Cobalt-Activated Amorphous MoSx Nanodots Grown In Situ on Natural

Subscriber access provided by Drexel University Libraries

Article

Co-Activated Amorphous MoSx Nanodots Grown In Situ on Natural Attapulgite Nanofibers for Efficient Visible-Light-Driven Dye-Sensitized H2 Evolution Xiangyu Liu, Yuan Xue, Yonggang Lei, Fang Wang, and Shixiong Min ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01785 • Publication Date (Web): 12 Oct 2018 Downloaded from http://pubs.acs.org on October 21, 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.

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 35 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 Nano Materials

1

Co-Activated Amorphous MoSx Nanodots Grown In

2

Situ on Natural Attapulgite Nanofibers for Efficient

3

Visible-Light-Driven Dye-Sensitized H2 Evolution

4

Xiangyu Liu‡, Yuan Xue‡, Yonggang Lei, Fang Wang* and Shixiong Min*

5

School of Chemistry and Chemical Engineering, Key Laboratory of Electrochemical Energy

6

Conversion Technology and Application, North Minzu University, Yinchuan, 750021, P. R.

7

China.

8

KEYWORDS. amorphous MoSx, attapulgite (ATP) nanofibers, Co doping, dye-sensitization, H2

9

evolution, visible light

10

11 12 13 14

15

ACS Paragon Plus Environment

1

ACS Applied Nano Materials 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 35

1

ABSTRACT. In-situ grown amorphous MoSx catalysts in an organic dye-sensitized system have

2

shown promising performance for catalyzing H2 evolution; however, the inevitable aggregations

3

and the low intrinsic activity of active sites of thus-obtained MoSx catalysts should be addressed

4

to further enhance their activity. Herein, we report an exceptionally active catalyst of in situ grown

5

Co-activated amorphous MoSx nanodots (15 MΩ) obtained by an YL-100B-

15

D water-purification system. (NH4)2MoS4 was synthesized from (NH4)6Mo7O24 (15 g) and

16

(NH4)2S solution (21%) (200 mL) according to the reported procedure.46 Raw attapulgite (ATP)

17

were obtained from Linze County of Gansu Province in China and purified by a suspension-

18

sedimentation method using SHMP as an dispersing agent. In a typical procedure, 100 g of raw

19

ATP was dispersed into 2.0 L of water containing 3.0 g of SHMP under vigorously stirring for 2

20

h to obtain a homogenous ATP suspension. Then, the thus-obtained ATP suspension was tip-

21

ultrasonicated for 1 h and allowed statically settled overnight. The purified ATP was collected

22

from the suspension by high-speed centrifugation and freezing-dried. After purification, the


5


Page 6 of 35

1

associated minerals such as calcite and dolomite in raw ATP was completely removed only a trace

2

amount of quartz could be observed in purified ATP (Figure S1).

3

2.2 Synthesis of ATP/Co(OH)2 hybrid and Co(OH)2. In a typical synthesis of ATP/Co(OH)2

4

hybrid, 500 mg of purified ATP was dispersed into 500 mL of water by ultrasonication, to which

5

a calculated amount of CoCl2·6H2O (1.25 mmol) as the Co source and HMT (22.5 mmol) as the

6

hydroxide ions (OH-) source were added under magnetic stirring. The nominal loading amount of

7

Co(OH)2 on ATP is ca. 18.9 wt.%. Afterwards, the obtained suspension was refluxed at 95 oC for

8

5 h under stirring with a N2 atmosphere protection, during which the HMT will gradually hydrolyze

9

to release OH- that subsequently reacted with Co2+ to exclusively form Co(OH)2 nanosheets by

10

avoiding the oxidation under inert atmosphere. The obtained products were filtered, washed with

11

water and ethanol, and dried at a vacuum oven at 80 oC overnight. In addition, ATP/Co(OH)2

12

hybrids with different contents of Co(OH)2 (4.5 and 31.7 wt.%) were also synthesized using above

13

procedures by changing the adding amount of CoCl2·6H2O at a fixed molar ratio of 18 for

14

CoCl2·6H2O to HMT. For a comparison, Co(OH)2 was synthesized by the exact same procedures

15

for the preparation of ATP/Co(OH)2 hybrid except the addition of ATP.

16

2.3. In Situ Photochemical Synthesis of Catalysts. Free amorphous MoSx catalysts were

17

prepared by in situ photoreduction of (NH4)2MoS4 during the ErB-sensitized photocatalytic H2

18

evolution reaction (see below in Section 2.5). After 5 h irradiation, the produced products were

19

filtered, washed with distilled water and anhydrous ethanol, and freezing-dried. For comparison,

20

Co-MoSx, ATP/MoSx, and ATP/Co-MoSx catalysts were also synthesized by the exact same

21

procedures for preparation of MoSx catalysts in the presence of Co(OH)2, ATP, and ATP/Co(OH)2,

22

respectively.


6

Page 7 of 35 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

2.4 Characterization. Transmission electron microscopy (TEM) and high-resolution TEM

2

(HRTEM) images were taken with a FEI Talos F200s field emission transmission electron

3

microscope. X-ray diffraction (XRD) patterns were obtained with a Rigaku Smartlab

4

diffractometer with a nickel filtrated Cu Kβ radiation. X-ray photoelectron spectroscopy (XPS)

5

was performed on an X-ray photoelectron spectrometer (Thermo Scientific Escalab-250Xi, a

6

monochromatic Al KR X-ray source). The zeta potential (ζ potential) was measured using a

7

Zetasizer Nano-ZS90 (Malvern Instruments, UK). UV–vis absorption spectra were taken with a

8

Thermo Scientific–Evolution 220 spectrophotometer.

9

2.5 Dye-sensitized Photocatalytic H2 Evolution Experiments. Dye-sensitized photocatalytic

10

H2 evolution experiments were performed in a sealed quartz reaction cell with a top flat window

11

for light irradiation and a silicone rubber septum was fixed on its side for sampling. A 30-W white-

12

light LED lamp was used as the light source with a cut-off filter of 450 nm. In a typical experiment,

13

a certain amount of the catalyst precursor (NH4)2MoS4 was dissolved in 100 mL of 10% (v/v)

14

aqueous TEOA solution (pH 8) containing 0.2 mM ErB and Co(OH)2 (1.9 mg), ATP (8.1 mg), or

15

ATP/Co(OH)2 (10 mg) if needed. After removing the dissolved oxygen by repeated evacuation-

16

N2 filling process, the reaction suspension was irradiated under stirring for photocatalytic H2

17

evolution. The amount of evolved H2 was determined using an gas chromatograph (GC) (Tech

18

comp, GC-7900) with a thermal conductivity detector (TCD), a 5 Å molecular sieve column (4

19

mm×5 m), and N2 as carrier gas. In the stability test of catalysts, in-situ grown catalysts were

20

separated by centrifugation every 5 h irradiation and redispersed into the fresh TEOA solution

21

containing fresh ErB, and all the reaction conditions were the same as the above photocatalytic

22

reaction.


