Iron-substituted cubic silsesquioxane pillared clays: Synthesis, characterization and acid catalytic activity

Abstract

Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mössbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol asa probe reaction.

Insertion of Iron Decorated Organic–Inorganic Cage-Like Polyhedral Oligomeric Silsesquioxanes between Clay Platelets by Langmuir Schaefer Deposition

“…To synthesize POSS, the controlled hydrolysis of 3-(2-aminoethylamino)-propyltrimethoxysilane in an ethanol/water 14:1 v/v solution was performed. Simultaneously 30 mL of an aqueous FeCl 2.4 H 2 O (0.1 mol/L) solution was prepared and added to 20 mL of the above solution; incubation of the mixture for 24 h engendered the formation of iron decorated cage-like species [24,44,45].…”

“…POSS are made of a core-shell three-dimensional (3D) cage-like structure that can be fabricated through hydrolytic condensation reactions of organosilicon monomers RSiOH 3 [22,23]. If properly functioned, POSS can be bonded with metal ions to form metal substituted silsesquioxanes [24,25].…”

“…In the same context Huh et al [25] studied iron-modified POSS as adsorbent of cesium ions, methylene blue, and chrysoidine. Moreover, clay-POSS hybrids have been studied as catalysts [24] and novel additives in polymeric systems for the fabrication of nanocomposites since they improve thermal stability and thermal retardancy [36,37].…”

“…Considering these advantages, in this work, we aim at fabricating nanostructured thin films where iron decorated POSS is sandwiched between organo-modified clay platelets. Iron was chosen as the metal ion grafted to POSS because of its low toxicity and high abundance that render it an excellent candidate for industrial applications [24]. The proposed experimental approach provides an alternative for hybrid synthesis that avoids aggregation phenomena; the latter are undesirable in applications such as anti-reflection coatings with high and low refractive index multilayers [41] or photofunctional films [42].…”

Synthesis and application of pillared clay heterogeneous catalysts for wastewater treatment: a review

“…Recently, PILCs have been dened as porous materials of the 21 st century and have attracted much attention from both academic and industrial research point of view. [68][69][70][71] Their high specic surface area, large micropore volume, upper acid site concentration, increased hydrophobicity and the increase in the density of sorption sites make them an excellent adsorbent and catalyst for removal of pollutants in wastewater. 4,71 The removal of contaminants present in wastewater streams generated by various industrial processes has emerged as a signicant concern during past decade.…”