Noble-Metal-Free Iron Phosphide Cocatalyst Loaded Graphitic

Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Noble-metal-free iron phosphide cocatalyst loaded graphitic carbon nitride as an efficient and robust photocatalyst for hydrogen evolution under visible light irradiation Hui Zhao, Junwei Wang, Yuming Dong, and Pingping Jiang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01665 • Publication Date (Web): 14 Aug 2017 Downloaded from http://pubs.acs.org on August 17, 2017

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 free 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 accessible to all readers and 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 Sustainable Chemistry & Engineering 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 29

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 Sustainable Chemistry & Engineering

Noble-metal-free iron phosphide cocatalyst loaded graphitic carbon nitride as an efficient and robust photocatalyst for hydrogen evolution under visible light irradiation Hui Zhao1,*, Junwei Wang1, Yuming Dong2, Pingping Jiang2

1. Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution

Control,

Jiangsu

Engineering

Technology

Research

Center

of

Environmental Cleaning Materials, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology (NUIST), 219 Ningliu Road, Nanjing 210044, China 2. Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China

*

Corresponding

author.

E-mail

address:

[email protected].

1

ACS Paragon Plus Environment

[email protected];


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

ABSTRACT Photocatalytic hydrogen (H2) evolution from water is a promising and sustainable approach for solar-to chemical energy conversion. However, the development of an efficient, robust and low-cost visible-light-driven photocatalyst for H2 evolution is still one of the great challenges. Graphitic carbon nitride (g-C3N4) is an attractive candidate but the activity of pristine g-C3N4 is largely limited. Herein, for the first time, we report the noble-metal-free iron phosphide cocatalyst decorated graphitic carbon nitride (g-C3N4/FexP) as a photocatalyst for the highly efficient and stable H2 evolution from water splitting irradiated by visible light. The peak H2 evolution rate of g-C3N4/FexP is ca. 277 times higher than that of pristine g-C3N4, and is almost comparable with the g-C3N4 modified by noble metal Pt cocatalyst. Additionally, g-C3N4/FexP demonstrates almost negligible photocatalytic degradation capability after five repeated cycles. Based on the detail analyses of photoluminescence and surface photovoltage spectra, we find the presence of FexP cocatalyst significantly accelerates the separation and transfer of photogenerated electrons of g-C3N4, hence resulting in the high photocatalytic efficiency of g-C3N4/FexP for H2 production. In addition, the adjacent Fe and P atoms in FexP act as dual proton adsorption sites to synergistically facilitate the fast H2 generation from water. Keywords: graphitic carbon nitride, iron phosphide, hybrid photocatalyst, hydrogen evolution

2


Page 2 of 29

Page 3 of 29

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


INTRODUCTION Nowadays the energy crisis and environmental pollution caused by fossil fuel combustion have been highly valued in the world. To help solve the shortage problem of fossil fuel and mitigate the environmental issue, the development of green renewable energy has received a great deal of attention. Hydrogen (H2) is currently pursued as a clean energy due to the high heat and product water alone during combustion. Since solar energy is essentially infinite and the harvesting process is inherently environmentally benign, the generation of H2 from water via photocatalysis is widely regarded as a valuable and promising approach.[1-3] In view of effectively utilizing solar energy (ca.43% for visible light) and large-scale application of a photocatalyst, the construction of a low-cost visible-light-driven photocatalyst with high efficiency and good durability are of great importance in the H2 evolution reaction. As a metal-free polymer semiconductor photocatalyst, graphitic carbon nitride (g-C3N4) combines the advantages of non-toxicity, high stability, earth-abundant elemental composition and easy availability.[4-6] Together with the appropriate band gap and position, g-C3N4 has been an attractive low-cost photocatalyst for H2 evolution under the irradiation of visible light.[7-12] However, the H2 evolution activity of pristine g-C3N4 is relatively low due to the fast recombination of the photogenerated electron-holes pairs. In order to accelerate the charge separation and transfer of g-C3N4, coupling with a cocatalyst has been identified as a feasible and effective strategy.[13,14] Noble metal Pt is widely used and considered as the best 3



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

cocatalyst for g-C3N4 in H2 evolution reaction.[15-17] However, the large-scale application of such system is largely limited by the high cost and extremely rarity of Pt. As a result, the development of an effective, low-cost, noble-metal-free cocatalyst has attracted lots of researchers’ interest. In recent years, several earth-abundant metal compounds have emerged as good candidate cocatalysts for g-C3N4, including MoS2,[18,19] NiSx (x =1 and 2),[20-22] CoS,[20,23] and Ni(OH)2.[24,25] However, these cocatalysts are reported to have the drawback of instability during the photocatalytic reaction.[26] Transition metal phosphides, such as Ni2P, CoP, MoP, FeP and Fe2P, are an important class of compounds with metallic characteristics and good electrical conductivity.[27] They have been found to have the high electrochemical catalysis activity and good stability for the H2 evolution reaction in acid or alkali solutions.[27] Based on the high electron-transfer activity and good stability, at present typical Ni2P and CoP have been used as efficient cocatalysts for g-C3N4 to accelerate the charge transfer and separation, resulting in the enhanced H2 evoltuion activity. For example, Yan et al prepared the noble-metal-free CoP/g-C3N4 hybrid photocatalyst that showed much higher H2 evolution activity than pristine g-C3N4 due to the good absorption ability of visible light, highly effective separation and low charge recombination rate in the presence of CoP cocatalyst.[28] Chen and Xu et al reported the significantly enhanced H2 evolution activity of g-C3N4 after loading CoP cocatalyst and revealed the unique P(δ-)-Co(δ+)-N(δ-) surface bonding states led to the accelerated charge transfer and separation, resulting in the high photocatalytic activity of CoP/g-C3N4.[29] 4