7


Page 8 of 35

1

The monochromatic quantum yields for the H2 evolution were measured under the condition

2

similar to the above photocatalytic reaction except the light source was equipped with various

3

band-pass filters (450, 475, 500, 520, 550, and 600 nm). The photon flux of incident light was

4

determined using a Ray virtual radiation actinometer (Apogee MQ-500, silicon ray detector, light

5

spectrum, 389-692 nm; measurement range, 0~4000 μmol m-2 s-1). The apparent quantum yields

6

(AQY) was calculated from the ratio of the number of reacted electrons during H2 evolution to the

7

number of incident photons according to the following equation (1):

AQY (%)  8

9

2  number of evolved H 2 molecules 100 number of incident photons

(1)

3. RESULTS AND DISCUSSION

10

X-ray diffraction (XRD) characterizations were first performed to reveal the growth of Co(OH)2

11

on ATP (ATP/Co(OH)2). Figure 1a shows the XRD patterns of the purified ATP, pristine

12

Co(OH)2, and as-synthesized ATP/Co(OH)2 hybrid. The XRD pattern of purified ATP show four

13

typical diffraction peaks belonging to (110), (200), (040), and (400) planes at 8.6°, 14.2°, 19.9°,

14

and 26.8°, respectively, without significant XRD peaks of quartz impurities, showing that the ATP

15

is highly pure.53 As to the pristine Co(OH)2, six characteristic peaks at 19.1°, 32.6°, 38.3°, 51.5°,

16

58.1°, and 61.7°, which can be indexed to (001), (100), (101), (102), (110), and (111) crystalline

17

planes of the β-Co(OH)2 (JCPDS No. 30-0443), respectively.55 In the XRD pattern of as-

18

synthesized ATP/Co(OH)2 hybrid, the diffraction peaks ascribed to (001), (101), and (102) planes

19

of the β-Co(OH)2 could be observed, whereas the main diffraction peak of ATP weakened

20

remarkably, which might be due to the structural modification of ATP nanosheets by Co(OH)2

21

through chemical coupling. The growth of Co(OH)2 on ATP was further identified by TEM


8

Page 9 of 35 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

analysis. As shown in Figure 1b, the purified ATP is the closed parallel aggregations of nanofibers

2

with a length up to several micrometers and a width of 30~50 nm with no observable impurities.

3

In the TEM image of ATP/Co(OH)2 hybrid (Figure 1c), a large number of Co(OH)2 nanosheets

4

(lateral size: ca. 300~500 nm) were found to interconnect with the one-dimensional ATP

5

nanofibers, which is further confirmed by its corresponding selected area electron diffraction

6

(SAED) pattern (Figure 1d), where obvious diffraction rings originated from (002), (100), and

7

(110) planes could be clearly observed. Therefore, these results firmly demonstrated the successful

8

growth of Co(OH)2 on ATP leading to ATP/Co(OH)2 hybrid.

9

Afterwards, the H2 evolution catalysts, free MoSx, ATP/MoSx, and ATP/Co-MoSx, were

10

synthesized by an in situ photosensitization method from a ErB-TEOA system under visible light,

11

as schematically illustrated in Figure 1e. It was observed that accompanying with the formation

12

of catalysts, the evolution of H2 could be confirmed by gas chromatography, indicating that the in

13

situ generated catalysts then acted as the active catalysts for catalyzing the subsequent H2 evolution

14

reaction from the same sensitization system.46-49 Control experiments showed that the absence of

15

any of the ErB, light, and TEOA leds to no or trace H2 evolution. Figure 2a displays the H2

16

evolution activity catalyzed by free MoSx, ATP/MoSx, and ATP/Co-MoSx catalysts from the ErB-

17

TEOA system. With free MoSx alone, only 13.5 μmol of H2 can be produced after a 5 h irradiation

18

reaction. However, the loading of MoSx on ATP support (ATP/MoSx) drastically enhances the H2

19

evolution activity. Total amount of 93.3 μmol of H2 could be produced over ATP/MoSx catalyst

20

in 5 h reaction, which is about 7 times higher than that of over free MoSx catalyst. Significantly,

21

when MoSx was loaded on ATP/Co(OH)2 hybrid to form ATP/Co-MoSx catalyst, the H2 evolution

22

amount can be remarkably increased to 907.5 μmol after a 5 h reaction, which is 67.2 and 9.7 times

23

that of free MoSx and ATP/MoSx catalysts, respectively.


9


Page 10 of 35

1

Several comparison experiments were also carried out to highlight the important roles of ATP

2

and the Co species in enhancing the catalytic activity of MoSx catalyst. As shown in Figure 2b,

3

without the loading of MoSx, pristine ATP and in situ sulfurized ATP show no activity toward H2

4

evolution, indicating that the MoSx catalyst is the active component for H2 evolution reaction, and

5

the possibility of trace metal species within ATP after sulfurization as H2 evolution catalysts can

6

be excluded. With ATP/Co(OH)2 hybrid being used as the catalyst, the ErB-sensitized system

7

shows an average H2 evolution rate of 17.8 μmol h-1, indicating that the Co(OH)2 could act as an

8

active catalyst for H2 evolution, consistent with previous observations in the literature.56 After the

9

ATP/Co(OH)2 hybrid was sulfurized with (NH4)2S, the resulted hybrid shows much higher H2

10

evolution rate of 44.4 μmol h-1, probably due to the formation of active Co-S species. In addition,

11

when Co(OH)2 was used as the support for MoSx catalyst, the resulted Co-MoSx hybrid catalyst

12

exhibits a much higher H2 evolution rate of 70.5 μmol h-1 compared to free MoSx (2.7 μmol h-1)

13

and ATP/MoSx (18.7 μmol h-1) catalysts. Moreover, the physical mixture of Co(OH)2/MoSx

14

prepared by mixing in situ formed MoSx (centrifugated and washed with water and ethanol) with

15

Co(OH)2 at a similar Co(OH)2:MoSx mass ratio shows much inferior activity (10.6 μmol h-1) to in

16

situ formed Co-MoSx hybrid catalyst, suggesting that certain highly active species generated in

17

situ during the photochemical reduction of the precursor (MoS42-) of MoSx in the presence of

18

Co(OH)2 (see detailed discussion below) is important to achieve a high H2 evolution activity.

19

These results demonstrate that both ATP and Co(OH)2 are absolutely necessary and can

20

synergistically improve the catalytic H2 evolution activity of in-situ generated MoSx catalysts. In

21

addition, the performance of ATP/Co-MoSx catalyst for H2 evolution was compared with various

22

ATP/M-MoSx (M=Ni, Fe, Cu, Zn) catalysts prepared using exact same procedure as ATP/Co-

23

MoSx catalyst from corresponding ATP/metal hydroxide supports and (NH4)2MoS4. As shown in


10

Page 11 of 35 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

Figure S2, the ATP/Co-MoSx catalyst outperforms other ATP/M-MoSx catalysts for H2 evolution.

2

The Co, Ni, Fe, and Cu can obviously promote the H2 evolution activity of MoSx on ATP and

3

follows the order of Co>Ni>Fe>Cu, while the Zn will deteriorate the activity of MoSx catalysts,

4

consistent with the activity trend observed for transition metal-promoted MoSx catalyst for

5

electrocatalytic and photocatalytic H2 evolution.57 DFT calculations demonstrated that these metal

6

dopants, especially Co doing can efficiently decrease the hydrogen bonding energy (∆GH) of S-

7

edges by forming active Co-S-Mo coordination,57,58 thus an enhanced HER activity could be

8

achieved.

