María A. Ayude

Prussian Blue onto Activated Carbon as a Catalyst for Heterogeneous Fenton-Like Processes

The main goal of this contribution is the development of a new heterogeneous Fenton-like oxidation system based on Prussian Blue supported over a commercially available granular activated carbon (GAC). The catalysts were prepared following basically three different approaches: (i) Prussian Blue (Fe3(Fe(CN)6)2) particles adsorbed onto the GAC by impregnation, (ii) Prussian Blue nanoparticles (PBNP) prepared ex-situ and adsorbed onto the GAC; and (iii) PBNP prepared in-situ onto the GAC. The catalysts were characterized by SEM, EDS, BET surface area and Fe content. Their performance in the catalytic wet peroxide oxidation of a model azo dye, Orange G, was tested in a batch lab-scale stirred reactor. Activity and stability runs were carried out and analyzed in terms of dye discoloration, Total Organic Carbon removal, UV-vis spectra and degree of iron leaching.

“Soluble” vs. “insoluble” Prussian blue based catalysts: influence on Fenton-type treatment

The influence of the synthesis procedure of supported Prussian blue nanoparticles (PBNP) on their activity and stability as a Fenton-type catalyst is studied. Hence, two catalysts are synthesized by adsorbing onto a support of PBNP formed ex situ through the reaction between FeCl3 and K3Fe(CN)6 using H2O2 as reducing agent, and following different washing protocols. A third catalyst is prepared through a two-step impregnation process with FeCl3 and K4[Fe(CN)6] aqueous solutions. The catalysts are tested in the orange G Fenton-type oxidation. The fresh and used catalysts are characterized by BET surface area, SEM, EDS, TEM, Mossbauer spectroscopy, total iron content and UV-vis spectrophotometry. It is demonstrated that under the synthesis conditions employed, the “insoluble” form of Prussian blue is promoted in the ex situ procedure, whereas the two-step impregnation process leads to the “soluble” Prussian blue formation. The washing of the just-prepared catalysts at the reaction temperature helps in eliminating the unreacted species. Those catalysts based on “insoluble” Prussian blue nanoparticles exhibit better behaviour in terms of stability. Significant removals are attained (100% azo dye, 60% TOC), at pH = 3, 343 K after thirteen successive cycles of 300 min. The best catalyst displays the smallest amount of total “free” Fe leached without releasing PBNP, ferrocyanide or ferricyanide ions into the reaction media. Reversible adsorption–desorption of organic intermediates avoids the loss of activity due to blockage of sites and/or pores.