An Insight into the Crucial Factors for Photochemical Deposition of

Subscriber access provided by Kaohsiung Medical University

Article

An Insight into the Crucial Factors for Photochemical Deposition of Cobalt Cocatalyst on g-C3N4 Photocatalyst Na Zhao, Linggang Kong, Yuming Dong, Guang-Li Wang, Xiuming Wu, and Pingping Jiang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01590 • Publication Date (Web): 27 Feb 2018 Downloaded from http://pubs.acs.org on March 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31 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

ACS Applied Materials & Interfaces

An

Insight

into

the

Crucial

Factors

for

Photochemical Deposition of Cobalt Cocatalyst on g-C3N4 Photocatalyst Na Zhao, Linggang Kong, Yuming Dong*, Guangli Wang, Xiuming Wu and Pingping Jiang International Joint Research Center for Photoresponsive Molecules and Materials, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, People's Republic of China. KEYWORDS: photocatalysis; hydrogen generation; photochemical; water splitting; transition metal; crucial factors.

ABSTRACT

Photochemical preparation of inexpensive hydrogen evolution cocatalysts is of greatly significance and challenging. Currently, the crucial factors in photochemical preparation of nonnoble metal are still unknown. In this work, taking Co/g-C3N4 composite photocatalysts as a case, complexing agent and sacrificial agent were found as the crucial factors for photochemical deposition process. Cobalt was supported on the electron outlet points of g-C3N4 in one hour and the ratio of Co in Co/g-C3N4 composite photocatalyst can be regulated by changing irradiation time of the preparation process. The optimized hydrogen evolution rate of Co/g-C3N4 was about

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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 2 of 31

11.48 µmol h-1, which was 75 times more than pure g-C3N4. The photocatalytic H2 evolution rate was stable after 48 h. The mechanism for the high activity of Co/g-C3N4 composites was explored by surface photovoltage spectra and photoluminescence spectra. Co effectively promoted the separation of the photogenerated electrons and holes of g-C3N4 and improved the H2 production rate.

INTRODUCTION

As the growing energy crisis and the serious environmental pollution, the demand for producting low-cost and clean energy sources is urgent right now. Photocatalytic hydrogen production has attracted more and more attention.(1) In the past few decades, various semiconductors have been proposed for hydrogen production via water splitting. Although great achievements have been achieved, it is still a significant challenge to develop a high-efficiency, low-cost and environment-friendly photocatalyst. The whole process of the hydrogen production from water consists of three major portions: effective absorption of sunlight, the separation and transfer of the photo generated carriers and interfacial oxidation and reduction reaction. The process of the light absorption only needs 10-1510-9 s, the separation and transfer of the photo generated charge usually needs 10-5 s and the process of the surface reaction needs 10-6-10-3 s. The speed of chemical reaction limits the whole process of the photocatalysis.(2)-(3) Furthermore, the lag of the surface reaction would lead to more recombination of the photo-generated electrons and holes. Up to now, various photo-active materials, such as TiO2, CdS, ZnO, La5Ti2Cu(S1-xSex)5O7 and carbon-based nanocomposites, have been investigated for hydrogen evolution reactions.(4)-(8) Recently, intensive researches have been reported on a metal-free polymeric photocatalyst, graphitic carbon nitride (g-C3N4) and the


2

Page 3 of 31 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


modified g-C3N4 in photocatalysis since the pioneering report in 2009.(9)-(39) g-C3N4 has attracted more attention because of its appropriate bandgap for the efficient utilization of visible light, non-toxic characteristics, and high stability. However, the photocatalytic efficiency of g-C3N4 alone is very low. Introduction of cocatalyst is greatly necessary to enhance the HER activity of g-C3N4.(23)-(25) Composed of earth-abundant elements, transition metals are low cost as cocatalysts. For example, many cobalt compounds have been proposed as cocatalysts in photocatalytic systems and revealed outstanding performance and excellent durability, including Co, Co(OH)2, CoSe2, CoP and Co2P.(40)-(43) Therefore, the combination of cobalt based cocatalyst and g-C3N4 is promising for development of efficient and inexpensive photocatalyst. Although the cocatalyst-supported composite photocatalyst synthesized by the conventional method accelerates the hydrogen production rate to a certain extent, the physical distribution of the cocatalyst and photo-active materials are random. Precisely deposition of hydrogen evolution reaction (HER) cocatalyst on electron outlets of photo-active materials is desirable for the enhancement of photocatalytic rate, because of the key role of cocatalysts in the transfer of electrons. Recently, photochemical deposition of noble metals such as Pt as HER cocatalyst at the electron outlet has been approved by Can Li’s Group, and the sample revealed higher activity than those with cocatalysts randomly deposited.(45)-(47) And their intensive works revealed great advantage and promising application of photochemical deposition route for preparation of HER cocatalyst. Because platinum is rare and expensive, it is greatly necessary to develop photochemical preparation method for HER cocatalysts composed of earth-abundant elements.(48) As expected, many efforts have been made on the photochemical preparation of transition metals. Due to the difference of electronegativity, the photochemical deposition of transition metal is much more difficult than noble metals. In our previous work, a photoreduction deposition route


3


Page 4 of 31

of nickel on g-C3N4 was proposed.(49) However, the key factors which affect the deposition of transition metal on photo-active materials are still unknown. In this work, we focus on the key factors for photoreduction deposition, which can blaze new trails for the preparation of photocatalyst. Taking above condition into consideration together, the key factors in photodeposition are studied and discussed by the case of cobalt on g-C3N4. The present system displays excellent performance of photocatalytic hydrogen evolution.

