Step-by-Step Improving Photocatalytic Hydrogen Evolution Activity of

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Step-by-Step Improving Photocatalytic Hydrogen Evolution Activity of NH2UiO-66 by Constructing Heterojunction and Encapsulating Carbon Nanodots Xin Zhang, Hong Dong, Xiaojun Sun, Dou-Dou Yang, JingLi Sheng, Hong-Liang Tang, Xiang-Bin Meng, and Feng-Ming Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01740 • Publication Date (Web): 10 Aug 2018 Downloaded from http://pubs.acs.org on August 11, 2018

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ACS Sustainable Chemistry & Engineering

Step-by-Step Improving Photocatalytic Hydrogen Evolution Activity of NH2-UiO-66 by Constructing Heterojunction and Encapsulating Carbon Nanodots Xin Zhang,† Hong Dong,† Xiao-Jun Sun,* Dou-Dou Yang, Jing-Li Sheng, Hong-Liang Tang, Xiang-Bin Meng and Feng-Ming Zhang* Key Laboratory of Green Chemical Engineering and Technology of College of Heilongjiang Province, College of Chemical and Environmental Engineering, School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150040, P. R. China.

E-mail addresses of the corresponding authors: [email protected] (X.-J. Sun) [email protected] (F.-M. Zhang)

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Abstract Carbon nanodots (CDs) have attracted enormous attention in photocatalytic area for their high light harvesting and outstanding electron transfer ability. In this work, NH2-UiO-66 was firstly composited with g-C3N4 to construct NH2-UiO-66/g-C3N4 heterojunction. Then, CDs was incorporated into the pores of NH2-UiO-66 by the pore space of the framework serving as confined nanoreactors to construct a CD@NH2-UiO-66/g-C3N4 ternary composite. The ultrasmall CDs stransformed from incapsulated glucose in the pores of NH2-UiO-66 were uniform distributed in MOFs and extensively improve photocatalytic hydrogen evolution activity of the composite under visible light irradiation. The optimum photocatalytic H2-evolution rate of CD@NH2-UiO-66/g-C3N4 composite with CDs content of 2.77 wt% is to 2.930 mmol·h-1·g-1 under visible-light irradiation, which is 32.4, 38.6 and 17.5 times as high as that of bulk g-C3N4, NH2-UiO-66 and NH2-UiO-66/g-C3N4, respectively. The remarkable enhancement of the photocatalytic activity should be that CDs as cocatalysts effectively increase the transport properties of electrons and the efficient charge separation. Moreover, CD@NH2-UiO-66/g-C3N4

nanocomposites

showed

excellent

stability

during

the

photocatalytic process as determined by XRD and TEM analyses for the sample after reaction. The results of mechanism investigation reveals that CDs in the ternary composite serve as electron transfer mediation to facilitate charge separation, enhancing light absorption and extending the lifetime of photo-induced carriers. The present work shows that encapsulating CDs into the pores of MOFs is an efficient strategy to improve the activity of MOF-based photocatalyst. Keywords: Carbon nanodots, Metal-organic frameworks, Heterojunctions, Photocatalytic hydrogen evolution, Cocatalysts, Introduction Energy crisis, emerged from industrial development and rapid depletion of fossil fuels, has urged us to seek renewable and environment-friendly energy resources.1-2 Clean hydrogen generation by splitting water with sunlight has been regarded as one of the green sustainable avenues to address the energy and environmental crisis in the future.3-5 The searching for robust and visible light-active semiconductor photocatalysts is vastly pursued by researchers for effective utilization of the solar spectrum and efficient improvement of H2 evolution.6-7 Metal-organic frameworks (MOFs), as an immerging class of porous crystalline materials composed of metal ions (or metal cluster) and organic ligands, have exhibited widespread applications in gas storage/separation, sensing, drug delivery, catalysis and proton conductivity.8-11 More recently, MOFs have been regarded as a type of special semiconductor for photocatalytic H2 evolution due to their diverse and designable frameworks with definite structural information, high surface area and the potential further functionality.12 Moreover,