9

Furthermore, the variations in activity for H2 evolution catalyzed by different concentrations of

10

MoSx for both free MoSx and ATP/Co-MoSx catalysts were investigated and compared, as shown

11

in Figure 2c. Overall, the average H2 evolution rates increase rapidly with increasing MoSx

12

concentration for both type of catalysts and slow down when the concentration of MoSx is larger

13

than 0.05 mM. The ATP/Co-MoSx catalysts at each MoSx concentration show much higher activity

14

than free MoSx catalysts and an enhancement factor of as high as 67 is obtained at 0.05 mM MoSx.

15

At higher MoSx concentrations, the enhancement factor was decreased, probably due to the

16

aggregations of excess Co-MoSx on ATP, which will largely block the active sites for H2 evolution

17

(Figure S3). Moreover, at higher MoSx concentrations, even though a larger amount of H2 is

18

evolved, the turnover number (TON) decreases because of the limited lifetime of the system

19

(Figure S4). The highest TON of 346 is achieved at 0.01 mM MoSx, which is much higher than

20

the previously reported values.46-49 In contrast to ATP/Co-MoSx catalyst, the TONs of H2 evolution

21

over free MoSx catalyst are low and increases with the MoSx concentration and reaches a plateau

22

at MoSx concentrations higher than 0.1 mM, indicating that the H2 evolution activity of free MoSx

23

catalyst is limited by the limited number of exposed active sties at higher MoSx concentrations. In


11


Page 12 of 35

1

addition, the effect of mass ratio of Co(OH)2 to ATP in ATP/Co(OH)2 hybrids on the catalytic H2

2

evolution activity of resulted ATP/Co-MoSx catalysts were also investigated. With increasing

3

Co(OH)2 content on ATP support, the diffraction peaks of ATP reduced while the diffraction peaks

4

corresponding to Co(OH)2 become evident as confirmed by the XRD analysis in Figure S5,

5

indicating the gradual covering of ATP by Co(OH)2. As shown in Figure S6, the optimum loading

6

amount of Co(OH)2 of ATP/Co(OH)2 hybrids is found to be 18.9 wt.%, at which the obtained

7

ATP/Co-MoSx catalyst exhibits an optimum H2 evolution activity at a fixed concentration of

8

MoSx. At low Co(OH)2 content, there is no enough Co source that can be provided to form

9

effective Co-MoSx catalyst on ATP, leading to a low activity, while at high Co(OH)2 content, the

10

active sites of formed Co-MoSx catalyst may be blocked, showing activity deterioration. Figure

11

2d shows the apparent quantum yield of H2 evolution catalyzed by ATP/Co-MoSx catalyst from

12

ErB-TEOA. The highest AQY value was estimated to be 47.7% at 500 nm, which is in good

13

agreement with the maximum absorption wavelength of ErB during the H2 evolution (Figure S7),

14

indicating that the light absorption of ErB governs the H2 evolution from this system.

15

In order to gain insight into the superior photocatalytic H2 evolution activity of ATP/Co-MoSx

16

catalyst from ErB-TEOA system under visible light, the microstructural analyses were first

17

performed on resulted catalysts. The XRD patterns in Figure 3a reveal that the in-situ generated

18

free MoSx catalyst is amorphous, while the XRD pattern of ATP/Co-MoSx catalyst is identical to

19

the purified ATP without the preservation of Co(OH)2 structures on ATP. Considering that the

20

preparation of ATP/Co-MoSx catalyst was started from the ATP/Co(OH)2 hybrid and (NH4)2MoS4

21

precursors, this result indicates that the formation of ATP/Co-MoSx catalyst proceeds via the in

22

situ photoreduction of [MoS4]2- to amorphous MoSx with the Co doping from Co(OH)2 forming

23

amorphous Co-doped MoSx on ATP. The transmission electron microscopy (TEM) and high-


12

Page 13 of 35 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

resolution TEM (HRTEM) images in Figure 3b present the typical aggregated structure and

2

amorphous nature of free MoSx catalyst. The sizes of free MoSx catalyst are in the range of 150 to

3

300 nm. When ATP was used as the support, the in situ grown MoSx particles show no significant

4

change on size but the their dispersion is improved due to the presence of ATP (Figure 3c). By

5

strong contrast, as shown in the TEM image of ATP/Co-MoSx catalyst in Figure 3d, a large

6

number of tiny Co-MoSx nanodots with a size smaller than 5 nm are observed on the surfaces of

7

ATP nanofibers. From its HRTEM image in Figure 3e, the Co-MoSx nanodots are found to be

8

amorphous and highly dispersed on the surface of ATP nanofibers, implying the presence of Co-

9

MoSx as abundant surface active sites.49 In addition, the high angle annular dark field-scanning

10

transmission electron microscopy (HAADF-STEM) image of ATP/Co-MoSx catalyst in Figure 3f

11

and corresponding element mappings demonstrate the uniform distribution of the Mo, Co, and S

12

elements on the surface of ATP nanofibers, indicating the uniform doping of MoSx with Co and

13

the high distribution of Co-MoSx nanodots on ATP nanofibers. The drastic differences in both size

14

and dispersion of Co-MoSx nanodots on ATP as compared to free MoSx and MoSx on ATP

15

(ATP/MoSx) highlights the important roles of ATP/Co(OH)2 support for mediating the growth of

16

MoSx, where the Co(OH)2 nanosheets would act as the sacrificial Co sources to react with MoS42-

17

during photoreduction process while ATP could act as the large surface area support to anchor the

18

in situ formed Co-MoSx catalyst, as a result, the large size Co(OH)2 nanosheets (ca. 300~500 nm)

19

on ATP vanished and eventually Co-MoSx nanodots were loaded on the surfaces of ATP

20

nanofibers. In order to further clarify this important role of Co(OH)2 nanosheets, the formation

21

behaviors of MoSx on free Co(OH)2 nanosheets in the absence of ATP was also investigated by

22

TEM analysis, as shown in Figure S8. It is found that the two-dimensional hexagonal structures

23

of Co(OH)2 nanosheets is severely destroyed during the photoreduction of [MoS4]2-and a number


13


Page 14 of 35

1

of aggregated nanoparticles (ca.100~300 nm) formed on the surfaces of broken Co(OH)2

2

fragments. This result indicates that the ultrathin Co(OH)2 nanosheets with abundant exposed Co

3

sites indeed act as an sacrificial Co source to react with MoS42- during photoreduction process,

4

leading to the formation of Co-MoSx nanoparticles. Therefore, it can be safely inferred that a

5

Co(OH)2/MoS42- assembly with the microstructure similar to its molecular analogue

6

[CoII(MoVIS4)2]2- might form upon mixing of Co(OH)2 and MoS42-,44,49 which will then be reduced

7

to Co-MoSx nanoparticles by the electrons of excited dye. It should also be noted that the size of

8

Co-MoSx catalyst on ATP is much smaller than free Co-MoSx nanoparticles, which can be

9

explained by the fact that the smaller size Co(OH)2 nanosheets on ATP as compared to free

10

Co(OH)2 nanosheets should be more active to react with MoS42-, thus leading to a rapid nucleation

11

of in situ formed Co-MoSx, consequently, Co-MoSx nanodots were grown on ATP. Moreover, zeta

12

potential (ξ) measurements were also performed to get insight into the formation of MoSx in the

13

presence of different supports, as shown in Table S1. It could be observed that the negatively

14

charged surfaces of purified ATP could be changed to be positively charged after growth of

15

Co(OH)2 nanosheets, which will greatly facilitate the adsorption of negatively charged [MoS4]2-

16

and ErB anions during the in situ photochemical synthesis, thus a highly dispersed Co-MoSx with

17

reduced size could be confinedly grown on the high surface area ATP nanofibers. As to the

18

synthesis of ATP/MoSx catalyst, the electrostatic repulsion between ATP and [MoS4]2- is

19

unfavorable to the adsorption of [MoS4]2- and nucleation of in-situ formed MoSx, finally leading

20

to the formation of large-size MoSx particles on ATP, while the absence of ATP will further result

21

in a severe aggregation during the growth of free MoSx.

