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UltraNano was set to study the feasibility of making nanoporous membranes using common processes in the semiconductor industry. Nanoporous membranes offer, among other things, the option of desalting water in an energy-efficient and environmentally friendly manner or separating volatile components as an alternative to distillation. Many new nanoporous materials have been reported recently. Successful applications in the field of catalysis, sensors and separations, including first examples of small-scale nanofiltration, indicate the potential of such materials for application in the field of nanofiltration on a larger scale. However, at the start of the project there was a lack of good, simple methods to realize this scale-up for ultra-thin (sub-micron), nanoporous membranes.
In UltraNano the focus was on transforming ultraporous membranes into nanoporous membranes. To this end, atomic layer deposition (ALD) was employed to first form a tailored, precursor layer onto an ultraporous membrane. This precursor layer consisted of ZnO, a building block that in combination with 2 methylimidazole as an organic linker can be used to form a metal-organic framework (MOF) called Zeolitic Imidazolate Framework-8 (ZIF-8). The ZnO-coated microsieves were placed carefully in a stand, which was placed the bottom of an autoclave, and allowed to react with 2 methylimidazole, which present as a liquid at the bottom of the autoclave. After a number of evacuated cycles the solution was autoclaved at 150 °C for different duration, ranging from 1 to 18 h.
The treated microsieves were characterized with several techniques. Scanning Electron Microscopy (SEM) showed reduction of the pore size upon the autoclave treatment from 450 nm (i.e. macropore) down to ~20 nm (i.e. mesopore) after 18 h, with an optical coating thickness of 256 nm as measured by ellipsometry. X-ray photoelectron spectroscopy (XPS) confirmed the presence of ZIF-8 onto the membrane.
To conclude, ALD was successfully employed to prepare a MOF coating on an ultraporous membrane, reducing the pore diameter by a factor of >20, down to 20 nm. A further reduction by a factor 2 – required to make it to the regime of nanofiltration, or ideally even a full pore filling – may be at reach by, e.g. prolonged reaction times or starting with a thicker precursor layer, before performing gas selectivity and permeability tests.
In dit project wordt de haalbaarheid bestudeerd voor het maken van nanoporeuze membranen met behulp van gangbare processen in de halfgeleiderindustrie. Nanoporeuze membranen bieden onder meer de mogelijkheid om op energie-efficiënte en milieuvriendelijke manier water te ontzouten of het scheiden van vluchtige componenten als alternatief voor destillatie. Recent zijn veel nieuwe nanoporeuze materialen gerapporteerd. Succesvolle toepassingen op het gebied van katalyse, sensoren en scheidingen, waaronder ook eerste voorbeelden van kleinschalige nanofiltratie, geven de potentie van dergelijke materialen aan voor een toepassing op het gebied van nanofiltratie op grotere schaal. Echter, het ontbreekt momenteel aan goede, eenvoudige methoden om deze opschaling voor ultradunne (sub-micron), nanoporeuze membranen te realiseren. In dit project zal wordt een methode bestudeerd en geïmplementeerd waarmee dit wel mogelijk is.