g-C3N4 for Enhanced

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2D-2D heterostructured UNiMOF/g-C3N4 for enhanced photocatalytic H2 production under visible-light irradiation Aihui Cao, Lijuan Zhang, Yun Wang, Huijun Zhao, Hong Deng, Xueming Liu, Zhang Lin, Xintai Su, and Fan Yue ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05396 • Publication Date (Web): 27 Dec 2018 Downloaded from http://pubs.acs.org on December 27, 2018

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ACS Sustainable Chemistry & Engineering

2D-2D

heterostructured

UNiMOF/g-C3N4

for

enhanced

photocatalytic H2 production under visible-light irradiation Aihui Caoa, Lijuan Zhangb, Yun Wangc, Huijun Zhaoc, Hong Dengb, Xueming Liub, Zhang Linb, Xintai Sub, Fan Yuea* a

Ministry Key Laboratory of Oil and Gas Fine Chemicals, College of the Chemistry and

Chemical Engineering, Xinjiang University, Urumqi 830046, China. b

The Key Laboratory of Pollution Control and Ecosystem Restoration in Industry Clusters

(Ministry of Education), School of Environment and Energy, South China University of Technology, Guangzhou 510006, China c

Centre for a Clean Environment and Energy Griffith University Gold Coast Campus,

Queensland 4222, Australia *Corresponding author E-mail: [email protected] ABSTRACT: Based on ultrathin two-dimensional (2D) nickel metal organic framework (UNiMOF) nanoflakes and 2D g-C3N4 nanoflakes, fresh visible-light-driven 2D/2D heterostructure catalysts were designed, which was assembled with a simplistic electrostatic selfassembly process. The photocatalytic performance of UNiMOF/g-C3N4 for H2 production evaluated in visible light. The hydrogen evolution of 25.0% UNiMOF/g-C3N4 (UNG-25.0) heterojunction was 20.03 µmol h-1, which was greater than that of pure g-C3N4. In addition, the 1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

UNG composites also presented more excellent photocatalytic activity than that of bulk NiMOF/gC3N4 (BNG) hybrid. This enhanced performance may depend on cooperative potentiation between UNiMOF and g-C3N4 efficiently lowering recombination of carriers. This work showed that constructing 2D-2D heterojunctions provide a feasible approach to obtain highly capable catalysts for photocatalytic decomposition of water. KEYWORDS: Ultrathin NiMOF; carbon nitride; heterojunction; photocatalytic hydrogen evolution. INTRODUCTION To alleviate the energy crisis, water splitting into hydrogen evolution has become a hot issue since researchers discovered this phenomenon.1 To fully utilize efficient, nontoxic, and stable solar light,2 researchers have discovered oxides and the nitrogen oxides semiconductor3 shown the photocatalytic activity. However, most semiconductors could only absorb the 4% UV light from the available sunlight, which greatly prevent its feasible applications for solar energy.4 Consequently, it is extremely necessary to prepare some photocatalysts responding to visible light. g-C3N4, as a kind of nonmetal semiconductor material, has appealed the notice of many researchers, because of its simple synthesis process, superior electronic band position, good chemical stability and “earth-abundant” reserves.5-7 However, owing to speedy recombination of carriers, bare gC3N4 with low photocatalytic efficiency was unfavorable for H2 evolution. Subsequently, some modification strategies aimed at improving photocatalytic activity of pristine g-C3N4 had been developed, including doping element, controlling morphology,8-10 forming the heterojunction11-13

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and coupling with co-catalysts.14, 15 Among all these strategies, forming the heterojunction had been considered as a promising way to improve photocatalytic efficiency. Considering merits of heterojunction, most composites associated with g-C3N4 had been reported, for instance TiO2/gC3N4,16 ZnO/g-C3N4,17 WO3/g-C3N4,18 CdS/g-C3N4,19 Bi2WO6/g-C3N4, 20 and Ag3PO4/g-C3N4.21 These composites displayed excellent catalytic activity than pure g-C3N4, which had been described in water splitting and photocatalytic degradation. Constructing heterojunction can accelerate separation of carriers improving photocatalytic performance. Although various heterostructures have been constructed, the construction of heterostructures is remain big challenges. Metal organic framework (MOF) as an cribellate material composed of metal nodes and organic connectors has been broadly utilized in field of gas storage and catalysis.22 Previous studies showed that MOFs and metal oxide semiconductors have similar properties, such as being able to generate electron-hole pairs by photoexcitation.23 Metal ions in metal oxides are linked through oxygen ions, while organic links in MOFs have similar functions on oxygen ions in metal oxides.24 Therefore, it can be considered that the outer orbit of metal center constituted the conductive band position of MOF, the outer orbit of the organic connector composed the valence band position of MOF.25 In recent years, MOFs as photocatalysts has aroused tremendous attentions. For example, Zr-MOFs was applied to CO2 reduction.26,

