Enhancing reactive oxygen species generation and photocatalytic

performance via adding oxygen reduction reaction catalysts into the

photocatalysts

Shuquan Huang,a Yuanguo Xu,a* Ting Zhou,a Qingqing Liu,a Yan Zhao,b Liquan Jing,a Hui Xu,b

Huaming Lib*

a School of Chemistry and Chemical Engineering, School of Pharmacy, Jiangsu University, Zhenjiang 212013, PR

China. b Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China.

*E-mail: xuyg@ujs.edu.cn; lhm@ujs.edu.cn

Methods

1. Characterization

X-ray diffraction (XRD) patterns were monitored on a Bruker D8 diffractometer equipped with Cu-K (λ = 1.5418 Å). FT-IR spectra were measured via a Nicolet Model Nexus 470 FT-IR spectrometer by using the KBr disks. Scanning electron microscopy (SEM) measurements were obtained by a field emission microscope (JEOL JWSM-7001F) and the energy-dispersive X-ray spectroscope (EDS) was collected at an acceleration voltage of 10 kV simultaneously. Transmission electron microscopy (TEM) images were observed on a JEOL JEM-2010 transmission electron microscope. The XPS spectra were probed by using an ESCALab MKII X-ray photo-electron spectrometer with Mg Kα radiation. The magnetic properties of the samples were performed on a vibrating sample magnetometer (Quantum Design Corporation, USA) with a maximum applied field of ± 2 T. The UV–vis diffuse reflectance spectra were measured by using BaSO4 as a reference on a UV-3600Plus UV–vis spectrophotometer (Shimadzu Corporation, Japan). The photoluminescence (PL) intensity of the prepared samples were collected on a Varian Cary Eclipse spectrometer. The oxygen temperature programmed desorption (O2-TPD) analysis was performed on a Micromeritics, AutoChem II 2920. The oxygen temperature programmed desorption (O2-TPD) analysis was performed on a Micromeritics, AutoChem II 2920. The procedures were as followed: (1) each sample (150 mg) was pretreated under He flow (20 mL/min) at 150 for 40 min; (2) the sample was purged with 5% O℃ 2/He gas flow for 2h at room temperature for O2 adsorption; (3) the sample was heated to 800 at a heating rate of 10 /min℃ ℃ under a pure He gas flow. The signal of O2 desorption was measured by thermal conductivity detector.

2. Electrochemical measurements2.1 Photocurrent measurements and electrochemical impedance measurementsThe photocurrent measurements and the electrochemical impedance spectroscopy were conducted in a standard three-electrode electrochemical cell at room temperature on an electrochemical workstation (CHI 660e, Chenhua Instrument Company, Shanghai, China). The standard three-

electrode setup was used with the ITO-coated glass as photoelectrode, a Pt foil as counter electrode, and an Ag/AgCl electrode as reference electrode.Preparing of the working electrodes: 5.0 mg as-synthesized photocatalysts were dispersed in 1 mL of ethylene glycol, of which 20 µL suspensions were then uniformly dropped onto a 1 cm × 0.5 cm indium tin oxide (ITO)-coated glass. Subsequently, the ITO-coated glass was heated at 70℃ in a drying oven for 12 h.The photocurrents were measured on a CHI 660e electrochemical station (Shanghai Chenhua, China) in ambient conditions under irradiation of a 250 W Xe lamp (CHF-XM35-500W, Beijing Chang Tuo). The three electrodes were inserted in a quartz cell filled with 0.1 M PBS electrolyte. The photoresponse of the prepared photoelectrodes (i.e., I-t) was operated by measuring the photocurrent densities under chopped light irradiation (light on/off cycles: 20 s) at a bias potential of 0.29 V vs. Ag/AgCl.The O2 control photocurrents were also measured on the CHI 660e electrochemical station with the same light source, reference electrode and counter electrode. In a typical procedure, the 3% Ag3PO4@CoFe2O4 modified ITO working electrodes and PBS electrolyte were kept at flowing N2

