Self-Coupled g-C3N4 van der Waals Heterojunctions for Enhanced

Article Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

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Self-Coupled g‑C3N4 van der Waals Heterojunctions for Enhanced Photocatalytic Hydrogen Production Haiyun Li,†,∥ Hao Tian,†,∥ Xiaodeng Wang,† Mingyu Pi,‡ Shengsheng Wei,§ Hancheng Zhu,§ Dingke Zhang,*,‡ and Shijian Chen*,†

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†

Chongqing Key Laboratory of Soft Condensed Matter Physics and Smart Materials, College of Physics, Chongqing University, Chongqing 401331, China ‡ College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China § Key Laboratory of UV-Emitting Materials and Technology, Northeast Normal University, Ministry of Education, Changchun 130024, China S Supporting Information *

ABSTRACT: Constructing junctions can efficiently improve the photocatalytic performance by suppressing the recombination of photogenerated electron−hole pairs and prolonging the lifetime of carriers. In this work, we exploited a facile method to fabricate g-C3N4 nanosheet (g-CNNS)/g-C3N4 nanofiber (g-CNNF) heterojunctional composites. The valence and conductive band offsets between g-CNNS and g-CNNF cause band bending, and van der Waals (vdW) heterojunctions are constructed at the interface of g-CNNS and g-CNNF. Because of the shorter diffusion distance of charge carriers and spontaneous electron motion, g-CNNS/g-CNNF vdW heterojunctions with intimate contact can effectively suppress the recombination of the photoexcited electron and hole and thus increase the carrier lifetime and further enhance the photocatalytic performance. Under the visible-light irradiation, these heterojunctions exhibit a 3 times higher photocatalytic hydrogen evolution rate of 1375.9 μmol g−1 h−1 compared with pristine g-CNNS. This work demonstrates that the fabricated vdW heterojunctions can effectively prolong the carrier lifetime through separating the photogenerated electron−hole pairs and provide a new perspective to design and develop the 2D photocatalysts with high charge-transfer efficiency. KEYWORDS: self-coupled carbon nitride, visible-light photocatalysis, van der Waals heterojunction, charge separation and transfer, hydrogen production

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INTRODUCTION Hydrogen produced by semiconductor photocatalysis is one of the most ideal ways to settle the current environmental contamination and energy crisis.1 Graphitic carbon nitride (gC3N4) is a nonmetallic semiconductor material with a graphene lamellar structure and is made of Earth-abundant elements.2,3 The most interesting characteristics of g-C3N4 are that its band gap of 2.4−2.8 eV4−12 (depending on the different synthesis environment and precursors) is across the window of the redox of water, enabling a broad absorption of light in the visible-light range. Due to the unique semiconducting band structure and its chemical stability and excellent thermal properties, g-C3N4 becomes a potential photocatalyst for splitting water, degrading organic pollutants, NO purification, and air cleaning.13−26 However, as with most semiconducting materials, the high photogenerated electron− hole recombination ratio leads to a low quantum efficiency for g-C3N4, which seriously limits its practical applications in the field of photocatalysis. Former studies have shown that the band gap structures, including the band energies, light © XXXX American Chemical Society

absorption, and charge transfer for g-C3N4, are the decisive factors for the photocatalytic performance.27−29 Thus far, the focus on improving the photocatalytic activity of g-C3N4 is to modify morphologies and construct heterojunctional structures. Heterojunctions constructed by different semiconductors with different band structures can effectively facilitate the separation of the carrier at the interfaces, thereby reducing carrier recombination.30 There were many attempts to construct heterojunctions with two electronic bands matched semiconductors, such as SnS2/g-C3N4, CaIn2S4/gC 3 N 4 , TiO 2 /g-C 3 N 4 , MnO 2 /g-C 3 N 4 , and Ag 3 PO 4 /gC3N4.31−36 However, there is always a lattice-mismatching problem for constructing heterojunctions with two different semiconductor materials. A heterojunction made of the same semiconductor materials with different morphologies and different structural phase can solve the above issue. It is wellReceived: January 22, 2019 Accepted: May 28, 2019 Published: May 28, 2019 A

DOI: 10.1021/acsaem.9b00150 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

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ACS Applied Energy Materials

Figure 1. SEM images of (a) g-CNNS, (c) g-CNNF, and (d) g-CNNS/g-CNNF. (e) XRD patterns for an enlarged profile of the dominant (002) peak of g-CNNS, g-CNNF, and g-CNNS/g-CNNF (3:1), respectively. TEM images of (b) g-CNNS, (f),g-CNNF, and (g−i) g-CNNS/g-CNNF.

