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Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight
Accepted Manuscript Full Length Article Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight Dongmei Ma, Junbo Zhong, Jianzhang Li, Li Wang, Rufang Peng PII: DOI: Reference:
S0169-4332(18)30679-2 https://doi.org/10.1016/j.apsusc.2018.03.018 APSUSC 38766
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
11 December 2017 27 February 2018 2 March 2018
Please cite this article as: D. Ma, J. Zhong, J. Li, L. Wang, R. Peng, Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight, Applied Surface Science (2018), doi: https://doi.org/10.1016/j.apsusc. 2018.03.018
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Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight Dongmei Maa,b, Junbo Zhongb,*, Jianzhang Lib, Li Wangb, Rufang Penga,c,* a
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, 621010, P
R China b
Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan, College of
Chemistry and Environmental Engineering, Sichuan University of Science and Engineering, Zigong, 643000, P R China c
The State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials,
Southwest University of Science and Technology, Mianyang, 621010, P R China *Corresponding author (E-mail: [email protected], [email protected]) Dongmei Ma, E-mail address: [email protected] Junbo Zhong, E-mail address: [email protected] Jianzhang Li, E-mail address: [email protected] Li Wang, E-mail address: [email protected] Rufang Peng, E-mail address: [email protected]
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Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight Abstract As an excellent photocatalyst which can compete with TiO 2, BiOCl has triggered increasing attention. However, the practical application of BiOCl has been significantly limited by the fast recombination of the photoinduced electron-hole charge pairs. In this study, to further enhance the separation efficiency of photoinduced electron-hole charge pairs of BiOCl, a series of efficient BiOCl photocatalysts were prepared by C 70 surface modification. The trapping experiments reveal that the main active species were determined to be superoxide radicals (O 2•−) and holes (h+) under simulated sunlight irradiation. The surface photovoltage spectroscopy (SPS) demonstrates that separation of the photoinduced electron-hole pairs has been significantly promoted, forming more ·OH, proven by terephthalic acid photoluminescence probing technique. The photocatalytic evaluation results display that the C70/BiOCl photocatalysts exhibit much higher photocatalytic activity in decolorization of rhodamine B (RhB) than that of the bare BiOCl under the simulated sunlight irradiation. The excellent electron acceptability of C70 is conducive to the separation of the photogenerated carriers and results in efficient formation of O2•−, proven by the results of SPS and electron spin-resonance (ESR), therefore the photocatalytic performance of C70/BiOCl has been greatly improved. Based on all these observations, an enhancement mechanism in photocatalytic performance of C70/BiOCl was proposed. Keywords: Photocatalysis; C70; BiOCl; O2•−; Charge separation
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1. Introduction With the rapid development of industrialization process, the environmental pollution caused by exhaust gases, organic and inorganic pollutants is becoming a great environmental crisis [1-9]. Among all the technologies developed, semiconductor photocatalytic technology has been regarded as an efficient and green approach to decompose the environmental contaminants, because this technology can effectively utilize the solar energy and completely eliminate the organic pollutants rapidly. Among the photocatalysts studied [10-14], bismuth oxychloride (BiOCl), known as one of the most important bismuth oxyhalides, endowed with nontoxicity, low cost and ease of preparation, has been widely investigated for its outstanding photocatalytic performance due to its unique layered structure [15-21]. However, the photocatalytic activity of BiOCl is greatly limited by its high recombination rate of photogenerated carriers [22-28]. Therefore, it is absolutely necessary to improve the separation efficiency of photogenerated carriers, promoting the photocatalytic performance of BiOCl. As well known, the photocatalysis process initiates from the separation of photogenerated carriers. The photogenerated electrons and holes transfer to the surfaces of photocatalysts, and then can form reactive species such as hydroxyl radical (·OH) and superoxide radicals (O2•−) by the redox reactions. Many studies have substantially shown that construction of composite photocatalyst can effectively enhance the separation of photogenerated carriers [29-40]. The photocatalysts modified by nanocarbon materials not only have low cost and high chemical stability, but also the synergistic effect between two materials can significantly improve the photocatalytic activity of the semiconductor photocatalyst [41-46]. Nanocarbon materials include carbon nanotubes, graphene, fullerenes and the like. Nanocarbon materials have special 3
electrical, physical and chemical properties, such as large specific surface area, high thermal stability as well as excellent ability to accept electrons [47-50]. Among the nanocarbon materials, C70, a less symmetrical fullerene, has drawn much attention for its novel properties due to the delocalized conjugated structure [51-58]. C70 has excellent electron acceptability [59]. Hsiao and coworkers prepared C70-TiO2 nanowire with chemical bonding. The results reveal that C70-TiO2 nanowire shows much better photocatalytic performance than TiO 2 under the UV illumination, originating from excellent electron acceptor ability of C70 [60]. Therefore, if couple C70 with BiOCl, then high separation efficiency of the photogenerated carriers will be anticipated, significantly enhancing the photocatalytic performance. Herrin, we reported in-situ preparation of C70/BiOCl for the first time. A series of experiments were carried out to investigate the relationship between the C 70 modification and the photocatalytic performance of BiOCl. Under simulated solar illumination, photocatalytic activities of the photocatalysts were evaluated using RhB as a model pollutant. The photocatalytic activities of the C70 modified BiOCl photocatalysts were significantly improved. The enhanced photocatalytic activity of C70/BiOCl was originated from the highly efficient separation of the photogenerated carriers, resulting in the efficient formation of O2•−.
