- Email: [email protected]
Effect of molecular weight of polyethylene glycol on the sheet-thickness and photocatalytic performance of MoS2 nanoparticles
Accepted Manuscript Full Length Article Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles Guanghui Li, Pingping Lei, Min Zhou, Weiguo Wang, Dongnan Li, Chunrong Yang, Nengbin Hua, Song Chen PII: DOI: Reference:
S0169-4332(18)33091-5 https://doi.org/10.1016/j.apsusc.2018.11.023 APSUSC 40868
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
14 August 2018 25 October 2018 4 November 2018
Please cite this article as: G. Li, P. Lei, M. Zhou, W. Wang, D. Li, C. Yang, N. Hua, S. Chen, Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles, Applied Surface Science (2018), doi: https://doi.org/10.1016/j.apsusc.2018.11.023
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles Guanghui Lia,, Pingping Leib, Min Zhouc, Weiguo Wanga, Dongnan Lia, Chunrong Yanga, Nengbin Huaa, Song Chena a
College of Materials Science and Technology, Fujian University of Technology, Fuzhou, 350118,
China b
College of Materials, Xiamen University, Xiamen, 361005, China
c
Fujian academy of building research, Fuzhou, 350025, China
Abstract Molybdenum disulfide (MoS2) nanomaterials have attracted considerable attention recently owing to its unique photoelectrochemistry property and promising applications in the conversion of solar energy to chemical energy and environmental purification. Flower-like MoS2 photocatalyst was synthesised via hydrothermal method in this work. To achieve the MoS2 nanoparticles with various sheet-thickness, polyethylene glycols (PEG) with deferent molecular mass were employed as additives in the preparation process. The effects of the molecular weight of PEG on the micro structure and crystal structure of MoS2 nanoparticles were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD). The photocatalytic properties of assynthesized products were evaluated by the degradation of methylene blue (MB) under ultraviolet irradiation. The results suggest that the molecular weight of PEG could affect the sheet thickness of the MoS2 particles. In addition, the degradation rate of MB show that the photocatalytic
Corresponding author. E-mail address: [email protected] (Guanghui Li). 1
performance of MoS2 nanoparticles is closely related to their sheet thickness, the photocatalytic activity reduced with the decrease of sheet thickness of MoS2 nanoparticles which is mainly attributed to the reduction of the active sites. Keywords: PEG; molecular weight; MoS2 nanoparticles; Sheet-thickness; Photocatalytic performance; Hydrothermal method
1. Introduction Energy shortage and the environmental contamination are current two global challenges which are mainly due to the rapid industrial development and population growth. Sunlight is an natural energy resource which possesses great potential in driving environment-friendly photochemical reactions. Photocatalyst plays an important role in such a conversion. Common photocatalytic materials include metal-nanoparticle composites[1], metal-free organic compounds[2] and semiconductors[3-5]. Photocatalysis induced by light absorption of metal nanoparticles has become a promising strategy for developing efficient visible-light-responsive composite materials, a lot of work has been done on structure design, preparation and catalytic mechanism of photocatalysts and great advances have been achieved in the past few decades[6-8]. The holes generated in the valence band and the electrons in the conduction band of semiconductor may react with surface-bound species to produce hydroxyl radicals and radical anions, and the hydroxyl radicals and radical anions are the primary oxidizing species in the photocatalytic oxidation processes, which result in the occurrence of various redox reactions[9]. Therefor, semiconductors have been widely used as photocatalysts. Single transition metal oxide and chalcogenide (such as TiO2, ZnO, NiO, ZnS and CdS) is the most popular category of photocatalytic semiconductors due to their low cost and excellent chemical stability[10-14]. In 2
addition to single transition metal oxides and chalcogenides, the photocatalytic properties of complex metal oxides and chalcogenides (e.g., binary and ternary metal compounds), nitrides, carbides and phosphides in forms of nanoparticle, one-dimensional (1D) and thin film nanostructures have also been widely investigated[15-23]. Two dimensional (2D) materials have attracted great attention for their unique physical and chemical properties [24-26] and their potential applications in transistors [27], batteries [28,29], and catalysis [30]. As one of the most interesting layered materials, MoS2 is considered to be a promising catalyst in a variety of areas such as hydrodesulfurization (HDS) [31-33], hydrogen evolution reaction (HER) [34-36], hydrogen generation [37] and photocatalytic degradation of organic pollutants [38-41]. Previous experimental and computational studies suggest that the photocatalytic activity of MoS2 correlates with the number of catalytically active edge sites [42,43]. To date, increasing attention has been focused on the improvement of photocatalytic properties of MoS2 nanomaterials [44,45], and massive efforts have been made to investigate the effects of synthesis strategies, construction of heterojunction on the photocatalytic activity of MoS2 catalytic materials [46,47]. However, to our knowledge, there have been few recent investigations on the preparation of MoS2 nanoparticles with desired sheet-thickness and relationship between sheet-thickness of MoS2 nanoparticles and photocatalytic performance. In this study, we synthesized the flower-like MoS2 via hydrothermal method and investigated the effects of molecular weight of PEG on the sheet thickness and photocatalytic properties of the as-prepared MoS2 nanoparticles. Results indicated that the degradation rate of methylene blue (MB) depends on the sheet-thickness of MoS2 nanoparticles, the increase of sheet-thickness is beneficial to the improvement of catalytic performance of MoS2 nanoparticles. Moreover, the 3
mechanism of changes in photocatalytic activities was also briefly discussed.
2. Experimental procedures 2.1. Preparation of samples The hydrothermal process was performed in a 50 mL para-polystyrene-lined hydrothermal synthesis autoclave reactor. Chemical reagents used in this work were all of analytical purity and used without further purification. In a typical synthesis, 370.8 mg of hexaammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24·4H2O) and 639.4 mg of thiourea (Mo:S ratio=1:4) were dissolved in 40 mL of a 3 wt% aqueous solution of PEG and stirred for 20 minutes then hydrochloric acid was added into the above mixed solution with stirring for another 10 minutes to adjust the pH=2, and then the mixed solution was transferred into the autoclave reactor and the reactor was placed for hydrothermal treatment at 220 degrees Celsius for 8 h. Lastly, the autoclave reactor was cooled down naturally and black flower-like MoS2 in the form of powder was obtained from the solution in the autoclave reactor through the process of centrifugation, washing with deionized water and ethanol, and drying in an oven at 60 degrees Celsius for 12 h. PEG200, PEG4000 and PEG8000 were used as additive in hydrothermal treatment process, correspondingly, the resulting MoS2 products were labeled as P1 , P2 and P3. The above process was repeated without adding PEG under the identical conditions, and the sample was labeled as P0. 2.2. Characterization of samples XRD was recorded using a D8 advance (Bruker-AXS) diffractometer equipped with Cu Kα radiation at a scanning rate of 2°/min; the morphology of the samples was investigated by FESEM using a Nova NanoSEM 450 field-emission scanning electron microscope; HRTEM was performed using a JEM-2100 transmission electron microscope at an accelerating voltage of 200 4
kV. 2.3. Photocatalytic test of samples The degree of MB decomposition under Ultraviolet (UV) irradiation was used to evaluate the photocatalytic performance of prepared nano-MoS2 samples. The sample (10 mg) was dispersed into 50 ml MB aqueous solution (the concentration of MB is 10 mg/L). The suspensions were stirred in the dark for 30 min to reach the adsorption-desorption equilibrium. For the UV test, the suspensions were exposed to the irradiation produced by a 36 W Ultraviolet lamp with the wavelength of 365 nm. During the UV irradiation, about 5 mL of the suspension was taken out at given time intervals and centrifuged at 5000 rpm for about 10 min to remove the residual photocatalyst powder. The concentration of MB was determined by a UV-2600 spectrophotometer at λmax of 664 nm using deionized water as a reference sample.
