Constructing solid-gas-interfacial Fenton reaction over

Transcription

1 Constructing solid-gas-interfacial Fenton reaction over alkalinized-c 3 N 4 photocatalyst to achieve apparent quantum yield of 49% at 420 nm Yunxiang Li,, Shuxin Ouyang,,,,* Hua Xu,,, Xin Wang,, Yingpu Bi, # Yuanfang Zhang, and Jinhua Ye,,,,* TU-NIMS Joint Research Center, School of Materials Science and Engineering, Tianjin University, Tianjin , P. R. China Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin , P. R. China Key Lab of Advanced Ceramics and Machining Technology, Ministry of Education, Tianjin , P. R. China # State Key Laboratory for Oxo Synthesis & Selective Oxidation, and National Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, CAS, Lanzhou , P. R. China International Center for Materials Nanoarchitectonics (WPI-MANA) and Environmental Remediation Materials Unit, National Institute for Materials Science (NIMS), Japan *Author to whom correspondence should be addressed. oysx@tju.edu.cn; jinhua.ye@nims.go.jp S-1

2 Contents Table S1. C 3 N 4 -based photocatalysts for gaseous pollutant degradation... 4 Figure S1. Comparison of product yield over various photocatalysts and corresponding samples loaded with Fe SI-1 Measurement of H 2 O Figure S2. K 2p XPS spectrum of the CNK-OH Figure S3. ph values of filtrate and solution of CNK-OH suspensions Figure S4. SEM (left) and TEM (right) images of the obtained samples Figure S5. STEM-EDS elemental mapping of CNK-OH&Fe Figure S6. Amounts of products yield and AQY over CNK-OH as a function of the amount of NaOH in feedstock Figure S7. Photoactivity comparison of typical IPA oxidation over the as-prepared samples Table S2. Photon number and UPN at different wavelength for the measurement of AQY Figure S8. Photoactivity comparison of typical IPA oxidation over the N-TiO 2 samples with various nitridation temperature Figure S9. Comparison of acetone (a) and CO 2 (b) evolution over N-TiO 2, N-TiO 2 &Fe and optimized CNK-OH&Fe sample Figure S10. Long-term experiment of IPA photooxidization over CNK-OH&Fe Figure S11. Comparison of product evolution amounts over SiO 2 -based samples and CNK-OH&Fe.. 17 Figure S12. Synchronous illumination XPS (SIXPS) spectra Figure S13. Photoelectrochemical properties of samples Figure S14. Steady-state and time-resolved photoluminescence spectroscopy Table S3. Best fitted parameters of time-resolved PL spectra (Fig. S13b) SI-2: Construction of quick transfer and conversion channel for photocarrier Figure S15. Optical properties of as-synthesized samples Table S4. Surface area, XRD peak FWHM, light absorption, and utilized photon number of all samples SI-3: Non-critical factors in photocatalytic reaction Figure S16. H 2 O 2 production under different atmosphere for solid samples Figure S17. Comparison of absorption spectra of DPD/POD-samples solution Figure S18. Time course of H 2 O 2 production over CNK-OH Figure S19. Influence of CNK-OH&Fe on the absorption spectra of DPD/POD-H 2 O S-2

3 Figure S20. ESR spectra of as-prepared samples Figure S21. Comparison of C 3 N 4 -based photocatalysts in acetone evolution and H 2 O 2 production Figure S22. Cycle test of IPA photodegradation over CNK-OH&Fe Table S5. Concentrations of oxygen-related species over CNK-OH&Fe before reaction and after reaction References S-3

