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Facile gel-based morphological control of Ag/g-C3N4 porous nanofibers for photocatalytic hydrogen generation Jiangpeng Wang, Jingkun Cong, Hui Xu, Jinming Wang, Hong Liu, Mei Liang, Junkuo Gao, Qing-Qing Ni, and Juming Yao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02608 • Publication Date (Web): 21 Sep 2017 Downloaded from http://pubs.acs.org on September 24, 2017

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ACS Sustainable Chemistry & Engineering

Facile gel-based morphological control of Ag/g-C3N4 porous nanofibers for photocatalytic hydrogen generation

Jiangpeng Wang,a‡ Jingkun Cong,a‡ Hui Xu,b* Jinming Wang,a Hong Liu,a Mei Liang,a Junkuo Gao,a,c*, Qingqing Nid, Juming Yaoa a

The Key laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of

Education, National Engineering Lab for Textile Fiber Materials and Processing Technology (Zhejiang), College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China. b

Institute of Coordination Bond Metrology and Engineering, College of Materials Science and

Engineering, China Jiliang University, Hangzhou 310018, China. c

State Key Laboratory of Silicon Materials, College of Materials Science and Engineering,

Zhejiang University, Hangzhou 310027, China d

Department of Mechanical Engineering & Robotics, Shinshu University, 3-15-1 Tokida, Ueda,

Nagano 386-8576, Japan

Corresponding Author J. Gao: [email protected];

H. Xu: [email protected]; ‡ These authors have equal contribution to this paper.

1

ACS Paragon Plus Environment


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Abstract: Developing novel methods to prepare g-C3N4 nanocomposites with controlled morphologies is highly desirable because this type of materials have been widely studied as promising photocatalysts. In this report, we develop a new and facile supramolecular hydrogel approach as self-template to fabricate porous nanofiber-type Ag/g-C3N4 nanocomposites with significantly enhanced photocatalytic hydrogen evolution behaviors. The Ag/g-C3N4 nanofibers possess high specific surface areas, extended absorption in the visible light region and promoted photoinduced electron-hole separation capability. The as-prepared porous fiber-type Ag/g-C3N4

exhibit

highly-efficient

hydrogen

evolution

under

visible-light

illumination (625 µmol h-1 g-1), which could reach nearly 6.6 times of that of the pristine g-C3N4. This work highlights a feasible but simple strategy for the preparation of g-C3N4 nanocomposite fibers with enhanced photocatalytic activity. Keywords: Carbon nitride; Nanofiber; Supramolecular hydrogel; photocatalytic hydrogen generation; Nanocomposites

Introduction Since the landmark report on n-type TiO2 for photoeletrochemical splitting of water in 1972, the photocatalytic production of hydrogen technology has been considered as one of the most important approaches to address global energy crisis and environmental issues.1-10 Among various photocatalysts investigated, graphitic carbon nitride (g-C3N4) has been receiving enormous research 2


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interests in photocatalytic hydrogen production due to its visible-light-driven bandgap, nontoxicity, excellent chemical stability, and low cost.11-17 However, the photocatalytic efficiency of bulk g-C3N4 (quantum efficiency = 0.1% at 420-460 nm) is still far from satisfaction, mainly because of the small surface areas, low optical absorption in the visible region, and fast rate of photogenerated charge recombination.18 Synthesis of nanostructures with controllable morphologies is an efficient strategy to improve the photocatalytic activities, because well-defined nanomaterials not only accelerate the separation of photogenerated charge carriers but also facilitate mass transfer.19-26 Although extensive researches have been carried out for the modifications of g-C3N4 synthesis, those with well-controlled morphologies are still rare. One efficient strategy to construct nanostructures is hard-template approach, which is controllable and flexible to synthesize g-C3N4 with different morphologies in a precise manner.27-31 However, this method involves pre-prepared templates and requires more complicated steps to remove the template matrix. Another strategy is organic supramolecular approach, which mainly uses pre-organized organic molecule assemblies

as

ordered

textures

to

obtain

the

preformed

micro-

or

nanostructures.32-36 However, the choice of precursors is limited because not all precursors will form hydrogen bonding in solvents. On the other hand, nanocomposite approach has been demonstrated to be an important strategy to improve the photocatalytic performance of g-C3N4.37-40 For instance, many 3



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novel metal/semiconductor nanocomposite photocatalysts have been designed on the basis of surface plasmon resonance (SPR) of metal nanoparticles.41-46 However, it still remains a big challenge to simultaneously achieve both nanostructures and nanocomposites approach in g-C3N4 through a facile and cost-effective strategy. Metal–organic supramolecular networks, self-assembled from metallic nodes and organic ligands through metal coordination, hydrogen bonding and π-π interactions, have been widely employed to construct various functional nano-/micro-structures.47-50 In particular, the chemical structure of melamine allows that it not only forms H-bonding and π-stacking but also coordinates with different metal ions. Thus, distinguishing melamine as a fascinating scaffold

component

can

be

used

to

develop

desired

metal-organic

supramolecular nano-architecture.51-53 By using proper thermal condensation conditions, metal–melamine supramolecular complexes would be good self-templates to generate g-C3N4 nanostructures with well-defined morphology. The metal-organic supramolecular approach has several advantages: (1) The diverse metal ions and the flexible reaction conditions such as temperature, solvent, and molar ratio, can lead to highly tailorable metal-melamine structures, which could subsequently influence the morphologies of the as-formed g-C3N4; (2) The metal components in the metal–organic supramolecular complexes can easily lead to the metal or metal oxide/g-C3N4 nanocomposites upon heating; and (3) The metal–organic supramolecular approach is simple, facile and 4


