Boron Carbon Nitride Semiconductors Decorated with CdS

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Boron Carbon Nitride Semiconductors Decorated with CdS Nanoparticles for Photocatalytic Reduction of CO2 Min Zhou, Sibo Wang, Pengju Yang, Caijin Huang, and Xinchen Wang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b00104 • Publication Date (Web): 23 Apr 2018 Downloaded from http://pubs.acs.org on April 23, 2018

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Boron Carbon Nitride Semiconductors Decorated with

CdS

Nanoparticles

for

Photocatalytic

Reduction of CO2 Min Zhou1, Sibo Wang1, Pengju Yang1, Caijin Huang1 and Xinchen Wang1,2* 1. State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, 350002, P. R. China 2. Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia.

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ABSTRACT: Ternary boron carbon nitride (BCN) semiconductors have been developed as emerging metal-free photocatalysts for visible-light reduction of CO2,, but the achieved efficiency is still not satisfying. Herein, we report that the CO2 photoreduction performance of bulk BCN semiconductor can be substantially improved by surface engineering with CdS nanoparticles. The CdS/BCN photocatalysts are characterized completely by diverse tests (e.g., XRD, FTIR, XPS, DRS, SEM, TEM, N2 sorption, PL, and transient photocurrent spectroscopy). Performance of the CdS/BCN heterostructures is evaluated by reductive CO2 conversion reactions with visible light under benign reaction conditions. Compared with bare BCN material, the optimized CdS/BCN photocatalyst exhibits a 10-fold-enhanced CO2 reduction activity and high stability, delivering a considerable CO production rate of 12.5 µmol h-1 (250 µmol h-1 g-1) with triethanolamine (TEOA) as the reducing agent. The reinforced photocatalytic CO2 reduction activity is mainly assigned to the obviously improved visible-light harvesting and the greatly accelerated separation/transport kinetics of light-triggered electron-hole pairs. Furthermore, a possible visible-light-induced CO2 reduction mechanism is proposed on the base of photocatalytic and photo(electro)chemical results.

KEYWORDS: Boron carbon nitride; CO2 reduction; CdS; heterostructure; photocatalysis.


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INTRODUCTION The construction of clean and renewable energy systems is attracting significant research attention in the 21st century so as to overcome the great demand of limited fossil fuels for energy-providing.1-7 Reductive conversion of CO2 into added-value products by sunlight is promising to explore new alternatives for sustainable energy supply, which is also accompanied by enormous positive effects to relieve global warming effect.8-14 Up to date, a wealth of transition metal materials, as well as their hybrids, have been employed as photocatalysts for solar CO2 fixation with encouraging achievements. However, most of the examined materials (e.g., TiO2,7,15-17 ZrO2,18 MgO,19 Ga2O3,20 ZnGa2O4,21 Zn2GeO422) can only response to UV light, which seriously limits the utilization of solar energy. Therefore, it is highly desirable for developing efficient and stable photocatalysts responsive to visible-light, particularly the candidates made of lightweight and abundant elements, to operate the reduction of CO2 from the viewpoint of practical applications.23-25 The metal-free hexagonal boron nitride (h-BN), featuring with high thermal and chemical stabilities, is a wide bandgap semiconductor.26,27 We have recently demonstrated that the physicochemical properties of h-BN can be readily tuned through carbon doping, producing the new semiconductor material, namely boron carbon nitride (BCN).28 The ternary BCN semiconductor possesses a conjugated sp2 hybridized electron system with carbon incorporated into the lattice. By adjusting the degree of carbon incorporation, the bandgap of BCN could be delicately modulated to optimize the catalytic functions. The BCN semiconductor is revealed to be an active photocatalyst for target photoredox reactions with visible light, such as H2O splitting and CO2 reduction.28 When cooperated with a ruthenium photosensitizer, the BCN catalyst manifests a considerable performance for reductive splitting of CO2 into CO under mild


