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Research Article | Open Access

Volume 2022 |Article ID 9805879 |

Hai−Bo Huang, Ning Zhang, Jian−Ying Xu, Yu−Hang Xu, Ya−Feng Li, Jian Lü, Rong Cao, "Photocatalytic CO2–to–Ethylene Conversion over Bi2S3/CdS Heterostructures Constructed via Facile Cation Exchange", Research, vol. 2022, Article ID 9805879, 10 pages, 2022.

Photocatalytic CO2–to–Ethylene Conversion over Bi2S3/CdS Heterostructures Constructed via Facile Cation Exchange

Received09 Aug 2022
Accepted03 Oct 2022
Published21 Oct 2022


Solar-driven CO2 conversion to multicarbon (C2+) products has emerged as a key challenge, yet this calls for a systematic investigation on the overall reaction process and mechanism at an atomic level based on the rational design of highly selective photocatalysts. Herein, we report the synthesis of compact Bi2S3/CdS heterostructures via facile cation exchange, by which a unique pathway of CO2–to–C2H4 photoconversion is achieved. Specifically, the BCS–30 shows an optimal C2H4 production rate of 3.49 μmol h−1 g−1 based on the regulation of band structures and energy levels of photocatalysts by controlled growth of Bi2S3 at CdS surface. Both experimental and theoretical results (DFT calculations) identify Bi atoms as new catalytic sites for the adsorption of CO and formation of CO−CO dimers that further hydrogenate to produce ethylene. Overall, this work demonstrates vast potentials of delicately designed heterostructures for CO2 conversion towards C2+ products under mild photocatalytic conditions.

1. Introduction

The conversion of carbon dioxide (CO2) into transportable chemicals has captured unparallel research attention because of the increasing quest for mitigating anthropogenic carbon emissions related to the consumption and depletion of traditional fuels such as coal, crude oil, and natural gases [14]. Moreover, the synthesis of multicarbon (C2+) products from CO2 is highly attractive due to their versatile applications in the chemical and energy industries, albeit the uncontrollable C–C coupling in thermocatalytic hydrogenation of CO2 over heterogeneous catalysts [57]. Nevertheless, this is extremely challenging due to the chemical inertness of CO2, the competing formation of methane (CH4), and the slow kinetics of proton and electron transport [810]. In particular, the high-energy density ethylene (C2H4) is one of the most important feedstocks with high commercial value for polymer production [1113]. As known, a twelve-electron transfer process and multiple hydrogenation steps are involved in the conversion of CO2 to C2H4, which generally resulted in restricted conversion efficiency and unexpected products, i.e., CH4, carbon monoxide (CO) and formic acid (HCOOH). To address these issues, copper-based materials are currently the most promising catalysts for CO2 reduction into hydrocarbons via electrochemical catalysis based on alkaline flow cells [1416], coupled to traditional iron-based catalysts and composite oxide catalysts (i.e., Cu−ZnO−Al2O3/zeolite) [17] that normally require additional input of power energy.

Most notably, great importance has been contemporarily focused on solar-driven photocatalysis that mimics the natural photosynthesis as an essential pathway to convert solar energy into clean and renewable chemical energy [1820]. In a typical photocatalytic process, photogenerated charge carriers (electron and hole pairs) are induced upon the absorption of photons with energy greater than the bandgaps of semiconductor photocatalysts. Once photocarriers are separated and transported to the photocatalyst surface, redox reactions might take place by involving either donors (with holes) or acceptors (with electrons), thereby leading to the transformation of various substrates. Therefore, the discovery of viable and efficient photocatalysts is generally considered as the key engine for the development of environmental and energy photocatalysis including nitrogen (N2) fixation, hydrogen (H2) production, and CO2 reduction. In contrast to the production of C2H4 and other C2+ products via electrochemical CO2 reduction [2124], however, not much success has been accomplished in CO2 reduction through viable photocatalytic systems hitherto.