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cost-effective.54 However, to the best of our knowledge, the synthesis of metal /g-C3N4 nanocomposite nanostructure with well-controlled morphology by metal–organic supramolecular approach has been rarely explored. Here, we report a new metal–organic supramolecular hydrogel approach for the preparation of porous nanofiber-type Ag/g-C3N4 nanocomposites with significantly enhanced photocatalytic hydrogen production properties (Scheme 1). The Ag–melamine supramolecular hydrogels obtained by simply mixing the precursors in aqueous solution was utilized to synthesize the Ag/g-C3N4 nanocomposites. The high surface areas, fast photogenerated-charge separation and the surface plasmonic enhanced visible-light absorption lead to the significantly improved photocatalytic hydrogen production performance.

Scheme 1. Preparation of porous nanofiber-like Ag/g-C3N4 from Ag-melamine supramolecular hydrogels.

Experimental Materials and Method 5



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All chemicals were purchased from Alfa Aesar, TCI chemical and Aldrich and used without further purification. Powder X-ray diffraction data were recorded

on

a

Bruker

D8

Advance

diffractometer

with

a

graphite-monochromatized Cu Ka radiation. FTIR spectra were recorded from KBr pellets by using a Perkin Elmer FTIR SpectrumGX spectrometer. Thermogravimetric analysis (TGA) was carried out on a TA Instrument Q500 Thermogravimetric Analyzer at a heating rate of 20℃/min up to 800℃under N2 atmosphere. UV-Vis absorption spectra were obtained using a Hitachi U-2900 spectrophotometer. Elemental analyses were obtained from a ThermoFinnigan Instruments

Flash

EA1112

microelemental

analyser.

The

Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface areas. The N2 adsorption-desorption isotherms at 77 K were measured on a Micrometrics ASAP 2010 system to evaluate their pore structures. All the samples were degassed at 120 ℃for 2 h before the surface area measurements. The morphologies of the photocatalysts were observed by field emission scanning electron microscopy (FE-SEM, Vltra55, Carl Zeiss) and transmission electron microscopy (TEM, JEM-2100). X-ray photoelectron spectroscopy (XPS) data were obtained with a Thermal Fisher Scientific K-Alpha electron spectrometer. The optical diffuse reflectance spectra were measured on a Hitachi UH4150 UV-Vis-NIR spectrometer equipped with an integrating sphere. BaSO4 was used as the reference material, and the polycrystalline samples were ground well before the measurement. The absorption (α/S) data 6


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were calculated from the reflectance using the Kubelka–Munk function: α/S = (1-R)2/2R, in which R is the reflectance at a given wavelength, α is the absorption coefficient, and S is the scattering coefficient. PL spectra of the sample powders were taken on a Hitachi F4600 fluorescence spectrometer. The PL lifetime was taken on an Edinburgh Instrument F900, both the excitation and emission slits are 1.5 nm. The excitation wavelengths are 370 nm. Synthesis of Ag-melamine supramolecular hydrogels AgMA-n with different Ag/melamine ratios were synthesized. For AgMA-1, AgNO3 (40 mg, 0.5 mmol) and melamine (750 mg, 6 mmol) was added to water (10 mL) in a glass bottle (20 mL). The mixture was heated to 90 oC in an oven for 10 min and a clear solution was obtained. After that, the solution was cooled to RT to form the hydrogels. Then, the hydrogel was freeze-dried. For AgMA-2, AgNO3 (40 mg, 0.5 mmol) and melamine (375 mg, 3 mmol) was added to water (10 mL) in a glass bottle (20 mL). The mixture was heated to 90 o

C in an oven for 10 min and a clear solution was obtained. After that, the

solution was cooled to RT to form the hydrogels. Then, the hydrogel was freeze-dried. For AgMA-3, AgNO3 (40 mg, 0.5 mmol) and melamine (125 mg, 1 mmol) was added to water (10 mL) in a glass bottle (20 mL). The mixture was heated to 90 oC in an oven for 10 min and a clear solution was obtained. After that, the solution was cooled to RT to form the hydrogels. Then, the hydrogel was freeze-dried. Synthesis of Ag-g-C3N4 nanocomposites 7



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Ag-g-C3N4-n was fabricated by heating AgMA-n precursors in furnace at 550℃ for 4 hours under Ar with a heating rate of 2℃/min. Photocatalytic hydrogen generation Photocatalytic reactions were carried out in a closed-gas circulation system. The reaction cell was made up of Pyrex glass with a quartz window suitable for vertical illumination. A 300 W Xe lamp was used as a light source. A 420 nm cut-off filter was employed to screen the UV light. In all tests, 50 mg of catalyst was suspended in 100mL of an aqueous solution containing triethanolamine (TEOA) (10mL) as the sacrificial electron donor and 1 wt% Pt as the cocatalyst. Prior to the reaction, the system was evacuated several times by a mechanical pump to remove air. The reaction suspension was stirred with a magnetic stirrer under illumination. The gases in the reaction system were circulated with a glass piston pump. The reaction was carried out for 4 h and the amount of hydrogen evolved was analyzed by gas chromatograph (Techcomp GC7900; Molecular sieve-5A, TCD detector, Ar carrier gas). Results and Discussion Synthesis and characterization The Ag-melamine hydrogels were facilely and efficiently prepared by heating different molar ratios of Ag+/melamine in water (AgMA-1 with the Ag+/melamine molar ratio of 1:12; AgMA-2 with the Ag+/melamine molar ratio of 1:6; AgMA-3 with the Ag+/melamine molar ratio of 1:2). Note that when the molar ratio of Ag+/melamine is smaller than 1:12, no hydrogels were 8


