Photocatalytic Mechanism Regulation of Bismuth Oxyhalogen via Changing Atomic Assembly Method

Transcription

1 Supporting Information Photocatalytic Mechanism Regulation of Bismuth Oxyhalogen via Changing Atomic Assembly Method Yang Bai, & Xian Shi, & Ping-Quan Wang, &* Haiquan Xie, # Liqun Ye, &,# * & School of Oil & Natural Gas Engineering, Southwest Petroleum University, Chengdu , China. # Henan Key Laboratory of Environmental and Energy Photocatalysis; Engineering Technology Research Center of Henan Province for Solar Catalysis; Collaborative Innovation Center of Water Security for Water Source Region of Mid-route Project of South-to-North Water Diversion of Henan Province; College of Chemistry and Pharmaceutical Engineering; Nanyang Normal University, Nanyang , China. *Correspondence author: Southwest Petroleum University; Nanyang Normal University, China. yeliquny@163.com (L Ye) baiyanghyq@foxmail.com (P.Q Wang) S-1

2 Part 1: Materials Preparation and characterization Materials Preparation BiOBr (BiOI): 1 mmol of Bi(NO 3 ) 3.5H 2 O was dissolved in 20 ml deionized water and 20 ml EG containing 1mmol KBr (KI) was added dropwise. The precipitates were collected after continuous stirring for 3 h, washed repeatedly with deionized water, and dried at 80 C for 10 h. BiOBr 0.5 I 0.5 : 0.5mmol KBr and 0.5 mmol KI were dissolved in 20 ml EG and added into 20 ml aqueous solution containing 1 mmol of Bi(NO 3 ) 3.5H 2 O dropwise. The precipitates were collected after continuous stirring for 3 h, washed repeatedly with deionized water, and dried at 80 C for 10 h. 0.5BiOBr/0.5BiOI: 0.05 mol of KI and 1 mmol of Bi(NO 3 ) 3.5H2O were dispersed in 20mL of deionized water under ultrasonication for 30 min. Then 20mL of EG containing 0.5 mmol KBr was added into above aqueous solution dropwise. The precipitates were collected after continuous stirring for 3 h, washed repeatedly with deionized water, and dried at 80 C for 10 h. Characterization X-ray diffraction patterns (XRD) were recorded by Smart Lab X-ray diffractometer (Rigaku, Tokyo, Japan) operating at 40 ma and 40 kv using Cu Kα radiation. The 2θ range of XRD patterns were taken over Transmission electron microscopy (TEM) images were obtained by a JEOL JEM-2100F (RH) Field Emission Electron Microscope working at 200 kv. X-ray photoelectron spectroscopy (XPS) data were obtained by Thermo ESCALAB 250XI X-ray photoelectron spectrometer (Al Ka, 150 W, C 1s ev).uv-vis diffuse reflectance spectra (DRS) were obtained using UV-Vis S-2

3 spectra (Perkin Elmer, Lambda 650s, BaSO 4 as a reference). A Quantachrome Autosorb-IQ automated gas sorption system was used to measure the specific surface area. Figure S1 XRD patterns of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5 : (a) 5-15, and (b) Figure S2 TEM image of (a) BiOBr 0.5 I 0.5 and (b) 0.5BiOBr/0.5BiOI. S-3

4 Figure S3 XPS spectra of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiO Br 0.5 I 0.5 : (a) survey, (b) Bi 4f, (c) Br 3d, and (d) I 3d. Figure S4 Valence band XPS of BiOBr 0.5 I 0.5, BiOBr and BiOI. S-4

5 Figure S5 DRS spectra of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5 (a); band gaps of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5 (b). Figure S6 Nitrogen adsorption-desorption isotherm and pore size distribution of BiOI, BiOBr, BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI. Additional discussion: Figure S1(a) and S1(b) displayed the enlarged XRD patterns for comparing and distinguishing 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5. For (001) peaks (Figure S1(a)), 0.5BiOBr/0.5BiOI at 2θ=9.65 and 10.86, interplanar spacing data of (110) planes were 0.91nm and 0.81nm, were entirely different from BiOBr 0.5 I 0.5 at 2θ=10.06, S-5