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conditions. Although BCN displays great opportunities for photocatalytic CO2 transformation, the involvement of a ruthenium dye photosensitizer hampers the sustainable development of the established system. Besides, the quantum yield of BCN for CO2 photoreduction still needs to be further upgraded for practical implementation. The weak optical absorption in visible-light region and the high recombination of photoexcited charges are the main reasons that greatly restrict the efficiency of BCN semiconductor for CO2 reduction photocatalysis. To fully activate the potential of conjugated BCN photocatalyst, our research effort is concentrated on the development of BCN composite materials with suitable semiconductor light harvesters aiming to enhance photo absorption and promote charge transfer kinetics, simultaneously.29-35 As an important visible light transducer, CdS semiconductor exhibits high optical response and has been widely applied as photoharvester for diverse photoredox catalysis.36-46 Therefore, we are inspired to employ CdS nanoparticles to hybridize with BCN semiconductor to assemble CdS/BCN heterostructures for reductive CO2 conversion. Herein, CdS/BCN hybrids are prepared through a facile photodeposition process,39,41 and are completely investigated by various tests (e.g., XRD, FTIR, XPS, DRS, SEM, TEM, and N2 adsorption measurements). When evaluated as photocatalysts for visible-light CO2 conversion, the optimal CdS/BCN heterostructure shows a considerable performance for deoxygenative reduction of CO2 with a CO formation rate of 12.5 µmol h-1 (250 µmol h-1 g-1), which is substantially enhanced by 10 folds when comparing with the bare BCN material. Moreover, no evident decrease in the catalytic performance of CdS/BCN is observed after repeated operation for five cycles. The enhanced performance of reductive CO2 photosplitting is attributed to the obviously boosted photoabsorption and greatly accelerated transfer kinetics of light-stimulated


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electron-hole pairs. Furthermore, a possible visible-light-induced CO2 reduction mechanism is proposed on the base of photocatalytic and photo(electro)chemical results. EXPERIMENTAL SECTION Materials. Boric acid (H3BO3) was obtained from Aladdin biological technology co., Ltd. (Shanghai). Cadmium chloride (CdCl2·2.5H2O), elemental sulfur (S8), urea (H2NCONH2), cobalt chloride (CoCl2), starch (C12H22O11), bipyridine (bpy), silicon dioxide (SiO2), ethanol (C2H5OH), triethanolamine (TEOA), acetonitrile (MeCN), N’N-dimethylformaide (DMF), dichloromethane (DCM), and tetrahydrofuran (THF) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). High-purity CO2 and nitrogen (N2) gas (99.999 %) were provided by Fuzhou Lianzhong Industrial Gases Co., Ltd. The 13CO2 was 97 % in purity. Synthesis of BCN. Boron acid, urea, and starch (weight ratio: 1:2:5) were ground fully with an agate mortar, followed by a heat treatment in ammonia atmosphere at 1250 ˚C for 5 hours.28 After calcination, the obtained products were washed with hot HCl solution (80 °C, 60 mL, 0.1 M) to eliminate the remaining B2O3, and the obtained sample was denoted as BCN. Synthesis of CdS/BCN. BCN (100 mg), S8 (9 mg) and CdCl2·H2O (60 mg) were dispersed in 80 mL of ethanol under the protection of N2 atmosphere. Then, the resultant mixture was exposed to light illumination (λ > 420 nm) for 30, 60, to 90 min, respectively.39,41 After photodeposition, the obtained products were rinsed with ethanol and H2O several times to remove the unreacted raw materials. The obtained samples were labelled as CdS/BCN-30, CdS/BCN-60 and CdS/BCN-90, respectively. Unless otherwise stated, the used sample for characterizations and photocatalysis was the CdS/BCN-60 sample. The reference CdS samples were synthesized through the similar