27

Dye-sensitized MOF had been reported for

photocatalytic hydrogen production.28 Very recently, Xiu-Li Yang groups reported MOFs photosensitized TiO2 co-catalyst applied in photocatalytic dye degradation.29 Although MOFs 3 ACS Paragon Plus Environment


have made great progress in the field of photocatalytic water decomposition, these materials are still constrained by the low efficiency of photocatalytic conversion efficiency, limited light harvesting, or poor stabilities. Very recently, ultrathin two-dimensional (2D) nanosheets (UMOF), have been reported in photoelectrocatalysis.30 Comparing with three-dimensional (3D) polymers and bulk 2D MOFs, UMOFs possessed most merits i.e: effective electron transfer can be promoted by nanometer thickness; more exposed catalytic active surfaces to ensure optimal catalytic activity by efficiently interacting with unsaturated metal sites;31 apparent surface atomic structures and bonding preparation to be simply recognizable and tunable.32 Based on the above advantages of 2D MOFs, interesting results can be obtained by using it in photocatalytic water decomposition to produce hydrogen. To augment photocatalytic activity of pure g-C3N4, a novel 2D/2D heterojunction photocatalyst was designed coupling UNiMOF and g-C3N4 (named as UNG-x, x is the mass content of UNiMOF in hybrids) via an electrostatic self-assembly method. Photocatalytic efficiency of individually gC3N4 and UNiMOF was very low in visible light. However, the formation of heterojunction at their interfaces can greatly cause decrease of recombination of carriers. The UNG-25.0 sample exhibited better photocatalytic performance (20.03 µmol h-1) with EQE of 0.979% at 420 nm. The excellent catalytic performance of UNG ascribed the structure of 2D/2D heterojunction as well as special thickness of UNiMOF. Above results indicate the great potential of highly efficient hydrogen-producing photocatalytic materials using MOFs-g-C3N4 2D heterostructure. EXPERIMENTAL SECTION


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Materials ：Urea, NiCl2·6H2O (99.99%, AR grade) and CoCl2·6H2O (99.99%, AR grade) were got from Sinopharm Co., Ltd. Benzene dicarboxylic acid (BDC) and N, N-dimethylformamide (DMF, (CH3)2NCHO) were obtained in Alfa Aesar Co. Triethanolamine (TEOA) and Methanol (CH3OH) were attained from Tianjin Zhiyuan Co. Ltd. Triethylamine (TEA) was obtained from Tianjin Fuyu Co. Ltd. All reagents had not been purified. Synthesis of g-C3N4 ：According to a modified reported literature,33 g-C3N4 was prepared using polycondensation reaction. Synthesis of UNiMOF：UNiMOF was prepared by ultrasonic assisted method.34 Typically, the mixed solution consisted of 32 mL DMF, 2 mL water and 2 mL ethanol were put into a polytetrafluoro-ethylene (PTFE) tube, then 0.75 mmol of BDC was dispersed, and followed by the ultra-sonication of mixture for 15 minutes. Subsequently, 0.75 mmol of NiCl2·6H2O was added into the over suspension and continually ultrasonicated. Thereafter, a certain amount of TEA was rapidly put into above solution getting the uniform colloidal suspension. At last, above solution was ultra-sonicated for 8 h (40 Hz). After 8 h, above solution was centrifugalized, washed and dried getting UNiMOF sample. Similarly, UCoMOF was also synthesized by ultrasonic method, except that 0.75 mmol of Ni2+ was replaced by 0.75 mmol of Co2+. Synthesis of bulk NiMOF and bulk CoMOF：We prepared the bulk NiMOF and bulk CoMOF materials by a hydrothermal method.34 First, 0.75 mmol BDC and 0.75 mmol NiCl2·6H2O were added to the mixed solution consisted of 32 mL DMF, 2 mL water and 2 mL ethanol, and the mixture solution shifted to 100 mL Teflon vessel for reaction at 140 oC for 48 h. The preparation 5 ACS Paragon Plus Environment