One key step to produce C2+ products is the CO−CO coupling that requires at least two catalytically active sites with an appropriate separation. Alternatively, a two-step tandem process is involving individually the conversion of CO2 to carbon monoxide (CO), followed by combination with H+ to form C2+ hydrocarbons, a process that requires the inhibition of methane (CH4) production. This could be achieved based on the rational design of functionally well-defined photocatalysts via sophisticated control of surface/interface structures for multiple-step chemical conversions [25]. To this end, heterostructure photocatalysts are promising in creating such functional surface/interface to realize tandem photocatalysis, since crystallographically matched phases within a heterostructure ideally satisfy the spatial control of catalytic sites in this scenario [2628]. In situ growth of heterostructures can generate high-quality compact interface that facilitates efficient carrier transport. Furthermore, heterostructures combining narrow- and wide-bandgap semiconductors as visible-light-driven photocatalysts generally possess highly active sites and advanced structural features [29]. In this context, the cadmium sulfide (CdS) has a suitable bandgap (2.4 eV) that endows an excellent visible light absorption capacity for solar utilization [30], and thus CdS-based heterojunction materials formed by a simple synthetic method of cation-exchange exhibit excellent photocatalytic performance [31, 32]. Meanwhile, the bismuth sulfide (Bi2S3) with direct and narrow bandgap is considered as an excellent candidate to combine with CdS for CO2 photoreduction into value-added chemicals [33]. More importantly, the conduction band potential of Bi2S3 is more negative than most semiconductors, which allows suitable alignment of energy levels (bandgap, valence, and conduction band potentials) for CO2 photoreduction. However, it remains a daunting challenge for the controlled synthesis of viable heterostructure photocatalysts with the purpose of CO2 photoreduction into C2+ products.

We demonstrate herein the rational design and synthesis of heterostructure photocatalysts for tandem CO2–to–C2H4 conversion that couples individual steps within a chemically complicated pathway. The interface engineering via controlled cation exchange at the surface of CdS nanorods (NRs) gave rise to a series of Bi2S3/CdS (BCS–t) heterostructures that exhibited particularly efficient capacity for CO2 photoreduction under visible irradiation. Remarkably, as-prepared BCS–t photocatalysts achieved a unique CO2 reduction pathway to produce C2H4, of which the BCS–30 showed an optimal C2H4 production rate of 3.49 μmol h−1 g−1. Overall, the current research outlines a new strategy for CO2 photoreduction into C2+ products by first time using a bismuth-based material.

2. Results and Discussion

We successfully synthesized BCS–t composites with the design strategy illustrated in Figure 1(a). Phase and composition of CdS, Bi2S3, and BCS–t heterostructures were studied by powder X–ray diffractions (PXRD) and X–ray photoelectron spectrometry (XPS). As shown in Figure 1(b) and S1, the main characteristics of pristine CdS were assigned to the hexagonal phase of wurtzite CdS (JCPDS: 41–1049) [34]. Upon cation exchange with Bi3+, diffraction peaks of the orthogonal Bi2S3 (JCPDS: 17–0320) were observed, which was rational since the Bi2S3 possesses a smaller (ca. ) than CdS (ca. ), and thus, CdS could partially transform to Bi2S3 in the presence of Bi3+ ions [35]. Moreover, the intensity of hexagonal CdS characteristics gradually decreased, while those of orthorhombic Bi2S3 peaks evidently increased with extended time of ion exchange. A nearly complete exchange was achieved after 120 min, which resulted in the formation of an orthorhombic Bi2S3 phase [35]. In addition, XPS spectra was performed to analyze the surface chemical composition and valence state of various elements in these samples. The XPS survey spectrum clearly showed the existence of Cd, S, and Bi elements in the representative BCS–30 (Figure 1(c)). As shown in Figure 1(d), the two peaks at binding energies of ca. 158.6 eV and ca. 163.9 eV corresponded to Bi 4f5/2 and Bi 4f7/2 orbits, respectively, indicating the presence of Bi3+ in BCS–30 [36]; the characteristics at ca. 161.6 eV and ca. 162.8 eV were assigned to S 2p3/2 and S 2p1/2, respectively, and the split energy of ca.1.2 eV was the fingerprint for S2– [37]; the two peaks around ca. 404.8 eV and ca. 411.5 eV were attributable to Cd 3d5/2 and Cd 3d3/2, respectively, which were typical for Cd2+ in sulfides (Figure 1(e)) [38]. Consequently, the elemental composition of all samples was analyzed by means of the inductive coupled plasma emission spectrometer (ICP) as presented in Supplementary Table 1.