Page 4 of 29

Page 5 of 29

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


In our recent studies, Ni2P and CoP loaded g-C3N4 composites were found to exhibit efficient and stable performance in photocatalytic H2 evolution reaction.[30,31] Fe is the most abundant transition metal and its price is typically at least two orders of magnitude less than that of other highly abundant and catalytically relevant metals, including Ni and Co.[26,32] These advantages make Fe based phosphides become attractive alternative cost-effective cocatalysts. For example, Du et al reported the enhanced photocatalytic H2 production activity of CdS in water under visible light using noble-metal-free Fe2P as an active cocatalyst.[33] Fu et al constructed FeP/CdS composite photocatalyst with much higher visible-light-driven H2 evolution activity than pristine CdS.[26] Lewis and Schaak et al confirmed FeP as cocatalyst deposited on TiO2 surface showed exceptionally active for sustained H2 evolution under UV light irradiation.[32] However, according to our knowledge, there is no relevant study available in the literature about Fe based phosphides as cocatalysts for g-C3N4 to obtain improved H2 generation performance by photocatalysis. As a result, in this work the g-C3N4 modified by iron phosphide cocatalyst (g-C3N4/FexP) is obtained for the first time. They are synthesized by two-step hydrothermal and phosphidation method. The loading mass of FexP can be adjusted by systematically controlling the amount of FeOOH precursor generated form the initial hydrothermal process. The structural characteristics of g-C3N4/FexP are well characterized and recognized. The photocatalytic activity of g-C3N4/FexP is discussed in H2 generation reaction. The stability of g-C3N4/FexP is evaluated in cycling experiments. The H2 evolution activity of g-C3N4/FexP is compared with that of noble 5



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

metal Pt loaded g-C3N4. The interfacial charge transfer is investigated between g-C3N4 and FexP and a possible photocatalytic mechanism is proposed for g-C3N4/FexP in H2 evolution reaction.

EXPERIMENTAL SECTION Preparation Preparation of pristine g-C3N4: A simple heating treatment method is used to prepare pure g-C3N4, which has been reported in our previous work.[30,31] In short, urea (40 g) is added in a crucible with a cover and heated at 550 oC for 4 h in a muffle stove. The heating rate is controlled at 2 oC min-1. The resultant yellow-colored product is washed with H2O and then dried at 120 oC. Finally, pristine g-C3N4 production is obtained. Preparation of g-C3N4/FeOOH composite: The g-C3N4/FeOOH composite is prepared using a hydrothermal method. In a typical synthesis, g-C3N4 (200 mg) is added into water (22 mL). The mixture is sonicated for 180 min. The FeSO4·7H2O with different masses (3.5, 6.9, 13.0 and 25.5 mg) and hydrogen peroxide (30 wt.%, 6 mL) are then added into the mixture. After stirring for 30 min, the suspension is transferred to a Teflon-lined autoclave (50 mL) that maintains at 150 oC for 6 h. The resultant product is separated, washed with water and ethanol and dried at 80 oC. The g-C3N4/FeOOH composite is finally obtained. Pristine FeOOH is prepared using the same method without adding g-C3N4. The XRD patterns and SEM image of pristine FeOOH are provided in Fig. S1. Preparation of g-C3N4/FexP composite: The low-temperature phosphidation method 6


Page 6 of 29

Page 7 of 29

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


reported in our previous work is used to prepare g-C3N4/FexP composite.[30,31] In a typical synthesis, the as-obtained g-C3N4/FeOOH (100 mg) and monohydrate sodium hypophosphite (50 mg) are mixed together and grinded to a fine powder. The mixture is then calcinated at 300 oC for 2 h at a heating rate of 2 oC min-1 in an argon gas atmosphere. The obtained product is washed with water and ethanol and dried at 80 oC. The resultant product is denoted as g-C3N4/FexP-Y (Y = 0.04, 0.08, 0.15 and 0.22 wt.%), where Y represents the measured weight percent of Fe. The same procedure is used to obtain phosphidation-treated g-C3N4 in the condition of pristine g-C3N4 (100 mg) and monohydrate sodium hypophosphite (50 mg). Pristine FexP is prepared by the same method using FeOOH (30 mg) and monohydrate sodium hypophosphite (150 mg). The XRD patterns and TEM image of pristine FexP are provided in Fig. S2. Characterization The XRD patterns are recorded on a XRD-6000 X-ray diffractometer (Shimadzu, Japan) using Cu Kα radiation at the wavelength of λ = 1.541 Å. The TEM image, EDX spectrum and elemental mapping are collected using EDX analysis on a Tecnai G2 F20 scanning transmission electron microscopy instrument (FEI, USA). The SEM images are collected on a JSM-6340F scanning electron microscope (JEOL, Japan). The FTIR spectra are recorded using Perkin Elmer Fourier Transform Infrared Spectrometer GX (Perkin-Elmer, USA). X-ray photoelectron spectroscopy (XPS) analysis is conducted using an ESCALAB 250 Xi X-ray photoelectron spectrometer (Thermo, USA) with Al Ka line as the excitation source (hν = 1484.8 eV) and adventitious carbon (284.8 eV for binding energy) is used as reference to correct the 7



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 8 of 29

binding energy of a sample. The inductively coupled plasma optical emission spectrometer (ICP-OES) with the model of Agilent 725 (Agilent, USA) is used to measure the content of Fe element. UV-vis diffuse reflectance spectra are measured on

a

Lambda

750

UV/vis/NIR

spectrophotometer

(Perkin-Elmer,

USA).