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formed. Ag/g-C3N4 nanocomposites with different concentrations of Ag NPs were obtained through the heat treatment of AgMA-n at 550 oC for 4 h under Ar atmosphere, and named as Ag-g-C3N4-1 from AgMA-1, Ag-g-C3N4-2 from AgMA-2 and Ag-g-C3N4-3 from AgMA-3, accordingly. The morphologies of the as-prepared Ag-melamine hydrogels were studied via SEM. As shown in Figure 1(a-c), all the Ag-melamine hydrogels displayed nanofiber structures. The length of the nanofibers can reach several hundred micrometers. After heat treatment, the nanofiber-like structures were remained as seen in Figure 1(d-f), which indicates that the Ag-melamine hydrogels could serve as the self-templated agents. The morphologies of Ag/g-C3N4 nanocomposites were further investigated via TEM. As displayed in Figure 2, Ag-g-C3N4-1 and Ag-g-C3N4-2 showed porous nanofiber-like structures. No obvious Ag NPs were observed in Ag-g-C3N4-1, while small Ag NPs were decorated on the surface of nanofibers in Ag-g-C3N4-2. Interestingly, Ag-g-C3N4-3 had a nanotube-like structure with Ag NPs adhered on the surface.

Figure 1. (a) SEM image of AgMA3. (b) SEM image of AgMA2. (c) SEM image of AgMA1. (d) SEM image of

Ag-g-C3N4-3. (e) SEM image of Ag-g-C3N4-2. (f) SEM image of Ag-g-C3N4-1. 9



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Figure 2. (a) TEM image of Ag-g-C3N4-1. (b) TEM image of Ag-g-C3N4-2. (c) TEM image of Ag-g-C3N4-3.

The XRD patterns of g-C3N4 and Ag/g-C3N4 porous nanofibers were shown in Figure 3. The strong peak located at 27.3o of g-C3N4 is a characteristic interlayer stacking reflection, indexed as the (002) peak. The small diffraction peak at around 13.0o of g-C3N4 is related to the (100) in-plane structural repeating motif. For Ag/g-C3N4 porous nanofibers, the peak around 27.4o is the characteristic peaks of g-C3N4, which should be assigned to the interlayer stacking of the (002) peak.55 After hybridized with Ag, the (002) peak of g-C3N4 demonstrated almost no shift. The peaks at 38o and 44o correspond to the (111) and (200) planes of the cubic phase of Ag, which confirmed the formation of Ag/g-C3N4 nanocomposites.56-58 With the increasing concentrations of Ag, the peaks of Ag become stronger.

Figure 3. XRD patterns of the synthesized Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3. 10


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Elemental analysis data of all the samples are displayed in Table S1. The total amounts of C, N and H elements in Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are 88.64%, 74.29% and 45.25%, respectively. The rest part is the metallic Ag component. With the increasing ratio of Ag/melamine in the hydrogel precursors, the amount of Ag component increased from 11.36% in Ag-g-C3N4-1 to 54.75% in Ag-g-C3N4-3. The contents of Ag in all the samples were also confirmed via TG analysis (Figure S2). After the decomposition of g-C3N4 part, the residue contents for Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are about 11%, 26% and 55%, respectively. Since the calculated N/C molar ratios in Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are 1.51, 1.49 and 1.46, respectively, Ag-g-C3N4-1 demonstrates smaller N/C ratio compared with bulk g-C3N4 obtained at the same condition (1.51 vs 1.52). When the content of Ag is increased in the samples, reduced N/C ratios are observed, indicating that the Ag component could promote the polymeric condensation in the melamine-based precursors. The FTIR spectra of Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are shown in Figure S3. The peaks in the range of 1200~1650 cm-1 are the typical stretching modes of CN heterocycles. The peaks in the region of 800~810 cm-1 are the characteristic breathing modes of the triazine units.59 The broad peak around 3300 cm-1 can be assigned to the stretching vibration of NH or NH2 groups. The surface chemical compositions of Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 were revealed by X-ray photoelectron spectroscopy (XPS). The 11



