Construction of a Noble-Metal-Free Photocatalytic H2 Evolution

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Construction of Noble-Metal-Free Photocatalytic H2 Evolution System using MoS2/Reduced Graphene Oxide Catalyst and Zinc Porphyrin Photosensitizer Yong-Jun Yuan, Daqin Chen, Jiasong Zhong, Ling-Xia Yang, Jing-Jing Wang, Zhentao Yu, and Zhigang Zou J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b08290 • Publication Date (Web): 19 Oct 2017 Downloaded from http://pubs.acs.org on October 19, 2017

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The Journal of Physical Chemistry

Construction of Noble-Metal-Free Photocatalytic H2 Evolution System using MoS2/Reduced Graphene Oxide Catalyst and Zinc Porphyrin Photosensitizer †

†

†

‡

Yong-Jun Yuan, Daqin Chen,*, Jiasong Zhong, Ling-Xia Yang , Jing-Jing Wang§, Zhen-Tao ‡

Yu,*, Zhi-Gang Zou †

‡

College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou

310018, People’s Republic of China. ‡

National Laboratory of Solid State Microstructures and Collaborative Innovation Center of

Advanced Microstructures, Jiangsu Key Laboratory for Nano Technology ,College of Engineering and Applied Science, Nanjing University, Nanjing 210093, People’s Republic of China. §

College of Materials, Xiamen University, Xiamen 361005, People’s Republic of China.

ACS Paragon Plus Environment

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ABSTRACT. Exploiting noble-metal-free hydrogen evolution catalysts and light-harvesting molecular photosensitizers is of huge interest for photocatalytic H2 generation. Here we report a hybrid system consisting of MoS2/reduced graphene oxide (MoS2/RGO) catalyst, Zn(II)5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin

([ZnTMPyP]4+)

photosensitizer

and

triethanolamine (TEOA) as a sacrificial electron donor for photocatalytic H2 production under visible light irradiation. Through the optimizing the component proportion of MoS2/RGO catalyst, the [ZnTMPyP]4+-MoS2/RGO-TEOA photocatalytic system showed the highest H2 evolution rate of 2560 µmol h-1 g-1 at pH 7 when the ratio of MoS2 to graphene is 5:1. An apparent quantum yield of 15.2% at 420 nm was observed under optimized reaction conditions. The excellent photocatalytic result can be attributed to the improved charge carrier transfer by graphene which acts as an electron transfer bridge, as demonstrated by photoluminescence quenching and photoluminescence decay studies. It is believed that these findings would open a promising strategy to develop noble-metal-free and visible-light-responding solar-to-H2 conversion system.


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1. INTRODUCTION Solar hydrogen evolution via photocatalytic water splitting provides a sustainable and lowcarbon method to process the global issues of energy crisis and environmental pollution.1-3 During the past four decades, photocatalytic methods for H2 generation have been examined in three

main

embodiments,

including

semiconductor-based

devices,4-7

molecule-based

homogeneous systems,8,9 and organic-inorganic hybrid systems.10-12 Among these systems, organic-inorganic hybrid photocatalytic H2 evolution systems, however, have recently attracted increased attention because the photophysical and electrochemical properties of organic photosensitizer (PS) can be readily tuned at the molecular level.13-15 Such a H2 evolution system typically comprises of a PS for solar light harvesting and a heterogeneous hydrogen evolution reaction catalyst for receiving the electron from the excited PS, and the reduced catalyst will then reduce protons to H2. For hybrid photocatalytic H2 production systems, the first step is the photon capture by the light-harvesting PS. That is, the PS is analogous to the photosynthetic pigments. So far, metal-free organic dyes and noble-metal complexes have been widely utilized as PSs in hybrid photocatalytic H2 production systems. Examples of such hybrid systems include those based on noble-metal complex PSs (eg, Ru(Ⅱ) 、 Ir( Ⅲ ) and Pt(Ⅱ) complexes) and Pt-loaded TiO2 catalyst.16-18 Others have been successful employing organic dyes in the place of noble-metal complex PSs.19-21 However, these photocatalytic H2 production systems are either expensive (eg, Ru(Ⅱ)、Ir(Ⅲ), Pt(Ⅱ) PSs and Pt-based catalysts) or unstable (eg, organic dyes), which limit their practical application in the field of solar H2 generation. Therefore, it is highly desirable to design noble-metal-free as well as durable PSs and catalysts for H2 production in a hybrid system.


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Porphyrins are large π-conjugated aromatic macrocycles with a high electronic delocalization and an intense absorption in the visible region. Since metal porphyrin complexes possess superior chemical and thermal stability as well as tunable photophysical property, they have been widely investigated as PSs in the field of dye-sensitized solar cells and optical cells.2225

Besides, the use of metal porphyrins either as hydrogen evolution reaction catalysts or as PSs

for H2 production received increasing attention in recent decades.26-32 However, most reported photocatalytic H2 generation systems involving porphyrins PSs are together with Pt catalyst,33-35 there is relatively few study regarding the utilization of noble-metal-free catalyst.36,37 Therefore, the development of photocatalytic H2 production systems employing metal porphyrins PSs and nonprecious metal catalysts remains a great challenge. In recent years, we have demonstrated that zinc porphyrins can act active PSs for solar H2 generation in combination with a MoS2/TiO2 or MoS2/ZnO catalyst.38,39 However, these zinc porphyrin PSs exhibited poor photocatalytic activities with a maximum turnover number (TON) of 341, which could be attributed to the poor charge transfer efficiency between excited zinc porphyrin PS and catalyst. The significantly improving the performance of zinc porphyrin PSs and developing of robust zinc porphyrin-based photocatalytic H2 generation systems remain challenging. Graphene, a novel two-dimensional carbon nanomaterial, has been regarded as a rising star in material science, and graphene-based photocatalytic materials have become one of the hottest topics in the field of photocatalytic water splitting.40,41 More importantly, graphene exhibits a large specific surface area and superior electrical conductivity, which are valuable in promoting charge carrier separation. Graphene has been incorporated with semiconductors to improve the efficiency of photochemical reactions.42-44 Accordingly, it is expected that the combination of graphene-based catalyst and zinc porphyrin PS is promising to obtain a highly-


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efficient and durable solar H2 generation system. In this work, we report a hybrid system for photocatalytic generation of H2 from water consisting of a zinc porphyrin PS ([ZnTMPyP]4+, Scheme 1), MoS2-decorated reduced graphene oxide (MoS2/RGO) catalyst, and triethanolamine (TEOA) as the sacrificial electron donor. The graphene component could confine the growth of MoS2 and provides abundant selectively exposed edge sites for H2 evolution reaction and could also act as an excellent electron conductor to accelerate the electron transfer from photoexcited PS to MoS2, improving the photocatalytic H2 production activity. A high apparent quantum yield of 15.2% was obtained at 420 nm. This study would open up a new possibility for the development of noble-metal-free hybrid photocatalytic H2 production system by using transition metal porphyrin complex as the PS and MoS2/graphene as the catalyst.

Scheme 1. Chemical structural formula of zinc porphyrin ([ZnTMPyP]4+) PS.

