Supplementary Material for

Two types of cooperative nitrogen vacancies in polymeric carbon

nitride for efficient solar-driven H2O2 evolutionYao Xie a, b, Yunxiang Li b, c, Zhaohui Huang a*, Junying Zhang d, Xiaofang Jia d, Xu-

Sheng Wang b, e, Jinhua Ye b, c, f, g*

a Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid

Wastes, School of Materials Science and Technology, National Laboratory of Mineral

Materials, China University of Geosciences, Beijing 100083, P. R. China

b International Center for Materials Nanoarchitectonics (WPI-MANA), National

Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044,

Japan

c Graduate School of Chemical Sciences and Engineering, Hokkaido University,

Sapporo 060-0814, Japan

d Key Laboratory of Micro-nano Measurement, Manipulation and Physics (Ministry of

Education) & Department of Physics, Beihang University, Beijing, China

e State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the

Structure of Matter (FJIRSM), Chinese Academy of Sciences (CAS), Fuzhou, Fujian,

350002, P. R. China.

f TJU-NIMS International Collaboration Laboratory, School of Material Science and

Engineering, Tianjin University, Tianjin 300072, P. R. China

g Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),

Tianjin 300072, P. R. China

1

*Correspondence: huang118@cugb.edu.cn (Z. Huang), jinhua.ye@nims.go.jp (J.Y.)

Synthesis

For the purpose of comparative investigate of the role of N2C vacancy, the sample only

N2C vacancy introduced was obtained as follows, 4 g urea (the yield is estimated to be

~ 200 mg according to the synthesis of pristine CN) was mixed with 0.03g KOH and

then calcined that mixtures under the same condition of synthesis of CN to obtain in

situ synthesized sample which was referred to as CN(V1). To explore the role of NHx

vacancy, NHx vacancy was introduced into CN(V1) referred to as CN(V1 + V2) which

was obtained by calcining CN(V1) under the same condition of synthesis of CKCN-M

without KOH.

Photocatalytic H2O2 evolution

The photocatalytic H2O2 production reactions were carried out with 20 mg

photocatalyst suspended in an aqueous solution (80 mL solution containing 20 vol%

ethanol (95%) as a sacrificial electron donor) in a glass reaction cell with O2 purging

under the irradiation of a simulated sunlight AM1.5 (56.8 mW/cm2). The

concentration of H2O2 was determined by colorimetric method employing N,Ndiethyl-

1,4-phenylene-diamine sulfate (DPD, 97%, Aldrich) reagent. Briefly, the time

dependent H2O2 generation was measured as follows: 1 mL filtration from reaction

solution was dispersed into the reagent solution ( 50 μL DPD solution (0.1 g of DPD

was dissolved in 10 mL 0.1 M H2SO4), 50 μL POD solution (10 mg of peroxidase

(POD) was dissolved in 10 mL water), and 0.3 mL buffer solution (10 mL of 0.1 M

2

Na2HPO4 solution and 90 mL of 0.1 M NaH2PO4 solution were mixed together)), then

monitored by the absorption of the solution at 551 nm and determined with UV–vis

spectrophotometer. And Figure S1 shows the linear fitting spectra of concentration of

H2O2 vs. UV-vis absorption intensity. Apparent quantum efficiency (AQE) was

measured by using an AM1.5 lamp combined with wavelength-dependent band-pass

filters (MIF-W, Optical Coatings Japan Co., Japan). A radiant power energy meter

(Ushio Spectroradiometer, USR-40) was applied to measure the number of incident

photons. The AQE was calculated according to the following equations,

AQE=( Number of prpduced H 2O2 molecules ) ×2

Number of incident photons× 100 %

.

Electrochemical and photoelectrochemical measurements

The photoelectrochemical properties were evaluated in a conventional three electrode

cell system on CHI Instruments CHI660D electrochemical workstation. ITO/product

sample as the working electrode, an Ag/AgCl electrode as the reference electrode and

a Pt wire used as the counter electrode. 0.1M Na2SO4 aqueous solution was used as

the electrolyte.

