Foto-reattori a membrana per la valorizzazione del CO2

In questo lavoro è stata studiata la foto-riduzione del CO2 sotto irraggiamento con luce UV-Visibile, accoppiando per la prima volta la tecnologia del reattore continuo a membrana con l’utilizzo di catalizzatori a base di C3N4 puro o compositi C3N4-TiO2 dispersi in una matrice polimerica di Nafion

CO2 reduction by C3N4-TiO2 Nafion photocatalytic membrane reactor as a promising environmental pathway to solar fuels

We investigated CO2 photocatalytic reduction coupling, for the first time in literature, the assets offered by the continuous operating mode using C3N4-TiO2 photo-catalyst embedded in a dense Nafion matrix. The reactor performance was analyzed under UV–vis light in terms of productivity, selectivity and converted carbon. Reaction pressure was specifically investigated for its effect as a “driver” in determining reactor performance, modulating products removal from the reaction volume. In addition, the membrane reactor performance was explored as a function of H2O/CO2 feed molar ratio and contact time. The higher feed pressure (5 bar) led to a lesser MeOH production and a greater amount of HCHO, owing to a hindered desorption, which promoted partial oxidation reactions. Total converted carbon instead did not vary significantly with reaction pressure. Membrane reactor with C3N4-TiO2 photocatalyst resulted more performant than other photocatalytic membrane reactors in terms of carbon converted (61 μmol gcatalyst−1 h−1

Hybrid photocatalytic membranes embedding decatungstate for heterogeneous photooxygenation

The incorporation of decatungstate in polymeric membranes provides new heterogeneous photocatalysts for the oxidation of organic substrates under oxygen atmosphere at 25 C. Photocatalytic membranes have been prepared yielding polymeric films with a high thermal, chemical and mechanical stability (PVDF, PDMS, Hyflon). Surface spectroscopy techniques including transmittance and reflectance UV-Vis and FT-IR have been used to assess the photocatalyst integrity within the polymeric support. Catalyst screening has been performed under both homogeneous and heterogeneous photooxygenation conditions. The photocatalyst activity has been evaluated in terms of the substrate conversion, turnover numbers, and recycling experiments. A membrane induced selectivity behavior has been evidenced by comparison with homogeneous oxidations

Catalytic Membranes and Membrane Reactors: An Integrated Approach to Catalytic Process with a High Efficiency and a Low Environmental Impact

The design of new heterogeneous photooxygenation systems able to employ visible light, oxygen, mild temperatures, and solvent with a low environmental impact has been investigated. In particular, the heterogenization of decatungstate (W10O324 12), a polyoxometalate with photocatalytic activity in oxidation reactions, has been carried out in polymeric membranes of polyvinylidenefluoride. The polymeric catalytic membranes prepared by phase inversion technique have been successfully applied in the aerobic mineralization of phenol in water, which was used as an example of organic pollutant. In order to evaluate the effect of the polymeric environment on the overall catalyst behavior, we have also heterogenized the decatungstate (opportunely functionalized) in perfluorinated membrane made of Hyflon. The photocatalytic composite membranes are characterized by different and tuneable properties depending on the nature of the polymeric micro-environment, in which the catalyst is confined. Moreover, the selective separation function of the membrane results in enhanced performance in comparison with homogeneous reactions

Heterogenization of polyoxometalates on the surface of plasma-modified polymeric membranes

Novel catalytic membranes have been prepared by linking phosphotungstic acid H(3)PW(12)O(40) (W12), a polyoxometalate having interesting properties as photocatalyst, on the surface of plasma-modified membranes. Porous flat-sheet membranes made of polyvinylidene fluoride (PVDF) have been prepared by a phase-inversion technique induced by a nonsolvent. These membranes have been modified by plasma treatments on the surface to graft N-containing polar groups that are able to act as binding sites with W12 (PVDF-NH2-W12). A comparison of the surface and bulk properties of the native and modified PVDF membranes has been reported. Catalytic activity of the PVDF-NH2-W12 membranes has been evaluated in the aerobic degradation reaction of phenol in water. Catalytic tests have been carried out in a membrane reactor operating in continuous mode. Better catalytic performances have been observed for the W12 heterogenized on PVDF membrane than for W 12 in a homogeneous phase. Moreover, PVDFNH2-W12 membranes have given proof of their complete stability under photo-oxidation conditions and their good recycle. This study has shown the possibility of heterogenizing catalysts by a controlled modification of the membrane surface via a plasma technique. This new method is very versatile and can be easily extended to other catalysts. Further studies are actually in progress with other catalysts belonging to the polyoxometalates group

Solvent-free, heterogeneous photooxygenation of hydrocarbons by Hyflon® membranes embedding a fluorous-tagged decatungstate

Hybrid fluoropolymeric membranes with 25% loading of the fluorous-tagged (RfN)4W10O32 effect the solvent-free photooxygenation of benzylic C–H bonds with up to 6100 TONs in 4 hours

Immobilization of tungsten catalysts on plasma modified membranes

Novel catalytic membranes were developed by coupling low-temperature plasma treatments with the chemical immobilization of W-based catalysts. Poly(vinylidene fluoride) membranes were pre-treated with Ar, and then treated with NH3 RF glow discharges in order to obtain a surface rich in amino groups, which are suitable anchor sites for the immobilization of tungsten-based heterogeneous catalysts. In particular, (WO42-), we have focused our interest on tungstate ions 4 which catalyze the oxidation of secondary amines to nitrones, and on decatungstate (W10O324-) and phospho tungstate (W12PO403-) ions, which can both be used as catalysts for the degradation of organic pollutants such as phenol