Supplementary Information for. Fabrication of Gold/Titania Photocatalyst for CO 2. Reduction based on pyrolytic Conversion of the Metal-

Transcription

1 Supplementary Information for Fabrication of Gold/Titania Photocatalyst for CO 2 Reduction based on pyrolytic Conversion of the Metal- Organic Framework NH 2 -MIL-125(Ti) loaded with Gold Nanoparticles. Kira Khaletskaya, 1 Anna Pougin, 2 Raghavender Medishetty, 1 Christoph Rösler, 1 Christian Wiktor, 1 Jennifer Strunk 3 and Roland A. Fischer*,1 1 Department of Inorganic Chemistry II, Ruhr University Bochum, Universitätsstrasse 150, Bochum, Germany 2 Laboratory of Industrial Chemistry, Ruhr University Bochum, Universitätsstraße 150, Bochum, Germany 3 MPI CEC, Stiftstraße 34-36, Mülheim an der Ruhr, Germany Germany and Center for Nanointegration Duisburg-Essen (CENIDE), Duisburg, Germany

2 S1. Instrumental Details X-ray Diffraction (XRD). For the structural analysis of NH 2 -MIL-125, GNP/NH 2 -MIL-125, TiO 2 and GNP/TiO 2 D8-Advance Bruker AXS diffractometer with CuKα radiation (λ = Å), Göbel mirror with a slit width of ; θ-2θ scan; 2θ = 5-90, continuous mode, position sensitive detector, 25 C and Ni-filter were employed. The samples were filled into standard capillaries (diameter of 0.7 mm) and measured in Debye-Scherer geometry. The activated powders were filled in a glovebox under inert atmosphere (Ar). The phase purity of MOF materials was verified by comparison with calculated PXRD pattern of NH 2 -MIL-125 based on Crystallographic Information Files (CIF) provided by G. Ferey. 1 Transmission Electron Microscopy (TEM). Bright-field TEM measurements of NH 2 -MIL- 125, GNP/NH 2 -MIL-125, TiO 2 and GNP/TiO 2 were carried out on a Tecnai G2 F20 and Philips CM20 microscopes with an acceleration voltage of 200 kv at the department of Mechanical Engineering, Ruhr-University Bochum. HAADF-STEM Imaging and STEM-EDX. HAADF-STEM imaging and spatially resolved EDX analysis of GNP/TiO 2 was performed on a Tecnai G2 F20 microscope with Super-X EDX detector operated at 200 kv at the department of Mechanical Engineering, Ruhr- University Bochum. N 2 Sorption. Nitrogen sorption measurements were performed on a Bel-Japan Belsorp-Mini equipment with nitrogen gas ( %) at 77 K at the Laboratory of Industrial Chemistry, Ruhr-University Bochum. The specific surface areas of the guest-free (activated) NH 2 -MIL-125, GNP/NH 2 -MIL-125, TiO 2 and GNP/TiO 2 materials were calculated applying the BET model. 2 Prior the measurements, all samples were evacuated in dynamic vacuum (p = 10-7 mbar) at temperatures at 150 C for 2 h. Thermo Gravimetric Analysis (TGA). A Netzsch STA 409 PC TG-DSC apparatus was used for all TGA measurements. A heating rate of 5 K/min was applied and the sample (sample weight approximately 5-10 mg) measurements were performed in a temperature range from 303 to 873 K with a stream of nitrogen ( %, 300 ml/min). Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The IR spectra were collected in a Protègè 460 Spectrometer by Nicolet at the Laboratory of Industrial

3 Chemistry, Ruhr-University Bochum. All powder samples were measured with dilution in a Harrick environmental cell (HVC-DRP-2) to allow the adjustment of gas atmosphere and temperature. In order to remove the surface bound H 2 O, the samples were exposed to a flow of Ar for 1 h. The temperature was regulated to be slightly above room temperature at 35 C. The temperature stability tests of adsorbed species in case of GNP/TiO 2 material, obtained through pyrolysis of GNP/NH 2 -MIL-125, were performed by applying a linear heating ramp with 5 C/min to a maximum temperature of 600 C in continuous Ar flow. The obtained spectra were converted to log (1/R). Raman Spectroscopy. The Raman spectra of GNP/TiO 2 and TiO 2 materials were recorded with Alpha300R WITec spectrometer at the Chair of Physical Chemistry II - Laser spectroscopy and Biophotonics in Bochum. The spectrometer was equipped with a MCT detector and a 532 nm Nd:YAG Laser. The scanline measurement of TiO 2 material was performed over 200 µm of the sample resulting in 201 points with 5x0.5s per spectrum. All spectra were measured at 40 mw. Photoreactor Setup. The photocatalytic test reaction of CO 2 reduction was performed in a homemade, vacuum tight, metal sealed photoreactor. The main elements are the gas supply, the saturator, the reactor, the analysis devices (GC and QMS) and the pumping system. The home-made gas-phase photoreactor with a volume of approximately 27 ml was constructed on the basis of the design presented by Grimes et al. 3,4 at the Laboratory of Industrial Chemistry at Ruhr-University Bochum. A sample was spread on glass tray on the bottom of the reactor to obtain a homogeneous light distribution. A 200 W Hg/Xe (Newport Oriel) lamp was used to irradiate the sample through a quartz window allowing for high transmissions of highenergy UV light. Thus, the light irradiance at the sample was 220 mw/cm 2. Furthermore, the wavelength of the lamp output was 90 % in the range between 250 and 800 nm (IR range is neglected and filtered out by a water-cooled filter). The reaction was performed in the batch mode and product gases were analyzed by Gas Chromatography (GC), which was equipped with TCD and FID detectors (Shimadzu 14B). Two Porapak N columns and one molecular sieve column were used for separation. Sample Cleaning Procedure. Prior to all activity tests the samples (each 50 mg) were cleaned inside the reactor with a well-established cleaning method developed by Mul et al. 5 In order to remove contaminants from the catalyst surface, the samples were illuminated in a gas flow atmosphere of 26 Nml/min of 0.6 % of H 2 O in He. The flow mode and illumination were kept running overnight for 12 h. To check the cleaning for completeness, another cleaning step in batch mode was performed afterwards. Over the course of 2 h the desorbing