Rotating disk electrode (RDE) measurements

The measurements were performed on a CHI Instruments CHI660D advanced

electrochemical system with a three-electrode cell using a saturated calomel electrode

and a C rod electrode as the reference and counter electrode, respectively. The

3

working electrode was prepared as follows: catalysts (3 mg) were dispersed in IPA

(0.5 ml) containing 20µL Nafion (5 wt%) by ultrasonication. The slurry (5µL) was

put onto a disk electrode and dried at room temperature. The linear sweep

voltammogram (LSV) were obtained in an O2-saturated 0.1 M phosphate buffer

solution (pH 7.6) with a scan rate 10 mV s−1. The electron transfer number (n)

involved in the overall O2 reduction was determined by the slopes of the Koutecky–

Levich plots with the following equations:

j-1 = jk-1 + B-1ω-1/2 (S1)

k (slope) = B-1 (S2)

B = 0.2nFν-1/6CD2/3 (S3)

Where j is the current density, jk is the kinetic current density, ω is the rotating speed

(rpm), F is the Faraday constant (96485 C mol−1), ν is the kinetic viscosity of water

(0.01 cm2 s−1), C is the bulk concentration of O2 in water (1.2×10−6 mol cm−3), and D is

the diffusion coefficient of O2 (1.9×10−5 cm2 s−1), respectively.

DFT calculation

The corresponding band structures and density of state (DOS) are calculated using the

Vienna Ab-initio simulation package (VASP) codes with the projector augmented

wave (PAW) potentials [1,2]. We employ the Perdew-Burke- Ernzerhof of generalized

gradient approximation (GGA-PBE) for exchange- correlation energy [3]. Given the

4

absence of strong bonding interactions between g-C3N4 and adsorbate, the PBE that

formed with van der Waals (vdW) correction (PBE-D2)[4]. The cutoff energy for the

plane-wave basis, the self-consistent total-energy difference and the convergence

criterion for forces on atoms were set to 450 eV, 10−4 eV and 0.02 eV/ Å, respectively.

Monkhorst-Pack grid of 1×1×2 is selected in the first Brillouin zone BZ. In band

structure and DOS.

Results and discussion

Figure S5 shows UV–vis diffuse reflectance spectra of as-prepared samples, with

increasing KOH usage, the prepared samples became a progressively darker yellow

and then finally orange, meanwhile a progressive redshift in the absorption edge was

observed. Moreover, the band gap of CKCN-0.03 was narrower and the valence band

maximum became slightly larger than CN. The cyano groups (−¿C≡N) and N

vacancies formed from molecular structure change of polymeric carbon nitride via

calcining with KOH may affect the light response range and band structure.

As can be seen in Figure 2b that the activity decreased when the KOH usage over than

0.03 g. Table 1 shows the percentage of N coordination type of as-prepared samples

determined by XPS, the NHx content decreased with increasing the KOH usage,

indicating the increase of NHx vacancies. The other evidence is the intensity of the N–

H stretching peaks in FT-IR spectra (Figure 1b) decreased with increasing the KOH

usage. The NHx vacancy will act as the recombination center when it is excess (Small,

2018, 14(9): 1703142; Appl. Catal., B Environ., 2020, 262: 118308.). Figure S15c

shows the photoluminescence (PL) spectra of pristine and modulated polymeric

5

carbon nitride. Notably, the PL intensity decreased rapidly when the KOH usage was

increased from 0 to 0.03 g due to the NHx vacancy which acted as the role of making

more efficient photoexcited charge separation. And then the PL intensity increased

when the KOH usage over than 0.03 g which is attributed to that the excess NHx

vacancy acted as the recombination center, that led to a decrease in activity.

And it became inactivation when the KOH usage increased to 0.15 g. Comparing with

the XRD spectra of pristine carbon nitride (CN), some impurity peaks were detected

in the XRD spectra of CKCN-0.15 (Figure S6) (The diffraction peaks of KOH were

also detected, suggesting the usage of KOH is excess.). It indicates that when the

KOH usage increased to 0.15 g the structure of carbon nitride was destroyed. The

transition energy of CKCN-0.15 had an obvious marginal blue shift leading to a

narrower absorption of light (Figure S7). Besides the band structure of CKCN-0.15

also was changed and the band gap became wider (Figure S8). As a result, it became

inactivation when the KOH usage increased to 0.15 g.

Generally, specific surface area, range of light response and band structure are

considered to be important factors affecting photocatalytic activity, nevertheless they

are not the main factors contributing to the huge activity enhancement of this work.

