Polyethyleneimine (PEI) based thin film nanocomposite (TFN) total heat exchange membranes (THEMs) composed of shaped ZIF-8 crystalline Micro-leaves (ZIF-L)

A novel strategy was developed to build high-performance thin film composite (TFC) total heat exchange membranes (THEMs) by in situ growing ZIF-8 crystalline micro-leaves (ZIF-L) from Polyethyleneimine (PEI) coated on polysulfone (PSF) ultra-filtration substrates. It was found that flexible PEI polymeric chains could tightly cross-link and seal large masses of ZIF-L micro-leaves (ZIF/PEI wt. ratio up to 18.5) to thwart CO2 permeation, on top of PSF substrate. Such PEI cross-linking could also effectively open up the internal channels of ZIF-L micro-leaves to enhance moisture permeance and latent heat recovery without trading off CO2 gas barring property. ZIF-L in varied shapes protruded into the air stream could provide ultra-rough surfaces with increased surface area for improved total energy recovery efficiency. Optimized PEI/ZIF-L TFC THEMs showed ultra-low CO2 permeance of 0.5–8 GPU and ultra-high total heat recovery rates of 68–74%.