4 Table S1. C 3 N 4 -based photocatalysts for gaseous pollutant degradation Samples g-c 3 N 4 /WO 3 1 g-c 3 N 4 /WO 3 2 Pollutant Product Yield ( mol/h) UPN a ( mol/h) CH 3 CHO CO 2, CH 3 CHO CO 2, Reaction Conditions 100 mg catalyst, LED lamp, = 435 nm 50 mg catalyst, > 420 nm g-c 3 N 4 /Bi 2 O 3 3 g-c 3 N 4 /TiO 2 4 (CH 3 ) 2 CHOH Acetone, HCHO CO 2, mg catalyst, 300 W Xe lamp, 420 nm 800 nm 300 mg catalyst, UV lamp HT-g-C 3 N 4 5 NO NO 2, 0.3 NO 2 -, 0.2 (NO 3 ) -, mg catalyst, W-type fluorescent lamps, > 380 nm g-c 3 N 4 /P25 6 (M400) NO NO 2, 0.4 NO x, mg catalyst, 500-W Hg lamp, 420 nm 700 nm g-c 3 N 4 /GO 7 NO NO 2, 0.6 NO x, mg catalyst, A 150 W halide lamp, > 400 nm a mg catalyst, CO This work (CH 3 ) 2 CHOH 2, 23.1 (AQY = 49% 300 W Xe lamp, Acetone, at 420 nm) > 400 nm UPN: Utilized photon number, which was calculated via the transfer electrons in photooxidization reaction S-4

5 Figure S1. Comparison of product yield over various photocatalysts and corresponding samples loaded with Fe 3+. Notes: the loading amount of Fe 3+ was adjusted to 0.1 wt% for all samples except CN according to previous report 8 ; Semiconductor [ZnO, WO 3, SrTiO 3, TiO 2 (P25)]-Fe 3+ were also prepared in a similar fashion as described in Preparation of the samples Section except that ph value of ZnO, WO 3, SrTiO 3 solution was adjust to ~3 in case the generation of Fe(OH) 3 ; the IPA photodegradation test over oxides with or without Fe 3+ were conducted under full-arc Xe lamp, CN and CN-Fe were irradiated with visible light ( > 400 nm). S-5

6 SI-1 Measurement of H 2 O 2 1. KMnO 4 titration method This method utilizes the reduction of KMnO 4 by H 2 O 2 in H 2 SO 4 as shown in equation S1. The concentration of H 2 O 2 was measured with KMnO 4 titration method [c(kmno 4 ) = 1 mmol L 1 ] with the addition of 1 ml 3.68 mol L 1 H 2 SO 4 solution. The concentration of H 2 O 2 is equivalent to the concentration of KMnO 4 solution when the solution turns into the pink after the addition of KMnO 4 solution and maintains the color of solution for 30 s. 9 The sample was firstly irradiated with gaseous IPA (ca mol, keep the same with the IPA amount used in photoactivity test) under visible light ( > 400 nm) and then was dispersed into 5 ml distilled water; finally, the filtrate of the suspension was used to measure the amount of H 2 O 2. Note: the detection limit is 0.2 mol 10. 5H 2 O 2 +2KMnO 4 +3H 2 SO 4 2MnSO 4 + K 2 SO 4 +5O 2 +8H 2 O (S1) 2. DPD method When the production of H 2 O 2 is very limited, colorimetric DPD method 11 was adopted to determine the amount of H 2 O 2, The DPD method is based on the oxidation of N, N-diethyl-p-phenylenediamine (DPD) catalyzed with horsedish peroxides (POD) by H 2 O 2. As shown below, two molecules of DPD are oxidized by H 2 O 2 with POD as catalyst to produce the radical cation (DPD + ). The radical cation DPD + forms a stable color, with the maximum absorption at 510 nm. Samples (15 mg) were first irradiated without gaseous IPA (unless other specified), then they were dispersed into the DPD solution [27 ml H 2 O, 3 ml buffer (1*10-3 Mol Na 2 HPO 4 and 9 *10-3 Mol NaH 2 PO 4 dissolved in 100 ml distilled water), 6 l CH 3 OH, 50 l (0.1g DPD dissolved in 10 ml 0.5 M H 2 SO 4 ), 50 l (10 mg POD dissolved in 10 ml distilled water)], stirred for 5 min, finally 3mL filtrates of suspensions were detected by UV-visible spectrophotometer (UV-2700, Shimadzu, Japan). S-6