(110)
(105)
P3
(103)
(100)
(002)
3. Results and discussion
Intensity(a.u.)
P2
P1
P0
10
20
30
40
2-Theta/degree
50
60
Fig. 1. XRD patterns of P0, P1, P2 and P3
The crystal structure and phase purity of the samples were investigated by XRD technique and 5
the results are shown in Fig. 1. The diffraction peaks are well consistent with the standard pattern of hexagonal MoS2 (JCPDS No. 24-0513), the diffraction patterns show five broad peaks at 13.9°, 33.1°, 39.3°, 49.5°, and 58.9° corresponding to (002), (100), (103), (105), and (110) planes respectively, no impurity peaks are discerned. The peaks at 13.9° is corresponding to the c-plane and can be used to study the structure of MoS2. The diffraction intensity ratio between (002) and (100) peaks (I(002)/(100)) can be used to evaluate the number of stacking layers of MoS2, a smaller I(002)/(100) ratio means a shorter c axis and less stacking of MoS2 layers. The I(002)/(100) ratios of P0, P1, P2 and P3 samples are 1.84, 1.52, 1.21 and 1.13 respectively, implies that the molecular weight of PEG play an important role in the growth of MoS2 grains, the sheet thickness decreases as molecular weight of PEG increases, this is consistent with the observation from FESEM.
Fig. 2. Morphology of MoS2 microspheres. (A-C) FESEM images of (A) P0, (B) P1, and (C) P3; (D) HRTEM image of P3.
FESEM images (Fig. 2A-C) indicate that the flower-like particles are composed of thin nanosheets, the sheet thickness of P0 and P1 samples are 28nm and 23nm respectively, however, 6
the sheet thickness of P3 sample is significantly reduced to 13nm, which means the addition of PEG8000 inhibited the grains growing along the c-axis direction significantly, and less areas of the {100} facets were exposed on the crystal surface [48]. Previous studies on the catalytic activity of MoS2-based catalysts indicated that the active sites located at the edge, compared with those at the basal plane, contribute largely to the catalytic activities of MoS2 [42,43]. Accordingly, a decrease in the sheet thickness of MoS2 means a reduction in the active sites located at the edge, this is supported by the photocatalytic performance test of MoS2 samples below. Fig. 2D shows the HRTEM image of P3 sample, where the interlayer spaces are measured to be 0.64 nm and 0.28 nm, in good agreement with the value for the (002) plane and (100) plane of the hexagonal MoS2 phase. Photocatalytic measurements of MoS2 nanoparticles were performed in MB aqueous solution under UV irradiation, and the time-dependent normalized concentration changes (Ct/C0; Ct: the concentration of MB at different time, C0: the initial concentration of MB) of MB during the photocatalysis process are shown in Fig. 3. As blank sample (without addition of MoS2), MB molecules are very stable and the concentration did not reduce even expose in UV irradiation at 60 min. The blue color of MB aqueous solution continually declined which confirmed the MB molecules were degraded by photocatalysts (P0, P1 ,P2 and P3).
7
1.1 1.0 0.9
Ct /C0
0.8 0.7 0.6 Blank P1 P2 P3 P0
0.5 0.4 0.3
0
10
20 30 40 Irradiation time/min
50
60
Fig. 3. Degradation rate–irradiation time curves of the P0, P1, P2, P3 and blank
1.0
ln(C0 /Ct)
0.8
P1, k=0.0163 P0, k=0.0097 P2, k=0.0055 P3, k=0.0018
0.6
0.4
0.2
0.0
10
20
30
40
50
60
Irradiation time/min Fig. 4. The ln(C0/Ct) versus time curve of MB photodegradation
When the initial concentration of dyes is low, the degradation rate could be ascribed as a pseudo-first-order kinetics reaction according to a Langmuir Hinshelwood model: ln(C0/Ct) = kt, where k is the apparent first-order rate constant. From the fitting curves, the degradation rate constants (k) of samples obtained are shown in Fig. 4. P1 sample exhibited excellent photocatalytic activity among all four samples, attributing to the highest degradation rate constant, k, of 1.63×10-2 min-1, which is 1.7 times of that of P0, 2.9 times of that of P2 and 9.1 times of that
8
of P3. Change trend of k is in agreement with the I(002/(100) value, which confirms that the more areas of the {100} facets of MoS2 are exposed on the crystal surface, the better the catalytic performance.
4. Conclusions In conclusion, we prepared the flower-like MoS2 nanoparticles with various sheet-thickness via hydrothermal method and investigated the effect of molecular weight of PEG on the sheetthickness and photocatalytic performance of MoS2 nanoparticles. Results show that the sheetthickness of MoS2 nanoparticles is affected remarkably by the molecular weight of PEG during the hydrothermal process, reduction in the sheet-thickness of MoS2 nanoparticles leads to a poor performance of its catalytic ability, the degradation rate of MB decreased from 64.2% to 11.2% when the sheet-thickness decreased from 23 nm to 13 nm. Therefore, to improve the catalytic performance of MoS2 nanoparticles by increasing the active sites, future research should consider exploring the effective preparation approaches to control the growth of MoS2 grains along the caxis direction.
Acknowledgments We thank Xingfang Huang, Yan Lin and Yanyi Huang for technical assistance and Baozhen Lin for valuable discussion. This work was supported by the Fujian University of Technology scientific research fund (GY-Z09001); Research Foundation of Education Bureau of Fujian Province, China (JA15332); Natural Science Foundation of Fujian Province, China (2018J01625) and National Natural Science Foundation of China (51401053).
