Facile One-Step Synthesis of Hybrid Graphitic Carbon Nitride and

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Facile One Step Synthesis of Hybrid Graphitic Carbon Nitride and Carbon Composites as High Performance Catalysts for CO2 Photocatalytic Conversion Yangang Wang, Xia Bai, Hengfei Qin, Fei Wang, Yaguang Li, Xi Li, Shifei Kang, Yuanhui Zuo, and Lifeng Cui ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03472 • Publication Date (Web): 26 Apr 2016 Downloaded from http://pubs.acs.org on April 27, 2016

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ACS Applied Materials & Interfaces

Facile One Step Synthesis of Hybrid Graphitic Carbon Nitride and Carbon Composites as High Performance Catalysts for CO2 Photocatalytic Conversion Yangang Wang a, Xia Bai a, Hengfei Qin b, Fei Wang a, Yaguang Li a, Xi Li b, Shifei Kang a,*, Yuanhui Zuo a, Lifeng Cui a,* a

Department of Environmental Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China

b

Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China

*

Corresponding

authors.

Tel/Fax:

+86

21

55277504.

E-mail

[email protected] (S.F. Kang), [email protected] (L.F. Cui). 1 ACS Paragon Plus Environment

address:


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ABSTRACT: Utilizing and reducing carbon dioxide is a key target in the fight against global warming. The photocatalytic performance of bulk graphitic carbon nitride (g-C3N4) is usually limited by its low surface area and rapid charge carrier recombination. To develop g-C3N4 more suitable for photocatalysis, researchers have to enlarge its surface area and accelerate the charge carrier separation. In this work, novel hybrid graphitic carbon nitride and carbon (H-g-C3N4/C) composites with various carbon contents have been developed for the first time by a facile one-step pyrolysis method using melamine and natural soybean oil as precursors. The effect of carbon content on the structure of H-g-C3N4/C composites and the catalytic activity for the photoreduction of CO2 with H2O were investigated. The results indicated that the introduction of carbon component can effectively improve the textural properties and electronic

conductivity of

the

composites,

which

exhibited

imporved

photocatalytic activity for the reduction of CO2 with H2O in comparison with bulk g-C3N4. The highest CO and CH4 yield of 22.60 µmol/g-cat. and 12.5 µmol/g-cat., respectively, were acquired on the H-g-C3N4/C-6 catalyst with the carbon content of 3.77 wt. % under 9 h simulated solar irradiation, which were more than twice as high as that of bulk g-C3N4. The remarkably increased photocatalytic performance arises from the synergistic effect of hybrid carbon and g-C3N4. KEYWORDS: Hybrid, Graphitic carbon nitride, Carbon composite, Photocatalyst, CO2 reduction

1. INTRODUCTION

2 ACS Paragon Plus Environment

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The increasing level of atmospheric carbon dioxide (CO2) owing to the fossil fuel combustion is acknowledged as the main cause of climate change.1 Therefore, there is an urgent need to convert CO2 into industrially beneficial compounds (e.g. CO, CH4, CH3OH, HCOOH), which is of great significance to environmental protection and energy recycling. Among various methods that have been utilized for CO2 management, the efficient photocatalytic reduction of CO2 with H2O is regarded as one of the most promising and challenging techniques.2-9 To date, the majority of researches are focused on designing and developing efficient photocatalysts that can selectively reduce CO2 to valuable substances and hydrocarbon fuels. However, low photocatalytic activities have hindered its development because of the intrinsic physicochemical properties of semiconductors. Thus, seeking higher-efficiency photocatalysts that can largely improve CO2 conversion and yields has been a worldwide continuing endeavor.10-19 Recently, graphitic carbon nitride (g-C3N4), a new kind of metal-free conjugated polymer semiconductor with narrow band gap energy of 2.7 eV, has attracted a great deal of scientific interest since Wang et al. reported its excellent photocatalytic activity in water splitting.20 The components of this polymer are all earth-abundant elements of great focus (e.g. C, H, and a small proportion of H), which are different from traditional inorganic semiconductor photocatalysts. The g-C3N4 has been used in many fields owing to its peculiar thermal stability, unique band structure and low cost of preparation such as pollutant treatment, water splitting, organic synthesis, energy conversion and electrochemical sensors.21-26 However, the photocatalytic activity of