To gain further insights into structural details of BCS–t heterostructures, microstructure and morphology were investigated by SEM, TEM, and HR–TEM (Figures 1(f) and 1(g), and Figures S2–S4). The pristine CdS showed a rod-like morphology with an average diameter of ca. 50 nm and length of 200 nm to 300 nm. Morphology of the representative BCS–30 revealed that Bi2S3 nanoparticles were decorated on the surface of CdS nanorods (NRs) with high dispersity, and no clear change in the microstructure of CdS NRs was observed. In the HRTEM image (Figure 1(g)), lattice fringes with spacing of ca. 0.23 nm and ca. 0.35 nm were ascribed to the (1 0 2) crystal plane of hexagonal CdS and (3 1 0) crystal plane of orthorhombic Bi2S3, respectively. Moreover, elemental mapping analyses of BCS–30 were studied to verify the successful and homogeneous dispersion of Bi2S3 on CdS NRs. As shown in Figure 1(h), the mapping images of Bi, Cd, and S contents suggested a uniform distribution of each element in BCS–t samples. It was therefore concluded that Bi2S3 nanoparticles was successfully deposited on the surface of CdS NRs via cation exchange, which might create intimate contacts and compact interface between Bi2S3 and CdS counterparts.

UV–vis diffuse reflectance spectra (DRS) of CdS and Bi2S3 are displayed in Figure S5. The pristine CdS showed an absorption edge around 525 nm, and Bi2S3 showed strong absorption in the whole ultraviolet–visible region. In comparison, the light absorption range of BCS–t heterostructures was further extended from UV to the visible light region. Therefore, the corresponding bandgaps of CdS and Bi2S3 were estimated to ca. be 2.36 and ca. 2.04 eV (Figures S4b and S4d), respectively. To better understand the effect of band structure on charge separation efficiency and photocatalytic activity, Mott−Schottky diagrams were investigated. As shown in Figure S6, the positive tangent slopes in the Mott–Schottky indicated that both CdS and Bi2S3 were typical n-type semiconductors [39, 40]. Thus, the flat band potential () of CdS and Bi2S3 were calculated as ca. −1.25 and ca. −0.77 V vs. Ag/AgCl (ca. −1.05 and ca. −0.57 V vs. NHE), respectively. Furthermore, the valence band (VB) of CdS and Bi2S3 were determined to be ca. 1.31 and ca. 1.47 V vs. NHE, respectively. Based on the energy alignment, Bi2S3 and CdS in BCS–t can be organized into either -scheme or type-II heterojunction.

In the system of CO2 photoreduction with various catalysts, CO and C2H4 were identified as major products of CO2 photoreduction, and H2 was produced via the reduction of water vapor. As shown in Figure S7a, the CO production rate of pristine CdS was ca. 10.5 μmol g−1 h−1 which was considerably higher than those of BCS–t heterostructures. Notably, CO was the sole detectable product of CO2 photoreduction with CdS NPs, whereas C2H4 production was observed for BCS–t photocatalysts. Since the single Bi2S3 did not produce CO products, the active site of CO production was likely at the surface of CdS, and thus, a -scheme heterojunction might form between CdS and Bi2S3 counterparts. Moreover, the C2H4 production rate of BCS–t was synergically regulated by Bi2S3 : CdS ratios as neither of the individual CdS nor Bi2S3 was able to yield C2+ products. Especially, the BCS–30 showed the maximum yield of 3.49 μmol h−1 g−1 under visible irradiation, which was roughly 1.5, 1.7, and 3.0 times those of BCS–15, BCS–60, and BCS–120, respectively (Figure 2(a)). Therefore, it was clear that the C2H4 production capacity of heterostructure photocatalysts was readily tuned via delicate control on the process of cation exchange, which demonstrated that moderate decoration of Bi2S3 at CdS surface was crucial to modulate photocatalytic activity of BCS–t.

On the other hand, the H2 production of BCS–t followed a similar trend to that of C2H4 production, in which the BCS–30 exhibited the highest production rate of 2971 μmol h−1 g−1 (Figure S7b). Moreover, the amount of consumed electrons in CO2 photoreduction over BCS–t heterostructures was calculated based on the production of CO (2 e) and C2H4 (12 e). Results showed that BCS–t photocatalysts generally processed enhanced electron utilization than those of CdS and Bi2S3, among which BCS–30 achieved the highest amount of electron transport for CO2 photoreduction (Figure 2(b)). Moreover, BCS−30 exhibited the best photoelectron selectivity for CO2 photoreduction to carbonaceous products (Figure S7c). In addition, the applicability of BCS–30 was tested by long-term experiments, in which the photocatalyst exhibited both stable photocatalytic activity (Figures S8a–S8c) and phase crystallinity (Figure S8d), which was also demonstrated by TEM (Figure S9) and XPS (Figure S10) recorded on recycled BCS–30.