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XPS spectra of Ag-g-C3N4-1 were given in Figure 4(a-c). The high resolution XPS spectrum of C 1s shows two peaks at 284.9 and 288.4 eV, which could be assigned to the C-C coordination and N=C-N2 coordination (C atom bonded to three N atoms in the lattice), respectively.55 The spectrum for N 1s can be fitted well with four peaks at 398.8 eV, 399.7 eV, 401.4 eV and 404.6 eV, respectively. The peak at 398.8 eV can be attributed to N atoms in C=N-C groups.60 The three other peaks are ascribed to the sp2 hybridized N atoms bonded to three C atoms (N-C3), sp3 hybridized terminal N of heptazine ring (C-NH), and positive charge localization in heptazine rings, respectively.59 The peaks of Ag 3d at 368.1 eV and 374.1 eV belong to a typical level of Ag0, which correspond to Ag 3d5/2 and Ag 3d3/2 states respectively, indicating the existence of metallic Ag specie in the composite.61 The XPS spectra of Ag-g-C3N4-2 are similar to that of Ag-g-C3N4-1, as seen in Figure 4(d-f). The high resolution XPS spectrum of C 1s shows two peaks at 284.8 (C-C) and 288.3 eV (N=C-N2), respectively. The spectrum for N 1s can be fitted well with four peaks at 398.9 eV (C=N-C), 399.8 eV (N-C3), 401.4 eV (C-NH) and 404.6 eV (positive charge localization in heptazine rings), respectively. The peaks of Ag 3d at 368.0 eV and 374.1 eV could be assigned to a typical level of Ag0. The XPS spectra of Ag-g-C3N4-3 are also similar to that of Ag-g-C3N4-1, as seen in Figure S4.

12


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Figure 4. XPS spectra of the synthesized Ag-g-C3N4-1 and Ag-g-C3N4-2. (a) C 1s spectra of Ag-g-C3N4-1. (b) N 1s spectra of Ag-g-C3N4-1. (c) Ag 3d spectra of Ag-g-C3N4-1. (d) C 1s spectra of Ag-g-C3N4-2. (e) N 1s spectra of Ag-g-C3N4-2. (f) Ag 3d spectra of Ag-g-C3N4-2.

The BET surface areas of Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are 9.8, 18.5 and 26.0 m2 g-1, respectively, while the BET surface area of bulk g-C3N4 is 5.2 m2g-1 (Figure S5). The porous Ag/g-C3N4 nanofibers showed obvious increase of BET surface areas compared with bulk g-C3N4. With the increase of Ag amount, the BET surface areas of Ag-g-C3N4-n are improved, indicating that the hydrogel-based approach could improve the surface areas of g-C3N4. The BJH (Barrett–Joyner– Halenda) pore-size distribution curves (Figure S6) reveal that all of the Ag-g-C3N4-n exhibit a narrow peak centered at 2.57 nm, indicating the existence of mesopores in the Ag/g-C3N4 nanofibers. Optical properties

13



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The optical properties of Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 nanofibers were studied via UV-vis absorption spectra, steady state and time-resolved photoluminescence (PL) emission spectra. UV-vis diffuse reflectance spectra of Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3 are shown in Figure 5. Compared with pure g-C3N4, all the Ag/g-C3N4 samples show the broadened absorption in the visible light region, which may enhance the efficiency for the utilization of solar energy. This phenomenon is mainly attributed to the SPR effect of Ag nanoparticles.45 Obviously, with the increase of Ag content, stronger absorption in the visible region is displayed, which confirms that Ag nanoparticles can improve the light absorption in visible region.

Figure 5. The solid state UV-vis diffusion reflectance spectra of g-C3N4, Ag-g-C3N4-1, Ag-g-C3N4-2 and Ag-g-C3N4-3.

The steady state and time-resolved PL spectra of all the samples are studied in detail, which are useful to reveal the migration, transfer and separation efficiency of the photo-generated charge carriers. As seen in the stead state PL spectra in Figure 6(a), g-C3N4 shows a strong PL emission with a peak at 480 14


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nm when excited with 375 nm light source. The emission of Ag-g-C3N4-1 also displays a maximum at 480 nm, yet the spectrum is obviously broadened to the bathochromic region. Compared with g-C3N4, the emission peak of Ag-g-C3N4-2 is red-shifted to 577 nm, indicating a new transfer pathway is formed for the photo-generated charge carriers of g-C3N4. For Ag-g-C3N4-3, almost no PL emission is observed. The recombination of photo-generated charge carriers was also investigated via the time resolved spectroscopy, as shown in Figure 6(b). Under excitation of 370 nm, the decay curves of g-C3N4, Ag-g-C3N4-1 and Ag-g-C3N4-2 fit well with biexponential decay. Ag-g-C3N4-1 shows increased PL lifetimes compared with bulk g-C3N4. The PL lifetime of Ag-g-C3N4-2 (10.19 ns) is 50% larger than that of pure g-C3N4 (6.70 ns). The results illuminated that the Ag component in g-C3N4 especially in Ag-g-C3N4-2 could efficiently inhibit the recombination of charge carriers, thus would improve the photocatalytic activities.

Figure 6. (a) The steady state PL spectra of Ag-g-C3N4 and g-C3N4 with excitation wavelength of 375 nm. (b) Time resolved PL decay spectra of Ag-g-C3N4-1, Ag-g-C3N4-2 and g-C3N4, monitored at 488 nm, 488 nm and 577 nm, respectively.

Photocatalytic activity 15



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The photocatalytic activities of the Ag-g-C3N4 nanofibers were investigated for photocatalytic hydrogen evolution from a water/triethanloamine solution under visible light illumination. As shown in Figure 7(a), about 75 µmol of H2 was generated over Ag-g-C3N4-1 catalyst after four hours’ illumination, which is 2.9 times higher than the amount of H2 generated over bulk g-C3N4 (19

µmol). About 125 µmol of H2 was generated over Ag-g-C3N4-2 catalyst after 4 hours’ illumination (625 µmol h-1 g-1), which is 6.6 times as that of bulk g-C3N4. No H2 evolution is observed for Ag-g-C3N4-3. The results indicate that with the increase of Ag content up to 26 wt%, the photocatalytic activity of samples is improved

compared

with

bulk

g-C3N4.

