Alternative etching methods to expand nanocasting, and use in the synthesis of hierarchically porous nickel oxide, zinc
- PDF / 388,245 Bytes
- 7 Pages / 584.957 x 782.986 pts Page_size
- 114 Downloads / 193 Views
Jan-Henrik Smått Center for Functional Materials and Laboratory of Physical Chemistry, Åbo Akademi University, Porthansgatan 3-5, FIN-20500, Turku, Finland
Martin G. Bakkerb) Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487-0336 (Received 1 February 2013; accepted 8 May 2013)
Nanocasting into silica templates for preparation of mesoporous materials has up to now been limited to those metal oxides and metals that can withstand the harsh silica etching processes currently used. Two new methods of removing the silica template are reported, either by dissolving the silica in methanolic base or by dissolution in aqueous base under an external potential. The utility of these methods is demonstrated in the synthesis of hierarchically porous zinc oxide, nickel oxide, and copper monoliths that would dissolve or react using other template removal methods. The successful etching of monolithic zinc oxide using methanolic base etching can be explained by the reduced solubility of zinc oxide in methanol compared with an aqueous base, while it also reduces the formation of hydroxides when etching the nickel oxide and copper monoliths. Alternatively, the formation of highly soluble copper oxide/hydroxide can be avoided by holding the copper monolith at a sufficiently negative potential while etching with an aqueous base.
I. INTRODUCTION
Hierarchically porous materials are of great interest for various applications such as catalysis, advanced batteries, and solar cells.1,2 Currently, there are several classes of these materials available, such as metal foams,3 aerogels, xerogels,4 and a variety of materials produced by spinodal decomposition.5 These materials are produced by direct synthesis from precursors. For many materials for which no direct templating method is available, it is often possible to produce them by nanocasting.6–13 Nanocasting uses a hard template, usually either silica or carbon, as a mold for another material. The mold is then removed leaving a replica. For hierarchically porous materials, it is possible to replicate only the mesoscale structure, giving a negative replica at the mesopore level and positive replica at the macropore level of the original structure. Typical synthesis methods for hierarchically porous materials yield powders. However, a monolithic form consisting of a macroscopic single piece is advantageous in some applications. In catalysis, a monolithic form allows
a)
Present Address: ThruPore Technologies LLC, Box 870204, Tuscaloosa, AL 35487-0204 b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.153 J. Mater. Res., Vol. 28, No. 17, Sep 14, 2013
http://journals.cambridge.org
Downloaded: 12 Mar 2015
for easy separations of products from the catalyst,14 and in separations, hierarchically porous stationary phases are significantly faster than traditional packed columns.15,16 We have demonstrated the use of nanocasting to produce hierarchically porous monoliths of carbon,17 metal oxides,18 and most recently some metals
Data Loading...
