Catalytic Activity of Ag/SiO2 and Ag/Co3O4 Hierarchically Porous Monoliths for Hydrogenation of Dyes

In this work, the synthesis of silver (Ag) supported on hierarchically porous silica (SiO2), and cobalt oxide (Co3O4) monoliths and the catalytic activity of these monoliths for the hydrogenation of methylene blue (MB) and methyl orange (MO) dyes in water is reported. The SiO2 monoliths were synthesized using a sol-gel technique. The Co3O4 monoliths were prepared by nanocasting, using the SiO2 monoliths as template. Loading of Ag nanoparticles on the SiO2 and Co3O4 monoliths, was done by a solution infiltration method using aqueous silver nitrate (AgNO3) solution followed by reduction with ethylene glycol. The resulting monoliths were characterized by XRD, BET-SA, and SEM, and the catalytic activity of the monoliths was studied for the hydrogenation of MB and MO by sodium borohydride (NaBH4). Careful control experiments allowed the overall rate of the Ag catalyzed reaction to be corrected for the rates of the non-catalyzed reaction and the rates of dye adsorption on the supports and Ag nanoparticles. Ag supported on SiO2 gave the fastest hydrogenation for MB, Ag on Co3O4 gave the fastest MO hydrogenation.