Mesoporous silica based catalysts for the oxidation of azodyes in waste water

Abstract

Iron-containing catalysts supported on mesoporous silica samples that differ in the methods of their preparation (commercial KSS silica gel, MSM-41 mesoporous silicalite, and silica gels obtained under laboratory conditions by means of spray drying and drying in supercritical СО₂) are synthesized. Their porous structure is studied via low-temperature nitrogen adsorption. Their catalytic activity and stability in the oxidation of carmoisine (an anionic dye) with a 3% hydrogen peroxide solution in water at 60°C and рН 3 are compared. The initial carmoisine and catalyst concentrations in solution are 20 mg/L and 3 g/L, respectively, and the molar Н₂О₂/carmoisine ratio is 459/1. The KSS-based catalyst demonstrates the highest activity and stability with respect to the outwashing of an active component into a solution: the conversion of carmoisine on this catalyst is as high as 99% for 30 min, while the concentration of iron ions in solution (0.27 mg/L) does not exceed the maximum allowable concentration. After the support is preimpregnated with aluminum, the degree of iron outwashing into a solution is more than halved. The synthesized catalysts are of interest with regard to the purification of waste water containing organic admixtures.