The

remarkably

increased

photocatalytic activities of Ag/g-C3N4 nanocomposites can be explained as the enhanced absorption of light in the visible light region, high separation efficiency of photogenerated electron-holes, and prolonged lifetime of charge carries. The introduction of Ag into g-C3N4 can form porous nanofiber structures and improve the surface areas. Also, Ag nanoparticles in the nanocomposites can obviously enhance the light absorption in visible region. As confirmed via the steady and time resolved PL spectra, a new transfer pathway is formed for the photo-generated charge carriers of Ag-g-C3N4 which could efficiently inhibit the recombination of charge carriers when compared with g-C3N4. However, when the Ag content is too high as seen in Ag-g-C3N4-3 (55 wt%), no photocatalytic activity is observed, which may result from that large number of defects caused by the high Ag content because 16


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defects hamper the charge transfer process. Furthermore, the photocatalytic stability of Ag-g-C3N4-2 was studied in a three-run test experiments. Almost no decrease in the H2 evolution was observed after a three-run test, indicating that Ag-g-C3N4-2 has good photocatalytic stability for visible-light driven H2 generation (Figure 7(b)). Also, the SEM image (Figure S7) and XRD pattern (Figure S8) of Ag-g-C3N4-2 after photocatalysis showed no difference with the fresh catalyst, indicating the high photocatalytic stability of Ag-g-C3N4 nanocomposites.

Figure 7. (a) Photocatalytic H2 evolution of the samples under visible light illumination. (b) Three-run test of photocatalytic H2 evolution of compound Ag-g-C3N4-2.

Conclusions In conclusion, a new and facile metal–organic supramolecular hydrogel approach

for

the

preparation

of

porous

nanofiber-like

Ag/g-C3N4

nanocomposites has been developed. The Ag–melamine supramolecular hydrogels with nanofiber structures acted as self-templated agents to prepare the Ag/g-C3N4 nanocomposites through heat treatment. The as-obtained Ag/g-C3N4

porous

nanofibers

show

higher

surface

areas,

faster

photogenerated-charge separation and enhanced visible-light adsorption 17



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compared with bulk g-C3N4, which leads to the significantly improved photocatalytic hydrogen evolution performance. Our results clearly suggest that metal-melamine supramolecular hydrogels would be promising precursors for the fabrication of g-C3N4 nanocomposites with controllable morphologies, leading to efficiently enhanced photocatalytic activities.

Supporting Information TGA curves, IR spectra, XPS spectra of the samples. The Supporting Information is available free of charge on

the ACS Publications website.

AUTHOR INFORMATION Corresponding Author J. Gao: [email protected];

H. Xu: [email protected];

‡ These authors have equal contribution to this paper.

Acknowledgements This work is supported by the National Natural Science Foundation of China (51402261 and 51602301 and 51672251) and Science Foundation of Zhejiang Sci-Tech University (ZSTU) under Grant No. 13012138-Y. J. G. acknowledges the financial support from the Qianjiang talents plan of Zhejiang Province (QJD1502019).

Notes

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The authors declare no competing financial interest.

REFERENCES (1)

Tee, S. Y.; Win, K. Y.; Teo, W. S.; Koh, L. D.; Liu, S.; Teng, C. P.; Han, M. Y. Recent Progress in Energy‐

Driven Water Splitting. Adv. Sci. 2017, 4, 1600337. (2)

Ghosh, S.; Kouamé, N. A.; Ramos, L.; Remita, S.; Dazzi, A.; Deniset-Besseau, A.; Beaunier, P.; Goubard,

F.; Aubert, P.-H.; Remita, H. Conducting polymer nanostructures for photocatalysis under visible light. Nat. Mater. 2015, 14, 505-511. (3)

Zou, X. X.; Zhang, Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem. Soc. Rev.

2015, 44, 5148-5180. (4)

Fujishima, A.; Honda, K. TiO2 photoelectrochemistry and photocatalysis. Nature 1972, 238, 37-38.

(5)

Gu, P.-Y.; Wang, Z.; Xiao, F.-X.; Lin, Z.; Song, R.; Xu, Q.-F.; Lu, J.-M.; Liu, B.; Zhang, Q. An ambipolar

azaacene as a stable photocathode for metal-free light-driven water reduction. Mater. Chem. Frontiers 2017, 1, 495-498. (6)

Zhang, Q.; Liu, Y.; Bu, X.; Wu, T.; Feng, P. A Rare (3, 4)‐Connected Chalcogenide Superlattice and Its

Photoelectric Effect. Angew. Chem. Int. Ed. 2008, 47, 113-116. (7)

Zhang, S.; Yang, H.; Huang, H.; Gao, H.; Wang, X.; Cao, R.; Li, J.; Xu, X.; Wang, X. Unexpected ultrafast

and high adsorption capacity of oxygen vacancy-rich WO x/C nanowire networks for aqueous Pb 2+ and methylene blue removal. J. Mater. Chem. A 2017, 5, 15913-15922. (8)

Zhang, S.; Yang, H.; Gao, H.; Cao, R.; Huang, J.; Xu, X. One-pot synthesis of CdS irregular nanospheres

hybridized with oxygen-incorporated defect-rich MoS2 ultrathin nanosheets for efficient photocatalytic hydrogen evolution. Acs Appl. Mater. Inter. 2017, 9, 23635-23646. (9)