6 interplanar spacing data of (110) plane was 0.87nm. 0.5BiOBr/0.5BiOI combining the same (001) peaks of BiOBr and BiOI indicated the successful combination of two pure components, while BiOBr 0.5 I 0.5 had only one different (001) signal implied BiOBr 0.5 I 0.5 was newly formed single crystal structure. The same phenomenon about (102) peak was also found in Figure 1c. The mainly peak at and matched well with the (102) peak of BiOBr and BiOI respectively but different from BiOBr 0.5 I 0.5 at It can be concluded that 0.5BiOBr/0.5BiOI formed by successful combination of BiOI and BiOBr maintaining original structures of two pure components may display different performances from BiOBr 0.5 I 0.5, a new single crystal monomer formed by chemical combination with the same elements. TEM images BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI were shown in Figure S2. TEM images of BiOI 0.5 Br 0.5 (Figure S2(a)) and 0.5BiOBr/0.5BiOI (Figure S2(b)) demonstrated the same architecture and size. It implied that shape and specific surface area cannot induce the difference of photocatalytic activity between BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI. We could see from the figures that BiOBr 0.5 I 0.5 was pure compound different from the 0.5BiOBr/0.5BiOI formed by BiOBr coupling with BiOI in agreement witn XRD analysis. Figure S3 showed the X-ray photoelectron spectrometer (XPS) spectra of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5. In Figure S3(a), the survey spectrum showed the same elements (Bi, O, I, Br and contaminative C) for 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5, indicating the high purity of 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5 samples. Figure S3(b) showed the Bi 4f7/2 and Bi 4f 5/2 peaks of 0.5BiOBr/0.5BiOI were at ev and ev, and the Bi 4f7/2 and Bi 4f 5/2 peaks of BiOBr 0.5 I 0.5 were at ev and ev, suggesting that Bi 3+ existed in these two samples. The band energies of ev was corresponding to Br 3d (Figure S3(c)), and the band energies of ev and ev were corresponding to I 3d 5/2 and I 3d 3/2 (Figure S3(d)), which associated with Br - and I - in these two samples, respectively. Figure S4 showed the valance band XPS spectra of BiOI, BiOBr and BiOBr 0.5 I 0.5 and the VB position was 1.23 ev, 1.96 ev and 1.41 ev, respectively. S-6

7 Figure S5(a) showed the comparison of the UV vis DRS spectra and (b) of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5. BiOI and BiOBr, had fundamental adsorption edges at nm and nm, respectively. As for coupling and solid solution, 0.5BiOBr/0.5BiOI showed adsorption edges at nm and BiOBr 0.5 I 0.5 was of nm. It can be observed from the spectra that BiOBr absorbed visible light slightly while the absorption edge of BiOI extended nearly about the whole visible light region demonstrated strong visible light response of BiOI than BiOBr. And the absorption edges of BiOI/BiOBr and BiOBr 0.5 I 0.5 both had obvious red shift proved I element involved in forming structure of coupling or solid solution. Figure S5(b) revealed the calculation results of BiOI, BiOBr, 0.5BiOBr/0.5BiOI and BiOBr 0.5 I 0.5 were of 1.68 ev, 2.67 ev, 1.87 ev and 1.78 ev, respectively. The nitrogen adsorption desorption isotherms of BiOI, BiOBr, BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI were carried out and the results are presented in Figure S6. The curves of these four samples were matched well with a type IV isotherm with an indistinct H3 hysteresis loop. When the relative pressure (P/P0) increasing, it can be observed there were more adsorbed volumes. The experimental results implied there were many heterogeneous pores on the surface of these four samples which were regarded as slit pores accumulated by flaky particles. The corresponding BET surface areas of BiOI, BiOBr, BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI were of m 2 g -1, m 2 g -1, m 2 g -1 and 9.33 m 2 g -1, respectively. S-7

