Supporting Information

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1 Supporting Information Synthesis, Anion Exchange, and Delamination of Co-Al Layered Double Hydroxide. Assembly of the Exfoliated Nanosheet/Polyanion Composite Films and Magneto-optical Studies Zhaoping Liu, Renzhi Ma, Minoru Osada, Nobuo Iyi, Yasuo Ebina, Kazunori Takada, Takayoshi Sasaki Advanced Materials Laboratory, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, , Japan Figure S1. FT-IR spectrum of the as-prepared Co-Al-CO 3 LDH sample. The strong peaks at 1356 and 790 cm 1 belong to the ν3 vibration and bending modes of CO 3 2, respectively. The broad band centered at 3440 cm 1 is assigned to the O H stretching modes of interlayer water molecules and of H-bonded OH groups. The presence of a shoulder at around 3080 cm 1 suggests that the water molecules are H-bonded to CO 3 2 in the interlayer. The weak band at 1607 cm 1 is due to the bending mode of water molecules. Other absorption bands below 800 cm 1 are associated with metal-oxygen (M-O) stretching and bending modes. sasaki.takayoshi@nims.go.jp S1

2 Figure S2. TG/DTG/DTA curves of the Co-Al-CO 3 LDH sample recorded in air atmosphere with the final decomposition product being Co 2 AlO 4 spinel. The TG/DTG curves display two very close stages of weight loss processes. The first one that took place up to 205 ÜC can be assigned to removal of interlayer water molecules and CO 2 (from intercalated CO 3 2 ). This assignment is reasonable since a weight loss of about 15.6% at this stage is in good agreement with the calculated one (15.7%) on the basis of the empirical formula, [Co 0.67 Al 0.33 (OH) 2 ][(CO 3 ) H 2 O]. Correspondingly, there is an intense endothermic peak at 192 ÜC in the DTA curve. The second weight loss stage, which is associated with a relatively weaker endothermic peak at 216 ÜC in the DTA curve, can be mainly attributed to the thermal decomposition of brucite-like layers through the removal of OH groups as water molecules. A weak and broad exothermic peak at around 880 ÜC is due to the crystallization process of the Co 2 AlO 4 spinel. The total weight loss (~31.3%) is in good agreement with the expected value (31.1%) for the estimated composition. Figure S3. SEM images of the Co-Al-CO 3 LDH samples prepared with various concentrations of total metal salts: (a) 60, (b) 30, (c) 7.5, and (d) 3 mm. Note that the molar ratio of Co 2+ /Al 3+ was fixed at 2/1. S2

3 Figure S4. SEM image of the sample prepared with a large excess of urea. Figure S5. (a) FT-IR spectrum of Cl -LDH obtained by treating the CO 3 2 -LDH with a NaCl-HCl mixed solution. In this spectrum, the absorption at 1356 and 790 cm 1 due to CO 3 2 ions disappeared, indicating thorough decarbonation. (b) TG curve of the Cl -LDH sample recorded in air atmosphere. The first stage of weight loss (8.1%) below 160 ºC is due to the removal of interlayer water molecules. The latter stages of weight loss can be assigned totally to the dehydroxylation and the removal of interlayer anions. The total weight loss (32.3%) is consistent with the calculated value (32.0%) on the basis of the empirical formula, [Co 0.66 Al 0.34 (OH) 2 ][Cl H 2 O]. Note that the final product was a spinel phase of Co 2 AlO 4 as revealed by XRD characterization. Figure S6. SEM images of Cl -LDH obtained by treating the CO 3 2 -LDH in a NaCl-HCl mixed solution. S3

4 Figure S7. FT-IR spectra of (a) NO 3 -, (b) ClO 4 -, (c) acetate-, (d) lactate-, (e) dodecylsulfate-, and (f) oleate-ldhs samples prepared by the anion-exchange process using the decarbonated LDH (Cl -LDH) as the precursor. The intense absorption peak at 1384 cm 1 in spectrum a is attributed to N-O stretching vibration mode of NO 3 ions. The sharp absorption bands in the range of cm 1 in spectrum b are characteristic of ClO 4 ions. The strong bands at 1560 and 1420 cm 1 in spectra c, d, and f are assigned to the stretching mode of the carboxyl (CO 2 ). In spectra e and f, the strong bands in the cm 1 region, at 2925 and 2853 cm 1, are due to the asymmetric and symmetric CH 2 stretching vibrations, respectively, in the alkyl chain of dodecylsulfate and oleate, while the relatively weak band at 2955 cm 1 is due to the stretching vibration of the terminal CH 3 group of the hydrocarbon tail; the band occurring near 1470 cm 1 in the spectra arises from the CH 2 bending (or scissor) mode. In addition, the series of absorbance bands in the range of cm 1 in spectrum e are due to the stretching mode of sulfate (OSO 3 ). These features clearly indicate the incorporation of these anions. S4

5 Figure S8. SEM images of (a) NO 3 -, (b) ClO 4 -, (c) acetate-, (d) lactate-, (e) dodecylsulfate-, and (f) oleate-ldhs samples prepared by the anion-exchange process using the decarbonated LDH (Cl -LDH) as the precursor. The mean platelet thicknesses of acetate-, lactate-, dodecylsulfate-, and oleate-ldhs were estimated to be about 50, 60, 100, and 120 nm, respectively. S5

6 Figure S9. Low- and high-magnification SEM images of (a, b) the gel-like sample obtained by mixing 0.1 g of Co-Al-NO 3 LDH with 0.75 cm 3 of formamide, and (c, d) the particles recovered by dispersing such a gel-like sample in water. Figure S10. XRD pattern of the sample recovered by treating the gel-like sample with a copious amount of water. Inset is a magnified view of the pattern in the high angular region. Note that the gel-like sample was obtained by mixing 0.1 g of NO 3 -LDH (d 003 = 0.89 nm) with 0.75 cm 3 of formamide. S6

7 Figure S11. Tapping-mode AFM images of the nanosheets that were derived from (a) Cl -, (b) ClO 4 -, (c) acetate-, and (d) dodecylsulfate-ldh samples. Figure S12. UV-vis absorbance spectra of multilayer film of (LDH/PSS) n assembled on a quartz glass substrate, which were measured after each ten cycles. Nanosheet concentration was 0.5 g dm 3 ; PSS concentration was 1.5 g dm 3 ; Deposition periods in nanosheet suspension and PSS solution were 10 and 15 min, respectively. The observed absorbance at 193 nm is plotted against the number of deposition cycles in the inset. S7