Zhang, S.; Gao, H.; Li, J.; Huang, Y.; Alsaedi, A.; Hayat, T.; Xu, X.; Wang, X. Rice husks as a sustainable

silica source for hierarchical flower-like metal silicate architectures assembled into ultrathin nanosheets for adsorption and catalysis. J. Hazard. Mater. 2017, 321, 92-102. (10) Gao, J.; Miao, J.; Li, Y.; Ganguly, R.; Zhao, Y.; Lev, O.; Liu, B.; Zhang, Q. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells. Dalton Trans. 2015, 44, 14354-14358. (11) Xu, J.; Antonietti, M. The Performance of Nanoparticulate Graphitic Carbon Nitride as an Amphiphile. J. Am. Chem. Soc. 2017, 139, 6026-6029. (12) Ong, W. J.; Tan, L. L.; Ng, Y. H.; Yong, S. T.; Chai, S. P. Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability? Chem. Rev. 2016, 116, 7159-7329. (13) Liu, J.; Wang, H. Q.; Antonietti, M. Graphitic carbon nitride "reloaded'': emerging applications beyond (photo)catalysis. Chem. Soc. Rev. 2016, 45, 2308-2326. (14) Cao, S. W.; Low, J. X.; Yu, J. G.; Jaroniec, M. Polymeric Photocatalysts Based on Graphitic Carbon Nitride. Adv. Mater. 2015, 27, 2150-2176. (15) Liu, J.; Liu, Y.; Liu, N. Y.; Han, Y. Z.; Zhang, X.; Huang, H.; Lifshitz, Y.; Lee, S. T.; Zhong, J.; Kang, Z. H. Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway. Science 2015, 347, 970-974.

19



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

(16) Zheng, Y.; Lin, L.; Wang, B.; Wang, X. Graphitic Carbon Nitride Polymers toward Sustainable Photoredox Catalysis. Angew. Chem. Int. Ed. 2015, 54, 12868-12884. (17) Liu, J.; Wang, H.; Antonietti, M. Graphitic carbon nitride “reloaded”: emerging applications beyond (photo) catalysis. Chem. Soc. Rev. 2016, 45, 2308-2326. (18) Cao, S. W.; Yu, J. G. g-C3N4-Based Photocatalysts for Hydrogen Generation. J. Phys. Chem. Lett. 2014, 5, 2101-2107. (19) Lau, V. W. h.; Klose, D.; Kasap, H.; Podjaski, F.; Pignié, M. C.; Reisner, E.; Jeschke, G.; Lotsch, B. V. Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time‐Delayed Hydrogen Generation. Angew. Chem. Int. Ed. 2017, 56, 510-514. (20) Zhang, J. S.; Zhang, M. W.; Yang, C.; Wang, X. C. Nanospherical Carbon Nitride Frameworks with Sharp Edges Accelerating Charge Collection and Separation at a Soft Photocatalytic Interface. Adv. Mater. 2014, 26, 4121-4126. (21) Zheng, Y.; Lin, L.; Ye, X.; Guo, F.; Wang, X. Helical graphitic carbon nitrides with photocatalytic and optical activities. Angew. Chem. Int. Ed. 2014, 53, 11926-11930. (22) Zhang, S.; Gao, H.; Liu, X.; Huang, Y.; Xu, X.; Alharbi, N. S.; Hayat, T.; Li, J. Hybrid 0D–2D Nanoheterostructures: In Situ Growth of Amorphous Silver Silicates Dots on g-C3N4 Nanosheets for Full-Spectrum Photocatalysis. Acs Appl. Mater. Inter. 2016, 8, 35138-35149. (23) Kang, Y. Y.; Yang, Y. Q.; Yin, L. C.; Kang, X. D.; Liu, G.; Cheng, H. M. An Amorphous Carbon Nitride Photocatalyst with Greatly Extended Visible-Light-Responsive Range for Photocatalytic Hydrogen Generation. Adv. Mater. 2015, 27, 4572-4577. (24) Han, Q.; Wang, B.; Zhao, Y.; Hu, C. G.; Qu, L. T. A Graphitic-C3N4 "Seaweed" Architecture for Enhanced Hydrogen Evolution. Angew. Chem. Int. Ed. 2015, 54, 11433-11437. (25) Han, Q.; Wang, B.; Gao, J.; Qu, L. Graphitic Carbon Nitride/Nitrogen-Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts. Angew. Chem. Int. Ed. 2016, 55, 10849-10853. (26) Gao, J.; Miao, J.; Li, P.-Z.; Teng, W. Y.; Yang, L.; Zhao, Y.; Liu, B.; Zhang, Q. A p-type Ti( IV)-based metal-organic framework with visible-light photo-response. Chem. Commun. 2014, 50, 3786-3788. (27) Zhao, Z.; Dai, Y.; Lin, J.; Wang, G. Highly-Ordered Mesoporous Carbon Nitride with Ultrahigh Surface Area and Pore Volume as a Superior Dehydrogenation Catalyst. Chem. Mater. 2014, 26, 3151-3161. (28) Liang, Q.; Li, Z.; Yu, X.; Huang, Z.-H.; Kang, F.; Yang, Q.-H. Macroscopic 3D Porous Graphitic Carbon Nitride Monolith for Enhanced Photocatalytic Hydrogen Evolution. Adv. Mater. 2015, 27, 4634-4639. (29) Liu, J.; Huang, J.; Zhou, H.; Antonietti, M. Uniform graphitic carbon nitride nanorod for efficient photocatalytic hydrogen evolution and sustained photoenzymatic catalysis. ACS Appl. Mater. Inter. 2014, 6, 8434-8440. (30) Hu, M.; Reboul, J.; Furukawa, S.; Radhakrishnan, L.; Zhang, Y.; Srinivasu, P.; Iwai, H.; Wang, H.; Nemoto, Y.; Suzuki, N.; Kitagawa, S.; Yamauchi, Y. Direct synthesis of nanoporous carbon nitride fibers using Al-based porous coordination polymers (Al-PCPs). Chem. Commun. 2011, 47, 8124-8126. (31) Su, F. Z.; Mathew, S. C.; Lipner, G.; Fu, X. Z.; Antonietti, M.; Blechert, S.; Wang, X. C. mpg-C3N4-Catalyzed Selective Oxidation of Alcohols Using O-2 and Visible Light. J. Am. Chem. Soc. 2010, 132, 16299-16301.

