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Supporting Information for “Highly Efficient Visible Light-Induced O2 Generation by Self-Assembled Nanohybrids of Inorganic Nanosheets and Polyoxometalate Nanoclusters” Jayavant L. Gunjakar, Tae Woo Kim, In Young Kim, Jang Mee Lee, and Seong-Ju Hwang* Center for Intelligent Nano-Bio Materials (CINBM), Department of Chemistry and Nano Sciences, Ewha Womans University, Seoul 120-750, Korea Figure S1│Structural study. Powder XRD patterns of the (a) ZCV-1, (b) ZCV-2, (c) ZCW-1, and (d) ZCW-2 nanohybrids calcined at 300 °C. : The effect of calcination at 300 C on the crystal structure of the as-prepared Zn-CrLDHPOM nanohybrids is examined with powder X-ray diffraction (XRD) analysis. As plotted in Fig. S1, all the present nanohybrids calcined at 300 C commonly show the suppression of a series of intense (00l) peaks at low angle region with a broad hump feature at 2 = 3040. The disappearance of the (00l) reflections corresponding to basal planes strongly suggests the destruction of intercalation structure after calcination at 300 C. However, even with the absence of (00l) reflections, the in-plane (110) peak is still discernible at 2 = ~62 for all the present nanohybrids calcined at 300 C. This observation demonstrates that, despite the frustration of the pillared structure, a fraction of the Zn-Cr-LDH nanosheets is still maintained upto 300 C. Figure S2│ XANES spectroscopy. (a) Zn K-edge and (b) Cr K-edge XANES spectra of the asprepared nanohybrids of (i) ZCV-1, (ii) ZCV-2, (iii) ZCW-1, (iv) ZCW-2, (vviii) their derivatives calcined at 200 C, (ix) the pristine Zn-Cr-LDH, (x) ZnO/Cr2O3, and (xi) CrO3. (c) W LIII-edge and (d) V K-edge XANES spectra of the as-prepared nanohybrids of (i) ZCW-1/ZCV1, (ii) ZCW-2/ZCV-2, (iiiiv) their derivatives calcined at 200 C, (v) WO2/V2O4, Na2WO4·2H2O/V2O5, and (vii) V2O3. (vi) Figure S3│ XANES spectroscopy. (a) Zn K-edge and (b) Cr K-edge XANES spectra of the asprepared nanohybrids of (i) ZCV-1, (ii) ZCV-2, (iii) ZCW-1, (iv) ZCW-2, (vviii) their derivatives calcined at 300 C, (ix) the pristine Zn-Cr-LDH, (x) ZnO/Cr2O3, and (xi) CrO3. (c) W LIII-edge and (d) V K-edge XANES spectra of the as-prepared nanohybrids of (i) ZCW-1/ZCV1, (ii) ZCW-2/ZCV-2, (iiiiv) their derivatives calcined at 300 C, (v) WO2/V2O4, Na2WO4·2H2O/V2O5, and (vii) V2O3. (vi) : The effects of hybridization and heat-treatment on the local crystal and electronic structures of the host Zn-Cr-LDH material are investigated with XANES spectroscopy at Zn K-edge and Cr K-edge. The Zn K-edge XANES spectra of the as-prepared ZCW and ZCV nanohybrids and their calcined derivatives are plotted in Fig. S2a, as compared with those of the pristine Zn-CrLDH and bulk ZnO. The as-prepared ZCW and ZCV nanohybrids as well as the pristine Zn-CrLDH exhibit nearly identical edge positions to that of ZnO, indicating the divalent oxidation state of zinc ions in these compounds. Like the pristine Zn-Cr-LDH compound, all of the asprepared ZCW and ZCV nanohybrids display a broad and intense main-edge peak A, a typical spectral feature of the Zn-containing LDH compound.[1,2] This strongly suggests that the layered lattice of the Zn-Cr-LDH nanosheets remains intact after the hybridization with POM nanoclusters. For all the present Zn-Cr-LDHPOM nanohybrids, the heat-treatment at 200 C gives rise to only a negligible spectral variation, indicating the maintenance of the Zn-Cr-LDH lattice upon calcination at this temperature. As shown in Fig. S3a, the calcination of the asprepared nanohybrids at 300 C does not induce a marked change of the edge energy, indicating the maintenance of divalent Zn oxidation state after the heat-treatment. In contrast to the reference ZnO, the ZCW and ZCV nanohybrids calcined at 300 C commonly exhibit the poorly resolved XANES features in the energy region of 9660–9670 eV, strongly suggesting the maintenance of Zn-Cr-LDH nanosheets. However, in comparison with the spectra of the asprepared nanohybrids, the present spectra of the 300 C-calcined materials display a significant broadening of the peak A, reflecting the increase of structural disorder upon the calcination process. The variation of POM content in the present nanohybrids has little influence on the overall spectral features of the present nanohybrids, confirming negligible influence of guest POM species on the local atomic arrangement of host Zn-Cr-LDH lattice. Fig. S2b represents the Cr K-edge XANES spectra of the Zn-Cr-LDHPOM nanohybrids and their calcined derivatives, as compared with several reference spectra. All of the present materials show a pre-edge peak P corresponding to the dipole-forbidden 1s 3d transition, whose intensity reflects sensitively the local structure and oxidation state of chromium ions.