Novel Mixed-Dimensional Photocatalysts Based on 3D Graphene

Subscriber access provided by UNIV OF LOUISIANA

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Novel Mixed-dimensional Photocatalysts Based on 3D Graphene Aerogel Embedded with TiO2/MoS2 Hybrid Hui Qiao, Zongyu Huang, Shengqian Liu, Yue Tao, Hu Zhou, Mengyu Li, and Xiang Qi J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 02 Apr 2019 Downloaded from http://pubs.acs.org on April 2, 2019

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 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

The Journal of Physical Chemistry

Novel Mixed-Dimensional Photocatalysts Based on 3D Graphene Aerogel Embedded with TiO2/MoS2 Hybrid Hui Qiao, Zongyu Huang*, Shengqian Liu, Yue Tao, Hu Zhou*, Mengyu Li, Xiang Qi Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, and School of Physics and Optoelectronic, Xiangtan University, Hunan 411105, People’s Republic of China School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, People’s Republic of China

*

Corresponding author: School of Physics and Optoelectronic, Xiangtan University,

Hunan 411105, P. R. China E-mail address: [email protected] (Z. Y. Huang) *

Corresponding author: School of Chemistry and Engineering, Hunan University of

Science and Technology, Xiangtan, 411201, P. R. China E-mail address: [email protected] (H. Zhou)

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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 25

Abstract The

ternary

mixed-dimensional

TiO2/MoS2/Graphene-aerogel,

0D

(zero

dimensional) TiO2 nanoparticles loaded on 2D (two dimensional) MoS2 nanosheets and TiO2/MoS2 hybrid embedded into the 3D (three dimensional) graphene aerogel, was successfully prepared by self-assembly hydrothermal reduction process. The macroscopic appearance of TiO2/MoS2/Graphene-aerogel is recorded using a digital camera. The microstructure of TiO2/MoS2/Graphene-aerogel with three-dimensional interconnected porous network structure was characterized by scanning electron microscope and transmission electron microscope. UV-Vis absorption spectra tests show that TiO2/MoS2/Graphene-aerogel possesses enhanced light absorption properties. The photocatalytic performance of TiO2/MoS2/Graphene-aerogel was tested by the photoelectrochemical system, and it is verified that the photocurrent density of as-prepared TiO2/MoS2/Graphene-aerogel is greatly improved to 105 A/cm2 at voltage of 0.6 V, it is approximately 10 times than of sole TiO2. The improved photocatalytic activity is due to the enormous specific surface area caused by the multiaperture structure of the unique 3D graphene aerogel, maximized reactive sites, good conductivity, and positive coupling effect with TiO2/MoS2 heterojunction. This study indicates that TiO2/MoS2/Graphene aerogel-based photocatalysts have excellent potential for photocatalytic H2 production and photocatalytic degradation.


Page 3 of 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


1. Introduction As an excellent photocatalyst, titanium dioxide (TiO2) has been widely studied in the field of photoelectrochemistry due to its high catalytic activity, environmental stability, nontoxicity and cheap cost

1-3.

Nevertheless, its narrow light absorption

range, which can only absorb ultraviolet light with a wavelength below 400 nm

4-6,

the rapid spontaneous recombination of photogenerated electron-hole pairs severely limit the further development and photocatalytic applications of TiO2 7-9. Therefore, It is urgent to explore the effective routes for improving photocatalytic activity of TiO2. It is well known that the present of co-catalyst would be in favor of improving the photocatalytic performances of TiO2 10-13. O. Carp

14

et al. demonstrated that the use

of Pt as a cocatalyst to modify TiO2 can significantly improve the efficiency of photocatalytic water splitting to produce H2. Similarly, S. Sakthivel 15 et al deposited various noble metals (Pt, Au and Pd) on TiO2 to improve photocatalytic activity. Unfortunately, these noble metal are rare and expensive, thus, it is necessary to look for a low-cost and efficient co-catalyst from the perspective of both practical applications and commercial interests. Molybdenum disulfide (MoS2) as a promising non-precious metal co-catalyst has been extensively studied due to its excellent chemical and electronic properties Kanda

22

16-21.

et al deposited MoS2 nanoparticles on the surface of TiO2 nanoparticles to

show high photocatalytic hydrogen production activity. Zhou

23

et al had found that

the MoS2-modified TiO2 nanobelts even behaved superior photocatalytic activity under visible-light irradiation. According to previous reports, the hybridization of TiO2 and MoS2 will form a type II heterojunction because the conduction band (CB) level of TiO2 is lower than that of MoS2 24-25. Therefore, the generated photogenerated



electrons will gather in the CB of TiO2 due to the existence of an energy barrier, the holes (h+) are injected into the valence band (VB) of MoS2 and spontaneously react with the electrolyte to reduce the recombination of electron holes and prolong electron life. However, most of the literatures have been following the strategy, in which the MoS2 co-catalyst was loading or coating on surface of TiO2 photocatalyst. Recently, Ren

26

et al loaded TiO2 nanoparticles on two-dimensional (2D) MoS2 nanosheets to

synthesize mixed-dimensional TiO2/MoS2 hybrid and confirmed that the TiO2/MoS2 hybrid has higher photocatalytic activity than sole TiO2 nanoparticles. The superior photocatalytic performances were due to the good conductivity and special twodimensional layered structure of 2D MoS2, which would provide support plant for loading of TiO2 nanoparticles and increase the additional high reactivity sites. Nevertheless, irreversible agglomerates are prone to occur in nanostructures, as well as in the nano-sized hybrids, and result in loss of active sites and reduction of photocatalytic activity 27. In order to overcome the obstacles of agglomeration, a new three-dimensional (3D) macrostructure graphene model (graphene hydrogel/aerogel) had been reported recently

28-31.