22

The surface chemical states of ATP/Co-MoSx catalyst were investigated by X-ray photoelectron

23

spectroscopy (XPS), as shown in Figure 4 and Table 1. The Co 2p spectrum of ATP/Co(OH)2


14

Page 15 of 35 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

(Figure 4a) shows that the Co 2p3/2 (Co 2p1/2) peak occurs at 781.12 eV (797.26 eV), indicating

2

the existence of a Co with an oxidation state of +2.59 It is worth noting that apart from the two

3

spin-orbit doublets characteristic of Co2+ (781.99 and 797.34 eV), a new Co 2p3/2 (Co 2p1/2) peak

4

ascribed to the complex heterobimetallic sulfide is found at 779.29 eV (794.69 eV) in the Co 2p

5

spectrum of ATP/Co-MoSx catalyst, showing the in situ formation of “CoMoS” phase, consistent

6

with that reported in the literature.43,47,49 In addition, it is found that the Co-MoSx catalyst on ATP

7

contains 41.5% of sulfided Co species and 58.5% of Co oxide/hydroxide. This result indicates that

8

the Co(OH)2 nanosheets on ATP could release Co ions as an dopant to react with MoS42-, which

9

cannot only can activate the unsaturated S atoms of MoSx by forming CoMoS sites but also ensure

10

the firm deposition of in situ formed Co-MoSx on ATP nanofibers. It should be also mentioned

11

that Co species exist in the form of oxide/hydroxide or Co-S could contribute to the H2 evolution

12

but their activities are relatively low, as shown in Figure 2b. This result indicates that the enhanced

13

performance of ATP/Co-MoSx catalyst might be account for the formation of active “CoMoS”

14

phase. In addition, as shown in Figure 4b, the fitting of the Mo 3d region reveals that there exist

15

three Mo species for both free MoSx and ATP/Co-MoSx catalysts, indicating the presence of MoSx

16

species on ATP in ATP/Co-MoSx catalyst. For free MoSx catalyst, the Mo 3d5/2 (3d3/2) peak

17

ascribed to MoIVSx species (62.4%) occurs at binding energy of 228.53 eV (231.63 eV), while the

18

Mo 3d5/2 peaks at higher binding energies of 229.83 eV (231.63 eV) and 232.33 eV (235.43 eV)

19

are assigned to molybdenum oxysulfide type MoVOSx (20.1%) and a small amount of MoVIO3

20

(17.5%), respectively.34-36 By contrast, ATP/Co-MoSx catalyst presents an increased MoVOSx

21

(29.4%) and MoVIO3 (28.2%) species and decreased MoIVSx (42.4%) species, which can be

22

attributable to the oxidation occurring during the photocatalytic H2 production process, consistent

23

with the observations on amorphous CoMoSx catalysts. In addition, the binding energies of MoIVSx


15


Page 16 of 35

1

and MoVOSx species for ATP/Co-MoSx catalyst are shifted toward high energy region compared

2

to that of free MoSx catalyst, probably due to the incorporation of Co dopant. Analysis of the S 2p

3

XPS spectra in Figure 4c of free MoSx and ATP/Co-MoSx catalysts reveals the presence of both

4

monosulfide S2- and disulfide (S2)2- ligands, with minor sulfates at higher binding energies.34-36

5

Compared to free MoSx catalyst, the content of S2- ligand increases while the (S2)2- ligand decrease

6

accordingly, indicating that the Co dopant may attack the bridging (S2)2- to form “Co-S-Mo”

7

coordination. According to the fitting results of XPS, the S/Mo ratio is determined to be 2.97:1 for

8

both free MoSx and ATP/Co-MoSx catalysts and the stoichiometry for Co-MoSx catalyst is

9

calculated to be Co0.88Mo1.25S3.71. Similar to ATP/Co-MoSx catalyst, the XPS analysis (Figure S9)

10

of free Co-MoSx catalyst also shows the formation of “CoMoS” phase during the photochemical

11

synthesis of MoSx particles in the presence Co(OH)2, further confirming the role of Co(OH)2 as

12

an sacrificial Co source for the reaction with MoS42- precursor to lead to the formation of Co-MoSx

13

catalyst during photochemical reduction.

14

All of the aforementioned results thus demonstrate that the high performance of the ATP/Co-

15

MoSx catalyst in catalyzing photocatalytic H2 evolution can be ascribed to the presence of

16

ATP/Co(OH)2 serving as an active matrix, which can provide a large surface area and Co dopant

17

for effectively growing amorphous Co-activated MoSx. The large surface area of ATP nanofibers

18

confines the growth of small Co-MoSx nanodots with high dispersion, affording an abundance of

19

active sites for H2 evolution reaction. On the other hand, the accessible Co dopant released from

20

Co(OH)2 lead to the in situ formation of highly active “CoMoS” sites featuring low overpotential

21

for H2 evolution, thus rendering the ATP/Co-MoSx catalyst with high H2 evolution activity.


16

Page 17 of 35 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

Furthermore, the stability of catalytic H2 evolution over ATP/Co-MoSx catalyst was

2

investigated, including free MoSx catalyst for comparison, as shown in Figure 5. In the first run

3

reaction, the initial H2 evolution rate catalyzed by in situ generated ATP/Co-MoSx catalyst from

4

ErB-TEOA system is high and the activity of sensitization system decreases gradually with the

5

reaction time, which is probably due to the degradation of ErB during the reaction (Figure S7).

6

After completion of the first run reaction, the ATP/Co-MoSx catalyst was collected by high-speed

7

centrifugation and washed, and the fresh EY and TEOA were added. It is found that although the

8

H2 evolution activity of ATP/Co-MoSx catalyst decrease gradually with reaction run, the ATP/Co-

9

MoSx catalyst still shows reasonable H2 evolution activity in the third run reaction, whereas the

10

free MoSx catalyst totally deactivates after the first run reaction. The TEM analysis (Figure S10)

11

of ATP/Co-MoSx catalyst after recycling stability testing reveals that the density of loaded Co-

12

MoSx is remarkably reduced as compared to the fresh catalyst. XPS analysis (Figure S11) of used

13

ATP/Co-MoSx catalyst also indicates that the contents of Mo and S decrease significantly as

14

compared to fresh catalyst, while only trace signal corresponding to Co could be observed. These

15

results clearly indicate that the loss in activity for ATP/Co-MoSx catalyst is due to the leaching of

16

Co-MoSx from the surfaces of ATP. Our ongoing efforts are now being devoted to enhancing the

17

H2 evolution stability of ATP/Co-MoSx catalyst by improving the synthetic procedures.