[3] While a very intense pre-edge peak P is observable for the reference CrO3 compound with tetrahedral Cr6+ ion, all the Zn-Cr-LDHPOM nanohybrids and the pristine Zn-Cr-LDH exhibit only a weak intensity for the pre-edge peak P. This finding clearly demonstrates the presence of Cr3+ ions in octahedral geometry for all the present nanohybrids, like the pristine Zn-Cr-LDH.[1] All the present materials display several main-edge peaks A, B, and C, which are assigned as dipole-allowed transitions from 1s orbital to unoccupied 4p ones. These main-edge spectral features of the pristine Zn-Cr-LDH compound remain nearly unchanged upon the self-assembly with POM nanoclusters and the heat-treatment at 200 C, underscoring the maintenance of the Zn-Cr-LDH nanosheets after the hybridization and calcination processes. As shown in Fig. S3b, the edge position of the nanohybrids calcined at 300 C remains nearly the same as that of the reference Cr2O3, confirming the maintenance of trivalent oxidation state of chromium ions. In contrast to the edge energy, the heat-treatment at 300 C induces significant spectral variations like the appearance of the additional pre-edge peak P' and the main-edge feature A, as observed in the reference Cr2O3. This finding reveals the transformation of the local structural environment of chromium ions to the Cr2O3-type structure. Like Zn K-edge XANES spectra, there is no significant change in Cr K-edge spectra upon the change of POM content, confirming that the amount of guest POM species has little influence on the chemical bonding nature of the host Zn-Cr-LDH lattice. The local symmetry and oxidation state of guest POM nanoclusters in the present Zn-CrLDHPOM nanohybrids and their calcined derivatives are also examined using XANES analysis at W LIII-edge and V K-edge. The W LIII-edge XANES spectra of the as-prepared ZCW nanohybrids and their derivatives calcined at 200 and 300 C are plotted in Figs. S2c and S3c, as compared with those of references WO2 and Na2WO4·2H2O. All of the present materials show broad and intense white-line peak A corresponding to dipole-allowed transitions from the 2s level to unoccupied 5d states.[4,5] Considering the fact that W 5d orbitals are separated into t2g (or e) and eg (or t2) orbitals under an octahedral (or tetrahedral) crystal field, the observed broad peak A consists of overlapped features related to 2s 5dt2g (or 5de) and 2s 5deg (or 5dt2) transitions. Since the crystal field of tetrahedral symmetry is weaker than that of the octahedral one,[47] the reference Na2WO4·2H2O with tetrahedral WO4 unit shows a narrower full-width-athalf-maximum (FWHM) for the peak A than the reference WO2 with WO6 octahedral units. Both the ZCW nanohybrids display broader FWHM than Na2WO4·2H2O, confirming the maintenance of the octahedral symmetry of W7O246 nanoclusters in the ZCW nanohybrids. Upon the heattreatment at 200 and 300 C, there is no remarkable change in the spectral feature of the asprepared nanohybrids, indicating negligible change of chemical bonding nature of polyoxotungstate nanoclusters even with the collapse of intercalation structure. The V K-edge XANES spectra of the as-prepared ZCV nanohybrids and their derivatives calcined at 200 and 300 C are plotted in Fig. S2d and S3d, as compared with the reference spectra of V2O4, V2O5, and V2O3. All of the present materials display not only a pre-edge peak P corresponding to the 1s 3d transition but also main-edge peaks A, B, and C corresponding to the 1s 4p transitions. The intensity of the pre-edge peak P is much stronger for the ZCV nanohybrids than for the corundum-structured V2O3 containing VO6 octahedra. Since the intensity of this pre-edge peak P is proportional to the deviation of local symmetry from centrosymmetric octahedral one,[8,9] the observed high intensity of the pre-edge peak for the