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photodeposition method with inactive SiO2 as the support, and the obtained sample was designated as CdS-60. Characterization. Powder X-ray diffraction (XRD) tests were carried out on a Bruker D8 Advance X-ray diffractometer (Cu Kα1 radiation, λ = 1.5406 Å). A Nicolet (thermos Nicolet Nexus) 670 FTIR spectrometer was employed to collected the Fourier transform infrared (FTIR) spectra. X-ray photoelectron spectroscopy (XPS) analysis was operated on a PHI Quantum 2000 XPS system with C 1s binding energy (284.6 eV) as the reference. A Vario MICRO was used to conduct the elemental analysis of samples. Inductively coupled plasma mass spectrometry (ICPMS) measurements were manipulated on XSRIES 2. Field-emission scanning electron microscope (SEM, Hitachi New Generation SU8010) and transmission electron microscopy (TEM, JEOL model JEM 2010 EX) were utilized to examine the morphologies of the samples. Optical absorption of the materials was determined by a Varian Cary 500 Scan UV-vis spectrophotometer and barium sulfate was used as the reference. The room temperature photoluminescence (PL) characterizations were carried out on an Edinburgh FI/FSTCSPC 920 spectrophotometer. The average lifetime τ = (A1τ12 + A2τ22 + A3τ32)/(A1τ1 + A2τ2 + A3τ3).47 N2 sorption tests were conducted on Micromeritics ASAP2020. A BAS Epsilon Electrochemical System was used to perform the electrochemical analysis in a three-electrode cell (counter electrode: Pt plate; reference electrode: Ag/AgCl). Fluorine-tin oxide (FTO) glass was used as the conductive substrate to prepare the working electrode. Typically, the sample (5 mg) was totally dispersed in DMF (1 ml) by sonication to gain a slurry. Afterwards, the resultant slurry was spread onto the FTO glass with the area of ca. 0.25 cm2. The transient photocurrent response spectra were collected in Na2SO4 aqueous solution (0.2 M) with a 300 W xenon lamp (λ ≥ 420 nm) as light source, and the applied bias potential was - 0.4 V vs. Ag/AgCl (pH = 6.8).


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Measurements. Products of CO2 photoreduction reactions was analyzed by an Agilent 7820A gas chromatography (GC; thermal conductivity detector, TCD; TD-01 packed column; oven temperature: 50 °C; inlet temperature: 120 °C; detector temperature: 200 °C). Ar was used as the carrier gas (13 mL min-1). The CO gas produced from 13CO2 isotope experiments was examined by a gas chromatography-mass spectrometer (GC-MS, HP 5973). The equipped column in GCMS analysis was HP-MOLESIEVE (Agilent Technologies, 30 m × 0.32 mm, Serial number: USD 130113H). The temperatures of the inlet and oven were 200 °C and 45 °C, respectively. Helium (He) was used as carrier gas (0.6 mL min-1). Photocatalytic test. In a typical photocatalytic CO2 reduction reaction, photocatalyst (50 mg), bpy (20 mg), solvent (6 mL, acetonitrile: H2O = 2: 1), TEOA (1 mL) and CoCl2 (1 µmol) were added into a gas-closed quartz glass reactor (80 mL in volume). The reaction system was filled with high purity CO2 gas (1 atm). A 300W Xe lamp was used as the light source with the incident light controlled by a 420 nm long-pass cutoff filter and the irradiation window of the reactor was ca. 6 cm2. Cooling water was employed to keep the reaction temperature at 40 °C. During photocatalysis, the reaction system was energetically stirred. After reaction, the generated gaseous products (CO and H2) were sampled and quantified by the GC. The cycle experiments were conducted by directly recovering the used catalysts and then re-dispersing the catalysts into a fresh solution. RESULTS AND DISCUSSION Power XRD characterizations are first conducted to analyze the crystal structure and phase of asprepared CdS/BCN composites. The peak position in XRD pattern (Figure 1a) of pristine BCN is consistent with the results of reported works.28,44,48 The characteristic XRD peak located at 2θ of 26 ° is ascribed to (002) plane of BCN, while the other peak at 43° is attributed to (100) plane of


