Synthesis of Thick Mesoporous γ-Alumina Films, Loading of Pt Nanoparticles, and Use of the Composite Film as a Reusable Catalyst

Abstract

Nanocrystalline mesoporous gamma-Al2O3 film of high thickness has been developed and characterized. The films were prepared on ordinary glass substrates by a single dip-coating method using boehmite (AlOOH) sols derived from aluminum tri-sec-butoxide in presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent. The dried films were heat-treated at 500 degrees C in air to remove the organics and strengthen the network. The GIXRD of the heat-treated (500 degrees C) film shows a broad peak in the low-angle region supporting the formation of worm-hole-like disordered mesostructures. The high-angle GIXRD, FTIR, and TEM of the films confirm the formation of gamma-Al2O3. N2 adsorption-desorption analyses showed that the heat-treated (500 degrees C) film has a BET surface area of 171 m(2) g(-1) with a pore volume of 0.188 cm(3) g(-1) and mean pore diameter 4.3 nm. Pt nanoparticles (NPs) (approximately 2.7 mol % with respect to the equivalent AlO(1.5)) were generated inside the mesopores of the heat-treated films simply by soaking H2PtCl6 solutions into it, and followed by thermal decomposition at 500 degrees C. The surface area and pore volume of the Pt-incorporated film have been reduced to 101 m(2) g(-1) and 0.119 cm(3) g(-1) respectively, confirming the inclusion of Pt NPs inside the pores. FESEM and TEM studies revealed uniform distribution of Pt NPs (2-8.5 nm; average diameter 4.9 nm) in the films. Catalytic properties of the Pt-incorporated films were investigated in two model (one inorganic and other organic) systems: reduction of hexacyanoferrate(III) ions by thiosulfate to ferrocyanide, and p-nitrophenol to p-aminophenol. In both the cases, the catalyst showed excellent activities, and the reduction reactions followed smoothly, showing isosbestic points in the UV-visible spectra. The catalyst films can be separated easily after the reactions and reused several times.

Mesoporous Colloidal Superparticles of Platinum‐Group Nanocrystals with Surfactant‐Free Surfaces and Enhanced Heterogeneous Catalysis

“…To solve this problem, supporting substrates such as polymers, carbon compounds, silica, or alumina are usually used to prevent aggregation of nanoparticle catalysts. [ 34 ] However, the supporting substrates would block partial surfaces of the catalysts and may involve in the reactions to infl uence the catalytic performance. [ 35 ] In addition, the catalytic activity of Pt nanoparticles also depends on how the Pt nanoparticles are immobilized on the supporting substrates.…”

Reduction of 4‐Nitrophenol as a Model Reaction for Nanocatalysis

“…In the case of the SiO 2 support surface, Au NPs gradually detach and form large aggregates, which dramatically reduce active surface areas. [88,108] A thick, nanocrystalline, mesoporous γ-Alumina fi lm has been employed on glass substrates as a support material for Pt NPs [108] (Figure 13.32).…”

“…Furthermore, their large-scale application is hindered by a reduction in catalytic activity due to particle aggregation. To overcome these disadvantages, metal nanocomposite catalysts have been immobilized onto solid supports such as inorganic oxide [89,90,93,100,106,109,110], ion exchange resins [70,71,87], alumina [88,108], titania [11], polymer microspheres [78,91,[97][98][99], polystyrene [5,72,76,77,79,92,96,104,105], nanotubes [103], carbon spheres [101,102], and biomolecule beads [58]. Th ese supports must not take part in the catalytic mechanism, i.e., they must be inert.…”

Two New Fluorogenic Aptasensors Based on Capped Mesoporous Silica Nanoparticles to Detect Ochratoxin A

“…From another point of view, nanomaterials for sensing applications have played a great role in recent years due to their capacity to provide rapid, simple, and sensitive responses to target analytes . Moreover, of the nanomaterials used in sensing protocols, mesoporous silica nanoparticles (MSNs) have been widely employed due to some of their remarkable properties, such as large load capacity and the possibility to modify their surface easily with several groups due to the presence of silanol groups (SiOH), which have excellent reactivity . Moreover, MSNs can be functionalized with different (bio)molecules that can act as “molecular gates” to obtain hybrid gated organic–inorganic capped supports for the design of systems able to release an entrapped payload upon the application of specific stimuli .…”