18

4. CONCLUSIONS

19

In summary, we have developed an exceptionally active H2 evolution catalyst by confinedly

20

growing amorphous MoSx nanodots in situ on Co(OH)2 modified ATP (ATP/Co(OH)2) nanofibers

21

during photocatalytic H2 evolution in a ErB-TEOA system under visible light irradiation. The

22

Co(OH)2 on ATP could act as a sacrificial Co source to induce the formation of highly active


17


Page 18 of 35

1

“CoMoS” sites during the in situ growth of amorphous MoSx and the ATP nanofibers provides a

2

large area confinement surface to greatly reduce the size of in situ loaded Co-MoSx, as a result,

3

Co-MoSx nanodots with size smaller than 5 nm was uniformly grown on the surface of ATP.

4

Therefore, the thus-obtained ATP/Co-MoSx catalyst exhibits remarkably improved catalytic

5

activity for H2 evolution compared to free MoSx catalyst (67.2 times enhancement) and a AQY as

6

high as 47.7% at 500 nm owing to the abundance of exposed active sites and the presence of

7

additional “CoMoS” active sites. Moreover, ATP/Co-MoSx catalyst shows improved stability over

8

free MoSx catalyst during recycling H2 evolution reactions. Accordingly, this work is expected to

9

promote the development of high performance H2 evolution catalysts based on MoSx-based

10

hybrids.

11

ASSOCIATED CONTENT

12

Supporting Information.

13

XRD patterns of raw and purified ATP, activity comparison of different ATP/M-MoSx (M=Co,

14

Ni, Fe, Cu, Zn) catalysts, calculated enhancement factor, calculated turnover numbers of H2

15

evolution, zeta potentials, UV-vis absorption spectra of ErB during H2 evolution reactions, XRD

16

patterns of ATP/Co(OH)2 hybrids with different Co(OH)2 content, the H2 evolution acidity of

17

ATP/Co-MoSx prepared from different ATP/Co(OH)2 hybrids, TEM images and XPS spectra of

18

Co-MoSx catalyst, and TEM image and XPS spectra of ATP/Co-MoSx after recycling reactions.

19

AUTHOR INFORMATION

20

Corresponding Author

21

*E-mail: [email protected]; [email protected]


18

Page 19 of 35 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

Author Contributions

2

‡These authors contributed equally.

3

Notes

4

The authors declare no competing financial interest.

5

ACKNOWLEDGMENT

6

This work is supported by the National Natural Science Foundation of China (Grant No.

7

21763001, 21463001), the Natural Science Foundation of Ningxia Hui Autonomous Region

8

(2018AAC02011), the Foundation of State Key Laboratory of High-Efficiency Utilization of

9

Coal and Green Chemical Engineering (Grant No. 2017-K26), the Key Scientific Research

10

Projects in 2017 at North Minzu University (Grant No. 2017KJ20), the Key Scientific Research

11

Projects of the Higher Education Institutions of Ningxia Hui Autonomous Region (Grant No.

12

NCX2017143), the Foundation of Key Laboratory of Electrochemical Energy Conversion

13

Technology and Application.

14

REFERENCES

15

(1) Bard, A. J.; Fox, M. A. Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and

16

17 18

19 20

Oxygen. Acc. Chem. Res. 1995, 28, 141-145. (2) Esswein, A. J.; Nocera, D. G. Hydrogen Production by Molecular Photocatalysis. Chem. Rev. 2007, 107, 4022-4047. (3) Kudo, A.; Miseki, Y. Heterogeneous Photocatalyst Materials for Water Splitting. Chem. Soc. Rev. 2009, 38, 253-278.


19


1 2

3 4

5 6

7 8

9

(4) Abe, R. Recent Progress on Photocatalytic and Photoelectrochemical Water Splitting under Visible Light Irradiation. J. Photochem. Photobiol., C 2010, 11, 179-209. (5) Chen, X.; Shen, S.; Guo, L.; Mao, S. Semiconductor-based Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503-6570. (6) Yang, J.; Wang, D.; Han, H.; Li, C. Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis. Acc. Chem. Res. 2013, 46, 1900-1909. (7) Ma, Y.; Wang, X.; Jia, Y.; Chen, X.; Han, H.; Li, C. Titanium Dioxide Based Nanomaterials for Photocatalytic Fuel Generations. Chem. Rev. 2014, 19, 9987-10043. (8) Zhou, X. Z.; Sun, H.; Zhang, H. Z.; Tu, W. X. One-pot Hydrothermal Synthesis of CdS/NiS

10

Photocatalysts for High H2 Evolution from Water under Visible Light. Int. J. Hydrogen

11

Energy 2017, 42, 11199-11205.

12

Page 20 of 35

(9) Guan, S. D.; Fu, X. L.; Zhang, Y.; Peng, Z. J. Beta-NiS Modified CdS Nanowires for

13

Photocatalytic H2 Evolution with Exceptionally High Efficiency. Chem. Sci. 2018, 4, 1574-

14

1585.

15

(10)

Lang, D.; Cheng, F. Y.; Xiang, Q. J. Enhancement of Photocatalytic H2 Production

16

Activity of CdS Nanorods by Cobalt-based Cocatalyst Modification. Catal. Sci. Technol.

17

2016, 6, 6207-6216.

18 19

(11)

Huang, Z.-F.; Song J.; Li, K.; Tahir, M.; Wang, Y.-T.; Pan, L.; Wang, L.; Zhang, X.;

Zou, J.-J. Hollow Cobalt-Based Bimetallic Sulfide Polyhedra for Efficient All-pH-Value


20

Page 21 of 35 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

Electrochemical and Photocatalytic Hydrogen Evolution. J. Am. Chem. Soc. 2016, 138, 1359-

2

1365.

3

(12)

Cao, S.; Chen, Y.; Kang, L.; Lin, Z. S.; Fu, W. F. Enhanced Photocatalytic H2-Evolution

4

by Immobilizing CdS Nanocrystals on Ultrathin Co0.85Se/RGO-PEI Nanosheets. J. Mater.

5

Chem. A 2015, 3, 18711-18717.

6 7

8 9 10

11

(13)

Zhang, W.; Xu, R. Hybrid Photocatalytic H2 Evolution Systems Containing Xanthene

Dyes and Inorganic Nickel Based Catalysts. Int. J. Hydrogen Energy 2012, 37, 17899-17909. (14)

Zeng, D. Q.; Xiao, L.; Ong, W. J.; Wu, P. Y.; Zheng, H. F.; Chen, Y. Z.; Peng, D. L.

Hierarchical ZnIn2S4/MoSe2 Nanoarchitectures for Efficient Noble-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light. ChemSusChem 2017, 10, 4624-4631. (15)

Tian, J.; Cheng, N.; Liu, Q.; Xing, W.; Sun, X. Cobalt Phosphide Nanowires: Efficient

12

Nanostructures for Fluorescence Sensing of Biomolecules and Photocatalytic Evolution of

13

Dihydrogen from Water under Visible Light. Angew Chem., Int. Ed. 2015, 54, 5493-5497.