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BCN. After modification with CdS, the peak position of BCN is unchanged, but the peak intensity is decreased slightly, indicating the basic graphitic structure of BCN maintains well in the final CdS/BCN materials. The characteristic diffraction peaks of CdS are clearly observed in the XRD pattern of CdS/BCN-90, which are perfectly indexed to the crystal planes of hexagonal CdS.39 These observations suggest that the crystal structures of CdS and BCN are well developed in the CdS/BCN samples. The chemical structures of CdS/BCN are examined by FTIR spectroscopy. As shown in Figure 1b, the characteristic variations assigned to typical BCN material are clearly seen for all the samples, revealing the successful evolution of BCN structure. The vibration of in-plane B-N bonds is located at 1380 cm-1 and the other location at 780 cm-1 is assigned to the out-of-plane B-N-B bending vibration.49,50 To justify the molar ratio of the BCN material, elemental analysis is performed. The results (Table S1) show that the molar ratio of B/C/N in the boron carbon nitride sample is ca. 8.5/1.0/5.9, that is, the empirical formula of the boron carbon nitride semiconductor is B8.5CN5.9, designated as BCN for clarity. The surface chemical compositions and valence states of elements in CdS/BCN-60 are studies by XPS.50-52 The presence of B, C, N, Cd and S elements are discerned in the survey spectrum (Figure 2a). The B 1s high-resolution XPS spectrum is resolved into three sub-peaks with binding energy of 189.8, 190.4 and 192.0 eV, ascribing to B-C, B-N and B-O bands, respectively (Figure 2b). In the result of XPS analysis for C 1s (Figure 2c), the peaks located at 283.5, 284.6 and 286.2 eV are belonging to C-B, C-C and C-N bonds. Figure 2d shows the N 1s XPS spectrum, in which the three peaks centered at 397.9, 398.6 and 400.5 eV are ascribed to the binding energy of N-B, N-C and N-H bonds. As for the Cd 3d high resolution XPS spectrum (Figure 2e), the spin orbit of Cd 3d5/2 locates at around 405.41 eV, while the Cd 3d3/2 peak lies at 412.20 eV. The spin orbit separation (∆) of the Cd 3d orbital is 6.79 eV, which


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demonstrates the valence state of Cd element in CdS/BCN is Cd2+.39,41 In addition, the signals peaks positioned at 161.5 eV and 162.9 eV in S 2p spectrum (Figure 2f) are S 2p1/2 and S 2p3/2 spin orbits, indicating the S2- state exists in the sample.39,53-55 The peak locations of Cd2+ and S2in the XPS spectra are in accordance with CdS of reported work.39 The amounts of CdS in the final materials are determined by elemental analysis and ICP measurements. Results indicate that the amount of CdS in the CdS/BCN-30, CdS/BCN-60 and CdS/BCN-90 samples are 8.09 wt.%, 13.25 wt.% and 16.62 wt.%, respectively (Table S2). SEM, TEM and N2 sorption tests are carried out to obtain more details about morphological and porous characteristics of CdS/BCN hybrids. Figure 3a demonstrates the SEM images of bare BCN. The size distributions of BCN and CdS particles are presented in the Figure S1 and Figure S2. In the SEM image of CdS/BCN (Figure 3b), some small nanoparticles are clearly seen compared to that of the bare BCN (Figure 3a and Figure S2a), indicating CdS nanoparticles are tightly coupled on BCN surface. The CdS/BCN sample is further examined by TEM (Figure 3c). Figure 3d indicates the high-resolution TEM (HRTEM) image of CdS/BCN, and the distinct lattice fringes reflect the well-defined crystal structures of CdS and BCN in the composite. The lattice fringe with d-spacing of 0.352 nm is identified to (002) crystal plane of hexagonal CdS,39 while the lattice spacing of 0.34 nm is indexed to the (002) interlayer of BCN.28 To study the dispersion and distribution of the components, elemental mapping characterizations are performed. As shown in Figure S3, B, C, N, Cd and S elements are witnessed, reflecting the CdS nanoparticles are evenly deposited and distributed on the surface of BCN semiconductor. SEM and TEM characterizations further confirm the successful fabrication of CdS/BCN hybrid materials. N2 sorption tests are conducted to gain the information about surface properties and porous characteristics of CdS/BCN sample. Both BCN and CdS/BCN-60 samples exhibit the


