Green palladium nanoparticles prepared with glycerol and supported on maghemite for dye removal application

Abstract

This study aims to synthesize palladium nanoparticles (PdNPs) in presence of glycerol as green reducing/stabilizing agent, supported on γ-Fe2O3 (maghemite), as catalysts for dye removal. Three materials were prepared with different Pd loadings, from 0.43 to 0.63 wt%. PdNPs at the surface were composed of Pd0, Pd2+ and Pd4+ species, at average oxidation state of +1.6 and Pd2+:Pd0 atomic ratio up to 1:0.9, which showed that glycerol was able to partially reduce Pd2+. PdNPs of spherical shaped clumps morphology, predominantly well dispersed on the γ-Fe2O3 surface were formed. High resolution scanning transmission electron microscopy images of the materials with higher Pd content revealed PdNPs smaller than 5 nm with crystal interplanar distance compatible with Pd(0). The catalysts were applied in the adsorption as well as in the heterogeneous Fenton degradation of the azo dye methyl orange with 90% of decolourization after 240 min. It was possible to observe an improvement in the catalytic activity with the Pd content increase as well as with the PdNPs size distribution. The dye removal followed pseudo-first-order kinetics. The effect of catalyst dosage and temperature were evaluated. The acidic character of the iron compounds as well as of the glycerol acidic hydrogens constituents of the catalyst can be released in the reaction medium, being responsible to adjust the reaction pH to 3, which is the optimum pH for Fenton process.