14

(16)

Xing, M. Y.; Qiu, B. C.; Du, M. M.; Zhu, Q. H.; Wang, L. Z.; Zhang, J. L. Spatially

15

Separated CdS Shells Exposed with Reduction Surfaces for Enhancing Photocatalytic

16

Hydrogen Evolution. Adv. Funct. Mater. 2017, 27, 1702624.

17

(17)

Wang, X. J.; Tian, X.; Sun, Y. J.; Zhu, J. Y.; Li, F. T.; Mu, H. Y.; Zhao, J. Enhanced

18

Schottky Effect of a 2D-2D CoP/g-C3N4 Interface for Boosting Photocatalytic H2 Evolution.

19

Nanoscale 2018, 10, 12315-12321.


21


1

(18)

Ma, B.; Xu, H.; Lin, K.; Li, J.; Zhan, H.; Liu, W.; Li, C. Mo2C as Non-Noble Metal Co-

2

catalyst in Mo2C/CdS Composite for Enhanced Photocatalytic H2 Evolution under Visible

3

Light Irradiation. ChemSusChem 2016, 9, 820-824.

4

(19)

Yue, X. Z.; Yi, S. S.; Wang, R. W.; Zhang, Z. T.; Qiu, S. L. A Novel Architecture of

5

Dandelion-like Mo2C/TiO2 Heterojunction Photocatalysts towards High-performance

6

Photocatalytic Hydrogen Production from Water Splitting. J. Mater. Chem. A 2017, 5,

7

10591-10598.

8 9

(20)

Pan, Y. X.; Peng, J. B.; Xin, S.; You, Y.; Men, Y. L.; Zhang, F.; Duan, M.; Cui, Y.; Sun,

Z.; Song, J. Enhanced Visible-Light-Driven Photocatalytic H2 Evolution from Water on

10

Noble-Metal-Free CdS-Nanoparticle-Dispersed Mo2C@C Nanospheres. ACS Sustainable

11

Chem. Eng. 2017, 5, 5449-5456.

12

(21)

Li, L.; Deng, Z.; Yu, L.; Lin, Z.; Wang, W.; Yang, G. Amorphous Transitional Metal

13

Borides as Substitutes for Pt Cocatalysts for Photocatalytic Water Splitting. Nano Energy

14

2016, 27, 103-113.

15

Page 22 of 35

(22)

Wang, X.; Yu, H.; Yang, L.; Shao, L.; Xu, L. A Highly Efficient and Noble Metal-Free

16

Photocatalytic System using NixB/CdS as Photocatalyst for Visible Light H2 Production from

17

Aqueous Solution. Catal. Commun. 2015, 67, 45-48.

18

(23)

Ma, B.; Liu, Y.; Li, J.; Lin, K.; Liu, W.; Zhan, H. Mo2N: An Efficient Non-Noble Metal

19

Cocatalyst on CdS for Enhanced Photocatalytic H2 Evolution under Visible Light Irradiation.

20

Int. J. Hydrogen Energy 2016, 41, 22009-22016.


22

Page 23 of 35 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


(24)

Ma, B.; Wang, X.; Lin, K.; Li, J.; Liu, Y.; Zhan, H.; Liu, W. A Novel Ultraefficient Non-

2

Noble Metal Composite Cocatalyst Mo2N/Mo2C/Graphene for Enhanced Photocatalytic H2

3

Evolution. Int. J. Hydrogen Energy 2017, 42, 18977-18984.

4

(25)

Hinnemann, B.; Moses, P. G.; Bonde, J.; Jorgensen, K. P.; Nielsen, J. H.; Horch, S.;

5

Chorkendorff, I.; Nørskov, J. K. Biomimetic Hydrogen Evolution: MoS2 Nanoparticles as

6

Catalyst for Hydrogen Evolution. J. Am. Chem. Soc. 2015, 127, 5308-5309.

7

(26)

Kibsgaard, J.; Chen, Z.; Reinecke, B. N.; Jaramillo, T. F. Engineering the Surface

8

Structure of MoS2 to Preferentially Expose Active Edge Sites for Electrocatalysis. Nat.

9

Mater. 2012, 11, 963-969.

10 11 12

(27)

Vrubel, H.; Merki, D.; Hu X. Hydrogen Evolution Catalyzed by MoS3 and MoS2

Particles. Energy Environ. Sci. 2012, 5, 6136-6144. (28)

Hou, Y.; Laursen, A. B.; Zhang, J.; Zhang, G.; Zhu, Y.; Wang, X.; Dahl, S.;

13

Chorkendorff, I. Layered Nanojunctions for Hydrogen-Evolution Catalysis. Angew Chem.,

14

Int. Ed. 2013, 52, 3621-3625.

15

(29)

Zong, X.; Yan, H.; Wu, G.; Ma, G.; Wen, F.; Wang, L.; Li, C. Enhancement of

16

Photocatalytic H2 Evolution on CdS by Loading MoS2 as Cocatalyst under Visible Light

17

Irradiation. J. Am. Chem. Soc. 2008, 130, 7176-7177.

18

(30)

Zong, X.; Na, Y.; Wen, F.; Ma, G.; Yang, J.; Wang, D.; Ma, Y.; Wang, M.; Sun, L.; Li,

19

C. Visible Light Driven H2 Production in Molecular Systems Employing Colloidal MoS2

20

Nanoparticles as Catalyst. Chem. Commun. 2009, 30, 4536-4538.


23


1

(31)

Xiang, Q.; Yu, J.; Jaroniec, M. Synergetic Effect of MoS2 and Graphene as Cocatalysts

2

for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles. J. Am. Chem.

3

Soc. 2012, 134, 6575-6578.

4

(32)

Min, S.; Lu, G. Sites for High Efficient Photocatalytic Hydrogen Evolution on a Limited-

5

layered MoS2 Cocatalyst Confined on Graphene Sheets: The Role of Graphene. J. Phys.

6

Chem. C 2012, 116, 25415-25424.

7

(33)

Page 24 of 35

Lei, Y.; Yang, M.; Hou, J.; Wang, F.; Cui, E.; Kong C.; Min, S. Thiomolybdate [Mo3S13]2-

8

Nanocluster: A Molecular Mimic of MoS2 Active Sites for Highly Efficient Photocatalytic

9

Hydrogen Evolution. Chem. Commun. 2018, 54, 603-606.

10 11

12

(34)

Merki, D.; Fierro, S.; Vrubel, H.; Hu, X. Amorphous Molybdenum Sulfide Films as

Catalysts for Electrochemical Hydrogen Production in Water. Chem. Sci. 2011, 2, 1262-1267. (35)

Benck, J. D.; Chen, Z.; Kuritzky, L. Y.; Forman, A. J.; Jaramillo, T. F. Amorphous

13

Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production: Insights into the

14

Origin of Their Catalytic Activity. ACS Catal. 2012, 2, 1916-1923.