2. EXPERIMENTAL SECTION Materials: Zinc acetate (Zn(CH3COO)2), sodium molybdate dehydrate (Na2MoO4·2H2O), and thioacetamide (CH3CSNH2) were purchased from Sinopharm Chemical Reagent Co., Ltd. Graphene oxide was purchased from Xianfeng Nano-materials Technology Co., Ltd (Nanjing,


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China). All reagents were used as received without further purification, and deionized water was used in all experiments. Synthesis of MoS2/RGO catalyst: The MoS2/RGO composite catalysts were prepared by hydrothermal reaction of graphene oxide nanosheets powders in an aqueous solution with sodium molybdate dehydrate and thioacetamide. The nominal weight ratios of sodium molybdate dehydrate to graphene oxide were 50:1, 20:1, 10:1, 5:1, 2:1, 1:1, 1:2 and 1:4, and the obtained MoS2/RGO samples were labeled as M50G1, M20G1, M10G1, M5G1, M2G1, M1G1, M1G2 and M1G4 catalysts, respectively. In a typical synthesis, 10 mg of graphene oxide nanosheets was dissolved in 35 mL of aqueous solution consisting of 100 mg sodium molybdate dehydrate and 20 mg thioacetamide to form a transparent solution. The obtained mixed solution was then transferred into 50 mL Teflon-lined stainless steel autoclave, and then kept in an electric oven at 210 oC for 24 h. After the autoclave cooled to room temperature, the black product was collected by centrifugation, washed with deionized water and ethanol, dried at 80 oC for 12 h to obtain the M10G1 sample. Other MoS2/RGO catalysts with different ratios of MoS2 to RGO were prepared by changing the amount of precursors with the same method. For comparison, pure MoS2 catalyst was prepared through the same procedures in the absence of graphene oxide. Synthesis of [ZnTMPyP]4+: The [ZnTMPyP]4+ PS was synthesized according to literature procedure.45 Typically, 1 mmol H2TPyP ligand and 1.2 mmol zinc acetate were added into 50 ml of propionic acid, then the mixed solution was heated at reflux with constant stirring for 3 h. After cooling to room temperature, the solvent was removed under reduced pressure and the isolated solids were purified by alumina column chromatography (CHCl3/pyridine as the eluent, 1:1, v/v). After drying under high vacuum at 60 oC, the product was then treated with iodomethane at room temperature to obtain the [ZnTMPyP]4+ PS.


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Photocatalytic hydrogen production: The photocatalytic H2 evolution experiments were carried out in a 350 ml Pyrex glass reactor with a top window connected to a gas-closed system. A 300 W Xe lamp combined with a UV-cutoff filter (λ > 420 nm) and an output intensity of 200 mW/cm2 was used as light source and was positioned 5 cm away from the glass reactor. In a typical photocatalytic hydrogen production experiment, 40 mg MoS2/RGO catalyst powder was dispersed with constant stirring in 250 ml aqueous solution containing 0.2 M TEOA and a certain concentration of [ZnTMPyP]4+ PS. The pH value of reaction solution was adjusted by addition of concentrated hydrochloric acid. Prior to irradiation, the reaction solution was degassed several times to remove dissolved air completely. The amount of evolved H2 was determined by using a gas chromatograph (JieDao, GC1609, MS-5A column, TCD, Ar carrier). The temperature of reaction solution was maintained at 293 K provided by water-circulation equipment. The apparent quantum efficiency (AQY) of H2 evolution system at 420 nm was estimated according to the following equations: nphotons =

Pλ hc

AQY[%] =

=

×t

number of reacted electrons number of incident photons

(1) × 100

2 × number of evolved H 2 molecules number of incident photons

× 100

(2)

where P is the input optical power; λ is the wavelength of light source; h is Planck’s constant; c is light speed; and t is the irradiation time. Characterization: X-ray diffraction (XRD) analysis were taken by using a Bruker D8 Advance X-ray diffractometer (Germany) with Cu Kα-source (λ = 0.15406 nm). The 2θ angular regions between 10o and 80o were investigated at a scan rate of 5o min-1. UV-visible absorption spectrum of solution was analyzed by using Varian Cary 50 UV-vis spectrophotometer. The field emission


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scanning electron microscopic (FE-SEM) images of samples were obtained with a Carl Zeiss Gemini (vltra 55) field emission scanning electron microscope. The transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM) images were performed using a JEOL JEM 2010 transmission electron microscope, using a 200 KV accelerating voltage. X-ray photoelectron spectroscopy (XPS) analysis was performed on a VG ESCALAB MKII XPS photoelectron spectrometer with an Al Kα X-ray source. The XPS spectrum was calibrated with respect to the binding energy of C1s peak at 284.8 eV. Raman analysis was measured on a J-Y T64000 Raman spectrometer with a 514.5 nm laser. Photoluminescence (PL) spectra were obtained on an Edinburgh FS5 spectrofluorometer. The emission decay curves were recorded on an Edinburgh LifeSpecⅡspectrofluorometer equipped with a 465 nm picoseconds laser as the light source, and the error is less than 2%. 3. RESULTS and DISCUSSIONS The phases of as-prepared bare RGO, MoS2 and MoS2/RGO composites were determined by XRD, and the results were shown in Figure 1a. As for the bare RGO sample, a broad diffraction peak appearing at 24.6o is attributed to the characteristic (002) plane of graphene, indicating that the graphene oxide was transferred to reduced graphene oxide.46 The XRD patterns of pure MoS2 and MoS2/RGO composites show four main peaks at 14.0o, 33.2o, 39.8o and 59.2o, which are assigned to the (002), (100), (103) and (110) planes of hexagonal MoS2 (JCPDS card no. 751539), respectively.47,48 It has to be noted that the intensity of all the diffraction peaks of MoS2 increases with decreasing proportion of RGO in the MoS2/RGO composites, especially the (002) plane peak, indicating that the introduction of RGO considerably inhibits the (002) plane growth of MoS2 crystals in the composites. It is worth noting that all MoS2/RGO composites are


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principally composed of a hexagonal MoS2 and show no diffraction peaks of RGO. The main reason for this phenomenon may be due to both the weak peak of graphene and the fact that the graphene nanosheets do not stack during the hydrothermal process. That is, the graphene nanosheets can act as a novel substrate for the growth of MoS2 crystals, which inhibits the stacking of graphene during the hydrothermal process. On the other hand, the introduction of graphene nanosheets can also restrain the growth of MoS2 crystals in the MoS2/RGO composites, resulting in the lower intensity of all the diffraction peaks of MoS2.49

Figure 1. (a) XRD patterns of RGO, MoS2 and MoS2/RGO composites; (b) Raman spectra of RGO, MoS2 and MoS2/RGO composites.