ZCV nanohybrid strongly suggests the non-centrosymmetric local environment of vanadium ions in these materials. All of the present ZCV nanohybrids exhibit similar positions of the mainedge peaks A, B, and C, which are similar to those of V2O5 but higher than those of V2O4. This result provides strong evidence for the pentavalent oxidation state of vanadium ions in these materials. The observed V K-edge XANES spectra of the present ZCV nanohybrids are fairly similar to the previously reported data of n-hexylammonium decavanadate (n- C6H13NH3)6(V10O28)∙2H2O, confirming the stabilization of decavanadate nanoclusters in the present nanohybrid materials.[810] The heat-treatments at 200 and 300 C have little influence on the overall spectral feature of the as-prepared nanohybrids, indicating the maintenance of the decavanadate nanoclusters after the calcination process. Figure S4│ Surface morphological study of nanohybrids calcined at 300 °C. FE-SEM images of the (a) ZCW-1, (b) ZCW-2, (c) ZCV-1, and (d) ZCV-2 nanohybrids. : The crystal morphology of the Zn-Cr-LDHPOM nanohybrids calcined at 300 C are probed with field emission-scanning electron microscopy (FE-SEM) analyses. As illustrated in the Fig. S4, the heat-treatment at 300 C has little influence on the porous stacking structure and highly anisotropic 2D shape of the LDH–POM nanohybrids, underscoring the high morphological stability of these materials. Figure S5│ EDS–elemental mapping analysis of the as-prepared Zn-Cr-LDH–POM nanohybrids and their calcined derivatives. EDS–elemental maps and (center) FE-SEM images of the (a) ZCW-1, (b) ZCW-2, (c) ZCV-1, and (d) ZCV-2 nanohybrids. The data in the left, middle, and right columns represent the FE-SEM images of the as-prepared nanohybrids and their derivatives calcined at 200 and 300 °C, respectively. Figure S6│HRTEM EDS–elemental line profile. (a) ZCW-1 and (b) ZCV-1 nanohybrids; red (zinc), cyan (chromium), violet (oxygen), and green (tungsten/vanadium). : The spatial distributions of component elements in the as-prepared Zn-Cr-LDHPOM nanohybrids and their calcined derivatives are examined with EDSelemental mapping analysis. As illustrated in the Fig. S5, all of the component elements, i.e. zinc, chromium, tungsten, vanadium, and oxygen, are uniformly distributed in entire parts of the as-prepared nanohybrid materials, clearly demonstrating the homogeneous hybridization of the Zn-Cr-LDH nanosheets and POM nanoclusters without any phase separation. The special elemental distributions of ZCW-1 and ZCV-1 nanohybrids are also investigated with elemental EDS line profile using EDS machine installed with HR-TEM. As illustrated in Fig. S6, the elemental EDS line profiles of the both nanohybrids clearly demonstrate the homogeneous distribution of zinc, chromium, tungsten, vanadium, and oxygen elements along the lines centered in the crystallites of the both nanohybrids. The heat-treatments at 200 and 300 C give rise to only a negligible frustration in the elemental distribution of the as-prepared ZnCr-LDHPOM nanohybrids, confirming the maintenance of intimate mixing between the two components after calcinations. This finding provides strong evidence for no occurrence of any phase separation upto 300 C. ICP spectrometry and CHNS elemental analysis for the Zn-Cr-LDH–POM nanohybrids. : The chemical compositions of the Zn-Cr-LDH–POM nanohybrids are quantitatively determined with ICP and CHNS elemental analyses. The CHNS analysis reveals the presence of nitrogen element in all the present nanohybrids, suggesting the incorporation of nitrate ions as a charge compensator. Based on the ICP and CHNS elemental analysis, the chemical compositions of the as-prepared Zn-Cr-LDH–POM nanohybrids Zn0.64Cr0.36(OH)20.057(W7O39)0.89H2O0.09NO3, 0.07NO3, are determined to be Zn0.68Cr0.32(OH)20.076(W7O39)0.15H2O Zn0.66Cr0.33(OH)20.056(V10O28)0.80H2O0.09NO3, and Zn0.64Cr0.36(OH)2 0.061(V10O28)1.00H2O0.10NO3 for ZCW-1, ZCW-2, ZCV-1, and ZCV-2, respectively. This result clearly demonstrates the tunability of the chemical composition of the present Zn-CrLDH–POM nanohybrid materials synthesized by the self-assembly method. Figure S7│ N2 adsorption–desorption isotherm measurement for the calcined derivatives of the Zn-Cr-LDH–POM nanohybrids. N2 adsorptiondesorption isotherms of the (a) ZCW-1, (b) ZCW-2, (c) ZCV-1, and (d) ZCV-2 nanohybrids calcined at 300 °C. Table S1. BET surface area of the Zn-Cr-LDHPOM nanohybrids calcined at 200 and 300 C Sample BET area (m2g1) Sample BET area (m2g1) ZCW-1 calcined at 200 C 48 ZCV-1 calcined at 200 C 128 ZCW-1 calcined at 300 C 37 ZCV-1 calcined at 300 C 89 ZCW-2 calcined at 200 C 70 ZCV-2 calcined at 200 C 133 ZCW-2 calcined at 300 C 57 ZCV-2 calcined at 300 C 91 : The surface area and pore structure of the Zn-Cr-LDHPOM nanohybrids calcined at 300 C is investigated with N2 adsorptiondesorption isotherm measurements. As shown in Fig. S7, the heat-treatment at 300 C causes a significant weakening of the hysteresis, indicating the partial destruction of mesoporous stacking structure at these temperatures. The surface areas of the present Zn-Cr-LDHPOM nanohybrids are calculated based on the fitting analysis with the BrunauerEmmettTeller (BET) equation. As summarized in Table S1, the calcination at 200 and 300 C induces the significant depression of the surface area, a result of the decrease of interlayer spacing and the partial destruction of pillared structure. Figure S8│ Pore size analysis for the calcined derivatives of the Zn-Cr-LDH–POM nanohybrids. Pore size distribution curves of the Zn-Cr-LDHPOM nanohybrids of ZCV-1 (dot dashed lines), ZCV-2 (dashed lines), ZCW-1 (solid lines), and ZCW-2 (dotted lines). The plots (a), (b), and (c) represent the calculated curves of the as-prepared nanohybrids and their derivatives calcined as 200 and 300 C, respectively. : The pore-size distribution curves of the as-prepared Zn-Cr-LDHPOM nanohybrids and their derivatives calcined 200 and 300 C are calculated on the basis of the Barrett–Joyner–Halenda (BJH) method. As plotted in Fig. S8, all of the as-prepared nanohybrids have mesopores with a broad pore size distribution of average diameter of ~3–8 nm. In comparison with the ZCV nanohybrids showing somewhat broad distribution of pore size, the ZCW nanohybrids possess much narrower distribution of pore size, implying the higher order of porous stacking structure in the latter system. The heat-treatment at 200–300 C gives rise to a significant narrowing of the pore size distribution of the present nanohybrids with the average diameter of ~3–3.5 nm. This result indicates the improved ordering of mesopores via the removal of larger mesopores in the as-prepared materials. Judging from the fact that all the present nanohybrids have much smaller basal spacing of ~1 nm than the pore diameter, the mesopores in these materials are formed by the house-of-cards stacking structure of layered crystallites, as suggested from the FE-SEM results. Figure S9│ Diffuse reflectance UV–vis spectroscopic analysis for the calcined derivatives of the Zn-Cr-LDH–POM nanohybrids. Diffuse reflectance UV–vis spectra of the ZCW-1 (dashed-dotted lines), ZCW-2 (dot-dot-dashed lines), ZCV-1 (dashed lines) and ZCV-2 (dotted lines) nanohybrids calcined at 300 C. : The band structure and optical property of the Zn-Cr-LDHPOM nanohybrids calcined at 300 C are investigated with diffuse reflectance UVvis spectroscopy. As plotted in Fig. S9, the visible light absorption ability of the as-prepared nanohybrids is well-maintained after the heattreatment at 300 C, indicating the maintenance of the electronic coupling between Zn-Cr-LDH and POM components. Figure S10│ PL spectroscopic analysis for the calcined derivatives of the Zn-Cr-LDH– POM nanohybrids. PL spectra of the ZCW-1 (dot-dashed lines), ZCW-2 (dot-dot-dashed lines), ZCV-1 (dashed lines), and ZCV-2 (dotted lines) nanohybrids calcined at 300 °C. : The charge transfer between Zn-Cr-LDH nanosheets and POM nanoclusters after the calcination at 300 C is investigated with photoluminescence (PL) spectroscopy. As plotted in Fig. S10, the depressed PL signal of the present Zn-Cr-LDHPOM nanohybrids is wellmaintained upto 300 C, confirming the maintenance of the electronic coupling between Zn-CrLDH and POM components. Figure S11│ Comparative photocatalyst tests of the calcined Zn-Cr-LDH–POM nanohybrid with several references. Time-dependent photoproduction of O2 gas under visible light illumination (λ 420 nm) by the ZCW-1 nanohybrid calcined at 200 C (close circles), the pristine Zn-Cr-LDH (open circles), the pristine ammonium polyoxotungstate (triangles), the