Gas storage in porous aromatic frameworks (PAFs)

A series of porous aromatic frameworks (PAFs) were synthesized via a Yamamoto-type Ullmann reaction containing quadricovalent Si (PAF-3) and Ge (PAF-4). These PAFs are thermally stable up to 465 °C for PAF-3 and 443 °C for PAF-4, corresponding to a 5% weight loss according to the TG pattern. As PAF-1, they exhibit high surface areas (up to 2932 m2 g−1) and excellent adsorption ability to hydrogen, methane and carbon dioxide. Low pressure gas uptake experiments on PAFs show PAF-3 has the highest heat of adsorption (Qst) of hydrogen (6.6 kJ mol−1) and carbon dioxide (19.2 kJ mol−1), while PAF-4 has the highest Qst for methane adsorption (23.2 kJ mol−1) among PAFs. Gas molecule recognition at 273 K was performed and results show only greenhouse gases such as carbon dioxide and methane could be adsorbed onto PAFs.