CdS Composite for Photocatalytic

Subscriber access provided by University of Glasgow Library

Article

Amine-functionalized graphene/CdS composite for photocatalytic reduction of CO

2

Kyeong Min Cho, Kyoung Hwan Kim, Kangho Park, Chansol Kim, Sungtak Kim, Ahmed Al-Saggaf, Issam Gereige, and Hee-Tae Jung ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b01908 • Publication Date (Web): 06 Sep 2017 Downloaded from http://pubs.acs.org on September 6, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 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

ACS Catalysis

Amine-functionalized graphene/CdS composite for photocatalytic reduction of CO2 Kyeong Min Cho1, Kyoung Hwan Kim1, Kangho Park1, Chansol Kim1, Sungtak Kim2, Ahmed AlSaggaf3, Issam Gereige3 and Hee-Tae Jung1* 1) Department of Chemical & Biomolecular Engineering (BK-21 plus), and KAIST Institute for Nanocentury, Korea Advanced Institute of Science & Technology (KAIST), 335 Gwahangno, Yuseong-gu, Daejeon 305-701 (Korea) 2) Carbon Resources Conversion Catalytic Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeongro, Yuseong-gu, Daejeon 34114, Republic of Korea 3) Saudi Aramco, Research and Development Center, Dhahran 31311 (Saudi Arabia)

Abstract

This study provides the significant enhancement in the CO2 photoconversion efficiency by the functionalization of a reduced graphene oxide/cadmium sulfide composite (rGO/CdS) with amine. The amine-functionalized graphene/CdS composite (AG/CdS) was obtained in two steps: Graphene oxide (GO) was selectively deposited via electrostatic interaction with CdS nanoparticles modified with 3-aminopropyltriethoxysilane. Subsequently, ethylenediamine

ACS Paragon Plus Environment

1

ACS Catalysis

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 2 of 21

(NH2C2H4NH2) was grafted by the N,N′-dicyclohexylcarbodiimide coupling reaction between the amine group of ethylenediamine and the carboxylic group of GO. As a result, a few layers of amine-functionalized graphene wrapped CdS uniformly, forming a large interfacial area. Under visible light, the photocurrent through the AG/CdS significantly increased because of enhanced charge separation in CdS. The CO2 adsorption capacity on AG/CdS was four times greater than that on rGO/CdS at 1 bar. These effects resulted in a methane formation rate of 2.84 µmol/g·h under visible light and CO2 at 1 bar, corresponding to 3.5 times that observed for the rGO/CdS. Interestingly, a high methane formation rate (1.62 µmol/g·h) was observed for the AG/CdS under CO2 at low pressure (0.1 bar), corresponding to 20 times greater than that observed for the rGO/CdS. Thus, the enhanced performance for photocatalytic reduction of CO2 on the AG/CdS is due to the improved CO2 adsorption related to the amine groups on amine-functionalized graphene, which sustains the strong absorption of visible light and superior charge-transfer properties as compared with those of graphene.