9
References [1] X. Chen, Y. Li, X. Pan, D. Cortie, X. Huang, Z. Yi, Photocatalytic oxidation of methane over silver decorated zinc oxide nanocatalysts, Nat. Commun. 7 (2016) 12273. [2] W. Li, L. Li, H. Xiao, R. Qi, Y. Huang, Z. Xie, X. Jing, H. Zhang, Iodo-BODIPY: a visiblelight-driven, highly efficient and photostable metal-free organic photocatalyst, RSC Adv. 3 (2013) 13417–13421. [3] S. Zinatloo-Ajabshir, M. Salavati-Niasari, M. Hamadanian, Praseodymium oxide nanostructures: novel solvent-less preparation, characterization and investigation of their optical and photocatalytic properties, RSC Adv. 5 (2015) 33792-33800. [4] P. Li, T. He, Common-cation based Z-scheme ZnS@ZnO core-shell nanostructure for efficient solar-fuel production, Appl. Catal. B-Environ. 238 (2018) 518-524. [5] M. Goudarzi, M. Salavati-Niasari, Using pomegranate peel powders as a new capping agent for synthesis of CuO/ZnO/Al2O3 nanostructures; enhancement of visible light photocatalytic activity, Int. J. Hydrogen Energ. 43 (2018) 14406-14416. [6] J. Li, S. K. Cushing, P. Zheng, T. Senty, F. Meng, A. D. Bristow, A. Manivannan, N. Wu, Solar hydrogen generation by a CdS-Au-TiO2 sandwich nanorod array enhanced with Au nanoparticle as electron relay and plasmonic photosensitizer. J. Am. Chem. Soc. 136 (2014) 84388449. [7] G. Mojgan, M. Noshin, M. K. Mehdi, B. Samira, S. N. Masoud, Biosynthesis and characterization of silver nanoparticles prepared from two novel natural precursors by facile thermal decomposition methods, Sci. Rep. 6 (2016): 32539. [8] X. Meng, L. Liu, S. Ouyang, H. Xu, D. Wang, N. Zhao, J. Ye, Nanometals for solar-to10
chemical energy conversion: from semiconductor-based photocatalysis to plasmon-mediated photocatalysis and photo-thermocatalysis, Adv. Mater. 28 (2016) 6781–803. [9] C. S. Turchi, D. F. Ollis, Photocatalytic degradation of organic water contaminants: mechanisms involving hydroxyl radical attack, J. Catal. 122 (1990) 178–192. [10] S. Zinatloo-Ajabshir, M. Salavati-Niasari, Facile route to synthesize zirconium dioxide (ZrO2) nanostructures: Structural, optical and photocatalytic studies, J. Mol. Liq. 216 (2016) 545-551. [11] S. Hu, P. Qiao, L. Zhang, B. Jiang, Y. Gao, F. Hou, B. Wu, Q. Li, Y. Jiang, C. Tian, W. Zhou, G. Tian, H. Fu, Assembly of TiO2 ultrathin nanosheets with surface lattice distortion for solarlight-driven photocatalytic hydrogen evolution, Appl. Catal. B-Environ. 239 (2018) 317-323. [12] S. Zinatloo-Ajabshir, M. Salavati-Niasari, Nanocrystalline Pr6O11: synthesis, characterization, optical and photocatalytic properties, New. J. Chem. 39 (2015) 3948-3955. [13] B.S.M. Al Balushi, F. Al Marzouqi, B. Al Wahaibi, A.T. Kuvarega, S.M.Z. Al Kindy, Y. Kim, R. Selvaraj, Hydrothermal synthesis of CdS sub-microspheres for photocatalytic degradation of pharmaceuticals, Appl. Surf. Sci. 457 (2018) 559-565. [14] F. Motahari, M. R. Mozdianfard, F. Soofivand, M. Salavati-Niasari, NiO nanostructures: synthesis, characterization and photocatalyst application in dye wastewater treatment, Rsc Adv. 4 (2014) 27654-27660. [15] W. K. Jo, S. Kumar, S. Eslava, S. Tonda, Construction of Bi2WO6/RGO/g-C3N4 2D/2D/2D hybrid Z-scheme heterojunctions with large interfacial contact area for efficient charge separation and high-performance photoreduction of CO2 and H2O into solar fuels, Appl. Catal. B-Environ. 239 (2018) 586-598. [16] F. Soofivand, F. Mohandes, M. Salavati-Niasari, Silver chromate and silver dichromate 11
nanostructures: sonochemical synthesis, characterization, and photocatalytic properties, Mater. Res. Bull. 48 (2013) 2084-2094. [17] F. Beshkar, M. Salavati-Niasari, Facile synthesis of nickel chromite nanostructures by hydrothermal route for photocatalytic degradation of acid black 1 under visible light, J. Nanostruct. 5 (2015) 17-23. [18] I. Papailias, N. Todorova, T. Giannakopoulou, N. Ioannidis, N. Boukos, C. P. Athanasekou, D. Dimotikali, C. Trapalis, Chemical vs thermal exfoliation of g-C3N4 for NOx removal under visible light irradiation, Appl. Catal. B-Environ. 239 (2018) 16-26. [19] M. Salavati-Niasari, F. Soofivand, A. Sobhani-Nasab, M. Shakouri-Arani, A. Y. Faal, S. Bagheri, Synthesis, characterization, and morphological control of ZnTiO3 nanoparticles through sol-gel processes and its photocatalyst application, Adv. Powder Technol. 27 (2016) 2066-2075. [20] M. Ghiyasiyan-Arani, M. Masjedi-Arani, M. Salavati-Niasari, Facile synthesis, characterization and optical properties of copper vanadate nanostructures for enhanced photocatalytic activity, J. Mater. Sci. - Mater. El. 27 (2016) 4871-4878. [21] J. F. Wang, J. Chen, P. F. Wang, J. Hou, C. Wang, Y.H. Ao, Robust photocatalytic hydrogen evolution over amorphous ruthenium phosphide quantum dots modified g-C3N4 nanosheet, Appl. Catal. B-Environ. 239 (2018) 578-585. [22] M. Mahdiani, F. Soofivand, F. Ansari, M. Salavati-Niasari, Grafting of CuFe12O19 nanoparticles on CNT and graphene: Eco-friendly synthesis, characterization and photocatalytic activity, J. Clean. Prod. 176 (2018) 1185-1197. [23] S. Zinatloo-Ajabshir, M. S. Morassaei, M. Salavati- Niasari, Facile fabrication of Dy2Sn2O7SnO2 nanocomposites as an effective photocatalyst for degradation and removal of organic 12