known that g-C3N4 synthesized by different precursors, like urea and melamine, exhibited different morphologies and similar band structures,37 which provides a new idea in the construction of isotype heterojunctions with enhanced photocatalytic performance. In addition, there are some remarkable strategies to upgrade the photocatalytic hydrogen evolution performance of g-C3N4, for instance, the surface hydroxylation of g-C3N4 for an 11-fold enhancement in H2 generation rate,38 a precursor-reforming protocol to mesoporous g-C 3 N 4 achieving 27.8% quantum efficiency (AQE), 39 and a precursor-surface-etching route without using a template to achieve porous g-C3N4 nanosheets for both the photocatalytic reduction and oxidation reaction.40 Since the successful isolation of graphene, low-dimensional materials have arisen rapidly. The van der Waals (vdW) heterostructure refers to a 2D materials interacting with another 2D material through the surface vdW forces, opening a new path for basic scientific research and applied device designs, showing an amazing prospect in a variety of fields. In the photocatalytic field, vdW heterostructures can combine the advantages of its semiconductor structure to improve its electronic and optical properties. This idea has stimulated intensive investigation, from both an experimental and theoretical view. For example, mono- and bilayer graphene devices were exfoliated on single-crystal h-BN substrates, leading to a 10-fold growth in the electronic quality of h-BN/ graphene in comparison with graphene.41 Few-layer graphene and g-C3N4, black phosphorus, and g-C3N4 metal-free vdW heterostructures enhanced the visible-light response, improving the photocatalytic performance.42 Growing MoS2 on WS2 to construct 2D/2D MoS2/WS2 vdW heterostructures leads to

ultrafast charge transfer within 50 fs, holding great promise for future optoelectronic and photovoltaic applications43 and efficient charge carrier separation/isolation on the n-MoS2/pSi heterostructure for solar cells.44 Inspired by the vdW heterostructure and isotype g-C3N4 heterojunctions, we fabricated an isotype vdW g-CNNS/gCNNF heterojunction, called the mixed-dimensional selfcoupled g-C3N4 vdW heterojunction, enhancing the photocatalytic water splitting activities of g-C3N4 via efficiently separating the electron−hole pairs. Compared with those of gCNNS and g-CNNF, the enhanced photocatalytic activity of the g-CNNS/g-CNNF heterojunction could be attributed to efficient carrier separation, diversion across the vdW heterojunction interface, and about 4 and 3 times longer lifetime of photogenerated charge carriers. The present work confirmed that the reasonable treatment of the precursor as well as the design of a self-coupled heterojunction could provide new insight to exploit novel high-efficiency visible-light self-coupled photocatalysts.

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RESULTS AND DISCUSSION The morphologies of the prepared composites were viewed by SEM. As shown in Figure 1a, the bulk g-C3N4 after ultrasonic treatment was composed of stacked nanosheets.45 For the acidized melamine precursor, an optical picture (Figure S1a) showed an obvious fiber morphology. After calcining at 500 °C for 2 h, the fiber morphology was maintained, and the color was changed from white to yellowish indicating the formation of g-C3N4 (Figure S1b). SEM images (Figure 1c and Figure S2d−e) clearly showed a fiber morphology containing very long fibers with 100−200 nm diameters. The melamine and B


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Figure 2. (a) XPS survey spectra, (b) high-resolution C 1s, and (c) N 1s of g-CNNS, g-CNNF, and g-CNNS/g-CNNF (3:1).

Figure 3. (a) UV−vis spectra of g-CNNS, g-CNNF, and g-CNNS/g-CNNF. (b) Corresponding plots of (αhν)1/2 vs photo energy. (c) XPS VB spectra of g-CNNS and g-CNNF.

indicating the construction of graphitic stacking C3N4 layers. This diffraction peak at 27.5° corresponded to the interlayer stacking of aromatic units of C−N, attributing to the (002) plane of the stacking of the conjugated aromatic system.3 Moreover, the diffraction angle of the (002) peak for g-CNNF (27.4°) was slightly shifted to a smaller angle compared with that of g-CNNS (27.8°) which might be due to the fact that the acidization of melamine reduced the condensation process consistent with the SEM result. Notably, the overlapped diffraction peaks of both components of g-CNNS and g-CNNF indicate the formation of the g-CNNS/g-CNNF heterostructure (Figure 1e). Furthermore, with the increase of the mass ratio of acidized melamine to melamine, the (002) peak shifted to a smaller angle, attributing to the result above (Figure S2i). Combining the SEM and XRD patterns, we can speculate that

acidized melamine (with a ratio of 3:1) were used as precursors. The prepared composites exhibited distinct 2D, 1D mixed-dimensional morphologies (Figure 1d). Notably, distinct 1D g-CNNF spread out on the surface of materials. The evolution of the morphology with the mass ratios of melamine to acidized melamine is shown in Figure S2f−h. It was shown that the morphology of the composites became porous and crumbly with the increase of the mass ratio of acidized melamine to melamine. Upon comparison with gCNNS, the g-CNNS/g-CNNF possessed a thinner lamellar structure indicating that the condensation process was reduced while using mixtures as precursors. The XRD patterns for gCNNS, g-CNNF, and g-CNNS/g-CNNF (3:1) are presented in Figure 1e. Only one intense peak at around 27.5° in the XRD patterns was observed for all of the composites, C


