Osmium Nanoparticles-Polypropylene Hollow Fiber Membranes Applied in Redox Processes

Abstract

Composite membranes play a very important role in the separation, concentration, and purification processes, but especially in membrane reactors and membrane bioreactors. The development of composite membranes has gained momentum especially through the involvement of various nanoparticles, polymeric, oxide, or metal, that have contributed to increasing their reactivity and selectivity. This paper presents the preparation and characterization of an active metal nanoparticle-support polymer type composite membrane, based on osmium nanoparticles obtained in situ on a polypropylene hollow fiber membrane. Osmium nanoparticles are generated from a solution of osmium tetroxide in tert-butyl alcohol by reduction with molecular hydrogen in a contactor with a polypropylene membrane. The composite osmium-polypropylene hollow fiber obtained membranes (Os-PPM) were characterized from the morphological and structural points of view: scanning electron microscopy (SEM), high resolution SEM (HR-SEM), energy dispersive spectroscopy analysis (EDAX), X-ray diffraction analysis (XRD), Fourier transform Infrared (FTIR) spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry (TGA, DSC). The process performance was tested in a redox process of p-nitrophenol and 10-undecylenic (10-undecenoic) acid, as a target substance of biological or biomedical interest, in solutions of lower aliphatic alcohols in a membrane contactor with a prepared composite membrane. The characteristics of osmium nanoparticles-polypropylene hollow fiber membranes open the way to biological and biotechnological applications. These membranes do not contaminate the working environment, operate at relatively low temperatures, provide a large contact area between reactants, allow successive oxidation and reduction operations in the same module, and help to recover the reaction mass by ultrafiltration. The results obtained show that the osmium-polypropylene composite membrane allows the reduction of p-nitrophenol or the oxidation of 10-undecylenic acid, the conversion depending on the concentration in the lower aliphatic alcohol, the nature of the lower aliphatic alcohol, and the oxidant or reducing flow through the membrane contactor.

Osmium Recovery as Membrane Nanomaterials through 10–Undecenoic Acid Reduction Method

“…Obtaining composite membranes of osmium nanoparticles-polymer type has aroused special interest, because they can be used both in reduction and oxidation processes [15,16].…”

“…They include the following: silver, gold, copper, nickel, palladium, and platinum [12][13][14]. Recently, osmium nanoparticles have been used for oxidation or reduction processes with oxygen and hydrogen gas in contactor-type membrane systems [15,16].…”

“…An extremely important aspect of the previous research was the adhesion of osmium nanoparticles to the polymeric support on which they were obtained [15,16].…”

“…The reduction with hydrogen gas leads to aggregates of osmium nanoparticles, of micron size, on the polymeric membrane, which are disaggregated after a catalytic process, both in reduction and oxidation, creating the possibility to disperse in the reaction medium [16]. The appearance of the composite osmium nanoparticles-polymer membrane is compact, especially after the oxidation of 10-undecenoic acid (UDA) [15].…”

“…Thus, one very interesting compound, with a presumptive reducing character, is 10-undecenoic acid (or 10-undecylenic acid-UDA), which has been recently oxidized in a process catalyzed by osmium nanoparticles [15,16]. This acid is known for its multiple technical uses: obtaining polymers (polyamides, polyesters, polyurethanes), biodiesel, biomedicine, sports medicine, and cosmetics [27][28][29][30].…”