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Although the graphene component in MoS2/RGO composites was not observed in the XRD patterns, it can be determined by the following Raman, TEM and XPS analysis. As shown in Figure 1b, the Raman spectrum of bare graphene shows D and G bands at 1341 and 1588 cm-1, respectively. The D band is attributed to the defects and the disordering atomic arrangements of sp3 hybridized carbon atoms, while the G band arises from the plane vibration of sp2 carbon atoms of graphite layer.50 For the bare MoS2 nanosheets, the characteristic peaks are observed at 1 376 and 402 cm-1, which are assigned to E2g and A1g modes 2H-MoS2, respectively.[51] The

Raman spectrum of MoS2/RGO composites, that is Mo1G1, Mo1G5 and Mo10G1, show both D and G bands of graphene as well as the characteristic Raman vibrations of MoS2, confirming that these composites are comprised of RGO and MoS2. More importantly, the intensity ratio of the characteristic Raman vibrations of MoS2 (A1g) to the peak of graphene (D) increases with increasing amounts of MoS2, which is consistent with the composition of MoS2/RGO composites. Figure 2 shows a general view of the morphologies of graphene, MoS2, Mo1G1, Mo5G1 and Mo10G1 synthesized by hydrothermal route. The SEM image illustrated in Figure 2a reveals that the RGO consists of randomly aggregated, thin, crumpled sheets closely associated with each other and forming a disordered solid. As shown in Figure 2b, the free MoS2 obtained through the proposed method consists of large-scale nanosheets that are tightly aggregated together. From the SEM observation, the size of MoS2 nanosheets was observed to be approximately 400-600 nm. After the graphene was incorporated, the synthesized Mo1G1 composite displays a 2D nanoflake structure shown in Figure 2c and d, in which the MoS2 was homogeneously grown on the surface of graphene. When the ratio of MoS2 to RGO increases to 5, the morphology of asprepared RGO/MoS2 composite interestingly changes to a 3D sphere-like architecture, in which plentiful nanosheets in the range 100-300 nm are tightly stacked together (Figure 2e and f).


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Figure 2. SEM images of (a) RGO, (b) MoS2, (c,d) Mo1G1, (e,f) Mo5G1 and (g,h) Mo10G1 composites prepared by hydrothermal route. Similar 3D morphology was also observed for the Mo10G1 composite illustrated in Figure 2g and h. The 3D sphere-like architecture of MoS2/RGO composites was resulted from the graphene self-assembling.52 That is, when the graphene oxide was reduced to RGO during the hydrothermal process, and the flexible graphene is self-assembled into a 3D sphere-like


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architecture by partially overlapping or coalescing. The 3D architectural RGO/MoS2 composites would not only increase the contact area for charge carrier transfer but also provide more active sites for H2 evolution reaction, which could play key factors in determining the photocatalytic performance of MoS2/RGO catalysts.

Figure 3. (a,b) TEM images of RGO, inset of (b) is the magnified HRTEM image of RGO. (c) TEM image of MoS2. (d-f) TEM images Mo1G1. (g-i) TEM images of Mo5G1. (j-l) TEM images of Mo10G1.


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To further investigate the microstructure, the bare RGO, MoS2 and MoS2/RGO composites were characterized by TEM and HRTEM. Figure 3a shows that the bare RGO displays a layered crystal, and the wrinkles on the graphene sheets are clearly observed. The HRTEM image illustrated in Figure 3b shows that the thickness of graphene was observed to be approximately 8-10 nm. Furthermore, visible lattice fringes of 0.34 nm were observed in the magnified HRTEM image inset in Figure 3b, which can be attributed to the (001) plane of graphite.53 Figure 3c shows the HRTEM image of bare MoS2 with interlayer spacing of 0.62 nm, and the single MoS2 nanosheets mainly comprise 12-15 layers. The TEM images of Mo1G1, Mo5G1 and Mo10G1 composites illustrated in Figure 3d-l reveal that the spatial structure of MoS2/RGO composites changes form typical 2D nanoflake to 3D sphere-like architecture with increasing amounts of MoS2, which is consistent with the SEM characterization. From the TEM images of MoS2/RGO composites, it can be clearly seen that the layered MoS2 nanosheets with a length of 50-100 nm were successfully grown on the surface of RGO. The HRTEM images in Figure 3f, I and l show typical 2D MoS2 with an interlayer distance of 0.62 nm, which can be assigned to the (002) plane of hexagonal MoS2.54 Comparing with the HRTEM image of free MoS2, its can be seen that the thickness of MoS2 (5-10 nm) in MoS2/RGO composites is quite thinner than that of bare MoS2 (12-15 nm, illustrated in Figure 3c), indicating the graphene sheets greatly inhibit the grown of MoS2 layers, which is good agreement with the XRD analysis. The XPS analysis was employed to determine the atomic valence states and chemical composition of MoS2/RGO composites, in particular Mo and C. The wide scan spectrum illustrated in Figure 4a shows the binding energy peaks at 163.1, 230.2 and 284.8, which are attributed to S 2s, Mo 3d and C 1s, respectively. Binging energy of 229.6 and 232.8 eV in the high resolution Mo 3d spectra (Figure 4b) are indicative of Mo 3d5/2 and Mo3d3/2, which


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correspond to Mo4+ in a hexagonal structure.55 Figure 4c shows the high resolution XPS spectra of S 2p, where doublet peaks located at 162.4 (S 2p3/2) and 163.6 eV (S 2p1/2) were observed.48 The high resolution C 1s XPS spectrum in Figure 4d can be divided into four peaks located at 284.8 (C-C bond), 286.6 (C-O bond), 287.5 (C=O bond) and 288.2 eV (O-C=O bond).46

Figure 4. (a) XPS spectra of Mo5G1 catalyst; high resolution XPS spectra of Mo5G1 for (b) Mo, (c) S and (d) C 1s. Figure 5 shows the UV-visible absorption spectra of [ZnTMPyP]4+ in aqueous solution, where characteristic porphyrin absorption of a Soret band at 430 nm and Q-bands at 570 nm and 615 nm were observed. Meanwhile, the emission spectrum of [ZnTMPyP]4+ shows a strong emission at 630 nm and a relatively weak emission at 670 nm. Besides, the [ZnTMPyP]4+ complex has suitable redox potentials for photocatalytic H2 evolution reaction.[56,57] Owing to the excellent photophysical and electrochemical properties, [ZnTMPyP]4+ has often been used as an attractive photosensitizer for photocatalytic H2 production.56-59


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Figure 5. UV-Vis absorption and emission spectra of [ZnTMPyP]4+ in aqueous solution. Photocatalytic H2 production experiments were carried out under visible light irradiation (λ > 420 nm) at 293 K in aqueous solutions containing 0.2 mM [ZnTMPyP]4+, 0.2 M TEOA and 40 mg various MoS2/RGO composite catalysts at pH 7. TEOA was used as the sacrificial electron donor because it is capable of transferring an electron to photosensitizer for photoinduced electron transfer reaction.60 The reaction mechanism of TEOA for photocatalytic H2 production was illustrated in Scheme S2. Control experiments under visible light irradiation in the absence of any component of [ZnTMPyP]4+, MoS2/RGO and TEOA produced no appreciable amount of H2. Previously reports have shown that the MoS2 can act as an efficient H2 evolution catalyst after it was loaded on the surface of semiconductor photocatalysts, and the active sites are attributed to the active S atoms on its exposed edges.61-63 In the [ZnTMPyP]4+-MoS2-TEOA photocatalytic system, no appreciable H2 was observed after 4 h of visible light irradiation, which could be assigned to the unavailable electron transfer between [ZnTMPyP]4+ and MoS2 verified by the photoluminescence decay study (Figure S1). It is worth noting that the introduction of graphene can efficiently accelerate electron transfer from [ZnTMPyP]4+ to MoS2.