KEYWORDS: photocatalyst, carbon dioxide, graphene, amine, CO2 activation


2

Page 3 of 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

ACS Catalysis

Developing a system for the highly efficient photoconversion of carbon dioxide (CO2) is a tremendous challenge for addressing global climate change. The photocatalyst absorbs photons in sunlight, which have energies greater than its band gap energy, leading to electron-hole pair generation. The generated electrons are then used to reduce CO2 into valuable fuels such as carbon monoxide (CO), methane (CH4), and methanol (CH3OH). [1, 2] Generally, singlecomponent inorganic semiconductors are not suitable photocatalysts for CO2 photoreduction as they barely satisfy all critical requirements of the process, including strong light absorption, rapid charge separation, favorable CO2 adsorption, and selective CO2 reduction. [3, 4] A number of hybrid materials, which include heterojunction inorganic semiconductors, immobilized organic photosensitizers, functional metals, and conductive carbon materials, have been incorporated into inorganic semiconductor to improve their photoreduction performance. [4–7] In particular, graphene/semiconductor composites have attracted interest because of the ability of graphene to improve the surface area and photocatalytic performance, caused by the transfer of electrons between graphene and the semiconductor, as well as light absorption. [8-12] The formation rate of CH4 on CdS nanorods with graphene under visible light is 10 times that on bare CdS nanorods. This difference results from the facile charge transfer from the nanorods to graphene. [13] Similarly, the incorporation of graphene into two-dimensional (2D) mesoporous TiO2 significantly enhances the photodegradation of methylene blue because of the facile charge transfer resulting from the increase in the interfacial area between 2D TiO2 and 2D graphene. [14] Despite the significant light-harvesting enhancement achieved via the improvement of the charge transfer using graphene-based photocatalysts, CO2 photoreduction is still not efficient because of shortcomings in their design for CO2 activation. [15]


3

ACS Catalysis

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 4 of 21

Herein, we developed an amine-functionalized graphene/CdS composite (AG/CdS) that exhibits significant CO2 adsorption, as well as efficient light absorption and charge-transfer properties, which enhance CO2 photoconversion performance. So far, all of the reported graphene-based photocatalysts are based on reduced graphene oxide (rGO). [16, 17] The use of rGO in heterogeneous photocatalyst enhances electron transfer because of its high electrical conductivity. It simultaneously loses its functional groups, enabling interaction with CO2. Therefore, a crucial research topic related to graphene-based photocatalyst is the preparation of surface-modified graphene that retains its good charge-transfer properties. The developed AG/CdS exhibits several significant advantages over those used in previously reported CO2 photoconversion systems. First, the CdS is attractive visible-light-driven photocatalyst for CO2 conversion among the various inorganic semiconductors due to its narrow bandgap of 2.4 eV. In addition, negative conduction band edge position of CdS could provide electrons with higher reduction potential. [13, 16, 31] Second, amine groups on graphene contribute to CO2 activation, which boosts the catalytic conversion of CO2. AG on the CdS surface enhances CO2 adsorption by 13 times at 0.1 bar and by 4 times at 1 bar. Third, AG wrapping of CdS nanoparticles provides a path for the efficient transfer of photogenerated electrons. Thus, the photocurrent through the AG/CdS under visible light is 10 times that through bare CdS. This increase is indicative of the efficient light harvesting caused by the introduction of graphene electron-transfer channels. On this composite, the conversion rate of CO2 into CH4 is 2.84 µmol/g·h under visible light, 3.5 times that of the conversion on rGO/CdS. Interestingly, AG/CdS enables CH4 production (1.62 µmol/g·h) under low-pressure CO2 (0.1 bar). Therefore, we expect AG/CdS to be a promising composite that can markedly enhance the photocatalytic conversion of CO2.


4

Page 5 of 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

ACS Catalysis

Figure 1. Morphology of the AG/CdS. a) Schematic of the synthesis of the AG/CdS. b) SEM image of the AG–CdS nanoparticles. c) SEM image of the CdS nanoparticles (yellow arrow denotes graphene). d) TEM image of the AG/CdS; inset shows a high-magnification image. Figure 1a shows the overall procedure for fabricating the AG/CdS. CdS nanoparticles were synthesized by solvothermal reactions at 140 °C using cadmium acetate and excess thiourea. Graphene oxide (GO) was incorporated into the surface of CdS particles to prepare the GO/CdS. First, the CdS surface was treated with 3-aminopropropyltriethoxysilane (APTES) to generate positive charges on the CdS surface. [18] During mixing with a few exfoliated GO layers, positively charged CdS particles electrostatically interacted with negative charged GO at pH 6. [19] The GO/CdS was then functionalized with amine by grafting ethylenediamine