Shi

28

and his colleagues had firstly reported a facile hydrothermal

process to prepare graphene hydrogel (aerogel) with a unique cylindrical structure, which is a stable 3D porous network structure formed by self-assembling graphene oxide (GO) during hydrothermal reduction. It is worth noting that this graphene aerogel (hydrogel) not only retains the large specific surface area characteristics of the graphene sheets, but also forms a porous network structure having a pore size of several micrometers by mutual support between the graphene sheets, which makes 3D graphene aerogels are most likely to be good support materials for embedding other nano-functional structures. Li

32

et al reported that three-dimensional graphene


Page 4 of 25

Page 5 of 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


aerogel embedded with Fe2O3 nanoparticles, which demonstrated that Fe2O3 nanoparticles were well loaded on the graphene network via a one-pot hydrothermal method. Gao

33

et al confirmed that the visible light absorption characteristics of

Au/TiO2 can be significantly enhanced by embedding in graphene hydrogels. Han

29

et al successfully loaded two types of functional nanoparticles (TiO2 and CdS) into 3D graphene aerogel, and it possessed novel physicochemical properties and exhibited enhanced light absorption. Based on the similar routes, Han et al also inserted both of TiO2 and MoS2 into 3D graphene aerogel, in which 3D graphene aerogel interconnect network as an anchor support frame, the TiO2 as photocatalyst, and the MoS2 as co-catalyst. It had been reported to possess enhanced photocurrent, extremely efficient charge separation properties and superior durability

34.

Unfortunately, MoS2 and TiO2 were randomly embedding into the as-reported ternary aerogel, and it is hard to guarantee the formation of the TiO2/MoS2 hybrid. Therefore, it is reasonably believed that the photocatalytic performances in TiO2/MoS2/Graphene aerogel would be further improved by TiO2/MoS2 hybrid modification. In this paper, considering the advantages of 3D graphene aerogels and 0D/2D TiO2/MoS2

hybrid,

we

have

successfully

synthesized

3D

ternary

TiO2/MoS2/Graphene-aerogel, which 0D TiO2 nanoparticles were loaded on the 2D MoS2 nanosheets to form the binary heterojunction with tight connection, and then the TiO2/MoS2 hybrid was embedding into the interconnected network of 3D graphene aerogel. The as-prepared TiO2/MoS2/Graphene-aerogel can not only fully utilize the coupling between the three materials, but also the mixed dimension structure of 0D, 2D and 3D can make full use of the advantages of various dimensional materials to maximize the photocatalytic performance of the material. The as-prepared 3D TiO2/MoS2/Graphene-aerogel exhibited interconnected porous graphene skeletons,



and the TiO2/MoS2 hybrid was uniformly deposited on the graphene sheets. Photoelectrochemical test results show that TiO2/MoS2/Graphene-aerogel has enhanced photocurrent density, good light absorption and excellent durability. The present work is expected that 3D graphene-based aerogel composites will become promising photocatalyst.

2. Experimental section 2.1 Preparation of 3D ternary TiO2/MoS2/Graphene-aerogel 2D MoS2 nanosheets were prepared via a typical hydrothermal intercalation and exfoliation process

35.

A certain amount of exfoliated MoS2 nanoplatelets, 25 ml of

diethylene glycol (DEG), hydrochloric acid (about 36-38%) pretreated 0.5 ml of Ti(OBu)4 were sufficiently mixed. After that, the above solution was sealed in a 50 ml Teflon-lined autoclave and maintained at 150° C for 12 hours to obtain 0D/2D TiO2/MoS2 hybrid. Thereafter, the above mixed solution was transferred to a sealed 50 ml Teflon-lined autoclave and kept at 150 ° C for 12 hours to obtain 0D/2DTiO2/MoS2 hybrid. Sole TiO2 nanoparticles was synthesized without adding pristine MoS2 nanosheets as the control sample. 3D ternary TiO2/MoS2/Graphene-aerogel was prepared under a typical hydrothermal process. In detail, a certain amount of the as-prepared 0D/2D TiO2/MoS2 hybrid was added into 30 ml of GO aqueous solution (the concentration is 3 mg/ml), and then the as-prepared solution was placed into Teflon-lined autoclave (50 ml). After holding at 180 ° C for 12 hour, black column, i.e. 3D graphene hydrogel embedding with TiO2/MoS2 hybrid, would be obtained. The result hydrogel