For specific surface area (Table S1), it was reduced from 71.3 (CN) to 45.3 m2 g-1

(CKCN-0.03), whereas the photocatalytic H2O2 evolution rate was greatly improved

from 10.5 to 152.6 µmol h-1 (Figure 3c). For range of light response, the absorption

edge of CCN and CN(V1) are around 430 and 450 nm respectively (Figure S5a and

Figure S11a), the absorption edge and intensity are quite different, while the

6

photocatalytic H2O2 evolution rate of them is 28.9 and 30.5 µmol h-1 (Figure 3c),

respectively, very close to each other. For band structure, what is more noteworthy,

the band structure and light response range of CN(V1) and CN(V1 + V2) are almost

same (Figure S11) while the photocatalytic H2O2 evolution rate increased from 30.5 to

99.1 µmol h-1 (Figure 3c). Therefore, the cyano groups (−¿C≡N) and N vacancies

formed from molecular structure change of polymeric carbon nitride should be the

principle factor determining the photocatalytic activity. Notably, the cyano group (−¿

C≡N) content in CN(V1) and CN(V1 + V2) are 3.9% and 4.2% (Table S3),

respectively, quiet close to each other while the photocatalytic H2O2 evolution rate are

30.5 and 99.1 µmol h-1, indicating the cyano group (−¿C≡N) is also not the main

factor contributing to the remarkably boosted activity in our case.

Figure S1. a) The standard spectra of the DPD/POD solution with different concentration of H2O2.

b) The linear fitting spectra of concentration of H2O2 vs. UV-vis absorption intensity.

7

Figure S2. SEM images of a) CN, b) CCN, c) CKCN-0.03, and d) CKCN-0.1A. And TEM images

of a) CN and b) CKCN-0.03.

Table S1. BET specific surface areas (m2 g-1) of prepared samples.

CN CCN CKCN-0.03 CKCN-0.1

71.3 47.9 45.3 6.5

8

Figure S3. N2 adsorption-desorption isotherms for pristine and modulated polymeric carbon

nitride.

Figure S4. TEM image of CKCN-0.03 with corresponding elemental mapping (a1–a3). The colours

of red, orange and green represent the elemental components of C, N and K, respectively.

9

Table S2. N/C atomic ratios of pure and modulated polymeric carbon nitride determined by

organic elemental analyzer (OEA) and XPS.

Samples OEA XPS

CN 1.51 1.64

CCN 1.49 1.58

CKCN-0.03 1.45 1.32

CN(V1) 1.47 1.51

CN(V1 + V2) 1.46 1.38

Table S3. Percentage of C coordination type determined by XPS.

C coordination

typeN–C=N –C≡N

CN 100% 0%

CCN 99.2% 0.8%

CKCN-0.03 93.1% 6.9%

CKCN-0.1 76.0% 24.0%

CN(V1) 96.1% 3.9%

CN(V1 + V2) 95.8% 4.2%

10

Figure S5. a) UV–vis DRS, b) Plots of transformed Kubelka–Munk function versus photon

energy. Inset in (a) shows a digital photograph of samples prepared (from left to right are CN,

CCN, CKCN-0.01, CKCN-0.03 and CKCN-0.1). c) VB XPS.

Figure S6. XRD patterns of the pristine and modulated polymeric carbon nitride.

11

Figure S7. UV–vis DRS and digital photograph of the pristine and modulated polymeric

carbon nitride.

Figure S8. Plots of transformed Kubelka–Munk function versus photon energy.

12

Figure S9. The photocatalytic decomposition of H2O2 (C0 = 1 mmol/L) in pure water under the irradiation of a simulated sunlight.

Table S4. Summary of some reported polymeric carbon nitride based photocatalysts for H2O2

production.

