To explore the potential of Zn(NH3)(CO3) for selective CO2 separation, this study uses single crystal X-ray diffraction and powder X-ray diffraction to determine the structure of Zn(NH3)(CO3) in detail; performs adsorption analyses for the compound, using N2, H2, and CO2 as adsorbates; and, to increase the feasibility of synthesizing Zn(NH3)(CO3), develops a singlepot synthesis approach based on urea hydrolysis and solvothermal aging. The developed singlepot synthesis method proves highly controllable, and potentially demonstrates an approach for the synthesis of other microporous structures. The Zn(NH3)(CO3) structure has a noteworthy inorganic helical framework that consists of a big helix of (ZnOCO)4 with two ammines (NH3) pendant from every other zinc, and a small helix of (ZnOCO)2. In terms of adsorption capacity and CO2 selectivity, Zn(NH3)(CO3) adsorbed 0.550 mmol g-1 CO2 at 293 K and 4500 mmHg, but only 0.047 mmol g-1 N2 and 0.084 mmol g-1 H2 at the same temperature and pressure. This behavior demonstrates considerable equilibrium selectivities-31 and 63for the separation of CO2 from H2 and CO2 from N2, respectively. During adsorption, the pendant ammines act as the gates of check-valves: applied pressure opens the gates for adsorption, and during desorption, the gates are closed, trapping the adsorbates, until a reduction of pressure to near-atmospheric levels. Therefore, low-pressure H4 hysteresis is observed, which means gas storage at near-atmospheric pressures can be done with the Zn(NH3)(CO3) framework. Additionally, the compound proves structurally stable, with an adsorption decrease of 0.8% after 20 adsorption/desorption cyclesa factor that, considered with the other characteristics of Zn(NH3)(CO3), renders this compound a promising new candidate for separation of CO2 from H2 and N2.
A zirconium tungstate (ZrW2O8) precursor was synthesized by a novel sol-gel method
with zirconium oxychloride and tungstic acid as the zirconium and tungsten sources, respectively.
Heat treatment at 600oC for 10 hours was adequate to crystallize the precursor. Use of excess
zirconium source and the concentration of hydrochloric acid were found to affect the phase purity
and crystallization temperature of ZrW2O8. Sizes of particles obtained were in submicron range in
the absence of a microemulsion system. On the other hand, using water/oleylamine/hexane reverse
micelle microemulsion technique monodispersed particles with sizes between 10 to 100nm were
obtained. Nanoparticles were then successfully dispersed in a solvent with a carrier polymer to
produce ZrW2O8 nanofibers with electrospinning technique.
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