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Room temperature stable COx-free H2 production from methanol with magnesium oxide nanophotocatalysts

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Science Advances  02 Sep 2016:
Vol. 2, no. 9, e1501425
DOI: 10.1126/sciadv.1501425
  • Scheme 1 Process of synthesis of MgO NPs and activity in H2 production from methanol photodecomposition.
  • Fig. 1 Composition and morphology characterization of MgO NPs.

    (A) XRD pattern of various-sized MgO NPs. (B) TEM image of 85-nm-sized porous MgO NPs, with a plane size distribution analysis (inset). (C to F) Temperature effect on NP size. TEM images of MgO NPs with different sizes obtained from the thermolysis of 2 mmol of Mg(acac)2·2H2O in OM/OA/ODE = 4:1:5 (molar ratio) at different temperatures for the same reaction time of 30 min: 265°C (C), 280°C (D), 300°C (E), and 320°C (F). From the TEM images, the average sizes of MgO NPs can be estimated to be ~40 nm (C), ~85 nm (D), ~115 nm (E), and ~170 nm (F), respectively.

  • Fig. 2 Crystal structure analysis of MgO NP.

    (A and B) TEM (A) and HAADF-STEM (B) image of a single porous MgO NP with a diameter of ~85 nm. Inset of (A): Enlarged TEM images for the edge and center of the MgO NPs. (C and D) HRTEM image (C) and the corresponding SAED pattern (D) recorded from (A).

  • Fig. 3 Optical properties of MgO nanocrystals.

    (A and B) Room temperature UV-vis absorption (A) and PL (λex = 270 nm) spectra (B) of differently sized porous MgO NPs. a.u., arbitrary units.

  • Fig. 4 H2 production from methanol photodecomposition based on ~85-nm MgO nanocrystals.

    (A) Illumination wavelength effect using the long-wave pass filters with different cut-on wavelengths. (B) MgO concentration effect with constant 3 mg of MgO powder dispersed in different volumes of methanol. (C) Performance endurance of H2 production by continuing to use the same MgO (3 mg)/methanol (8 ml) reaction materials for the whole three-cycle testing. (D) XRD pattern for MgO after a total 48-hour photocatalytic reaction.

  • Fig. 5 Schematic diagram of proposed hydrogen production mechanism for MgO nanocrystals.

    On the basis of the UPS results (fig. S11), the valence band maximum for MgO, that is, Ev, is ~−10.5 eV relative to vacuum. Combined with the 7.8-eV band gap of MgO, we infer a conduction band minimum, Ec, of −2.7 with respect to the vacuum energy level (Evac = 0). The energy levels of the absorption at 4.6 eV arise from surface excitons, as described in the main text. The energy levels of the emission in MgO are derived from the PL spectrum of 85-nm-sized MgO in Fig. 3B, that is, an emission peak at 330 nm with a broad shoulder at around 400 nm. NHE, normal hydrogen electrode.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/9/e1501425/DC1

    fig. S1. FTIR analysis of synthesized and oxygen plasma–treated MgO NPs.

    fig. S2. SEM image and EDX analysis of synthesized MgO NPs.

    fig. S3. Temperature-dependent experiments of synthesized MgO NPs.

    fig. S4. Solvent composition–dependent experiments of synthesized MgO NPs.

    fig. S5. Digital photographs of different-sized MgO colloidal solution.

    fig. S6. Optical properties for ~85-nm MgO nanocrystals and H2 production from methanol photodecomposition.

    fig. S7. Specific surface area of four different-sized MgO NPs.

    fig. S8. TEM and SAED images of an MgO NP with a size of 40 nm.

    fig. S9. The rate pattern of H2 production for ~85-nm MgO nanocrystals.

    fig. S10. SEM analysis and H2 production of commercial MgO, SiO2, and TiO2 (P25).

    fig. S11. Chromatogram analysis of a mixture of gases.

    fig. S12. Chromatogram analysis of a mixture of gases.

    fig. S13. UPS spectrum for ~85-nm-sized MgO NPs.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. FTIR analysis of synthesized and oxygen plasma–treated MgO NPs.
    • fig. S2. SEM image and EDX analysis of synthesized MgO NPs.
    • fig. S3. Temperature-dependent experiments of synthesized MgO NPs.
    • fig. S4. Solvent composition–dependent experiments of synthesized MgO NPs.
    • fig. S5. Digital photographs of different-sized MgO colloidal solution.
    • fig. S6. Optical properties for ~85-nm MgO nanocrystals and H2 production from methanol photodecomposition.
    • fig. S7. Specific surface area of four different-sized MgO NPs.
    • fig. S8. TEM and SAED images of an MgO NP with a size of 40 nm.
    • fig. S9. The rate pattern of H2 production for ~85-nm MgO nanocrystals.
    • fig. S10. SEM analysis and H2 production of commercial MgO, SiO2, and TiO2 (P25).
    • fig. S11. Chromatogram analysis of a mixture of gases.
    • fig. S12. Chromatogram analysis of a mixture of gases.
    • fig. S13. UPS spectrum for ~85-nm-sized MgO NPs.

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