Materials Science

Mesoporous Oxides via Carbonates

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Science  23 Aug 2013:
Vol. 341, Issue 6148, pp. 823
DOI: 10.1126/science.341.6148.823-a

Mesoporous oxide materials have potential applications in light harvesting and catalysis and as electrode materials. Thin films of these materials are most often formed through a soft-templating process in which a precursor gel is patterned by nanoscale micelles that form from diblock copolymers during solvent evaporates. This route has proven difficult with some oxides, notably zinc oxide (ZnO) and cobalt oxide (Co3O4), because of problems with the three main types of precursors (alkoxides, nanoparticles, and thermally decomposed precursors). Eckhardt et al. show that both mesoporous zinc and cobalt oxides can be formed from soft templates by first forming mesoporous metal carbonates. These materials were formed with triblock poly(ethylene) oxide (PEO)–poly(butadiene) (PB) copolymer (PEO-PB-PEO) micelles and used metal nitrates and citric acid in mixed ethanolwater solvent as the precursor. This solution was dip-coated on substrates at room temperature and then heated for 1 hour at 250°C for zinc and 200°C for cobalt to form the carbonates. Additional heating (25 min at 400°C for zinc and 20 min at 300°C for cobalt) formed the oxides. For zinc, the amorphous wall of the mesoporous carbonate transformed into the crystalline oxide and increased the surface area. For cobalt, the carbonate appeared to retain the micelle template, and mesoporosity developed only in the final thermal processing step as spinel oxide phase walls formed.

Chem. Mater. 25, 2749 (2013).

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