A highly microporous zeolite imidazolate framework ZIF-8 has been synthesized, rapidly in about 1 h (if the 24-h drying step is not considered) and at room conditions, while using dimethylformamide as solvent and polyethylene glycol (20,000 g/mol) as soft template. The as-prepared ZIF-8 was characterized by FTIR spectroscopy, XRD, TEM, TG and DSC analyses, and N-2 adsorption. ZIF-8 is made up of uniform hexagonal particles with an average particle size of 150 nm. It shows unique textural properties, being microporous and presenting a specific surface area of 1694 m(2)/g and a total pore volume of 0.67 cm(3)/g. ZIF-8 was then considered as adsorbent of carbon dioxide CO2, methane CH4 and nitrogen N-2 at various temperatures (273 to 353 K) and under pressures up to 40 bar. At 298 K and 40 bar, ZIF-8 shows a CO2 uptake of 547 mg(CO2)/g and a CH4 uptake of 211.58 mg(CH4)/g a N-2 uptake of 136.37.58 mg(N-2)/g, respectively, which is to our knowledge the highest capacity ever reported for a ZIF-8 sample. In good agreement with the microporous nature of ZIF-8, the uptake of CO2 onto the surface is driven by physisorption, the process being exothermic and spontaneous parameters (Delta H degrees = - 4.1 kJ/mol, Delta S degrees = - 9.71 J/mol, Delta G = - 1.2 kJ/mol at 298 K)