of bulk CoMOF was just similar with that of bulk NiMOF. Synthesis of UNG: Composites of UNiMOF/g-C3N4 named as UNG-x (x = 0, 6.25, 11.76, 16.67, 21.05, 25.0, 28.57 and 33.33), where x was the mass percent. The preparation of UNG-x by the simple methods as follows ： As-prepared g-C3N4 and UNiMOF with different mass were dispersed in 80 mL of methyl alcohol to form a shallow green solution with ultra-sonification for 60 min, and then gradually removed the methyl alcohol under heating at 70 oC. In addition, the synthesized UCoMOF/g-C3N4 was named as UCG-x (x = 25.0), which was similar with that of UNiMOF. The preparation of bulk NiMOF/g-C3N4 called BNG-x (x = 25.0) was just like UNiMOF/g-C3N4. Catalysts characterization: By X-ray diffraction (XRD, BRUKER D8 with Cu kα radiation), the crystal structure of samples can be got. Morphology and composition of material were described by a transmission electron microscopy (TEM, HitachiH-600). AFM measurements were tested on an Asylum MFP-3D instrument. An ultraviolet-visible (UV-vis) adsorption spectrum was determined by a Hitachi spectrophotometer. Ultraviolet photoelectron spectroscopy (UPS) and valance band X-ray photoelectron spectroscopy (VBXPS) were tested by Thermo Fisher Company (ESCALAB 250 xi). The zeta potential was recorded on a Nanozs 90 (Malvern), the solvent was ethanol. All the data of zeta potential were the average of three times. Photoluminescence Spectra (PL) of the composites were characterized with a fluorescence spectrophotometer (HitachiF-4500) with exciting wavelength of 370 nm. XPS analysis was carried out with an Al Kα (1486.8 eV) Xray source and Thermo XPS ESCALAB 250 xi device. 6 ACS Paragon Plus Environment

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Photoelectrochemical (PEC) measurements：Electrochemical measurements were tested by a CHI660D electrochemical workstation (Chenhua Instrument, Shanghai, China). The equipment used three-electrode system included a counter electrode, reference electrode and the working electrodes. The method of working electrode was as follows: under magnetic stirring, 5 mg catalyst was dispersed in 1 mL ethanol to obtain uniform solution, and then the mixture solution was pasted onto an FTO (1.5 cm × 2.5 cm) class substrate with same size and parallel thickness. Furthermore, prepared electrode baked at 110 oC for 14 h under the vacuum condition. The electrolyte was 0.5 M of Na2SO4 aqueous solution. Photocatalytic H2 generation test ： The photocatalytic activity was valued by a quartz glass photo-reactor bought from Perfect Light Company of China. The 300 W Xe lamp with 420 nm cut-off filter was used as a source of visible light. During testing, 50 mg catalyst was put in 90 mL water mixed with TEOA (10 mL) without deposition of co-catalyst. Next, make sure the whole system is in a vacuum. Last, the hydrogen concentration was evaluated by a thermal conductive detector. External quantum efficiency (EQE) was measured by 420 nm filter and calculated using the equation (1): 𝐸𝑄𝐸(%) =

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑒 𝐻2 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 × 2 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑝ℎ𝑜𝑡𝑜𝑛𝑠

RESULTS AND DISCUSSION


(1)


Figure 1. Diagram of the preparation of the UNG heterojunction. Preparation of UNG sample divided into two steps shown in Figure 1. First step was to get gC3N4 nanosheet by ultrasound in methyl alcohol solution. Next, as prepared UNiMOF with mass ratio append to g-C3N4 solution, and then UNiMOF coated on the plan of g-C3N4 by an electrostatic self-assembly interaction and  stacking. Evidently, the zeta potential of UNiMOF was 31.5 mV dispersed in ethanol solution seen in Figure S1, whereas the dispersed g-C3N4 in ethanol was negative charge consistent with the previously reported.35 This results further proved that the heterostructure may form between UNiMOF and g-C3N4 via an electrostatic self-assembly process. Figure 2 exhibited XRD patterns of samples, two obvious diffraction peaks of UNG-25.0 and BNG-25.0 could be clearly observed in the degree around 13.0o and 27.7o, respectively matching to (001) and (002) plane of g-C3N4. The two planes mainly attributed to the inter-planar stacking peak of the tri-s-triazine unit and the lattice plane structure.36, 37 Besides, the same crystalline phase 8 ACS Paragon Plus Environment