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functional nanoparticles can be also introduced into the pores of their frameworks to increase photocatalytic efficiency.13 Therefore, these unique merits enable MOFs serve as a promising candidate for visible-light responsive photocatalytic application. Nevertheless, similar to traditional semiconductors, most MOFs photocatalysts also suffered from high electron-hole recombination rate and poor visible-light harvesting, which dramatically influence photocatalytic performance of MOFs.14-15 Although great efforts were made to enhance photoabsorption of MOFs, such as using dye-like ligands to construct frameworks or anchoring visible-light responsive groups to the host frameworks,16-18 the H2 evolution activities of MOF-based photocatalysts are not ideal for the high recombination rate of electron-hole pairs. To improve the photocatalitic activities of semiconductor，constructing heterojunction is an effective strategy to make sure the opposite migration of electrons and holes by conduction-band (CB) and valence-band (VB) offsets.19-23 The key of the construction of heterojunctions is suitable band edges, which can match well with another semiconductor. 24-26 More importantly，the effective cocatalyst loaded into semiconductor photocatalyst plays an essential role in the production of photocatalytic H2 evolution.27-29 It is known that precious metal species such as Pt and Au are usually used in most cases as cocatalysts to promote the transfer of photoinduced electron, while precious metals are rare and expensive.30-31 Thus, it is necessary to develop non-precious metal cocatalysts. Carbon nanodots (CDs) as cocatalysts exhibit unique photo-induced electron transfer, photoluminescence, which can further improve catalytic activity.32-33 Although CDs have been explored in photocatalytic applications, encapsulating CDs into the pores of MOFs to improve the catalytic activity has not been reported until now.34-35 Recently, MOFs have been served as templates for the synthesis of CDs with well-defined and different sizes by the pore space of MOFs serving as confined nanoreactors.36-41 However, the attempt of using the incorporated CDs as cocatalysts of MOF-based composites has not been reported until now. In this work, a ultra-stable and visible-light responsive MOF, NH2-UiO-66, was chosen as a typical MOF model to improve its hydrogen evolution performance by constructing effective heterojunction with g-C3N4 and incorporating CDs into the pores of NH2-UiO-66 to build a CD@NH2-UiO-66/g-C3N4 ternary composite photocatalyst. The optimum photocatalytic H2-evolution rate of CD@NH2-UiO-66/g-C3N4 composite with CDs content of 2.77 wt% is to 2.930 mmol·h-1·g-1 under visible-light irradiation, which is 32.4, 38.6 and 17.5 times as high as that of bulk g-C3N4, NH2-UiO-66 and NH2-UiO-66/g-C3N4, respectively. This work provides a novel strategy to effectively enhance photocatalytic activities of MOF-based composites by incorporating CDs into their pore space. Results and discussion



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Herein, bulk g-C3N4 was firstly prepared according to reported method, and then was exfoliated to thin sheet via sonication. NH2-UiO-66/g-C3N4 was prepared by situ self-assembly method, while CD@NH2-UiO-66/g-C3N4 composite was prepared by immersing NH2-UiO-66/g-C3N4 in glucose solution and then calcining at 240 °C for 4 h under N2 flow to transform glucose into CDs (Scheme 1). The phase component of CD@NH2-UiO-66/g-C3N4 samples (weight ratio of NH2-UiO-66 and g-C3N4 is 5:1) were studied by X-ray diffraction (XRD). As displayed in Figure 1a, the XRD patterns of pure g-C3N4 showed two characteristic diffraction peaks at 13.0°and 27.4°, corresponding to the (100) peak of in-plane structural packing motif and the (002) peak of interlayer stacking of aromatic segments, respectively.42-45 For NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4, the XRD patterns mach well with the simulated patterns of NH2-UiO-66 from X-ray single crystal diffraction and characteristic peak of g-C3N4. Notably, no obvious diffraction peaks were observed from CDs due to the low content or disorder structure of CDs.

Scheme 1. Schematic illustration for the synthesis of CD@NH2-UiO-66/g-C3N4. Fourier transform infrared (FT-IR) spectra were measured to characterize chemical character