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bulk g-C3N4 is relatively limited due to various factors including low specific surface area, rapid recombination of charge carriers, or low efficiency of light quantum. With the aim to further utilize the advantage of g-C3N4, many attempts have been suggested to improve the properties of the bulk g-C3N4 such as designing appropriate textural properties,27 doping with heteroatoms,28-29 and coupling with other components.30 Among all the strategies, great interest is devoted to coupling g-C3N4 with carbonaceous materials, such as fullerene,31 MWNT,32 graphene,11 oxide graphene,33 carbon nanospheres,34 or mesoporous carbon.35 Doping g-C3N4 with carbon elements not only increases the additional light absorption but also improves the photocatalytic efficiency of g-C3N4. Unfortunately, although many efforts have been made to fabricate various g-C3N4/carbon composite catalysts, these catalysts have not been yet utilized for CO2 photoreduction due to complex procedures or expensive chemicals relatively. The research on facile and efficient methods to prepare novel g-C3N4/carbon composites with high surface area, large pore volume, and higher photoactivity is highly desirable but remains a rigorous challenge. We report here for the first time on a facile one-pot pyrolysis method for the synthesis of hybrid graphitic carbon nitride and carbon (H-g-C3N4/C) composites to address the drawbacks of bulk g-C3N4. In this synthesis, we engineer available soybean oil as carbon source without any template. The structures of the H-g-C3N4/C composite

catalysts

with

various carbon

contents

were characterized

by

thermogravimetric (TG) analysis, X-ray diffraction (XRD), elemental analysis, nitrogen adsorption–desorption, transmission electron microscopy (TEM), scanning


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electron microscopy (SEM), photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FT-IR) spectroscopy. Their photocatalytic activities were examined toward the reduction of CO2 with H2O under simulated solar irradiation. As far as we know, there are no reports on the application of hybrid graphitic carbon nitride and carbon composite catalysts for CO2 photoreduction. 2. EXPERIMENTAL SECTION 2.1 Chemicals Melamine was purchased from the Sinopharm Chemical Reagent Co. (China). Soybean oil was obtained from China National Cereals & Oils & Foodstuffs (Group) Co., Ltd., and the main chemical composition of the soybean oil is triglyceride. All chemicals used were of analytical grade. 2.2 Catalyst Preparation The synthesis process of the H-g-C3N4/C composite catalysts by one-step pyrolysis method is actually very simple. Typically, melamine powder and soybean oil with the weight ratio of x:1 (where x can be varied from 1 to 10) were ground together for 10 min in an agate mortar to make the mixture homogenous, which was then transferred into a quartz boat and calcined at the temperature 600 oC for 2 h (heating ramp 2 oC min-1) under N2 flow. After cooling to 25 oC, the obtained H-g-C3N4/C composite catalysts were crushed and denoted as H-g-C3N4/C-x. For comparison, a bulk g-C3N4 was synthesized via thermal polycondensation of melamine powder at 600 oC according to literature.36 The yield of prepared H-g-C3N4/C-1, H-g-C3N4/C-2, 5 ACS Paragon Plus Environment


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H-g-C3N4/C-6, H-g-C3N4/C-10 and bulk g-C3N4/C samples were 3.2 %, 4.4 %, 15.9 %, 25.4 % and 27.8 %, respectively. 2.3 Catalyst Characterization The powder XRD patterns were determined on a Rigaku D/MAX-2550VB/PC diffractometer at 40 kV and 40 mA (CuKα1 radiation, λ = 1.5406 Å). SEM images were taken using a TESCAN VEGA-3-SBH scanning electron microscope with an acceleration voltage of 25 kV. TEM images were performed on a JEOL JEM-2010 electron microscope operating at 200 kV. Nitrogen adsorption-desorption isotherms were recorded on a BeiShiDe 3H-2000PS4 apparatus at 77 K (samples were vacuum-degassed at 200 °C for 6 h in advance). Specific surface areas were computed via the multipoint Brumauer–Emmett–Teller (BET) method. Total pore volume (Vt) was determined at a relative pressure of 0.99. The pore size distributions were derived from the desorption branches using the Barrett–Joyner–Halanda (BJH) method. TG analysis was carried out on a PerkinElmer STA-8000 analyzer (America), and the experiment temperature ranged from 50 oC to 1200 oC at a constant heating rate of 10 o