8 Part 2: Photocatalytic RhB degradation and CO 2 conversion Experimental Procedure RhB degradation: Photocatalytic activity was evaluated by the degradation of RhB under visible-light irradiation using a 300-W Xe lamp with a UV-cutoff filter (λ> 400nm). An amount of 0.05g of photocatalyst was each suspended in a 100 ml aqueous solution of 20 mg/l RhB. Before illumination, the suspensions were magnetically stirred in the dark for 1 h to ensure the establishment of an adsorption- desorption equilibrium between the photocatalysts and RhB. Then, the UV-vis adsorption spectrum of the centrifuged solution was recorded using a UV-vis spectrophotometer. The experimental result was shown in Figure 2(a). CO 2 conversion: Photocatalytic CO 2 conversion results were obtained by a Labsolar-Ⅲ AG closed 350 ml gas system (Beijing Perfect light Technology Co., Ltd China) g of BiOBr/BiOI and BiOI 0.5 Br 0.5 samples were uniformly dispersed onto a cm 2 glass sheet and it was put in a reaction cell (Pyrex glass). Above system was firstly thoroughly vacuum-treated to remove the air completely before light irradiation. Subsequently, 10 ml H 2 SO 4 (2 M) was added into the reactor to achieve 1 atm CO 2 gas with NaHCO 3. Then the reactor was operated under a 300 W high pressure xenon lamp with 400 nm cutoff filter (PLS-SXE300, Beijing Perfect light Technology Co., Ltd China) maintaining the photoreaction temperature at 15 C with DC-0506 low-temperature thermostat bath (Shanghai Sunny Hengping Scientific Instrument Co., Ltd China). At each time interval, about 1 ml of gas was taken from the reaction cell with subsequent qualitative analysis by GC9790II gas chromatography (GC, Zhejiang Fuli Analytical Instrument Co., Ltd China) equipped with a flame ionization detector (FID, GDX-502 columns). The quantification of the production yield was based on a calibration curve. The outlet gases were determined to be CO, CH 4 and CO 2. The experimental result was shown in Figure 2(b). [1, 2] S-8

9 Additional discussion: The photocatalytic activities of BiOI, BiOBr, BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI were evaluated by photodegradation of RhB and CO 2 conversion under visible-light irradiation, the degradation results were shown in Figure 2(a). Over 120 min degradation, BiOBr 0.5 I 0.5 performed best and degraded about 90% of RhB and coupled 0.5BiOBr/0.5BiOI also had favourable photocatalytic performances and degraded about 70% of RhB. If the main photocatalytic mechanism of solid solution and coupling was separation of electrons and holes, solid solution should also have better CO 2 conversion than coupling, but CO 2 conversion results in Figure 2(b) showed 0.5BiOBr/0.5BiOI photocatalyst had best CO 2 conversion ability with about 15 μmol g -1 after 2 h irradiation, which was about 2 times than BiOBr 0.5 I 0.5 (8 μmol g -1 ). Figure S7 Photocatalytic stability experiments of BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI for RhB degradation (a) and CO 2 conversion (b). S-9

10 Part 3: Photocatalytic Trapping Experiment Experimental Procedure For detecting the active species during photocatalytic reactivity, singlet oxygen ( 1 O 2 ), superoxide radical (O 2 ) and electron (e ) were investigated by adding 2 mmol TEMPO (a quencher of 1 O 2 ), BQ (a quencher of O 2 ) and AgNO 3 (a quencher of e - ), respectively. Figure S8 Trapping experiment of active species during the photocatalytic degradation of RhB over (a) BiOBr 0.5 I 0.5 and (b) 0.5BiOBr/0.5BiOI. Additional discussion: Figure S8 revealed the trapping experimental results of active species during the photocatalytic reaction of BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI. For BiOBr 0.5 I 0.5, it can be seen that the photocatalytic degradation of RhB decreased obviously with the addition of 2 mmol TEMPO (a quencher of 1 O 2 ), while the degradation of RhB almost had no change. It can be concluded that singlet oxygen was the main active species of solid soltion for RhB degradation. For 0.5BiOBr/0.5BiOI, degradation of RhB decreased obviously with the addition of 2 mmol BQ (a quencher of O 2 ) and AgNO 3 (a quencher of e ), respectively, which demonstrated that O 2 generated by e - and oxygen was the main active species under visible light irradiation. S-10

11 Part 4: Evaluation of 1 O 2 and O 2 generation [3,4] Experimental Procedure NBT ( mol L -1, exhibiting an absorption maximum at 259 nm) and TMB (0.1 g L -1, exhibiting an absorption maximum at 380 nm) were used to determine the amount of photocatalytic O 2 and 1 O 2 generation. 10 mg of photocatalysts were added into 50 ml NBT aqueous and sampling ever 10 min; 1 mg of photocatalysts was added 16 ml HAc/NaAc buffer solution (ph=3.6) and 4 ml distilled water, then 2 mg TMB was added in and sampling every 3 min. Both of them were stirred under a xenon lamp. The production of O 2 was quantitatively analysed by detecting the concentration of NBT and 1 O 2 was analysed by the oxidation rate of TMB with a UV-vis spectrophotometer. ESR Tests 50 μl of aqueous suspension of samples (2 mg L 1 ) was mixed with 500 μl of TEMP ( M) solution. After being illuminated for 5 min, the mixture was characterized using a Bruker EMX plus model spectrometer operating at the X-band frequency (9.4 GHz) at room temperature for 1 O 2 test. The O 2 trapping ESR tests were also performed as described above, except the use of DMPO ( M) as the spin-trapping agent. A xenon lamp (50 W) was used as the light source. S-11