of

g-C3N4,

NH2-UiO-66,

CD@NH2-UiO-66,

NH2-UiO-66/g-C3N4

and

CD@NH2-UiO-66/g-C3N4 samples (Figure S1). The typical peaks of g-C3N4 is similar to that reported previously.46 A small absorption peak observed at 800 cm-1 in the FT-IR spectra of g-C3N4, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4, is attributed to the breathing mode of the triazine ring. For the limited amount of CDs in composites, there are no obvious differences in the FT-IR spectra of NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 with variable CDs content (Figure S2). Thermogravimetric analysis (TGA) under nitrogen atmosphere shows that NH2-UiO-66 can keep its structural integration below 480 °C (Figure S3). The NH2-UiO-66/g-C3N4 hybrid material also shows the similar stability to that of its parent NH2-UiO-66, while the NH2-UiO-66/g-C3N4/glucose shows more weight loss before structure decomposition for the formation of CDs. The porosity of the as-synthesized NH2-UiO-66, NH2-UiO-66/g-C3N4, CD@NH2-UiO-66 and CD@NH2-UiO-66/g-C3N4 was investigated by N2 absorption experiments at 77 K (Figure 1b and S4). The


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Brunanuer-Emmett-Teller (BET) surface areas calculated from the N2 adsorption results of NH2-UiO-66, NH2-UiO-66/g-C3N4, CD@NH2-UiO-66 and CD@NH2-UiO-66/g-C3N4 are 989.8, 727.6, 696.1 and 462.6 m2 g−1, while the pore volumes are 0.540, 0.473, 0.458 and 0.336 cm3 g-1, respectively. The smaller pore volume and size of CD@NH2-UiO-66 than that of the parent NH2-UiO-66 are in accordance with fact of the formation of CDs in the pores of NH2-UiO-66.

Figure 1. (a) XRD patterns of g-C3N4, simulated NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4. (b) N2 adsorption-desorption isotherms at 77 K for NH2-UiO-66, NH2-UiO-66/g-C3N4, CD@NH2-UiO-66 and CD@NH2-UiO-66/g-C3N4. (c) SEM image of CD@NH2-UiO-66/g-C3N4.

(d)

Images

of

EDS

elemental

mapping

for

CD@NH2-UiO-66/g-C3N4. The morphology of CD@NH2-UiO-66/g-C3N4 was observed with scanning electron

micrographs (SEM). As shown in Figure 1c and S5, NH2-UiO-66 exhibited angulated particles with an average size around 200 nm and coated on the surface of sheet-like g-C3N4. The energy-dispersive spectroscopy (EDS) elemental mapping images exhibit an uniform distribution of C, N, O, Zr elements throughout CD@NH2-UiO-66/g-C3N4 (Figure 1d and Figure S6). According to the results of EDS and TGA the contents of CDs transformed from 50 mM glucose solutions are about 2.77 wt%, respectively. The transmission electron microscope (TEM) image for CD@NH2-UiO-66/g-C3N4 also shows the good combination of NH2-UiO-66 and g-C3N4. Moreover, CDs with good distribution in CD@NH2-UiO-66/g-C3N4 also can be visualized by TEM observations (Figure 2b, S7 and 8) and its average size was calculated to be around 0.7 nm. The surface hydrophilicity performed for g-C3N4 and CD@NH2-UiO-66/g-C3N4

shows

the

contact

angles

for

g-C3N4

and

CD@NH2-UiO-66/g-C3N4 are 57°and 44°, respectivley, indicating a better hydrophilicity of CD@NH2-UiO-66/g-C3N4 (Figure S9).48



Page 6 of 15

Figure 2. (a) TEM images of CD@NH2-UiO-66/g-C3N4. (b) TEM image of CDs in CD@NH2-UiO-66/g-C3N4. Mott-Schottky

plots

and the sizes of

g-C3N4,

distribution of NH2-UiO-66,

nanoparticle (inset). (c) NH2-UiO-66/g-C3N4

and

CD@NH2-UiO-66/g-C3N4. (d) DRS spectra and tauc plots of g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 (inset). The