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Figure 4. (a) Room-temperature PL spectra, (b) time-resolved PL, (c) and photocurrent transient responses of g-CNNS, g-CNNF, and g-CNNS/gCNNF (3:1). (d) Schematic band structure alignment of g-CNNS/g-CNNF.

structures of C and N in nanosized fibers were modified. Moreover, the peak positions of C 1s and N 1s in the gCNNS/g-CNNF heterojunctions were located between gCNNS and g-CNNF, consistent the XRD and SEM results, which further confirms the successful formation of g-CNNS/gCNNF heterojunctional composites. Figure 3a shows the UV−vis absorption spectra of g-CNNS, g-CNNF, and g-CNNS/g-CNNF (3:1). The absorption edges were located at 475, 451, and 459 nm for the g-CNNS, gCNNF, and g-CNNS/g-CNNF (3:1), according to the Tauc− David Mott equation (eq 1):

the crystal interactions take place under the condensation process and the degree of the interaction influenced by the precursors’ composition. TEM images were acquired to further characterize the structure of g-CNNS, g-CNNF, and g-CNNS/g-CNNF. As shown in Figure 1b,f, g-CNNS is composed of stacked thick layers, and g-CNNF showed a fiber morphology with about 200 nm diameters, in agreement with the SEM results. Figure 1g−i shows the morphology of the g-CNNS/g-CNNF heterojunction. The bright area and black fibers were considered as g-CNNS and g-CNNF, respectively, according to the TEM images of g-CNNS and g-CNNF. The black gCNNF in TEM images indicated that g-CNNF stacked on the g-CNNFS surface, further confirming the formation of the vdW heterojunction. The N2 sorption isotherms for specific surface were tested. As shown in Figure S7, the specific areas of g-CNNF, g-CNNS, and g-CNNS/g-CNNF are 22.427, 8.020, and 11.920 m2 g−1, respectively. One can see that g-CNNF has a much larger specific surface area than g-CNNS, and the formation of the g-CNNS/g-CNNF vdW heterojunction reasonably retains the specific surface area of g-CNNS. The chemical compositions of the composites were characterized by XPS. Only C, N, and O elements were detected in the XPS survey spectrum (Figure 2a) for the gCNNS, g-CNNF, and g-CNNS/g-CNNF (3:1), which confirmed the high purity of the composites. Oxygen found in all composites was due to surface contamination. As shown in Figure 3, both the C 1s and N 1s peak are identical for all of the composites, which indicates that all of the composites are typical g-C3N4. As depicted in Figure 2b, two peaks at 284.5 and 288.1 V belong to the C 1s. The peak at 284.5 eV is ascribed to adventitious carbon species, and the peak at 288.1 eV is ascribed to the tertiary carbon C−(N)3 in the g-C3N4 lattice.46 Figure 2c shows that the N 1s peak can be fitted into three peaks, corresponding to three different types of nitrogen states. The peak at 398.2 eV is ascribed to C−N−C species, the peak at 399.2 eV to tertiary nitrogen N−(N)3 species, and the peak at 400.7 eV to N−H groups.47 However, both C 1s and N 1s peaks show a slight blue shift in g-CNNF compared to those in the g-CNNS, which showed that the electronic

αhν = A(hν − Eg )n

(1)

where h, ν, α, and Eg are Planck’s constant, light frequency, the absorption coefficient, and band gap; exponent n represents the nature of the sample transition and is defined to be 2 for an indirectly allowed transition. The fitting results indicate that the corresponding band gaps of g-CNNS, g-CNNF, and gCNNS/g-CNNF (3:1) are 2.50, 2.66, and 2.56 eV, respectively (Figure 3b). The band gap of g-CNNF had a blue shift of 0.16 eV compared to that of g-CNNS, which indicated that the band gap of carbon nitride was highly dependent on the precursors and preparation methods.48 The band edge of gCNNS/g-CNNF (3:1) was located between g-CNNS and gCNNF, which further favored the electronic coupling of these two components in the g-CNNS/g-CNNF heterojunctions. The slight deviations in band gap of g-CNNS and g-CNNF provide great potential for the construction of heterojunctions with a well-matched lattice.37,47 Furthermore, the XPS valence band (VB) spectra were measured for the g-CNNF and g-CNNs as shown in Figure 3c, which revealed that the VB maxima of g-CNNS and g-CNNF were 1.54 and 1.78 eV, respectively. With the band gap energy difference as shown in Figure 2b taken into account, the conductive bands (CBs) of g-CNNS and g-CNNF were estimated to be −0.96 and −0.88 eV, respectively. Thus, CB has an offset of 0.08 eV, and VB has offset of 0.24 eV between g-CNNS and g-CNNF. The VB and CB offsets cause the band bending at the interfaces of g-CNNS/g-CNNF heterojuncD