Photoluminescence (PL) spectra are recorded on a RF5301 spectrofuorophotometer (Shimadzu, Japan) with an excitation wavelength of 325 nm. The surface photovoltage (SPV) spectrum is determined based on a self-made instrument.[33] Photocatalytic H2 evolution The photocatalytic experiments are performed in a 37 mL flask at ambient temperature using a 300 W Xe lamp equipped with a UV cut off filter (λ > 420 nm). The intensity of the light source is estimated to be 180 mW cm-2. 10 mg of photocatalyst is added to a solution mixture of 9 mL water and 1 mL triethanolamine (TEOA). Before each experiment, the suspension is purged with N2 gas for 30 min to remove oxygen. The amount of generated H2 at intervals is measured by gas chromatography (Agilent 7890A) with thermal conductivity detector.

RESULTS AND DISCUSSION Photocatalyst structure Fig. 1 shows the XRD patterns of pristine g-C3N4 and g-C3N4/FexP composites with different FexP loading amounts. Pristine g-C3N4 and g-C3N4/FexP composites all have two distinct diffraction peaks at 27.6o and 13.0o that can be indexed to the (022) and (110) planes of g-C3N4 with graphitic structure (JCPDS#87-1526). This result indicates that the introduction of FexP does not incur obvious change on the structure 8


Page 9 of 29

of g-C3N4. According to the XRD patterns of pristine FexP (Fig. S2), we find the as-obtained pristine FexP has a mixed crystal structure of FeP (JCPDS#65-2595) and Fe2P (JCPDS#51-0943). As to the as-prepared g-C3N4/FexP composites, no diffraction peak assigned to FexP is observed. This is due to the low loading mass of FexP on g-C3N4 surface. When the loading content of FexP is significantly increased (g-C3N4/FexP-2.58), as presented in the inset of Fig. 1, the FexP (x = 1 and 2) diffraction peaks are found to be more apparent. @

g-C3N4/FexP-0.22 g-C3N4/FexP-0.15

*# FeP Fe P

#

2

g-C3N4/FexP-0.08

@ g-C N 3 4

g-C3N4/FexP-0.04

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


#

pristine g-C3N4

@

* * **

10

10

20

**

##

*

20 30 40 50 2 theta (degree)

30 40 2 theta (degree)

50

*

60

60

Fig. 1 XRD patterns of pristine g-C3N4 and g-C3N4/FexP composites. The inset is the XRD patterns of g-C3N4/FexP-2.58.

Fig. 2a presents the TEM image of g-C3N4/FexP-0.08. The FexP are found to be deposited on g-C3N4 surface. The loaded FexP has a nanorod morphology that is consistent with pristine FexP (Fig. S2b). In order to determine the morphology of g-C3N4, The section 1 is chosen to be magnified. A layered structure is clearly observed for g-C3N4 (Fig 2b). On the basis of EDX spectrum of FexP (section 2), it is clearly found elemental Fe and P (Fig. 2c). The weak signal of C and N arises from g-C3N4 matrix. The emerging Cu signal results from Cu grid used for obtain TEM

9



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

image. When FexP (section 3) is characterized by HRTEM technique, it is found two interplanar spacings of ca. 0.20 and 0.27 nm (Fig. 2d). They are in good accordance with the (201) lattice plane of Fe2P and (011) lattice plane of FeP, respectively. The same results are obtained for g-C3N4/FexP-2.58, as shown in Fig. S3.

Fig. 2 TEM image of g-C3N4/FexP-0.08 (a); TEM image of g-C3N4 in g-C3N4/FexP-0.08 (b); EDX spectrum (c) and HRTEM image (d) of loaded FexP in g-C3N4/FexP-2.58.

The XPS spectra of typical g-C3N4/FexP-0.08 are recorded in Fig.3. In the high resolution XPS spectrum of C1s (Fig. 3a), there are three deconvolution peaks at 284.8, 286.1 and 288.4 eV, respectively. They are corresponding to graphite carbon atoms, carbon atoms in C-NH2 species and the sp2-hybridized carbon in the aromatic ring (N-C=N).[28] As displayed in the high resolution N1s spectrum, three

10


Page 10 of 29

Page 11 of 29

deconvolution peaks at 398.9, 400.0 and 401.1 eV observed are assigned to the sp2 N atoms in the triazine units, bridging N in the N-(C)3 of N-H and N in the heterocycles and cyano groups, respectively.[34] These results are well consistent with that for g-C3N4 alone. There is a weak peak appeared at 404.4 eV that can be attributed to terminal nitrate groups, charging effects, or π excitations.[17] Due to the low loading amount and self-resistance to XPS signal of FexP, there is very weak XPS signal observed for FexP,[35,36] as shown in Fig. S4. However, a peak is found to appear at 133.3 eV in the high resolution P2p spectrum (Fig. S4a). It is typical for P-N coordination indicating that some C in g-C3N4 is probably replaced by P in the phosphidation process.[37,38] However, in the FTIR spectrum of g-C3N4/FexP-0.08 (Fig. S5), no obvious vibration evidence of P-doing (at around 950 cm-1[39,40]) is observed. This result indicates a very small amount of P-doping exists. In order to clearly identify the XPS signals of loaded FexP on g-C3N4 surface, the g-C3N4/FexP-2.58 is selected to be investigated. As shown in Fig. 3c, besides the peak at 133.3 eV, a new peak appears at 129.4 eV. It is attributed to the P in FexP.[35,36] Fig. 3d gives the high resolution XPS spectrum of Fe2p. The peak at 707.3 eV corresponds to Fe2p3/2 that is in good accordance with that in FexP.[35,36]

292

(b)

288.4 eV

C1s

398.9 eV

N1s Intensity (a.u.)