EXPERIMENTAL SECTION

Chemicals. All reagents, including thiourea (99%), triethanolamine (TEOA) (78%), cobaltchloride (99%), sodium hypophosphite monohydrate (98%), methanol (99.5%), lactic acid (85%), ascorbic acid (99.7%) and ethyl alcohol (99.75%), were purchased from Sinopharm Chemical Reagent Co. Ltd. and used without further purification. Preparation of g-C3N4 nanosheets. The g-C3N4 nanosheets used in this study were fabricated as follows.(50)-(52) Firstly, 20 g thiourea in a crucible was heated to 550 oC with a ramp rate of 2 o

C min-1 and maintained at this temperature for 2 h under air atmosphere. Then the resultant

yellow bulk g-C3N4 was ground into fine powder and heated at 500 oC for another 2 h under ambient pressure. Finally, light yellow powder of g-C3N4 nanosheets was obtained. Synthesis of Co/g-C3N4 composite. Photodeposition method was the essential synthetic method in this system. Firstly, g-C3N4, TEOA, an aqueous solution of CoCl2 (0.1 M), NaH2PO2 (0.5 M) and water were added in a 25 mL flask under sonication. Then the mixture was purged with pure nitrogen gas for 40 min to remove air. After irradiation under 300 W Xe lamp


4

Page 5 of 31 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


equipped with an AM 1.5 G filter for 50 minutes, the sediments were washed with deionized water and ethyl alcohol and dried in the vacuum drying oven. The ratio of Co is regulated by adjusting the irradiation time. Characterization methods. X-ray diffraction (XRD) patterns were recorded on a D8 X-ray diffractometer (Bruker AXS, German) to detect the composition and phase of the sample. To analyze the size and lattice fringe, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) images were recorded on a JEM-2100 transmission electron microscope (JEOL, Japan). The Tecnai G2 F20 scanning transmission electron microscope (STEM, USA) was used to exam the EDS elemental mapping. The AA-220/220Z atomic absorption spectrophotometry (Varian, USA) was used to measure the ratio of Co in Co/g-C3N4. To discover surface species of sample, the ESCALAB 250 Xi (Thermo, USA) X-ray photoelectron spectrometer with Al Kα line as the excitation source (hν = 1484.8 eV) was used to measure X-ray photoelectron spectroscopy (XPS) analysis. The UV-3600 spectrophotometer (Shimadzu, Japan) was used to measure the UV-vis absorption spectra. The Nicolet 6700 infraredspectrometer (Thermal, USA) with a DLaTGS detector over the 4000-800 cm-1 range was used to record the fourier transform infrared (FTIR) spectra. The fluorescence spectrophotometer (Cary Esclipse, Varian, USA) was used to carry out the photoluminescence (PL) measurements. The fluorescence spectrophotometer (Edinburgh Instruments, FL-1057) was used to survey the time-resolved photoluminescence emission spectra (374 nm excitation) and emission quantum yields. The surface photovoltage (SPV) was measured by a self-made equipment to research the charges features.(53) Photocatalytic hydrogen production. The photocatalytic tests were put into a 25 mL flask and the light source was a 300 W Xe lamp with an AM 1.5G filter. 5 mg of prepared Co/g-C3N4


5


Page 6 of 31

composite was added to a 25 mL flask with 15 mL 20 vol% TEOA aqueous solution. Then the mixture is purged with pure nitrogen gas for 40 minutes after sonication for 5 minutes. Hydrogen evolution was detected by gas chromatography (FL-1057 using a 5 Å molecular sieve column, argon as a carrier gas) with a thermal conductivity detector (TCD). Quantum yields (Q.Y.) defined by the equation as follows and measured using a 300 W Xe lamp with a 400 nm (±5 nm) band-pass filter:

Q.Y. (%) =

=

number of reacted electrons × 100% number of incident photons number of evolved H2 molecules × 2 × 100% number of incident photons

The optical power density was 0.045 mw cm-2, surveyed by a radiometer (CEL-NP2000), matching with the number of incident photons (2.1 × 1019 photons per s).

RESULT AND DISCUSSION

The crucial factors of photochemical strategy. In order to explored the influences of various factors on the formation of Co/g-C3N4 composite catalysts, different control experiments were made to investigate the key factors of photodeposition. Firstly, the H2 production activity of Co-T/g-C3N4 (T=0, 20, 30, 40, 50, 60 and 120 minutes) with different photoreduction deposition time were investigated. The photocatalytic HER rates in 20 vol% TEOA aqueous solution were shown in Figure S1. It was obviously to see that the hydrogen production rate was very low for pure g-C3N4, which might be caused by fast recombination of electrons and holes. The hydrogen production reached to 1.24 µmol h-1 when


6

Page 7 of 31 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


the time of deposition was 20 minutes, which was significantly higher than that of pure g-C3N4. And the highest hydrogen production rate reached to 11.48 µmol h-1 when the time of deposition was 50 minutes, which was about 75 times as much as pure g-C3N4. The results showed that the combination of electrons and holes were suppressed because of the synergistic effect of Co and g-C3N4. From Figure S1, the rates of hydrogen production were 9.33 µmol h-1 and 4.97 µmol h-1 when the time of deposition were 60 minutes and 120 minutes. The results showed that the hydrogen yield were dropped when the deposition time were longer than 50 minutes, which would be caused by blocking of the ability to absorb light of g-C3N4. So the photodeposition time of Co/g-C3N4 was set at 50 min and Co-50/g-C3N4 sample was widely used in next experiments. Secondly, control experiments were carried out to illustrate the necessity of every reagent on the synthesis of Co/g-C3N4 composites. The various experiment conditions were listed as shown in Table 1. There was no sediment because of the lack of g-C3N4 in system D, which indicated that g-C3N4 was fatal for the formation of Co particles. Then the obtained catalysts A, B and C were gathered and then H2 evolution activity was tested under same conditions. As we can see in Figure 1a, the HER activity of sample A (11.48 µmol h-1) was much higher than that of sample B (0.62 µmol h-1) and C (0.26 µmol h-1). We can see that g-C3N4 and irradiation were indispensable to prepare the Co/g-C3N4 composites. In a word, the control-experiments demonstrated the necessary conditions for the photodeposition of Co. Table 1. Preparation Conditions for Control Experiments. H2O

Irradiation

Heating

Sample

gC3N4 (mg)

TEOA (78%) (mL)

CoCl2 (0.1 M) (mL)

NaH2PO2 (0.5 M) (mL)

(mL)

(min)

( C)

H2 evolution (µmol h-1)

A

20

2

2

2

4

50

__

11.48

B

20

2

2

2

4

__

60

0.62


o

7


Page 8 of 31

C

20

2

0

2

6

50

__

0.26

D

0

2

2

2

4

50

__

0.57

Table 2. Control Experiments with Different Complexing Agent.