Page 6 of 25

Page 7 of 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


are further washed and freeze-dried for further use. The TiO2/Graphene-aerogel was also controllably prepared using the same route. 2.2 Characterizations X-ray diffraction (MAX-2500 with Cu Ka radiation) and Raman spectra (Renishaw InVia Raman microscope with 532 nm excitation laser) are used to examine the crystal structure of as-prepared TiO2/MoS2/Graphene-aerogel hybrid. In the diffuse reflection mode, the UV–Vis absorption spectra (ISR-2200, Shimadzu) of sole

TiO2

nanoparticle,

TiO2/MoS2

hybrid,

TiO2/Graphene-aerogel

and

TiO2/MoS2/Graphene-aerogel were was carried out. Scanning electron microscopy (SEM, Tescan Vega 3 SBH) and transmission electron microscopy (TEM, JEM 2100) are used to observe the growth morphologies and microstructures of the as-samples. 2.3 Photoelectrochemical (PEC) measurements The PEC tests were performed based on three-electrode system, in which photoanode as working electrode, Pt flake and Ag/AgCl as reference and counter electrode, respectively. The measurement were performed in Na2SO4 electrolyte (0.5 M, PH=7). Sole TiO2 nanoparticle, TiO2/MoS2 hybrid, TiO2/Graphene-aerogel, and TiO2/MoS2/Graphene-aerogel were separately coated on indium tin oxide (ITO, 20 mm × 10 mm ×1 mm) as photoanode. The electrochemical workstation (CHI660D,) was used to control the bias potential change and record the photocurrent generated. The light irradiation intensity with 120 mW/cm2 was provide by a 350-W xenon arc lamp. The scan rate was fixed at 10 mV/s during all the linear sweep voltammograms measurements.



3. Results and discussion Insert image in Figure 1(a) is the digital photograph of the as-prepared Ternary TiO2/MoS2/Graphene-aerogel, it is clear that there is a complete 3D cylindrical graphene hydrogel macrostructure. As shown in SEM images (Figure 1(a) and (b)), a 3D porous network aerogel structure having a pore size of several micrometers was obviously appeared in the as-prepared TiO2/MoS2/Graphene-aerogel sample, in which it was clearly observed that the 2D MoS2 nanosheets were supported on the graphene sheets. In addition, the graphene sheets are relatively thin and slightly wrinkled, which means that graphene sheets undergo an efficient self-assembly process. From the TEM image (Figure 1(c)), it is clear that 0D TiO2 nanoparticles with diameters of 30-40 nm are supported on 2D MoS2 nanosheets to form the 0D-2D hybrid. In the meanwhile, the TiO2/MoS2 hybrid is anchored on graphene supports. Figure 1(d) is the corresponding HRTEM image, the lattice fringes with a pitch of d=0.35 nm, d=0.189 nm and d=0.62 nm can be specified as the (101), (200) lattice plane of TiO2 and the (002) plane of MoS2, respectively. Figure 1(d) is the corresponding HRTEM image, the lattice fringes with a pitch of d=0.189 nm, d=0.35 nm, and d=0.62 nm representing the (200), (101) lattice plane of TiO2 and the (002) plane of MoS2, respectively. In brief, the characterization results prove that, the ternary TiO2/MoS2/Graphene-aerogel with 3D porous network structure is successfully realized through hydrothermal treatment. As mentioned above, the special 3D porous configuration based on graphene aerogel is advantageous for enhancing the contact between the interfaces and inhibiting gather and dissolution of nano-structures, thereby improving photocatalytic activity and structural stability. Therefore, it is believed that this unique structure of the ternary composite TiO2/MoS2/Grapheneaerogel would possess excellent photoelectrochemistry and photocatalytic activity.


Page 8 of 25

Page 9 of 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


Figure

2(a)

shows

the

X-ray

diffraction

pattern

of

the

as-prepared

TiO2/MoS2/Graphene-aerogel. It is obvious that the diffraction peaks of 25.28, 37.8, 48.05, 53.83, 55.06, 62.69 and 75.03 were corresponding to the standard characteristic peaks position of (101), (004), (200), (105), (211), (204), (215) lattice plane of TiO2 (Red sign, JCPDS card No. 21-1272). The others peak of lattice diffraction match well with the standard characteristic peaks position of MoS2 with (Black sign JCPDS file no. 37-1492). Therefore, it is considered that the lattice structure of the raw material do not destroy during the hydrothermal process. While, it was noted that no characteristic peak of the carbon material was found, which may be because the lower diffraction intensity of the characteristic peak of the graphene. In order to further clarify the characterizations of ternary TiO2/MoS2/Graphene-aerogel, the Raman spectra test was carried out, and the characterization results are shown in Figure 2(b). The out-of-plane Alg and in-plane E2g vibration modes of the MoS2 nanosheets were observed at 384 cm-1 and 406 cm-1 in the Raman spectrum, respectively

37-38.

Raman

characteristic peaks located at 147 cm-1, 513 cm-1 and 639 cm-1 can be ascribed to the E1g, A1g and Eg vibration modes of TiO2

39.