In order to trace the origin of carbonaceous products, 13CO2 isotope labeling experiments were performed. As shown in Figures 2(c) and 2(d), gas chromatography and mass spectrometry (GC–MS) analysis clearly identified 13C2H4 and 13CO, which indicated the input of CO2 as viable carbon sources. Moreover, control substrate experiments under the same catalytic conditions without adding H2O and MeCN or by replacing CO2 with Ar could give rise to only trace or extremely low amount of carbon products (Figures S11a–S11c). Alternatively, the BCS–30 remained producing a detectable amount of ethylene with inorganic Na2S and Na2SO3 aqueous solution as sacrificial reagents. Surprisingly, significant amount of C2H4 were produced by replacing the CO2 with CO as the reaction substrates (Figure S8d). These are conclusive evidence for viable C2H4 production, and the formation of CO might be a key step that initiates CO2–to–C2H4 conversion with BCS–t photocatalysts.

The photoluminescence (PL) quenching technique was used to study the separation efficiency of photoinduced electron–hole pairs in CdS, Bi2S3, and BCS–t. As shown in Figure S12a, the CdS exhibited strong characteristic PL emission centered at ca. 750 nm, whereas BCS–t displayed largely decreased PL intensity with increasing Bi2S3 contents. PL results demonstrated that the separation efficiency of photogenerated electrons and holes in BCS–t heterostructures was markedly improved by virtue of the synergistic effect between CdS and Bi2S3 counterparts. The improved separation efficiency of photocarriers in these heterostructure photocatalysts was further confirmed by electrochemical impedance spectroscopy (EIS) analyses (Figure S12b), in which the BCS–t generally showed smaller arc resistance radius than the pristine CdS, suggesting much enhanced separation and transfer of charge carriers in BCS–t heterostructures.

In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed to monitor the possible intermediate species during the process of CO2 photoreduction in this current system. First, CO2 and H2O molecules were absorbed at the surface of BCS–t for 10 min in dark. Upon visible light irradiation, new peaks that gradually intensified with reaction progressing were observed in DRIFTS spectra (Figures 3(a) and 3(b)). These peaks were assigned to HCO3 (1226 cm–1), m–CO32– (1306/1508 cm–1), b–CO32– (1363 cm–1), HCOOH (1338 cm–1), and COOH (1558 cm–1). More importantly, absorption characteristics of key intermediates, including OCCO (1578 cm–1), CH2 (1397/1474 cm–1), and C2H4 (1436/1686 cm–1), were successfully captured as a proof of photocatalytic CO2–to–C2H4 conversion [41]. However, similar tests with the CdS photocatalyst solely revealed absorption peaks of COOH and CO, which supported the unique role of BCS–t photocatalysts in the formation of key intermediates for CO2–to–C2H4 production conversion (Figure S13).

To further reveal the mechanism of CO2–to–C2H4 conversion in this current system, DFT calculations were performed to investigate the pathway of CO2 photoreduction, as detailed in the Supporting Information. First, the conversion products CH4 and C2H4 are a competing reaction; however, the rate determining step (RDS) for both pathways is that the coupling of CO to form OCCO has a lower corresponding free energy than the hydrogenation of CO to form CHO (Figure 3(c)). This means that the final product of the ground will not be methane, but will go to the option of producing ethylene. Computational intermediate models formed by CH4 and C2H4 are provided in the Supporting Information (Figure 4 and Figure S14). Then, we performed calculations for the various pathways from CO2 to ethylene, and the most likely route is pathway4 due to the lowest RDS (Figures S15 and S16). The production of C2H4 from CO2 possibly occurs through CO2CO → OCCO → CHCO → CHCOH → CHCHOH → CH2CHOH → C2H4 chain reactions, in which Bi atoms are new catalytic sites for the adsorption of CO and the formation of CO−CO dimers, which further hydrogenate to produce ethylene.