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10.31 ns for g-CNNS and 23.61 ns for g-CNNF to 95.73 ns in the g-CNNS/g-CNNF heterojunction. These results support the PL results to confirm that the formation of heterojunctions is conducive to suppressing the electron−hole recombination. Photocurrent transient responses can serve as direct proof for the separation efficiency of photogenerated carriers. As shown in Figure 4c, all of the g-CNNS, g-CNNF, and gCNNS/g-CNNF electrodes exhibited fast photocurrent responses via on−off cycles under visible-light irradiation. The g-CNNS/g-CNNF heterojunction electrode exhibited a significantly higher photocurrent as compared to g-CNNS and g-CNNF, which indicated that more photogenerated electrons could participate in the catalytic reaction.49 Since the formation of g-CNNS/g-CNNF heterojunctions promotes charge separation, the enhanced photocurrent shows a higher electron/hole pair separation efficiency.50 To verify the rapid charge transport and efficient carrier separation in the g-CNNS/g-CNNF vdW heterojunctions, photocatalytic water reduction was carried out. As shown in Figure 5a, under visible-light irradiation (λ ≥ 420 nm), the photocatalytic H2 evolution rates of g-CNNS and g-CNNF are 462.2 and 514.7 μmol g−1 h−1, respectively. However, the photocatalytic hydrogen production performance of g-CNNS/ g-CNNF increased gradually and then reduced with the increase of the g-CNNF content. The g-CNNS/g-CNNF (3:1) heterojunction exhibited the highest H2 generation rate (1375.9 μmol g−1 h−1), 2.98 and 2.67 times that over single g-CNNS and g-CNNF, and it exhibited a good stability without obvious decay in 9 h of the experiments. As listed in Table S1, g-CNNS/g-CNNF shows a favorable performance compared to the previous reports on the composition of gC3N4, demonstrating that fabricating the vdW heterojunction can effectively optimize the solar-to-hydrogen conversion efficiency. Photocatalytic Mechanism. On the basis of the results and analyses, it can be known that rapid charge transport and efficient carrier separation are the predominant factors that influence the photocatalytic performance.51 Herein, a possible photocatalytic mechanism of the photoexcited charge carrier transfer is proposed, as illustrated in Figure 4d. As the gCNNS/g-CNNF heterojunctions are subjected to visible-light irradiation, electrons in the VB would be exited to the CB, and holes are generated in the VB at both g-CNNS and g-CNNF sides. The offsets of 0.08 eV of the CB and 0.24 eV of the VB drive the diversion of photogenerated electrons and holes, respectively. The recombination of electron/hole pairs is greatly reduced due to the spatial separation of photogenerated

tions, as illustrated in Figure 4d. An analysis of absorption edges and band structure of g-CNNS/g-CNNF further verifies the formation of a heterostructure: two different absorption edges at 475 and 451 nm were distinguished in the spectra corresponding to g-CNNS and g-CNNF, respectively, which confirms the formation of a heterostructure (Figures S3 and S4). To reveal the separation efficiency of photogenerated charge carriers, PL emission measurements were carried out. As shown in Figure 4a, the broad luminescence peak at around 450 nm corresponds to the direct recombination of photogenerated electron−hole pairs. The g-CNNS has a strong PL emission, which indicated a rapid recombination of photogenerated electron−hole pairs. As for g-CNNF, the PL emission peak intensity is lower than that of g-CNNS, which might attribute to the lower visible-light absorption. By comparison, the g-CNNS/g-CNNF heterojunctional composites exhibited a very weak PL emission compared with gCNNS and g-CNNF; it even has a strong visible-light absorption (Figure 2a). The obvious quenched PL emission implied that the charge recombination process was dramatically inhibited by the efficient charge separation at the gCNNS/g-CNNF junctional interfaces. Hence, the inherent drawback of fast charge recombination for pristine g-C3N4 has been efficiently settled via the fabrication of the vdW heterojunction, which would be beneficial for the photocatalytic performance. To further confirm that the carrier lifetime was prolonged through constructing g-CNNS/g-CNNF heterojunctions, we measured the time-resolved fluorescence decay spectra of gCNNS, g-CNNF, and g-CNNS/g-CNNF, as shown in Figure 4b. By fitting the decay spectra (Figure S5a−e), the radiative lifetimes can be obtained as given in Table 1. The short Table 1. Photoemission Decay Lifetime of g-CNNS, gCNNF, and g-CNNS/g-CNNF samples lifetime

g-CNNS

M:AM = 5:1

M:AM = 3:1

M:AM = 5:1

g-CNNF

τ1 (ns) τ2 (ns)

1.89 10.31

5.57 30.49

9.10 95.73

7.61 93.05

3.40 23.61

lifetimes, caused by the nonradiative recombination of charge carriers, are 1.89 and 3.40 ns for g-CNNS and g-CNNF, respectively, and it increased up to 9.10 ns in the g-CNNS/gCNNF heterojunction. The long lifetime of charge carriers attributing to the free exciton recombination increased from

Figure 5. (a) Photocatalytic hydrogen production performance of g-CNNS, g-CNNF, and g-CNNS/g-CNNF (7:1; 5:1; 3:1; 1:1; 1:3; 1:5). (b) Stability tests of g-CNNS/NF (3:1). E



