Improved stability of zeolitic imidazolate framework-8 photocatalytic coating on polyurethane foam via polyelectrolyte multilayer surface modification

Polycrystalline zeolitic imidazolate framework-8 (ZIF-8) layers have been coated on polyurethane (PU) foam substrate by a combined seed anchoring and secondary growth process. A polyelectrolyte multilayers (PEMs) primer was used to enhance the initial anchoring of the ZIF-8 seed crystals on the PU surface. X-Ray diffraction confirmed that the three-step process (PEM primer, MOF seed adsorption, secondary growth) produced a dense and homogeneous coating of ZIF-8 crystals on the PU foam substrate. The thickness of the ZIF-8 coating was observed by scanning electron microscopy (SEM) and was found to increased from 270 nm to 420 nm when the PEM primer was used when compared to the PU surface deposition. The PU/PEMs/ZIF-8/ foams were tested for their photocatalytic degradation of methylene blue (MB) under UV light and displayed a 4 folds increase in methylene blue (MB) adsorbtion over ZIF-8/PU foam. The photodegradation of MB was also increased from 31% in ZIF-8/PU to 51% in ZIF-8/PEMs/PU foams. Finally, The superior efficiency of the PEMs anchored seeds displayed outstanding photocatalytic efficiency with reusability up to 4 cycles when compared to the without PEMs modified one that lost their performance after only 1 cycle of the photodegradation test.