5

ACS Catalysis

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 6 of 21

(NH2C2H4NH2) via a coupling reaction with N,N′-dicyclohexylcarbodiimide (DCC) at 85 °C. In this step, the amine group of ethylenediamine reacts with the carboxylic group of GO. Theresulting AG/CdS consisted of CdS nanoparticles coated with AG (Figure 1a). Figure 1b shows the synthesized CdS nanoparticles were predominantly spherical, with an average diameter of ~140 nm (± 17.3 nm). The diameter was determined by averaged measurements of approximately 100 particles in the scanning electron microscopy (SEM) images. Uniform CdS nanospheres are obtained by aggregation of small nanocrystallites with hexagonal phase in the presence of excess thiourea, which inhibited growth of CdS nanocrystallites. The particle size could be controlled by varying the duration of the solvothermal reaction (Figures S1 and S2). [20] Synthesized GO consisted of 2D flakes with dimensions of ~5 µm, which predominantly exfoliated into single layers in water (Figure S3). [21] After the hybridization of CdS and GO followed by amine functionalization, careful inspection of the SEM images of the AG/CdS revealed that graphene layers are uniformly distributed on the CdS nanoparticle surfaces (Figure 1c). As estimated from the TEM images, 7–10 graphene layers were observed on the CdS nanoparticle surface (Figures 1d and S4).


6

Page 7 of 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

ACS Catalysis

Figure 2. Chemical states of the AG/CdS. a) FTIR spectra of GO/CdS (black) and AG/CdS (red). b) XPS C1s spectra of GO and AG. d) Results for carbon and nitrogen content analysis of the AG/CdS. Inset shows a photograph of each sample. e) Suggested mechanism for the amine functionalization of graphene oxide. To verify the amine functionalization of the graphene/CdS composite, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and elemental analysis were conducted (Figure 2). In the FTIR spectra of the GO/CdS, stretching vibrations of epoxide bonds (C–O–C, 1400 cm−1), carbon–carbon double bonds (C=C, 1610 cm−1), and carbon–ketone bonds (C=O, 1720 cm−1), as well as the bending of hydroxide bonds (C–OH, 3300 cm−1), typical of GO, were observed. [22] After the deposition of ethylenediamine on the GO/CdS, new peaks were observed, corresponding to carbon-nitrogen (C–N, 1220 and 1150 cm−1), amine (N–H, 1570 cm−1), and carbon-oxygen double (C=O, 1620 cm−1) bonds. Absorption peaks observed at ~3200 cm−1 and ~2900 cm−1 corresponded to amine (–NH2) and alkane (–CH2) groups,


7

ACS Catalysis

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 8 of 21

respectively. [23] These results indicated that the oxygen groups of GO undergo reduction and convert into amine groups (Figure 2a). XPS was employed to further confirm the amine functionalization of the AG/CdS (Figure 2b and 2c). In the XPS spectrum of GO, sp3 carbon (C–C or C=C, ~284.4 eV) and various oxygen functional groups, such as carbon-oxygen bond (C–O–C or C–OH, ~286.6 eV), carbon-oxygen double bond (C=O, ~287.6 eV), and carboxylic acid group (C(O)=O, ~288.7 eV), were observed. [24] After the functionalization of GO with ethylenediamine, oxygen functional groups were decreased significantly and new peak at 285.5 eV corresponding to the C–N were generated (Figure 2c). This result is in good agreement with the N1s XPS spectra, indicative of carbon– amine bonds (C–N, ~398.2 eV) and amide bonds (N–C(O), ~399.7 eV; Figure S5). [25] Elemental analysis was conducted for the AG/CdS, and results were plotted versus graphene loading (Figure 2d). AG/CdS with various graphene content were prepared by controlling the loading of graphene oxide during synthesis of GO/CdS (x in AG/CdS-x denotes the graphene weight percentage in the composite). The CdS sample contained trace amounts of nitrogen (0.17 %) that came from the decomposition of the sulfur source, thiourea. [26] After the reduction of GO/CdS, the nitrogen content (0.2%) did not change (Figure S6). On the other hand, the nitrogen content of the AG/CdS gradually increased (0.51, 0.57, 0.91, and 1.40 %) with increasing graphene loading (0.5, 1, 2, and 5 wt%). The linear relationship between the amine content and graphene content confirm the functionalization with ethylenediamine of GO, and not the CdS surface. The carbon content of the AG/CdS was greater than that of the rGO/CdS probably because of the alkyl chain of ethylenediamine. On the basis of the results obtained from FTIR spectroscopy, XPS, and elemental analysis, the AG/CdS was synthesized by