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type IV sorption isotherms of N2 with an H1 type hysteresis loop (Figure S4), pointing to the porous features of the materials. However, compared with unmodified BCN, the BET surface of CdS/BCN-60 is decreased. This is because CdS nanoparticles alter the basic texture and surface morphology of BCN support (e.g., collapse/block of mesopores), resulting in the reduction in surface area. Optical absorption of BCN and CdS/BCN materials are checked by DRS. All the samples show the classic semiconductor light absorption features (Figure 4). In the optical range lower 500 nm, the CdS/BCN samples exhibit a major light absorption in comparison with BCN. However, composting of CdS nanoparticles may not change the inherent band structure of BCN semiconductor, because the decoration of small quantity of CdS nanoparticles does not alter the structure of BCN semiconductor. The enhanced optical response of visible light is mainly benefited from the sensitization effect of CdS nanoparticles. The increased visible light absorption greatly contributes to the harvesting of photons, and typically favorable for boosting photoredox catalysis such as CO2 photoreduction. The band gap of BCN is about 2.64 eV determined from the Tauc plot (Figure S5b). The conduction band (CB) position of BCN is around -0.56 V calculated from the Mott-Schottky plot (Figure S5c).28,56,57 Thus, the valence band (VB) of BCN is 2.08 V. It has been proved the CB and VB positions of CdS are ca. -1.01 V and 1.39 V, respectively.58 Therefore, the band structures of BCN and CdS are determined (Figure S5d). The separation-recombination rate of the light-generated charges on BCN and CdS/BCN-60 is investigated by PL and transient photocurrent response analysis. In the PL spectra (Figure 5a), the center of broad emission peak for bare BCN is ca. 520 nm. Strikingly, the PL intensity of CdS/BCN-60 is substantially diminished. The finding suggests that the recombination rate of


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photoinduced electron-hole pairs is greatly reduced, mainly due to the construction of an adaptive heterojunction between BCN and CdS to realize built-in electric filed to promote charge transfer. In addition, the decrease in PL intensity may also compatible to the fast quenching of an excited state in principle.56,59 The charge separation of CdS/BCN is further demonstrated by photo(electro)chemical experiments.60,61 In the results of transient photocurrent spectra (Figure 5b), the current intensity of CdS/BCN-60 is evidently higher than of bare BCN, which strongly indicates the enhanced mobility of charge carriers over the composite materials.62,63 PL lifetimes analysis demonstrates that the average lifetime of CdS/BCN-60 is 5.08 ns and the lifetime of pure BCN is 4.49 ns at 298 K (Figure 5c). The average PL lifetime can be regarded as a crude yet rational indicator to estimate the separation efficiency of photoexcited charges carriers. This result reveals that CdS decorated BCN samples can offer more free charges to catalyze surface redox reactions. Additionally, electrochemical impedance spectroscopy (EIS) study demonstrates that CdS/BCN-60 manifests a reduced semidiameter in the Nyquist plots (Figure 5d), suggesting the fast interfacial charge transfer of the heterostructured material. These results of photo(electro)chemical measurements validate that prolonged lifetime and accelerated separation/transport kinetics of photogenerated charges are realized for CdS/BCN-60 sample, which are highly desirable for reductive CO2 transformation reactions. The above-mentioned results demonstrate that CdS decoration is effective to adjust the texture, optical and electronic properties of metal-free BCN semiconductor, and thus should improve the performance of BCN for target photoredox catalysis. The catalytic performance of the CdS/BCN composites is evaluated by visible-light-driven reductive CO2 conversion reactions carried out in H2O/MeCN mixture with TEOA as the electron donor and Co(bpy)32+ as the cocatalyst. As shown in Figure 6a, the pristine BCN only exhibits a moderate activity (1.2 µmol