4 hydrocarbon species accumulated inside the reactor and could be detected by the GC. The sample was ready for an activity test when a blank chromatogram was observed. Table S1. Quantum efficiencies of photo conversions of CO 2 to CH 4 Sample Au/TiO 2 0,022 TiO 2 from MOF 0,011 P25 0,012 Aurolite by STREM 0,009 Quantum efficiencies have been calculated according to the following equation, where the number of events marks 8 electrons per produced CH 4 molecule and number of photons are obtained through lamp output intensity measurements. The intensity of the lamp (through the reactor window, with IR filter installed) was measured with a photodiode to result in 220 mw/cm 2. With an area of 2 cm 2 of exposed catalyst and given the fact that the TiO 2 samples absorb photons of a wavelength between 350 and 420 nm, mainly (additional absorption for Au modified samples between 500 and 550 nm was taken into account for Au containing samples). S2. Additional Characterization Figure S1. PXRD diffractograms of PVP-stabilized gold nanoparticles (blue trace) compared to the calculated pattern of Au (black trace).

5 Figure S2. Bright field TEM image of PVP-stabilized gold nanoparticles. The average particles size is 2.1 ± 0.8 nm.

6 Figure S3. N 2 sorption isotherms (77 K) of NH 2 -MIL-125 (blue) and GNP/NH 2 -MIL-125 (green). Adsorption and desorption branches are shown with open and closed symbols respectively. Figure S4. TGA data of as synthesized GNP/NH 2 -MIL-125 (orange trace), as synthesized NH 2 -MIL- 125 (black trace), activated GNP/NH 2 -MIL-125 (green trace) and activated NH 2 -MIL-125 (blue trace) measured in the temperature range of C.

7 Figure S5. TGA data of GNP/TiO 2 (green trace) and TiO 2 (blue trace) measured in the temperature range of C. Figure S6. FT Raman spectra of GNP/TiO 2 (green) and TiO 2 (blue) measured at room temperature. TiO 2 reference sample consists of rutile and anatase phases. The blue spectrum (top) highlights the rutile and blue spectrum (bottom) the anatase crystallites in the same sample.

8 Figure S7. DRIFT spectra of GNP/TiO 2 before photocatalytic CO 2 reduction obtained after heating from RT to 600 C. Figure S8. N 2 sorption isotherms (77 K) of GNP/TiO 2. Adsorption and desorption branches are shown with open and closed symbols, respectively.

9 Figure S9. Time-course of ethane and propane evolution observed for GNP/TiO 2 (red) and TiO 2 (blue) materials additionally to methane formation during two subsequent CO2 reduction experiments. Figure S10. Comparison of methane evolution observed for GNP/TiO 2 (black), TiO 2 (red) and P-25 (blue) reference material illustrated as product amount in [ppm] versus time in [h]. The photocatalytic CO 2 reduction within 6 hours of illumination was performed only within one run for P-25 and is 15 ppm. This CH 4 amount is in a good accordance to the CH 4 amount of 14 ppm produced in case of TiO 2 material without GNPs during the first CO 2 reduction experiment.

10 Figure S11. DRIFT spectra of GNP/TiO 2 (purple) and TiO 2 (petrol) before and of GNP/TiO 2 (orange) and TiO 2 (turquoise) after two runs of photocatalytic CO 2 reductions measured at room temperature. Figure S12. PXRD data of GNP/TiO 2 (orange) and TiO 2 (turquoise) after two runs of photocatalytic CO 2 reductions compared to the calculated pattern of anatase (black) and rutile (red).

11 References: (1) Dan-Hardi, M.; Serre, C.; Frot, T.; Rozes, L.; Maurin, G.; Sanchez, C.; Férey, G. A New Photoactive Crystalline Highly Porous Titanium(IV) Dicarboxylate. J. Am. Chem. Soc. 2009, 131, (2) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60, (3) Roy, S. C.; Varghese, O. K.; Paulose, M.; Grimes, C. A. Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons. ACS Nano 2010, 4, (4) Varghese, O. K.; Paulose, M.; LaTempa, T. J.; Grimes, C. A. High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. Nano Lett. 2009, 9, (5) Yang, C.-C.; Vernimmen, J.; Meynen, V.; Cool, P.; Mul, G. Mechanistic study of hydrocarbon formation in photocatalytic CO2 reduction over Ti-SBA-15. J. Catal. 2011, 284, 1-8.