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electrons and holes, which is conducive to boosting the photocatalytic activity.52 Benefiting from the suitable thermodynamic potential for photocatalytic H2 evolution, kinetically, electrons on the CB of g-CNNF could migrate toward the surface to initiate a reaction with H+. As for the g-CNNS/gCNNF heterojunction, the interface of the 2D/2D heterojunction is distinctly large, which provides a wide transfer channel for electrons, resulting in an accelerated high-efficiency separation.53−55 More importantly, vdW bonds between gCNNS and g-CNNF are beneficial for electron transport, and g-C3N4 has an excellent electron mobility to enhance the charge transport rate.43,56−59 Meanwhile, nanosized g-CNNF can shorten the distance for the migration of electrons with the reduction in thickness to further separate the electron−hole pairs.

CONCLUSION In summary, the g-CNNS/g-CNNF vdW heterojunction has been constructed successfully by annealing the mixture of melamine and acidized melamine. Structural and band characterization shows that g-CNNS composited with gCNNF was successfully compounded. The self-coupled gC3N4 heterojunctions prominently enhance the carrier migration, separate the photogenerated electron/hole pairs, and significantly enhance the photocatalytic activity. By adjusting the weight ratio of precursors, the highest H2 production rate of g-CNNS/g-CNNF (3:1) (1375.9 μmol h−1g−1) is nearly 2.98 and 2.67 times higher than that of pristine g-CNNS and g-CNNF and displays an admirable durability after 3 continuous experiment runs. This work may shed light on optimization of 2D photocatalysts through fabricating vdW heterojunctions to improve the solar-tohydrogen conversion efficiency. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.9b00150. Experimental details, photographs, SEM images, XRD patterns, ns-level time-resolved PL spectra, and a comparison of the optimized photocatalytic activity with the literature values (PDF)

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REFERENCES

(1) Momirlan, M.; Veziroglu, T. N. Current Status of Hydrogen Energy. Renewable Sustainable Energy Rev. 2002, 6, 141−179. (2) 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. 2009, 8, 76−80. (3) Yan, S. C.; Li, Z. S.; Zou, Z. G. Photodegradation Performance of g-C3N4 Fabricated by Directly Heating Melamine. Langmuir 2009, 25, 10397−10401. (4) Xu, K.; Li, X.; Chen, P.; Zhou, D.; Wu, C.; Guo, Y.; Zhang, L.; Zhao, J.; Wu, X.; Xie, Y. Hydrogen Dangling Bonds Induce Ferromagnetism in Two-dimensional Metal-free Graphitic-C3N4 Nanosheets. Chem. Sci. 2015, 6, 283−287. (5) Zhang, J.; Sun, J.; Maeda, K.; Domen, K.; Liu, P.; Antonietti, M.; Fu, X.; Wang, X. Sulfur-mediated Synthesis of Carbon Nitride: Bandgap Engineering and Improved Functions for Photocatalysis. Energy Environ. Sci. 2011, 4, 675−678. (6) Zhang, J.; Zhang, M.; Lin, L.; Wang, X. Sol Processing of Conjugated Carbon Nitride Powders for Thin-film Fabrication. Angew. Chem., Int. Ed. 2015, 54, 6297−301. (7) Zhang, J.; Chen, X.; Takanabe, K.; Maeda, K.; Domen, K.; Epping, J. D.; Fu, X.; Antonietti, M.; Wang, X. Synthesis of a Carbon Nitride Structure for Visible-Light Catalysis by Copolymerization. Angew. Chem., Int. Ed. 2010, 49, 441−444. (8) Bojdys, M. J.; Mueller, J.-O.; Antonietti, M.; Thomas, A. Ionothermal Synthesis of Crystalline, Condensed, Graphitic Carbon Nitride. Chem. - Eur. J. 2008, 14, 8177−8182. (9) Cui, Y.; Zhang, J.; Zhang, G.; Huang, J.; Liu, P.; Antonietti, M.; Wang, X. Synthesis of Bulk and Nanoporous Carbon Nitride Polymers from Ammonium Thiocyanate for Photocatalytic Hydrogen Evolution. J. Mater. Chem. 2011, 21, 13032−13039. (10) Xu, J.; Wu, H.-T.; Wang, X.; Xue, B.; Li, Y.-X.; Cao, Y. A New and Environmentally Benign Precursor for The Synthesis of Mesoporous g-C3N4 with Tunable Surface Area. Phys. Chem. Chem. Phys. 2013, 15, 4510−4517. (11) Cui, Y.; Ding, Z.; Fu, X.; Wang, X. Construction of Conjugated Carbon Nitride Nanoarchitectures in Solution at Low Temperatures for Photoredox Catalysis. Angew. Chem., Int. Ed. 2012, 51, 11814− 11818. (12) Lin, Z.; Wang, X. Nanostructure Engineering and Doping of Conjugated Carbon Nitride Semiconductors for Hydrogen Photosynthesis. Angew. Chem., Int. Ed. 2013, 52, 1735−1738. (13) Chen, C.; Ma, W.; Zhao, J. Semiconductor-mediated Photodegradation of Pollutants under Visible-light Irradiation. Chem. Soc. Rev. 2010, 39, 4206−4219. (14) Tong, H.; Ouyang, S.; Bi, Y.; Umezawa, N.; Oshikiri, M.; Ye, J. Nano-photocatalytic Materials: Possibilities and Challenges. Adv. Mater. 2012, 24, 229−251. (15) Liu, S.; Yu, J.; Jaroniec, M. Anatase TiO2 with Dominant HighEnergy {001} Facets: Synthesis, Properties, and Applications. Chem. Mater. 2011, 23, 4085−4093. (16) Wang, Y.; Wang, X.; Antonietti, M. Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry. Angew. Chem., Int. Ed. 2012, 51, 68−89. (17) Wang, X.; Blechert, S.; Antonietti, M. Polymeric Graphitic Carbon Nitride for Heterogeneous Photocatalysis. ACS Catal. 2012, 2, 1596−1606. (18) Devi, L. G.; Kavitha, R. A Review on Non Metal Ion Doped Titania for The Photocatalytic Degradation of Organic Pollutants under UV/solar Light: Role of Photogenerated Charge Carrier Dynamics in Enhancing The Activity. Appl. Catal., B 2013, 140, 559− 587. (19) Liu, G.; Niu, P.; Cheng, H.-M. Visible-Light-Active Elemental Photocatalysts. ChemPhysChem 2013, 14, 885−892. (20) Li, J.; Zhang, Z.; Cui, W.; Wang, H.; Cen, W.; Johnson, G.; Jiang, G.; Zhang, S.; Dong, F. The Spatially Oriented Charge Flow