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Figure 6. (a) Photocatalytic H2 production upon visible light irradiation (λ > 420 nm) of aqueous solutions containing 0.2 mM [ZnTMPyP]4+, 0.2 M TEOA and 40 mg various MoS2/RGO catalysts at pH 7. (b) The effect of pH on H2 evolution in aqueous solutions containing 0.2 mM [ZnTMPyP]4+, 0.2 M TEOA and 40 mg Mo5G1 composite catalyst. To further investigate the interaction between [ZnTMPyP]4+ and MoS2/RGO, the Mo5G1 sample separated from [ZnTMPyP]4+ aqueous solution was investigated by XPS analysis. As shown in Figure S2, the XPS spectra of [ZnTMPyP]4+/Mo5G1 sample exhibits new peaks at 1020.3 and 1043.1 eV, which can be assigned to Zn 2p3/2 and Zn 2p1/2 in [ZnTMPyP]4+, respectively.55 The result indicates that the [ZnTMPyP]4+ can efficiently absorb on the surface of MoS2/RGO, which would play a key factor in improving the electron transfer between [ZnTMPyP]4+ PS and MoS2/RGO catalyst. As shown in Figure 6a, all MoS2/RGO composites are active catalysts, and


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their photocatalytic activities were compared. As can be seen, a much more efficient H2 evolution system was achieved with Mo5G1 catalyst compared to other MoS2/RGO composite catalysts, which can be attributed to the following reasons. When the ratio of RGO to MoS2 is less than 1:5, the activities of MoS2/RGO composite catalysts increase with the increasing content of RGO in the MoS2/RGO composites. This phenomenon is related to the fact that RGO can improve the electron transfer from [ZnTMPyP]4+ to MoS2. However, a further increase of RGO proportion in MoS2/RGO composite catalysts results in a decreasing H2 evolution activity, which could be assigned to the decreasing active sites for H2 generation reaction. After 4 h of visible light irradiation, the turnover number (TON = n(H)/n(MoS2)) with respect to MoS2 exhibited in Mo50G1, Mo20G1, Mo10G1, Mo5G1, Mo2G1, Mo1G1 Mo1G2 and Mo1G4 catalysts were estimated to be 0.4, 1.0, 2.8, 3.8, 3.3, 3.2, 3.0 and 1.8, respectively. The highest activity of H2 evolution system was achieved with Mo5G1 catalyst, which can be attributed to the balance between the benefit of high electrical conductivity of graphene at high graphene content and the need for MoS2 as active sites for H2 generation reaction. These results are consistent with previously reports in which MoS2/RGO composites were used as the catalysts.64,65 Furthermore, control experiment shows that the photocatalytic system consists of 0.2 mM [ZnTMPyP]4+, 40 mg RGO and 0.2 M TEOA produced only 15 µmol H2 after 4 h of visible light irradiation, indicating that the RGO can as an active catalyst for H2 generation reaction. The initial pH value of H2 production system has a marked effect on H2 evolution rate. As illustrated in Figure 6b, the effect of pH value on photocatalytic H2 evolution activity was investigated in aqueous solution consisting of 0.2 mM [ZnTMPyP]4+, 40 mg Mo5G1 catalyst and 0.2 M TEOA under visible light irradiation (λ > 420 nm). The highest H2 evolution efficiency was observed at pH value of 7, achieving a H2 evolution rate of 2560 µmol h-1 g-1. When the pH


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values of reaction solution are ranging from 7 to 10, the H2 production rates decrease along with the increasing pH values, which could be assigned to the reduced concentration of H+. On the other hand, at pHs lower than 7 the TEOA becomes protonated, resulting in the formation of TEOAH+. Because of TEOAH+ is a much less efficient sacrificial electron donor, and the lower pH thereby inhibits the regeneration of [ZnPyMP]4+, which is one of the essential steps for catalyzed H2 production.

Figure 7. (a) Photocatalytic H2 production in aqueous solutions composed of 40 mg Mo5G1 catalyst, 0.2 M TEOA and various concentration of [ZnTMPyP]4+ at pH 7. (b) Effect of catalyst amount on the photocatalytic H2 generation from a system composed of 0.2 mM [ZnTMPyP]4+, 0.2 M TEOA and various amount of Mo5G1 catalyst at pH 7.


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After optimizing the reaction condition of pH value, the effect of [ZnTMPyP]4+ concentration on H2 evolution activity was also investigated in aqueous solutions containing of 40 mg Mo5G1 catalyst, 0.2 M TEOA and a certain amount of [ZnTMPyP]4+ at pH 7. Figure 7a shows the dependence of the steady rate of H2 evolution on the concentration of [ZnTMPyP]4+. When the concentration of [ZnTMPyP]4+ was increased to 0.30 from 0.05 mM, the mole of H2 was increased to 356 from 72 µmol after 4 h of visible light irradiation. However, as the concentration of [ZnTMPyP]4+ was increased to 300 mM, it appears that the amount of H2 produced reaches a plateau (Figure S3). This phenomenon can be related to the optical properties of the [ZnTMPyP]4+ PS; if enough [ZnTMPyP]4+ is present in the system, all the light from the Xe lamp will be harvested and additional [ZnTMPyP]4+ will have no effect. Furthermore, the rate of H2 generation was found to depend on the content of MoS2/RGO composite catalyst. As shown in Figure 7b, the amount of Mo5G1 catalyst can directly influence the photocatalytic H2 evolution. The results show that the H2 evolution efficiency increases remarkably with Mo5G1 catalyst content to a maximum at 40 mg, and then decreases gradually. In the present study, when the amount of Mo5G1 catalyst is less than 40 mg, the H2 generation efficiency increases gradually with the increasing content of Mo5G1 catalyst, which could be assigned to the increasing density of active sites for H2 generation reaction. When the content of Mo5G1 catalyst exceeds 40 mg, the photocatalytic activities decrease gradually with the increasing content of Mo5G1 catalyst. This phenomenon can be assigned to the fact that these larger amounts of black MoS2/RGO catalyst can block light absorption by the [ZnTMPyP]4+ PS. Similar results were also observed in previous studies in which MoS2/RGO composites were used as catalysts.64,65 In order to evaluate the photocatalytic durability of [ZnTMPyP]4+-MoS2/RGO-TEOA system, 24 h cycle H2 production experiments for six times every 4 h were performed. The photocatalytic