contaminants, J. Colloid Interf. Sci. 497 (2017) 298-308. [24] J. Li, Y. Wang, C. Liu, S. Li, Y. Wang, L. Dong, Z. Dai, Y. Li, Y. Lan, Coupled molybdenum carbide and reduced graphene oxide electrocatalysts for efficient hydrogen evolution, Nat. Commun. 7 (2016) 11204. [25] Y. Du, S. Guo, Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications, Nanoscale 8 (2016) 2532–2543. [26] G. R. Bhimanapati, Z. Lin, V. Meunier, Y. Jung, J. Cha, S. Das, D. Xiao, Y. Son, M. S. Strano, V. R. Cooper, L. Liang, S. G. Louie, E. Ringe, W. Zhou, S. S. Kim, R. R. Naik, B. G. Sumpter, H. Terrones, F. Xia, Y. Wang, J. Zhu, D. Akinwande, N. Alem, J. A. Schuller, R. E. Schaak, M. Terrones, J. A. Robinson, Recent advances in two-dimensional materials beyond graphene, Acs Nano 9 (2015) 11509–11539. [27] L. Li, Y. Yu, G. J. Ye, Q. Ge, X. Ou, H. Wu, D. Feng, X. H. Chen, Y Zhang, Black phosphorus field-effect transistors, Nature Nanotech. 9 (2014) 372–377. [28] J. Song, D. Wang, Advanced sulfur cathode enabled by highly crumpled nitrogen-doped graphene sheets for high-energy-density lithium-sulfur batteries, Nano Lett. 16 (2015) 864–870. [29] H. Wang, H. Jiang, Y. Hu, Z. Deng, C. Li, Interface engineering of few-layered MoS2 nanosheets with ultrafine TiO2 nanoparticles for ultrastable Li-ion batteries, Chem. Eng. J. 345 (2018) 320–326. [30] S. Dou, L. Tao, J. Huo, L. Dai, Etched and doped Co9S8/graphene hybrid for oxygen electrocatalysis, Energ. Environ. Sci. 9 (2016) 1320–1326. [31] Z. Wu, V. M. L. Whiffen, W. Zhu, D. Wang, K. J. Smith, Effect of annealing temperature on Co-MoS2 nanosheets for hydrodesulfurization of dibenzothiophene, Catal. Lett. 144 (2014) 261– 13
267. [32] C. Zhang, P. Li, X. Liu, T. Liu, Z. Jiang, C. Li, Morphology-performance relation of (Co)MoS2 catalysts in the hydrodesulfurization of FCC gasoline, Appl. Catal. A- Gen. 556 (2018) 20–28. [33] J.V. Lauritsen, F. Besenbacher, Atom-resolved scanning tunneling microscopy investigations of molecular adsorption on MoS2 and CoMoS hydrodesulfurization catalysts, J. Catal. 328 (2015) 49–58. [34] X. Dai, K. Du, Z. Li, H. Sun, Y. Yang, W. Zhang, X. Zhang, Enhanced hydrogen evolution reaction on few-layer MoS2 nanosheets-coated functionalized carbon nanotubes, Int. J. Hydrogen Energy 40 (2015) 8877–8888. [35] X. Hai, W. Zhou, S. Wang, H. Pang, K. Chang, F. Ichihara, J. Ye, Rational design of freestanding MoS2 monolayers for hydrogen evolution reaction, Nano Energy 39 (2017) 409–417. [36] C. Zhang, L. Jiang, Y. Zhang, J. Hu, M. K. H. Leung, Janus effect of O2 plasma modification on the electrocatalytic hydrogen evolution reaction of MoS2, J. Catal. 361 (2018) 384–392. [37] H. I. Karunadasa, E. Montalvo, Y. Sun, M. Majda, J. R. Long, C. J. Chang, A molecular MoS2 edge site mimic for catalytic hydrogen generation, Science 335 (2012) 698–702. [38] C. Zhu, L. Zhang, B. Jiang, J. Zheng, P. Hu,S. Li, M. Wu, W. Wu, Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation, Appl. Surf. Sci. 377 (2016) 99–108. [39] M. Sabarinathan, S. Harish, J. Archana, M. Navaneethan, H. Ikeda, Y. Hayakawa, Controlled exfoliation of monodispersed MoS2 layered nanostructures by a ligand-assisted hydrothermal approach for the realization of ultrafast degradation of an organic pollutant, Rsc Adv. 6 (2016) 14
109495-109505. [40] Q. Li, N. Zhang, Y. Yang, G. Z. Wang, D. H. L. Ng, High efficiency photocatalysis for pollutant degradation with MoS2/C3N4 heterostructures, Langmuir 30 (2014) 8965-8972. [41] L. Shi, W. Ding, S. P. Yang, Z. He, S. Q. Liu. Rationally designed MoS2/protonated g-C3N4 nanosheet composites as photocatalysts with an excellent synergistic effect toward photocatalytic degradation of organic pollutants, J. Hazard. Mater. 347 (2018) 431-441. [42] J. Zhang, J. Wu, H. Guo, W. Chen, J. Yuan, U. Martinez, G. Gupta, A. Mohite, P. M. Ajayan, J. Lou, Unveiling active sites for the hydrogen evolution reaction on monolayer MoS2, Adv. Mater. 29 (2017) 1701955. [43] T. F. Jaramillo, K. P. Jørgensen, J. Bonde, J. H. Nielsen, S. Horch, I. Chorkendorff, Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts, Science 317 (2007) 100-102. [44] J. Kibsgaard, Z. Chen, B. N. Reinecke, T. F. Jaramillo, Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis, Nature Mater. 11 (2012) 963– 969. [45] J. Shi, Y. Zhang, Y. Hu, X. Guan, Z. Zhou, L. Guo, NH3-treated MoS2 nanosheets as photocatalysts for enhanced H2 evolution under visible-light irradiation, J. Alloys Compd. 688 (2016) 368–375. [46] B. Sheng, J. Liu, Z. Li, M. Wang, K. Zhu, J. Qiu, J. Wang, Effects of excess sulfur source on the formation and photocatalytic properties of flower-like MoS2 spheres by hydrothermal synthesis, Mater. Lett. 144 (2015) 153–156. [47] Y. Hou, Z. H. Wen, S. M. Cui, X. R. Guo, J. H. Chen, Constructing 2D porous graphitic C3N4 15
nanosheets/nitrogen-doped
graphene/layered
MoS2
ternary
nanojunction
with
enhanced
photoelectrochemical activity, Adv. Mater. 25 (2013) 6291-6297. [48] C. Altavilla, M. Sarno, P. Ciambelli, A novel wet chemistry approach for the synthesis of hybrid 2D free-floating single or multilayer nanosheets of MS2@oleylamine (M=Mo, W), Chem. Mater. 23 (2011) 3879–3885.
16
▶MoS2 nanoparticles were synthesized via simple hydrothermal approach. ▶As additive, the molecular weight PEG has a significant effect on the Sheet-thickness of MoS2 nanoparticles. ▶Photocatalytic performance of MoS2 nanoparticles is closely related to their Sheet-thickness. ▶Kinetic analysis revealed the differences in the catalytic performance of as-prepared samples.