15 16 17 18 19

(36)

Vrubel, H. Hu, X. Growth and Activation of an Amorphous Molybdenum Sulfide

Hydrogen Evolving Catalyst. ACS Catal. 2013, 3, 2002-2011. (37)

Morales-Guio, C. G.; Hu, X. Amorphous Molybdenum Sulfides as Hydrogen Evolution

Catalysts. Acc. Chem. Res. 2014, 47, 2671-2681. (38)

Yu, H.; Xiao, P.; Wang, P.; Yu, J. Amorphous Molybdenum Sulfide as Highly Efficient

20

Electron-Cocatalyst for Enhanced Photocatalytic H2 Evolution. Appl. Catal. B: Environ. 2016,

21

193, 217-225.

22

(39)

Nguyen, M.; Tran, P. D.; Pramana, S. S.; Lee, R. L.; Batabyal, S. K.; Mathews, N.; Wong,


24

Page 25 of 35 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

L. H.; Grätzel, M. In Situ Photo-assisted Deposition of MoS2 Electrocatalyst onto Zinc

2

Cadmium Sulphide Nanoparticle Surfaces to Construct an Efficient Photocatalyst for

3

Hydrogen Generation. Nanoscale 2013, 5, 1479-1482.

4

(40)

Fu, X.; Zhang, L.; Liu, L.; Li, H.; Meng, S.; Ye, X.; Chen, S. In Situ Photodeposition of

5

MoSx on CdS Nanorods as a Highly Efficient Cocatalyst for Photocatalytic Hydrogen

6

Production. J. Mater. Chem. A 2017, 5, 15287-15293.

7

(41)

Li, Y.; Wang, H.; Peng, S. Tunable Photodeposition of MoS2 onto a Composite of Reduced

8

Graphene Oxide and CdS for Synergic Photocatalytic Hydrogen Generation. J. Phys. Chem. C

9

2014, 118, 19842-19848.

10

(42)

Xu, Y.; Li, Y.; Wang, P.; Wang, X.; Yu, H. Highly Efficient Dual Cocatalyst-Modified

11

TiO2 Photocatalyst: RGO as Electron-Transfer Mediator and MoSx as H2-Evolution Active

12

Site. Appl. Surf. Sci. 2018, 430, 176-183.

13

(43)

Chen, Y.; Tran, P. D.; Boix, P.; Ren, Y.; Chiam, S.; Li, Z.; Fu, K.; Wong, L. H.; Barber, J.

14

Silicon Decorated with Amorphous Cobalt Molybdenum Sulfide Catalyst as an Efficient

15

Photocathode for Solar Hydrogen Generation. ACS Nano 2015, 9, 3829-3836.

16

(44)

Lei, Y.; Hou, J.; Wang, F.; Ma, X.; Jin, Z.; Xu, J.; Min, S. Boosting the Catalytic

17

Performance of MoSx Cocatalysts over CdS Nanoparticles for Photocatalytic H2 Evolution by

18

Co Doping via a Facile Photochemical Route. Appl. Surf. Sci. 2017, 420, 456-464.

19

(45)

Liu, W.; Wang, X.; Yu, H.; Yu, J. Direct Photoinduced Synthesis of Amorphous CoMoSx

20

Cocatalyst and Its Improved Photocatalytic H2-Evolution Activity of CdS. ACS Sustainable

21

Chem. Eng. 2018, 6, 12436-12445.

22 23

(46)

Zong, X.; Xing, Z.; Yu, H.; Bai, Y.; Lu, G.; Wang, L. Photocatalytic Hydrogen Production

in a Noble-Metal-Free System Catalyzed by In Situ Grown Molybdenum Sulfide Catalyst. J.


25


1 2

Page 26 of 35

Catal. 2014, 310, 51-56. (47)

Hou, J.; Lei, Y.; Wang, F.; Ma, X.; Min, S.; Jin, Z.; Xu, J. In-situ Photochemical

3

Fabrication of Transition Metal-Promoted Amorphous Molybdenum Sulfide Catalysts for

4

Enhanced Photosensitized Hydrogen Evolution. Int. J. Hydrogen Energy 2017, 42, 11118-

5

11129.

6

(48)

Xu, J.; Li, Y.; Peng, S. Photocatalytic Hydrogen Evolution over Erythrosin B-sensitized

7

Graphitic Carbon Nitride with In Situ Grown Molybdenum Sulfide Cocatalyst. Int. J.

8

Hydrogen Energy 2015, 40, 353-362.

9

(49)

Min, S.; Hou, J.; Lei, Y.; Liu, X.; Li, Y.; Xue, Y.; Cui, E.; Yan, W.; Hai, W.; Wang, F.

10

CoAl-layered Double Hydroxide Nanosheets as An Active Matrix to Anchor an Amorphous

11

MoSx Catalyst for Efficient Visible Light Hydrogen Evolution. Chem. Commun. 2018, 54,

12

3243-3246.

13

(50)

Mu, B.; Wang, A. One-pot Fabrication of Multifunctional Superparamagnetic

14

Attapulgite/Fe3O4/Polyaniline Nanocomposites Served as an Adsorbent and Catalyst Support.

15

J. Mater. Chem. A 2015, 3, 281-289.

16

(51)

Lu, L.; Li, X. Y.; Liu, X. Q.; Wang, Z. M.; Sun, L. B. Enhancing the Hydrostability and

17

Catalytic Performance of Metal-Organic Frameworks by Hybridizing with Attapulgite, a

18

Natural Clay. J. Mater. Chem. A 2015, 3, 6998-7005.

19

(52)

Miao, S.; Liu, Z.; Zhang, Z.; Han, B.; Miao, Z.; Ding, K.; An G. Ionic Liquid-Assisted

20

Immobilization of Rh on Attapulgite and Its Application in Cyclohexene Hydrogenation. J.

21

Phys. Chem. C 2007, 111, 2185-2190.

22 23

(53)

Zhang, J.; Liu, X. Photocatalytic Hydrogen Production from Water under Visible Light

Irradiation Using a Dye-sensitized Attapulgite Nanocrystal Photocatalyst. Phys. Chem. Chem.


26

Page 27 of 35 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 2


Phys. 2014, 16, 8655-8660. (54)

Zhang, J.; Chen, A.; Wang, L.; Li, X.; Huang, W. Striving Toward Visible Light

3

Photocatalytic Water Splitting Based on Natural Silicate Clay Mineral: The Interface

4

Modification of Attapulgite at the Atomic-Molecular Level. ACS Sustainable Chem. Eng.

5

2016, 4, 4601-4607.

6

(55)

Liu, Z.; Ma, R.; Osada, M.; Takada, K.; Sasaki, T. Selective and Controlled Synthesis of

7

r- and β-Cobalt Hydroxides in Highly Developed Hexagonal Platelets. J. Am. Chem. Soc. 2005,

8

127, 13869-13874.

9

(56)

Zhang, L.; Zheng, R.; Li. S.; Liu, B.; Wang, D.; Wang, L.; Xie T. Enhanced Photocatalytic

10

H2 Generation on Cadmium Sulfide Nanorods with Cobalt Hydroxide as Cocatalyst and

11

Insights into Their Photogenerated Charge Transfer Properties. ACS Appl. Mater. Interfaces

12

2014, 6, 13406-13412.

13

(57)

Merki, D.; Vrubel, H.; Rovelli, L.; Fierro S.; Hu, X. Fe, Co, and Ni Ions Promote the

14

Catalytic Activity of Amorphous Molybdenum Sulfide Films for Hydrogen Evolution. Chem.

15

Sci. 2012, 3, 2515-2525.

