Supplementary Information

Transcription

1 Supplementary Information Visible Photocatalytic Water Splitting and Photocatalytic Two-Electron Oxygen Formation over Cu and Fe Doped g-c 3 N 4 Zhen Li a,b, Chao Kong a,b, Gongxuan Lu a* a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China b University of Chinese Academy of Science, Beijing , China. *Corresponding author: gxlu@lzb.ac.cn. Tel.: S1

2 Experimental Section Preparation of the g-c 3 N 4, Fe/ C 3 N 4 and Cu/ C 3 N 4 photocatalysts. Typically, 20 g of urea powder was put into a crucible with a cover and then heated to 550 C within 30 min in a muffle furnace under the protection of nitrogen and maintained at this temperature for 3 h. g-c 3 N 4 was obtained after cooling down to room temperature. For preparation of the Fe/C 3 N 4 and Cu/C 3 N 4 photocatalysts, a calculated amount of FeCl 3 and CuCl 2 aqueous solution was added into 20 g of urea powder. Then the mixture was put into a crucible with a cover and heated to 550 C within 30 min in a muffle furnace under the protection of nitrogen and maintained at this temperature for 3 h. The resultant powder was cooled to room temperature, washed with ultrapure water, collected by filtration and finally dried at room temperature. S2

3 Photocatalytic O 2 evolution activity and AQE measurements. Photocatalytic experiments were performed in a sealed Pyrex flask (150 ml) with a flat window (an efficient irradiation area of 14 cm 2 ) and a silicone rubber septum for sampling at ambient temperature. The reaction system was constructed by adding10mg catalysts to 100 ml 2.5% H 2 O 2 aqueous solution (0.1mg/ml). The light source was a 300-W Xe lamp, which equipped with either a 420 nm cutoff filter or various band-pass filters. Photon flux of the incident light was determined using a Ray virtual radiation actinometer (FU 100, silicon ray detector, light spectrum, nm; sensitivity, µvµmol -1 m -2 s -1 ). Prior to irradiation, the suspension of the catalysts was dispersed by ultrasonic treatment for 30 min and degassed by bubbling Ar gas for 20 min. The amount of O 2 evolution was measured using gas chromatography (Aglient 6820, TCD, 13 column, Arcarrier), and the AQE was calculated from the ratio of the number of reacted electrons during oxygen evolution to the number of incident photons by the follow equation: AQE [%] = 2 number of evolved O 2 molecules / number of incident photos 100 S3

4 Working Electrode Preparation and Photoelectrochemical Measurements Photocurrent responses of catalyst samples were measured on an electrochemical analyzer (CHI660E) in a homemade standard three-compartment cell, consisting of an organic glass enclosure with a quartz window and a 1.2 cm diameter opening opposite the window to the work electrode was clamped. The working electrodes were prepared by drop-coating sample suspensions directly onto the precleaned indium tin oxide glass (ITO glass) surface by microsyringe with an infrared heat lamp to speed drying. The surface of working electrode exposed to the electrolyte was a circular film with the geometrical surface areas of1 cm 2. Platinum foil was used as a counter electrode and a saturated calomel electrode (SCE) was used as the reference electrode. The supporting electrolyte was 2.5% H 2 O 2 aqueous solution mixed with 0.1 M Na 2 SO 4 aqueous solution. A 300-W Xe lamp with an optical cutoff filter (λ 420 nm) was used for excitation light source. The unbiased anodic photocurrent was investigated with an amperometric current-time technique. S4

5 Characterizations Transmission electron microscopy (TEM) images were taken with a Tecnai-G2-F30 field emission transmission electron microscope operating at accelerating voltage of 300 kv. The X-ray diffraction patterns (XRD) of the samples were recorded on a Rigaku B/Max-RB X-ray diffractometer with a nickel-filtrated Cu Kα radiation. The accelerating voltage and current were 40 kv and 30 ma, respectively. XPS analysis was performed using a VG ScientificESCALAB210-XPS photoelectron spectrometer with a Mg KRX-ray resource. The fluorescence decay times were measured using the Horiba Jobin Yvon Data Station HUB operating in time-correlated single photon counting mode (TCSPC) with the time resolution of 200 ps. Nano LED diode emitting pulse sat 460 nm with 1 MHz repetition rate was used as an excitation source. Light-scattering Ludox solution was used to obtain the instrument response function (prompt). The time ranges are0.055 ns/channel in 4096 effective channels. Horiba Jobin Yvon DAS6 fluorescence decay analysis software was used to fit the model functions to the experimental data. FT-IR spectra were measured on a Nexus 870 FT-IR spectrometer from KBr pellets asthe sample matrix. UV-vis diffuse reflectance spectra were obtained with a Shimadzu UV-3600 UV-vis-near-IR spectrophotometer. BaSO4 was used as a reflectance standard. The field-emission scanning electron microscopy (FESEM) images were recorded on a JSM-6701F scanning electron microscope operated at an accelerating voltage of 5 kv. The loading amount was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). S5