In addition, the characteristic peaks

observed at 1325 cm-1 and 1585 cm-1 correspond to the G peak and the D peak of graphene, and due to the GO is continuously reduced during the hydrothermal process, the D-peak intensity associated with the defect is larger than the G peak 40-42. In order to explore the light absorption properties of TiO2/MoS2/Graphene-aerogel, UV-Vis absorption spectra of TiO2 nanoparticles, TiO2/MoS2 hybrid, TiO2/Grapheneaerogel and TiO2/MoS2/Graphene-aerogel were systematically studied. It can be clearly seen from Figure 3 that sole TiO2 can only absorb light in the wavelength range of 400 nm.

43.

Meanwhile, TiO2/MoS2 hybrid and TiO2/Graphene-aerogel

exhibit higher absorbance of visible light compared to sole TiO2. As to the



Page 10 of 25

TiO2/MoS2/Graphene-aerogel, its light absorption is further enhanced compared to the binary controlled samples and the light absorption wavelength is range of 200 nm to 800 nm, which is attributed to the narrow bandgap of MoS2, as well as the large specific surface area and wide optical absorption spectrum range of graphene aerogel with 3D interconnect network structures. From the above discussion about optical properties, ternary TiO2/MoS2/Graphene-aerogel has enhanced light absorbance, and implied the possible excellent photocatalytic activity in photoelectrochemistry. The

photocatalytic

TiO2/Graphene-aerogel

performance and

properties

of

the

TiO2/MoS2/Graphene-aerogel

TiO2, were

TiO2/MoS2, evaluated

by

photoelectrochemical tests. According to Faraday's law, it is found that the amount of H2 released in photoelectrochemical systems is proportional to the photocurrent density

44.

Therefore, all experimental datas here are expressed in terms of

photocurrent density. Figure 4(a) is a linear sweep voltammogram (LSV) curves of TiO2/MoS2/Graphene-aerogel and other controlled samples, showing the current changes with the bias voltage (0-1 V) of the photoanode under light and non-light conditions. The results show that the photocurrent density of TiO2/MoS2/Grapheneaerogel is the highest at the same bias potential, compared with sole TiO2, TiO2/MoS2 and binary TiO2/Graphene-aerogel under the same bias potential. In addition, the photoresponse switching behavior of as-prepared ternary aerogel was performed at bias potential with 0.6 V, as shown in Figure 4(b). It can more directly reflect the photocurrent enhancement effect of TiO2/MoS2/Graphene-aerogel, which is about 10 times that of sole TiO2. The enhancement of photocatalytic performance is attributed to the fact that MoS2 nanosheets as a co-catalyst provides an additional reactive site, and restrained electron-hole recombination due to the type-II band alignment in TiO2/MoS2 hybrid with closed connections. Besides, the fast electron mobility and


Page 11 of 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


transport of the 3D porous network graphene further promotes the separation of electron holes and prolongs the lifetime of photo-generated electrons thereby increasing photocurrent density and enhancing photocurrent density. Simultaneously , This structure can not only fully utilize the coupling between the three materials, but also the mixed dimension structure of 0D, 2D and 3D can make full use of the advantages of various dimensional materials to maximize the photocatalytic performance of the material. As shown in Figure 5, the electrochemical impedance spectroscopy (EIS) spectra of sole TiO2, TiO2/MoS2, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel were displayed to further investigate the photocatalytic activity enhancement mechanism of TiO2/MoS2/Graphene-aerogel. The arc radius of the EIS spectral curve indicates the resistance between the surface of the electrode material and the interface layer. The smaller the radius of the arc, the faster the charge transfer rate. It was apparent that TiO2/MoS2/Graphene-aerogel has minimal electrical resistance. In addition, the resistance of TiO2/MoS2 hybrid is much smaller than sole TiO2, it is believed to be attributed to the fact that MoS2 nanosheets act as cocatalysts to provide electron transfer channels and positive coupling between TiO2/MoS2 hybrids.At the same

time,

the

graphene-aerogel

ones

(TiO2/Graphene-aerogel

and

TiO2/MoS2/Graphene-aerogel) have the lower resistance compared to the graphenefree ones (sole TiO2 and TiO2/MoS2), which is resulted from the excellent electrical conductivity of the graphene and the good electron mobility of the 3D porous network structure. This result is consistent with test results of photocurrent density (Figure 4(a) and Figure 4(b)). Figure 6(a) shows the photocurrent density of the TiO2/MoS2/Graphene-aerogel under different biases (0-0.8 V). It is noted that all of the curves exhibit distinct