8

Page 9 of 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

ACS Catalysis

ethylenediamine functionalization of GO/CdS, in which the carboxylic group of GO reacts with the amine group in ethylenediamine via DCC coupling reaction (Figure 2e).


9

ACS Catalysis

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 10 of 21

Figure 3. CO2 adsorption and light-harvesting property of CdS composite. a) CO2 adsorption isotherms at 25 °C. b) UV–vis diffuse reflectance spectra of AG/CdS. c) Transient photocurrent under visible light (420 nm) (Figure 3c). Photocurrent measurements were carried out using a threeelectrode system. The working photoelectrode was prepared by deposition onto ITO glass and immersed in aqueous 0.5 M Na2SO4 electrolyte and the applied voltage is 0.2 V versus Ag/AgCl reference electrode. CdS exhibited a small photocurrent (0.18 mA/cm2) under visible light. Despite the strong visible-light absorption of CdS, the rapid recombination of electrons and holes in inorganic semiconductors lowers the light-harvesting efficiency. [31] On the other hand, the rGO/CdS and AG/CdS electrodes exhibited a highly improved photocurrent (1.7 and 2.4 mA/cm2) as compared with that of the bare CdS electrode. Such marked enhancement is caused by the efficient electron-transfer path provided by graphene. The photocurrent through the AG/CdS electrode was slightly stronger, with slow saturation response and recovery behavior as compared with those observed for the rGO/CdS electrode. These results may be due to the trapping of electrons by amine groups at the graphene/electrode interface. [32, 33] Further, electrochemical impedance spectroscopy (EIS) was conducted to characterize the charge separation property (Figure 3d). The EIS measurement was carried out at dark condition under 0.5 M Na2SO4 electrolyte. The semicircle diameter of Nyquist plot indicates the charge transfer resistance between catalyst and electrolyte. [34] While the CdS has very large diameter due to its low conductivity, rGO/CdS improved charge transfer property due to heterojunction of conductive graphene. Similarly, AG/CdS show low charge transfer resistance, indicating amine functionalized graphene provide effective charge transfer pathway. Therefore, AG increases CO2 adsorption while maintaining good charge-transfer properties and light absorption, which are advantages of a graphene-based photocatalyst.


12

Page 13 of 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

ACS Catalysis

Figure 4. CO2 photoreduction on the CdS composites. a) Photoreduction of CO2 (1 bar) on AG/CdS with varying graphene content under visible light (>420 nm). b) CO2 photoreduction and CH4/CO ratio on the CdS, G/CdS, and Ag/CdS under CO2 at 1 bar (40 °C) and c) under lowpressure CO2 (0.1 bar, 40 °C). d) Cyclic photoreduction of CO2 on the rGO/CdS and AG/CdS. e) Graphical illustration of the proposed mechanism of CO2 photoreduction on the AG/CdS. To evaluate the activity of the AG/CdS for CO2 photoreduction, a photocatalytic reaction was conducted under visible light (λ > 420 nm) in the presence of pure CO2 and water vapor at 40 °C. Control experiments were conducted without light, CO2, and an inorganic photocatalyst (CdS), which is inactive in the reaction (Figure S9). Methane (CH4) and carbon monoxide (CO) were the main products obtained from CO2 reduction. Bare CdS produced trace amounts of CO (0.088 µmol/g·h) and CH4 (0.124 µmol/g·h) predominantly by rapid fast electron-hole recombination. In contrast, AG exhibited substantial enhancement of CO2 reduction. A drastic increase in the CH4