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system was evacuated every 4h of visible light irradiation, and then the process was carried out for repeated cycles. As shown in Figure 8a, the cycle tests revealed that the amount of H2 production was proportional to the irradiation time, and the total amount of H2 generation for each cycle experiment was almost the same. Notably, the H2 generation rate during the sixth cycle is 90% that of the first cycle, indicating that both [ZnTMPyP]4+ and MoS2/RGO catalyst have excellent stability for visible-light-driven H2 evolution. Furthermore, the stability of [ZnTMPyP]4+ PS was also demonstrated by UV-Vis spectroscopy and the result was illustrated in Figure S4, in which the [ZnTMPyP]4+ separated from the [ZnTMPyP]4+-Mo5G1-TEOA system by centrifugation after 24 h of visible light irradiation shows absorption spectrum similar to that of fresh [ZnTMPyP]4+. The present system exhibits much higher stability than those similar systems.38,39 After 24 h of visible light irradiation, 1447 µmol H2 was evolved from reaction system and the turnover number with respect to MoS2 (exhibited in Mo5G1 catalyst) and [ZnTMPyP]4+ were estimated to be 14 and 58, respectively. There is no doubt that the H2 generation reaction indeed proceeds catalytically. Under the optimization reaction conditions, the wavelength dependence of photocatalytic H2 generation in the [ZnTMPyP]4+-MoS2/RGO-TEOA system was investigated. Figure 8b shows the AQY as a function of the incident light wavelength, the AQY first increases and then decreases with the increasing wavelength. A maximum AQY of 15.2% was obtained at 420 nm, which is very close to the major absorption wavelength of the [ZnTMPyP]4+ (Figure 5), indicating the H2 generation reaction is driven by [ZnTMPyP]4+. Although this system exhibits a lower apparent quantum yield than those of photocatalytic systems based on

Eosin Y/RGO/NiSx (32.5%),10 and Eosin

Y/RGO/MoS2 (24%)

photocatalysts,14 its activity is comparable to those of many other photocatalytic systems based on Eosin Y/RGO/Pt (9.7%),19 N749/RGO/Pt (0.21%) photocatalysts.12


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Figure 8. (a) Cyclic H2 evolution from a system composed of 0.2 mM [ZnTMPyP]4+, 0.2 M TEOA and 40 mg Mo5G1 catalyst at pH 7 under visible light irradiation from a 300 W Xe lamp (λ > 420 nm). (b) The apparent quantum yield of [ZnTMPyP]4+-MoS2/RGO-TEOA system at different wavelength of incident light.

Emission quenching measurement was used to study the excitation and transfer of photogenerated electron between [ZnTMPyP]4+ and MoS2/RGO. As shown in Figure 9a, with the addition of MoS2/RGO catalysts into the aqueous solution of [ZnTMPyP]4+, the emission of [ZnTMPyP]4+ was quenched obviously. Under excitation at 400 nm, the quenching efficiency of [ZnTMPyP]4+ solution at 610 nm was found to be 51%, 55%, 59%, 63%, 69, 71%, 74% and 79%


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in the presence of 50 µg·ml-1 Mo50G1, Mo20G1, Mo10G1, Mo5G1, Mo2G1, Mo1G1, Mo1G2 and Mo1G4, respectively. The emission quenching is related to the photoinduced electron transfer from excited [ZnTMPyP]4+ to MoS2/RGO composites, which would be one of the key factors in determining the photocatalytic performance. It is worth noting that the emission quenching efficiency increases with the increasing proportion of graphene in the MoS2/RGO composites, which could be attributed to the increasing surface and the strong electron-withdrawing capability of RGO. These results show that the excited state of [ZnTMPyP]4+ can be dynamically

Figure 9. Steady-state photoluminescence of [ZnTMPyP]4+ aqueous solution (20 µM) upon addition of different MoS2/RGO composite catalysts (a) or increasing amounts of Mo1G1 (b), Mo5G1 catalysts (c) and TEOA (d), the samples were excited at λex = 400 nm.


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quenched by RGO/MoS2 catalysts. Meanwhile, the emission intensity decreases with increasing amounts of MoS2/RGO catalysts (Figure 9b,c). Furthermore, the photoluminescence decay study was applied to investigate the electron-transfer kinetics from the excited state of [ZnTMPyP]4+ to different MoS2/RGO catalysts. Figure S5 shows the PL decay results of the [ZnTMPyP]4+ added with different MoS2/RGO composite catalysts. For the original [ZnTMPyP]4+, the PL decay curve can be fitted with a double exponential function with an excited lifetime of 1.72 ns corresponding to the excited state behavior of [ZnTMPyP]4+ ([ZnTMPyP]4+*).58 Interestingly, after the addition of 50 µg·ml-1 Mo20G1, Mo5G1, Mo1G1, Mo1G4 and RGO catalysts into the aqueous solution of [ZnTMPyP]4+, the excited-state lifetime decreased to 1.56, 1.47, 1.39, 1.31 and 1.28 ns, respectively. The lifetime decreases with the increasing proportion of RGO in MoS2/RGO composites, which is consistent with the trend of the emission intensity results (Figure 9a). Then, quenching study was also used to identify the possible electron transfer from TEOA to [ZnTMPyP]4+*. As shown in Figure 9d, the [ZnTMPyP]4+* cannot be reductively quenched by TEOA, indicating the electron transfer from TEOA to [ZnTMPyP]4+* would not occur in this study.

Figure 10. Proposed mechanism for photocatalytic H2 generation in [ZnTMPyP]4+-MoS2/RGOTEOA system under visible light irradiation.


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Based on these above-mentioned photoluminescence emission quenching results, it can be concluded that [ZnTMPyP]4+* can be quenched by MoS2/RGO catalyst through oxidative quenching pathway. As illustrated in Figure 10, under visible light irradiation, the electrons in the highest occupied molecular orbital (HOMO) electrons of [ZnTMPyP]4+ are excited to the lowest unoccupied molecular orbital (LUMO), creating excited-state [ZnTMPyP]4+*. The oxidation potential of [ZnTMPyP]4+* vs. normal hydrogen electrode (NHE) is -1.09 V,66 which is more negative than the graphene/graphene•− redox potential (-0.16 V vs. NHE),67 thus providing the thermodynamic driving force for efficient electron transfer from [ZnTMPyP]4+* to RGO. In addition, the graphene/graphene•− redox potential is also more negative than the conduction band of MoS2 nanosheets (-0.13 V vs. NHE),5 providing ample driving force for the electron transfer from electron-rich graphene to MoS2.68 The edges of MoS2 crystallites can act as the active sites for H2 evolution reaction after they accepted electrons from RGO. Furthermore, the oxidized [ZnTMPyP]4+ ([ZnTMPyP]5+) has a higher oxidation potential than that of TEOA and can be regenerated by reduction with TEOA.66 During the photocatalytic reaction processes, the RGO acted as a conductive electron transport bridge to efficiently accelerate the electron transfer from [ZnTMPyP]4+* to MoS2, thus resulting in the high photocatalytic performance of [ZnTMPyP]4+MoS2/RGO-TEOA system. 4. CONCLUSION In summary, we have constructed an efficient hybrid system for visible-light-driven H2 generation from water by utilizing [ZnTMPyP]4+ as the photosensitizer, MoS2/RGO as the catalyst and TEOA as the sacrificial electron donor. Under the optimized reaction conductions, irradiation of [ZnTMPyP]4+-MoS2/RGO-TEOA system resulted in efficient H2 evolution at a constant of 2560 µmol h-1 g-1 for MoS2/RGO catalyst and an apparent quantum yield of 15.2% at


