Synthesis and characterization of Cu 2 O/Pt/TiO 2 hybrid materials for photocatalytic valorization of CO 2

Transcription

1 Synthesis and characterization of Cu 2 O//TiO 2 hybrid materials for photocatalytic valorization of CO 2 Dina Lofficial [],[2], A. Fécant [], D. Uzio [], E. Puzenat [2], C. Geantet [2] [] [2]

2 . Context Energy demand and environmental issue [] CO 2 emissions from fossil fuel combustion [2] May 203: [CO 2 ] measured at Mauna Loa station = 400ppm First time in history A fossil fuels addicted civilization living on an earth with limited resources CO 2 : A greenhouse gas more and more concentrated in the atmosphere 2 [] new global dictator/ [2]

3 . Context Energy demand and environmental issue Let s learn from Nature! Natural process : Photosynthesis [3] Solar spectra received on earth surface [4] Solar light: An inexhaustible energy (86000TW [5] ) completely free [3] [4] Preventing UV light damage of the light sensitive materials using a highly protective UV absorbing coating, M. Zayat, P. garcia parejo, D. levy, Chem. Soc. Rev., 36, , [5] World Energy Outlook 200, International Energy Agency, 200

4 2. Proposed strategy To mimic photosynthesis process Z scheme of light capture and processing realised in natural oxygenic photosynthesis [6] Mimicking characteristics: Global equation of oxygenic photosynthesis: 2n CO 2 + 2n H 2 O + photons 2(CH 2 O) n +2n O 2 [6] Photosynthesis, 6th Ed., D.O. Hall and K.K. Rao, Cambridge University Press, p. 70, 999. Separation of redox carriers Limitation of charges recombination process 2. 2 photons absorption sites Incremental increase of redox potential to form (NADPH+H + ) and absorption of 2 photons around nm (more photons) instead of one around nm or UV Let s have a look in photocatalysis and semiconductor science! 4

5 2. Proposed strategy using inorganic semiconductors Operating principle of SC n M SC p heterojunction n type SC Metal P type SC H + +. OH H 2 O E F CB h + CB e e e h + h + h+ VB e CO 2 VB. CO2 Anode (SC) Cathode (SC2) Physical separation of oxidation and reduction sites + Reach suitable redox potentials (absorption of less energetic λ, absorption in visible rang) + Recombination probability ( E between e and h + ) 5

6 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors 6

7 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors n type SC Metal P type SC CB e CB e e CO 2 H + +. OH H 2 O E F h + e h + h + h+ VB. CO2 VB Anode (SC) Cathode (SC2) 7

8 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors n type SC Metal P type SC CB e CB e e CO 2 H + +. OH H 2 O E F h + e h + h + h+ VB. CO2 VB Anode (SC) Cathode (SC2) 8

9 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors Selection of the trio SC(anode)-M-SC2 (cathode) operative for photocatalytic CO 2 reduction 3 H 2 O oxidation feasible V/NHE (25 C, atm) 2 H 2 O/O 2 0 CO 2 /HCOOH - Ef CO 2 reduction feasible -2 Cu2O 2 O TiO2 2 Candidates 9

10 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors Selection of the trio SC(anode)-M-SC2 (cathode) operative for photocatalytic CO 2 reduction 3 H 2 O oxidation feasible V/NHE (25 C, atm) 2 H 2 O/O 2 0 CO 2 /HCOOH - Ef CO 2 reduction feasible -2 Cu2O 2 O TiO2 Candidates 2 SC 2 (cathode) Cu 2 O M CO 2 h + e - H + HCOOH CH 3 OH CH 4 + H 2 O e - TiO 2 SC2 (anode) h + e - H + + O 2 0 H 2 O

11 2. Proposed strategy To mimic photosynthesis process using inorganic semiconductors Selection of the trio SC(anode)-M-SC2 (cathode) operative for photocatalytic CO 2 reduction 3 H 2 O oxidation feasible V/NHE (25 C, atm) 2 H 2 O/O 2 0 CO 2 /HCOOH - Ef CO 2 reduction feasible -2 Specific synthesis strategy : Successive photodeposition Cu2O 2 O TiO2 Candidates 2 SC 2 (cathode) Cu 2 O M TiO 2 SC2 (anode) CO 2 h + e - e - H + h + e - HCOOH CH 3 OH CH 4 + H 2 O H + + O 2 H 2 O

12 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Cu 2 O Cu 2 O Cu 2 O 2 nd step Results rst step TiO 2 P25 2

13 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite rst step : Photodeposition of nanoparticles on TiO 2 Cl 2 6 Cl 2 Cl e e e TiO 2 P25 Aim: To localize metal particles on the semiconductor electronic pathways SC + 4hυ 4e + 4h + Cl e + 6Cl CH 3 OH + H 2 O + 4h + HCOOH + 4H + CH 3 OH +H 2 O + Cl HCOOH + 4HCl + 2 Cl 3

14 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite TiO 2 P25 XPS analysis TEM analysis % wt. /TiO 2 Control of particle size on TiO 2 P25 CPS (arb.units) +δ 2 platinum states : Binding Energy (ev) Medium size : 3.3nm Min:.7nm Max: 6.7nm 90 % as ( 4f 7/2 = 70,4 ev) 0 % as δ+ ( 4f 7/2 = 72,0eV) 4

15 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Cu δ+ Selective covering TiO 2 P25 preparation technique Deposition mechanism : Photoreduction= change of oxidation degree Preferential deposition of MxOy over metallic sites charged by e Log [Cu 2+ ] TOT Log [Cu + ] TOT Cu Cu 2+ ph Photoreduction Cu 2 O Cu 2 O(c) CuO(cr) Cu(OH) 2 4 Cu + Cu(OH) ph