20


Page 20 of 24

Page 21 of 24

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


(32) Yu, H.; Shi, R.; Zhao, Y.; Bian, T.; Zhao, Y.; Zhou, C.; Waterhouse, G. I.; Wu, L. Z.; Tung, C. H.; Zhang, T. Photocatalysis: Alkali‐Assisted Synthesis of Nitrogen Deficient Graphitic Carbon Nitride with Tunable Band Structures for Efficient Visible‐Light‐Driven Hydrogen Evolution. Adv. Mater. 2017, 29, 1605148. (33) Tong, Z.; Yang, D.; Sun, Y.; Nan, Y.; Jiang, Z. Tubular g-C3N4 Isotype Heterojunction: Enhanced Visible-Light Photocatalytic Activity through Cooperative Manipulation of Oriented Electron and Hole Transfer. Small 2016, 12, 4093-4101. (34) Shalom, M.; Inal, S.; Fettkenhauer, C.; Neher, D.; Antonietti, M. Improving carbon nitride photocatalysis by supramolecular preorganization of monomers. J. Am. Chem. Soc. 2013, 135, 7118-7121. (35) Cui, Y. J.; Ding, Z. X.; Fu, X. Z.; Wang, X. C. Construction of Conjugated Carbon Nitride Nanoarchitectures in Solution at Low Temperatures for Photoredox Catalysis. Angew. Chem. Int. Ed. 2012, 51, 11814-11818. (36) Jun, Y.-S.; Lee, E. Z.; Wang, X.; Hong, W. H.; Stucky, G. D.; Thomas, A. From Melamine-Cyanuric Acid Supramolecular Aggregates to Carbon Nitride Hollow Spheres. Adv. Funct. Mater. 2013, 23, 3661-3667. (37) Jiang, W.; Luo, W.; Zong, R.; Yao, W.; Li, Z.; Zhu, Y. Polyaniline/Carbon Nitride Nanosheets Composite Hydrogel: A Separation‐Free and High‐Efficient Photocatalyst with 3D Hierarchical Structure. Small 2016, 12, 4370-4378. (38) Wang, N. N.; Zhou, Y.; Chen, C. H.; Cheng, L. Y.; Ding, H. M. A g-C3N4 supported graphene oxide/Ag3PO4 composite with remarkably enhanced photocatalytic activity under visible light. Catal. Commun. 2016, 73, 74-79. (39) Shi, M. J.; Wu, T. H.; Song, X. F.; Liu, J.; Zhao, L. P.; Zhang, P.; Gao, L. Active Fe2O3 nanoparticles encapsulated in porous g-C3N4/graphene sandwich-type nanosheets as a superior anode for high-performance lithium-ion batteries. J. Mater. Chem. A 2016, 4, 10666-10672. (40) Zhao, Z. W.; Sun, Y. J.; Dong, F. Graphitic carbon nitride based nanocomposites: a review. Nanoscale 2015, 7, 15-37. (41) Meng, X.; Liu, L.; Ouyang, S.; Xu, H.; Wang, D.; Zhao, N.; Ye, J. Nanometals for Solar-to-Chemical Energy Conversion: From Semiconductor-Based Photocatalysis to Plasmon-Mediated Photocatalysis and Photo-Thermocatalysis. Adv. Mater. 2016, 28, 6781-6803. (42) Neyts, E. C.; Ostrikov, K.; Sunkara, M. K.; Bogaerts, A. Plasma Catalysis: Synergistic Effects at the Nanoscale. Chem. Rev. 2015, 115, 13408-13446. (43) Zhang, G. G.; Lan, Z. A.; Lin, L. H.; Lin, S.; Wang, X. C. Overall water splitting by Pt/g-C3N4 photocatalysts without using sacrificial agents. Chem. Sci. 2016, 7, 3062-3066. (44) Zhuang, J. Y.; Lai, W. Q.; Xu, M. D.; Zhou, Q.; Tang, D. P. Plasmonic AuNP/g-C3N4 Nanohybrid-based Photoelectrochemical Sensing Platform for Ultrasensitive Monitoring of Polynucleotide Kinase Activity Accompanying DNAzyme-Catalyzed Precipitation Amplification. ACS Appl. Mater. Inter. 2015, 7, 8330-8338. (45) Fontelles-Carceller, O.; Munoz-Batista, M. J.; Fernandez-Garcia, M.; Kubacka, A. Interface Effects in Sunlight-Driven Ag/g-C3N4 Composite Catalysts: Study of the Toluene Photodegradation Quantum Efficiency. ACS Appl. Mater. Inter. 2016, 8, 2617-2627. (46) Fu, Y. S.; Huang, T.; Zhang, L. L.; Zhu, J. W.; Wang, X. Ag/g-C3N4 catalyst with superior catalytic performance for the degradation of dyes: a borohydride-generated superoxide radical approach. Nanoscale 2015, 7, 13723-13733.