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420 nm. Such system exhibits high photocatalytic H2 evolution activity due to the positive effect of graphene in improving the charge transfer rate from [ZnTMPyP]4+* to MoS2. The reaction mechanism of [ZnTMPyP]4+-MoS2/RGO-TEOA system for photocatalytic H2 evolution was investigated in detail by luminescence quenching studies, and the results showed that the excited state of [ZnTMPyP]4+ can be quenched by MoS2/RGO catalyst through oxidative quenching pathway. This research provides insight into the design and construction of cost-effective and stable photocatalytic H2 production system that is consisting of only earth-abundant elements. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Additional information including photoluminescence decay curves, XPS spectra, UV-Vis absorption spectra and concentration dependence curve. AUTHOR INFORMATION Corresponding Author: *E-mail: [email protected];*E-mail: [email protected] ORCID: Yong-Jun Yuan: 0000-0002-1823-3174; Daqin Chen: 0000-0003-0088-2480; Wen-Guang Tu: 0000-0002-0800-9777. NOTE The authors declare no competing financial interest. ACKNOWLEDGMENT


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This research was supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No. LQ16B030002, the National Natural Science Foundation of China under Grant No. 51502068 and 51772071, the Zhejiang Provincial Natural Science Foundation for Distinguished Young Scholars under Grant No. LR15E020001 and the National Basic Research Program of China under Grant No. 2013CB632404. REFERENCES 1. Lewis, N. S.; Nocera, D. G. Powering the Planet: Chemical Challenges in Solar Energy Utilization. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 15729-15735. 2. Ma, Y.; Wang, X. L.; Jia, Y. S.; Chen, Y. S.; Han, H. X.; Li, C. Titanium Dioxide-based Nanomaterials for Photocatalytic Fuel Generations. Chem. Rev. 2014, 114, 9987-10043. 3. Yuan, Y. J.; Yu, Z. T.; Chen, D. Q.; Zou, Z. G. Metal-complex Chromophores for Solar Hydrogen Generation. Chem. Soc. Rev. 2017, 46, 603-631. 4. Zhang, P.; Zhang, J. J.; Gong, J. L. Tantalum-based Semiconductors for Solar Water Splitting. Chem. Soc. Rev. 2014, 43, 4395-4422. 5. Yin, X. L.; Li, L. L.; Jiang, W. J.; Zhang, Y.; Zhang, X.; Wan, L. J.; Hu, J. S. MoS2/CdS Nanosheets-on-Nanorod Heterostructure for Highly Efficient Photocatalytic H2 Generation under Visible Light Irradiation. ACS Appl. Mater. Interfaces. 2016, 8, 15258-15266. 6. Luna, A. L.; Dragoe, D.; Wang, K.; Beaunier, P.; Kowalska, E.; Ohtani, B.; Uribe, D. B.; Valenzuela, M. A.; Remita, H.; Colbeau-Justin, C. Photocatalytic Hydrogen Evolution Using Ni–Pd/TiO2: Correlation of Light Absorption, Charge-Carrier Dynamics, and Quantum Efficiency. J. Phys. Chem. C 2017, 121, 14302–14311. 7. Fang, L. J.; Li, Y. H.; Liu, P. F.; Wang, D. P.; Zeng, H. D.; Wang, X. L.; Yang, H. G. Facile Fabrication of Large-Aspect-Ratio g-C3N4 Nanosheets for Enhanced Photocatalytic


26

Page 27 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Hydrogen Evolution. ACS Sustainable Chem. Eng. 2017, 5, 2039-2043. 8. Li, X. Q.; Wang, M.; Zheng, D. H.; Han, K.; Dong, J. F.; Sun, L. C. Photocatalytic H2 Production in Aqueous Solution with Host-guest Inclusions formed by Insertion of an FeFehydrogenase Mimic and an Organic Dye into Cyclodextrins. Energy Environ. Sci. 2012, 5, 8220-8224. 9. Kim, D.; Whang, D. R.; Park, S. Y. Self-Healing of Molecular Catalyst and Photosensitizer on Metal-Organic Framework: Robust Molecular System for Photocatalytic H2 Evolution from Water. J. Am. Chem. Soc. 2016, 138, 8698-8701. 10. Kong, C.; Min, S. X.; Lu, G. X. Dye-Sensitized NiSx Catalyst Decorated on Graphene for Highly Efficient Reduction of Water to Hydrogen under Visible Light Irradiation. ACS Catal. 2014, 4, 2763-2769. 11. Han, Z. J.; Qiu, F.; Eisenberg, R.; Holland, P. L.; Krauss, T. D. Robust Photogeneration of H2 in Water Using Semiconductor Nanocrystals and a Nickel Catalyst. Science 2012, 338, 1321-1324. 12. Huang, J.; Wang, D. D.; Yue, Z. K.; Li, X.; Chu, D. M.; Yang, P. Ruthenium Dye N749 Covalently Functionalized Reduced Graphene Oxide: A Novel Photocatalyst for Visible Light H2 Evolution. J. Phys. Chem. C 2015, 119, 27892-27899. 13. Yuan, Y. J.; Yu, Z. T.; Liu, X. J.; Cai, J. G.; Guan, Z. J.; Zou, Z. G. Hydrogen Photogeneration Promoted by Efficient Electron Transfer from Iridium Sensitizers to Colloidal MoS2 Catalysts. Sci. Rep. 2014, 4, 4045. 14. Min, S. X.; Lu, G. X. Sites for High Efficient Photocatalytic Hydrogen Evolution on a Limited-layered MoS2 Cocatalyst Confined on Graphene Sheets-the Role of Graphene. J. Phys. Chem. C 2012, 116, 25415-25424.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 35

15. Tran, P. D.; Wong, L. H.; Barberb, J.; Loo, J. S. C. Recent Advances in Hybrid Photocatalysts for Solar Fuel Production. Energy Environ. Sci. 2012, 5, 5902-5918. 16. Kim, W.; Tachikawa, T.; Majima, T.; Li, C. H.; Kim, H. J.; Choi, W. Tin-porphyrin Sensitized TiO2 for the Production of H2 under Visible Light. Energ. Environ. Sci. 2010, 3, 1789-1795. 17. Yuan, Y. J.; Zhang, J. Y.; Yu, Z. T.; Feng, J. Y.; Luo, W. J.; Ye, J. H.; Zou, Z. G. Impact of Ligand Modification on Hydrogen Photogeneration and Light-harvesting Applications Using Cyclometalated Iridium Complexes. Inorg. Chem. 2012, 51, 4123-4133. 18. Zhang, J.; Du, P. W.; Schneider, J.; Jarosz, P.; Eisenberg, R. Photogeneration of Hydrogen from Water Using an Integrated System Based on TiO2 and Platinum(II) Diimine Dithiolate Sensitizers. J. Am. Chem. Soc. 2007, 129, 7726-7727. 19. Min, S. X.; Lu, G. X. Dye-Sensitized Reduced Graphene Oxide Photocatalysts for Highly Efficient Visible-Light-Driven Water Reduction. J. Phys. Chem. C 2011, 115, 13938-13945. 20. Han, W. S.; Wee, K. R.; Kim, H. Y.; Pac, C.; Nabetani, Y.; Yamamoto, D.; Shimada, T.; Inoue, H.; Choi, H.; Cho, K.; et al. Hydrophilicity Control of Visible-Light Hydrogen Evolution and Dynamics of the Charge-Separated State in Dye/TiO2/Pt Hybrid Systems. Chem. Eur. J. 2012, 18, 15368-15381. 21. Park, Y.; Kim, W.; Monllor-Satoca, D.; Tachikawa, T.; Majima, T.; Choi, W. Role of Interparticle Charge Transfers in Agglomerated Photocatalyst Nanoparticles: Demonstration in Aqueous Suspension of Dye-Sensitized TiO2. J. Phys. Chem. Lett. 2013, 4, 189-194. 22. Li, L. L.; Diau, E. W. G. Porphyrin-sensitized Solar Cells. Chem. Soc. Rev. 2013, 42, 291304. 23. Zhang, A.; Li, Cheng.; Yang, F.; Zhang, J.; Wang, Z.;Wei, Z.; Li, W. An Electron Acceptor with Porphyrin and Perylene Bisimides for Efficient Non-Fullerene Solar Cells. Angew.


