Physical and Optical Properties of Inverse Opal CeO2 Photonic Crystals

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• 作者：Geoffrey I. N. Waterhouse ; James B. Metson ; Hicham Idriss ; Dongxiao Sun-Waterhouse
• 刊名：Chemistry of Materials
• 出版年：2008
• 出版时间：February 12, 2008
• 年：2008
• 卷：20
• 期：3
• 页码：1183 - 1190
• 全文大小：864K
• 年卷期：v.20,no.3(February 12, 2008)
• ISSN：1520-5002

文摘

Inverse opal ceria (CeO₂) films and powders, exhibiting three-dimensional ordered macroporous (3DOM) structures and a photonic band gap (PBG) in the visible region, were successfully fabricated using the colloidal crystal template approach. Colloidal crystals templates, comprising polymethylmethacrylate (PMMA) spheres of diameter ~325 nm arranged on a face-centered cubic (fcc) lattice, were prepared by self-assembly from aqueous colloidal suspensions of PMMA spheres. After drying, the interstitial spaces in the PMMA colloidal crystals were filled with a ceria sol–gel precursor, and then the resulting structure calcined at 400 °C to remove the polymer template. The ceria inverse opals obtained were characterized by SEM, XRD, BET, porosity, and UV–vis transmittance measurements and showed fcc ordering of macropores (diameter around 240 nm) within a CeO₂ nanocrystal matrix. The CeO₂ volume fraction in the inverse opals was 17–18 vol %, and its surface area was 51 m² g⁻¹. Both the PMMA colloidal crystals and CeO₂ inverse opals behaved as 3-dimensional photonic crystals, with PBGs at 877 and 485 nm, respectively. Filling the macropores of the CeO₂ inverse opal with solvent caused a redshift in the position of the PBG, with the magnitude of the shift being directly proportional to the refractive index of the solvent. Refractive index sensing with a sensitivity of n = 0.001 or better is achievable using inverse opal CeO₂ thin films. Inverse opal CeO₂ powders showed improved thermal stability at 800 °C compared to non-networked ceria nanoparticles of similar initial crystallite size and surface area, suggesting that inverse opal architectures may be useful in applications where retention of large surface area during high temperature operation is important (e.g., heterogeneous catalysis).