C min-1 in Ar atmosphere. XPS spectra were recorded on a RBO upgraded

PHI-5000C ESCA system (Pekin Elmer) employing a monochromated Al Kα X-ray source (hν=1486.6 eV). The FT-IR spectra were obtained on a Nicolet iS10 spectrometer by using KBr pellet techniques. Elemental analyses (C, N, H) were measured by a Euro EA3000 elemental analyser. EIS measurements were carried out using a CHI 660B electrochemical workstation with a frequency range between 0.01 Hz and 100 kHz at 0.24 V at the open circle voltage. Photoluminescence (PL)


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spectroscopy was performed on a Hitachi F-7000 spectrophotometer at room temperature. 2.4 Photocatalytic Measurements The photocatalytic reduction of CO2 experiments were performed in a homemade stainless steel reactor (volume: 2700 ml). In each experiment, 0.1 g of catalyst powder was uniformly distributed on the stainless omentum and then fixed it in the center of reactor. Before the reaction, the reactor was vacuum-treated for three times, and then purged with the CO2 + H2O mixture at about 20 ml min-1 for 2 h until reaching the adsorption-desorption equilibrium. After that, the experiment was started by tightly closing the reactor and switching on the Xe arc lamp (500W). The substrate was about 15 cm away from the Xe arc lamp, the reaction temperature was kept constant at 30 o

C and the pressure was maintained at about 110 KPa. During the irradiation, the gas

phase products were taken at different time points and measured by using a gas chromatography. 3

RESULTS AND DISCUSSION

The carbon content of H-g-C3N4/C composite catalysts was determined by thermogravimetric analysis. Figure 1a shows the TG curves of all catalysts from 50 oC to 1200 oC at a heating rate of 10 oC min-1 under Ar flow. The weight loss of H-g-C3N4/C composite catalysts and bulk g-C3N4 with the same steep downtrend occurring from 540 oC to 750

o

C were observed, which is assigned to the

decomposing of g-C3N4. In addition, there is a slightly weight loss in the range of 750-1100 oC for the H-g-C3N4/C composites compared to bulk g-C3N4 with no residue, 7 ACS Paragon Plus Environment


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indicating that the introduction of carbon enhances the thermal stability of the composites. Thus the content of carbon in the H-g-C3N4/C composites could be easily calculated from the TG curves, and the actual weight percentage of carbon in composites for H-g-C3N4/C-10, H-g-C3N4/C-6, H-g-C3N4/C-2 and H-g-C3N4/C-1 is computed to be 1.02, 3.77, 9.41 and 13.02, respectively. To further reveal the different element contents in the H-g-C3N4/C composites, elemental analyses (C, N, H) were carried out and the obtained data are listed in Table 1. It can be found that the C/N atomic ratio in bulk g-C3N4 is 0.78, after introducing the hybrid carbon, the C/N ratios are increased to 0.8, 0.87, 0.99, and 1.09 for H-g-C3N4/C-10, H-g-C3N4/C-6, H-g-C3N4/C-2, and H-g-C3N4/C-1, respectively, which are in accordance with the TG analysis. The photos of the H-g-C3N4/C composites are shown in Figure 1b, the bright yellow of bulk g-C3N4 became brownish-black color after introducing carbon, and this color darkened gradually with the rise of carbon content. Thus, it is supposed that the introduction of carbon component will alter the optical properties and surface chemical states of the g-C3N4. The composite catalysts were investigated by XRD to understand their phase composition. Clearly, all of the samples feature two distinct diffraction peaks and no impurity can be detected, indicating that the composites have similar crystal structure (Figure 2). Two characteristic peaks indexed as the (100) and (002) reflections of g-C3N4 could be observed. The weaker peak at 13.0 o corresponding to an interlayer distance of 0.68 nm is assigned to the in-plane repeated unites, and the stronger one at 27.5