13

ACS Catalysis

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 14 of 21

formation rate was observed with increasing graphene content. At high graphene loading (5 wt%), the activity decreased, which is due to shielding of light absorption in CdS and poor interfacial charge transfer of composite. [7, 28] The AG/CdS-2 exhibited a high CH4 formation rate (2.84 µmol/g·h; Figure 4a). In the presence of rGO, the conversion rate of CO2 on rGO/CdS similarly increased. The CH4 formation rate reached 0.804 µmol/g·h at 2 wt% graphene (Figure S10). Notably, the rate of photoreduction of CO2 into CH4 on the AG/CdS was enhanced by 23 and 3.5 times relative to those on CdS and rGO/CdS, respectively. In addition, the CH4/CO ratio increased to 15.8, indicating that AG promotes the multi-electron reduction of CO2. These enhancements in AG/CdS as compared with the rGO/CdS are mainly due to CO2 activation, which is the rate-determining step in CO2 reduction. [15] Under CO2 at low pressure (0.1 bar), a high formation rate of CH4 on the AG/CdS was observed (1.62 µmol/g·h), whereas a low formation rate of CH4 on the rGO/CdS was observed (0.087 µmol/g·h; Figure 4c). Thus, AG permits the conversion of CO2 at low pressure into CH4, which is in good agreement with the high adsorption of CO2 at low pressure. Interestingly, our AG/CdS exhibited long-term stability for CO2 photoreduction under visible light. It maintained high CO2 conversion over 10 cycles (84.7%; Figure 4d). It showed no obvious changes in macroscopic morphology and chemical states, as confirmed by the SEM image and FTIR spectra (Figure S10). Similarly, the rGO/CdS maintained its photocatalytic efficiency over 10 cycles (92.5%). Indeed, the poor photostability of CdS is one of the major issues associated with the CdS photocatalyst, related to photooxidation. [33] Notably, the introduction of AG layers considerably enhanced the stability of the CdS photocatalyst. We conducted in situ FTIR spectroscopy at 313 K under 0.1 bar CO2 to verify the adsorption species on AG/CdS (Figure S11). The peaks in the region of 1300~1700 cm-1 can be assigned


14

Page 15 of 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

ACS Catalysis

with chemisorbed CO2. The bands at 1626, 1551, 1486, 1423, 1396 and 1325 cm-1 were presented, which have been associated with the alkylammonium carbamate ion pairs. This species is obtained by interaction with two adjacent amine molecules. In addition, the peaks at 1657 and 1527 cm-1 were assigned to carbamic acid formed on isolated amine group. [35] These chemisorbed species formed in the presence of amine-functionalized graphene, therefore the functionalized amine can activate the CO2. Figure 4e shows the possible mechanism for the photocatalytic reduction of CO2 by the AG/CdS system. CO2 is adsorbed and activated on AG via interaction with amine groups even at low CO2 concentrations. CdS absorbs visible light and generates energetic electrons and holes. A few layers of graphene then transfer the electrons before recombination. The activated CO2 molecule is reduced into CH4, which requires eight electrons under visible light and diluted CO2. Therefore, AG is a promising cocatalyst material for various inorganic photocatalyst composites for CO2 reduction.