Sample

gC3N4 (mg)

Complexing CoCl2 NaH2PO2 Agent (0.1 M) (0.5 M) (2 mL) (mL) (mL)

H2O

Irradiation

(mL)

(min)

Mass

H2 fraction evolution (µmol h-1)

A

20

TEOA (78%)

2

2

4

50

2.630 wt%

11.48

A1

20

Ethyl alcohol (99.75%)

2

2

4

50

0.064 wt%

0.42

A2

20

Lactic acid (85%)

2

2

4

50

0.046 wt%

0.09

A3

20

H2O

2

2

4

50

0.116 wt%

0.75

Table 3. Control Experiments with Different Sacrificial Agent

Sample

gC3N4 (mg)

TEOA (78%) (2mL)

CoCl2 (0.1 M) (mL)

Sacrificial Agent (2 mL)

H2O

Irradiation

Mass

A

20

2

2

B1

20

2

B2

20

2

H2 evolution (µmol h-1)

(mL)

(min)

fraction

NaH2PO2 (0.5M)

4

50

2.630 wt%

11.48

2

Ascorbic acid (99.7%)

4

50

0.820 wt%

0.41

2

Eethyl alcohol

4

50

0.210 wt%

0.11

(99.75%) B3

20

2

2

H2O

4

50

0.096 wt%

0.08

B4

20

2

2

Lactic acid (85%)

4

50

0.078 wt%

0.05


8

Page 9 of 31 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


Interestingly, we found the complexing agent and the sacrificial agent are necessary for photoreduction deposition. In order to prove their key roles, we carried out a series of contrast experiments to understand this phenomenon. At first, we studied the role of complexing agent TEOA in the reaction, and the experimental conditions were showed in Table 2. When we changed TEOA to ethyl alcohol, lactic acid and H2O, respectively, the color of the corresponding samples A1, A2 and A3 were all lighter than that of sample A. The differences of the color were showed in Figure 1(b), which matched with their hydrogen production properties. As shown in Scheme 1, the [Co(TEOA)2]2+ complex formed in presence of TEOA in the solution.(54) However, no complex was found in the case of ethyl alcohol, lactic acid and H2O. In order to further explore the function of complex, the current-potential curves (J-V) of pure H2O, 20 vol% TEOA aqueous solution, 0.6 mM CoCl2 in 20 vol% TEOA aqueous solution and 0.6 mM CoCl2 in pure H2O were investigated. From Figure 2, the observed reduction potential of pure Co2+ was determined as -1.24 V vs NHE, and that was -0.91 V vs NHE when Co2+ and TEOA were mixed. Because the conductive band of g-C3N4 is about -1.25 V, which is slightly higher than the reduction potential of Co2+. Therefore, Co2+ is difficult to be reduced by photo-generated electrons of g-C3N4. Due to the great challenge, the photochemical deposition of transition metal is rare up to now. Through the [Co(TEOA)2]2+ complex, photoreduction of bivalent cobalt becomes easier. This is the key discover of this work. The conclusion is coincident with the photochemical reaction results in Figure 1(b), which illustrated the necessity of complexing agent in the photochemical reduction of transition metal. In addition, we also explored the necessity of the sacrificial agent in photodeposition process by control experiments in Table 3. The color of these samples were different. As shown in Figure 1c, when the color was deeper, the photocatalytic activity was higher. The same phenomenon


9


was also observed in Figure 1b. Then we suspected that the tendency of the color associated with the load of cobalt, and our guess was proved by the results of atomic absorption (Table 2 and Table 3). The influence of different sacrificial agent on reaction results was different. As we can see from the Table 3, when we used the NaH2PO2 as sacrificial agent, the hydrogen production rate was 11.48 µmol h-1, which was more than ascorbic acid, ethyl alcohol, H2O and lactic acid. As we know, the reduction rate in presence of different sacrificial agent was different, and NaH2PO2 is a proper sacrificial agent for photoreduction of transition metal. (55)

a

12

b 12 H2 evolution（ µmolh-1）

H2 evolution（ µmolh-1）

10

A

A1

A2

A3

10

8 6 4 2 0 A

B

c 12 H2 evolution（ µmolh-1）

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 10 of 31

D

C

A

B1

B2

B3

8 6 4 2 0 A

A1

A2

A3

B4

10 8 6 4 2 0 A

B1

B2

B3

B4

Figure 1. (a) Contrast of the photocatalytic H2 evolution rate of sample A, B, C and D obtained in Table 1. (b) The color and hydrogen rate of different samples with various complexing agent in Table 2. (c) The color and hydrogen rate of different samples with various sacrificial agent in Table 3.


10

Page 11 of 31

Scheme 1. Structure of complex compound.

-1.4 conductive band of g-C3N4 -1.25V

-1.2

Potential (Vrs.NHE)

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


-1.24V

-1.0 -0.91V

-0.8 -0.6 -0.4

pure H2O 20 vol%TEOA aqueous solution 0.6 mM CoCl2 in 20 vol%TEOA aqueous solution 0.6 mM CoCl2 in pure H2O

-0.2 0.0 0.0

0.5

1.0

1.5

2.0

Current (mA) Figure 2. The current-potential curves (J-V) of different solutions. Glassy carbon electrode was used as the working electrode, and all the scanning rates were 0.1 V/s. Formation and characterization. As XRD patterns in Figure 3, both pure g-C3N4 and Co/gC3N4 composites showed peak at 28.0°, which was indexed to the (100) lattice fringe diffractions


11


of g-C3N4 (JCPDS 87-1526).(56) This indicated that the structural characters of g-C3N4 were not changed in the deposition process of Co. The diffraction peaks of Co were located at 41.683°, 44.762° and 47.568°, matching with the (100), (002), and (101) lattice diffractions of Co (JCPDS 05-0727), respectively. Obviously, the intensity of the diffraction peak of Co was enhanced with the increase of Co content.

♦g-C3N4 ♥ Co

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 12 of 31

♥ ♥♥

Co-120/g-C3N4 ♦

Co-50/g-C3N4

♦

10

pure g-C3N4 20

30

40

50

60

70

80

90

2theta(degree) Figure 3. Powder XRD patterns of pure g-C3N4, Co-50/g-C3N4 and Co-120/g-C3N4. TEM images of Co/g-C3N4 showed the morphology features of the nanoparticles (NPs) affiliated to the nanosheets and the size of the cobalt particles were 50-200 nm (Figure 4a). The HRTEM image indicated that Co NPs have a lattice fringe with lattice fringes of 0.203 nm, assigning to the (002) plane (Figure 4b). The EDX spectrum (Figure 4c) showed the existence of Co, C and N element in the Co/g-C3N4 composites, and no other element was observed. Figure 4d showed the element distribution of C, N and Co in Co/g-C3N4 by scanning transmission electron microscope (STEM) image and the corresponding EDS elemental mapping images. We


12

Page 13 of 31 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


can find that C and N fully coincided with the area of g-C3N4, and Co particles dispersed uniformly on the surface of g-C3N4.