Photocatalysts Light sourceReaction

solution

H2O2 evolution

rateReference

CKCN-0.03

(20 mg)

AM1.5,

simulated solar

80 ml solution

containing 20

vol.% EtOH

152.6 μmol/h or

1.91 mMh-1

(AQE = 11.9 %

at 420 nm)

This

work

RF523 (50 mg) λ >420 nm

(Xe lamp,

light

intensity at

30 mL of

distilled water,

O2

61.6 μmol for

24 h (AQE =

7.6 % at 420

5

13

420−700

nm: 140.3 W

m−2)

nm)

C3N4/AQ

(-COOH)

(50 mg)

AM1.5,

simulated solar

30 ml distilled

water

30 μmol for

60 h 6

DCN-15A

(50 mg)

AM1.5, visible

light

(λ > 420 nm)

60 ml solution

containing 20

vol.% IPA, O2

12.1μmol for

2.5 h7

KPD-CN-7.5

(20 mg)

300 W Xe arc

lamp, visible

light (λ ≥420

nm)

40 ml solution

containing 10

vol.%

EtOH, O2

1.7 mM for

7 h (AQE = 8 %

at 420 nm)

8

OCN-500

(50 mg)

Xe-lamp

λ≥420nm

50 ml solution

containing 10

vol.% IPA, O2

730 μmol for

5 h (AQE =

10.2 % at 420

nm)

9

AKCN (0.5 g

L−1)

Xe-lamp

λ≥420nm

0.5 g L-1

solution

containing 10

vol.% EtOH,

phosphate

3.4 mM for 3 h 10

14

buffer (0.1 M,

pH 3) , O2.

Cv-g- C3N4 (100

mg)

300 W

Xe arc lamp,

visible light (λ

≥420 nm)

100 mL of

distilled water,

O2

91 μMh-1

11

Ag@U-g-

C3N4-NS-1.0

(100 mg)

300 W

Xe arc lamp

100 mL of

distilled water,

pH 3, O2

75 μM for 70

min12

Au–Pt–Ni NRs Electrocatalysis

electrolyte

KOH (0.1 M)

reference

electrode

Hg/HgO,

working voltage

was set constant

at 0.5 V versus

RHE, O2

20 mg/L for 10

h

(0.6 mM for 10

h)

13

HTNT-CD

(20 mg)

350 W Xenon

lamp, visible

light (λ ≥420

nm)

15 mL of

distilled water,

O2

95.3 μmol for

3 h14

15

Au/TiO2

(200 mg)

high-pressure

mercury lamp

(λ > 300 nm)

200 ml solution

containing 4%

EtOH with NaF

(0.1 mol dm-3) ,

O2

14 mM for 23 h 15

Figure S10. Apparent quantum efficiency (AQE) of H2O2 production as a function of irradiation

wavelength (CKCN-0.03 as the photocatalyst).

Figure S11. a) Plots of transformed Kubelka–Munk function versus photon energy of CN(V1)

(green) and CN(V1 + V2) (pink). b) VB XPS of CN(V1) (green) and CN(V1 + V2) (pink) and c)

16

band structure alignments for CN(V1) (green) and CN(V1 + V2) (pink).

Figure S12. Room temperature ESR spectra for CKCN-0.03 and CN(V1).

10 20 30 40 50

Inte

nsity

(a.u

.)

2 Theta (degree)

(100)(002)

CN(V1+V2)

CN(V1)

CKCN-0.03

CCN

BCN

Figure S13. XRD spectra for pure and modulated polymeric carbon nitride.

17

Figure S14. C 1s and N 1s XPS spectra of CN(V1) and CN(V1 + V2). The red line and blue line

represent the peak simulation and baseline. The deconvoluted peaks was identified from the pink,

green and navy blue line.

Figure S15. Characterization of the pristine and modulated polymeric carbon nitride. a) UV–vis

DRS, b) Electrochemical impedance spectra (EIS), c) Photoluminescence spectra.

18

Figure S16. LSV curves of CN (a), CN(V1) (b) and CN(V1 + V2) (c) measured on RDE analysis at

different rotating speeds.

19

Figure S17. Calculation model of polymeric carbon nitride (1: N3C structure; 2: N2C structure).

Figure S18. Calculated band structure of polymeric carbon nitride with NHx vacancy.

Figure S19. Density-functional theory calculations. a) Structure models of polymeric carbon

nitride. b) Calculated band structure and c) corresponding DOS of polymeric carbon nitride.

20

Figure S20. Adsorption models and corresponding adsorption energy for OOH* on the active site

of N2C vacancy.

Figure S21. Adsorption models and corresponding adsorption energy for OOH* on the active site

21

of NHx vacancy.

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