ambient for 1h prior to the measurements. Subsequently, the N2 pretreatment working electrodes were inserted in a quartz cell filled with N2 pretreatment 0.1 M PBS electrolyte and collected the photocurrents signals and named as 3% Ag3PO4@CoFe2O4 in N2. After several steady turn-off cycles, paused the measurement and O2 was slowly bubbled into the quartz cell for another 1h. After that, restarting to collect the photocurrents signals and named as 3% Ag3PO4@CoFe2O4 in O2.The electrochemical impedance spectroscopy was measured on a CHI 660e electrochemical station (Shanghai Chenhua, China) in ambient conditions. The three electrodes were inserted in a quartz cell filled with 0.1 M PBS electrolyte with a frequency range from 0.01 Hz to 10 kHz at a bias potential of 0.29 V vs. Ag/AgCl.

2.2 Electrocatalytic activity measurementThe electrocatalytic activity for the ORR of the samples was studied with the rotating ring-disk electrode (RRDE) technique using a miniature rotator system (ALS Co., Ltd). The RRDE electrode consisted of a catalyst-coated glassy carbon (GC) disk (0.0706 cm2 of geometric surface area). The electrochemical measurements were conducted in a standard three-electrode electrochemical cell at room temperature. The working electrode was the catalyst film-coated GC disks. A Pt-ring was used as the counter electrode, and an Ag/AgCl (3 M Cl, Cypress) electrode in a double-junction chamber was used as the reference electrode. The electrolyte was 0.1 M KOH solution prepared from ultrapure water.

Figures

Fig. S1. (a) TEM image of CoFe2O4 NPs; (b) Size distribution histogram with Gaussian-fitting curve of the as-prepared CoFe2O4 NPs; (c) The Zeta potential of CoFe2O4 suspension with different pH values.

Fig. S2. SEM images of the as-prepared samples before hydrothermal treatment: (a) pure CoFe2O4; (b) pure Ag3PO4 (Na2HPO4); (c) CoFe2O4/Ag3PO4 composites (Na2HPO4); (d) pure Ag3PO4 (Na3PO4); (e) Ag3PO4@CoFe2O4 composites (Na3PO4); (f) enlarged image of Ag3PO4@CoFe2O4 composites (Na3PO4).

Fig. S3. XPS survey spectra of the as-prepared pure Ag3PO4 and 3% Ag3PO4@CoFe2O4

composite.

Fig. S4. The Ag+ ions concentration in the photocatalytic disinfection process.

Fig. S5. (a) Kinetic fit for the degradation of MO with the as-prepared samples. (b) Time dependent absorption spectra of MO solution in the presence of 3% Ag3PO4@CoFe2O4 composite.

Table 1. Kinetic constants and regression coefficients of MO degradation under visible-light irradiation.

Sample The zero orderkinetic equation

Kinetic constant(k, min-1)

R2

3% Ag3PO4@CoFe2O4 -ln(C/C0) = 0.02046 t 0.12816 0.986271% Ag3PO4@CoFe2O4 -ln(C/C0) = 0.02895 t 0.08750 0.982055% Ag3PO4@CoFe2O4 -ln(C/C0) = 0.04190 t 0.05405 0.95028Ag3PO4 -ln(C/C0) = 0.05036 t 0.01381 0.99772

Fig. S6. XRD patterns of (a) Ag3PO4, (b) 3% Ag3PO4@CoFe2O4 before and after photocatalytic reaction.

Fig. S7. (a) Photocatalytic degradation of BPA. (b) Photocatalytic degradation of 4-CP. (c) The HPLC of the BPA degraded solution for different times in the presence of pure Ag 3PO4. (d) The HPLC of the BPA degraded solution for different times in the presence of 3% Ag3PO4@CoFe2O4.

Fig. S8. Electrochemical impedance spectroscopy of the as-prepared samples.

Fig. S9. XPS-VB of (a) Ag3PO4; (b) 3% Ag3PO4@CoFe2O4.

Fig. S10. Tauc's plots of (αhv)2 vs. (hv) of (a) CoFe2O4 and (b) Ag3PO4.

Fig. S11. (a) O2-TPD profiles of Ag3PO4 and 3% Ag3PO4@CoFe2O4 composite. (b) The TG profiles of Ag3PO4 and 3% Ag3PO4@CoFe2O4 composite.