12 Figure S9 TMB measurement results of BiOBr 0.5 I 0.5 (a), 0.5BiOBr/0.5BiOI (b), BiOBr (c), and BiOI (d). Figure S10 NBT measurement results of BiOBr 0.5 I 0.5 (a), 0.5BiOBr/0.5BiOI (b), BiOBr (c), and BiOI (d). Additional discussion: S-12

13 The oxygen-containing functional groups of BiOX could influence singlet oxygen generation greatly. So we measured molecular oxygen activation properties of BiOI, BiOBr, BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI by using 3, 3, 5, 5 -tetramethylbenzidine (TMB) as probe molecule and we evaluated TMB oxidation by monitoring absorbance peaks at 380 nm, as shown in Figure S9. These four samples all revealed an increasing oxidation rate and solid solution BiOBr 0.5 I 0.5 exhibited best TMB oxidation activity, indicated more 1 O 2 genneration of solid solution structure. Meanwhile NBT measurements (Figure S10), evaluated by absorbance peaks at 259 nm, had finished to estimate the superoxide radical (O - 2 ) generated by as prepared samples, further evaluated electron-hole pairs separation efficiency. As shown in Figure S10, 0.5BiOBr/0.5BiOI performed best in NBT reduction obviously than other samples. The experimental results expounded coupling 0.5BiOBr/0.5BiOI could generate more O - 2 than BiOBr 0.5 I 0.5, implied the coupling had better separation of electrons and holes efficiency. In summary, when these four samples worked for degradation, solid solution performed best because more singlet oxygen generated by process of exciton photocatalytic process. When came to CO 2 conversion, the favourable separation of electrons and holes efficiency made coupling showed better reducibility. S-13

14 Part 5: Electrochemistry Figure S11. Transient photocurrent responses of BiOBr 0.5 I 0.5, 0.5BiOBr/0.5BiOI, BiOBr and BiOI. AS shown in Figure S11, the photocurrent for 0.5BiOBr/0.5BiOI revealed to be much higher than BiOBr 0.5 I 0.5 upon light irradiation, indicated 0.5BiOBr/0.5BiOI showed the better mobility and separation efficiency of the photo-induced carriers than BiOBr 0.5 I 0.5. In order to further explore the photocatalytic mechanisms of BiOBr 0.5 I 0.5 and 0.5BiOBr/0.5BiOI, photocatalytic activities measurements had been done to verify the basic characterization results and suppose we proposed. S-14

15 Part 6: References (1). Ye, L.; Jin, X.; Liu, C.; Ding, C.; Xie, H.; Chu, KH.; Wong, PK. Thickness-Ultrathin and Bismuth-Rich Strategies for BiOBr to Enhance Photoreduction of CO 2 Into Solar Fuels. Applied Catalysis B Environmental 2016, 187, (2). Ye, L.; Wang, H.; Jin, X.; Su, Y.; Wang, D.; Xie, H.; Liu, X.; Liu, X. Synthesis of Olive-Green Few-Layered BiOI for Efficient Photoreduction of CO 2 Into Solar Fuels Under Visible/Near-Infrared Light. Solar Energy Materials & Solar Cells 2016, (3). Wang, H.; Yang, X.; Shao, W.; Chen, S.; Xie, J.; Zhang, X.; Wang, J.; Xie, Y.; Ultrathin Black Phosphorus Nanosheets for Efficient Singlet Oxygen Generation. Journal of the American Chemical Society 2015, 137, (4). Wang, H.; Jiang, S.; Chen, S.; Li, D.; Zhang, X.; Shao, W.; Sun, X.; Xie, J.; Zhao, Z.; Zhang, Q. Enhanced Singlet Oxygen Generation in Oxidized Graphitic Carbon Nitride for Organic Synthesis. Advanced Materials 2016, 28, S-15