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h-1, 24 µmol h-1 g-1) for CO2-to-CO transformation reaction in the established catalytic system. Once CdS nanoparticles are decorated on BCN, the CdS/BCN-30 sample exhibits considerably improved activity. Further increasing the deposition amount of CdS nanoparticles, the CdS/BCN-60 sample affords the highest CO2 reduction activity, manifesting a CO-yielding rate of 12.5 µmol h-1 (250 µmol h-1 g-1), which is more than 10 times higher relative to the pristine BCN material. If excessive CdS nanoparticles are deposited on BCN, the catalytic performance of CdS/BCN-90 sample is however decreased, which may be caused by the light-shielding effect of CdS nanoparticles.41,42,64,65 The time-production plots of CO and H2 demonstrate that the reaction rate is almost unchanged during the first 1h reaction (Figure 6b). The control experiments indicate no CO2 reduction catalysis is observed when the reaction system is manipulated without the presence of visible light or TEOA (Table S3). Without CO2, only a small amount of H2 produces from the reaction system, which suggests the formed CO is derived from CO2 photoreduction. (Table S3, entry 6). Besides, without cobalt/bpy (Table S3, entry 3) or the CdS/BCN-60 catalyst (Table S3, entry 1), no CO and H2 are detected. Methanol and ethanol are also applied as alternative electron donors for the CO2 reduction reaction, but no detectable CO/H2 is produced (Table S3, entries 7-8). Furthermore, the photocatalytic CO2 reduction performance of CdS-60 is evaluated, and the results indicate that only 3.9 µmol of CO and 0.7 µmol of H2 produce from the reaction system under identical conditions, affording a CO selectivity of 84.8 % (Table S3, entry 2). Obviously, the CO2 reduction reactivity of CdS-60 sample is much inferior to that of CdS/BCN samples (Table S3, entries 9-11), but the selectivity of CO is comparable. The low activity of CdS-60 should be related to inefficient electron/hole separation/transfer and limited active sites.65 Reaction temperature and solvents of the catalytic system are also optimized to realize efficient photocatalytic CO2 reduction. Results reveal that


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the CO2 reduction system obtains the highest activity with H2O/MeCN as the reaction solvent under reaction temperature of 40 °C (Figure S6 and S7). The carbon origin of CO product generated from the CO2 photosplitting system is confirmed by

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C-labelled isotopic experiment. The results of GC-MS tests for the

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CO are presented in

Figure 7. As shown, the peak at 3.27 min in GC spectrum (Figure 7a) with the m/z value of 29 in MS spectrum (Figure 7b) is assigned to

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CO. The findings evidence the generated CO is

completely stemmed from reductive CO2 deoxygenation, and therefore, excluding possibility from other carbon-containing substances in the system. To examine the potential generation of liquid phase products, the supernatant of the reaction system is cross-checked by diverse analysis (e.g., ion chromatography, GC-MS and

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C NMR spectroscopy). It is confirmed that no

detectable liquid products such as formic acid and methanol are generated. Such a product distribution is in line with results of reported works.6,9,13,14,42,67 To check the stability of the hybrid photocatalyst, the CdS/BCN-60 solid is filtrated after photocatalysis, and then recovered and added into fresh reaction mixtures for cycling CO2 reduction operations. No substantial reduction of CO/H2 is noticed during five cycles (Figure 8a). In the fifth CO2 reduction reaction, the CO evolution of CdS/BCN-60 can still retain 80% of the initial activity. The decrease in CO2 photoreduction activity is mainly because of the inevitable loss of the photocatalyst during the multi-step recovery processes. However, the control experiment demonstrates that stability of CdS/BCN-60 composite for CO2 photoconversion is much superior to that of bare BCN sample (Figure S8). Moreover, after photocatalysis, the used CdS/BCN-60 sample is further analyzed by XRD (Figure 8b) and FTIR (Figure S9). The observations reveal the CdS/BCN-60 hybrid experience no noticeable alternation in crystal and