photo-induced “on-off” behaviors. With the increase of the voltage, the photocurrent density increases continuously, which is consistent with the LSV curves. The photocurrent density of TiO2/MoS2/Graphene-aerogel increasesd as the external voltage increases. Aa a rule, the result of enhancement of photocurrent density is because the external potential applied on the photoelectrode promotes the separation of electrons and holes, inhibits their composite recombination. In addition, there is an important factor to evaluate the photoresponse performance is the effect of light intensity on photocurrent density 45. Figure 6(b) clearly shows that as the intensity of the irradiated light increases from 60 to 140 mW/cm2, the photocurrent density of TiO2/MoS2/Graphene-aerogel increases linearly. Stability is an important factor in evaluating the performance of photocatalysts. As shown in Figure 6 (c), the LSV curve of the TiO2/MoS2/Graphene-aerogel is almost identical after 50 and 100 switching cycles. Furthermore, the continuous switching cycle stability measurement is in the inset of Figure 6(d), indicate that the photocurrent density is fairly stable only with slight fluctuation. The result of the attenuation of photocurrent density is because the sample slight drops from the photoanode in the process of testing. Structural model diagram and photocatalytic hydrogen production process schematic of 3D TiO2/MoS2/Graphene-aerogel are proposed to expose the possible mechanism of its photocatalytic enhancement, as displayed in Figure 7. The excellent photocatalytic properties of the as-prepared TiO2/MoS2/Graphene-aerogel is derived from the following aspects. The 3D graphene network structure has a large specific surface area, good adsorptivity and wide optical absorption spectrum range, making the active materials are fully in contact with the electrolytes. In addition, the hybridization of MoS2 and TiO2 will form a type-II heterostructure. Under sunlight irradiation, the generated photogenerated electrons will gather in the CB of TiO2 due


Page 12 of 25

Page 13 of 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


to the existence of an energy barrier, the holes (h+) are injected into the valence band (VB) of MoS2 and spontaneously react with the electrolyte to reduce the recombination of electron holes and prolong electron life. Besides, MoS2 nanosheets as a co-catalyst not only act as electron transport channels to facilitate the separation of electron-hole pairs, but also provide highly reactive sites for hydrogen evolution.

4. Conclusions In

summary,

the

three-dimensional

ternary

TiO2/MoS2/Grapehen-aerogel

combined with the advantages of 3D graphene aerogel and 0D/2D TiO2/MoS2 hybrid was prepared by a simple hydrothermal self-assembly method. The as-prepared TiO2/MoS2/Graphene-aerogel

exhibits

well

interconnected

3D

mesoporous

microstructure, superior light absorption performance, outstanding photocatalytic activity under sunlight irradiation. This unique multivariate mixed-dimension structure has important guiding significance for the development of high-performance photocatalysts and has potential applications in energy conversion and storage.

Conflicts of interest There are no conflicts of interest to declare.

Acknowledges This work was supported by the Grants from NNSF of China (Nos. 11504312, 21776067), NSF of Provincial Hunan (No. 2016JJ2132), Fund of Hunan Education Department (No. 15C1322), Xiangtan Science & Technology Program (No. CXYZD20172002), and the Program for Innocative Research Team in University (IRT_17R91).



References (1).

Fujishima, A.; Honda, K., Electrochemical Photolysis of Water at a Semiconductor Electrode.

Nature 1972, 238, 37-38. (2).

Luo, C.; Ren, X.; Dai, Z.; Zhang, Y.; Qi, X.; Pan, C., Present Perspectives of Advanced

Characterization Techniques in TiO2-Based Photocatalysts. ACS Appl. Mater. Interfaces 2017, 9, 23265-23286. (3).

Tian, L.; Xu, J.; Just, M.; Green, M.; Liu, L.; Chen, X., Broad Range Energy Absorption

Enabled by Hydrogenated TiO2 Nanosheets: From Optical to Infrared and Microwave. J. Mater. Chem. C 2017, 5, 4645-4653. (4).

Zhao, Z.; Tian, J.; Sang, Y.; Cabot, A.; Liu, H., Structure, Synthesis, and Applications of TiO2

Nanobelts. Adv. Mater. 2015, 27, 2557-2582. (5).

Frischknecht, A. K.; Yaccuzzi, E.; Plá, J.; Perez, M. D., Anomalous Photocurrent Response of

Hybrid TiO2: P3HT Solar Cells under Different Incident Light Wavelengths. Sol. Energy Mater. Sol. Cells 2016, 157, 907-912. (6).

Tanabe, I.; Ozaki, Y., Far-and Deep-Ultraviolet Spectroscopic Investigations for Titanium

Dioxide: Electronic Absorption, Rayleigh Scattering, and Raman Spectroscopy. J. Mater. Chem. C 2016, 4, 7706-7717. (7).

Liu, X.; Dong, G.; Li, S.; Lu, G.; Bi, Y., Direct Observation of Charge Separation on Anatase

TiO2 Crystals with Selectively Etched {001} Facets. J. Am. Chem. Soc. 2016, 138, 2917-2920. (8).

Mahadik, M. A.; Shinde, P. S.; Lee, H. H.; Cho, M.; Jang, J. S., Highly Efficient and Stable

3D Ni(OH)2/CdS/ZnIn2S4/TiO2 Heterojunction under Solar Light: Effect of an Improved TiO2/FTO Interface and Cocatalyst. Sol. Energy Mater. Sol. Cells 2017, 159, 475-487. (9).

