Iron-containing Silica Research Articles

Structural variations and generation of binding sites in Fe-loaded ZSM-5 and silica under the effect of UV-irradiation and their role in enhanced BTEX abatement from gas streams

Here, we have investigated the effect of UV-pretreatment on the physicochemical properties of an adsorbent. The UV-irradiated Fe-incorporated ZSM-5 (UV-FZ5) showed structural and chemical changes arising due to UV-cleaving of framework bonds resulting in a decreased crystallinity and change in the local environment of Fe species. More visible modifications were observed for UV-irradiated iron-containing silica (UV-Fe/AS) where silica network reconfiguration, increased hydroxyl density, and change in the Fe coordination were estimated. A 0.5–81.2% increase in BTEX adsorption was recorded for UV-irradiated adsorbents. These hiked performances were attributed to the increased pore size, increased hydroxyl density, and formation of newer isolated Fe3+ framework species. For FZ5, adsorption occurred via size-selective diffusion followed by hydrogen bonding and cation-pi interaction, whereas, for Fe/AS, diffusion was followed by cation-pi interactions. Moreover, adsorbents retained their adsorption capacity for multiple cycles and were found economically suitable for treating VOCs-contaminated air.

Synthesis and properties of magnetic superhydrophobic mesoporous Fe2O3–SiO2 composites

Ways to obtain Fe2O3–SiO2 iron-containing silica composites with organized mesoporous structure (MCM-41) and large specific surface area (up to 1476 m2 g–1) were considered. The influence exerted by the method used to synthesize the materials on their structure, texture characteristics, particle size, and magnetic properties were studied. The aggregative stability of samples was examined. It was shown that treatment of the resulting composites with compounds from the chlorosilane group affects their hydrophobic properties.

Low-cost Fe/SiO2 catalysts for continuous Fenton processes

Fe2O3/SiO2 materials were prepared using a simple sol-gel method and subsequent agglomeration to yield macroscopic particles of catalyst. The influence of silica source as well as the iron content in their physicochemical properties were studied and related with the catalytic performance and stability in a continuous intensified Fenton process. Likewise, the properties of these iron-containing silica materials were benchmarked with Fe2O3-SBA-15 as pelletized composite material of iron oxides particles embedded into a mesostructured silica support. The use of tetraethyl orthosilicate (TEOS) led to catalysts with specific surface areas around 250m2/g that is ten times higher than that obtained when using sodium silicate as silica source. Additionally, the size of crystalline hematite nanoparticles in Fe2O3/SiO2 materials varied from ca. 2–100nm when the iron content was increased from theoretical 5–20wt.%. Similar catalytic activity in terms of phenol and TOC removals were obtained with all the agglomerated materials, being phenol and TOC removals higher than 90 and 50% under steady conditions, respectively. However, the stability of the iron species was different depending of the silica source and the iron loading. Thus, Fe2O3/SiO2 materials prepared with sodium silicate instead of TEOS exhibited higher stability. Concerning the iron composition, the increased of the iron loading yielded to Fe2O3/SiO2 materials with iron species less susceptible to be leached-out. The Fe2O3/SiO2 material prepared with sodium silicate and a theoretical iron loading of 20wt.% achieved the highest resistance to the iron leaching. This material provided an expected lifetime of 760h under continuous operation in the intensified Fenton system that is quite superior to that calculated for the Fe2O3/SBA-15 catalysts. Likewise, the production cost is only 20% of that of the Fe2O3/SBA-15 catalyst due to the absence of expensive structure direct agents as well as lower energetic requirements.

Synthesis of ordered mesoporous silica membranes containing iron oxide nanocrystallites

This paper reports the first effort in synthesis of iron-containing ordered mesoporous silica membrane on porous α-alumina support by a dip-coating process. A pure silica sol and a series of iron-containing silica sol with Fe/Si molar ratio of 0.1, 0.2 and 0.3 were prepared using Pluronic P123 as template, tetraethylorthosilicate as silica source and hydrated iron nitrite as precursor under acid condition. The unsupported membranes were characterized by Fourier transform infra-red (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen isothermal adsorption measurement. Characterization revealed that iron species present as highly dispersed γ-Fe 2O 3 nanocrystals in hexagonal walls for higher iron-containing samples (Fe/Si = 0.2, 0.3). All unsupported membranes maintain ordered mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. Introduction of iron to silica matrix can decrease pore diameter and increase the wall thickness of mesopores. Scanning electron microscopy (SEM) studies show that the prepared supported membrane is defect-free and energy-dispersive spectroscopy (EDS) analysis further confirm the formation of continuous mesoporous layer on α-alumina porous support. The gas permeance results indicate the supported membranes exhibit Knudsen diffusion behavior confirming the good quality of the membrane.

Iron oxide–silica nanocomposites via sol–gel processing

Iron-containing silica nanocomposites were prepared via sol–gel processing using an iron-containing citrate solution. The samples were analysed via thermogravimetry, X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared (IR) spectroscopy. The effect of sintering temperature on the magnetic susceptibility of the composites was also studied.

ESR study of a sol-gel-derived amorphous Fe 2O 3-SiO 2 system

Iron-containing silica gels and glasses were prepared using the sol-gel method and the state of iron ions in them was examined by means of ESR spectroscopy. The iron ions were homogeneously distributed in both axial and orthorhombic crystal fields in the low concentration region in the gels. The fraction of iron ions at the former sites decreased while that at the latter sites increased with increasing the concentration of iron ions. At a higher concentration than 3 mol% of Fe2O3, Fe-O-Fe spin pairs appeared. In the glasses obtained by heating the gels, almost all the iron ions existed as spin pairs. Such a state of iron ions in the glasses was considered to depend on their chemical environment in the precursor gels.

Debye Temperature and Electrical Conduction of Fe2O3‐CaO‐SiO2 Glasses

The electrical conductivity of iron‐containing silica glasses was measured from 80 to 350 K. The conductivity data were analyzed based on the hopping conduction theory. The hopping binding energy (Wp) and disorder energy WD) were calculated from the activation energy at high and low temperatures. The disorder energy obtained was much lower than reported for FeO‐P2O5 glasses, but similar to that for vandium‐containing glasses.