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Gas exfoliation of graphitic carbon nitride to improve the

photocatalytic hydrogen evolution of metal-free 2D/2D g-

C3N4/graphdiyne heterojunction

Huayan Sia,c, Qixin Denga, Chen Yinb, Jingyuan Zhoub, Shuqing Zhangb, Yuxia

Zhanga, Zhichao Liua, Jianbin Zhangd, Jin Zhangb, Jing Kongc

Characterization

Infrared absorption spectra were obtained on KBr pellets on a Nicolet

NEXUS470 FTIR in the range of 500-4000 cm-1. Field emission scanning electron

microscopy (FESEM) measurement was performed by the Hitachi S-4800 instrument.

Transmission electron microscopy (TEM), scanning transmission electron microscopy

(STEM) images and Energy dispersive X-Ray spectroscopy (EDX) mappings were

acquired at an aberration-corrected FEI (Titan Cubed Themis G2) operated at 300 kV.

Surface analysis of the sample was examined by X-ray photoelectron spectroscopy

(XPS) using a Kratos Axis Ultra-DLD spectrometer. UV-Vis diffuse reflectance

spectra (DRS) were performed on a Hitachi U4100 spectrophotometer. Transient

photocurrent and electrochemical impedance spectroscopy (EIS) measurements were

performed on an electrochemical analyzer (CHI660E, CHI Shanghai, Inc.) in a

standard three-electrode configuration using the as-prepared nanocomposite/ITO

electrode as the working electrode, a Pt plate as the counter electrode, and Hg/Hg2Cl2

(saturated with KCl) as a reference electrode. A 300W Xe arc lamp with a sharp cut-

off filter served as a visible-light source (420 nm). The working electrodes were

prepared as follows: nanocomposites powder (5 mg) was added into ethanol (2 mL)

and dispersed using ultrasonication for 30 min. Then, 200 mL of the solution was

dropped onto a 1 cm1.5 cm Indium-Tin-oxide (ITO) glass substrate. Finally, the

dried electrode was calcined at 150 °C for 1 h in a N2 gas flow.

Photocatalytic hydrogen production

The photocatalytic hydrogen production experiments were carried out in a 200

mL quartz flask at ambient temperature and atmospheric pressure, which was sealed

with a silicone rubber septum. A 300 W xenon arc lamp with 400 nm by an

ultraviolet filter provides visible light. During the H2 evolution measurement, the

illumination source was positioned 15 cm away from the quartz flask reactor. The

focused illumination intensity on the flask was ca. 20 mW/cm2. The irradiation area was controlled as 3×3 cm2. In a typical photocatalytic experiment, 20

mg of photocatalyst powder was dispersed in 80 mL of triethanolamine (15 vol%)

solution, a certain amount of H2PtCl6 solution was added to this suspension. The

mixture was sonicated before irradiation, the system was bubbled with nitrogen for 30

min to remove air and to ensure that the reaction system is under an inertial condition.

The produced H2 was analyzed by gas chromatography (GC 7900, 5 A molecular

sieves column, TCD detector, Ar carrier) with an installed gas valve system. All the

measurement conditions for H2 production were kept the same to make sure that the

received results are comparable.

All calculations were performed using density functional theory (DFT) using the

Gaussian 03 package [1]. The hybrid functional B3LYP with the 6-31g basis set was

used to relax the geometric structures in this work.

Figure S1. Optimized structure of two layers g-C3N4 and N2-inserted interlayer of g-

C3N4 by density functional theory (the grey ball is carbon, the blue ball is nitrogen).

Figure S2.TEM graph of GDY

Figure S3. (a) The Raman spectra for GDY. (b) the high-resolution XPS spectra for C

1s in GDY

Figure S4. (a) UV−vis diffuse reflectance spectra of a. bulk g-C3N4, b. g-C3N4 NS, c.

g-C3N4/0.5%GDY, d. g-C3N4/1%GDY, e. g-C3N4/1.5%GDY, f. g-C3N4/2%GDY, g. g-

C3N4/10%GDY, h. GDY, (b) plots of the transformed Kubelka–Munk function versus

light energy for g-C3N4 and GDY.

Figure S5 (a) SEM and (b-e) the corresponding elemental mapping images of g-

C3N4/GDY heteojunction collected after photocatalytic hydrogen evolution reaction:

(b) the combination of signals in (c-e); (c) C, (d) N, and (e) Pt.

Figure S6 (a) The fluorescence spectra of a. bulk g-C3N4, b. g-C3N4 NS, c. g-

C3N4/0.5%GDY, d. g-C3N4/1%GDY, e. g-C3N4/1.5%GDY, f. g-C3N4/2%GDY, g. g-

C3N4/10%GDY, (b) Time-resolved fluorescence decay spectra of g-C3N4 and g-

C3N4/GDY heteojunction.

Figure S7 Mott-Schottky plots of (a) GDY and (b) g-C3N4

Table s1. Comparison of the photocatalytic H2 generation achieved by the g-C3N4 nanosheets made by different method.

method Co-catalyst Light source Measurement conditionsPhotocatalyst Rate of

H2 evolution (μmol h−1)Ref.

gas exfoliation 0.5 wt% Pt300W Xe lamp

(λ > 400 nm)

0.02 g photocatalyst, 15 vol%

triethanolamine solution146.82 this work

liquid-

exfoliation3 wt% Pt

300 W Xe lamp

(λ > 420 nm)

0.05 g photocatalyst, 10 vol%

triethanolamine solution93 [2]

thermal

oxidation etching6 wt% Pt

300 W Xe lamp

(λ > 420 nm)

0.05 g photocatalyst, 10 vol%

triethanolamine solution37 [3]

PhotocatalystCo-

catalystLight source Measurement conditions

Photocatal

yst Rate of

H2

evolution

(μmol h−1)

Ref.

g-C3N4/GDY0.5 wt%

Pt

300W Xe

lamp (λ >

400 nm)

0.02 g photocatalyst, 15 vol% triethanolamine

solution454.28

This

work

GD/g-C3N4 1 wt% Pt

350W Xe

lamp (λ >

420 nm)

0.05 g photocatalyst, 15 vol% triethanolamine

solution39.6 [4]

g-PAN/g-C3N41.5 wt%

Pt

300W Xe

lamp (λ >

400 nm)

0.1 g photocatalyst, 10 vol% triethanolamine

solution37 [5]

CNT/g-C3N4 1.2 wt%

Pt

300W Xe

lamp (λ >

0.1 g photocatalyst, 10 vol% triethanolamine

solution

39.4 [6]

420 nm)

Carbon

black/g-C3N43 wt% Pt Visible-light

0.1 g photocatalyst, 25 vol% methanol

solution68.9 [7]

Graphene/g-

C3N4

1.5 wt%

Pt

350W Xe

lamp (λ >

400 nm)

0.08 g photocatalyst, 25 vol% methanol

solution36.1 [8]

Table s2. Comparison of the photocatalytic H2 generation achieved by the g-C3N4

-based photocatalysts.

Table s3. The excited state lifetimes and their relative percentages in the g-C3N4/GDY and g-C3N4 NS.

sample1

[ns]-Rel%

2

[ns]-Rel%

3

[ns]-Rel%

g-C3N4/GDY

g-C3N4 NS

2.05-20.72

3.80-17.78

6.82-48.02

7.93-40.06

16.84-31.26

18.17-42.16

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