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Shijian Chen: 0000-0002-9523-6686 Author Contributions ∥

H.L. and H.T. equally contributed to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (NSFC) (Grant 51672031) for financial support. We also acknowledge the support from Project 2018CDJDWL0011 supported by the Fundamental Research Funds for the Central Universities and the sharing fund of large-scale equipment of Chongqing University. F


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ACS Applied Energy Materials and Photocatalysis Mechanism on Internal van der Waals Heterostructures Enhanced g-C3N4. ACS Catal. 2018, 8, 8376−8385. (21) Chen, P.; Wang, H.; Liu, H.; Ni, Z.; Li, J.; Zhou, Y.; Dong, F. Directional Electron Delivery and Enhanced Reactants Activation Enable Efficient Photocatalytic Air Purification on Amorphous Carbon Nitride Co-functionalized with O/La. Appl. Catal., B 2019, 242, 19−30. (22) Li, J.; Dong, X. a.; Sun, Y.; Jiang, G.; Chu, Y.; Lee, S. C.; Dong, F. Tailoring The Rate-determining Step in Photocatalysis via Localized Excess Electrons for Efficient and Safe Air Cleaning. Appl. Catal., B 2018, 239, 187−195. (23) Huang, H.; Tu, S.; Zeng, C.; Zhang, T.; Reshak, A. H.; Zhang, Y. Macroscopic Polarization Enhancement Promoting Photo- and Piezoelectric-Induced Charge Separation and Molecular Oxygen Activation. Angew. Chem., Int. Ed. 2017, 56, 11860−11864. (24) Yu, H.; Li, J.; Zhang, Y.; Yang, S.; Han, K.; Dong, F.; Ma, T.; Huang, H. Three-in-One Oxygen Vacancies: Whole Visible-Spectrum Absorption, Efficient Charge Separation, and Surface Site Activation for Robust CO2 Photoreduction. Angew. Chem., Int. Ed. 2019, 58, 3880−3884. (25) Chen, F.; Huang, H.; Ye, L.; Zhang, T.; Zhang, Y.; Han, X.; Ma, T. Thickness-Dependent Facet Junction Control of Layered BiOIO3 Single Crystals for Highly Efficient CO2 Photoreduction. Adv. Funct. Mater. 2018, 28, 1804284. (26) Huang, H.; Han, X.; Li, X.; Wang, S.; Chu, P. K.; Zhang, Y. Fabrication of Multiple Heterojunctions with Tunable Visible-lightactive Photocatalytic Reactivity in BiOBr-BiOI Full-range Composites Based on Microstructure Modulation and Band Structures. ACS Appl. Mater. Interfaces 2015, 7, 482−92. (27) Cheng, F. Y.; Yin, H.; Xiang, Q. J. Low-temperature Solid-state Preparation of Ternary CdS/g-C3N4/CuS Nanocomposites for Enhanced Visible-light Photocatalytic H2-production Activity. Appl. Surf. Sci. 2017, 391, 432−439. (28) Hou, Y.; Laursen, A. B.; Zhang, J.; Zhang, G.; Zhu, Y.; Wang, X.; Dahl, S.; Chorkendorff, I. Layered Nanojunctions for HydrogenEvolution Catalysis. Angew. Chem., Int. Ed. 2013, 52, 3621−3625. (29) Yan, H.; Yang, H. TiO2-g-C3N4 composite materials for photocatalytic H-2 evolution under visible light irradiation. J. Alloys Compd. 2011, 509, L26−L29. (30) Qu, Y.; Duan, X. Progress, Challenge and Perspective of Heterogeneous Photocatalysts. Chem. Soc. Rev. 2013, 42, 2568−2580. (31) He, Y.; Zhang, L.; Teng, B.; Fan, M. New Application of Zscheme Ag3PO4/g-C3N4 Composite in Converting CO2 to Fuel. Environ. Sci. Technol. 2015, 49 (1), 649−56. (32) Jiang, D.; Li, J.; Xing, C.; Zhang, Z.; Meng, S.; Chen, M. TwoDimensional CaIn(2)S(4)/g-C(3)N(4) Heterojunction Nanocomposite with Enhanced Visible-Light Photocatalytic Activities: Interfacial Engineering and Mechanism Insight. ACS Appl. Mater. Interfaces 2015, 7, 19234−42. (33) Zheng, Y.; Liu, J.; Liang, J.; Jaroniec, M.; Qiao, S. Z. Graphitic Carbon Nitride Materials: Controllable Synthesis and Applications in Fuel Cells and Photocatalysis. Energy Environ. Sci. 2012, 5, 6717− 6731. (34) Koci, K.; Reli, M.; Troppova, I.; Sihor, M.; Kupkova, J.; Kustrowski, P.; Praus, P. Photocatalytic Decomposition of N2O over TiO2/g-C3N4 Photocatalysts Heterojunction. Appl. Surf. Sci. 2017, 396, 1685−1695. (35) Kong, L.; Ji, Y.; Dang, Z.; Yan, J.; Li, P.; Li, Y.; Liu, S. g-C3N4 Loading Black Phosphorus Quantum Dot for Efficient and Stable Photocatalytic H2 Generation under Visible Light. Adv. Funct. Mater. 2018, 28, 1800668. (36) Zhang, Z.; Huang, J.; Zhang, M.; Yuan, L.; Dong, B. Ultrathin Hexagonal SnS2 Nanosheets Coupled with g-C3N4 Nanosheets as 2D/2D Heterojunction Photocatalysts Toward High Photocatalytic Activity. Appl. Catal., B 2015, 163, 298−305. (37) Dong, F.; Zhao, Z.; Xiong, T.; Ni, Z.; Zhang, W.; Sun, Y.; Ho, W.-K. In Situ Construction of g-C3N4/g-C3N4 Metal-Free Heterojunction for Enhanced Visible-Light Photocatalysis. ACS Appl. Mater. Interfaces 2013, 5, 11392−11401.