Figure 4. (a) TEM image and (b) HRTEM image of the Co-50/g-C3N4. (c) EDX spectrum of Co50/g-C3N4. (d) STEM elemental mapping images of C, N, and Co in Co-50/g-C3N4. XPS spectra were used to analyze the surface species and chemical states for Co-50/g-C3N4. In high-resolution XPS spectrum of C1s (Figure 5a), the peak at 284.8 eV and 288.2 eV in the highresolution C1s spectrum were due to graphite carbon atoms and the sp2-hybridized carbon in the aromatic ring (N-C=N) respectively. The high-resolution spectrum of N1s pointed out the different N species of g-C3N4 with triazine rings (C-N-C, 398.8 eV), tertiary nitrogen (N-(C)3, 400.1 eV) and amino functions (N-H, 401.2 eV).(56)-(57) On the other hand, the binding energy of Co 2p3/2 of Co-50/g-C3N4 (Figure 5c) is located at 781.3 eV, which matches with the Co(II) state


13


in Co-Nx. The chemical shift (781.3 eV) was higher than that of metallic Co (~779 eV) and Co oxide (~780 eV) because of the high electronegativity of N (3.04) compared to that of Co (1.88) and O (2.55), suggesting the presence of the cobalt-nitrogen bond.(58)-(61) The results of XPS spectra indicated that Co-50/g-C3N4 composite was obtained by photochemical strategy.

C1s

b

N1s

Intensity (a.u.)

Intensity (a.u.)

a

295

290

285

280

410 408 406

Binding energy (eV)

c

404 402

400 398 396 394

Binding energy (eV)

Co 2p

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 14 of 31

810

805

800

795

790

785

780

775

Binding energy (eV)

Figure 5. XPS analysis of the C 1s (a), N 1s (b) and Co 2p (c) spectrum of of Co-50/g-C3N4. The functional groups of pure g-C3N4 nanosheets and Co/g-C3N4 composites were detected by FTIR spectra as shown in Figure S2. All the samples revealed major absorption bands between 900 and 1800 cm-1, which were relative to the vibration characteristics of the triazine ring and CN stretching vibrations connected to a cross-linked structure. The wide band situate between 3100-3300 cm-1 was related to N-H and O-H because of the unreacted precursor or production


14

Page 15 of 31 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


exposed in air.(62) No change was observed in FTIR spectra after deposition of Co. The results indicated that the deposition of Co did not change the construction of g-C3N4. For Raman spectra in Figure S3, two feature Raman bands at around 1300 cm-1 and 1500 cm-1 respectively related to the disordered D and graphitic G.47 The Raman peaks between 600 and 800 cm-1 should be relevant to the in-plane rotation of sixfold rings in a graphitic carbon nitride layer.(63) The results also manifested that the structure of g-C3N4 did not change after the loading of Co. But the intensity of Raman peaks fromg-C3N4 reduced gradually with the increase of cobalt content, because the Co on the surface of g-C3N4 restrained the photons to the g-C3N4 in some extent. Meanwhile, the optical absorption of Co-T/g-C3N4 (T=0, 20, 50 and 120) were determined by UV-vis diffuse reflectance spectroscopy. According to these results in Figure S4, the absorption edge of pure g-C3N4 and Co/g-C3N4 was around 450 nm, which indicated a band gap of 2.75 eV. It showed that the band gap of g-C3N4 was not changed after loading of Co. There was an obvious promotion in the visible area after the loading of Co, which was coincided with the change of colour. According to the analysis of XRD, HRTEM, EDX and STEM elemental mapping, Co nanoparticles were successfully loaded on the surface of g-C3N4. Catalytic performance and mechanism. As shown in Figure S1, the highest hydrogen evolution rate of Co/g-C3N4 reached to 11.48 µmol h-1, which was about 75 times as much as pure g-C3N4. From the point of comparison with reported results, the photocatalytic activity was calculated as 2295 µmol h-1 g-1. In addition, the calculated quantum yield of Co-50/g-C3N4 for H2 production at 400 nm (±5 nm) was about 6.2%. It is obvious that both the quantum yield and


15


catalytic activity of Co/g-C3N4 is also higher than other works (Table S1). So the Co-50/g-C3N4 is one of the most predominant g-C3N4 based transition metal photocatalysts.

50

40

H2 evolution(µmol)

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 16 of 31

30

20

10

0 0

6

12

18

24

30

Time(h)

36

42

48

Figure 6. Cycling runs for photocatalytic hydrogen evolution of 48 h over Co-50/g-C3N4. In order to proved the stability of the catalyst, we did the cycle experiment as shown in Figure 6. The hydrogen production rate decreased slightly after irradiation for 48 h, which can be attributed to the sequential loss of the triethanolamine. The results indicated the good stability of the system during the photocatalytic reaction. The photocatalysts irradiated 48 h were characterized by XRD, TEM, IR and EDS mapping (Figure S5-S8). There was no change in these irradiated photocatalysts compared with fresh photocatalysts, which indicated that the Co/g-C3N4 was stable for photocatalytic H2 evolution.


16

—— pure g-C3N4

1.0

1.2

—— Co-50/g-C3N4

1.07

1.0

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


0.8 0.5 0.6 0.4 0.0

0.19

0.2

0.09 0.07

200

400

600

H2 evolution (µmolh-1）

Page 17 of 31

0.0 800

Wavelength (nm) Figure 7. UV-vis-diffuse reflectance spectra of pure g-C3N4 and Co-50/g-C3N4, and the H2 evolution rate of Co-50/g-C3N4 along with different light wavelength. Compared with pure g-C3N4, Co/g-C3N4 revealed stronger absorption for visible light (Figure S4). In order to prove whether the increased absorption of visible light was useful to the outstanding photocatalytic activity of Co-50/g-C3N4, the control experiments were carried out and the results were shown in Figure 7. The H2 production matched well with the UV-vis absorption spectrum of pure g-C3N4, not that of Co-50/g-C3N4. The results showed that the increased absorption in the visible area from Co almost ineffective to the high H2 evolution of Co-50/g-C3N4. So the Co as a cocatalyst in this composite photocatalyst was proved. The improved photocatalytic activity for hydrogen evolution was probably due to the fast interfacial transfer of photogenerated electron-hole pairs between g-C3N4 and Co. To prove the rate of electron-hole recombination that was blocked, we analyzed the emission quantum


17


efficiency of both g-C3N4 and Co-50/g-C3N4 (Figure S9). And the emission quantum yields defined by the following equation: E.Q.Y. (%) =

Ea - Ec × (La/Lc) × 100% Lc - La

After calculation, we concluded that the emission quantum yield of g-C3N4 is 5.34%, while the emission quantum yield of Co-50/g-C3N4 is 1.93%. The results showed that cobalt effectively inhibited the recombination of electron and hole, thereby enhancing its catalytic hydrogen production rate.