7 Figure S2. K 2p XPS spectrum of the CNK-OH. S-7

8 Figure S3. ph values of filtrate and solution of CNK-OH suspensions. Apparently, the alkalinity of suspension is stronger than that of filtrate, illustrating that hydroxyl groups were successfully grafted on the surface of the sample. Note: 10 mg CNK-OH was dispersed in 0.5 ml H 2 O. S-8

9 Figure S4. SEM (left) and TEM (right) images of the obtained samples. a, CN. b, CNK. c, CNK-OH. d, CNK-OH&Fe. S-9

10 Figure S5. STEM-EDS elemental mapping of CNK-OH&Fe. S-10

11 Figure S6. Amounts of products yield and AQY over CNK-OH as a function of the amount of NaOH in feedstock. The optimized amount of NaOH is g. S-11

12 Figure S7. Photoactivity comparison of typical IPA oxidation over the as-prepared samples. Acetone (a) and CO 2 (b) evolution over C 3 N 4 -based samples. S-12

13 Table S2. Photon number and UPN at different wavelength for the measurement of AQY Wavelength (nm) Photon number ( mol/s/m 2 ) 396 ± ± ± UPN ( mol/h) AQY (%) 57.9 ± ± ± 1.1 Notes Irradiation area: 7.06 cm ± ± ± ± 1.4 UPN: utilized photon number; UPN = [N(CO 2 ) * 6 + N(acetone)] AQY: Apparent Quantum Yield; AQY = [N(CO 2 ) * 6 + N(acetone)] / N(photons) * 100% S-13

14 Figure S8. Photoactivity comparison of typical IPA oxidation over the N-TiO 2 samples with various nitridation temperature. S-14

15 Figure S9. Comparison of acetone (a) and CO 2 (b) evolution over N-TiO 2, N-TiO 2 &Fe and optimized CNK-OH&Fe sample. Reaction conditions: catalyst, 50 mg; light source, AM 1.5, 100 mw cm -2. S-15

16 Figure S10. Long-term experiment of IPA photooxidization over CNK-OH&Fe. Reaction conditions: 300 W Xe lamp, visible light ( > 400 nm), 50 mg sample, ~28 mol IPA. The degradation and mineralization percentages of IPA were up to 99.9% in 20 min and 36 h, respectively. S-16

17 Figure S11. Comparison of product evolution amounts over SiO 2 -based samples and CNK-OH&Fe. S-17

18 Figure S12. Synchronous illumination XPS (SIXPS) spectra for (a) CNK, (b) CNK-OH, (c) CNK-OH&Fe, respectively. S-18

19 Figure S13. Photoelectrochemical properties of samples at a -200 mv bias potential vs. Ag/AgCl in a 0.2 M Na 2 SO 4 aqueous solution. a, Periodic on/off photocurrent response under visible-light irradiation ( > 400 nm). b, Electrochemical impedance spectroscopy (EIS) Nyquist plots in the light. S-19

20 Figure S14. Steady-state and time-resolved photoluminescence spectroscopy. a, Photoluminescence (PL) spectra of samples. b, the fitting curves of fluorescence decay of samples. S-20

21 Table S3. Best fitted parameters of time-resolved PL spectra (Fig. S13b) Samples Decay of times (ns) Fractional contribution Goodness of fit t parameter (χ 2 1 t 2 t 3 f 1 f 2 f 3 ) CN CNK CNK-OH CNK-OH&Fe S-21