(38) Yu, S.; Li, J.; Zhang, Y.; Li, M.; Dong, F.; Zhang, T.; Huang, H. Local Spatial Charge Separation and Proton Activation Induced by Surface Hydroxylation Promoting Photocatalytic Hydrogen Evolution of Polymeric Carbon Nitride. Nano Energy 2018, 50, 383−392. (39) Tian, N.; Zhang, Y.; Li, X.; Xiao, K.; Du, X.; Dong, F.; Waterhouse, G. I. N.; Zhang, T.; Huang, H. Precursor-reforming Protocol to 3D Mesoporous g-C3N4 Established by Ultrathin Selfdoped Nanosheets for Superior Hydrogen Evolution. Nano Energy 2017, 38, 72−81. (40) Huang, H.; Xiao, K.; Tian, N.; Dong, F.; Zhang, T.; Du, X.; Zhang, Y. Template-free Precursor-surface-etching Route to Porous, Thin g-C3N4 Nanosheets for Enhancing Photocatalytic Reduction and Oxidation Activity. J. Mater. Chem. A 2017, 5, 17452−17463. (41) Dean, C. R.; Young, A. F.; Meric, I.; Lee, C.; Wang, L.; Sorgenfrei, S.; Watanabe, K.; Taniguchi, T.; Kim, P.; Shepard, K. L.; Hone, J. Boron Nitride Substrates for High-quality Graphene Electronics. Nat. Nanotechnol. 2010, 5, 722−726. (42) Li, X.-H.; Chen, J.-S.; Wang, X.; Sun, J.; Antonietti, M. MetalFree Activation of Dioxygen by Graphene/g-C3N4 Nanocomposites: Functional Dyads for Selective Oxidation of Saturated Hydrocarbons. J. Am. Chem. Soc. 2011, 133, 8074−8077. (43) Hong, X.; Kim, J.; Shi, S.-F.; Zhang, Y.; Jin, C.; Sun, Y.; Tongay, S.; Wu, J.; Zhang, Y.; Wang, F. Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures. Nat. Nanotechnol. 2014, 9, 682−686. (44) Rehman, A. u.; Khan, M. F.; Shehzad, M. A.; Hussain, S.; Bhopal, M. F.; Lee, S. H.; Eom, J.; Seo, Y.; Jung, J.; Lee, S. H. nMoS2/p-Si Solar Cells with Al2O3 Passivation for Enhanced Photogeneration. ACS Appl. Mater. Interfaces 2016, 8, 29383−29390. (45) Lin, B.; An, H.; Yan, X.; Zhang, T.; Wei, J.; Yang, G. Fish-scale Structured g-C3N4 Nanosheet with Unusual Spatial Electron Transfer Property for High-efficiency Photocatalytic Hydrogen Evolution. Appl. Catal., B 2017, 210, 173−183. (46) Tian, J.; Ning, R.; Liu, Q.; Asiri, A. M.; Al-Youbi, A. O.; Sun, X. Three-Dimensional Porous Supramolecular Architecture from Ultrathin g-C3N4 Nanosheets and Reduced Graphene Oxide: Solution Self-Assembly Construction and Application as a Highly Efficient Metal-Free Electrocatalyst for Oxygen Reduction Reaction. ACS Appl. Mater. Interfaces 2014, 6, 1011−1017. (47) Yang, X.; Qian, F.; Zou, G.; Li, M.; Lu, J.; Li, Y.; Bao, M. Facile Fabrication of Acidified g-C3N4/g-C3N4 Hybrids with Enhanced Photocatalysis Performance under Visible Light Irradiation. Appl. Catal., B 2016, 193, 22−35. (48) Tahir, M.; Cao, C.; Mahmood, N.; Butt, F. K.; Mahmood, A.; Idrees, F.; Hussain, S.; Tanveer, M.; Ali, Z.; Aslam, I. Multifunctional g-C(3)N(4) Nanofibers: A Template-free Fabrication and Enhanced Optical, Electrochemical, and Photocatalyst Properties. ACS Appl. Mater. Interfaces 2014, 6, 1258−65. (49) Dai, K.; Lu, L.; Liang, C.; Liu, Q.; Zhu, G. Heterojunction of Facet Coupled g-C3N4/surface-fluorinated TiO2 Nanosheets for Organic Pollutants Degradation under Visible LED Light Irradiation. Appl. Catal., B 2014, 156, 331−340. (50) Ning, X.; Meng, S.; Fu, X.; Ye, X.; Chen, S. Efficient utilization of Photogenerated Electrons and Holes for Photocatalytic Selective Organic Syntheses in One Reaction System Using A Narrow Band Gap CdS Photocatalyst. Green Chem. 2016, 18, 3628−3639. (51) Feng, J. J.; Zhang, D. K.; Zhou, H. P.; Pi, M. Y.; Wang, X. D.; Chen, S. J. Coupling P Nanostructures with P-Doped g-C3N4 As Efficient Visible Light Photocatalysts for H2 Evolution and RhB Degradation. ACS Sustainable Chem. Eng. 2018, 6, 6342−6349. (52) Li, H.; Zhou, Y.; Tu, W.; Ye, J.; Zou, Z. State-of-the-Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance. Adv. Funct. Mater. 2015, 25, 998− 1013. (53) Fu, J.; Yu, J.; Jiang, C.; Cheng, B. g-C 3 N 4 -Based Heterostructured Photocatalysts. Adv. Energy Mater. 2018, 8, 1701503. G