(a) 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


284.8 eV 286.1 eV

290 288 286 284 Binding energy (eV)

282

400.0 eV 401.1 eV 404.4 eV

408 406 404 402 400 398 396 394 Binding energy (eV)

11



(c)

133.3 eV

P2p

(d)

129.4 eV

Fe2p

138

Intensity (a.u.)

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

136

134 132 130 128 Binding energy (eV)

Page 12 of 29

126

716

707.3 eV

712 708 704 Binding energy (eV)

700

Fig. 3 High resolution spectra of C1s (a) and N1s (b) in g-C3N4/FexP-0.08 and P2p (c) and Fe2p (d) in g-C3N4/FexP-2.58.

The UV-Vis diffuse reflection spectra of pristine FexP and g-C3N4 and g-C3N4/FexP composites with different FexP loading amounts are given in Fig. 4. Evidently, pristine FexP has a high adsorption in the range from 350 to 800 nm. On the other hand, pristine g-C3N4 has an absorption edge at about 450 nm, which corresponds to a band gap value of 2.71 eV for g-C3N4. When FexP is introduced, the g-C3N4/FexP shows nearly the similar absorption edge as compared to pristine g-C3N4, indicating that there is hardly obvious structural change of g-C3N4 observed in the loading process of FexP. However, in comparison with pristine g-C3N4, a broader absorption in the wavelength range from 450 to 800 nm is founded for g-C3N4/FexP composite photocatalysts. This is due to the introduction of FexP with high absorption ability of visible light. In addition, the absorption intensity for g-C3N4/FexP in the visible region gradually enhances with the increasing content of FexP loading. Based on these characterization techniques above, we can conclude that FexP component is successfully deposited on g-C3N4 surface.

12


Page 13 of 29

1.2 1.0 pristine g-C3N4

0.8


Abs.

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


0.6


0.4

pristine FexP

0.2 0.0

400

500 600 700 Wavelength (nm)

800

Fig. 4 UV-Vis diffuse reflection spectra of pristine FexP and g-C3N4 and g-C3N4/FexP

composites with different FexP loading amounts.

Photocatalytic activity Fig. 5a shows the photocatalytic H2 generation activity of different photocatalysts. During a reaction time of 2 h, the amount of H2 evolved over g-C3N4/FexP-0.08 composite catalyst reaches up to 166.4 µmol g-1. In comparison, the H2 evolution amounts over pristine g-C3N4 and the corresponding g-C3N4/FeOOH precursor are 0.6 and 1.2 µmol g-1, respectively. The H2 evolution rate over g-C3N4/FexP-0.08 is about 277 and 139 times that over pristine g-C3N4 and g-C3N4/FeOOH precursor, respectively. Besides, in order to exclude the effect of g-C3N4 with the same phosphidation treatment (phosphidation-treated g-C3N4), we investigate its H2 evolution activity but the corresponding H2 evolution amount is only 5.2 µmol g-1 in 2 h. This result demonstrates that phosphidation-treated g-C3N4 nearly has a negligible effect on the H2 generation over g-C3N4/FexP-0.08. In our recent work,[41] with the assistance of XPS technique, we discover the P-doping as a main action mode between P and g-C3N4 is existed in this phosphidation-treated g-C3N4 almost with the same doping amount as that in g-C3N4/FexP-0.08 due to the nearly unchanged XPS 13



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

peak area (Fig. S3a). As a result, the much lower H2 evolution amount of phosphidation-treated g-C3N4 also indicates the inappreciable effect of P-doing in g-C3N4/FexP-0.08. In addition, the mixture of g-C3N4 and FexP (0.12 wt.%) presents low H2 evolution amount of 7.6 µmol g-1 under the same condition. Based on these results, we could thus make a conclusion that the distinct enhancement of H2 generation activity over g-C3N4/FexP-0.08 results from the effective interaction between g-C3N4 and FexP species. The photocatalytic H2 evolution activity of g-C3N4/FexP composites largely depends on the loading amount of FexP. As given in Fig. 5b, when the weight percent of FexP increases to 0.12 wt.%, the highest H2 evolution amount could be obtained during the reaction time of 2 h. However, the H2 evolution activity gradually decreases with further increment in FexP loading which, on the one hand, originates from the excess of FexP species seriously blocking the absorption of the incident light by g-C3N4. This is supported by the UV-Vis diffuse reflection spectra of g-C3N4/FexP composites (Fig. 4) and well consistent with previous work.[19,21] On the other hand, the surplus FexP species reduce the oxidation reaction sites on g-C3N4 surface, thus leading to a decreased H2 evolution activity of g-C3N4/FexP.[42] The photocatalytic H2 evolution activity of g-C3N4/FexP-0.08 is compared with noble metal Pt cocatalyst modified g-C3N4. In order to maintain unchanged loading amount, the g-C3N4/Pt heterostructure with Pt weight percent of 0.12 wt.% (labeled as g-C3N4/Pt-0.12) is prepared via an in situ photodeposition method.[43] Under the same reaction conditions, the g-C3N4/FexP-0.08 nearly exhibits the equivalent H2 evolution 14


Page 14 of 29

Page 15 of 29

amount with g-C3N4/Pt-0.12, as shown in Fig. 5c. This result indicates that FexP possibly become an alternative cocatalyst for the replacement to expensive and scarce Pt due to its high efficiency and much low cost. Stability is a decisive factor when considering the practical application of a photocatalyst. In order to evaluate the stability of g-C3N4/FexP-0.08, we performed the time-circle H2 evolution experiment and the results are presented in Fig. 5d. After five runs of photocatalysis, negligible degradation in terms of H2 production is observed. This result demonstrates that g-C3N4/FexP-0.08 photocatalyst possesses stable activity for H2 generation. This robust photocatalytic stability possibly results from high efficient electron transfer between FexP and g-C3N4, and high stability of FexP for H2 evolution in aqueous media.[35,36] Such heterostructure may be expected to be a promising noble-metal-free candidate photocatalyst for H2 evolution with high

0

-1

H2 evolution (µ mol g )

40

(b) 200

g-C3N4/FexP-0.08

80

g-C3N4/FeOOH precursor

120 pristine g-C3N4

-1

160

Phosphidation-treated g-C3N4

(a) 200

mixture of g-C3N4 + FexP (0.12 wt.%)

efficiency.