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of UNiMOF and bulk NiMOF had completely presented in Figure 2, which revealed an obvious diffraction peaks at about 6o and three weak diffraction peaks going with the simulated NiMOF (no. 985792, space group of C2/m, Cambridge Crystallo graphic Data Centre).38 The four obvious diffraction peaks matched to (200), (001), (201) and (-201) crystal faces of NiMOF, respectively. Compare with UNiMOF, the bulk NiMOF displayed a high crystal phase. The XRD pattern of UNG-25.0 composites proved the existence of UNiMOF and g-C3N4. Besides, the XRD pattern of other composites showed in Figure S2.

Figure 2. XRD graph of the g-C3N4 and the corresponding UNG-x samples with different percentage amount of UNiMOF. Figure 3a indicated the TEM of the pure g-C3N4 with several stacking layers structure. The 2D nanosheet structure of UNiMOF was observed from the Figure 3b, in which the edges of the thinner nanosheets were slightly curled. The thickness of the UNiMOF was about 3.04 nm determined by AFM (Figure S3). As shown in Figure 3c, UNiMOF nanosheets were uniformly 9 ACS Paragon Plus Environment


adhered to the plane of g-C3N4 nanoflakes, which illustrated g-C3N4 co-exist with UNiMOF. Furthermore, by the HRTEM analysis (Figure 3e), some Ni particles can be discovered under the surface of UNiMOF, due to ultra-thin structure of NiMOF that can easily partial thermal decomposition under high energy electron beam irradiation.39 Figure 3f showed the distinguished connection between g-C3N4 and UNiMOF, which can form heterojunction. Elemental mapping analysis (Figure 3g-k) further proved that UNG-25.0 sample consisted of C, N, O, and Ni elements. In addition, the TEM image (Figure S4a) showed that bulk NiMOF had similar 2D morphology with UNiMOF, the composites of BNG, BCG and UCG also exhibited that the MOF stuck on surface of g-C3N4 (Figure S4b-d). Above results were in accordance with XRD.


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Figure 3. TEM and HERTEM image of pure g-C3N4 (a, d), pure UNiMOF (b, e), UNG-25.0 (c, f); HAADF-STEM image of UNG-25.0, and the (h) C, (i) N, (j) O, (k) Ni elemental mapping for the selected area in (g). XPS was measured to ascertain surface species and chemical states of g-C3N4, UNiMOF and UNG-25.0 presented in Figure 4a-d. As illustrated in Figure S5, entail spectrum of the UNG-25.0 composite demonstrated that the samples mainly consisted of C, N, O and Ni element at binding energy of 285 eV (C1s), 399 eV, (N1s), 531 eV (O1S) and 856.5 eV (Ni2p). Other peak at 856.5 eV was obviously observed from UNG-25.0 composite, which was mainly due to the existence of 11 ACS Paragon Plus Environment


Ni atoms. Figure 4a showed that two peaks of C1s centered at 285.1, 288.7 eV. At 288.7 eV was corresponded to C-N-C and C-(N)3 in the s-triazine rings.40 The peak at 285.1 eV can be considered as C-C, the peak of 286.1 eV was due to the presence of C-O.41, 42 Figure 4b displayed the N1s peak at 398.7, 399.7, and 400.9 eV, which corresponded to sp2 C-N-C, sp3 H-N-[C]3,40 and CNH. As shown in Figure 4c, the O1s peak at 531.45 eV can be ascribed to Ni-O coordination bonds in UNiMOF lattice, while the well-resolved peak at 532.84 eV can be allocated to µ3-OH group in UNiMOF.32 In Figure 4d, the peak at 873.1 and 879.2 eV were the characteristic Ni 2p1/2 peak and its satellite peak, respectively. The typical Ni 2p3/2 peak (855.6 eV) and its satellite peak (861.2 eV) were presented. Above analysis confirmed the existence of Ni2+ in UNiMOF.32


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Figure 4. XPS spectra of UNG-25.0 (a) C1s, (b) N1s, (c) O1s and (d) Ni2p. As showed in Figure 5a, pristine g-C3N4 and UNG-25.0 composite exhibited same UV-vis absorption peak near 450 nm matching to intrinsic band gap of g-C3N4 ascribing to -* transitions in heterocyclic ring.14, 43 And the UNiMOF only absorbed the UV-vis light before 350 nm. Besides, the band gap of samples also showed in Figure 5a.