Zhang, J.; Ma, X.; Zhang, L.; Lu, Z.; Zhang, E.; Wang, H.; Kong, Z.; Xi, J.; Ji, Z.,

Constructing a Novel N–P–N Dual Heterojunction between Anatase TiO2 Nanosheets with Coexposed {101},{001} Facets and Porous Zns for Enhancing Photocatalytic Activity. J. Phys. Chem. C 2017, 121, 6133-6140. (10).

Zhang, W.; Xiao, X.; Zheng, L.; Wan, C., Fabrication of TiO2/MoS2@ Zeolite Photocatalyst

and Its Photocatalytic Activity for Degradation of Methyl Orange under Visible Light. Appl. Surf. Sci. 2015, 358, 468-478. (11).

Zhang, W.; Xiao, X.; Li, Y.; Zeng, X.; Zheng, L.; Wan, C., Liquid-Exfoliation of Layered

MoS2 for Enhancing Photocatalytic Activity of TiO2/G-C3N4 Photocatalyst and Dft Study. Appl. Surf. Sci. 2016, 389, 496-506. (12).

Ji, T.; Liu, Q.; Zou, R.; Zhang, Y.; Wang, L.; Sang, L.; Liao, M.; Hu, J., Enhanced Uv-Visible

Light Photodetectors with a TiO2/Si Heterojunction Using Band Engineering. J. Mater. Chem. C 2017, 5, 12848-12856. (13).

Sousa-Castillo, A.; Comesaña-Hermo, M.; Rodriguez-Gonzalez, B.; Pérez-Lorenzo, M. s.;

Wang, Z.; Kong, X.-T.; Govorov, A. O.; Correa-Duarte, M. A., Boosting Hot Electron-Driven Photocatalysis through Anisotropic Plasmonic Nanoparticles with Hot Spots in Au–TiO2 Nanoarchitectures. J. Phys. Chem. C 2016, 120, 11690-11699.


Page 14 of 25

Page 15 of 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


(14).

Carp, O.; Huisman, C. L.; Reller, A., Photoinduced Reactivity of Titanium Dioxide. Prog.

Solid State Chem. 2004, 32, 33-177. (15).

Sakthivel, S.; Shankar, M. V.; Palanichamy, M.; Arabindoo, B.; Bahnemann, D. W.;

Murugesan, V., Enhancement of Photocatalytic Activity by Metal Deposition: Characterisation and Photonic Efficiency of Pt, Au and Pd Deposited on TiO2 Catalyst. Water Res. 2004, 38, 3001-3008. (16).

Yu, X. Y.; Hu, H.; Wang, Y.; Chen, H.; Lou, X. W., Ultrathin MoS₂ Nanosheets Supported on

N-Doped Carbon Nanoboxes with Enhanced Lithium Storage and Electrocatalytic Properties. Angew. Chem. Int. Ed. 2015, 54, 7395-7398. (17).

Xie, J.; Zhang, H.; Li, S.; Wang, R.; Sun, X.; Zhou, M.; Zhou, J.; Lou, X. W.; Xie, Y.,

Defect‐Rich MoS2 Ultrathin Nanosheets with Additional Active Edge Sites for Enhanced Electrocatalytic Hydrogen Evolution. Adv. Mater. 2013, 25, 5807-5813. (18).

Zhang, L.; Wu, H. B.; Yan, Y.; Wang, X.; Lou, X. W., Hierarchical MoS2 Microboxes

Constructed by Nanosheets with Enhanced Electrochemical Properties for Lithium Storage and Water Splitting. Energy Environ. Sci. 2014, 7, 3302-3306. (19).

Yin, L.; Hai, X.; Chang, K.; Ichihara, F.; Ye, J., Synergetic Exfoliation and Lateral Size

Engineering of MoS2 for Enhanced Photocatalytic Hydrogen Generation. Small 2018, 1704153. (20).

Ponraj, J. S.; Xu, Z.-Q.; Dhanabalan, S. C.; Mu, H.; Wang, Y.; Yuan, J.; Li, P.; Thakur, S.;

Ashrafi, M.; Mccoubrey, K., Photonics and Optoelectronics of Two-Dimensional Materials Beyond Graphene. Nanotechnology 2016, 27, 462001. (21).

Nan, F.; Li, P.; Li, J.; Cai, T.; Ju, S.; Fang, L., Experimental and Theoretical Evidence of

Enhanced Visible-Light Photoelectrochemical and Photocatalytic Properties in MoS2/TiO2 Nanohole Arrays. J. Phys. Chem. C 2018. 122, 15055-15062. (22).

Kanda, S.; Akita, T.; Fujishima, M.; Tada, H., Facile Synthesis and Catalytic Activity of

MoS₂/TiO₂ by a Photodeposition-Based Technique and Its Oxidized Derivative MoO₃/TiO₂ with a Unique Photochromism. J. Colloid Interface Sci. 2011, 354, 607-610. (23).

Zhou, W.; Yin, Z.; Du, Y.; Huang, X.; Zeng, Z.; Fan, Z.; Liu, H.; Wang, J.; Zhang, H.,

Synthesis of Few-Layer MoS2 Nanosheet-Coated TiO2 Nanobelt Heterostructures for Enhanced Photocatalytic Activities. Small 2013, 9, 140-147. (24).

