Synthesis of New Porous Metal-Organic Frameworks and Studies on Application in Carbon Dioxide Capture

Abstract

Two porous MOFs, [Zn4O(NTN)2]∙11DMA∙2H2O (SNU-150) (H3NTN= 6,6,6-nitrilotri-2-naphthoic acid, (DMA = N,N-dimethylacetamide) and [Zn5(NTN)4(DEF)2][NH2(C2H5)2]2∙8DEF∙6H2O (SNU-151) (DEF = N,N-diethylformamide) have been synthesized by using the same metal and organic building blocks but in the different solvent systems, in DMA and in the mixture of DEF and acetic acid, respectively. The framework of SNU-150 is neutral whereas SNU-151 is an anionic framework including diethyl ammonium cations as guests. Whether or not a small amount of acetic acid is added in the reaction mixture gives rise to totally different framework structures, since the acid hydrolyzes DEF solvent to produce diethyl ammonium cations that should be included in the cavities of the MOF. Desolvated solids [Zn4O(NTN)2] (SNU-150') and [Zn5(NTN)4][NH2(C2H5)2]2 (SNU-151'), respectively, were obtained by treatment of SNU-150 and SNU-151 with supercritical CO2. SNU-151' exhibits higher H2, CO2, and CH4 gas adsorption capacities than SNU-150', due to the stronger interaction of the gas molecules with the anionic framework and ammonium cations included in the channels, compared to that with neutral SNU-150'.