16 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Cu 2+ Selective covering TiO 2 P25 Photoreduction of Cu(NO 3 ) 2 : Selective coverage of HER sites followed by dehydrogenation of the scavenger isopropanol (SC + 2 hν 2e + 2 h + ) 2 Cu +II aq + 2 e + H 2 O Cu 2 O + 2 H + CH 3 CHOHCH h + CH 3 COCH 3 + 2H + 2Cu +II aq + CH 3 CHOHCH 3 + H 2 O Cu 2 O + CH 3 COCH 3 + 4H + H 2 production rate (micromol/min) Cu(NO 3 ) 2 aq CH 3 CHOHCH 3 CH 3 COCH 3 + H 2 H 2 production rate divided by 4.5, suggesting that 77% of sites are inaccessible Time (min) covering index 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, 0 Ɵ= (r/rmax) as a function of n Cu in the medium/n total surf ratio Cu/

17 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Cu 2+ Selective covering TiO 2 P25 Photoreduction of Cu(NO 3 ) 2 : Selective coverage of HER sites followed by dehydrogenation of the scavenger isopropanol r/rmax) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, 0 Influence of synthesis parameters on particles coverage by Cu layer: Ɵ= (r/rmax) as a function of n Cu in the medium/n total surf. ISOPROPANOL CONCENTRATION DEPENDENCE T= 25 C Cu (ICP)wt.% = 2,2 90vol% 50vol% vol% ncu cumul./n r/rmax) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, 0 Ɵ= (r/rmax) as a function of n Cu in the medium/n total surf. TEMPERATURE DEPENDENCE [Isopropanol]=50vol% Cu (ICP)wt.% = 2,2 0 C 25 C 47 C ncu cumul./n Higher coverage seems to be achieved with lower [isopropanol] and lower temperature 7

18 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Cu 2+ Selective covering TiO 2 P25 Photoreduction of Cu(NO 3 ) 2 : Selective coverage of HER sites followed by dehydrogenation of the scavenger isopropanol r/rmax) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, 0 Influence of synthesis medium on particles coverage by Cu layer: Ɵ= (r/rmax) as a function of n Cu in the medium/n total surf. ISOPROPANOL CONCENTRATION DEPENDENCE T= 25 C Cu (ICP)wt.% = 2,2 90vol% 50vol% vol% ncu cumul./n XPS analysis Less intense 4f signal for composite prepared in 5vol% of isopropanol (compared to ones prepared in 50vol%) 4f Higher coverage seems to be achieved with lower [isopropanol]

19 3. Synthesis and characterisation of Cu 2 O//TiO 2 composite Photoreduction of Cu(NO 3 ) 2 Cu 2 O TEM analysis TiO 2 P25 2.% wt. Cu (XRF) /2.5% wt. /TiO 2 CPS (arb. units) XPS analysis Cu 2 O//TiO 2 prepared in 5%isoprOH media: 2.2wt.%Cu (ICP) on wt.%/tio 2 73 % Cu 2 O 27% CuO Cu 2 O Cu x O y TiO 2 Cu x O y Presence of SC2 M SC junctions Cu x O y CuO Visible coverage of particle by Cu x O y layer. TiO Binding Energy (ev) Cu 2 O formation confirmed 9

20 4. CO 2 photocatalytic reduction test of Cu 2 O//TiO 2 composite Xe Hg UV lamp Ar 5mL/min Perfectly stirred and temperature controlled Pyrex reactor: Aqueous carbonate solution + catalyst Manual samples Automatic samples HPLC UV detector ( ml every 30min during 6h) µ GC TCD (every 6min during 20h) [HCOOH], [CH 3 COOH] % of :CO 2, H 2, CH 3 OH, CH 4 20

21 4. CO 2 photocatalytic reduction test of Cu 2 O//TiO 2 composite Liquid phase analysis after h of irradiation for different photocatalysts Cu 2 O TiO 2 P25 Evolution of oxalic acid amount mesured by HPLC: Carbonates photocatalytic reduction test of Cu 2 O//TiO 2 composite Cu 2 O//TiO 2 composite proved reactivity for carbonates photocatalytic reduction into different carboxylic acids especially into oxalic acid. (compounds not detected for /TiO 2 and TiO 2 ) Amount of oxalic acid produced (micromoles) 2,8,6,4,2 0,8 0,6 0,4 0,2 0 Initial rate of carbonates transformation into oxalic acid : 2 μmol.h.g cat Time (min) 2

22 5. Conclusions and perspectives Conclusions: Cu 2 O//TiO 2 seems to be synthesisable by photoreduction Cu 2 O//TiO 2 has been obtained by Cu(NO 3 ) 2 photoreduction onto /TiO 2 with more than 70% of Cu 2 O phase at the surface Synthesis in a weakly alcoholic medium at low temperature seems to lead to an higher coverage index Cu 2 O//TiO 2 seems to be active towards carbonates photocatalytic reduction into different carboxylic acids especially into oxalic acid (2 μmol.h.g cat ) /TiO 2 and TiO 2 seems to be inactive toward this reaction in our conditions Perspectives: To compare Cu 2 O//TiO 2 composite with classical photocatalysts such as TiO 2 in terms of energetic yield and apparent quantum efficiency of solar chemicals produced by photocatalytic reduction of CO 2 In case of interesting energy gain: to open this synthesis technique to a larger range of materials 22

23 Thanks to: IFPEN and IRCELYON for financial support Analytical services : Noëlle and Pascale (ICP), Luis (XPS), Julien (IR CO), Mimoune, Laurence and Florent (MET), Eugénie and Cedrik, Frédéric and Damia The Photo4E organizing committee 23