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Fullerenes/Graphite Carbon Nitride with Enhanced Photocatalytic Hydrogen Evolution Ability Limin Song, Tongtong Li, and Shujuan Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b09064 • Publication Date (Web): 19 Dec 2016 Downloaded from http://pubs.acs.org on December 19, 2016

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The Journal of Physical Chemistry

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Fullerenes/Graphite Carbon Nitride with Enhanced

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Photocatalytic Hydrogen Evolution Ability Limin Songa,*; Tongtong Lia, Shujuan Zhangb,*

3 a

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College of Environment and Chemical Engineering & State Key Laboratory of

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Hollow-Fiber Membrane Materials and Membrane Processes, Tianjin Polytechnic

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University, Tianjin 300387, P. R. China.

7

b

College of Science, Tianjin University of Science & Technology, Tianjin, 300457,

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P.R. China

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*Corresponding author. Tel./Fax: +86-22-83955458 E-mail address: [email protected]

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ABSTRACT:

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Graphite carbon nitride (g-C3N4) is an excellent photocatalytic hydrogen evolution

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material by water splitting, but enhancing its photocatalytic activity and stability is

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still a big challenge. In this study, by utilizing the super ability of fullerenes (C60) to

15

attract electrons, we synthesized C60/g-C3N4 photocatalytic composite materials with

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superior electronic separation efficiency. The addition of C60 greatly improves the

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photocatalytic hydrogen evolution ability of g-C3N4 for water splitting under visible

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light radiation. The highest hydrogen evolution amount reached 2268.6 µmol/g over

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15 mg/L C60/g-C3N4 after 10 h, which is 50.1 times that of g-C3N4 under the same

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water splitting condition. The hydrogen evolution amount over 15 mg/L C60/g-C3N4 in

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the 0.2 mol/L K2HPO4 system is 4161 µmol/g, indicating the addition of K2HPO4

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boosts the activity of C60/g-C3N4. The apparent quantum yield after 76 h was about

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5.8 %. The long-term photolysis water reaction for 76 h with rising photocatalytic

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activity exhibits that the C60/g-C3N4 has excellent stability in water spitting. We can

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regulate the photocatalytic activity of C60/g-C3N4 by changing the C60 concentration.

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Photoluminescence spectrum proves the super ability of C60 to attract electrons on the

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surface of C60/g-C3N4. Thus, C60 promotes electron separation efficiency on the

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surface of g-C3N4 and significantly enhances photocatalytic hydrogen evolution

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ability of g-C3N4.

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1. Introduction

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Graphite carbon nitride (g-C3N4), a new type of metal-free organic polymer

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semiconductor, has great and potential applications in the field of catalysis because of

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its excellence in water stability, thermal stability, chemical stability, light absorption

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capability, hardness and catalytic performance.1-4 Especially, it has attracted many

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researchers in the field of photocatalytic hydrogen evolution by photolysis water.5-9

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Pure g-C3N4 has a band gap about 2.7 eV, corresponding to an optical wavelength

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around 450 nm. Therefore, the photocatalytic ability of g-C3N4 can be induced

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through excitation under visible light radiation. However, g-C3N4 usually is poorly

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crystallized in the preparation, so the presence of numerous crystal defects would trap

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the photo-generated charges, decelerating their migration and inhibiting the

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photocatalytic performance of g-C3N4.10,11 To solve this problem, researchers have

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prepared many modified g-C3N4 materials, such as mesoporous structures,3,12 ion

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doping13-16 and composite semiconductors17-22. All these modification methods

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significantly improve the ability of photocatalytic hydrogen evolution of g-C3N4.

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Fullerenes (C60) molecules have a new type of conjugated and overlapped p-orbits.