pristine sodium metavanadate (squares), the physical mixture of Zn-Cr-LDH and ammonium polyoxotungstate (inverse triangles), and the physical mixture of Zn-Cr-LDH and sodium metavanadate (diamonds). : The photocatalytic activity of the 200 C-calcined ZCW-1 nanohybrid is compared with those of several references including the pristine Zn-Cr-LDH material, the pristine POM compounds and their physical mixtures. As illustrated in Fig. S11, the 200 C-calcined ZCW-1 nanohybrid is much more active for the photocatalytic generation of O2 molecules than the pristine Zn-CrLDH material, the pristine POM compounds, and their physical mixtures. The present results obviously demonstrate the advantage of the hybridization with POM in improving the photocatalytic activity of the pristine Zn-Cr-LDH. Figure S12│ Consecutive photocatalytic activity tests. Time-dependent photoproduction of O2 gas under visible light illumination ( > 420 nm) by the (left) ZCW-1 and (right) ZCV-1 nanohybrids for (a) the 1st cycle, (b) the 2nd cycle, and (c) the 3rd cycle. : To verify the photocatalytic stability and recyclability of the present Zn-Cr-LDHPOM nanohybrids, the three consecutive tests of visible light-induced O2 evolution are carried out for the most active nanohybrid materials of ZCW-1 and ZCV-1. The sacrificial agent AgNO3 is added just after each run to compensate the consumption of this sacrificial agent. As plotted in Fig. S12, both the ZCW-1 and ZCV-1 nanohybrids retain most of photocatalytic activity for consecutive three cycles, clearly demonstrating the high stability of their photocatalytic activity. Like the pristine Zn-Cr-LDH material, there occurs a slight depression of the photocatalytic activity with proceeding the cycle. This phenomenon is generally observed for most of O2evolution photocatalysts including the pristine Zn-Cr-LDH material, a result of the photodeposition of Ag on the surface sites of photocatalyst, leading to the masking of reaction sites. Figure S13│Structural and morphological study after photocatalytic activity tests. (Left) Powder XRD patterns of the ZCW-1 and ZCV-1 nanohybrids restored after the three consecutive photocatalytic activity tests. (Right) (a,b) FE-SEM images and (c,d) EDS elemental mapping data of the (top) ZCW-1 and (bottom) ZCV-1 nanohybrids restored after the threeconsecutive photocatalyst tests. : The effects of photoreaction on the crystal structure, crystal morphology, and chemical composition of the ZCW-1 and ZCV-1 nanohybrids are investigated along with the photodeposition of Ag metal on the surface of catalyst materials. As plotted in the left panel of Fig. S13, both the ZCW-1 and ZCV-1 nanohybrids restored from the three-consecutive photocatalytic reactions show a series of (00l) reflections and in-plane (110) peak, confirming the maintenance of their original intercalation structure and the in-plane structure of the LDH component after the photoreactions. In addition to these peaks of the nanohybrids, both the photoreacted materials display newly appeared XRD peaks of Ag metal, confirming the photodeposition of Ag on the surface of nanohybrids. As illustrated in the FE-SEM results of the right panel of Fig. S13, the porous stacking structures of the ZCV-1 and ZCW-1 nanohybrids remain nearly unchanged after the photoreactions, confirming their high morphological stability. Also, the EDS mapping data of ZCV-1 and ZCW-1 nanohybrids restored from the photoreactor clearly demonstrate the homogeneous distribution of Zn, Cr, V, W, and Ag elements without any phase separation, verifying the maintenance of hybrid structure composed of Zn-Cr-LDH and POM, and the uniform deposition of Ag metal on the surface of the hybrid photocatalyst. References 1. Gunjakar, J. L., Kim, T. W., Kim, H. N., Kim, I. Y. & Hwang. S. -J. Mesoporous layer-bylayer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability. J. Am. Chem. Soc. 133, 1499815007 (2011). 2. Woo, M. A. et. al. Mixed valent Zn-Co-layered double hydroxides and their exfoliated nanosheets with electrode functionality. J. Mater. Chem. 21, 42864292 (2011). 3. Jang, J. S. et. al. Photocatalytic water splitting over iron oxide nanoparticles intercalated in HTiNb(Ta)O5 layered compounds. J. Catal. 231, 213222 (2005). 4. Han, A. 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