17
S0169-4332(18)33091-5 https://doi.org/10.1016/j.apsusc.2018.11.023 APSUSC 40868
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
14 August 2018 25 October 2018 4 November 2018
Please cite this article as: G. Li, P. Lei, M. Zhou, W. Wang, D. Li, C. Yang, N. Hua, S. Chen, Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles, Applied Surface Science (2018), doi: https://doi.org/10.1016/j.apsusc.2018.11.023
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles Guanghui Lia,, Pingping Leib, Min Zhouc, Weiguo Wanga, Dongnan Lia, Chunrong Yanga, Nengbin Huaa, Song Chena a
College of Materials Science and Technology, Fujian University of Technology, Fuzhou, 350118,
China b
College of Materials, Xiamen University, Xiamen, 361005, China
c
Fujian academy of building research, Fuzhou, 350025, China
Abstract Molybdenum disulfide (MoS2) nanomaterials have attracted considerable attention recently owing to its unique photoelectrochemistry property and promising applications in the conversion of solar energy to chemical energy and environmental purification. Flower-like MoS2 photocatalyst was synthesised via hydrothermal method in this work. To achieve the MoS2 nanoparticles with various sheet-thickness, polyethylene glycols (PEG) with deferent molecular mass were employed as additives in the preparation process. The effects of the molecular weight of PEG on the micro structure and crystal structure of MoS2 nanoparticles were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD). The photocatalytic properties of assynthesized products were evaluated by the degradation of methylene blue (MB) under ultraviolet irradiation. The results suggest that the molecular weight of PEG could affect the sheet thickness of the MoS2 particles. In addition, the degradation rate of MB show that the photocatalytic
Corresponding author. E-mail address: [email protected] (Guanghui Li). 1
performance of MoS2 nanoparticles is closely related to their sheet thickness, the photocatalytic activity reduced with the decrease of sheet thickness of MoS2 nanoparticles which is mainly attributed to the reduction of the active sites. Keywords: PEG; molecular weight; MoS2 nanoparticles; Sheet-thickness; Photocatalytic performance; Hydrothermal method
1. Introduction Energy shortage and the environmental contamination are current two global challenges which are mainly due to the rapid industrial development and population growth. Sunlight is an natural energy resource which possesses great potential in driving environment-friendly photochemical reactions. Photocatalyst plays an important role in such a conversion. Common photocatalytic materials include metal-nanoparticle composites[1], metal-free organic compounds[2] and semiconductors[3-5]. Photocatalysis induced by light absorption of metal nanoparticles has become a promising strategy for developing efficient visible-light-responsive composite materials, a lot of work has been done on structure design, preparation and catalytic mechanism of photocatalysts and great advances have been achieved in the past few decades[6-8]. The holes generated in the valence band and the electrons in the conduction band of semiconductor may react with surface-bound species to produce hydroxyl radicals and radical anions, and the hydroxyl radicals and radical anions are the primary oxidizing species in the photocatalytic oxidation processes, which result in the occurrence of various redox reactions[9]. Therefor, semiconductors have been widely used as photocatalysts. Single transition metal oxide and chalcogenide (such as TiO2, ZnO, NiO, ZnS and CdS) is the most popular category of photocatalytic semiconductors due to their low cost and excellent chemical stability[10-14]. In 2
addition to single transition metal oxides and chalcogenides, the photocatalytic properties of complex metal oxides and chalcogenides (e.g., binary and ternary metal compounds), nitrides, carbides and phosphides in forms of nanoparticle, one-dimensional (1D) and thin film nanostructures have also been widely investigated[15-23]. Two dimensional (2D) materials have attracted great attention for their unique physical and chemical properties [24-26] and their potential applications in transistors [27], batteries [28,29], and catalysis [30]. As one of the most interesting layered materials, MoS2 is considered to be a promising catalyst in a variety of areas such as hydrodesulfurization (HDS) [31-33], hydrogen evolution reaction (HER) [34-36], hydrogen generation [37] and photocatalytic degradation of organic pollutants [38-41]. Previous experimental and computational studies suggest that the photocatalytic activity of MoS2 correlates with the number of catalytically active edge sites [42,43]. To date, increasing attention has been focused on the improvement of photocatalytic properties of MoS2 nanomaterials [44,45], and massive efforts have been made to investigate the effects of synthesis strategies, construction of heterojunction on the photocatalytic activity of MoS2 catalytic materials [46,47]. However, to our knowledge, there have been few recent investigations on the preparation of MoS2 nanoparticles with desired sheet-thickness and relationship between sheet-thickness of MoS2 nanoparticles and photocatalytic performance. In this study, we synthesized the flower-like MoS2 via hydrothermal method and investigated the effects of molecular weight of PEG on the sheet thickness and photocatalytic properties of the as-prepared MoS2 nanoparticles. Results indicated that the degradation rate of methylene blue (MB) depends on the sheet-thickness of MoS2 nanoparticles, the increase of sheet-thickness is beneficial to the improvement of catalytic performance of MoS2 nanoparticles. Moreover, the 3
mechanism of changes in photocatalytic activities was also briefly discussed.
2. Experimental procedures 2.1. Preparation of samples The hydrothermal process was performed in a 50 mL para-polystyrene-lined hydrothermal synthesis autoclave reactor. Chemical reagents used in this work were all of analytical purity and used without further purification. In a typical synthesis, 370.8 mg of hexaammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24·4H2O) and 639.4 mg of thiourea (Mo:S ratio=1:4) were dissolved in 40 mL of a 3 wt% aqueous solution of PEG and stirred for 20 minutes then hydrochloric acid was added into the above mixed solution with stirring for another 10 minutes to adjust the pH=2, and then the mixed solution was transferred into the autoclave reactor and the reactor was placed for hydrothermal treatment at 220 degrees Celsius for 8 h. Lastly, the autoclave reactor was cooled down naturally and black flower-like MoS2 in the form of powder was obtained from the solution in the autoclave reactor through the process of centrifugation, washing with deionized water and ethanol, and drying in an oven at 60 degrees Celsius for 12 h. PEG200, PEG4000 and PEG8000 were used as additive in hydrothermal treatment process, correspondingly, the resulting MoS2 products were labeled as P1 , P2 and P3. The above process was repeated without adding PEG under the identical conditions, and the sample was labeled as P0. 2.2. Characterization of samples XRD was recorded using a D8 advance (Bruker-AXS) diffractometer equipped with Cu Kα radiation at a scanning rate of 2°/min; the morphology of the samples was investigated by FESEM using a Nova NanoSEM 450 field-emission scanning electron microscope; HRTEM was performed using a JEM-2100 transmission electron microscope at an accelerating voltage of 200 4
kV. 2.3. Photocatalytic test of samples The degree of MB decomposition under Ultraviolet (UV) irradiation was used to evaluate the photocatalytic performance of prepared nano-MoS2 samples. The sample (10 mg) was dispersed into 50 ml MB aqueous solution (the concentration of MB is 10 mg/L). The suspensions were stirred in the dark for 30 min to reach the adsorption-desorption equilibrium. For the UV test, the suspensions were exposed to the irradiation produced by a 36 W Ultraviolet lamp with the wavelength of 365 nm. During the UV irradiation, about 5 mL of the suspension was taken out at given time intervals and centrifuged at 5000 rpm for about 10 min to remove the residual photocatalyst powder. The concentration of MB was determined by a UV-2600 spectrophotometer at λmax of 664 nm using deionized water as a reference sample.