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The electrons of C60 with low-energy lowest unoccupied molecular orbit (LUMO)

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are delocalized to form very large electron affinity (2.65 eV), so they have the super-

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strong electron-withdrawing ability.11 Regarding this advantage, we make C60

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closely couple with g-C3N4 to form composite semiconductors, which accelerates the

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migration of photo-generated electrons and inhibits the recombination of the

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photo-generated

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photocatalytic ability of g-C3N4. In this study, C60/g-C3N4 hybrid materials were

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prepared from a high-temperature calcination method, while the hydrogen evolution

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ability of g-C3N4 was regulated by adjusting the amount of C60 in the composition.

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An appropriate amount of C60 can significantly enhance the photocatalytic activity

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and stability of g-C3N4. The photocatalytic processes and enhancement mechanisms

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of C60/g-C3N4 were also elaborated.

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2. Experimental

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2.1. Synthesis of samples

electron-hole

pairs,

thereby

significantly

improving

the

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All the reagents were bought from Sinopharm Chemical Reagent Co. Ltd. The

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g-C3N4 was prepared as follows: 20 g of urea was added to a 30-mL crucible with

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cover, then heated up to 550 ◦C at a rate of 1 ◦C /min in a muffle furnace, and kept for

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3 hours. After the reaction, the furnace was cooled to room temperature, and then the

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samples were collected and grinded into powder. The C60/g-C3N4 was synthesized as

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follows: 10 mL of 5, 10, 15 and 20 mg/L C60 aqueous solution was added to 20 g of

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urea, and the other steps are same to the above process. The corresponding C60/g-C3N4

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samples were marked as CG5, CG10, CG15 and CG20.

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2.2. Characterization of samples

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The crystalline structures and phases of the samples were observed on a Rigaku

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D/max 2500 powder X-ray diffractometer (XRD, Rigaku Corporation, Japan) from

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2θ=10 to 60◦ using graphite monochromatized Cu Kα radiation of 1.5406 Å and

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operating at 40 kV and 40 mA. Their morphologies were measured on a high-

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resolution transmission electron microscope (HRTEM; JEM 2100, JEOL, Japan) at an

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accelerating voltage of 200 kV. Their surface chemical states were analyzed on an

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X-ray photoelectron spectroscope (XPS, Perkin-Elmer PHI5300, USA). Binding

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energy was calibrated by setting the adventitious C 1s peak at 284.6 eV. The

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ultraviolet visible (UV-vis) absorption spectra were measured on a UV-vis

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spectrophotometer (BaSO4, UV2700, Shimadzu, Japan). The photoluminescence (PL)

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spectra were recorded on an F-380 fluorescence spectrophotometer (Tianjin

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Gangdong Sci-Tech Development Co., Ltd. China) at room temperature with an

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excitation wavelength of 250 nm. Specific surface areas of Brunauer-Emmett-Teller

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(BET) were determined on a Micromeritics ASAP 2020M apparatus at the liquid

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nitrogen temperature of -196 °C.

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2.3. Activity measurement

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The photocatalytic H2 evolution activity was measured in a sealed 50-mL reaction

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tube under visible-light irradiation and room temperature (λ > 420 nm). In a typical

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process, 100 mg of a photocatalyst was added to 50 mL of an aqueous solution, which

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contained 1 wt.‰ Pt (H2PtCl6 as the precursor) as a co-catalyst and 5 mL of

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triethanolamine (TEOA, 10 vol%) as a sacrificial electron donor. A 5 W pure white

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light-emitting diode (LED) light source (6000 K, 10 × 5 W, λ > 420 nm; visible

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output power = 12.6 mW/cm2) was used. Prior to irradiation, the reaction system was

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air-removed for 30 min through a vacuum pump. During irradiation, the reaction

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system was stirred, intermittently sampled and analyzed for H2 evolution on a

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GC7890 gas chromatograph (Rainbow Chemical Instrument Co. Ltd., Shandong

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Lunan, China) equipped with a thermal conductivity detector and a 5 Å molecular

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sieve column (2 m × 3 mm, Ar).