15

ACS Catalysis

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 16 of 21

In summary, we prepared an AG/CdS that exhibits a high rate of photoreduction of CO2 into CH4 due to enhanced light harvesting and CO2 activation. The composite was obtained by the wrapping of GO on CdS by an electrostatic reaction and the grafting of ethylenediamine via interaction with carboxylic groups on GO. AG played significant roles in enhancing CO2 photoreduction. The intimate contact of AG with CdS enhanced charge transfer, resulting in a marked increase in photocurrent under visible light. CO2 was chemisorbed on the amine groups, with adsorption capacities corresponding to 4 and 13 times as high as that of the rGO/CdS under 1 and 0.1 bar, respectively. Indeed, AG activated CO2 by maintaining efficient electron transfer and light absorption properties. The resulting methane formation rate was 2.84 µmol/g·h, with high selectivity, corresponding to 3.5 times that observed with the rGO/CdS under visible light. In addition, the AG/CdS converted CO2 to methane at low pressure, with a rate of 1.62 µmol/g·h, in contrast, a low methane formation rate was obtained on the rGO/CdS. Graphene enhanced the photostability of the CdS-based photocatalyst, maintaining a conversion rate of 87% over 10 cycles. We anticipate that amine-functionalized graphene may be useful in various heterogeneous catalyst systems for the high-photoconversion performance of CO2.


16

Page 17 of 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

ACS Catalysis

ASSOCIATED CONTENT Supporting Information. Description of sample preparation and photoconversion tests. SEM, AFM, and TEM images; XRD, XPS, element analysis, CO2 isotherms, UV–Vis diffuse reflectance; and CO2 photoreduction results in figures. AUTHOR INFORMATION Corresponding Author *Email: [email protected] Author Contributions All authors have contributed to the writing of the manuscript and have approved its final version. ACKNOWLEDGMENT This work was funded by Saudi Aramco-KAIST CO2 Management Center. In addition, this research was supported by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (MSIP; grant no. 2015R1A2A1A05001844). REFERENCES 1. Dimitriou, I.; García-Gutiérrez, P.; Elder, R. H.; Cuéllar-Franca, R. M.; Azapaqic, A.; Allen, R. W. K. Energy Environ. Sci. 2015, 8, 1775-1789. 2. Habisreutinger, S. N.; Schmidt-Mende, L.; Stolarczyk, J. K. Angew. Chem. Int. Ed. 2013, 52, 7372-7408. 3. Tu, W.; Zhou, Y.; Zou, Z. Adv. Mater. 2014, 26, 4607-4626.


17

ACS Catalysis

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 18 of 21

4. Wang, J.-C.; Zhang, L.; Fang, W.-X.; Ren, J.; Li, Y.-Y.; Yao, H.-C.; Wang, J.-S.; Li, Z.-J. ACS Appl. Mater. Interfaces 2015, 7, 8631-8639. 5. Schreier, M.; Luo, J.; Gao, P.; Moehl, T.; Mayer, M. T.; Grätzel, M. J. Am. Chem. Soc. 2016, 138, 1938-1946. 6. Kang, Q.; Wang, T.; Li, P.; Liu, L.; Chang, K.; Li, M.; Ye, J. Angew. Chem. Int. Ed. 2014, 54, 841-845. 7. Wang, Y.; Bai, X.; Qin, H.; Wang, F.; Li, Y.; Li, X.; Kang, S.; Zuo, Y.; Cui, L. ACS Appl. Mater. Interfaces 2016, 8, 17212-17219. 8. Xiang, Q.; Cheng, B.; Yu, J. Angew. Chem. Int. Ed. 2015, 54, 11350-11366. 9. Low, J.; Yu, J.; Ho, W. J. Phys. Chem. Lett. 2015, 6, 4244-4251. 10. Wu, X.; Wen, L.; Lv, K.; Deng, K.; Tang, D.; Ye, H.; Du, D.; Liu, S.; Li, M. Appl. Surf. Sci. 2015, 358, 130-136. 11. Lv, K.; Fang, S.; Si, L.; Xia, Y.; Ho, W.; Li, M. Appl. Surf. Sci. 2017, 391, 218-227. 12. Han, B.; Liu, S.; Tang, Z.-R.; Xu, Y.-J. J. Energy Chem. 2015, 24, 145-156. 13. Yu, J.; Jin, J.; Cheng, B.; Jaroniec, M. J. Mater. Chem. A 2014, 2, 3407-3416. 14. Cho, K. M.; Kim, K. H.; Choi, H. O.; Jung, H.-T. Green Chem. 2015, 17, 3972-3978. 15. Chang, X.; Wang, T.; Gcong, J. Energy Environ. Sci. 2016, 9, 2177-2196. 16. Liu, S.; Weng, B.; Tang, Z.-R.; Xu, Y.-J. Nanoscale 2014, 7, 861-866.