o

with a distance of 0.33 nm can be attributed to the interlayer stacking of the


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aromatic systems.20 Noticeably, the increase of carbon content in the composites causes a reduction in the peak intensity of H-g-C3N4/C catalysts, which is in accordance with the TG results. Further observation of (002) peak shows that all H-g-C3N4/C samples have weaker and broader peaks compared with bulk g-C3N4. This observation could be attributed to the existence of carbon. Nevertheless, no distinct diffraction peaks corresponding to carbon are observed in Figure 2, which should be due to the formation of amorphous carbon. Nitrogen adsorption-desorption isotherms of above H-g-C3N4/C composite catalysts were shown in Figure 3a. The isotherms exhibit that all samples are of type IV with hysteresis loop at high relative pressure range of 0.5-0.95, suggesting the presence of some mesoporosity. The hysteresis loops are similar to the type H3, which are frequently observed on the aggregates of platelike nanoparticles forming slit-shaped pores.37 It should be mentioned that the mesoporous features of these composite catalysts become more significant with increasing the content of carbon, indicating the presence of carbon in g-C3N4 is beneficial for the formation of mesopores. As shown in the pore size distribution curves derived from the desorption branch of the isotherms (Figure 3b), all samples have relatively narrow distribution in pore sizes centered at around 4 nm. The textural properties of all samples are listed in Table 1. Compared with bulk g-C3N4, these H-g-C3N4/C composite catalysts have a relative larger BET surface area and pore volume, both values are increasing with the enhancement of carbon content. The enlargement of the specific surface area is probably due to the hindered crystal growth of graphitic carbon nitride by the



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introduction of hybrid carbon, which mainly arises from mesopores according to our measurement. The morphology and structural features of the H-g-C3N4/C composites were elucidated by SEM and TEM. Figure 4 exhibits the SEM and TEM images of the representative H-g-C3N4/C-6 sample and bulk g-C3N4. From Figure 4a, it can be clearly seen that the H-g-C3N4/C-6 displays crumpled multi-layer thin nanosheets with a typical wrinkled morphology, and the TEM image given in Figure 4b reveals that the domains with worm-like mesoporous channels are presented in these nanosheets, which is consistent with the result of BJH analysis. Such hierarchical nanostructures are highly desirable in heterogeneous catalytic systems since it is benefit to the reactive molecular diffusion/transfer. While the bulk g-C3N4 prepared without carbon exhibits a big and platelet-like morphology with less mesoporous characters, as shown in Figure 4c and 4d. The compositions and chemical states of the H-g-C3N4/C-6 and bulk g-C3N4 were studied by XPS. As shown in Figure 5, both bulk g-C3N4 and the H-g-C3N4/C-6 display distinct characteristic peaks of C 1s (~287 eV), N 1s (~400 eV) and O 1s (~533 eV). High resolution XPS spectra of C 1s, N 1s and O 1s are provided in Figure 5b-d, respectively. In the case of bulk g-C3N4, the C 1s peak is deconvoluted into two small peaks. The first peak at 284.6 eV is ascribed to the surface adventitious carbon or sp2 C-C bonds,36 while the second peak at 287.5 eV is assigned to the sp2-bonded carbon (the major carbon species in the g-C3N4 polymer) in N-containing aromatic rings (N-C=N).38 Different from the bulk g-C3N4, the C 1s XPS spectrum of 10 ACS Paragon Plus Environment

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H-g-C3N4/C-6 exhibits a new peak at 286.5 eV, this peak could be attributed to C=N bonds, which originate from the hybrid carbon, and the heating-induced generation of a C-O-C bond between g-C3N4 and carbon,39 functioning as a “bridge” linking g-C3N4 with the formed carbon, suggesting that there are some interactions between carbon and g-C3N4, which can be confirmed by the following FTIR results. The high resolution N 1s spectrum of bulk g-C3N4 (as shown in Figure 5c) can be also fitted into four different peaks at binding energies of 398.1, 399.3, 400.8, and 404.2 eV, which are respectively attributed to sp2 hybridized N bonded with C (C-N=C), the bridging tertiary N (N-(C)3), graphitic N, and amino functional groups (C-N-H).40-42 However, in case of H-g-C3N4/C-6, the N 1s peaks show a slight positive shift relative to that of bulk g-C3N4, perhaps caused by the partial doping carbon in the g-C3N4.43 In addition, the surface C/N ratio (atomic) has increased from 0.77 (for bulk g-C3N4) to 0.84 (for H-g-C3N4/C-6) according to the XPS analysis. The O 1s spectrum of bulk g-C3N4 can be deconvoluted into two peaks, and the binding energies of 532.9.0 eV and 533.9 eV can be ascribed to C-OH groups and adsorbed O2, respectively.44 Interestingly, a new peak appears at a low binding energy of ca. 531.6 eV for the O1s spectra of H-g-C3N4/C-6 compared to that of bulk g-C3N4, this signal is assigned to the generation of N-C-O species and suggests that the oxygen can directly bond with the sp2-hybridized C in the H-g-C3N4/C-6.45 To investigate the atomic structure of H-g-C3N4/C composites, the FT-IR spectra were carried out. As shown in Figure 6, all the H-g-C3N4/C composites manifest almost similar characteristic features to the bulk g-C3N4, proving that the structural 11 ACS Paragon Plus Environment