Figure 5. (a) UV spectra of g-C3N4, UNiMOF and UNG-25.0; (b) PL spectra of g-C3N4 and UNG-25.0; (c) UPS spectrum of UNiMOF; (d) Valance band XPS spectrum of UNiMOF. The separation efficiency of carriers was characterized by photoluminescence spectra. In Figure 13 ACS Paragon Plus Environment


5b, g-C3N4 showed a diffraction peak at 470 nm that mainly attributed to the high association of carries.16 Compared to pure g-C3N4, UNG-25.0 composite presented a weaker emission peak, which showed the composites had a high separation rate of carriers. Meanwhile, photocatalytic efficiency and light utilization were improved. Photocatalytic Activity The photocatalytic performance for hydrogen evolution of UNG composites with different UNiMOF contents was investigated using a water/TEOA mixture solution. As showed in Figure 6a, g-C3N4 revealed negligible photocatalytic activity. It is generally thought be due to the recombination of carriers and shortage of active site.5 However, UNG sample exhibited an ideal hydrogen evolution rate. The effect of UNiMOF content on H2 evolution was also systematically investigated, and as the content of UNiMOF increased, its photocatalytic performance increased gradually. The UNG-25.0 catalyst showed the best catalytic activity, and its photocatalytic rate can reach 20.03 μmol h-1. When content of UNiMOF exceeded 25%, photocatalytic performance decreased, possibly because high MOF loading can shelter the surfaceactive sites of g-C3N4 and prevent g-C3N4 contacting with sacrificial agents or water molecules. Other reason was that excessive MOF will shield the absorption of photons, thus reducing the photocatalytic activity. Furthermore, to observe universalism of UNiMOF, the other MOF modified g-C3N4 with equal content were prepared to compare the photocatalytic performance under the same conditions. As shown in Figure 6b, UCG, BNG and BCG samples exhibited weaker photocatalytic activity than that of UNG samples. Above results further proved that the ultrathin structure was available to transfer electron. Compare with UCG, UNG showed good photocatalytic 14 ACS Paragon Plus Environment

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activity. The main reason for this was that for a single UNiMOF, there were more unoccupied empty electron orbitals to provide more unsaturated Ni sites, which can easily reduce the hydrogen ions in water to produce hydrogen gas.34, 50 Further evaluation of photocatalytic activity of samples under UV light shown in Figure S6. It can be found that pure UNiMOF can use UV light carrying on the hydrogen evolution process. Compared with other nickel- or cobalt-based g-C3N4 shown in Table S1, the UNG sample exhibit higher catalytic activity.

Figure 6. (a) Photocatalytic H2 average evolution over UNG-x composites with different percentage amounts of UNiMOF; (b) H2 evolution over different MOF based g-C3N4; (c) Photostability value of UNG-25.0; (d) Schematic diagram of photocatalytic H2 evolution over UNG15 ACS Paragon Plus Environment


25.0. Photocatalytic Mechanism To research mechanism of UNG heterojunctions, band position of UNiMOF was further determined by UPS and VBXPS tests. Based on the linear extrapolation method,29, 44 the work function (f) was 5.44 eV gained by Equation (2). 𝜑 = 21.22 ― ∆𝐸 (2)

E stand for the energy distance from the Fermi level to the secondary cut-off (Figure 5c, He I, 21.22 eV).45 By formula (3),46 the Fermi level Ef of UNiMOF was 1.00 eV. 𝐸𝑓 = 𝜑 ― 4.44

(3)

A shown in Figure 5d, EVB` was 1.59 eV. The EVB` stands for the distance from the highest position of valence band to Fermi level of UNiMOF. Then, the valence band position of UNiMOF can be obtained by Equation (4).