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The apparent quantum yield (AQY) is calculated as follows:

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AQY= 2×number of evolved H2 molecules/ number of incident photons×100%

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3. Results and discussion

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3.1. Characterization of photocatalysts

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The XRD patterns of g-C3N4, C60 and CG5, CG10, CG15, CG20 characterizing

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their crystal structures are showed in Fig. 1. Clearly, a strong diffraction peak at 27.6°

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and a weak diffraction peak at 12.8° are found, which are assigned to (002) and (100)

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crystal planes, respectively. No impurity is found in Fig. 1a, indicating the presence of

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pure g-C3N4 phase. These results suggest that pure g-C3N4 can be obtained from our

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experimental method, which is consistent with another study.23 The XRD patterns of

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C60 are exhibited in Fig. 1b. Those crystal planes of (111), (220), (311), (222), (331),

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(024), (422) and (333) can be belonged to cubic phase of C60 (JCPDS No. 82-0505,

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space group: Pm3[202], a=b= c= 14.26 Å). CG5-20 show similar XRD patterns as

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g-C3N4 in Figs. 1c-1f. In addition to the two peaks at 27.6° and 12.8°, no other

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impurity is found in Fig. 1c-1f, which suggests the addition of C60 does not introduce

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new impurities into g-C3N4. Interestingly, the two main peaks of CG5-20 slightly shift

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to left, which suggests that additional C60 in urea may affect the crystal structure and

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performance of g-C3N4 in the calcination. The changeable structure and performance

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of g-C3N4 and additional C60 may significantly affect the photocatalytic activity of CG.

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No diffraction peaks of C60 are found in CG5 and CG10. This is because the addition

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of too little C60 does not result in the XRD diffraction peaks of C60. However, it is

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found that the CG15 and CG20 with excessive C60 has a weak peak from the (111)

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plane of C60 except the two main peaks at 27.6° and 12.8° of g-C3N4. The result

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exhibits that the C60 in CG keeps an original form.

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The morphologies of CG5-20 surveyed via TEM are shown in Fig. 2. The CG15

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has very thin cicada-wing-like sheets (Fig. 2a), which stack together layer by layer

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and extend to all directions. The thin-sheet structures of GC15 are very uniform (Fig.

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2b). These thin sheets provide large surface areas (201 m2/g) and abundant surface

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active sites, which help to improve the photocatalytic ability of CG15. The TEM

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images of CG5, CG10 and CG20 are shown in Fig. 2c, 2d and 2e. They have the

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morphologies like-sheet, which are similar to CG15. Those thin-sheets also stack

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together layer by layer. Their BET surface areas are 162.9, 199.9 and 202 m2/g for

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CG5, CG10 and CG20, respectively. The high-resolution image of CG15 exhibits the

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feature without obvious lattice fringes (Fig. 2f), which is consistent with the XRD

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result of weak crystallinity in Fig. 1. The weak crystallinity of CG15 is further proved

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by the corresponding diffuse diffraction rings in Fig. 2g. It is found that many small

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black spots are distributed on the surface of g-C3N4 evenly in Fig. 2f. We can clearly

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distinguish the lattice of small black dots in Fig. 2h. The lattice is consistent with (137)

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crystal planes of C60. It is clear that C60 particles are high dispersion on g-C3N4 under

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high temperature calcination. According to the energy-dispersive X-ray (EDX)

137

spectra (Fig. 2i), the composition of CG15 is CN1.25, but the atom ratio of N/C is

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lower than that of g-C3N4 (1.25 vs. 1.33), indicating the excess of C element in CG15.