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


0.12 wt.%

160 120 0.06 wt.%

80 0.23 wt.%

40

0.34 wt.%

0 Different FexP loading amount

Different photocatalyst

15



(d) 400

(c) 400

1st

g-C3N4/FexP-0.08


g-C3N4/Pt-0.12

300

-1

-1

H2 evolution (umol 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

200 100 0 0

1

2 Time (h)

3

4

2nd

Page 16 of 29

3rd

4th

5th

320 240 160 80 0 0

4

8 12 Time (h)

16

20

Fig. 5 (a) H2 evolution activities over different photocatalysts; (b) H2 evolution activities over g-C3N4/FexP composites with different FexP loading amounts,; (c) Comparison of photocatalytic H2 evolution activity between g-C3N4/FexP-0.08 and g-C3N4/Pt-0.12; (d) H2 evolution stability over g-C3N4/FexP-0.08 in the reused experiments. Notably, the involving content of FexP in g-C3N4/FexP composite is calculated by reference to FeP on basis of the measured Fe content.

Photocatalytic mechanism In the process of H2 evolution reaction over g-C3N4/FexP-0.08 photocatalyst, the g-C3N4 in g-C3N4/FexP-0.08 is excited under the irradiation of visible light and then produces electron-hole pairs. Contrast to pristine g-C3N4 facing the problem of rapid recombination of electron-hole pairs, the photogenerated electrons in conduction band (CB) of g-C3N4 could be easily transferred to surface FexP cocatalyst for H2O reduction to H2 in g-C3N4/FexP-0.08 composite due to the intimate contact with FexP cocatalyst. The holes in valence band (VB) of g-C3N4 are quickly quenched by TEOA sacrificial agent. The presence of FexP cocatalyst accelerates the separation and transfer of photogenerated electrons of g-C3N4 thus resulting in the enhanced photocatalytic activity in H2 evolution reaction. As shown in Fig. 6, the schematic diagram of H2 evolution over g-C3N4/FexP-0.08 photocatalyst is provided.

16


Page 17 of 29

Fig. 6 Schematic diagram of photocatalytic H2 evolution over g-C3N4/FexP-0.08 photocatalyst under visible light irradiation.

To verify the accelerated transfer and separation of photoexcited charges in g-C3N4/FexP-0.08, the PL and SPV experiments are performed and the results are given in Fig. 7. According to the PL spectra (Fig. 7a), it is found that the g-C3N4/FexP-0.08 has a lower peak intensity at about 450 nm in comparison with pristine g-C3N4. This result demonstrates the charge recombination of g-C3N4 can be efficiently suppressed with FexP modification.[30,31] In the SPV spectra (Fig. 7b), both pristine g-C3N4 and g-C3N4/FexP-0.08 present obvious positive photovoltage responses when irradiated by light ranging from 300 to 450 nm and the higher signal intensity is determined for g-C3N4/FexP-0.08 than pristine g-C3N4. These results indicate a stronger photoelectric intensity and higher separation efficiency of photogenerated charge for g-C3N4 in the presence of FexP coccatalyst.[33]

(a) 100 pristine g-C3N4

(b) 15

g-C3N4/FexP-0.08

Photovoltage (µ V)

80 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


60 40 20 0 400

450 500 550 Wavelength (nm)

600

pristine g-C3N4 g-C3N4/FexP-0.08

10

5

0 300

350

400 450 500 550 Wavelength (nm)

17


600


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

Fig. 7 Comparisons of PL spectra (a) and SPV spectra (b) between pristine g-C3N4 and

g-C3N4/FexP-0.08 composite photocatalyst. On the basis of XPS results of elemental Fe and P in g-C3N4/FexP composite (Fig. 3c and d), we find the peak of Fe2p is positively shifted in contrast to metallic Fe (706.8 eV[44]) while the P2p peak is negatively shifted with respect to elemental P (130. 2 eV[45]), implying a transfer of electron density from Fe to P. In this case, Fe and P atoms have a partial positive (δ+) and negative (δ-), respectively. Combined with previous research results,[26,35] we believe the FexP component in g-C3N4/FexP composite features pendant basic P(δ-) in close proximity to Fe(δ+), and that Fe(δ+) and P(δ-) can act as the hydride-acceptor and proton-acceptor centers, respectively. First, due to the presence of long pair electrons in 3d and 3p orbitals for Fe(δ+) and P(δ-), respectively, one proton from a H2O molecule can be adsorbed their surfaces forming a transition state of two molecules adsorption (step 1). The electrons of the H—O bond in a H2O molecule transfer to the O atom to produce a dual protonation transition state along with the releasing of OH- ions (step 2). The photogenerated electrons in CB of g-C3N4 transfer to the unoccupied d orbital of Fe(δ+) atom leading to the formation of the hydride at the Fe(δ+) center which then combines with the proton at adjacent P(δ-) center to form a H2 molecule (step 3). Evidently, the adjacent Fe and P atoms in FexP act as dual proton adsorption sites to produce a synergistic effect, contributing to the fast H2 generation from H2O. This result is in good accordance with that reported in the recent studies.[29,30] The schematic diagram of charge transfer and reaction mechanism for FexP on g-C3N4 surface is shown in Fig. 8.

