Porous Aerogels from Shape-Controlled Metal Nanoparticles Directly from Nonpolar Colloidal Solution

Abstract

Porous architectures of noble metal nanocrystals are promising for many catalytic as well as for fuel cell applications. Here we present the synthesis of porous, extremely lightweight aerogels of self-supported Pt nanocubes and nanospheres by direct destabilization from nonpolar colloidal solution using hydrazine monohydrate (N 2 H 4 •H 2 O) as gelation reagent. The template-free voluminous lyogels of the Pt nanocrystals are converted to macroscopic solid aerogel monoliths by supercritical drying. The aerogels from Pt nanocubes mostly exhibit (100) as the exposed crystal facets throughout the entire monolithic surface, while the aerogels from quasispherical Pt nanocrystals exhibit many crystal facets such as ( 111) and (100). Furthermore, the aerogels exhibit remarkably low densities of ∼0.19 g cm −3 ± 0.038 g cm −3 (∼0.9% of bulk Pt) and a specific surface area in the range of ∼6400−7000 m 2 mol −1 . The nanocube gels show better catalytic performance than the nanosphere gels when employed for asymmetric hydrogenation reaction, which is exemplarily shown for 4,4-dimethyldihydrofuran-2,3-dione to D-/L-pantolactone conversion with an excess of 9% for the D-enantiomer. Owing to their high specific surface area and certain type of exposed crystal facets, Pt aerogels developed here are highly promising for possible future applications in facet selective catalytic reactions.

Back Cover: Freeze–Thaw‐Promoted Fabrication of Clean and Hierarchically Structured Noble‐Metal Aerogels for Electrocatalysis and Photoelectrocatalysis (Angew. Chem. Int. Ed. 21/2020)

“…[36] Furthermore,h ierarchically structured pores,which are mainly made up of mesopores (2-50 nm, seen from the pore size distribution) and macropores (> 50 nm, seen from SEM and TEM observations), were found to afford substantially large Brunauer-Emmett-Teller (BET) surface areas (83.6 and 74.5 m 2 g À1 )and pore volumes (0.526 and 0.475 cm 3 g À1 )f or the Au-Pd and the Au-Pt aerogels,r espectively (Supporting Information, Figure S16, Table S1). These SSAs are larger than those of most reported NMAs (10-50 m 2 g À1 ) [11,13,14,20,28,37,38] and only smaller than af ew,s uch as the Pd aerogels prepared by Ca 2+ crosslinking (40-108 m 2 g À1 ), [39] Au-Pd-Pt aerogels prepared by salting-out method (122.7 m 2 g À1 ), [15] and the hierarchical silver aerogels prepared by (C(NO 2 ) 4 -mediated oxidation (43-160 m 2 g À1 ) (Supporting Information, Table S2). [16] Thesynergy of alarge specific surface area and al arge pore volume can concurrently provide abundant active sites and fast mass-transfer channels,which will be beneficial for catalytic applications as will be detailed in the next section.…”

“…wet gel ! aerogel, where the core lies in the sol-gel step.T he majority of NMAs are created following this approach, producing widespread materials with tailored ligament sizes (that is,t he diameter of the primary nanowires in the gel network), compositions,a nd microstructures.H owever,p reparing wet gels usually requires extra additives (such as dopamine,salts,ligands,oroxidants [12][13][14][15][16][17][18] )orelevated temperatures, [19,20] thus introducing various impurities or forming less-controlled microstructures.A dditionally,l ong gelation times (up to af ew weeks) and tedious procedures (such as ultracentrifugation) are also frequently encountered, thus impeding the material preparation. [11,21] Moreover,a ne fficient structure control over multiple scales,for example,from nanometers to micrometers,isstill in absence.…”

Patterning of Nanoparticle‐Based Aerogels and Xerogels by Inkjet Printing

“…photocatalysis, electrocatalysis, and photo‐electrochemical application like sensing . By controlling the destabilization process of the nanocrystals, it is possible to obtain nanoparticle networks in which the nanoparticles are connected to each other in a defined way . Nevertheless, there is a lack of possible techniques for forming these highly porous 3D aerogels into defined macroscopic shapes and patterns on conducting surfaces to make them suitable for spectro‐electrochemical measurements or sensing application.…”

Engineering Self‐Supported Noble Metal Foams Toward Electrocatalysis and Beyond

“…For NMAs, their extreme fragileness often poses difficulties in obtaining a regular shape, resulting in only a rough estimation of volumes and thus the corresponding densities. It is worth mentioning that certain work used tapped‐like density to characterize ρ a , where the volume of the aerogel is determined by inserting aerogel pieces into regular‐shaped vials . However, since significant unoccupied spaces could be generated due to imperfect stacking of those pieces, the volume can be largely overestimated.…”

“…It is worth mentioning that certain work used tapped-like density to characterize ρ a , where the volume of the aerogel is determined by inserting aerogel pieces into regular-shaped vials. [37] However, since significant unoccupied spaces could be generated due to imperfect stacking of those pieces, the volume can be largely overestimated. Thus far, the density estimation needs special care and is more convincing when measuring a monolithic aerogel with a relatively regular shape.…”