Fabrication of Metal and Metal Oxide Sponges by Self-Bubbled Triton X-45 Hydrogel Templates Farid Khan † and Stephen Mann* ,‡ Nanomaterials Laboratory, Department of Chemistry, Dr HariSingh Gour UniVersity, Sagar- 470003, India, and Centre for Organized Matter Chemistry, School of Chemistry, UniVersity of Bristol BS 8 1 TS, U.K. ReceiVed: August 06, 2009; ReVised Manuscript ReceiVed: September 15, 2009 Triton X-45 was used as a sacrificial template to synthesize macroporous Ag, Au, or CuO monoliths via thermal treatment. Continuous networks of pores with sizes varied from 100 nm to 6 μm can be prepared through the use of additives such as dextran, silica nanoparticles, and the swelling agent, 1,3,5 trimethylbenzene (TMB), suggesting that the use of Triton X-45 gel offers a versatile route to the preparation of intact inorganic structures with controllable morphology. Introduction Porous materials have been used extensively in molecular catalysis, biosensor technology, photonic crystals, gas absorp- tion, drug delivery, and nanoreactors. 1-4 The fabrication of macroporous materials requires microstructural templates such as colloidal crystals, which have been chemically infiltrated with a range of precursors to produce metal oxide or metallic monoliths with ordered micrometre scale porosity. 5 Recently, an alternative approach based on the use of a range of soft templates has been developed to prepare macroporous monoliths. For example, dextran hydrogels have been used to promote the thermally induced assembly of porous scaffolds of Ag, Au, CuO, and Fe oxide 6 and porous networks of Au beads prepared using emulsion-templated polymers. 7 Porous materials have also been synthesized in the presence of poly (ethyleneimine) hydrogels 8 and open-framework TiO 2 monoliths prepared using 1-buty-3 methyllimidazolium tetrafluoroborate 9 or starch gels as tem- plates. 10 Porous Ag monoliths have also been synthesized using a silica hydrogel as a templating agent. 11 In most cases, the monoliths exhibit disordered arrangements of macropores that are produced by thermally induced outgassing of the organic template in conjunction with localized deposition of the inorganic phase. In this paper, we report the use of gels of the surfactant Triton X-45 for the preparation of porous networks of Ag, Au, or CuO and investigate the influence that various additives, such as dextran, silica nanoparticles (Ludox), and the swelling agent 1,3,5 trimethylbenzene (TMB) 12 have on the fabrication process. Experimental Section Synthesis of Silver Sponges. Silver monoliths were prepared as follows. AgNO 3 (2.4 g, 54.54 wt %, 7.06 M, BDH) was dissolved in 2 g of distilled water (45.45 wt %) and added to 2.4 g of Triton X-45 (Fluka) at room temperature. The mixture was stirred for 10 min to form a gel which gradually became dark in color. The resulting gel was aged for 48 h at room temperature and then calcined at 600 °C for 2 h at a heating rate of 1 °C/min, followed by cooling at a rate of 1 °C/min to room temperature in a Carbolite EFl furnace. Ag/Triton X-45/dextran (M w ) 2 × 10 6 , Fluka), Ag/Triton X-45/Ludox (As-40, colloidal silica, 40 wt % suspension in water, Sigma-Aldrich) and Ag/Triton X-45/TMB (Fluka) mono- liths were prepared using the above protocol by adding 2.4 g of dextran (2.6 × 10 4 M, 34.87 wt %) in 4.5 g of water (65.22 wt %), 0.21 g of Ludox (4.03 × 10 2 M, 40 wt %), or 2.6 g of TMB (7.2 M, 86.5 wt %) separately to Ag/Triton X- 45 gel. The dextran- and TMB-containing gels were calcined at 600 °C with the above heating and cooling rates, whereas the Ag/ Triton X-45/Ludox gel was calcined at 800 °C for 2 h with heating and cooling rates of 2 °C/min. The calcined Ludox monolith was treated with 30% HF (Sigma, Aldrich) for 36 h, followed by repeated washing with water to remove silica from the monolith. Synthesis of Gold Sponges. Au/Triton X-45/dextran mono- liths were prepared by dissolving 2 g of AuCl 3 (Aldrich 99.99%) (21.67 M, 6.66 wt %) in 28 g of water (93.33 wt %) and adding 5.17 g of Triton X-45, followed by a paste of dextran prepared * To whom correspondence should be addressed. E-mail: s.mann@ bris.ac.uk. † Dr HariSingh Gour University. ‡ University of Bristol. Figure 1. SEM micrographs of Ag macroporous scaffolds prepared using Triton X-45 gel templates. Monoliths were prepared by calcination of (a) Ag/Triton X-45 gel, showing pores, 1-1.5 μm in size; scale bar ) 2 μm. (b) Ag/Triton X-45/dextran gel, showing increased pore sizes of 2-6 μm; scale bar ) 5 μm. (c) Ag/Triton X-45/Ludox gel after HF treatment, showing reduced pores sizes of 200-300 nm; scale bar ) 1 μm. (d) Ag/Triton X-45/TMB gel with wide range of pore sizes, from 1 to 3 μm; scale bar ) 5 μm. J. Phys. Chem. C 2009, 113, 19871–19874 19871 10.1021/jp9076068 CCC: $40.75  2009 American Chemical Society Published on Web 10/13/2009