18


Page 18 of 29

Page 19 of 29

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


Fig. 8 Schematic diagram of charge transfer and reaction mechanism for FexP

cocatalyst on g-C3N4 surface to accelerate H2 evolution

CONCLUSIONS In conclusion, a novel g-C3N4/FexP hybrid photocatalyst consist of earth-abundant elements has been presented. The highest H2 production activity is determined for typical g-C3N4/FexP-0.08, which is obviously higher than pristine g-C3N4, and is almost comparable with

noble

metal Pt decorated

g-C3N4. Additionally,

g-C3N4/FexP-0.08 shows robust stability for H2 generation. The introduction of FexP cocatalyst significantly accelerates the separation and transfer of photogenerated charges thus leading to the highly efficient H2 evolution activity of g-C3N4. Moreover, the adjacent Fe and P atoms in FexP act as dual proton adsorption sites to produce a synergistic effect, facilitating the fast generation of H2 from water. It is believed that this work is important for developing high-performance and low-cost photocatalytic materials in H2 evolution reaction.

ASSOCIATED CONTENT Supporting information Fig. S1: XRD patterns (a) and SEM image (b) of pristine FeOOH; Fig. S2: XRD

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

patterns (a) and TEM image (b) of pristine FexP; Fig. S3: TEM image (a) and STEM-EDX mapping (b) of g-C3N4/FexP-2.58, TEM (c) and HRTEM (d) images of loaded FexP in g-C3N4/FexP-2.58; Fig. S4: High resolution spectra of P2p (a) and Fe2p (b) in g-C3N4/FexP-0.08; Fig. S5: FTIR spectrum of g-C3N4/FexP-0.08. This information is available free of charge via the Internet at http://pubs.acs.org/.

AUTHOR INFORMATION Corresponding Author Dr. Hui Zhao: [email protected]; [email protected] Notes The authors declare no competing financial interest

ACKNOWLEDGEMENT The authors gratefully acknowledge the support from the Startup Foundation for Introducing Talent of NUIST (no. 2243141601061). The authors are very grateful to Prof. Zhichuan J. Xu and Dr. Shengnan Sun in Nanyang Technological University, Singapore for their help in preparation, characterization and performance of g-C3N4/FexP.

20


Page 20 of 29

Page 21 of 29

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


REFERENCES [1] Xiang Q.; Yu J.; Jaroniec M.; Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles. J. Am. Chem. Soc. 2012, 134, DOI 10.1021/ja302846n. [2] Wang Q.; Li J.; Bai Y.; Lian J.; Huang H.; Li Z.; Lei Z; Shangguan W. Photochemical Preparation of Cd/CdS Photocatalysts and Their Effcient Photocatalytic Hydrogen Production under Visible Light Irradiation. Green Chem. 2014, 16, DOI 10.1039/C3GC42466A. [3] Xie Y. P.; Yu Z. B.; Liu G.; Ma X. L.; Cheng H. M.; CdS-Mesoporous ZnS Core-Shell Particles for Efficient and Stable photocatalytic Hydrogen Evolution Under Visible Light. Energy Environ. Sci. 2014, 7, DOI 10.1039/C3EE43750G . [4] Li Y.; Ouyang S.; Xu H.; Wang X.; Bi Y.; Zhang Y.; Ye J.; Constructing Solid-Gas-Interfacial Fenton Reaction over Alkalinized-C3N4 Photocatalyst to Achieve Apparent Quantum Yield of 49% at 420 nm, J. Am. Chem. Soc. 2016,

138, DOI 10.1021/jacs.6b07272. [5] Ong W., Tan L., Ng Y.H., Yong S., Chai S., Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer to Achieving Sustainability? Chem. Rev. 2016, 116, DOI 10.1021/acs.chemrev.6b00075. [6] 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 Two-Electron Pathway, Science 2015, 347, DOI 10.1126/science.aaa3145. 21



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 29

[7] Wang X.; 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. Nature Mater. 2009, 8, DOI 10.1038/nmat2317. [8] Zhang J.; Chen X.; Takanabe K.; Maeda K.; Domen K.; Epping J. D.; Fu X.; Antonietti M.; Wang X.; Synthesis of a Carbon Nitride Structure for Visible-Light Catalysis by Copolymerization. Angew. Chem. Int. Ed. 2010, 49, DOI 10.1002/anie.200903886. [9] Wang Y.; Wang X.; Antonietti M.; Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: from Photochemistry to Multipurpose Catalysis to

Sustainable

Angew.

Chemistry.

Chem.

Int.

Ed.

2012,

51,

DOI

10.1002/anie.201101182. [10] Cao S.; Low J.; Yu J.; Jaroniec M.; Polymeric Photocatalysts Based on Graphitic Carbon Nitride. Adv. Mater. 2015, 27, DOI 10.1002/adma.201500033. [11] Lu D.; Wang H.; Zhao X.; Kondamareddy K. K.; Ding J.; Li C.; Fang P.; Highly Efficient Visible-Light-Induced Photoactivity of Z-Scheme g-C3N4/Ag/MoS2 Ternary Photocatalysts for Organic Pollutant Degradation and Production of Hydrogen.

ACS

Sustainable

Chem.

Eng.

2017,

5,

DOI 10.1021/acssuschemeng.6b02010. [12] Xu Q.; Chen B.; Yu J.; Liu G.; Making Co-condensed Amorphous Carbon/g-C3N4 Composites Performance

with

Improved

Using

Pt

as

Visible-Light Cocatalyst.

Photocatalytic

Carbon

22


2017,

H2-Production

118,

DOI

Page 23 of 29

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


10.1016/j.carbon.2017.03.052. [13] Cao S.; Yu J.; G-C3N4-Based Photocatalysts for Hydrogen Generation. J. Phys.