. .

b

g-C3N4

Pure g-C3N4 Co-50/g-C3N4

Co-50/g-C3N4

Intensity (a.u.)

Intensity (a.u.)

a

20

25

30

35

40

45

50

350

400

c

450

500

550

600

Wavelength (nm)

Time (ns)

pure g-C3N4 Co-50/g-C3N4

15

Photovoltage (µV)

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 18 of 31

10

5

0

300

350

400

450

500

Wavelength (nm)


18

Page 19 of 31 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


Figure 8. (a) Time-resolved photoluminescence decay spectra of g-C3N4 and Co-50/g-C3N4 with the excitation of 374 nm. (b) Photoluminescence spectra of pure g-C3N4 and Co-50/g-C3N4 with an excitation wavelength of 325 nm. (c) Surface photovoltage (SPV) spectra of pure g-C3N4 and Co-50/g-C3N4. As we can see that the time-resolved photoluminescence decay spectra of g-C3N4 and Co50/g-C3N4 (Figure 8a) revealed the average lifetimes of approximately 11.05 ns and 7.65 ns. This dramatically reduced lifetime clearly suggested significantly accelerated photoexciton dissociation in the Co/g-C3N4 sample, confirming that the Co promoted the separation of holes and electrons at the surface of the g-C3N4. Then we further proved that cobalt will improve the charge-separation efficiency, photoluminescence (PL) emission spectra was made as shown in Figure 8b. Both pure g-C3N4 and Co/g-C3N4 showed distinct emission band at about 450 nm under an excitation wavelength of 325 nm. However, the PL intensity of Co/g-C3N4 was much weaker than that of pure g-C3N4. The results suggested that the charge recombination of g-C3N4 was effectively suppressed by Co. In order to further study the mechanism, the surface photovoltage (SPV) of pure g-C3N4 and Co/g-C3N4 were determined. As shown in Figure 8c, pure g-C3N4 and Co/g-C3N4 revealed obvious positive photovoltage response in the rage of 300 to 400 nm, which matched well with the photo-active wavelength range of not Co but g-C3N4. These results indicated that the band gap of g-C3N4 was not changed after loading of Co, and the results further supported the cocatalyst function of Co obtained from Figure 7. At the same time, the photovoltage intensity of Co/g-C3N4 was much higher than that of pure g-C3N4. This suggested that the recombination of photogenerated electrons and holes were inhibited by Co visibly.(64)


19


Page 20 of 31

The schematic of photocatalytic H2 evolution mechanism for the Co/g-C3N4 composite was proposed in Scheme 2. At first, electron-hole pairs generate from the g-C3N4 under the irradiation of light. After that, the photogenerated electrons in the conduction band of g-C3N4 can be transferred to Co easily, and the electron–hole recombination rate in g-C3N4 was inhibited obviously at the same time. At last, the electrons were used by the Co to reduce H+ to H2 evolution.

Scheme 2. Proposed photocatalytic H2 production mechanism schematic of Co/g-C3N4 composite.

CONCLUSIONS In conclusion, the key factors in the process of photodeposition were discussed with the example of Co/g-C3N4. Complexing agent and sacrifical agent were indispensable in photoreduction deposition of transition metal elements such as cobalt. An efficient Co/g-C3N4 photocatalysts were prepared by photoreduction deposition method. And under optimum conditions, the H2


20

Page 21 of 31 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


evolution activity of Co/g-C3N4 composites was 11.48 µmol h-1 and the stablity of Co/g-C3N4 is good after irradiated 48 h. The results suggested that, photoreduction deposition of transition metal elements as cocatalyst was a good method to enhance the H2 production activity for hydrogen production. The system can suppress the charge recombination due to the effectively connected composite structure. This study provided an original insight for the photoreduction preparation of inexpensive and earth abundant metal. ASSOCIATED CONTENT

Supporting Information: Figure S1. Photocatalytic HER activity of Co-T/g-C3N4. Figure S2-S4. The FTIR spectra, Raman spectra and UV-vis diffuse reflectance spectra of Co-T/g-C3N4. Figure S5-S8. The XRD pattern, FTIR spectra, TEM image and EDX-Mapping image of Co-50/g-C3N4 after irradiation for 48 h. Figure S9. The emission quantum yields of g-C3N4 and Co-50/g-C3N4 compared with blank samples. Table S1. Photocatalytic H2 evolution over different semiconductors modified with cobalt-based cocatalysts.

AUTHOR INFORMATION

Corresponding Author *Yuming Dong, E-mail: [email protected], Fax: +86 510 85917763.

Author Contributions


21


Page 22 of 31

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The authors gratefully acknowledge the support from the National Natural Science Foundation of China (No. 21676123, 21575052), the Natural Science Foundation of Jiangsu Province (No. BK20161127), the Fundamental Research Funds for the Central Universities (JUSRP51623A), the Opening Foundation of Shandong Provincial Key Laboratory of Clean Production of Fine Chemicals (ZDSYS-KF201504) from Shandong Normal University, and MOE & SAFEA for the 111 Project (B13025). The authors also thank Dr. Jinze Lv for his kind help on SPV technology. REFERENCES (1) Liu, J.; Liu, Y.; Liu, N.; Han, Y.; Zhang, X.; Huang, H.; Lifshitz, Y.; Lee, S.; Zhong, J.; Kang, Z. Metal-Free Efficient Photocatalyst for Stable Visible Water Splitting via a TwoElectron Pathway. Science. 2015, 347, 970-974. (2) Cowan, A. J.; Barnett, C. J.; Pendlebury, S. R.; Barroso, M.; Sivula, K.; Grätzel, M.; Klug, D. R. Activation Energies for the Rate-Limiting Step in Water Photooxidation by Nanostructured α-Fe2O3 and TiO2. J. Am. Chem. Soc. 2011, 133, 10134-10140. (3) Schneider, J.; Matsuoka, M.; Takeuchi, M.; Zhang, J.; Horiuchi, Y.; Anpo, M.; Bahnemann, D. W. Understanding TiO2 Photocatalysis: Mechanisms and Materials. Chem. Rev. 2014, 114, 9919-9986.