2. Experimental section 2.1. Materials Fullerene (C70, 99.9%) was purchased from Yongxin Science and Technology Co., Ltd (Puyang China). All other chemical reagents (analytical grade) used in this work were purchased from Chengdu Kelong Chemical Reagents Factory and used as received. Deionized water was 4
utilized throughout the experimental part. All labware were cleaned by soaking in diluted HNO 3 solution for 24 h and washed by deionized water many times before the experiments. 2.2. Synthesis of C70/BiOCl photocatalysts For preparation of functional C70, desired C70 was ultrasonically dispersed in 3M HNO3 solution for 30 min, and then was refluxed for 72 h. The products were collected by centrifugation, washed with deionized water until pH =7.0 and dried at 353K overnight. C70/BiOCl photocatalysts were synthesized as the method reported in the Ref. [61]. Desired functionalized C70 and 5g Bi (NO3)3·5H2O were added into 20 mL glacial acetic acid with ultrasonic dispersion for 15 min, then 10 mL of KCl solution was slowly added into aforementioned solution with vigorous stirring (the molar of Cl- is equal to the molar of Bi3+), after intensely magnetic stirring for 30 min, the mixture was transferred into a 100 mL Teflon-lined stainless autoclave, maintained at 453K for 24 h, and then cooled to room temperature naturally. The solid was filtered, purified with deionized water/absolute ethanol many times, and dried at 80 ℃ overnight. A series of C70/BiOCl photocatalysts with different mass ratios of C70 (0.1%, 0.5%, 1.0%, 2.0% and 3.0%) were obtained and marked as 0.1%, 0.5%, 1.0%, 2.0% and 3.0%. The bare BiOCl was also prepared with the same procedure in the absence of C70. 2.3. Characterization of the samples The morphologies of the samples were observed on a FESEM UItra 55 scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). XRD patterns were conducted on a DX-2600 X-ray powder diffractometer with Cu Kα radiation. High-resolution transmission electron microscopy (HRTEM) was carried out on a Tecnai TEM G2 microscope at 300 kV. Specific surface area analysis was performed on a QUADRASORB automatic surface 5
analyzer (Quantachrome, America) using the Brunauer-Emmet Teller (BET) method. The UV-Vis diffuse reflectance spectra (DRS) of the samples were recorded in the range from 250 to 800 nm on a TU-1907 UV-vis spectrophotometer equipped with an integrated sphere attachment and BaSO4 was used as a reference. FT-IR spectra on pellets of the samples with KBr were recorded on a FT-IR 8201PC spectrometer (Nicolet, US). The SPS spectra of the samples were carried out on a home-made instrument. Photoluminescence (PL) emission spectra were measured using Cary Eclipse with the excitation wavelength of 312 nm. X-ray photoelectron spectroscopy (XPS) spectra were acquired on an ESCALAB MKII X-ray photoelectron spectrometer. The ESR spectra were performed on Bruker E 500 spectrometer. 2.4 Photocatalytic tests The photocatalytic activities of the as-prepared photocatalysts were investigated by the degradation of rhodamine B (RhB, 10 mg/L, pH = 7.0) under simulated solar irradiation. The photocatalytic experiments were conducted in a Phchem III photochemical reactor (Beijing NBET Technology Co., Ltd, China) with a 500 W Xe lamp under vigorously stirring. The dosage of catalysts was 1g/L, the volume of RhB solution was 50 mL. During the photolysis process, 4.0 mL suspension was collected and centrifuged to remove the photocatalyst at regular interval, the absorbance of RhB solution was measured at 554 nm. The blank test was also carried out as the same method without photocatalysts.