22 SI-2: Construction of quick transfer and conversion channel for photocarrier Synchronous illumination XPS (SIXPS) was adopted to study the electronic status of implanted K atom under light irradiation. The binding energy of K 2p shifts around 0.1 ev negatively when light is introduced (Fig. S11), indicating an electron-rich state of K after irradiation. Moreover, this type of electron-rich state should be an equilibrium status of input and output electron through the K joint between layers under light irradiation. Together with the earlier mentioned interaction between K and N for all the K modified samples (Fig. S1 and Fig. S2), it means that the interlayer K ions may construct the new interplanar carrier channel. Photoelectrochemical characterizations were used to explore the transfer efficiency of photocarriers. The measurements of photocurrent present a remarkable enhancement for CN, CNK, and CNK-OH in sequence (Fig. S12a). However, photocurrent of CNK-OH&Fe descends significantly compared to CNK-OH (Fig. S12a). This phenomenon can reasonably explained that the surface modified Fe 3+ can capture the photogenerated electrons, which is consistent with the ESR analyses that Fe 3+ can extract electrons effectively (Fig. 1b, Fig. 3b and Fig. S19b). The electrochemical impedance spectroscopy (EIS) further confirms the photoelectron conductivity. The semicircular Nyquist plots of samples are exhibited in Fig. S12b, in turn, with a decreased diameter for CN, CNK, and CNK-OH, demonstrating that the interlayer doped K ions and surface grafted hydroxyl groups indeed improve the electronic conductivity and therefore promote photocarriers separation. In view that loading treatment just influences the shallow surface properties, as expected, the Fe 3+ loading on surface barely affect the diameter of semicircular Nyquist plot (Fig. S12b). Fluorescence spectroscopy was applied to analyze the separation and transfer efficiency of carriers. As shown in Fig. S13, for the CN, CNK and CNK-OH, the PL intensity and fluorescence life time decrease in turn, indicating more efficient separation of electrons and holes. However, when loaded with Fe 3+, the PL intensity and fluorescence life time of CNK-OH&Fe is very similar to those of CNK-OH, S-22

23 indicating that the Fe 3+ modification is limited to shallow surface and doesn t change the nature of the bulk phase. In summary, the K implantation and hydroxyl group modification optimize the separation and transfer of photocarriers, namely, it realizes improvement of dynamics behaviors. Despite the Fe 3+ doesn t influence the transfer of photocarriers in bulk, it promote the utilization of photoelectron on surface. Hence, the K implantation, hydroxyl group modification, and Fe 3+ loading construct quick transfer and conversion channel for photocarrier, which contributes to more efficient photoelectrons transportation to the surface of material and to participate in the solid-gas interfacial Fenton reaction. S-23

24 Figure S15. Optical properties of as-synthesized samples. a, UV-visible absorption spectra of the as-prepared samples. b, The plots of the ( h ) 1/2 versus photon energy (h ). S-24

25 Table S4. Surface area, XRD peak FWHM, light absorption, and utilized photon number of all samples Surface area FWHM a Light absorption b Samples a FWHM: XRD peak. b Light absorption: Integration from 400 to 460 nm. c UPN: Utilized photon number = n(acetone) + n(co 2 )*6, where n(acetone) and n(co 2 ) represent evolved acetone and CO 2 in one hour, respectively. UPN c ( mol/h) (m 2 g -1 ) (º) (a.u.) CN CNK CNK-OH CNK-OH&Fe S-25

26 SI-3: Non-critical factors in photocatalytic reaction As shown in Table S1, the surface area of CNK-OH&Fe is ca. 5 times that of CNK, meanwhile the crystallinities and light absorptions are comparable for both of them, however, the former exhibits more than 31 times of photoactivity improvement calculated with utilized photon number [UPN = n(acetone) + n(co 2 )*6, where n(acetone) and n(co 2 ) represent the amounts of evolved acetone and CO 2, respectively], indicating that surface area isn t the key factor in the present photooxidation. Moreover, the surface area is comparable before and after Fe 3+ modification for CNK-OH. However, the UPN presents a remarkable improvement from mol/h to mol/h even when CNK-OH&Fe owns obvious disadvantages in both crystallinity and light absorption, revealing that light absorption and crystallinity aren t the main factors in the current photocatalytic reaction. Comparing the CNK-OH and CNK-OH&Fe samples, the main difference is the Fe 3+ loading, which contributes to a ~527 mol/h increment of UPN. Hence, the significant photoactivity enhancement is mainly ascribed to the Fe 3+ loading and underlying solid-gas interfacial Fenton reaction. S-26