Fan, X.; Xu, P.; Zhou, D.; Sun, Y.; Li, Y. C.; Nguyen, M. A. T.; Terrones, M.; Mallouk, T. E.,

Fast and Efficient Preparation of Exfoliated 2H MoS2 Nanosheets by Sonication-Assisted Lithium Intercalation and Infrared Laser-Induced 1t to 2H Phase Reversion. Nano Lett. 2015, 15, 5956-5960. (25).

Zhang, J.; Zhang, L.; Yu, W.; Jiang, F.; Zhang, E.; Wang, H.; Kong, Z.; Xi, J.; Ji, Z., Novel

Dual Heterojunction between MoS2 and Anatase TiO2 with Coexposed {101} and {001} Facets. J. Am. Ceram. Soc. 2017, 100, 5274-5285. (26).

Ren, X.; Qi, X.; Shen, Y.; Xiao, S.; Xu, G.; Zhang, Z.; Huang, Z.; Zhong, J., 2D Co-Catalytic

MoS2 Nanosheets Embedded with 1d TiO2 Nanoparticles for Enhancing Photocatalytic Activity. J. Phys. D Appl. Phys. 2016, 49, 315304. (27).

Zhang, J. X.; Liu, S.; Yan, C.; Wang, X. J.; Wang, L.; Yu, Y. M.; Li, S. Y., Abrasion

Properties of Self-Suspended Hairy Titanium Dioxide Nanomaterials. Appl. Nanosci. 2017, 7, 691-700.



(28).

Xu, Y.; Sheng, K.; Li, C.; Shi, G., Self-Assembled Graphene Hydrogel Via a One-Step

Hydrothermal Process. ACS Nano 2010, 4, 4324-4330. (29).

Han, W.; Ren, L.; Gong, L.; Qi, X.; Liu, Y.; Yang, L.; Wei, X.; Zhong, J., Self-Assembled

Three-Dimensional Graphene-Based Aerogel with Embedded Multifarious Functional Nanoparticles and Its Excellent Photoelectrochemical Activities. ACS Sustain. Chem. Eng. 2014, 2, 741–748. (30).

Fu, Y.; Wang, G.; Mei, T.; Li, J.; Wang, J.; Wang, X., Accessible Graphene Aerogel for

Efficiently Harvesting Solar Energy. ACS Sustain. Chem. Eng. 2017, 5, 4665-4671. (31).

Fan, Q.; Yang, M.; Meng, Q.; Cao, B.; Yu, Y., Activated-Nitrogen-Doped Graphene-Based

Aerogel Composites as Cathode Materials for High Energy Density Lithium-Ion Supercapacitor. J. Electrochem. Soc. 2016, 163, A1736-A1742. (32).

Li, X.; Wu, D.; Sheng, H.; Huang, Y.; Shuang, L.; He, M.; Fan, Z.; Feng, X., Self-Assembled

Fe2O3/Graphene Aerogel with High Lithium Storage Performance. ACS Appl. Mater. Interfaces 2013, 5, 3764-3769. (33).

Gao, M.; Peh, C.; Ong, W.; Ho, G., Green Chemistry Synthesis of a Nanocomposite Graphene

Hydrogel with Three-Dimensional Nano-Mesopores for Photocatalytic H2 Production. RSC Adv. 2013, 3, 13169-13177. (34).

Han, W.; Chen, Z.; Huang, Z.; Han, Z.; Long, R.; Xiang, Q.; Zhong, J., Enhanced

Photocatalytic Activities of Three-Dimensional Graphene-Based Aerogel Embedding TiO2 Nanoparticles and Loading MoS2 Nanosheets as Co-Catalyst. Int. J. Hydrogen Energy 2014, 39, 19502-19512. (35).

Ren, L.; Qi, X.; Liu, Y.; Hao, G.; Huang, Z.; Zou, X.; Yang, L.; Li, J.; Zhong, J., Large-Scale

Production of Ultrathin Topological Insulator Bismuth Telluride Nanosheets by a Hydrothermal Intercalation and Exfoliation Route. J. Mater. Chem. 2012, 22, 4921-4926. (36).

Hummers Jr, W. S.; Offeman, R. E., Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958,

80, 1339-1339. (37).

Lee, C.; Yan, H.; Brus, L. E.; Heinz, T. F.; Hone, J.; Ryu, S., Anomalous Lattice Vibrations of

Single-and Few-Layer MoS2. ACS Nano 2010, 4, 2695-2700. (38).

Tan, S. M.; Ambrosi, A.; Sofer, Z.; Huber, Š.; Sedmidubský, D.; Pumera, M., Pristine

Basal‐and Edge‐Plane‐Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties. Chem. Eur. J. 2015, 21, 7170-7178. (39).

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, 6575-6578. (40).

Ferrari, A. C.; Basko, D. M., Raman Spectroscopy as a Versatile Tool for Studying the

Properties of Graphene. Nat. Nanotechnol. 2013, 8, 235-246. (41).