16

(58)

Bonde, J.; Moses, P. G.; Jaramillo, T. F.; Nørskov, J. K.; Chorkendorff, I. Hydrogen

17

Evolution on Nano-particulate Transition Metal Sulfides. Faraday Discuss. 2009, 140, 219-

18

231.

19

(59)

Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R. Smart, R.

20

S. C. Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals,

21

Oxides and Hydroxides: Cr, Mn, Fe, Co and Ni. App. Surf. Sci. 2011, 257, 2717-2730.

22

23


27


Page 28 of 35

1

TABLE AND FIGURE CAPTION:

2

Table 1 The fitting results of XPS spectra of Co 2p, Mo 3d, and S 2p core levels for ATP/Co(OH)2

3

hybrid, free MoSx catalyst, and ATP/Co-MoSx catalyst.

4

Figure 1. (a) XRD patterns of ATP, Co(OH)2, and ATP/Co(OH)2 hybrid. (b-d) TEM images of

5

(b) ATP, (c) ATP/Co(OH)2 hybrid, and (d) the corresponding SAED pattern of ATP/Co(OH)2

6

hybrid. (e) Schematic illustration of the in-situ photochemical fabrication of amorphous MoSx,

7

ATP/MoSx, and ATP/Co-MoSx catalysts and the subsequent photocatalytic H2 evolution from

8

ErB-TEOA system under visible light irradiation.

9

Figure 2. (a) Time course of H2 evolution over different catalysts sensitized by ErB from TEOA

10

solution, 0.05 mM MoSx. (b) Comparison of average H2 evolution rate over different catalysts

11

from ErB-TEOA system, 0.05 mM MoSx. (c) Variations of H evolution rate from ErB sensitized

12

free MoSx and ATP/Co-MoSx catalysts at different MoSx concentrations. (d) The dependence of

13

AQY for H2 evolution over ErB sensitized ATP/Co-MoSx catalyst on the wavelength of incident

14

light, 0.05 mM MoSx. Reaction conditions: 100 mL TEOA solution, 10%, pH 8; ErB, 0.2 mM; 30-

15

W LED lamp, λ≥450 nm.

16

Figure 3. (a) XRD pattern of free MoSx and ATP/Co-MoSx catalysts. (b-d) TEM and HRTEM

17

images of (b) free MoSx (c) ATP/MoSx, and (d, e) ATP/Co-MoSx catalysts. The inset in panel (c)

18

is the corresponding SAED pattern. (f) HADDF-STEM image and corresponding Co, Mo, and S

19

element mappings of ATP/Co-MoSx catalyst.

20

Figure 4. High-resolution XPS spectra of (a) Co 2p core level for ATP/Co-MoSx catalyst and

21

ATP/Co(OH)2 hybrid. (b) Mo 3d and (c) S 2p core levels for ATP/Co-MoSx and free MoSx

22

catalysts.


28

Page 29 of 35 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

Figure 5. The stability of photocatalytic H2 evolution over ATP/Co-MoSx and free MoSx catalysts

2

from ErB-TEOA system. Reaction conditions: 100 mL TEOA solution, 10%, pH 8; ErB, 0.2 mM;

3

30-W LED lamp, λ≥450 nm.

4

5

6

Table 1 The fitting results of XPS spectra of Co 2p, Mo 3d, and S 2p core levels for

7

ATP/Co(OH)2 hybrid, free MoSx catalyst, and ATP/Co-MoSx catalyst. Sample MoIVSx 3d5/2 (3d3/2) (eV) MoVOSx 3d5/2 (3d3/2) (eV) MoVIO3 3d5/2 (3d3/2) (eV) Co2+ 2p3/2 (2p1/2) (eV) “CoMoS” 2p3/2 (2p1/2) (eV) (S2)22p3/2 (2p1/2) (eV) S22p3/2 (2p1/2) (eV) Sulfate 2p3/2 (2p1/2) (eV) S/Mo ratio Co/Mo ratio

ATP/Co(OH)2 -

781.12 (797.26)

Free MoSx 228.53 (231.63) 62.4% 229.83 (232.93) 20.1% 232.33 (235.43) 17.5% -

-

-

-

162.89 (164.09) 48.7% 161.29 (162.49) 47.6% 167.65 (168.85) 3.7% 2.97 -

-

-

ATP/Co-MoSx 228.71 (231.81) 42.4% 229.90 (233.00) 29.4% 232.09 (235.19) 28.2% 781.99 (797.34) 58.5% 779.29 (794.69) 41.5% 163.10 (164.30) 32.8% 161.61 (162.81) 56.9% 167.78 (168.97) 10.3% 2.97 0.70


29


Page 30 of 35

1 2

Figure 1.


30

Page 31 of 35

1

200 0

0

60

120

180

240

50

0

300

ATP/Co-MoSx

0

Co-MoSx

0

Co(OH)2/MoSx mixture

ATP/Co-MoSx

100

ATP/Co(OH)2/(NH4)2S

ATP/MoSx

ATP/Co(OH)2

Free MoSx

400

150

ATP/MoSx

600

(b)

Free MoSx

H2 evolution (mol )

800

200

ATP+(NH4)2S

(a)

ATP

-1

1000

Average H2 evolution rate (mol h )

2

time (min)

3 4

300 250

(c)

200

50

Free MoSx ATP/Co-MoSx

(d)

40

150 100

AQE (%)

-1

Average H2 evolution rate (mol h )

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 16

30 20

12 10

8 4 0

0.01

0.05

0.1 [MoSx] (mM)

0.3

0.5

0

450

475

500

520

550

600

Wavelength (nm)

Figure 2.

5 6 7 8 9 10 11


31


Page 32 of 35

1 2

Figure 3.


32

Page 33 of 35 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


(a)

ATP/Co-MoSx-Co2p

"CoMoS" Co 2p3/2

"CoMoS" Co 2p1/2 "CoMoS" Sat.

(b)

(c)

(2-)

S 2s (2-) S2 2s

ATP/Co-MoSx-Mo3d

ATP/Co-MoSx-S2p

(2-)

S 2p (2-) S2 2p Sulfate

4+

Mo 3d 5+ Mo 3d 6+ Mo 3d

"CoMoS" Sat.

2+

Co Sat. Co2+ 2p 1/2 2+

Co Sat. 2+

Co 2p3/2 MoSx-S2p

MoSx-Mo3d

2+

ATP/Co(OH)2-Co2p

Co 2p3/2

2+

Co 2p1/2

2+

Co Sat.

2+

Co Sat.

815 810 805 800 795 790 785 780 775 770 240

1 2

Binding energy (eV)

236

232

228

224

220170

Binding energy (eV)

168

166

164

162

160

158

Binding energy (eV)

Figure 4.

3

4

5

6

7

8

9

10 11 12


33


1000 ATP/Co-MoSx Free MoSx

800

H2 evolution (mol )

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 34 of 35

600

2

nd

rd

2

th

3

4

400 200 0

1

st

1

0

5

10

15

20

time(h)

Figure 5.

3

4

5

6

7 8 9 10 11 12 13 14 15 16 17


34

Page 35 of 35 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


Table of contents graphic

2 3 4


35

Cobalt-Activated Amorphous MoSx Nanodots Grown In Situ on Natural

Recommend Documents