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The UV–vis absorption spectra of g-C3N4, CG5, CG10, CG15, and CG20 (Fig. 3)

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show a very broad and intensive absorption from the ultraviolet to visible region. The

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pure g-C3N4 shows a visible-light absorption edge of 464.4 nm. The spectrum below

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464.4 nm suggests a charge-transfer process from the valence band produced by the

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orbitals of Nn- to the conduction band caused by the orbitals of Cn+.23 The band gap

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value of g-C3N4 was estimated to be 2.67 eV. Moreover, spectral shapes of the

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absorption edges of CG5, CG10, CG15, and CG20 are not significantly different from

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that of g-C3N4 (Fig. 3). This result suggests that a small addition of C60 does not

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significantly affect the optical properties of g-C3N4.

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The molecular structures of g-C3N4 and CG15 measured by FT-IR are showed in

149

Fig. 4. The peaks of g-C3N4 at 815, 1060, 1160-1700, and 3000-3700 cm-1 are

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assigned to the bending vibration of tristriazine heterocycle; additional CO32-; the

151

skeletal stretching vibration of aromatic C-N heterocycles; the adsorbed H2O and the

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terminal amino groups (-NH2 and -NH) in g-C3N4, respectively.24,25 The characteristic

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peaks of C60 at 527, 577, 1183 and 1428 cm-1 overlap those of g-C3N4 in Fig. 4. We

154

cannot distinguish the peaks of C60 in CG15, but for CG15 compared with g-C3N4, the

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intensities of all peaks are decreased and all peak positions shift to short wavelength,

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indicating the addition of C60 affects the electronic environment of g-C3N4.

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The surface compositions and states of g-C3N4 and CG15 characterized by XPS are

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shown in Fig. 5. The spectrum of CG15 (Fig. 5A) shows that its surface elements

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mainly include N, C and O. The additional O element may result from the O

160

contamination in air. No other impurities are found in Fig. 5A. The XPS peaks of

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g-C3N4 at 288.4 and 284.8 eV can be assigned to C1s in Fig. 5B, and they may result

162

from the C-N structure in the g-C3N426 and the C standard peak, respectively. The C1s

163

peaks of CG15 are fully consistent with those of g-C3N4 in Fig. 5B, indicating C60

164

added to g-C3N4 does not affect the C1s electronic structure of g-C3N4 because of the

165

mechanical mixing of C60 and g-C3N4. The N1s peaks of g-C3N4 at 398.5, 399.7 and

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401.1 eV in Fig. 5C belong to C-N-C, N-(C)3 and C-N-H, respectively.26 Moreover,

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the N1s peaks of CG15 are also fully consistent with those of g-C3N4 in Fig. 5C. The

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semiquantitative surface compositions of g-C3N4 and CG15 determined by XPS are

169

CN1.08 and CN1.16, respectively. Two values are similar. The CN1.08 and CN1.16 values

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are slightly lower than that of the CG15 composition obtained by EDX (CN1.25).

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Different measurement methods and semiquantitative analysis result in the above fact.

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3.2 Photocatalytic activity

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The photocatalytic H2 evolution activities detected over g-C3N4 and CG in 50-mL

174

sealed reaction tubes under visible-light irradiation (λ > 420 nm) are showed in Fig. 6.

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The H2 evolution amounts for g-C3N4, CG5, CG10, CG15 and CG20 are 45.3, 400.8,

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1286.5, 2268.6 and 197.5 µmol/g, respectively (Fig. 6A). All the CG samples show

8


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higher H2 evolution activity than that of g-C3N4, indicating that addition of C60

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obviously improves the H2 evolution ability of g-C3N4 under visible-light irradiation.

