Search the repository

A+ | A- | | SLO | ENG

Abstract: Manganese-functionalized silica with interparticle mesoporosity and isolated Mn sites (Mn/Si = 0.01) is an excellent Fenton catalyst for water cleaning. However, there is a problem that needs to be solved, i.e., Mn leaching from the silica support during the reaction. The solution may lie in using aerogels as the silicate supports for the manganese. The goal of this master thesis is the synthesis and characterization of manganese-functionalized silica aerogels with different Mn/Si molar ratios and a determination of their structural properties. The emphasis is on the preparation of manganese-functionalized silica aerogels with isolated manganese sites. Firstly, manganese-functionalized microporous and mesoporous silicates with a molar ratio Mn/Si = 0.005–0.02 were synthesized according to the literature and characterized as reference materials for manganese-functionalized aerogels. Manganese silicalite-1 (MnS-1) as a microporous zeolite-type silicate and manganese-functionalized silica (MnKIL-2) as a mesoporous silicate were prepared by the sol-gel process with a hydrothermal and solvothermal treatment, respectively. MnS-1 and MnKIL-2 with a molar ratio of Mn/Si ≤ 0.01 contain manganese as isolated sites in the silica framework and with a molar ratio of Mn/Si > 0.01 contain manganese as manganese oxides. Secondly, manganese-functionalized aerogels (MnAEG) with a molar ratio Mn/Si = 0.005–0.02, were prepared according to the acid-base of the sol-gel polymerization of a tetraethylorthosilicate precursor, which is followed in combination with a supercritical drying using CO2. The prepared materials were characterized using the following techniques: X-ray powder diffraction (XRD), energy-dispersive X-ray elemental analysis (EDX), nitrogen physisorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characterization results on manganese-functionalized aerogels (MnAEG) showed Mn oxide nanoparticles incorporated into the aerogel already at a low Mn concentration (Mn/Si = 0.005), which means that Mn aerogels are not promising silica supports for Mn catalysts applied for water cleaning, because they do not contain isolated Mn sites.
Keywords: : SiO2 aerogels, manganese-functionalized SiO2 aerogels, sol–gel process, CO2 supercritical drying
Published in RUNG: 02.09.2016; Views: 5859; Downloads: 239
Full text (4,37 MB)

Abstract: The development of efficient TiO2-based photocatalysts for water treatment is mainly performed by doping with transition metals or by establishing junctions between different phases, metal–semiconductor or semiconductor–semiconductor. We present, for the first time, the synthesis of Zr- and Mn-modified TiO2 by a redesigned sol–gel technique that allows the formation of heterometallic bridges on the TiO2 surface. Cations of the doping metals are located in the pores of mesoporous anatase and attached to the crystalline TiO2 walls. The presence of the Zr enhances the photoactivity of the TiO2 catalyst. However, the introduction of Mn decreases the photocatalytic efficiency in a nonadditive manner. The inhibition effect was assigned to the side reaction between hydroxyl radicals and Mn ions. The fact that Mn effectively scavenges the hydroxyl radicals and, consequently, inhibits the whole oxidation process is direct proof that hydroxyl radicals are the main reactive species in the photocatalytic oxidative processes on TiO2 surfaces in aqueous media and the process of COH generation is the rate-determining step, which was confirmed using a method based on the decolorization of a commercial dye Bezaktiv Blau in a reaction with Fenton’s reagent as a source of hydroxyl radicals.
Keywords: doping, manganese, oxidation, X-ray absorption spectroscopy, zirconium
Published in RUNG: 21.07.2016; Views: 4157; Downloads: 0
This document has many files! More...