22

Page 23 of 31 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


(4) Fan, W. Q.; Lai, Q. H.; Zhang, Q. H.; Wang, Y. Nanocomposites of TiO2 and Reduced Graphene Oxide as Efficient Photocatalysts for Hydrogen Evolution. J. Phys. Chem. C. 2011, 115, 10694-10701. (5) Lin, H. F.; Li, Y. Y.; Li, H. Y.; Wang, X. Multi-Node CdS Hetero-Nanowires Grown with Defect-Rich Oxygen-Doped MoS2 Ultrathin Nanosheets for Efficient Visible-Light Photocatalytic H2 evolution. Nano Res. 2017, 10, 1377-1392. (6) Lu, X. H.; Wang, G. M.; Xie, S. L.; Shi, J. Y.; Li, W.; Tong, Y. X.; Li, Y. Efficient Photocatalytic Hydrogen Evolution over Hydrogenated ZnO Nanorod Arrays. Chem.

Commun. 2012, 48, 7717-7719. (7) Nandy, S.; Hisatomi, T.; Katayama, M.; Minegishi, T.; Domen, K. Effects of Calcination Temperature on the Physical Properties and Hydrogen Evolution Activities of La5Ti2Cu(S1xSex)5O7

Photocatalysts. Part. Part. Syst. Char. 2018, 35, 1700275.

(8) Kumar, S.; Kumar, A.; Bahuguna, A.; Sharma, V.; Krishnan, V. Two-Dimensional CarbonBased Nanocomposites for Photocatalytic Energy Generation and Environmental Remediation Applications. Beilstein journal of nanotechnology. 2017, 8, 1571-1600. (9) Zhang, J. S.; Zhang, M. W.; Lin, L. H.; Wang, X. C. Sol Processing of Conjugated Carbon Nitride Powders for Thin-Film Fabrication. Angew. Chem. 2015, 127, 6395-6399. (10) Cui, Y. J.; Ding, Z. X.; Fu, X. Z.; Wang, X. C. Construction of Conjugated Carbon Nitride Nanoarchitectures in Solution at Low Temperatures for Photoredox Catalysis. Angew. Chem.

Int. Ed. 2012, 51, 11814-11818. (11) Shalom, M.; Inal, S.; Fettkenhauer, C.; Neher, D.; Antonietti, M. Improving Carbon Nitride Photocatalysis by Supramolecular Preorganization of Monomers. J. Am. Chem. Soc. 2013, 135, 7118-7121.


23


Page 24 of 31

(12) Kuriki, R.; Sekizawa, K.; Ishitani, O.; Maeda, K. Visible-Light-Driven CO2 Reduction with Carbon Nitride: Enhancing the Activity of Ruthenium Catalysts. Angew. Chem. Int. Ed.

2015, 54, 2406-2409. (13) Lin, Z. Z.; Wang, X. C. Nanostructure Engineering and Doping of Conjugated Carbon Nitride Semiconductors for Hydrogen Photosynthesis. Angew. Chem. Int. Ed. 2013, 52, 1735-1738. (14) Zhang, G. G.; Zhang, M. W.; Ye, X. X.; Qiu, X. Q.; Lin, S.; Wang, X. C. Iodine Modified Carbon Nitride Semiconductors as Visible Light Photocatalysts for Hydrogen Evolution.

Adv. Mater. 2014, 26, 805-809. (15) Zhang, J. S.; Zhang, M. W.; Yang, C.; Wang, X. C. Nanospherical Carbon Nitride Frameworks with Sharp Edges Accelerating Charge Collection and Separation at a Soft Photocatalytic Interface. Adv. Mater. 2014, 26, 4121-4126. (16) Mane, G. P.; Talapaneni, S. N.; Lakhi, K. S.; Ilbeygi, H.; Ravon, U.; Al-Bahily, K.; Mori, T.; Park, D. H.; Ajayan Vinu, A. Highly Ordered Nitrogen-Rich Mesoporous Carbon Nitrides and Their Superior Performance for Sensing and Photocatalytic Hydrogen Generation. Angew. Chem. Int. Ed. 2017, 56, 8481-8485. (17) Zheng, Y.; Lin, L. H.; Ye, X. J.; Guo, F. S.; Wang, X. C. Helical Graphitic Carbon Nitrides with Photocatalytic and Optical Activities. Angew. Chem. 2014, 126, 12120-12124. (18) Ong, W. J.; Putri, L. K.; Tan, Y. C.; Tan, L. L.; Li, N.; Ng, Y. H.; Wen, X. M.; Chai, S. P. Unravelling Charge Carrier Dynamics in Protonated g-C3N4 Interfaced with Carbon Nanodots as Co-Catalysts toward Enhanced Photocatalytic CO2 Reduction: A Combined Experimental and First-Principles DFT Study. Nano Res. 2017, 10, 1673-1696.


24

Page 25 of 31 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) Liu, X. T.; Pang, F.; He, M. Y.; Ge, J. P. Confined Reaction inside Nanotubes: New Approach to Mesoporous g-C3N4 Photocatalysts. Nano Res. 2017, 10, 3638-3647. (20) Ong, W. J. 2D/2D Graphitic Carbon Nitride (g-C3N4) Heterojunction Nanocomposites for Photocatalysis: Why Does Face-to-Face Interface Matter? Front. Mater. 2017, 4, 11. (21) Wu, K. H.; Huang, Y. J.; Teng, H. Oligomer-Incorporated Polymeric Layer Framework of Graphitic Carbon Nitride for Effective Photocatalytic Hydrogen Evolution. Part. Part. Syst.

Charact. 2018, 35, 1700221. (22) Zhou, M. J.; Hou, Z. H.; Chen, X. B. The Effects of Hydrogenation on Graphitic C3N4 Nanosheets for Enhanced Photocatalytic Activity. Part. Part. Syst. Charact. 2018, 35, 1700038. (23) Zeng, D. Q.; Ong, W. J.; Zheng, H. F.; Wu, M. D.; Chen, Y. Z.; Peng, D. L.; Han, M. Y. Ni12P5 Nanoparticles Embedded into Porous g-C3N4 Nanosheets as a Noble-Metal-Free Hetero-Structure Photocatalyst for Efficient H2 Production under Visible Light. J. Mater.