Sahu, R. S.; Bindumadhavan, K.; Doong, R., Boron-Doped Reduced Graphene Oxide-Based

Bimetallic Ni/Fe Nanohybrids for the Rapid Dechlorination of Trichloroethylene. Environ. Sci. Nano 2017, 4, 565-576. (42).

Wang, K.; Dong, X.; Zhao, C.; Qian, X.; Xu, Y., Facile Synthesis of Cu2O/CuO/RgO

Nanocomposite and Its Superior Cyclability in Supercapacitor. Electrochim. Acta 2015, 152, 433-442.


Page 16 of 25

Page 17 of 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


(43).

Zhou, W.; Yin, Z.; Du, Y.; Huang, X.; Zeng, Z.; Fan, Z.; Liu, H.; Wang, J.; Zhang, H.,

Synthesis of Few‐Layer MoS2 Nanosheet‐Coated TiO2 Nanobelt Heterostructures for Enhanced Photocatalytic Activities. Small 2013, 9, 140-147. (44).

Banerjee, S.; Mohapatra, S. K.; Das, P. P.; Misra, M., Synthesis of Coupled Semiconductor by

Filling 1d TiO2 Nanotubes with Cds. Chem. Mater. 2008, 20, 6784-6791. (45).

Qiao, H.; Yuan, J.; Xu, Z.; Chen, C.; Lin, S.; Wang, Y.; Song, J.; Liu, Y.; Khan, Q.; Hoh, H.

Y., Broadband Photodetectors Based on Graphene–Bi2Te3 Heterostructure. ACS Nano 2015, 9, 18861894.



Figure Captions Figure 1 (a) low and (b) high magnification SEM images of TiO2/MoS2/Grapheneaerogel (The illustration in Figure 1 (a) is a digital photograph depicting the macroscopic shape of the as-prepared TiO2/MoS2/Graphene-hydroge). (c), (d) TEM images of TiO2/MoS2/Graphene-aerogel. Figure 2 (a) XRD pattern of TiO2/MoS2/Graphene-aerogel, (b) Raman spectra TiO2/MoS2/Graphene-aerogel, TiO2/MoS2 byhrid and GO, respectively. Figure 3 UV–Vis diffuse reﬂectance spectra (DRS) of sole TiO2, TiO2/MoS2 hybrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel. Figure 4 (a) LSV curves of sole TiO2, TiO2/MoS2 byhrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel in 0.5 M Na2SO4. (b) Photocurrent density of sole TiO2, TiO2/MoS2 byhrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel 0.6 V. Figure 5 EIS Nynquist plots of sole TiO2, TiO2/MoS2 hybrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel in 0.5 M Na2SO4. Figure 6 (a) photocurrent density of TiO2/MoS2/Graphene-aerogel under different biases (0-0.8V). (b) photocurrent density of TiO2/MoS2/Graphene-aerogel under different sunlight intensity. (c), (d) cycling stability and long-term stability test of TiO2/MoS2/Graphene-aerogel. Figure 7 (a) Structural model diagram and (b) photocatalytic hydrogen production process schematic of as-prepared TiO2/MoS2/Graphene-aerogel.


Page 18 of 25

Page 19 of 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


Figure 1

Figure 1 (a) low and (b) high magnification SEM images of TiO2/MoS2/Grapheneaerogel ( The illustration in Figure 1 (a) is a digital photograph depicting the macroscopic shape of the as-prepared TiO2/MoS2/Graphene-hydroge). (c), (d) TEM images of TiO2/MoS2/Graphene-aerogel.



Figure 2

Figure 2 (a) XRD pattern of TiO2/MoS2/Graphene-aerogel, (b) Raman spectra TiO2/MoS2/Graphene-aerogel, TiO2/MoS2 byhrid and GO, respectively.


Page 20 of 25

Page 21 of 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


Figure 3

Figure 3 UV–Vis diffuse reﬂectance spectra (DRS) of sole TiO2, TiO2/MoS2 byhrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel.



Figure 4

Figure 4 (a) LSV curves of sole TiO2, TiO2/MoS2 byhrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel in 0.5 M Na2SO4. (b) Photocurrent density of sole TiO2, TiO2/MoS2 byhrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel 0.6 V.


Page 22 of 25

Page 23 of 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


Figure 5

Figure 5 EIS Nynquist plots of sole TiO2, TiO2/MoS2 hybrid, TiO2/Graphene-aerogel and TiO2/MoS2/Graphene-aerogel in 0.5 M Na2SO4.



Figure 6

Figure 6 (a) photocurrent density of TiO2/MoS2/Graphene-aerogel under different biases (0-0.8V). (b) photocurrent density of TiO2/MoS2/Graphene-aerogel under different sunlight intensity. (c), (d) cycling stability and long-term stability test of TiO2/MoS2/Graphene-aerogel.


Page 24 of 25

Page 25 of 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


Figure 7

Figure 7 Structural model diagram and photocatalytic hydrogen production process schematic of as-prepared TiO2/MoS2/Graphene-aerogel.

TOC


Novel Mixed-Dimensional Photocatalysts Based on 3D Graphene

Recommend Documents