28

Page 29 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Chem. Int. Ed. 2017, 56, 2694-2698. 24. Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-sensitized Solar Cells with 13% Efficiency Achieved Through the Molecular Engineering of Porphyrin Sensitizers. Nat. Chem. 2014, 6, 242-247. 25. Xie, Y. S.; Tang, Y. Y.; Wu, W. J.; Wang, Y. Q.; Liu, J. C.; Li, X.; Tian, H.; Zhu, W. H. Porphyrin Cosensitization for a Photovoltaic Efficiency of 11.5%: A Record for NonRuthenium Solar Cells Based on Iodine Electrolyte. J. Am. Chem. Soc. 2015, 137, 1405514058. 26. Graham, D. J.; Nocera, D. G. Electrocatalytic H2 Evolution by Proton-Gated Hangman Iron Porphyrins. Organometallics 2014, 33, 4994-5001. 27. Lee, C. H.; Dogutan, D. K.; Nocera. D. G. Hydrogen Generation by Hangman Metalloporphyrins. J. Am. Chem. Soc. 2011, 133, 8775-8777. 28. Mondal, B.; Sengupta, K.; Rana, A.; Mahammed, A.; Botoshansky, M.; Dey, S. G.; Gross, Z.; Dey, A. Cobalt Corrole Catalyst for Efficient Hydrogen Evolution Reaction from H2O under Ambient Conditions: Reactivity, Spectroscopy, and Density Functional Theory Calculations. Inorg. Chem. 2013, 52, 3381-3387. 29. Lei, H. T.; Han, A. L.; Li, F. W.; Zhang, M. N.; Han, Y. Z.; Du, P. W.; Lai, W. Z.; Cao, R. Electrochemical, Spectroscopic and Theoretical Studies of a Simple Bifunctional Cobalt Corrole Catalyst for Oxygen Evolution and Hydrogen Production. Phys. Chem. Chem. Phys. 2014, 16, 1883-1893. 30. Han, Y. Z.; Fang, H. Y.; Jing, H. Z.; Sun, H. L.; Lei, H. T.; Lai, W. Z.; Cao. R. Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

Evidence for a Homolytic Hydrogen-Evolution Reaction. Angew. Chem. Int. Ed. 2016, 55, 5457-5462. 31. Lei, H. T.; Fang, H. Y.; Han, Y. Z.; Lai, W. Z.; Fu, X, F,; Cao. R. Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles. ACS Catal. 2015, 5, 51455153. 32. Ladomenoua, K.; Natalib, M.; Iengoc, E.; Charalampidisa, G.; Scandolab, F.; Coutsolelos, A. G. Photochemical Hydrogen Generation with Porphyrin-Based Systems. Coord. Chem. Rev. 2015, 304, 38-54. 33. Zhang, W.; Lai, W. Z.; Cao, R. Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrinand Corrole-Based Systems. Chem. Rev. 2017, 117, 3717-3797. 34. Kim, W.; Tachikawa, T.; Majima, T.; Li, C.; Kim, H. J.; Choi, W. Tin-Porphyrin Sensitized TiO2 for the Production of H2 under Visible Light. Energy Environ. Sci. 2010, 3, 1789-1795. 35. Zhu, M. S.; Li, Z.; Xiao, B.; Lu, Y. T.; Du, Y. K.; Yang, P.; Wang, X. M. Surfactant Assistance in Improvement of Photocatalytic Hydrogen Production with the Porphyrin Noncovalently Functionalized Graphene Nanocomposite. ACS Appl. Mater. Interfaces. 2013, 5, 1732-1740. 36. Lazarides, T.; Delor, M.; Sazanovich, I. V.; McCormick, T. M.;

Georgakaki, I.;

Charalambidis, G.; Weinstein, J. A.; Coutsolelos, A. G. Photocatalytic Hydrogen Production from a Noble Metal Free System Based on a Water Soluble Porphyrin Derivative and a Cobaloxime Catalyst. Chem. Commun. 2014, 50, 521-523. 37. Salzl, S.; Ertl, M.; Knör, G. Evidence for Photosensitised Hydrogen Production from Water in the Absence of Precious Metals, Redox-Mediators and Co-catalysts. Phys. Chem. Chem. Phys. 2017, 19, 8141-8147.


30

Page 31 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


38. Yuan, Y. J.; Lu, H. W.; Ji, Z. G.; Zhong, J. S.; Ding, M. Y.; Chen, D. Q.; Li, Y. H.; Tu, W. G.; Cao, D. P.; Yu, Z. T.; et al. Enhanced Visible-Light-Induced Hydrogen Evolution from Water in a Noble-Metal-Free System Catalyzed by ZnTCPP-MoS2/TiO2 Assembly. Chem. Eng. J. 2015, 275, 8-16. 39. Yuan, Y. J.; Tu, J. R.; Ye, Z. J.; Lu, H. W.; Ji, Z. G.; Hu, B.; Li, Y. H.; Cao, D. P.; Yu, Z. T.; Zou, Z. G. Visible-Light-Driven Hydrogen Production from Water in a Noble-Metal-Free System Catalyzed by Zinc Porphyrin Sensitized MoS2/ZnO. Dyes and Pigments 2015, 123, 285-292. 40. Han, C.; Zhang, N.; Xu, Y. J. Structural Diversity of Graphene Materials and Their Multifarious Roles in Heterogeneous Photocatalysis. Nano Today 2016, 11, 351-372. 41. Zhang, N.; Yang, M. Q.; Liu, S. Q.; Sun, Y. G.; Xu, Y. J. Waltzing with the Versatile Platform of Graphene to Synthesize Composite Photocatalysts. Chem. Rev. 2015, 115, 10307-10377. 42. Yang, M. Q.; Han, C.; Xu, Y. J. Insight into the Effect of Highly Dispersed MoS2 versus Layer-Structured MoS2 on the Photocorrosion and Photoactivity of CdS in Graphene-CdSMoS2 Composites. J. Phys. Chem. C 2015, 119, 27234-27246. 43. Yang, M. Q.; Zhang, N.; Pagliaro, M.; Xu, Y. J. Artificial Photosynthesis over GrapheneSemiconductor Composites. Are We Getting Better? Chem. Soc. Rev. 2014, 43, 8240-8254. 44. Mizutaru, T.; Marzun, G.; Kohsakowski, S.; Barcikowski, S.; Hong, D.; Kotani, H.; Kojima, T.; Kondo, T.; Nakamura, J.; Yamamoto, Y. Peptide Cross-linkers: Immobilization of Platinum Nanoparticles Highly Dispersed on Graphene Oxide Nanosheets with Enhanced Photocatalytic Activities. ACS Appl. Mater. Interfaces. 2017, 9, 9996-10002. 45. Harriman, A.; Porter, G.; Walters, P.; Photo-oxidation of Metalloporphyrins in Aqueous Solution. J. Chem. Soc. Faraday Trans. 1 1983, 79, 1335-1350.