E

VB

= 𝐸𝑉𝐵′ + 𝐸𝑓 (4)

The conduction band position of UNiMOF (-0.92 eV) was obtained by Equation (5)47: 𝐸𝑔 = 𝐸𝑉𝐵 ―𝐸𝐶𝐵

(5)

Eg was the band gap of UNiMOF estimated by Tauc method48 shown in Figure 5a. From above results, we can get a possible mechanism-based UNG-25.0 illustrated in Figure 6d. The band positions of g-C3N4 were -1.17 and +1.63 eV,49 that of UNiMOF was calculated at -0.92 and +2.59 eV. Because the energy position of CB edge of UNiMOF was more positive than that 16 ACS Paragon Plus Environment

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of g-C3N4, the photo-excited electrons can rapidly shift from g-C3N4 to UNiMOF, where UNiMOF can provide many unsaturated Ni sites for reducing the hydrogen ion in water to produce hydrogen gas.34,

50, 51

Besides, the ultrathin structure of UNiMOF can shorten the transfer distance of

photocarriers. Meanwhile, the holes in the VB location of g-C3N4 can be occupied by sacrificial agent. Hence, UNG heterojunction can inhibit the recombination of carriers in the process of carrier transfer, thus improve the photocatalytic activity. Recycling stability was crucial to value the quality of photocatalysts and the practical applications. As displayed in Figure 6c, the stability of the UNG-25.0 sample was estimated by performing three consecutive cycle experiments under similar irradiation condition. After three recycles, the photocatalytic activity of UNG endowed unobvious degradation indicating that the UNG-25.0 samples held good stability. Furthermore, results of XRD and TEM before and after recycling experiment revealed the stability of UNG-25.0 photocatalyst shown in Figure S7 and Figure S8. A preliminary conclusion can be drawn that the UNG-25.0 photocatalyst had a better stability.

Figure 7. (a) Photocurrent response diagram of UNG-25.0 and pure g-C3N4; (b) EIS Nyquist plots 17 ACS Paragon Plus Environment


of g-C3N4 and UNG-25.0. To further support above-proposed mechanism of UNG-25.0 sample, the photocurrent and impedance of samples were e verified. Figure 7a showed the I-t graph of pure g-C3N4 and UNG composite in visible light by on and off cycle operations. The UNG produced higher photocurrent than pure g-C3N4. This result suggested that UNiMOF/g-C3N4 photocatalyst had a weak recombination activity of carriers, and the effective charge separation strengthening the photocatalytic activity. Furthermore, the photocurrent analysis was uniform with that of small radius of semicircular Nyquist plots shown in Figure 7b. CONCLUSIONS A novel 2D-2D UNiMOF/g-C3N4 heterojunction was fabricated for H2 evolution via electrostatic self-assembly way. UNG heterojunction showed a heightened photocatalytic hydrogen production and displayed a good stability and reproducibility. The EQE of UNG-25.0 can get 0.979% at 420 nm in visible light. The outstanding photocatalytic activity of UNG samples was mainly ascribed to 2D/2D heterogeneous structure and the ultrathin thickness of UNiMOF. The work shows that 2D heterojunction of MOFs/C3N4 has great potential in the domain of photocatalytic hydrogen production. ASSOCIATED CONTENT Supporting Information The zeta potentials of samples in ethanol solution; XRD graph of g-C3N4 and the corresponding UNG composites; AFM image of the UNiMOF sample; TEM image of bulk NiMOF (a), BNG (b), 18 ACS Paragon Plus Environment

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BCG (c), UCG (d); XPS the entail spectrum of the UNG-25.0 sample; Photocatalytic H2 average evolution of samples under UV light; XRD of UNiMOF/g-C3N4 composites before and after hydrogen evolution reaction; TEM of UNiMOF/g-C3N4 composites before (a)and after (b) hydrogen evolution react; Comparisons of photocatalytic activities for g-C3N4 /transition metal compound based cocatalysts. AUTHOR INFORMATION Corresponding author: Fan Yue *E-mail: [email protected] Notes The authors declare t no conflict of interest. ACKNOWLEDGMENTS the National Natural Science Foundation of China (Grant No. 21777046), the Guangdong Innova tive and Entrepreneurial Research Team Program (No. 2016ZT06N569), and Guangzhou Science and Technology Project (No. 201803030002). REFERENCES 1. Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M., A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2008, 8 (1), 76-80. DOI 10.1038/nmat2317. 2. Moniz, S. J. A.; Shevlin, S. A.; Martin, D. J.; Guo, Z.-X.; Tang, J., Visible-light driven heterojunction photocatalysts for water splitting – a critical review. Energy Environ. Sci. 2015, 8 19 ACS Paragon Plus Environment


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For Table of Contents Use Only

Synopsis: Prepared UNiMOF/g-C3N4 heterojunction as photocatalytic materials for water splitting exhibit a favorable hydrogen evolution of 20.03 molh-1 at visible light irradiation.


g-C3N4 for Enhanced

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