(110)
(105)
P3
(103)
(100)
(002)
3. Results and discussion
Intensity(a.u.)
P2
P1
P0
10
20
30
40
2-Theta/degree
50
60
Fig. 1. XRD patterns of P0, P1, P2 and P3
The crystal structure and phase purity of the samples were investigated by XRD technique and 5
the results are shown in Fig. 1. The diffraction peaks are well consistent with the standard pattern of hexagonal MoS2 (JCPDS No. 24-0513), the diffraction patterns show five broad peaks at 13.9°, 33.1°, 39.3°, 49.5°, and 58.9° corresponding to (002), (100), (103), (105), and (110) planes respectively, no impurity peaks are discerned. The peaks at 13.9° is corresponding to the c-plane and can be used to study the structure of MoS2. The diffraction intensity ratio between (002) and (100) peaks (I(002)/(100)) can be used to evaluate the number of stacking layers of MoS2, a smaller I(002)/(100) ratio means a shorter c axis and less stacking of MoS2 layers. The I(002)/(100) ratios of P0, P1, P2 and P3 samples are 1.84, 1.52, 1.21 and 1.13 respectively, implies that the molecular weight of PEG play an important role in the growth of MoS2 grains, the sheet thickness decreases as molecular weight of PEG increases, this is consistent with the observation from FESEM.
Fig. 2. Morphology of MoS2 microspheres. (A-C) FESEM images of (A) P0, (B) P1, and (C) P3; (D) HRTEM image of P3.
FESEM images (Fig. 2A-C) indicate that the flower-like particles are composed of thin nanosheets, the sheet thickness of P0 and P1 samples are 28nm and 23nm respectively, however, 6
the sheet thickness of P3 sample is significantly reduced to 13nm, which means the addition of PEG8000 inhibited the grains growing along the c-axis direction significantly, and less areas of the {100} facets were exposed on the crystal surface [48]. Previous studies on the catalytic activity of MoS2-based catalysts indicated that the active sites located at the edge, compared with those at the basal plane, contribute largely to the catalytic activities of MoS2 [42,43]. Accordingly, a decrease in the sheet thickness of MoS2 means a reduction in the active sites located at the edge, this is supported by the photocatalytic performance test of MoS2 samples below. Fig. 2D shows the HRTEM image of P3 sample, where the interlayer spaces are measured to be 0.64 nm and 0.28 nm, in good agreement with the value for the (002) plane and (100) plane of the hexagonal MoS2 phase. Photocatalytic measurements of MoS2 nanoparticles were performed in MB aqueous solution under UV irradiation, and the time-dependent normalized concentration changes (Ct/C0; Ct: the concentration of MB at different time, C0: the initial concentration of MB) of MB during the photocatalysis process are shown in Fig. 3. As blank sample (without addition of MoS2), MB molecules are very stable and the concentration did not reduce even expose in UV irradiation at 60 min. The blue color of MB aqueous solution continually declined which confirmed the MB molecules were degraded by photocatalysts (P0, P1 ,P2 and P3).
7
1.1 1.0 0.9
Ct /C0
0.8 0.7 0.6 Blank P1 P2 P3 P0
0.5 0.4 0.3
0
10
20 30 40 Irradiation time/min
50
60
Fig. 3. Degradation rate–irradiation time curves of the P0, P1, P2, P3 and blank
1.0
ln(C0 /Ct)
0.8
P1, k=0.0163 P0, k=0.0097 P2, k=0.0055 P3, k=0.0018
0.6
0.4
0.2
0.0
10
20
30
40
50
60
Irradiation time/min Fig. 4. The ln(C0/Ct) versus time curve of MB photodegradation
When the initial concentration of dyes is low, the degradation rate could be ascribed as a pseudo-first-order kinetics reaction according to a Langmuir Hinshelwood model: ln(C0/Ct) = kt, where k is the apparent first-order rate constant. From the fitting curves, the degradation rate constants (k) of samples obtained are shown in Fig. 4. P1 sample exhibited excellent photocatalytic activity among all four samples, attributing to the highest degradation rate constant, k, of 1.63×10-2 min-1, which is 1.7 times of that of P0, 2.9 times of that of P2 and 9.1 times of that
8
of P3. Change trend of k is in agreement with the I(002/(100) value, which confirms that the more areas of the {100} facets of MoS2 are exposed on the crystal surface, the better the catalytic performance.
4. Conclusions In conclusion, we prepared the flower-like MoS2 nanoparticles with various sheet-thickness via hydrothermal method and investigated the effect of molecular weight of PEG on the sheetthickness and photocatalytic performance of MoS2 nanoparticles. Results show that the sheetthickness of MoS2 nanoparticles is affected remarkably by the molecular weight of PEG during the hydrothermal process, reduction in the sheet-thickness of MoS2 nanoparticles leads to a poor performance of its catalytic ability, the degradation rate of MB decreased from 64.2% to 11.2% when the sheet-thickness decreased from 23 nm to 13 nm. Therefore, to improve the catalytic performance of MoS2 nanoparticles by increasing the active sites, future research should consider exploring the effective preparation approaches to control the growth of MoS2 grains along the caxis direction.
Acknowledgments We thank Xingfang Huang, Yan Lin and Yanyi Huang for technical assistance and Baozhen Lin for valuable discussion. This work was supported by the Fujian University of Technology scientific research fund (GY-Z09001); Research Foundation of Education Bureau of Fujian Province, China (JA15332); Natural Science Foundation of Fujian Province, China (2018J01625) and National Natural Science Foundation of China (51401053).
