Synthesis of novel catalytic composite nanofibers containing ruthenium nanoparticles stabilized by citric acid-β-cyclodextrin polymer
The elaboration of catalytic composite nanofibers (NFs) by electrospinning through a one-pot strategy is described. Firstly, aqueous colloidal suspensions of ruthenium nanoparticles (Ru NPs) formed by reduction of a Ru(III) salt with NaBH4 and stabilized by a poly(cyclodextrin citrate) (PCD) were prepared. Then, poly (vinyl alcohol) (PVA) of different molecular weights were dissolved in the colloidal suspensions that were electrospun. SEM analyses of the resulting nanowebs displayed uniform NFs, whose diameters ranged between 300 and 700 nm and enlarged upon increasing i) PVA molecular weight, ii) nanosuspension viscosity, iii) the amount of NaBH4 and iv) the PCD/Ru NPs concentration. TEM analysis confirmed that Ru NPs with a mean diameter around 2 nm were observed at the surface of NFs, embedded in the PVA matrix of NFs. HAADF-STEM and EDS mapping clearly showed that Ru NPs were homogeneously distributed onto and into the matrix of NFs. After their electrospinning, prepared nanowebs were submitted to a heat post-treatment at 160°C that was shown to trigger the PVA crystallization. In addition, the physical crosslinking of PVA chains by NaBO2 resulting from NaBH4 oxidation in the precursor suspension was also observed. Interestingly, SEM study evidenced that thermal post-treatment in combination with the presence of NaBO2 clearly improved the thermal stability of the synthesized composite nanowebs. Finally, catalytic hydrogenation tests showed the absence of RuNPs leaching from NFs in the reaction medium, and displayed good conversion of styrene into ethylbenzene.