Chem. A. 2017, 5, 16171-16178. (24) Zeng, D. Q.; Xu, W. J.; Ong, W. J.; Xu, J.; Ren, H.; Chen, Y. Z.; Zheng, H. F.; Peng, D. L. Toward Noble-Metal-Free Visible-Light-Driven Photocatalytic Hydrogen Evolution: Monodisperse Sub-15 nm Ni2P Nanoparticles Anchored on Porous g-C3N4 Nanosheets to Engineer 0D-2D Heterojunction Interfaces. Appl. Catal. B. 2018, 221, 47-55. (25) Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen. K.; Antonietti, M. A Metal-Free Polymeric Photocatalyst for Hydrogen Production from Water under Visible Light. Nat. Mater. 2009, 8, 76-80. (26) Zheng, Y.; Lin, L. H.; Wang, B.; Wang, X. C. Graphitic Carbon Nitride Polymers toward Sustainable Photoredox Catalysis. Angew. Chem. Int. Ed. 2015, 54, 12868-12884.


25


Page 26 of 31

(27) Gong, Y. T.; Li, M. M.; Wang, Y. Carbon Nitride in Energy Conversion and Storage: Recent Advances and Future Prospects. ChemSusChem. 2015, 8, 931-946. (28) Yin, S. M.; Han, J. Y.; Zhou, T. H.; Xu, R. Recent Progress in g-C3N4 Based Low Cost Photocatalytic System: Activity Enhancement and Emerging Applications. Catal. Sci.

Technol. 2015, 5, 5048-5061. (29) Ye, S.; Wang, R.; Wu, M. Z.; Yuan, Y. P. A Review on g-C3N4 for Photocatalytic Water Splitting and CO2 Reduction. Appl. Surf. Sci. 2015, 358, 15-27. (30) Zhang, G. G.; Lan, Z. A.; Lin, L. H.; Lin, S.; Wang, X. C. Overall Water Splitting by Pt/gC3N4 Photocatalysts without Using Sacrificial Agents. Chem. Sci. 2016, 7, 3062-3066. (31) Wu, M.; Yan, J. M.; Zhang, X. W.; Zhao, M.; Jiang, Q. Ag2O Modified g-C3N4 for Highly Efficient Photocatalytic Hydrogen Generation under Visible Light Irradiation. J. Mater.

Chem. A. 2015, 3, 15710-15714. (32) Wu, M.; Yan, J. M.; Tang, X. N.; Zhao, M.; Jiang, Q. Synthesis of Potassium-Modified Graphitic Carbon Nitride with High Photocatalytic Activity for Hydrogen Evolution.

ChemSusChem. 2014, 7, 2654-2658. (33) Zhang, G. G.; Lan, Z. A.; Wang, X. C. Surface Engineering of Graphitic Carbon Nitride Polymers with Cocatalysts for Photocatalytic Overall Water Splitting. Chem. Sci. 2017, 8, 5261-5274. (34) Zhang, J. S.; Zhang, G. G.; Chen, X. F.; Lin, S.; Möhlmann, L.; Dołęga, G.; Lipner, G.; Antonietti, M.; Blechert, S.; Wang, X. C. Co-Monomer Control of Carbon Nitride Semiconductors to Optimize Hydrogen Evolution with Visible Light. Angew. Chem. Int. Ed.

2012, 51, 3137-3241.


26

Page 27 of 31 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


(35) Zhang, J. S.; Zhang, M. W.; Sun, R. Q.; Wang, X. C. A Facile Band Alignment of Polymeric Carbon Nitride Semiconductors to Construct Isotype Heterojunctions. Angew. Chem. Int. Ed.

2012, 124, 10292-10296. (36) Sun, J. H.; Zhang, J. S.; Zhang, M. W.; Antonietti, M.; Fu, X. Z.; Wang, X. C. Bioinspired hollow semiconductor nanospheres as photosynthetic nanoparticles. Nat. Commun. 2012, 3, 1139. (37) Lin, L. H.; Wang, C.; Ren, W.; Ou, H. H.; Zhang, Y. F.; Wang, X. C. Photocatalytic overall water splitting by conjugated semiconductors with crystalline poly (triazine imide) frameworks. Chem. Sci. 2017, 8, 5506-5511. (38) Zhang, G. G.; Zang, S. H.; Lin, L. H.; Lan, Z. A.; Li, G. S.; Wang, X. C. Ultrafine Cobalt Catalysts on Covalent Carbon Nitride Frameworks for Oxygenic Photosynthesis. ACS Appl.

Mater. Interfaces. 2016, 8, 2287-2296. (39) Kang, Y. Y.; Yang, Y. Q.; Yin, L. C.; Kang, X. D.; Liu, G.; Cheng, H. M. An Amorphous Carbon Nitride Photocatalyst with Greatly Extended Visible-Light-Responsive Range for Photocatalytic Hydrogen Generation. Adv. Mater. 2015, 27, 4572-4577. (40) Zhang, G. G.; Zang, S. H.; Wang, X. C. Layered Co(OH)2 Deposited Polymeric Carbon Nitrides for Photocatalytic Water Oxidation. ACS Catal. 2015, 5, 941-947. (41) Zhang, G. G.; Zang, S. H.; Lan, Z. A.; Huang, C. J.; Li, G. S.; Wang, X. C. Cobalt Selenide: A Versatile Cocatalyst for Photocatalytic Water Oxidation with Visible Light. J. Mater.

Chem. A. 2015, 3, 17946-17950. (42) Popczun, E. J.; Read, C. G.; Roske, C. W.; Lewis, N. S.; Schaak, R. E. Highly Active Electrocatalysis of the Hydrogen Evolution Reaction by Cobalt Phosphide Nanoparticles.

Angew. Chem. 2014, 53, 5427-5430.