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The activity of g-C3N4 is improved with the addition of C60 from 5 to 15 mg/L, and

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then is reduced after the addition of 20 mg/L. The H2 evolution amount of CG15 is

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50.1 times that of g-C3N4, suggesting that an appropriate concentration of C60 favors

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the hydrogen production of g-C3N4. However, excessive C60 coating on the surface of

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g-C3N4 prevents photon absorption and close contact with H2O molecules, and

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therefore weakens the g-C3N4 activity. In order to further enhance the hydrogen

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production ability of CG15, we added 0.2 mol/L K2HPO4 to the reaction system. As

186

shown in Fig. 6B, the hydrogen evolution amount is 4161 µmol/g, which is 1.83 times

187

that of CG15. The improvement can be attributed to the synergy between enhanced

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proton reduction and TEOA photooxidation.5 The H2 evolution rates for g-C3N4, CG5,

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CG10, CG15 and CG20 after 10 h are 4.5, 40, 128, 227, and 20 µmol/g/h, respectively

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(Fig. 6C). The rate of CG15 is 50.1 times that of g-C3N4. All the C60-modified g-C3N4

191

samples show a significant improvement compared with g-C3N4, which is consistent

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with their hydrogen evolution amounts in Fig. 6A. The rate of CG15 in the K2HPO4

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system is 92.9 times that of g-C3N4, which further proves the phosphorylation of

194

K2HPO4 in the g-C3N4 hydrogen production. The AQYs of g-C3N4 and CG samples

195

are exhibited in Fig. 6D. It is very clear that the AQYs of all CG samples are higher

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than that of g-C3N4. The AQY of CG15 is 50.2 times that of g-C3N4. In order to

197

investigate the lifetime and reusability of the C60-modified g-C3N4, we measured the

198

long-term and reusability activity of CG15 in Fig. 7 and Fig. 8. It is observed that the

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hydrogen production amount of CG15 increases with time and does not decease

200

during 76 h (Fig. 7A). The hydrogen production amount reaches 7420.4 µmol/g. The

201

corresponding AQY of CG15 after 76 h is 5.8% (Fig. 7B). The above results suggest

202

that the C60/g-C3N4 has long lifetime under the photocatalytic condition because

203

g-C3N4 and C60 are resistant against corrosions from light, acids and bases. The

204

reusability experimental result is shown in Fig. 8. The hydrogen production amount

205

CG15 has reached 1105 µmol/g after the first test (after 4 h). The data don’t reduce

206

and increased to 1657.2 µmol/g after the fifth round in Fig. 8, suggests the CG15 has

207

a high reusability.

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3.3 Photocatalytic process and mechanism

209

In order to study the photocatalytic process and mechanism, the hydrogen

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production amount of 1 wt.‰ Pt/C60 (15 mg/L C60), C60/g-C3N4 (15 mg/L C60) and 1

211

wt.‰ Pt/C60/g-C3N4 (CG15) is survived under the same experimental condition.

212

Their activities are 40.1, 136.6 and 2268.6 µmol/g in Fig. 9, respectively. The

213

hydrogen production amount of 1 wt.‰ Pt/C60 is 40.1 µmol/g, shows that C60 can

214

absorb visible light and have the weak photocatalytic ability. It is found that

215

C60/g-C3N4 has a higher activity than that of 1 wt.‰ Pt/g-C3N4 (10.1µmol/g). The

216

hydrogen production amount of 1 wt.‰ Pt/C60/g-C3N4 greatly raises compared with

217

C60/g-C3N4 and 1 wt.‰ Pt/g-C3N4, which suggests that the synergies of Pt and C60

218

significantly enhance the photocatalytic ability of g-C3N4. The collaborative

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electron-absorbing of C60 and Pt greatly facilitates the separation of photo-generated

220

charges, and improves the utilization efficiency of photo-generated electrons, so as

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221

to enhance hydrogen production activity of the catalyst g-C3N4.

222

The PL spectra of g-C3N4 and CG15 prove the above result in Fig. 10. The

223

excitation wavelength is 250 nm in the PL spectra. Clearly, g-C3N4 shows two strong

224

emission peaks centered at 470 and 655 nm. Compared with CG15, the peak

225

intensity of CG15 is markedly quenched. It is clear that C60 has a very large electron

226

affinity of 2.65 eV. 11 At the same time, C60 shows a larger work function (4.81 eV)

227

than that of g-C3N4 (4.31 eV), which makes C60 have the super-strong

228

electron-withdrawing ability.