Chem. Lett. 2014, 5, DOI 10.1021/jz500546b. [14] Ran J.; Zhang J.; Yu J.; Jaroniec M.; Qiao S. Z.; Earth-Abundant Cocatalysts for Semiconductor-Based Photocatalytic Water Splitting, Chem. Soc. Rev. 2014, 43, DOI 10.1039/C3CS60425J. [15] Han Q.; Wang B.; Zhao Y.; Hu C.; Qu L.; A Graphitic-C3N4 "Seaweed" Architecture for Enhanced Gydrogen Evolution, Angew. Chem. Int. Ed. 2015, 54, DOI 10.1002/anie.201504985. [16] Zhang J.; Zhang M.; Yang C.; Wang X.; Nanospherical Carbon Nitride Frameworks with Sharp Edges Accelerating Charge Collection and Separation at A

Soft

Photocatalytic

Interface,

Adv.

Mater.

2014,

26,

DOI

10.1002/adma.201400573. [17] Martin D. J.; Qiu K.; Shevlin S. A.; Handoko A. D.; Chen X.; Guo Z.; Tang J.; Highly Efficient Photocatalytic H2 Evolution from Water Using Visible Light and Structure-Controlled Graphitic Carbon Nitride. Angew. Chem. Int. Ed. 2014, 53, DOI 10.1002/anie.201403375. [18] Zhao H.; Dong Y.; Jiang P.; Miao H.; Wang G.; Zhang J.; In Situ Light-Assisted Preparation of MoS2 on Graphitic C3N4 Nanosheets for Enhanced Photocatalytic H2

Production

from

J.

Water,

Mater.

Chem.

A

2015,

3,

DOI 10.1039/C5TA00402K. [19] Hou Y.; Laursen A. B.; Zhang J.; Zhang G.; Zhu Y.; Wang X.; Dahl S.; 23



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 24 of 29

Chorkendorff I.; Layered Nanojunctions for Hydrogen-Evolution Catalysis,

Angew. Chem. Int. Ed. 2013, 52, DOI 10.1002/anie.201210294. [20] Hong J.; Wang Y.; Wang Y.; Zhang W.; Xu R.; Noble-Metal-Free NiS/C3N4 for Efficient Photocatalytic Hydrogen Evolution from Water. ChemSusChem 2013, 6, DOI 10.1002/cssc.201300647. [21] Chen Z., Sun P., Fan B., Zhang Z., Fang X., In Situ Template-Free Ion-Exchange Process to Prepare Visible-Light Active g-C3N4/NiS Hybrid Photocatalysts with Enhanced Hydrogen Evolution Activity, J. Phys. Chem. C 2014, 118, DOI 10.1021/jp5000232. [22] Yin L.; Yuan Y.; Cao S.; Zhang Z.; Xue C.; Enhanced Visible-Light-Driven Photocatalytic Hydrogen Generation over G-C3N4 through Loading the Noble Metal-Free NiS2 Cocatalyst. RSC Adv. 2014, 4, DOI 10.1039/C3RA46362A. [23] Zhu Y.; Xu Y.; Hou Y.; Ding Z.; Wang X.; Cobalt Sulfide Modified Graphitic Carbon Nitride Semiconductor for Solar Hydrogen Production. Int. J. Hydro.

Energy 2014, 39, DOI 10.1016/j.ijhydene.2014.06.025. [24] Yu J.; Wang S.; Cheng B.; Lin Z.; Huang F.; Noble Metal-Free Ni(OH)2-G-C3N4 Composite

Photocatalyst

with

Enhanced

Visible-Light

Photocatalytic

H2-Production Activity. Catal. Sci. Technol. 2013, 3, DOI 10.1039/C3CY20878H. [25] Bi G.; Wen J.; Li X.; Liu W.; Xie J.; Fang Y.; Zhang W.; Efficient Visible-Light Photocatalytic H2 Evolution over Metal-Free g-C3N4 Co-Modified with Robust Acetylene Black and Ni(OH)2 as Dual Co-Catalysts, RSC Adv. 2016, 6, DOI 10.1039/C6RA03118H. 24


Page 25 of 29

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


[26] Chen H.; Lv X.J.; Cao S.; Zhao Z.Y.; Chen Y.; Fu W. F.; Robustly Photogenerating H2 in Water Using FeP/CdS Catalyst under Solar Irradiation, Sci.

Rep. 2016, 6, DOI 10.1038/srep19846. [27] Shi Y.; Zhang B.; Recent Advances in Transition Metal Phosphide Nanomaterials: Synthesis and Applications in Hydrogen Reaction, Chem. Soc. Rev. 2016, 45, DOI 10.1039/C5CS00434A. [28] 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,

DOI

10.1016/j.apcatb.2016.07.046. [29] Li C.; Du Y.; Wang D.; Yin S.; Tu W.; Chen Z.; Kraft M.; Chen G.; Xu R.; Unique P-Co-N Surface Bonding States Constructed on g-C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution, Adv. Funct. Mater. 2017, 27, DOI 10.1002/adfm.201604328. [30] Zhao H.; Sun S.; Jiang P.; Xu Z. J.; Graphitic C3N4 Modified by Ni2P Cocatalyst: An Efficient, Robust and Low Cost Photocatalyst for Visible-Light-Driven H2 Evolution from Water, Chem. Eng. J. 2017, 315, DOI 10.1016/j.cej.2017.01.034. [31] Zhao H.; Jiang P.; Cai W.; Graphitic C3N4 Decorated with CoP Cocatalyst: Enhanced and Stable Photocatalytic H2 Evolution Activity from Water under Visible-Light Irradiation, Chem. Asian J. 2017, 12, DOI 10.1002/asia.201601543. [32] Callejas J.F.; McEnaney J.M.; Read C.G.; Crompton J.C.; Biacchi A.J.; Popczun E.J.; Gordon T.R.; Lewis N.S.; Schaak R.E.; Eletrocatalytic and Photocatalytic 25