electronic

band

structures

of

g-C3N4,

NH2-UiO-66/g-C3N4

and

CD@NH2-UiO-66/g-C3N4 were further investigated by examining Mott-Schottky plots. As shown in Figure 2c, CD@NH2-UiO-66/g-C3N4, NH2-UiO-66/g-C3N4, NH2-UiO-66 and g-C3N4 exhibited positive slopes in the Mott-Schottky plots at frequencies of 500 Hz, which was an indication of the n-type semiconductors.49 The results of Mott-Schottky measurements indicate that the flat band position of NH2-UiO-66, g-C3N4, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 are about -0.79, -1.15, -0.72 and -0.68 V, respectively with reference to the saturated calomel electrode (SCE). It is widely recognized that the bottom of the conduction band in many n-type semiconductors is more negative by 0.15 V than the flat band potential.50 The conduction band (CB) of NH2-UiO-66, g-C3N4, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 can be estimated to be -0.64, -1.0, -0.57 and -0.53 V vs. NHE, respectively. The conduction band of CD@NH2-UiO-66/g-C3N4 is more negative than the redox potential of H+/H2 (-0.41 V vs. NHE, pH = 7). UV-vis diffuse reflectance spectroscopy (DRS) of g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 are shown in Figure 2d. Pure g-C3N4 absorbs lights from the UV through the visible range up to 440 nm, which belongs to the intrinsic absorption from valence to conduction band. The conversion of the guest glucose molecules in NH2-UiO-66 by low-temperature calcination (240 °C for 4 h in a stream of N2), the color of the resulting CD@NH2-UiO-66/g-C3N4 changes to brown-yellow (Figure S10). As compared to g-C3N4, NH2-UiO-66 and


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NH2-UiO-66/g-C3N4, the absorption edge of CD@NH2-UiO-66/g-C3N4 displays a remarkable red shift with the absorption region up to 800 nm. The corresponding bandgap of CD@NH2-UiO-66/g-C3N4 is 2.79 eV estimated by Tauc plots derived from the corresponding DRS, which is lower than that of NH2-UiO-66 (2.92 eV), g-C3N4 (2.93 eV) and NH2-UiO-66/g-C3N4 (2.86 eV). Combined with the band gap energy, the valence band (VB) position of NH2-UiO-66, g-C3N4, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 can be calculated, which is respectively at 2.28, 1.93, 2.29 and 2.26 V vs. NHE. As shown in Figure 3a, the result of electrochemical impedance spectroscopy (EIS) measurement indicates that the diameter of the CD@NH2-UiO-66/g-C3N4 was smaller than that of NH2-UiO-66, g-C3N4 and NH2-UiO-66/g-C3N4. Linear sweep voltammetry curves of g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 show that NH2-UiO-66, g-C3N4 and NH2-UiO-66/g-C3N4 exhibit much lower electrocatalytic H2-evolution overpotentials than CD@NH2-UiO-66/g-C3N4 (Figure S11), indicating that CDs can act as cocatalysts to efficiently improve the photocatalytic H2-evolution activity. The effective generation and instant separation of photoexicited charge carriers are prerequisite for photocatalytic reactions, which can be analyzed

by

photoluminescence

(PL)

emission

spectroscopy

(Figure

3b),

because

photoluminescence stems from the recombination of free charge carriers.51 Compared to g-C3N4, NH2-UiO-66 and NH2-UiO-66/g-C3N4, CD@NH2-UiO-66/g-C3N4 composite shows a much weaker emission profile, indicating a rapid charge transfer in CD@NH2-UiO-66/g-C3N4. Notably, time-resolved PL spectra (Figure 3c) reveal that the lifetime of CD@NH2-UiO-66/g-C3N4 is longer than those of g-C3N4 or NH2-UiO-66/g-C3N4, which indicates that CDs as cocatalysts effectively increase the transport properties of electrons.52 The transient photocurrent measurement was carried out to qualitatively investigate the separation efficiency of photoinduced charges during the photoreactions. To further understand the improved separation efficiency of photogenerated charge carriers, transient photocurrent response curves of g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 photocatalysts were measured with several visible light on-off cycles in a three electrode system, respectively. As shown in Figures 3d, the CD@NH2-UiO-66/g-C3N4 composite exhibited significantly higher photocurrent density than those of g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4 under the same conditions, proving that a higher separation efficiency of the photogenerated electron-hole pairs

was

achieved

after

incorporating

CDs.

All

of

these

results

indicate

that

CD@NH2-UiO-66/g-C3N4 possesses a higher efficiency of charge immigration and a more effective separation of photogenerated electron-hole pairs than its parent materials.



Figure

3.