229

photo-generated electron transfer from g-C3N4 to C60. It is sure that the addition of

230

C60 is crucial to promoting the separation of photo-generated charges.

Therefore,

the

PL result suggests a

quick

231

In order to investigate the process of photocatalytic hydrogen production over

232

CG15, we measured the concentrations of H2O2 in the photocatalytic reaction system

233

of g-C3N4 and CG15. The concentration of H2O2 in the CG15 system after 10 h is

234

2.57 times that of g-C3N4 (3.941 vs. 1.536 mg/L), indicating that the plenty H2O2

235

results from splitting water. The typical process is showed as follows:

236 237

(1) 2H2O → H2O2 + H2 According to reference,17 it is a two-electron two step pathway (2) and (3):

238

(2) 2H+ + 2e- → H2

239

(3) 2H2O → H2O2 + 2H+ + 2e-

240

(4) H2O2 → 1/2O2 + H2O

241

The existence of abundant H2 and H2O2 in the CG15 reaction system proves a

242

two-step process. Equation 4 shows an exothermic process and needs to be induced

∆G = 106.1 kJ/mol

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243

by a catalyst to split water to form H2O2. However, no O2 is generated in the CG15

244

photocatalytic reaction, indicating C60 does not induce the reaction, resulting in the

245

presence of abundant H2O2.

246 4. Conclusions 247

C60 is an efficient cocatalyst over g-C3N4 to enhance photocatalytic H2 production

248

under visible light irradiation. The H2 evolution amount of C60/g-C3N4 is 50.1 times

249

that of g-C3N4. The strong electron-absorbing action of C60 over g-C3N4 plays a

250

remarkable role in facilitating the separation and transfer of photogenerated charges.

251

Acknowledgements

252

This work was supported by Natural Science Foundation of Tianjin of China (Grant

253

14JCYBJC20500) and Graduate Program of Science and Technology Innovation of

254

Tianjin Polytechnic University (16114).

255

Reference:

256

(1) Groenewolt, M.; Antonietti, M. Synthesis of g-C3N4 nanoparticles in mesoporous

257

silica host matrices. Adv. Mater. 2005, 17, 1789-1792.

258

(2) Goettmann, F.; Fischer, A.; Antonietti, M.; Thomas, A. Chemical synthesis of

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mesoporous carbon nitrides using hard templates and their use as a metal-free catalyst

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for friedel-crafts reaction of benzene. Angew. Chem. Int. Ed. 2006, 45, 4467-4471.

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(3) Thomas, A.; Fischer, A.; Goettmann, F.; Antonietti, M.; Muller, J. O.; Schloglb,

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R.; Carlsson, J. M. Graphitic carbon nitride materials: variation of structure and

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morphology and their use as metal-free catalysts. J. Mater. Chem. 2008, 18,

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4893-4908.

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(4) Wang, Y.; Yao, J.; Li, H. R.; Su, D. S.; Antonietti, M. Highly selective

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Page 17 of 32

Figure:

180000

(100)

(002)

30000

160000

f

o

25000

140000

e d

20000

Intensity (a.u.)

120000

c

100000

15000 80000

60000

10000

40000

(311)

a (331) (024) (422) (333)

(222)

(220)

5000

(111)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20000

b

0

0 10

20

30

40

50

60

70

80

2Theta/degree

Fig. 1. X-ray diffraction patterns of samples. (a) g-C3N4, (b) C60 (c) CG5, (d) CG10, (e) CG15, (f) CG20. o: the (111) crystal plane of C60.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

18


Page 18 of 32

Page 19 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

20


Page 20 of 32

Page 21 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21



1000

C

i

800

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

N

600

400

200

0 0

1

2

3

4

5

Energy KeV

Fig. 2. TEM images of (a) and (b) CG15, (c) CG5, (d) CG10, (e) CG20, (f) and (h) HRTEM images of GC15, (g) The SAED pattern of CG15, (i) The EDX pattern of CG15.