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chemical structures, reaffirming the high stability of CdS/BCN heterojunction photocatalyst for the reaction. As last, a probable mechanism of the reductive CO2 splitting reaction catalyzed by CdS/BCN heterostructure is proposed (Scheme 1). The electron-hole pairs are generated on BCN and CdS semiconductors under illumination with visible light. Because CdS possesses CB more positive than that of BCN, resulting in the formation of an internal electric field within space charge region, which can effectively assist the separation and migration of photoinduced electron-hole charges. Consequently, the excited electrons (e-) can migrate rapidly from CB of CdS to that of BCN. The accumulated electrons will react with the adsorbed CO2 molecules on CdS/BCN surface to produce CO. Meanwhile, the H+ in the chemical system can be reduced by electrons as well, leading to the formation of H2. The holes (h+) are facilitated to transform from VB of BCN to that of CdS, and ultimately quenched by reducing agent TEOA. Therefore, the redox cycle of the reductive CO2 photoconversion reaction is accomplished.28,29,41,42,53 CONCLUSION In summary, we report the facile fabrication of CdS/BCN heterostructured photocatalysts for efficient reductive CO2 deoxygenation to CO with visible light under moderate conditions. The as-prepared CdS/BCN hybrids are completely characterized by various physicochemical tests. The optimized CdS/BCN composite photocatalyst exhibits a 10-fold-enhanced CO2-to-CO conversion activity together with high stability, compared to the pristine BCN material. The reinforced photocatalytic CO2 reduction efficiency is primarily assigned to the obviously improved visible-light harvesting and the greatly accelerated separation and transfers of photoinduced charge carriers. This work demonstrates that the CO2 photoreduction performance the emerging BCN photocatalyst can be substantially enhanced by surface modification with


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traditional semiconductors (e.g., CdS) to form heterostructures. It is anticipated that this work should bring prodigious opportunities to artificial photosynthesis by rational design and engineering of the conjugated BCN semiconductors to modulate their optical, physical and chemical properties to enhance the performance of target photoredox reactions (e.g., H2O splitting, CO2 fixation and organic synthesis).


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Figure 1. (a) XRD patterns and (b) FT-IR spectra of BCN and CdS/BCN samples.


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Figure 2. XPS spectra of CdS/BCN-60 (a) survey spectrum and the high resolution spectrum of (b) B 1s, (c) C 1s, (d) N 1s, (e) Cd 3d and (f) S 2p.


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Figure 3. SEM images of (a) BCN and (b) CdS/BCN-60, (c) TEM and (d) HRTEM images of CdS/BCN-60.


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Figure 4. DRS spectra of BCN and CdS/BCN samples.

Figure 5. (a) Room-temperature PL spectra, (b) transient photocurrent response, (c) timeresolved PL spectra, (d) EIS Nyquist plots of BCN and CdS/BCN-60 samples.


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Figure 6. (a) Photocatalytic CO2 reduction performance of different samples, and (b) time-yield plots of CO and H2 over CdS/BCN-60 sample.

Figure 7. Results of GC-MS analysis of the CO generated from the 13CO2 isotope experiments: (a) GC spectrum and (b) MS spectrum.


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Figure 8. (a) Production of CO/H2 in the stability tests of CdS/BCN-60 sample, and (b) powder XRD patterns of fresh and used CdS/BCN-60 samples.

Scheme 1. Possible reaction mechanism for CO2 photoreduction by CdS/BCN heterostructure.


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ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Additional photocatalyst characterization data. AUTHOR INFORMATION Corresponding Author * [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 21425309, 21761132002, 21173043, 21703039, U1662112), the National Postdoctoral Program for Innovative Talents (BX201600031), the China Postdoctoral Science Foundation (2017M612116) and the 111 Project.

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(67) Wang, S.; Guan, B. Y.; Lu, Y.; Lou, X. W., Formation of Hierarchical In2S3-CdIn2S4 Heterostructured Nanotubes for Efficient and Stable Visible Light CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 17305-17308. Table of Contents Graphic and Synopsis

The CdS/BCN heterostructured photocatalysts were synthesized by a facile photodeposition method, exhibiting obviously enhanced visible light absorption and greatly accelerated separation and transfer of photogenerated charge carriers. The optimized CdS/BCN hybrid manifested a 10-fold-enhanced CO2 reduction activity and high stability under visible light irradiation.


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Boron Carbon Nitride Semiconductors Decorated with CdS

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