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integrity of g-C3N4 remained intact after the introduction of hybrid carbon. The broad absorption peak ranging from 2800 to 3400 cm-1 originates from the stretching vibrational modes of the N–H and O–H, respectively, suggesting that the amino groups and adsorbed hydroxyl species still exist in the products. A series of peaks found in the region from 1200 to 1700 cm−1 could be assigned to the stretching modes like C(sp2)-N and C(sp2)=N in the CN heterocycles with peaks positioned at 1635, 1573, 1420, 1332 and 1250 cm-1. Additionally, the typical bending vibration of s-triazine units at ca. 807 cm

-1

is observed.46 Note that, after introducing the hybrid

carbon, the characteristic peak from the s-triazine vibration of bulk g-C3N4 depicts a slight shift to the lower wavenumber of ca. 802 cm−1 in the H-g-C3N4/C composites. The red shift of the peak suggests that some interactions between the “nitrogen pots” of g-C3N4 and carbon species have already appeared, which was consistent with the XPS results. Meanwhile, it should be pointed that the H-g-C3N4/C composites display a stronger FT-IR mode compared with bulk g-C3N4 owing to the enhancement of the exposed surface functional groups, which provides combination fundamental for the composites. Electrochemical impedance spectroscopy (EIS) was carried out to examine the charge transfer resistance and the separation efficiency of the photogenerated charge carriers, as a pivotal factor to the photocatalytic activity. Figure 7a exhibits the EIS Nyquist plots of the representative H-g-C3N4/C-6 and bulk g-C3N4. On the Nyquist diagram, a smaller radius indicates lower overall charge transfer resistance or in other words, higher charge transfer efficiency and more efficient separation of


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photo-excited electron-hole pairs.47,48 One can see that the arc radius of H-g-C3N4/C-6 is much smaller than that of bulk g-C3N4, indicating that the hybrid carbon in composites was of great benefit to enhance the separation and transfer efficiency of electrons and holes. Photoluminescence (PL) emission measurements were further used to characterize the efficiency of charge carrier trapping, immigration and separation in the H-g-C3N4/C composite catalysts. A lower PL intensity generally reflects a better sepatation of photogenerated charge carriers. Figure 7b shows the PL spectra of the representative H-g-C3N4/C-6 and bulk g-C3N4. It can be found that the PL intensity of H-g-C3N4/C-6 significantly decreases in comparison with bulk g-C3N4, indicating that introduction of hybrid carbon in g-C3N4 has accelerated electron-hole separation, which should be attributed to the electron transfer from g-C3N4 to carbon under light irradiation. These results thus suggest that the accelerated electron-hole separation of the H-g-C3N4/C composites allows them as promising catalysts for sun-light driven photocatalytic applications. Finally, the photocatalytic activity of the H-g-C3N4/C composite catalysts with different carbon contents toward gas-phase CO2 photoreduction under simulated solar irradiation was experimentally determined. Figure 8 illustrates how the two primary products (CO and CH4) evolve with irradiation time for all samples. Clearly, the yields of CO and CH4 both increase with the reaction time, and the carbon monoxide formation on H-g-C3N4/C composites is more favorable compared to methane formation. Interestingly, Figure 8 also shows that the production rates of solar fuel increase with the increase of carbon content from 1.02 wt % to 3.77 wt %. However, a



