performance towards CO₂ of the as-prepared MgAl-LDOs have been comparatively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption-desorption techniques, CO₂ temperature programmed desorption (CO₂-TPD) and CO₂ adsorption analyzer. With addition of Na₂SO₄, the morphologies of the samples transform from hierarchical assemblies assembled by hexagonal nanplatelets to hierarchical flower-like structure assembled by irregular nanoflakes. However, addition of F127 has no significant effect on the morphologies of the samples. The results also show that the adsorption capacity of these samples towards CO₂ relates with their surface basic site density resulted from different SMS and SDAs, and  the sample MgAl-N-F prepared by using magnesium nitrate and aluminium nitrate as SMS, and F127 as SDA has a maximum adsorption capacity (1.18 mmol g^-1). This work provides a simple and an efficient way to prepare MgAl-LDOs with controlled adsorption capacity towards CO₂ from cheap magnesium salts and aluminum salts by using different SDAs. 

[1] M. K. Ram Reddy, Z. P. Xu, G. Q. (Max) Lu, J. C. Diniz da Costa, Ind. Eng. Chem. Res., 45, 7504-7509 (2006).