6 Fig. S1 The meteorological chromatography spectrums of products catalyzed by Fe/C 3 N 4 (0.37wt%) under visible light in the water. (A), (B), (C) and (D) represented the reaction continued 0, 2, 4 and 10 hours, respectively. S6

7 Fig. S2 Hydrogen peroxide (H2O2) measurements were performed on 10.0 ml reaction suspension, which were taken immediately after the irradiation (a: Fe/C 3 N 4, b: Cu/C 3 N 4 ). For each test, the Cu/C 3 N 4 and Fe/C 3 N 4 dispersions were allowed to react for 12h under visible light irradiation. Then a 2.5 ml solution with 1% o-tolidine in 0.1 M HCl was added to the suspension. This mixture was allowed to react for 5 min. In the presence of peroxides, a blue color is formed very quickly resulting from the oxidation of o-tolidine. Subsequently, the dispersion was acidified with 1 M HCl (10 ml), which caused the color of the dispersion to turn yellow. The yellow-coloured species are the protonated form of the 2-electron oxidation product of o-tolidine formed. S7

8 a) b) Fig. S3 The effect of Fe and Cu concentration on the activity of O 2 evolution over g-c 3 N 4 photocatalyst under visible light irradiation (λ 420 nm). S8

9 Fig. S4 The effect of H 2 O 2 concentration on the activity of O 2 evolution over Cu/C 3 N 4 (0.42wt%) photocatalyst under visible light irradiation (λ 420 nm). S9

10 Fig. S5 the UV-vis absorption spectra of g-c 3 N 4, Fe/C 3 N 4 and Cu/C 3 N 4 photocatalysts. The trailing adsorption in the region of nm was due to the optical absorption of loaded Fe, Cu and their oxides in the visible region [JPCC 2008, 112, 15900; PCCP 2014, 16, 11054]. However, the blue-shift of adsorption edge had been observed, which was also reported in the previous report [Dalton Trans. 2012, 41, ]. In addition, the Fe and Cu also contribute the weak absorption to the slight blue-shift of adsorption edge and a trailing adsorption in the region of nm. S10

11 Fig. S6. The onset potentials of g-c 3 N 4, Fe/C 3 N 4 and Cu/C 3 N 4 photocatalysts for H 2 O 2 -splitting. S11

12 Fig. S7. The current-time curve of g-c 3 N 4, Cu/C 3 N 4 (0.42wt%) and Fe/C 3 N 4 (0.37wt%) photocatalysts under visible light irradiation (>420nm) and dark condition in mixed solution of 2.5% (v/v) H 2 O 2 and 0.1 M Na 2 SO 4. S12

13 a) b) c) d) e) f) Fig. S8 Transmission electron microscopy images of g-c3n4 (A), Fe/C3N4 (C) and Cu/C3N4 (E) photocatalysts; HRTEM images of g-c3n4 (B), Fe/C3N4 (D) and Cu/C3N4 (F) photocatalysts. S13

14 Fig. S9 The elemental mapping images of Fe/C 3 N 4 (A), Cu/C 3 N 4 (B) and g-c 3 N 4 (C) photocatalysts. S14

15 Fig. S10 The SEM images of Fe/C3N4 (A), Cu/C3N4 (B) and g-c3n4 (C) photocatalysts. S15

16 Fig. S11 The TEM images of Fe/C3N4 (A), Cu/C3N4 (B) and g-c3n4 (C) photocatalysts. S16

17 Fig. S12 The FT-IR spectra of g-c 3 N 4, Fe/C 3 N 4 (0.37wt%) and Cu/C 3 N 4 (0.42wt%) photocatalysts. S17

18 Fig. S13 The XPS survey spectra of g-c 3 N 4, Fe/C 3 N 4 and Cu/C 3 N 4 photocatalysts. S18

19 Fig. S14 The Fe and Cu XPS spectra of photocatalysts after reaction. S19

20 Fig. S15 The FT-IR spectra of Fe/C 3 N 4 photocatalyst before and after the H 2 O 2 -splitting reaction. S20

21 Species Energy (a.u) H 2 O OH HO O H 2 O O e h Fig. S16 The optimum result of energy calculation. S21

22 Fig. S17 The effect of H 2 O 2 concentration on the activity of H 2 evolution over Fe/C 3 N 4 (0.37wt%) photocatalyst under visible light irradiation in the water for 24 h. The results showed the amount of H 2 evolution gradually decreased with the H 2 O 2 concentration increased. S22

23 Fig. S18 The time-resolve florescence decay plots and static florescence spectra of g-c 3 N 4, Fe/C 3 N 4 and Cu/C 3 N 4 photocatalysts. S23