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 29

Hydrogen Production from Acidic and Neutral-pH Aqueous Solutions Using Iron Phosphide Nanoparticles, ACS Nano 2014, 8, DOI 10.1021/nn5048553. [33] Kong L.; Dong Y.; Jiang P.; Wang G.; Zhang H.; Zhao N.; Light-Assisted Rapid Preparation of a Ni/g-C3N4 Magnetic Composite for Photocatalytic H2 Evolution from Water, J. Mater. Chem. A 2016, 4, DOI 10.1039/C6TA03178A. [34] Yang S.; Gong Y.; Zhang J.; Zhan L.; Ma L.; Fang Z.; Vajtai R.; Wang X.; Ajayan P.M.; Exfoliated Graphitic Carbon Nitride Nanosheets as Efficient Catalysts for Hydrogen

Evolution

under

Visible

Light.

Adv.

Mater.

2013,

25,

DOI 10.1002/adma.201204453. [35] Jiang P.; Liu Q.; Liang Y.; Tian J.; Asiri A.M.; Sun X.; A Cost-Effective 3D Hydrogen Evolution Cathode with High Catalytic Activity: FeP Nanowire Arrays as

the

Active

Phase,

Angew.

Chem.

Int.

Ed.

2014,

53,

DOI 10.1002/anie.201406848. [36] Zhang Y.; Zhang H.; Feng Y.; Liu L.; Wang Y.; Unique Fe2P Nanoparticles Enveloped in Sandwichlike Graphited Carbon Sheets as Excellent Hydrogen Evolution Reaction Catalyst and Lithium-Ion Battery Anode, ACS Appl. Mater.

Interfaces 2015, 7, DOI 10.1021/acsami.5b08620. [37] Ma T. Y., Ran J.; Dai S.; Jaroniec M.; Qiao S. Z.; Phosphorus-Doped Graphitic Carbon Nitrides Grown in Situ on Carbon-Fiber Paper: Flexible and Reversible Oxygen

Electrodes,

Angew.

Chem.

Int.

DOI 10.1002/anie.201411125.

26


Ed.

2015,

54,

Page 27 of 29

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


[38] Zhou Y.; Zhang L.; Liu J.; Fan X.; Wang B.; Wang M.; Ren W.; Wang J.; Li M.; Shi J.; Brand New P-doped g-C3N4: Enhanced Photocatalytic Activity for H2 Evolution and Rhodamine B Degradation under Visible Light, J. Mater. Chem.

A 2015, 3, DOI 10.1039/C4TA05292G. [39] Ran J.; Ma T. Y.; Gao G.; Du X.; Qiao S. Z.; Porous P-Doped Graphitic Carbon Nitride Nanosheets for Synergistically Enhanced Visible-Light Photocatalytic H2 Production. Energy Environ. Sci. 2015, 8, DOI 10.1039/C5EE02650D. [40] Zhu Y. P.; Ren T. Z.; Yuan Z. Y.; Mesoporous Phosphorus-Doped G-C3N4 Nanostructured Flowers with Superior Photocatalytic Hydrogen Evolution Performance. ACS Appl. Mater. Inter. 2015, 7, DOI 10.1021/acsami.5b04947. [41] Zhao H.; Sun S.; Wu Y.; Jiang P.; Dong Y.; Xu Z. J.; Ternary Graphitic Carbon Nitride/Red Phosphorus/Molybdenum Disulfide Heterostructure: An Efficient and Low Cost Photocatalyst for Visible-Light-Driven H2 Evolution from Water,

Carbon 2017, 119, DOI 10.1016/j.carbon.2017.03.100. [42] Wang X.; Liu G.; Chen Z. G.; Li F.; Wang L.; Lu G. Q.; Cheng H. M.; Enhanced Photocatalytic Hydrogen Evolution by Prolonging the Lifetime of Carriers in ZnO/CdS Heterostructures. Chem. Commun. 2009, DOI 10.1039/B904668B. [43] Park H.; Choi W.; Hoffmann M. R.; Effects of the Preparation Method of the Ternary

CdS/TiO2/Pt

Hybrid

Photocatalysts

on

Visible

Light-Induced

Hydrogen Production, J. Mater. Chem. 2008, 18, DOI 10.1039/B718759A. [44] Rajesh B.; Sasirekha N.; Lee S. P.; Kuo H. Y.; Chen Y. W.; Investigation of Fe-P-B Ultrafine Amorphous Nanomaterials: Influence of Synthesis Paremeters 27



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

on Physicochemical and Catalytic Properties, J. Mol. Catal. A: Chem. 2008, 289, DOI 10.1016/j.molcata.2008.04.013. [45] Cao S.; Chen Y.; Wang C.; Lv X.; Fu W.; Spectacular Photocatalytic Hydrogen Evolution Using Metal-Phosphide/CdS Hybrid Catalysts under Sunlight Irradiation. Chem. Commun. 2015, 51, DOI 10.1039/C5CC01799H.

28


Page 28 of 29

Page 29 of 29

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


For Table of Contents Use Only

Synopsis: Cost-effective g-C3N4/FexP hybrid photocatalyst with earth-abundant elements exhibits the enhanced and stable visible-light-driven H2 evolution activity from water

29


Noble-Metal-Free Iron Phosphide Cocatalyst Loaded Graphitic

Recommend Documents