"Confocal microscopy shows us the nonselective pathways and other defect features within the membrane," says Snyder.
Confocal microscopy enabled Tsapatsis' group to understand why RTP-treated zeolite membranes achieved a better separation performance than conventionally processed membranes. While a high density of grain boundary defects were observed in conventionally treated membranes, very few defect features were identified in the RTP-treated films. This suggests that grain boundaries in the RTP-treated films are either smaller or less flexible.
This apparent decrease in the number, size and flexibility of grain boundaries in the RTP-treated membranes influences the achievable resolution of the molecular separations, the researchers say.
"A challenging separation that is commonly used to test zeolite membranes," says Snyder, "is that of the isomers orthoxylene and paraxylene. "Orthoxylene is slightly larger and should not pass readily through the pores. One would expect a perfect zeolite membrane to allow a permeation rate for paraxylene that is about two orders of magnitude higher than that of orthoxylene."
"A considerable increase in paraxylene/orthoxylene selectivity was observed for RTP-treated membranes," the researchers wrote in Science, "resulting in an attractive combination of paraxylene permeance and mixture separation factor."
The researchers concluded their article by saying, "If its beneficial effects on performance can be demonstrated for other zeolite types, compositions and microstructures, RTP could contribute, in combination with fast one-step deposition methods, to the realization of large-scale production of zeolite membranes."
|Contact: Kurt Pfitzer|