Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

Abstract

Palladium colloidal nanoparticles with an average size of approximately 2.4 nm have been incorporated into mesoporous inorganic thin films following a multistep approach. This involves the deposition of mesoporous titania thin films with a thickness of 200 nm by spin-coating on titanium plates with a superhydrophilic titania outer layer and activation by calcination in a vacuum furnace at 573 K. Nanoparticles have been confined within the porous titania network by dip-coating noble metal suspensions onto these mesoporous thin films. Finally, the resulting nanoconfined systems were used as substrates for the growth of oriented carbon nanotubes (CNTs) using plasma-enhanced chemical vapour deposition at 923 K in order to enhance their surface area. These CNTs were tested in the hydrogenation of phenylacetylene by hydrogen in a batch reactor. The initial reaction rate observed on a CNT/TiO 2 structured catalyst was considerably higher than that on 1 wt% Pd/TiO 2 thin films.

Block copolymer-templated synthesis of highly organized mesoporous TiO2-based films and their photoelectrochemical applications

“…Concentrated hydrogen chloride (HCl, 35-37 wt%) with a HCl/Ti molar ration of 1.6-2.0 is most commonly employed to control the hydrolytic reactivity of titanium alkoxides [16,[44][45][46][47][48]. Other acids, sulfuric acid [49], nitric acid [50][51][52], phosphoric acid [53,54], and acetic acid [14,55,56], have also been used in stabilizing Ti precursor in order to eliminate the accommodation of Cl − in resulting films.…”

“…Currently various heat-resistant substrates such as Pyrex glass [16,17,45,66], fused silica [51], transparent conductive oxide (TCO) [67][68][69][70][71], quartz [46], stainless steel [72][73][74], Ti foil [50], and silicon [15,75,76] have been employed for film deposition. The nature of coating substrates, particularly the surface roughness, has found to exert an influence on the mesostructural regularity of the mesoporous TiO 2 films [77].…”

“…Other applications, such as chemical energy storage (e.g. Li ion batteries [43,62] and supercapacitors [41]), luminescent devices [34,109,117], drug delivery [118], and advanced materials design [50], will not discussed in present review and interested readers can refer the related literature directly.…”

“…In addition, mesoporous Pd/TiO 2 films presented extended stability in catalytic activity without any reclaiming and reactivation. Catalytic tip-growth of carbon nanotubes in the presence of Pd nanoparticles was further developed to increase the surface area as well as the selectivity of the mesoporous Pd/TiO 2 films [50]. This methodology also has been extended to other metal nanoparticles and catalytic reactions, including bimetal, Pt 90 Sn 10 [108] in association with the hydrogenation of MBY (2-methyl-3-butyn-2-ol), Au [52] and Pd 25 Zn 75 [150] for the hydrogenation of citral, and Au for low-temperature water-gas shift (WGS) reaction [151].…”

Ordered Porous Nanomaterials: The Merit of Small

“…This method may be found in the literature with other names such as nanocasting [205,225,226], exotemplating [227], or repeated templating method [207]. Porous Al 2 O 3 supports prepared by anodic oxidation (AAO or anodized aluminium oxide) [228,229] were used initially as a mold to prepare carbons, metals, or other nanostructures by a variety of techniques such as electrodeposition [230], Chemical Vapour Deposition (CVD) [231][232][233], Plasma-Enhanced Chemical Vapour Deposition (PE-CVD) [234], or Atomic Layer Deposition [235]. The resulting materials have a pore size ranging from a few nanometers to several tens of nanometers.…”