18

Page 19 of 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

ACS Catalysis

17. Gan, Z.; Wu, X.; Meng, M.; Zhu, X.; Yang, L.; Chu, P. K. ACS Nano 2014, 8, 9304-9310. 18. Lee, J. S.; You, K. H.; Park, C. B. Adv. Mater. 2012, 24, 1084-1088. 19. Chen, Z.; Liu, S.; Yang, M.-Q, Xu, Y.-J. ACS Appl. Mater. Interface 2013, 23, 43094319. 20. Lin, G.; Zheng, J.; Xu, R. J. Phys. Chem. C 2008, 112, 7363-7370. 21. Kim, D. W.; Choi, J.; Kim, D.; Jung, H.-T. J. Mater. Chem. A 2016, 4, 17773-17781. 22. Mungse, H. P.; Khatri, O. P. J. Mater. Chem. A 2016, 4, 17773-17781. 23. Li, Z.; He, C.; Wang, Z.; Gao, Y.; Dong, Y.; Zhao, C.; Chen, Z.; Wu, Y.; Song, W. Photochem. Photobiol. Sci. 2016, 15, 910-919. 24. Kim, K. H.; Yang, M.; Cho, K. M.; Jun, Y.-S.; Lee, S. B.; Jung, H.-T. Sci. Rep. 2013, 3251. 25. Nam, Y. T.; Choi, J.; Kang, K. M.; Kim, D. W.; Jung, H.-T. ACS Appl. Mater. Interfaces 2016, 8, 27376-27382. 26. Takeuchi, K.; Yamamoto, S.; Hamamoto, Y.; Shiozawa, Y.; Tashima, K.; Fukidome, H.; Koitaya, T.; Mukai, K.; Suemitsu, M.; Morikawa, Y.; Yoshinobu, J.; Matsuda, I. J. Phys. Chem. C 2017, 121, 2807-2814. 27. Liu, S.; Xia, J.; Yu, J. ACS Appl. Mater. Interfaces 2015, 7, 8166-8175. 28. Tu, W.; Zhou, Y.; Liu, Q.; Yan, S.; Bao, S.; Wang, X.; Xiao, M.; Zou, Z. Adv. Funct. Mater. 2013, 23, 1743-1749.


19

ACS Catalysis

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 20 of 21

29. Potter, M. E.; Pang, S. H.; Jones, C. W. Langmuir 2016, 33, 117-124. 30. Li, Q.; Li, Xin; Wageh, S.; Al-Ghamdi, A. A.; Yu, J. Adv. Energy Mater. 2015, 5, 1500010. 31. Jin, J.; Yu, J.; Guo, D.; Cui, C.; Ho, W. Small 2015, 11, 5262-5271. 32. Leelavathi, A.; Madras, G.; Ravishankar, N. J. Am. Chem. Soc. 2014, 136, 14445-14455. 33. Tang, Y.; Hu, X.; Liu, C. Phys. Chem. Chem. Phys. 2014, 16, 25321-25329. 34. Singh, A. P.; Kodan, N.; Mehta, B. R.; Held, A.; Mayrhofer, L.; Moseler, M. ACS Catal. 2016, 6, 5311-5318. 35. Potter, M. E.; Cho, K. M.; Lee, J. J.; Jones, C. W. Chemsuschem, 2017, 10, 2192-2201.


20

Page 21 of 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

ACS Catalysis

Amie-functionalized graphene (AG) is demonstrated to improve the photocatalytic activity in CO2 reduction due to activate the stable CO2 molecule and transfer the charges effectively. AG/CdS shows enhanced conversion rate of CO2 into CO and CH4 under visible-light.


21

CdS Composite for Photocatalytic

Recommend Documents