27 Figure S16. H 2 O 2 production under different atmosphere for solid samples. a, Production of H 2 O 2 with various atmosphere when gaseous IPA (1000 mol) (iso-propanol) was added. The samples were first irradiated, then the powders was dispersed in 5 ml distilled water, finally the filtrates of suspensions were used to detecte H 2 O 2 by redox titration with KMnO 4. b, The influence of atmosphere on the absorption spectra of DPD/POD-H 2 O 2 in absence of IPA. The samples were first irradiated, then irradiated powders were dispersed in DPD solution, 3mL filtrates were determine with UV-visible spectrophotometer. It is notable that the variation trend of production of H 2 O 2 is consistent when gaseous IPA was added or not. Reaction conditions: 10 mg photocatalyst, reaction were 2 min and 4 min for (a) and (b) respectively, under visible-light irradiation ( > 400 nm), samples were purged with different atmosphere for 10 min. S-27

28 Figure S17. Comparison of absorption spectra of DPD/POD-samples solution. It should be noted that the samples were first irradiated under visible light without gaseous IPA, then powders were dissolved in DPD solution, 3mL filtrates were used to detect H 2 O 2 with UV-visible spectrophotometer. S-28

29 Figure S18. Time course of H 2 O 2 production over CNK-OH. Reaction Conditions: 10 mg sample, 300 W Xe lamp with an L42 filter ( > 400 nm). Notes: the samples were first irradiated with gaseous IPA, then powders were dissolved in 5 ml distilled water, finally the filtrates were used to detect H 2 O 2 with KMnO 4 redox titration. Notes: As shown above, the production rate of H 2 O 2 slows down after 4 min, which could be ascribed to the accumulation of H 2 O 2 on the surface of CNK-OH. Therefore, the rate in 4 min was used to estimate the production of H 2 O 2 in 60 min for 50 mg of CNK-OH&Fe sample. The rate of H 2 O 2 production is 1.74 mol min -1 for 10 mg sample. In 60 min, for 50 mg sample, Amount of H 2 O 2 = 1.74 ( mol min -1 )*60 min*[50(mg)/10(mg)] = 522 mol S-29

30 Figure S19. Influence of CNK-OH&Fe on the absorption spectra of DPD/POD-H 2 O 2. Notes: the powder of CNK-OH&Fe was first added into the base solution of H 2 O 2 (0.8 mol/5 ml) and stirred for 5 min, then the filtrate of above solution and origin base solution of H 2 O 2 were both used to measure the amount of H 2 O 2 with DPD method. S-30

31 Figure S20. ESR spectra of as-prepared samples. a, Confirmation of the single peak arose in ESR spectra of DMPO-spin adduct over the CN and the suspension of CNK-OH. b, ESR spectra of DMPO-spin adduct measured in the aqueous solution of CNK-OH&Fe before and after Ar purged. Note: Each group contrast experiment is conducted in the same conditions. S-31

32 Figure S21. Comparison of C 3 N 4 -based photocatalysts in acetone evolution and H 2 O 2 production. a, Amounts of acetone yield over C 3 N 4 -based samples with and without Fe 3+. b, H 2 O 2 production for solid C 3 N 4 -based samples. Reaction Conditions: 10 mg sample, 300 W Xe lamp with an L42 filter ( > 400 nm). Notes: the samples were first irradiated with gaseous IPA (1000 mol) for 2 min, then powders were dissolved in DPD solution, the filtrates were used to detect H 2 O 2 with DPD method. Note: the DPD and POD solution were adjusted from 50 l to 200 l to react with the mass H 2 O 2. Interestingly, it presents positive correlation between the photoactivity enhancement over C 3 N 4 -based samples and the amount of H 2 O 2 in situ generated on the surface of samples, further confirming the solid-gas Fenton process. S-32

33 Figure S22. Cycle test of IPA photodegradation over CNK-OH&Fe. Closed symbols, evolution amount of acetone; opened symbols, evolution amount of CO 2. S-33

34 Table S5. Concentrations of oxygen-related species over CNK-OH&Fe before reaction and after reaction Peak Location (ev) ( # B. R. / # A. R.) Species Proportion (B. R.) (at%) Proportion (A. R.) (at%) Samples before Adsorbed / reaction and after H 2 O cycle test / OH Samples before Adsorbed / reaction and after H 2 O cycle test / OH # B. R., before reaction; A. R., after reaction. S-34

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