Based on the above characterizations, a mechanism of solar-driven CO2–to–C2H4 conversion in the BCS–t is proposed as follows. CO2 and H2O molecules are first adsorbed at the surface of photocatalyst, which is excited by visible irradiation to generate photocarriers (h+ and e). Meanwhile, electrons quickly transport to catalyst surface and participate in CO2 photoreduction, and then, photogenerated electrons are accumulated at CBs of CdS and Bi2S3 in a BCS–t heterostructure, in which electrons also transfer from the CB of Bi2S3 to the VB of CdS through a -scheme electron migration scheme. In such a way, holes are accumulated at a lower energy level, and the redox ability is much stronger to achieve CO2 reduction while preventing the photocorrosion of CdS. CO2 molecules are readily reduced by photoelectrons to yield COOH, which is then hydrogenated to produce CO. Further hydrogenation via CO leads to dimerization into C2HxO [42]. Finally, these intermediates are further reduced to C2H4.

3. Conclusion

Although it appears extremely challenging to produce value-added C2+ chemicals from CO2 photoreduction, we present here a facile cation exchange strategy to synthesize Bi2S3/CdS (BCS–t) heterostructures which show vast potentials for solar-driven CO2–to–C2H4 conversion. The proposed synthetic pathway successfully creates catalytically active and compact interface between Bi2S3 and CdS counterparts in BCS–t, which leads to tandem photocatalysis for C2H4 production. Upon controlled growth of Bi2S3 at the surface of CdS, BCS–30 shows a maximal C2H4 production rate due to an optimal ratio of the two components. This work thus provides new insights into the design of viable photocatalysts for solar-driven CO2 photoreduction towards C2H4 production.

4. Materials and Methods

4.1. Preparation of CdS Nanorods (CdS NRs)

All chemicals were of analytical grade and directly used without further purification. The CdS nanorods were synthesized in a solvothermal system using ethylenediamine as both the structure directing agent and solvent. First, 3.0 mmol Cd(NO3)2·4H2O and 9.0 mmol CS(NH2)2 were dissolved in 30 mL mixed solvents of ethylenediamine and water () for 30 min with vigorous stirring. Then, the above solution was transferred to a 50 mL solvothermal autoclave, and the reaction was kept at 180°C for 12 h, followed by cooling naturally to room temperature. The orange−yellow product of CdS NRs was collected by centrifugation and washed several times with deionized water and dried at 70°C overnight.

4.2. Preparation of Bi2S3/CdS (BCS) Heterostructures

Bi2S3/CdS heterostructures were prepared by a simple ion exchange method in ethylene glycol (EG) solution. Briefly, 0.5 mmol CdS NRs were dissolved in 20 mL EG and sonicated for 15 min, followed by the addition of 1.5 mmol Bi(NO3)2·5H2O was added under constant stirring at 75°C for different time (15/30/60/120/240 min). The resultant brownish−yellow solid precipitates were collected by centrifugation and washed several times with deionized water and then were dried at 70°C overnight. The as-prepared BCS samples were denoted as BCS–t (, 30, 60, and 120). Complete exchange of Cd2+ with Bi3+ was realized after 240 min, and the sample was therefore denoted as Bi2S3.

4.3. Photocatalytic CO2 Reduction

The photocatalytic CO2 reduction was performed by using a sealed quartz reactor with an optically transparent quartz cover. In a typical experiment, 10 mg photocatalyst was loaded into a 210 mL quartz glass reactor containing 6.0 mL acetonitrile, 2.0 mL deionized water, and 2.0 mL triethanolamine. Before light irradiation, the reaction system was degassed with vacuum, and then photocatalytic reactions were carried out using a 300 W Xe–arc lamp (PLS–SX300D, Beijing) equipped with a UV cut filter (wavelength 400 nm) as the light source. Subsequently, the reaction system was vacuum degassed and backfilled with high-purity CO2 gas (99.99%), which was repeated for three times to ensure the reactor was finally backfilled with pure CO2. Before photocatalysis, dark reaction was first applied for 1 h to ensure the adsorption equilibrium. During a photocatalytic reaction, 1.0 mL gas was extracted hourly from a glass reactor using gas chromatography (GC–7820A, Shimadzu) equipped with flame ionization detector (FID) and capillary column (GC–GASPRO) and used for subsequent gas content/concentration analyses. The stability of photocatalysts was evaluated by continuous reactions using recovered solids and fresh solutions. Control substrate experiments were tested under the same catalytic condition without the addition of H2O or MeCN or by replacing CO2 with Ar. Alternatively, the photocatalytic reaction is carried out by using Na2S and Na2SO3 (NNS) aqueous solution as sacrificial agents. In the isotope tracking experiments by substituting 13CO2 for 12CO2 gas to demonstrate the origin of the product, other experimental conditions are the same as the photocatalytic CO2 reduction.