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decreased activity was caused with further increase of carbon content in H-g-C3N4/C-1 and H-g-C3N4/C-2 composites, suggesting that the carbon content is important for the optimal photocatalytic activity. The highest CO and CH4 yield of 22.6 and 12.59 µmol g-1-cat., respectively, are achieved with 3.77 wt % of carbon content in the sample H-g-C3N4/C-6 after 9 h of simulated solar irradiation, noticeably both values are much better than that of bulk g-C3N4. This enhanced activity of the H-g-C3N4/C composite catalysts is ascribed to the synergistic effect of hybrid carbon and g-C3N4. The introduction of hybrid carbon into the g-C3N4 can improve the electrical conductivity of the catalysts, increase light absorption and enhance

photoinduced electron-hole separation efficiency.49

Meanwhile, carbon content is a critical factor deciding the optimal photocatalytic activity: when the carbon content is above that in H-g-C3N4/C-6, a further increase would decelerate the CO2 photoreduction conversion. The reason is that carbon with an appropriate content can well disperse on the g-C3N4 surfaces, which contributes to the migration and separation of charge carriers. However, the carbon content above that in H-g-C3N4/C-6, the carbon overlaps as agglomerates to smother the surface of g-C3N4, thus partly block light absorption and decelerate the interfacial charge transfer, resulting in a decrease of CO2 photocatalytic conversion efficiency (as shown in Figure 9). 4. CONCLUSIONS Hybrid graphitic carbon nitride and carbon composite catalysts with different carbon contents were prepared via a facile one-pot pyrolysis method using melamine and


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natural soybean oil as precursors. After introduction of carbon in the g-C3N4, the hybrid composite catalysts show significantly improved catalytic activities for the photoreduction of CO2 with H2O. The optimal carbon content is determined to be 3.77 wt. % on the H-g-C3N4/C-6 sample with CO and CH4 yield of 22.60 µmol/g-cat. and 12.5 µmol/g-cat. under 9 h light irradiation, respectively, both values were more than twice as high as that of bulk g-C3N4. The remarkably increased performance of H-g-C3N4/C composite catalysts was ascribed mainly to the synergistic effect of hybrid carbon and g-C3N4, which is pivotal to the separation of photogenerated charge carriers. This study offers a new method to prepare various semiconductor-carbon hybrid materials with high performance for environmental applications.

ACKNOWLEDGEMENTS This work was supported by National Natural Science Foundation of China (21103024) and Program of Shanghai Pujiang Talent Plan (14PJ1406800).

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


Figure Captions Figure 1. (a) TG thermograms for heating all H-g-C3N4/C composite catalysts from 50 o

C to 1200 oC at a heating rate of 10 oC min-1 under Ar flow, (b) photos of the bulk

g-C3N4 and H-g-C3N4/C composite catalysts. Figure 2. XRD patterns of the bulk g-C3N4 and H-g-C3N4/C composite catalysts. Figure 3. (a) N2 adsorption-desorption isotherm and (b) corresponding pore size distribution curve of the bulk g-C3N4 and H-g-C3N4/C composite catalysts. Figure 4. Typical SEM and TEM images of (a,b) H-g-C3N4/C-6 and (c,d) bulk g-C3N4. Figure 5. XPS survey spectra of the H-g-C3N4/C-6 and bulk g-C3N4 (a); high-resolution XPS spectra of C 1s (b), N 1s (c), and O 1s (d) of the H-g-C3N4/C-6 and bulk g-C3N4. Figure 6. FT-IR spectra of the bulk g-C3N4 and H-g-C3N4/C composite catalysts. Figure 7. EIS profiles (a) and PL spectra (b) of the bulk g-C3N4 and H-g-C3N4/C-6 composite catalyst. Figure 8. Yields of CO (a) and CH4 (b) as functions of irradiation time over all catalysts. Figure 9. Plausible mechanism for the photoreduction of CO2 with H2O over the hybrid graphitic carbon nitride and carbon composites. Table 1. Textural properties of the g-C3N4 and H-g-C3N4/C composite catalysts.



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

Page 24 of 34

Table 1 Elemental analysis Sample

TG analysis

Surface

Pore

Pore

area

C/N (atomic ratio)

size

volume

2

(m /g)

(nm)

(cm3/g)

1.09

Hybrid inorganic carbon (wt. %) 13.02

1.04

65.4

4.2

0.674

1.92

0.99

9.41

0.95

34.4

3.9

0.277

55.92

2.25

0.87

3.77

0.83

10.6

4.0

0.165

39.74

57.85

2.41

0.80

1.02

0.77

9.8

3.9

0.137

39.11

58.36

2.53

0.78

—

0.75

7.3

—

0.109

C (wt. %)

N (wt. %)

H (wt. %)

C/N (atomic ratio)