Article

ACS Applied Energy Materials (54) Dutta, S. K.; Mehetor, S. K.; Pradhan, N. Metal Semiconductor Heterostructures for Photocatalytic Conversion of Light Energy. J. Phys. Chem. Lett. 2015, 6, 936−944. (55) 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 H-2 Generation under Visible Light Irradiation. ACS Appl. Mater. Interfaces 2016, 8, 15258−15266. (56) Kaake, L. G.; Moses, D.; Heeger, A. J. Coherence and Uncertainty in Nanostructured Organic Photovoltaics. J. Phys. Chem. Lett. 2013, 4, 2264−2268. (57) Gélinas, S.; Rao, A.; Kumar, A.; Smith, S. L.; Chin, A. W.; Clark, J.; Poll, T. S.; Bazan, G. C.; Friend, R. H. Ultrafast Long-range Charge Separation in Organic Semiconductor Photovoltaic Diodes. Science 2014, 343, 512−516. (58) Grancini, G.; Maiuri, M.; Fazzi, D.; Petrozza, A.; Egelhaaf, H. J.; Brida, D.; Cerullo, G.; Lanzani, G. Hot Exciton Dissociation in Polymer Solar Cells. Nat. Mater. 2013, 12, 29−33. (59) Jailaubekov, A. E.; Willard, A. P.; Tritsch, J. R.; Chan, W. L.; Sai, N.; Gearba, R.; Kaake, L. G.; Williams, K. J.; Leung, K.; Rossky, P. J.; Zhu, X. Y. Hot Charge-transfer Excitons Set The Time Limit for Charge Separation at Donor/acceptor Interfaces in Organic Photovoltaics. Nat. Mater. 2013, 12, 66−73.

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