Characterization of carbon dioxide separation membrane with polycation nano-layers
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Characterization of carbon dioxide separation membrane with polycation nano-layers
Tatsuya Funaoka, Yusuke Daiko, Atsushi Mineshige, Tetsuo Yazawa Department of materials science and chemistry, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280
ABSTRACT Ultrathin layers of positively charged poly(diallyl dimethylammonium) choloride (PDDA) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) were deposited on SiO2/ polyethylene glycol hybrid membranes via layer-by-layer assembly technique, and carbon dioxide absorption/separation properties were investigated. Quartz crystal microbalance (QCM) measurements revealed that both PDDA and PSS nanocoatings have a good affinity for CO2 absorption. PDDA-deposited film shows about two times higher CO2 ideal gas selectivity compared with unmodified silica film. INTRODUCTION The global warming caused by carbon dioxide emission is becoming an urgent environmental problem. The removal and separation of carbon dioxide from flue gas have been considered as a promising technology for green house gas emission control. Aqueous solutions of amine-based absorbent are used for capturing carbon dioxide. However, this absorption process is discontinuous and high in cost. Compared with the absorption method, membrane separation technique has advantages such as continuous process (rapid separation) and low operation cost. Thus membrane separation has attracted much attention for practical carbon dioxide separation [1]. Recently, active research has been carried out on inorganic-organic hybrids for carbon dioxide separation prepared by sol-gel method [2,3]. For practical application, membranes with high permeance and high selectivity for carbon dioxide are required. However, there is a trade-off relationship between gas permeance and selectivity; a membrane with high permeance shows low selectivity. In this study, we focused on layer-by-layer (LBL) self-assembly technique. LBL assembly has been widely used to fabricate various type of multilayered structures [4-7]. The LBL assembly offers an easy and inexpensive solution-process and allows a variety of materials to be incorporated within the film structures. As an outline of the technique, LBL assembly is mainly conducted through electrostatic interaction; oppositely charged materials such as polyelectrolytes are alternately deposited on a charged-substrate, and an insoluble polymer complex with a few nanometer thicknesses can be obtained at room temperature and ambient atmosphere. Considering high gas permeance, film thickness is a crucial aspect. We anticipated that such a positively or negatively charged ultrathin layers effectively improve the affinity for CO2 without a serious decrease of permeance because CO2 is also a polarizable molecule as Oį- = Cį+ = Oį-. The zeta-potentials of polyelectrolyte such as positively charged poly(diallyl dimethylammonium) choloride (PDDA) and negatively
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charged poly(sodium 4-styrenesulfonate) (PSS) are reached to approximately +50 and -50 mV, respectively [8]. In this study, PDDA an
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