Supporting Information for

Transcription

1 Supporting Information for 2D/2D g-c 3 N 4 /MnO 2 nanocomposite as a direct Z-scheme photocatalyst for enhanced photocatalytic activity Pengfei Xia, Bicheng Zhu, Bei Cheng, Jiaguo Yu, *,, and Jingsan Xu *, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 122 Luoshi Road, Wuhan, , P. R. China. jiaguoyu@yahoo.com School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, 2 George Street, Brisbane, QLD 4001, Australia. Jingsan.Xu@qut.edu.au Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia. jiaguoyu@yahoo.com S1

2 Characterizations A D/Max-RB X-ray diffractometer (Rigaku, Japan) was used to obtain X-ray diffraction (XRD) patterns. Photoluminescence (PL) emission spectra were recorded on a Fluorescence spectrophotometer (F-7000, Hitachi, Japan) using a xenon lamp as light source. Fourier transform infrared spectra (FTIR) were measured on an IR Affinity-1 FTIR spectrometer (Shimadzu, Japan). TEM images were obtained on a transmission electron microscope (JEM-2100F, JEOL, Japan) with an accelerating voltage of 200 kv. FESEM images were recorded on a field emission scanning electron microscope (JSM-7500, JEOL, Japan) with an accelerating voltage of 15 kv. Chemical states of elements were measured on an X-ray photoelectron spectroscopy (XPS) equipped with an ultra-high vacuum VG ESCALAB 210 electron spectrometer. The binding energy was calibrated with the C 1s peak at ev before analysis. UV visible diffuse reflectance spectra were obtained on a UV visible spectrophotometer (UV-2550, Shimadzu, Japan), using BaSO 4 as the reference standard. N 2 adsorption-desorption isotherms were measured on a Micromeritics ASAP 3020 equipment (USA). All as-synthesized samples were degassed at 180 C for 5 h prior to adsorption measurements. Specific surface area was determined by the multipoint Brunauer Emmett Teller (BET) method. Electrochemical measurements were carried out on an electrochemical workstation (CHI66E, China), using the Na 2 SO 4 solution as the electrolyte. Electron paramagnetic resonance (EPR) spectra are performed on an ESR spectrometer (MEX-nano, Bruker) with a modulation frequency of 100 khz and a microwave power of 15 mw. S2

3 DFT calculations Density functional theory (DFT) calculations were carried out using the Viennaab initio Simulation Package (VASP). The Perdew Burke Ernzerhof (PBE)of the generalized gradient approximation (GGA) was used as the exchange correlation function. An energy cutoff of 360 ev and a Monkhorst Pack k-point mesh of were used to perform geometry optimization and electronic property calculations. The energy and force convergence criteria were set as ev per atom and 0.03 ev Å 1, respectively.a vacuum space of 20 Å was used. The work function (Φ) is calculated using Φ= E Vac E F, where E Vac is the electrostaticpotential of the vacuum level and E F is the Fermi energy. Electrochemical measurements The as-prepared samples were mixed with alcohol to form homogeneous seriflux, which was uniformly flat on the FTO glass (1 x 1cm) by spin coating method. Then the mixed matrix was thoroughly dried at 60 in a vacuum drying oven to obtain the working electrodes. An Ag/AgCl electrode and Pt filament were used as the reference and counter electrode, respectively. Mott Schottky plots and electrochemical impedance spectroscopy (EIS) were tested in the electrolyte of 0.5M Na 2 SO 4 aqueous solution. Also, Transient photocurrent response was recorded on the electrochemical workstation under the irradiation of simulation sunlight. The bias voltage in above measurements is under open-circuit voltage. Photodegradation of Rhdamine B (RhB) In a typical experiment, a 300W xenon lamp was used as the light source. 50mg S3

4 as-prepared samples were added in a beaker with 50ml 10mg/L Rhdamine B solution under sonication. After 10 min, all above was placed in darkness for 1h to reach adsorption-desorption equilibrium. Every 10min, 5ml centrifuged RhB solution was sampled and determined using an UV-vis spectrophotometer (UV-1240, Shimadzu, Japan) at wavelength of 554 nm. Photodegradation of Phenol In current experiment, a 300W xenon lamp was used as the light source. 50mg as-prepared samples were added in a beaker with 50ml 50mg/L phenol solution under sonication. After 10 min, all above was placed in darkness for 1h to reach adsorption-desorption equilibrium. Several minutes later, 5ml centrifuged phenol solution with catalysts was sampled and centrifuged. Then the supernatant was determined using an UV-vis spectrophotometer (UV-1240, Shimadzu, Japan) at wavelength of 269 nm. EPR measurements The hydroxyl radicals ( OH) and superoxide anion radicals ( O 2 ) usually can be trapped by the 5,5-dimethyl-l-pyrroline N-oxide (DMPO), producing the ESR signals of their adducts. The mixed solution of DMPO/H 2 O and DMPO/CH 3 OH was prepared by the traditional method. Briefly, 10 mg as-fabricated samples and 40 µl DMPO were dissolved in 1 ml deionized water under the stirring condition. Then the mixture was irradiated under a 300W xenon lamp for 120s. After that, 0.1 ml mixture solution (containing DMPO- OH) was quickly detected by the ESR spectrometer. The detection method of DMPO- O 2 was identical to the DMPO- OH, except that the S4

5 deionized water was replaced by the methanol (CH 3 OH). Analysis The degradation efficiency of Rhdamine B was evaluated as the equation (1): (1) where η represents 他 he degradation efficiency; C 0 is the initial concentration of Rhdamine B solution; C t means the instantaneous concentration of Rhdamine B solution. To evaluate properties of photocatalytic degradation, the decomposition kinetics for as-prepared samples was quantitatively investigated based on Langmuir-Hinshelwood model. Their kinetic behaviors can be described as the equation (2): (2) where C 0 is the initial concentration of Rhdamine B solution; C t is the instantaneous concentration of Rhdamine B solution; Ka represents the apparent reaction rate constant. S5

6 Figure S1. The elemental mapping images of the 2D/2D g-c3n4/mno2 heterostructured photocatalyst. S6

7 Figure S2. The PL spectra of g-c 3 N 4 nanosheets, MnO 2 nanosheets and g-c 3 N 4 / MnO 2 nanocomposites. S7

8 Figure S3. The survey XPS spectra of MnO 2, g-c 3 N 4 nanosheets and g-c 3 N 4 /MnO 2 nanocomposites, respectively. S8

9 Figure S4. The XRD patterns of 2D/2D g-c 3 N 4 /MnO 2 heterostructured photocatalyst before and after photocatalytic reaction. S9