21



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

(47) Tian, J.; Xu, Z.-Y.; Zhang, D.-W.; Wang, H.; Xie, S.-H.; Xu, D.-W.; Ren, Y.-H.; Wang, H.; Liu, Y.; Li, Z.-T. Supramolecular metal-organic frameworks that display high homogeneous and heterogeneous photocatalytic activity for H2 production. Nat. Commun. 2016, 7, 11580. (48) Urgel, J. I.; Écija, D.; Lyu, G.; Zhang, R.; Palma, C.-A.; Auwärter, W.; Lin, N.; Barth, J. V. Quasicrystallinity expressed in two-dimensional coordination networks. Nat. Chem. 2016, 8, 657-662. (49) Chaudhari, A. K.; Han, I.; Tan, J. C. Supramolecular Materials: Multifunctional Supramolecular Hybrid Materials Constructed from Hierarchical Self‐Ordering of In Situ Generated Metal‐Organic Framework (MOF) Nanoparticles. Adv. Mater. 2015, 27, 4523-4523. (50) Cook, T. R.; Zheng, Y.-R.; Stang, P. J. Metal–organic frameworks and self-assembled supramolecular coordination complexes: comparing and contrasting the design, synthesis, and functionality of metal–organic materials. Chem. Rev. 2012, 113, 734-777. (51) Zhang, J.; Ou, C.; Shi, Y.; Wang, L.; Chen, M.; Yang, Z. Visualized detection of melamine in milk by supramolecular hydrogelations. Chem. Commun. 2014, 50, 12873-12876. (52) Roy, B.; Bairi, P.; Nandi, A. K. Supramolecular assembly of melamine and its derivatives: nanostructures to functional materials. Rsc Adv. 2014, 4, 1708-1734. (53) Sun, J.-K.; Xu, Q. Functional materials derived from open framework templates/precursors: synthesis and applications. Energy Environ. Sci. 2014, 7, 2071-2100. (54) Wang, J. P.; Xu, H.; Qian, X. F.; Dong, Y. Y.; Gao, J. K.; Qian, G. D.; Yao, J. M. Direct Synthesis of Porous Nanorod-Type Graphitic Carbon Nitride/CuO Composite from Cu-Melamine Supramolecular Framework towards Enhanced Photocatalytic Performance. Chem. Asian J. 2015, 10, 1276-1280. (55) Zhao, Z.; Sun, Y.; Dong, F. Graphitic carbon nitride based nanocomposites: A review. Nanoscale 2015, 7, 15-37. (56) Tian, K.; Liu, W.-J.; Jiang, H. Comparative investigation on photoreactivity and mechanism of biogenic and chemosythetic Ag/C3N4 composites under visible light irradiation. ACS Sustain. Chem. Eng. 2015, 3, 269-276. (57) Fei, J.; Gao, L.; Zhao, J.; Du, C.; Li, J. Responsive Helical Self‐Assembly of AgNO3 and Melamine Through Asymmetric Coordination for Ag Nanochain Synthesis. Small 2013, 9, 1021-1024. (58) Lu, D.; Wang, H.; Zhao, X.; Kondamareddy, K. K.; Ding, J.; Li, C.; Fang, P. Highly efficient visible-light-induced photoactivity of Z-scheme g-C3N4/Ag/MoS2 ternary photocatalysts for organic pollutant degradation and production of hydrogen. Acs Sustain. Chem. Eng. 2017, 5, 1436-1445. (59) Cao, Y.; Zhang, Z.; Long, J.; Liang, J.; Lin, H.; Lin, H.; Wang, X. Vacuum heat-treatment of carbon nitride for enhancing photocatalytic hydrogen evolution. J. Mater. Chem. A 2014, 2, 17797-17807. (60) Zhou, Z. X.; Wang, J. H.; Yu, J. C.; Shen, Y. F.; Li, Y.; Liu, A. R.; Liu, S. Q.; Zhang, Y. J. Dissolution and Liquid Crystals Phase of 2D Polymeric Carbon Nitride. J. Am. Chem. Soc. 2015, 137, 2179-2182. (61) Zhang, S.; Li, J.; Wang, X.; Huang, Y.; Zeng, M.; Xu, J. In situ ion exchange synthesis of strongly coupled Ag@ AgCl/g-C3N4 porous nanosheets as plasmonic photocatalyst for highly efficient visible-light photocatalysis. ACS Appl. Mater. Inter. 2014, 6, 22116-22125.

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For Table of Contents Use Only

A new and facile hydrogel approach for the preparation of porous Ag/g-C3N4 composite nanofibers with efficiently improved photocatalytic hydrogen evolution performance is developed.

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ACS Sustainable Chemistry & Engineering - ACS Publications

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