27


Page 28 of 31

(43) Tian, J. Q.; Liu, Q.; Asiri, A. M.; Sun, X. P. Self-Supported Nanoporous Cobalt Phosphide Nanowire Arrays: An Efficient 3D Hydrogen-Evolving Cathode over the Wide Range of pH 0-14. J. Am. Chem. Soc. 2014, 136, 7587-7590. (44) Huang, Z. P.; Chen, Z. Z.; Chen, Z. B.; Lv, C. C.; Humphrey, M. G.; Zhang, C. Cobalt Phosphide Nanorods as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Nano Energy. 2014, 9, 373-382. (45) Zhu, J.; Fan, F. T.; Chen, R. T.; An, H. Y.; Feng, Z. C.; Li, C. Direct Imaging of Highly Anisotropic Photogenerated Charge Separations on Different Facets of a Single BiVO4 Photocatalyst. Angew. Chem. Int. Ed. 2015, 127, 9239-9242. (46) Li, R. G.; Zhang, F. X.; Wang, D. E.; Yang, J. X.; Li, M. R.; Zhu, J.; Zhou, X.; Han, H. X.; Li, C. Spatial Separation of Photogenerated Electrons and Holes Among {010} and {110} Crystal Facets of BiVO4. Nat. Commun. 2013, 4, 1432-1438. (47) Mu, L. C.; Zhao, Y.; Li, A. L.; Wang, S. Y.; Wang, Z, L.; Yang, J. X.; Wang, Y.; Liu, T. F.; Chen, R. T.; Zhu, J.; Fan, F. T.; Li, R. G.; Li, C. Enhancing Charge Separation on High Symmetry SrTiO3 Exposed with Anisotropic Facets for Photocatalytic Water Splitting.

Energy Environ. Sci. 2016, 9, 2463-2469. (48) Indra, A.; Menezes, P. W.; Kailasam, K.; Hollmann, D.; Schröder, M.; Thomas, A.; Brückner, A.; Driess, M. Nickel As a Co-Catalyst for Fhotocatalytic Hydrogen Evolution on Graphitic-Carbon Nitride (sg-CN): What Is the Nature of the Active Species?

Chem.Commun. 2016, 52, 104-107. (49) Kong, L. G.; Dong, Y. M.; Jiang, P. P.; Wang, G. L.; Zhang, H. Z.; Zhao, N. Light-Assisted Rapid Preparation of a Ni/g-C3N4 Magnetic Composite for Robust Photocatalytic H2 Evolution from Water. J. Mater. Chem. A. 2016, 4, 9998-10007.


28

Page 29 of 31 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


(50) Zhao, H.; Dong, Y. M.; Jiang, P. P.; Miao, H. Y.; Wang, G. L.; Zhang, J. J. In Situ LightAssisted Preparation of MoS2 on Graphitic C3N4 Nanosheets for Enhanced Photocatalytic H2 Production from Water. J. Mater. Chem. A. 2015, 3, 7375-7381. (51) Niu, P.; Zhang, L. L.; Liu, G.; Cheng, H. M. Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities. Adv. Funct. Mater. 2012, 22, 4763-4770. (52) Wang, W. J.; Yu, J. C.; Xia, D. H.; Wong, P. K.; Li, Y. C. Graphene and g-C3N4 Nanosheets Cowrapped Elemental α-Sulfur as a Novel Metal-Free Heterojunction Photocatalyst for Bacterial Inactivation under Visible-Light. Environ. Sci. Technol. 2013, 47, 8724-8732. (53) Lyu, J. Z.; Gao, J. X.; Zhang, M.; Fu, Q.; Lu, L. N.; Hu, S.; Zhong, J. B.; Wang, S.; Li, J. Construction of Homojunction-Adsorption

Layer on Anatase TiO2 to

Improve

Photocatalytic Mineralization of Volatile Organic Compounds. Appl. Catal. B. 2017, 202, 664-670. (54) Dong, J. F.; Wang, M.; Li, X. Q.; Chen, L.; He, Y.; Sun, L. C. Simple Nickel-Based Catalyst Systems Combined With Graphitic Carbon Nitride for Stable Photocatalytic Hydrogen Production in Water. ChemSusChem. 2012, 5, 2133-2138. (55) Thomas, A.; Fischer, A.; Goettmann, F.; Antonietti, M.; Müller, J. O.; Schlojl, R.; Carlsson, J. M. Graphitic Carbon Nitride Materials: Variation of Structure and Morphology and Their Use as Metal-Free Catalysts. J. Mater. Chem. A. 2008, 18, 4893-4908. (56) Yi, S. S.; Yan, J. M.; Wulan, B. R.; Li, S. J.; Liu, K. H.; Jiang, Q. Noble-Metal-Free Cobalt Phosphide Modified Carbon Nitride: An Efficient Photocatalyst for Hydrogen Generation.

Appl. Catal. B. 2017, 200, 477-483.


29


Page 30 of 31

(57) Marcano, D. C.; Kosynkin, D. V.; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.; Alemany, L. B.; Lu, W.; Tour, J. M. Improved Synthesis of Graphene Oxide. ACS Nano. 2010, 4, 4806-4814. (58) Liu, Q.; Zhang, J. Y. Graphene Supported Co-g-C3N4 as a Novel Metal-Macrocyclic Electrocatalyst for the Oxygen Reduction Reaction in Fuel Cells. Langmuir. 2013, 29, 38213828. (59) Yuasa, M.; Yamaguchi, A.; Itsuki, H.; Tanaka, K.; Yamamoto, M.; Oyaizu, K. Modifying Carbon Particles with Polypyrrole for Adsorption of Cobalt Ions as Electrocatatytic Site for Oxygen Reduction. Chem. Mater. 2005, 17, 4278-4281. (60) Morozan, A.; Jegou, P.; Jousselme, B.; Palacin, S. Electrochemical Performance of Annealed Cobalt-Benzotriazole/CNTs Catalysts towards the Oxygen Reduction Reaction.

Phys. Chem. Chem. Phys. 2011, 13, 21600-21607. (61) Chen. P. W.; Li. K.; Yu. Y. X.; Zhang. W. D. Cobalt-Doped Graphitic Carbon Nitride Photocatalysts with High Activity for Hydrogen Evolution. Appl. Surf. Sci. 2017, 392, 608615. (62) Holst, J. R.; Gillan, E. G. From Triazines to Heptazines: Deciphering the Local Structure of Amorphous Nitrogen-Rich Carbon Nitride Materials. J. Am. Chem. Soc. 2008, 130, 73737379. (63) Yan, H.; Chen, Y.; Xu, S. Synthesis of Graphitic Carbon Nitride by Directly Heating Sulfuric Acid Treated Melamine for Enhanced Photocatalytic H2 Production from Water under Visible Light. Int. J. of Hydrogen Energy. 2012, 37, 125-133. (64) Cao, S. W.; Low, J. X.; Yu, J. G.; Jaroniec, M. Polymeric Photocatalysts Based on Graphitic Carbon Nitride. Adv. Mater. 2015, 27, 2150-2176.


30

Page 31 of 31 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


Table of Contents Graphic


31

An Insight into the Crucial Factors for Photochemical Deposition of

Recommend Documents