22


Page 23 of 32

1.4

1.2

CG10 1.0

Absorbtion (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CG20

0.8

g-C3N4 CG15

0.6

CG5

0.4

0.2

0.0 200

300

400

500

600

700

Wavelength (nm)

Fig. 3. UV-vis absorption spectra of the as-synthesized samples.

23


800

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Transmittance (a.u.)


Page 24 of 32

CG15

g-C3N4

0

500

1000

1500

2000

2500

3000

3500

-1

Wavenumber (cm )

Fig. 4. FT-IR spectra of the as-synthesized samples.

24


4000

4500

Page 25 of 32

Intensity (a.u.)

N1s

A

C1s O1s

0

200

400

600

800

1000

1200

1400

Bing energy (eV)

398.9 eV B

N1s CG15 Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


g-C3N4

399.7 eV 401.1 eV

390

392

394

396

398

400

402

404

406

408

410

412

Bing energy (eV)

288.4 eV C1s

C

284.8 eV g-C3N4

CG15 280

284

288

292

296

Bing energy (eV)

Fig. 5. XPS spectra of the as-synthesized g-C3N4 and CG15 samples. (A) Survey, (B) N1s, (C) C1s. 25



2500

A H2 production amount (µmol/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

CG15

2000

1500

CG10

1000

CG5

500

CG20 0

g-C3N4 0

2

4

6

8

Time (h)

26


10

12

Page 27 of 32

4500

B

H2 production amount (µmol/g)

4000 3500

CG15 + K2HPO4 3000 2500 2000

CG15

1500 1000 500 0

2

4

6

8

10

12

Time (h)

450

CG15 + K2HPO4

C

400 350 300

CG15

250 200

CG10

150 100

CG5

50

CG20

g-C3N4 0 1

2

3

4

5

6

0.018

CG15

D

0.016

The apparent quantum yields (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.014 0.012 0.010

CG10

0.008 0.006 0.004

CG5 0.002

CG20

0.000

g-C3N4 0

2

4

6

8

10

12

Time (h)

Fig. 6. (A) The H2 production amount of samples with different contents of C60. (B)The H2 production amount of samples with different contents of CG15 and CG15 27



+ K2HPO4. (C) The H2 production rate of samples. (D) The H2 production AQYs of samples.

8000

A


7000

CG15

6000 5000 4000 3000 2000 1000 0 0

10

20

30

40

50

60

70

80

50

60

70

80

Time (h)

0.06

B The apparent quantum yields (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

0.05

0.04

0.03

0.02

0.01

0.00 0

10

20

30

40

Time (h)

Fig. 7. (A) and (B) The long-term stability for CG15. 28


Page 29 of 32

1800

CG15

1600


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1400 1200 1000 800 600 400 200 0 0

5

10

15

20

Time (h)

Fig. 8. The H2 production amount of CG15 after 5 cycles.

29


25

30


2500

C60/g-C3N4

100

2000

Pt/C60/g-C3N4 1500

50 1000

Pt/C60

500

g-C3N4

0 0

2

4

6

8

10

Time (h)

Fig. 9. The H2 production amount of samples.

30


12


150


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Intensity (a.u.)

Page 31 of 32

g-C3N4

CG15 400

500

600

700

800

Wavelength (nm)

Fig. 10. The PL emission spectra of g-C3N4 and CG15 at the excitation wavelength of 250 nm.

31



TOC graphic

338

2500

C60/g-C3N4

100

2000

Pt/C60/g-C3N4 1500

50 1000

Pt/C60

500

g-C3N4

0 0

2

4

6

8

10

Time (h)

32


12


150


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 32

Graphite Carbon Nitride with ... - ACS Publications

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