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46. Wang, P.; Zhai, Y.; Wang, D.; Dong, S. Synthesis of Reduced Graphene Oxide-Anatase TiO2 Nanocomposite and Its Improved Photo-induced Charge Transfer Properties. Nanoscale 2011, 3, 1640-1645. 47. Chang, K.; Geng, D.; Li, X.; Yang, J.; Tang, Y.; Cai, M.; Li, R. Y.; Sun, X. L. Ultrathin MoS2/Nitrogen-Doped Graphene Nanosheets with Highly Reversible Lithium Storage. Adv. Energy. Mater. 2013, 3, 839-844. 48. Zhou, W.; Yin, Z.; Du, Y.; Huang, X.; Zeng, Z.; Fan, Z.; Liu, H.; Wang, J. Y.; Zhang, H. Synthesis of Few-Layer MoS2 Nanosheet-Coated TiO2 Nanobelt Heterostructures for Enhanced Photocatalytic Activities. Small 2013, 9, 140-147. 49. Chang, K.; Chen, W. X. L-Cysteine-Assisted Synthesis of Layered MoS2/Graphene Composites with Excellent Electrochemical Performances for Lithium Ion Batteries. ACS Nano 2011, 5, 4720-4728. 50. Park, S.; An, J.; Jung, I.; Piner, R. D.; An, S. J.; Li, X.; Velamakanni, A.; Ruoff, R. S. Colloidal Suspensions of Highly Reduced Graphene Oxide in a Wide Variety of Organic Solvents. Nano Lett. 2009, 9, 1593-1597. 51. Bang, G. S.; Woo Nam, K.; Kim, J. Y.; Shin, J.; Choi, J. W.; Choi, S. Y. Effective LiquidPhase Exfoliation and Sodium Ion Battery Application of MoS2 Nanosheets ACS Appl. Mater. Interfaces. 2014, 6, 7084-7089. 52. Xu, Y.; Sheng, K.; Li, C.; Shi, G. Self-Assembled Graphene Hydrogel via a One-Step Hydrothermal Process. ACS Nano 2010, 4, 4324-4330. 53. Chen, Z.; Ren, W.; Gao, L.; Liu, B.; Pei, S.; Cheng, H. M. Three-Dimensional Flexible and Conductive Interconnected Graphene Networks Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 424-428.


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Page 33 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


54. Yuan, Y. J.; Ye, Z. J.; Lu, H. W.; Hu, B.; Li, Y. H.; Chen, D. Q.; Zhong, J. S.; Yu, Z. T.; Zou, Z. G. Constructing Anatase TiO2 Nanosheets with Exposed (001) Facets/Layered MoS2 TwoDimensional Nanojunctions for Enhanced Solar Hydrogen Generation. ACS Catal. 2016, 6, 532-541. 55. Yuan, Y. J.; Tu, J. R.; Ye, Z. J.; Chen, D. Q.; Hu, B.; Huang, Y. W.; Chen, T. T.; Cao, D. P.; Yu, Z. T.; Zou, Z. G. MoS2-Graphene/ZnIn2S4 Hierarchical Microarchitectures with an Electron Transport Bridge between Light-Harvesting Semiconductor and Cocatalyst: A Highly Efficient Photocatalyst for Solar Hydrogen Generation. Appl. Catal. B. Environ. 2016, 188, 13-22. 56. Harriman, A.; Porter, G.; Richoux, M. C. Colloidal Platinum Catalysts for the Reduction of Water to Hydrogen, Photosensitised by Reductive Quenching of Zinc Porphyrins. J. Chem. Soc. Faraduy Trans. 2 1981, 77, 1939-1948. 57. Harriman, A.; Porter, G.; Richoux, M. C. Photosensitised Reduction of Water to Hydrogen Using Water-Soluble Zinc Porphyrins. J. Chem. Soc. Faraday Trans. 2 1981, 77, 833-844. 58. Kalyanasundaram, K. Photochemistry and Sensitized Evolution of Hydrogen from Water Using Water-Soluble Cationic Porphyrins. J. Chem. Soc. Faraday Trans. 2 1983, 79, 13651374. 59. Persaud, L.; Bard, A. J.; Campion, A.; Fox, M. A.; Mallouk, T. E.; Webber, S. E.; White, J. M. Photochemical Hydrogen Evolution via Singlet-State Electron-Transfer Quenching of Zinc Tetra(N-methyl-4-pyridy1)porphyrin Cations in a Zeolite L Based System. J. Am. Chem. Soc. 1987, 109, 7309-7314. 60. Kalyanasundaram, K. Hydrogen Evolution from Water by Visible Light, a Homogeneous Three Component Test System for Redox Catalysis. Helv. Chim. Acta. 1978, 61, 2720-2730.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 35

61. Sabbah, H.; Biennier, L.; Sims, I. R.; Georgievskii, Y.; Klippenstein, S. J.; Smith, I. W. M. Identification of Active Edge Sites for Electrochemical H2 Evolution from MoS2 Nanocatalysts. Science 2007, 317, 100-102. 62. Kibsgaard, J.; Chen, Z. B.; Reinecke, B. N.; Jaramillo, T. F. Engineering the Surface Structure of MoS2 to Preferentially Expose Active Edge Sites for Electrocatalysis. Nat. Mater. 2012, 11, 963-969. 63. Yuan, Y. J.; Lu, H. W.; Yu, Z. T.; Zou, Z. G. Noble-Metal-Free Molybdenum Disulfide Cocatalyst for Photocatalytic Hydrogen Production. ChemSusChem 2015, 8 , 4113-4127. 64. Xiang, Q. J.; Yu, J. G.; 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. 65. Chang, K.; Mei, Z. W.; Wang, T.; Kang, Q.; Ouyang, S. X.; Ye, J. H. MoS2/Graphene Cocatalyst for Efficient Photocatalytic H2 Evolution under Visible Light Irradiation. ACS Nano. 2014, 8, 7078-7087. 66. Akatsuka, K.; Ebina, Y.; Muramatsu, M.; Sato, T.; Hester, H.; Kumaresan, D.; Schmehl, R. H.; Sasaki, T.; Haga, M. Photoelectrochemical Properties of Alternating Multilayer Films Composed of Titania Nanosheets and Zn Porphyrin. Langmuir 2007, 23, 6730-6736. 67. Lin, Y.; Zhang, K.; Chen, W.; Liu, Y.; Geng, Z.; Pan, J. Z, N.; Yan, L. F.; Wang, X. P.; Hou, J. G. Dramatically Enhanced Photoresponse of Reduced Graphene Oxide with Linker-Free Anchored CdSe Nanoparticles. ACS Nano 2010, 4, 3033-3038. 68. Choi, S. H.; Shaolin, Z.; Yang, W. Layer-Number-Dependent Work Function of MoS2 Nanoflakes. J. Korean. Phys. Soc. 2014, 64, 1550-1555.


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Construction of a Noble-Metal-Free Photocatalytic H2 Evolution

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