(a)

EIS

spectra

for

g-C3N4,

NH2-UiO-66,

Page 8 of 15

NH2-UiO-66/g-C3N4

and

CD@NH2-UiO-66/g-C3N4. (b) PL spectra of for g-C3N4, NH2-UiO-66, NH2-UiO-66/ g-C3N4 and CD@NH2-UiO-66/ g-C3N4 at an excitation wavelength of 350 nm. (c) Time-resolved PL spectra for g-C3N4 NH2-UiO-66/g-C3N4 and CD@NH2-UiO-66/g-C3N4. (d) Transient photocurrent

response

curves

of

g-C3N4,

NH2-UiO-66,

NH2-UiO-66/g-C3N4

and

CD@NH2-UiO-66/g-C3N4. The photocatalytic H2 production activities of the prepared samples were evaluated with H2 production from water under visible irradiation ( > 420 nm) using sodium ascorbate as sacrificial agents. The different weight ratios of NH2-UiO-66 and g-C3N4 were investigated for hydrogen generation (Figure S12). As shown in Figure 4a, the g-C3N4, NH2-UiO-66, NH2-UiO-66/g-C3N4, CD/g-C3N4 and CD@NH2-UiO-66/g-C3N4 show photocatalytic H2-production rates of 0.090, 0.076, 0.167, 0.243 and 2.930 mmol·h-1·g-1, respectively. Although CDs enhance the photocatalytic activity of g-C3N4 under visible light irradiation, ultrasmall CDs stransformed from incapsulated glucose in the pores of NH2-UiO-66 extensively improve photocatalytic hydrogen evolution activity and effectively promote the charge

separation.

In

Figure

4b,

the

photocatalytic

H2

evolution

rate

for

CD@NH2-UiO-66/g-C3N4 composites with variable CDs contents were recorded. The photocatalytic activity was achieved at 2.77 wt% of CDs content with the corresponding H2-production rates of 2.930 mmol·h-1·g-1. At higher amounts of CDs, the rate of H2-production rates was declined, which could be ascribed to the loading of excessive CDs leading to the shielding of the g-C3N4 and NH2-UiO-66 active sites. In addition, the average hydrogen evolution rate for NH2-UiO-66/g-C3N4 composites of 2.77 wt% amount CDs content was 32.4, 38.6, 17.5 times higher than that of the g-C3N4, NH2-UiO-66, and NH2-UiO-66/g-C3N4, respectively. These results clearly demonstrate the photocatalytic


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activity of 2.77 wt% amount CDs content for CD@NH2-UiO-66/g-C3N4 composites has been significantly improved, which is attributed to the incorporation of CDs as cocatalysts to enhance visible-light harvesting, effective charge separation and high photoinduced reducibility. The photocatalytic activity of 2.77 wt% amount CDs content for CD@NH2-UiO-66/g-C3N4 composites exhibited high activity with the hydrogen production rate of 14.650 mmol·h-1·g-1 in 5 h (2.930 mmol·h-1·g-1), which is supper than most of MOF-based photocatalysts (table S1). The wavelength dependence of photocatalytic H2 evolution was also investigated in the range of 420-550 nm, the photocatalytic H2 production rate under different wavelengths matches very well with its light absorption property, indicating the H2 evolution is indeed a light-induced catalytic reaction (Figure S13). As shown in Figure 4c, the photocatalytic activity of CD@NH2-UiO-66/g-C3N4 after four cycles didn’t show apparent decrease demonstrating its stable performance. Moreover, according to the XRD diffraction patterns and TEM analyses (Figure S14 and 15), it was found that CD@NH2-UiO-66/g-C3N4 still maintained its structure and morphology after the photocatalytic H2 evolution.

Figure

4.

(a)

Photocatalytic

H2

generation

rates

for

g-C3N4,

NH2-UiO-66,

NH2-UiO-66/g-C3N4, CD/g-C3N4 and CD@NH2-UiO-66/g-C3N4 under visible light ( > 420 nm). (b) NH2-UiO-66/g-C3N4 composites with variable CDs content. (c) The recyclability of NH2-UiO-66/g-C3N4 composites with 2.77 wt% CDs content for the photocatalytic H2

evolution under visible-light irradiation. (d) The proposed mechanism for the photocatalytic process of CD@NH2-UiO-66/g-C3N4. Based on the results above, the tentative mechanism for the photocatalytic hydrogen evolution over the CD@NH2-UiO-66/g-C3N4 composite can be inferred as Figure 4d. Although g-C3N4 has the similar light absorption with NH2-UiO-66, the CB of g-C3N4 is much higher than that of NH2-UiO-66, which means that more photogenerated electrons from