4.4. In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

Thermo Scientific Nicolet 6700 spectrometer was used for the in situ DRIFTS over as–samples. An average of 128 scans was taken for each spectrum, which had a resolution of 4 cm–1. CO2 flow (40 mL/min) was bubbled into MeCN/H2O/TEOA (3 : 1 : 1) and then passed through the sample cell. The visible light irradiation was shed on the powder through a quartz window of the sample cell. The CO2 gaseous was kept steady before the light irradiation.

4.5. Computational Details

All the density functional theory (DFT) calculations were performed using the Vienna ab initio simulation package (VASP) [4346]. The projector augmented wave (PAW) method was used to describe the interactions between ion cores and valence electrons [47]. The GGA–PBE was employed to describe the exchange–correlation functional [48, 49]. The Kohn–Sham equations were expanded in a plane wave basis set with a cutoff energy of 400 eV. The Brillouin zone sampling was performed using Monkhorst–Pack -point grid [50]. According to XPS, the (102) surface of CdS was chosen to investigate the activity of Bi doped Bi@CdS catalyst. For the investigated catalyst, a supercell model with three atomic layers were constructed. During the optimization, the most bottom layer is fixed, and the other two layers are relaxed.

Data Availability

Data supporting the findings of this study are available in the main text or the supporting materials.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this article.

Authors’ Contributions

J. Lü, R. Cao, and H. Huang designed the project and cowrote the manuscript; H. Huang carried out most of the syntheses, characterizations and photocatalytic CO2 reduction tests in this work; N. Zhang assisted the syntheses and characterizations;, J. Xu, and Y. Xu assisted the photocatalytic CO2 reduction tests; Y. Li assisted the characterizations of materials. J. Lü and R. Cao cosupervised the overall project. All authors have given approval to the final version of the manuscript.


This work was financially supported by the NSFC (nos. 91622114, 21520102001, 21521061, and 21331006), the Open Project Program of the State Key Laboratory of Photocatalysis on Energy and Environment (grant no. SKLPEE–202008), Fuzhou University, and the Special Fund for Scientific and Technological Innovation of Fujian Agriculture and Forestry University (grant no. CXZX2019073G).

Supplementary Materials

Table S1: elemental analysis of BCS–t heterostructures. Figure S1: PXRD patterns of the CdS and BCS–t. Figure S2: SEM images of (a) CdS and (b) BCS–30. Figure S3: (a) TEM and (b) HR–TEM images of the CdS. Figure S4: (a) and (b) TEM, (c) HR–TEM, and (d–h) elemental distribution images of the BCS–30. Figure S5: (a) UV–vis DRS and (b) K–M plots of CdS; (c) UV–vis DRS and (d) K–M plots of Bi2S3. Figure S6: Mott–Schottky plots of (a) CdS and (b) Bi2S3. Figure S7: yields of (a) H2 and (b) CO in CO2 photoreduction over CdS and BCS–t under visible irradiation. Figure S8: long-term experimental photocatalytic activity of (a) C2H4, (b) CO, (c) H2 of the BCS–30, and (d) PXRD patterns of the BCS–30 before and after the long-term photocatalytic experiment. Figure S9: (a) TEM, (b) HR–TEM, and (c) elemental distribution images of the BCS–30 before and after the long-term photocatalytic experiment. Figure S10: (a) XPS full spectra, XPS spectra of (b) Cd 3d and (c) Bi 4f and S2p of the BCS–30 before and after the long-term photocatalytic experiment. Figure S11: photocatalytic activity of (a) H2, (b) CO, (c) C2H4 ( aqueous solution) of the BCS–30, and (d) comparison of ethylene activity in different gas atmosphere (inset: H2 production rate). Figure S12: (a) room temperature PL and (b) electrochemical impedance spectra of CdS, Bi2S3, and BCS–t. Figure S13: in situ DRIFTS for CdS in CO2 atmosphere under visible light irradiation. Figure S14: structural evolution of intermediates in the CH4 pathway on the BCS surface. Figure S15: the free energy diagram of the various pathways of CO2–to–C2H4 photoreduction on the BCS at . Figure S16: the structures of intermediates in various C2H4 production pathways on the BCS surface. (a) The CH2CHO pathway and (b) the CHC pathway. (Supplementary Materials)


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