9
References [1] X. Chen, Y. Li, X. Pan, D. Cortie, X. Huang, Z. Yi, Photocatalytic oxidation of methane over silver decorated zinc oxide nanocatalysts, Nat. Commun. 7 (2016) 12273. [2] W. Li, L. Li, H. Xiao, R. Qi, Y. Huang, Z. Xie, X. Jing, H. Zhang, Iodo-BODIPY: a visiblelight-driven, highly efficient and photostable metal-free organic photocatalyst, RSC Adv. 3 (2013) 13417–13421. [3] S. Zinatloo-Ajabshir, M. Salavati-Niasari, M. Hamadanian, Praseodymium oxide nanostructures: novel solvent-less preparation, characterization and investigation of their optical and photocatalytic properties, RSC Adv. 5 (2015) 33792-33800. [4] P. Li, T. He, Common-cation based Z-scheme ZnS@ZnO core-shell nanostructure for efficient solar-fuel production, Appl. Catal. B-Environ. 238 (2018) 518-524. [5] M. Goudarzi, M. Salavati-Niasari, Using pomegranate peel powders as a new capping agent for synthesis of CuO/ZnO/Al2O3 nanostructures; enhancement of visible light photocatalytic activity, Int. J. Hydrogen Energ. 43 (2018) 14406-14416. [6] J. Li, S. K. Cushing, P. Zheng, T. Senty, F. Meng, A. D. Bristow, A. Manivannan, N. Wu, Solar hydrogen generation by a CdS-Au-TiO2 sandwich nanorod array enhanced with Au nanoparticle as electron relay and plasmonic photosensitizer. J. Am. Chem. Soc. 136 (2014) 84388449. [7] G. Mojgan, M. Noshin, M. K. Mehdi, B. Samira, S. N. Masoud, Biosynthesis and characterization of silver nanoparticles prepared from two novel natural precursors by facile thermal decomposition methods, Sci. Rep. 6 (2016): 32539. [8] X. Meng, L. Liu, S. Ouyang, H. Xu, D. Wang, N. Zhao, J. Ye, Nanometals for solar-to10
chemical energy conversion: from semiconductor-based photocatalysis to plasmon-mediated photocatalysis and photo-thermocatalysis, Adv. Mater. 28 (2016) 6781–803. [9] C. S. Turchi, D. F. Ollis, Photocatalytic degradation of organic water contaminants: mechanisms involving hydroxyl radical attack, J. Catal. 122 (1990) 178–192. [10] S. Zinatloo-Ajabshir, M. Salavati-Niasari, Facile route to synthesize zirconium dioxide (ZrO2) nanostructures: Structural, optical and photocatalytic studies, J. Mol. Liq. 216 (2016) 545-551. [11] S. Hu, P. Qiao, L. Zhang, B. Jiang, Y. Gao, F. Hou, B. Wu, Q. Li, Y. Jiang, C. Tian, W. Zhou, G. Tian, H. Fu, Assembly of TiO2 ultrathin nanosheets with surface lattice distortion for solarlight-driven photocatalytic hydrogen evolution, Appl. Catal. B-Environ. 239 (2018) 317-323. [12] S. Zinatloo-Ajabshir, M. Salavati-Niasari, Nanocrystalline Pr6O11: synthesis, characterization, optical and photocatalytic properties, New. J. Chem. 39 (2015) 3948-3955. [13] B.S.M. Al Balushi, F. Al Marzouqi, B. Al Wahaibi, A.T. Kuvarega, S.M.Z. Al Kindy, Y. Kim, R. Selvaraj, Hydrothermal synthesis of CdS sub-microspheres for photocatalytic degradation of pharmaceuticals, Appl. Surf. Sci. 457 (2018) 559-565. [14] F. Motahari, M. R. Mozdianfard, F. Soofivand, M. Salavati-Niasari, NiO nanostructures: synthesis, characterization and photocatalyst application in dye wastewater treatment, Rsc Adv. 4 (2014) 27654-27660. [15] W. K. Jo, S. Kumar, S. Eslava, S. Tonda, Construction of Bi2WO6/RGO/g-C3N4 2D/2D/2D hybrid Z-scheme heterojunctions with large interfacial contact area for efficient charge separation and high-performance photoreduction of CO2 and H2O into solar fuels, Appl. Catal. B-Environ. 239 (2018) 586-598. [16] F. Soofivand, F. Mohandes, M. Salavati-Niasari, Silver chromate and silver dichromate 11
nanostructures: sonochemical synthesis, characterization, and photocatalytic properties, Mater. Res. Bull. 48 (2013) 2084-2094. [17] F. Beshkar, M. Salavati-Niasari, Facile synthesis of nickel chromite nanostructures by hydrothermal route for photocatalytic degradation of acid black 1 under visible light, J. Nanostruct. 5 (2015) 17-23. [18] I. Papailias, N. Todorova, T. Giannakopoulou, N. Ioannidis, N. Boukos, C. P. Athanasekou, D. Dimotikali, C. Trapalis, Chemical vs thermal exfoliation of g-C3N4 for NOx removal under visible light irradiation, Appl. Catal. B-Environ. 239 (2018) 16-26. [19] M. Salavati-Niasari, F. Soofivand, A. Sobhani-Nasab, M. Shakouri-Arani, A. Y. Faal, S. Bagheri, Synthesis, characterization, and morphological control of ZnTiO3 nanoparticles through sol-gel processes and its photocatalyst application, Adv. Powder Technol. 27 (2016) 2066-2075. [20] M. Ghiyasiyan-Arani, M. Masjedi-Arani, M. Salavati-Niasari, Facile synthesis, characterization and optical properties of copper vanadate nanostructures for enhanced photocatalytic activity, J. Mater. Sci. - Mater. El. 27 (2016) 4871-4878. [21] J. F. Wang, J. Chen, P. F. Wang, J. Hou, C. Wang, Y.H. Ao, Robust photocatalytic hydrogen evolution over amorphous ruthenium phosphide quantum dots modified g-C3N4 nanosheet, Appl. Catal. B-Environ. 239 (2018) 578-585. [22] M. Mahdiani, F. Soofivand, F. Ansari, M. Salavati-Niasari, Grafting of CuFe12O19 nanoparticles on CNT and graphene: Eco-friendly synthesis, characterization and photocatalytic activity, J. Clean. Prod. 176 (2018) 1185-1197. [23] S. Zinatloo-Ajabshir, M. S. Morassaei, M. Salavati- Niasari, Facile fabrication of Dy2Sn2O7SnO2 nanocomposites as an effective photocatalyst for degradation and removal of organic 12