g-C3N4 can transfer to the CB of NH2-UiO-66. Then, contributed to the incorporated CDs acting as effective cocatalyst, photogenerated electrons in the CB of NH2-UiO-66 could be effectively transferred to CDs and further reduce H+ into H2, while the holes reserved in g-C3N4 and NH2-UiO-66 enable the electron donor sodium ascorbate to be oxidized. In addition, the incorporation of CDs into NH2-UiO-66 enhances the light harvesting ability of the material at the same time which could lead an improvement in H2 production. Conclusion In summary, we have successfully synthesized a CD@NH2-UiO-66/g-C3N4 ternary composite by incorporating CDs into the pores of NH2-UiO-66. The incorporation of CDs effectively increases visible light absorption regions, prolongs lifetime of the charge carriers and retards recombination of charge carriers. As a result, CD@NH2-UiO-66/g-C3N4 exhibited a improved photocatalytic activity for visible-light-driven hydrogen evolution (λ > 420 nm) with the H2 evolution rate up to 2.930 mmol·g-1·h-1, that is 32.4, 38.6 and 17.5 times higher than that of g-C3N4, NH2-UiO-66 and NH2-UiO-66/g-C3N4, respectively. The significant improvement of photocatalytic properties in the ternary composite can mainly be ascribed to CDs as cocatalysts to effectively enhance interfacial charge transfer of electrons in the composite system leading to a decrease in the photoinduced charge recombination. Also the CD@NH2-UiO-66/g-C3N4 composites exhibit high stability to fully explore the long-term stability of CDs for photocatalytic H2 production. This research provides a new insight for incorporating CDs into MOF-based photocatalysts to increase the photocatalytic performance. Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.***. Additional characterization includes materials and synthetic, FT-IR, TG, SEM, EDS, HRTEM, photocatalytic performance of different weight ratios of NH2-UiO-66/g-C3N4, apparent quantum efficiencies, XRD patterns and TEM images. Corresponding Author *Xiao-Jun Sun, Email: [email protected]. *Feng-Ming Zhang, Email: [email protected]. Author Contributions †

These two authors contributed equally to this work.

Notes The authors declare no competing financial interest. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (No. 21676066 and 21501036), the special fund for scientific and technological innovation talents of Harbin Science and Technology Bureau (No. 2017RAQXJ101 and 2017RAQXJ057), and


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Activity

at

All

pH

Values.

Acs

Catalysis

2017,

7

(1),

98-102,

DOI:

10.1021/acscatal.6b02849. (5) Qu, K. G.; Zheng, Y.; Zhang, X. X.; Davey, K.; Dai, S.; Qiao, S. Z. Promotion of Electrocatalytic Hydrogen Evolution Reaction on Nitrogen-Doped Carbon Nanosheets with Secondary Heteroatoms. Acs Nano 2017, 11 (7), 7293-7300, DOI: 10.1021/acsnano.7b03290. (6) Elbanna, O.; Fujitsuka, M.; Majima, T. g-C3N4/TiO2 Mesocrystals Composite for H2 Evolution under Visible-Light Irradiation and Its Charge Carrier Dynamics. ACS Appl. Mater. Interfaces 2017, 9 (40), 34844-34854, DOI: 10.1021/acsami.7b08548. (7) Zhou, J.-J.; Wang, R.; Liu, X.-L.; Peng, F.-M.; Li, C.-H.; Teng, F.; Yuan, Y.-P. In situ growth of CdS nanoparticles on UiO-66 metal-organic framework octahedrons for enhanced photocatalytic hydrogen production under visible light irradiation.

Appl. Surf. Sci.

2015, 346, 278-283, DOI:

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TOC

Graphical Abstract Brief: NH2-UiO-66, was chosen as a typical MOF model to improve its hydrogen evolution performance by constructing effective heterojunction with g-C3N4. Then, uniform and ultrasmall CDs as effective cocatalysts were incorporated into the pores of NH2-UiO-66 to build a CD@NH2-UiO-66/g-C3N4 ternary composite photocatalyst, which increase visible-light absorption regions, prolong lifetime of the charge carriers, lead to the nanoscale effects and further block the recombination of charge carriers. Therefore, CDs into the pores of MOFs is an efficient strategy to improve the activity of MOF-based photocatalyst.


Step-by-Step Improving Photocatalytic Hydrogen Evolution Activity of

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