Synthesis of Porous Carbon Material from Metal-Organic Porous Materials

Abstract

Recently, study of new porous materials with high adsorption capacity is one of the most interesting issues. Porous carbon materials, such as activated carbons, are good candidates for gas storage because of high surface area, high adsorption capacity and exceptional chemical stability. In this thesis, new types of activated carbon materials, which are synthesized from metal–organic porous materials (MOPMs) precursors will be introduced and synthesis mechanism will be described. Gas sorption properties of these materials also have been investigated.The first part of the thesis introduces several porous carbon materials from different MOPMs. These carbon materials were obtained by carbonization at 1100 °C and gas sorption properties were characterized. The nitrogen sorption isotherms are hybrid type I—IV isotherm that suggests porous carbons have meso-porosity. The best result of H2 uptake at 1 bar and 77 K was 2.15 wt% for compound from Zn2(bdc)(L-lac)(dmf) and the CO2 adsorption capacity at 1 bar and room temperature was in range 10~14 wt% at 298 K and 1 bar. The sorption properties of carbon compounds could be, in general, compared with other porous carbon materials. For real industrial applications, chemical stability and reproducibility are very important. Our carbon compounds were tested for chemical stability and gas sorption reproducibility. Under water, acidic and basic condition, carbon compound was quite stable and gas sorption performance did not change. Also independent synthesis of 3 different batches of carbon compound results in the same gas sorption properties. These results confirm high stability and reproducibility.In second part, mechanism of MOPM carbonization is explained. Zn3(bpdc)3(dmf)2 was heated at various temperatures and these samples were characterized by variety techniques such as powder X-ray diffraction (PXRD), IR spectrum, energy dispersive X-ray spectroscopy (EDX) and N2 sorption measurements. After heating at 300 °C, structure of Zn3(bpdc)3(dmf)2 was decomposed to non-porous amorphous and when MOPM was heated at higher temperature than 400 °C, zinc oxide was formed, which could be confirmed by PXRD. Note that at this stage the carbon is micro-porous and after heating at higher temperature, the porous carbon acquired meso-porosity which was confined by N2 adsorption isotherm. After heating at 1100 °C, peaks of zinc oxide were disappeared because zinc oxides reacted with carbon to form zinc and carbon oxide (CO or CO2) and then zinc was evaporated. EDX data also supported that, because there was no signal of zinc after heating at 1100 °C. It indicated that after heating above 1100 °C, only carbon remained in the final product.In third part, correlation of surface area of the product and zinc to carbon ratio in MOPM precursor is explained. Carbon materials from low carbon content precursors tended to have higher surface area. To further verify our hypothesis we synthesized zinc (II) succinate and zinc (II) fumarate with lower carbon to zinc ratio. Porous carbon materials from these metal-organic complexes demonstrated 1850 and 1820 m2/g which was the highest surface value among our carbon compounds. These results clearly support that specific surface area depends on zinc to carbon ratio of MOPM precursor and could be successfully adjusted within certain range.