contaminants, J. Colloid Interf. Sci. 497 (2017) 298-308. [24] J. Li, Y. Wang, C. Liu, S. Li, Y. Wang, L. Dong, Z. Dai, Y. Li, Y. Lan, Coupled molybdenum carbide and reduced graphene oxide electrocatalysts for efficient hydrogen evolution, Nat. Commun. 7 (2016) 11204. [25] Y. Du, S. Guo, Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications, Nanoscale 8 (2016) 2532–2543. [26] G. R. Bhimanapati, Z. Lin, V. Meunier, Y. Jung, J. Cha, S. Das, D. Xiao, Y. Son, M. S. Strano, V. R. Cooper, L. Liang, S. G. Louie, E. Ringe, W. Zhou, S. S. Kim, R. R. Naik, B. G. Sumpter, H. Terrones, F. Xia, Y. Wang, J. Zhu, D. Akinwande, N. Alem, J. A. Schuller, R. E. Schaak, M. Terrones, J. A. Robinson, Recent advances in two-dimensional materials beyond graphene, Acs Nano 9 (2015) 11509–11539. [27] L. Li, Y. Yu, G. J. Ye, Q. Ge, X. Ou, H. Wu, D. Feng, X. H. Chen, Y Zhang, Black phosphorus field-effect transistors, Nature Nanotech. 9 (2014) 372–377. [28] J. Song, D. Wang, Advanced sulfur cathode enabled by highly crumpled nitrogen-doped graphene sheets for high-energy-density lithium-sulfur batteries, Nano Lett. 16 (2015) 864–870. [29] H. Wang, H. Jiang, Y. Hu, Z. Deng, C. Li, Interface engineering of few-layered MoS2 nanosheets with ultrafine TiO2 nanoparticles for ultrastable Li-ion batteries, Chem. Eng. J. 345 (2018) 320–326. [30] S. Dou, L. Tao, J. Huo, L. Dai, Etched and doped Co9S8/graphene hybrid for oxygen electrocatalysis, Energ. Environ. Sci. 9 (2016) 1320–1326. [31] Z. Wu, V. M. L. Whiffen, W. Zhu, D. Wang, K. J. Smith, Effect of annealing temperature on Co-MoS2 nanosheets for hydrodesulfurization of dibenzothiophene, Catal. Lett. 144 (2014) 261– 13
267. [32] C. Zhang, P. Li, X. Liu, T. Liu, Z. Jiang, C. Li, Morphology-performance relation of (Co)MoS2 catalysts in the hydrodesulfurization of FCC gasoline, Appl. Catal. A- Gen. 556 (2018) 20–28. [33] J.V. Lauritsen, F. Besenbacher, Atom-resolved scanning tunneling microscopy investigations of molecular adsorption on MoS2 and CoMoS hydrodesulfurization catalysts, J. Catal. 328 (2015) 49–58. [34] X. Dai, K. Du, Z. Li, H. Sun, Y. Yang, W. Zhang, X. Zhang, Enhanced hydrogen evolution reaction on few-layer MoS2 nanosheets-coated functionalized carbon nanotubes, Int. J. Hydrogen Energy 40 (2015) 8877–8888. [35] X. Hai, W. Zhou, S. Wang, H. Pang, K. Chang, F. Ichihara, J. Ye, Rational design of freestanding MoS2 monolayers for hydrogen evolution reaction, Nano Energy 39 (2017) 409–417. [36] C. Zhang, L. Jiang, Y. Zhang, J. Hu, M. K. H. Leung, Janus effect of O2 plasma modification on the electrocatalytic hydrogen evolution reaction of MoS2, J. Catal. 361 (2018) 384–392. [37] H. I. Karunadasa, E. Montalvo, Y. Sun, M. Majda, J. R. Long, C. J. Chang, A molecular MoS2 edge site mimic for catalytic hydrogen generation, Science 335 (2012) 698–702. [38] C. Zhu, L. Zhang, B. Jiang, J. Zheng, P. Hu,S. Li, M. Wu, W. Wu, Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation, Appl. Surf. Sci. 377 (2016) 99–108. [39] M. Sabarinathan, S. Harish, J. Archana, M. Navaneethan, H. Ikeda, Y. Hayakawa, Controlled exfoliation of monodispersed MoS2 layered nanostructures by a ligand-assisted hydrothermal approach for the realization of ultrafast degradation of an organic pollutant, Rsc Adv. 6 (2016) 14
109495-109505. [40] Q. Li, N. Zhang, Y. Yang, G. Z. Wang, D. H. L. Ng, High efficiency photocatalysis for pollutant degradation with MoS2/C3N4 heterostructures, Langmuir 30 (2014) 8965-8972. [41] L. Shi, W. Ding, S. P. Yang, Z. He, S. Q. Liu. Rationally designed MoS2/protonated g-C3N4 nanosheet composites as photocatalysts with an excellent synergistic effect toward photocatalytic degradation of organic pollutants, J. Hazard. Mater. 347 (2018) 431-441. [42] J. Zhang, J. Wu, H. Guo, W. Chen, J. Yuan, U. Martinez, G. Gupta, A. Mohite, P. M. Ajayan, J. Lou, Unveiling active sites for the hydrogen evolution reaction on monolayer MoS2, Adv. Mater. 29 (2017) 1701955. [43] T. F. Jaramillo, K. P. Jørgensen, J. Bonde, J. H. Nielsen, S. Horch, I. Chorkendorff, Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts, Science 317 (2007) 100-102. [44] J. Kibsgaard, Z. Chen, B. N. Reinecke, T. F. Jaramillo, Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis, Nature Mater. 11 (2012) 963– 969. [45] J. Shi, Y. Zhang, Y. Hu, X. Guan, Z. Zhou, L. Guo, NH3-treated MoS2 nanosheets as photocatalysts for enhanced H2 evolution under visible-light irradiation, J. Alloys Compd. 688 (2016) 368–375. [46] B. Sheng, J. Liu, Z. Li, M. Wang, K. Zhu, J. Qiu, J. Wang, Effects of excess sulfur source on the formation and photocatalytic properties of flower-like MoS2 spheres by hydrothermal synthesis, Mater. Lett. 144 (2015) 153–156. [47] Y. Hou, Z. H. Wen, S. M. Cui, X. R. Guo, J. H. Chen, Constructing 2D porous graphitic C3N4 15
nanosheets/nitrogen-doped
graphene/layered
MoS2
ternary
nanojunction
with
enhanced
photoelectrochemical activity, Adv. Mater. 25 (2013) 6291-6297. [48] C. Altavilla, M. Sarno, P. Ciambelli, A novel wet chemistry approach for the synthesis of hybrid 2D free-floating single or multilayer nanosheets of MS2@oleylamine (M=Mo, W), Chem. Mater. 23 (2011) 3879–3885.
16
▶MoS2 nanoparticles were synthesized via simple hydrothermal approach. ▶As additive, the molecular weight PEG has a significant effect on the Sheet-thickness of MoS2 nanoparticles. ▶Photocatalytic performance of MoS2 nanoparticles is closely related to their Sheet-thickness. ▶Kinetic analysis revealed the differences in the catalytic performance of as-prepared samples.
17