H-g-C3N4/C-1

47.56

50.72

1.72

H-g-C3N4/C-2

44.94

53.14

H-g-C3N4/C-6

41.83

H-g-C3N4/C-10 Bulk g-C3N4


Page 25 of 34

100

(b)

(a) 1

H-g-C3N4/C-1

80

Weight (%)

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


2

3

4

5

H-g-C3N4/C-2 60

H-g-C3N4/C-6 H-g-C3N4/C-10

40

g-C3N4

20 0 0

200

400

600

800

1000

1200

1: H-g-C3N4/C-1, 2: H-g-C3N4/C-2, 3: H-g-C3N4/C-6, 4: H-g-C3N4/C-10, 5: g-C3N4

o

Temperature ( C)

Figure 1



(002)

(100)

Intensity (a.u.)

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

Page 26 of 34

g-C3N4 H-g-C3N4/C-10 H-g-C3N4/C-6 H-g-C3N4/C-2 H-g-C3N4/C-1 10

20

30

40

50

60

70

2θ (degree) Figure 2


80

Page 27 of 34

600

(a)

3

Volume adsorbed (cm /g)

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


(b)

H-g-C3N4/C-1

450

H-g-C3N4/C-2

H-g-C3N4/C-1

H-g-C3N4/C-6 300

H-g-C3N4/C-2

H-g-C3N4/C-10 0.4

0.6

0.8

g-C3N4

H-g-C3N4/C-6

150

H-g-C3N4/C-10

g-C3N4 0 0.0

0.2

0.4

0.6

0.8

1.0 2

4

6

8

Pore size (nm)

Relative Pressure(P/P0)

Figure 3


10

12


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

(a)

(b)

(c)

(d)

Figure 4


Page 28 of 34

O1s

N1s

C1s

(a)

C1s

Intensity (a.u.)

O KLL

H-g-C3N4/C-6

Bulk g-C3N4

800

600

400

200

N1s

Bulk g-C3N4

292

0

402

288

286

284

282

O1s

Intensity (a.u.)

(c)

280

(d)

H-g-C3N4/C-6

Bulk g-C3N4

Bulk g-C3N4

404

290

Binding energy (eV)

H-g-C3N4/C-6

406

(b)

H-g-C3N4/C-6

Binding energy (eV)

Intensity (a.u.)

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


Intensity (a.u.)

Page 29 of 34

400

398

396

540

394

536

532

Binding energy (eV)

Binding energy (eV)

Figure 5


528

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

Transmittance (%)


Page 30 of 34

H-g-C3N4/C-1 H-g-C3N4/C-2 H-g-C3N4/C-6

( 802)

H-g-C3N4/C-10

( 807)

g-C3N4 4000

810 765

3200

2400

1600

800 -1

Wavenumber (cm ) Figure 6


Page 31 of 34

40

(b) g-C3N4

30

H-g-C3N4/C-6

20

10

0 20

30

40

50

g-C3N4

PL Intensity (a.u.)

(a)

-Z"/ohm

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


60

70

80

90

Z'/ohm

H-g-C3N4/C-6

400

440

480

520

Wavelength (nm)

Figure 7


560

600


25

14

H-g-C3N4/C-1

Yields of CH4 (µmol/g-cat.)

Yields of CO (µmol/g-cat.)

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

Page 32 of 34

H-g-C3N4/C-2

20

H-g-C3N4/C-6 H-g-C3N4/C-10

15

g-C3N4

10 5

(a) 0

H-g-C3N4/C-1

12

H-g-C3N4/C-2

10

H-g-C3N4/C-6 H-g-C3N4/C-10

8

g-C3N4

6 4 2

(b)

0

0

100

200

300

400

500

600

0

Irradiation time (min)

100

200

300

400

Irradiation time (min)

Figure 8


500

600

Page 33 of 34

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


Carbon CO, CH4

e¯ CB

e¯

VB

h+

Reduction

CO2

H2O Oxidation

H+, HO• H-g-C3N4/C

Figure 9



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

Page 34 of 34

Table of Contents Graphic Carbon CO, CH4

e CB

¯

Reduction

CO2

e¯

H2O VB

h+

Oxidation

H+, HO• H-g-C3N4/C

ACS Paragon Plus Environment

Facile One-Step Synthesis of Hybrid Graphitic Carbon Nitride and

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