3. Results and discussion 3.1. Characterization of the C70/BiOCl photocatalysts The BET surface areas of the C70/BiOCl photocatalysts were evaluated by the N2 adsorption/ 6
desorption analysis (Fig. 1). According to the IUPAC, the adsorption-desorption isotherms of the bare BiOCl indicates that BiOCl has macropores, while the isotherms of the 1% C70/BiOCl can be readily identified as type IV with a type H2 hysteresis loop, indicating the presence of mesopore. It is clear that couple C70 with BiOCl alters the type of the pore, which can be further supported by the observation of SEM. Usually, macropores results in low specific surface area, while mesopore is beneficial to the high specific surface area, which accords well with the results of specific surface area. The specific surface area of the bare BiOCl is 1.5 m2/g, however, the surface area of 1% C70/BiOCl photocatalysts is 11.0 m2/g. It is evident that C70 increases the BET surface area of BiOCl, which can not only provide more surface active sites, but also make photogenerated charge transport easier [47,48], which is conducive to the photocatalytic activity. The XRD patterns of C70/BiOCl photocatalysts were shown in Fig.2. All the peaks of samples are in good consistent with the values of the standard XRD pattern of BiOCl (JCPDS Card No. 82-0485). No typical C70 peaks were observed due to the high dispersion and the low content of C70 in the C70/BiOCl photocatalysts. Moreover, the diffraction intensity of (001) peaks of BiOCl significantly decreases, indicating that C70 inhibits the growth of the (001) crystal face originated from the strong interaction between C70 with BiOCl. The SEM morphologies of the samples were shown in Fig. 3a and 3b. It is clear that the BiOCl has irregular sheet structure with the thickness of 100 nm. However, the C70/BiOCl photocatalysts are micro-spherical structure, the microspheres are constructed by numerous nanosheets, revealing that C70 could significantly affect the morphology of BiOCl and it can be inferred that the existence of C70 results in forming flower-like structure of C70/BiOCl as hard template. Furthermore, Bi, Cl, O and C were all observed on the basis of the EDS patterns 7
(Fig. 3 f, g, h, and i), further confirming the successful combination of C70 and BiOCl. TEM and HRTEM analysis give further details of the material. Fig. 3d presents the HRTEM image of 1% C70/BiOCl (Fig.3c). As demonstrated in Fig. 3d, the 1% C70/BiOCl photocatalyst is highly crystalline. The lattice fringes of 0.340 nm and 0.368 nm can be assigned to the (101) and the (002) plane of BiOCl, respectively. However, no lattice fringes of C70 were observed by HRTEM image due to the amorphous state of C70 in the C70/BiOCl photocatalysts. In addition, XPS was also conducted to further confirm the existence of C70. As expected, the elements of O, Bi, Cl, and C were observed in the XPS spectrum of 1% C70/BiOCl (Fig. 4a). As shown in Fig. 4b, the peaks located at around 159.0 and 164.3 eV belong to the binding energies of the Bi 4f7/2 and Bi 4f5/2 peaks in the bare BiOCl, respectively [62]. After coupling of C70, the Bi 4f peaks, O1s peaks and the C1s peak slightly shift to high binding energy due to the interaction between C70 and BiOCl (Fig. 4b, 4c, 4d) [63]. It should be noted that the C1s peak of 1% C70/BiOCl can be deconvoluted into three components as shown in Fig. 4e, the main peak at 284.6 eV can be attributed to adventitious carbon and the C-C bond with sp2 orbital, the peaks centered at 285.7 and 288.6 eV can be assigned to the oxygenated carbon and nitrous carbon [64], respectively. The O1s high-resolution XPS spectrum of 1% C70/BiOCl shows two peaks with binding energies at 530.4 eV and 532.9 eV, which can be ascribed to crystal lattice oxygen and chemisorbed oxygen (the hydroxyl groups) (Fig. 4f) [65]. All the above results indicate that BiOCl has been successfully modified by C70 with a strong interaction. The FT-IR was used to investigate the chemical structure of the 1% C70/BiOCl photocatalysts. Fig. 5 presents a comparison of the FT-IR spectra of C70, BiOCl and 1% C70/BiOCl photocatalysts. In the case of C70, the broad peak at 3429 cm−1 is assigned to the hydroxyl group and the 8
surface-adsorbed water. The peak located at 523.9 cm−1 can be attributed to the characteristic peaks of BiOCl and 1% C70/BiOCl photocatalysts. Both the spectra of C70 and 1% C70/BiOCl photocatalysts exhibit characteristic vibration peaks of C70 (532.6, 574.7, 671.2, 642.2, 793.8, 1075.4, 1134.8, 1429.4, 1631.1 and 1728.3 cm−1) [66,67], indicating that the prepared photocatalysts contain C70. As an eff ective photocatalyst, the optical absorption properties are very crucial for its photocatalytic performance. The UV-Vis absorption spectra of the samples were shown in the Fig. 6. The bare BiOCl only shows absorption at UV light region, and the absorption edge is around 360 nm, as compared to the BiOCl, the absorption edges of C70/BiOCl photocatalysts have no obvious red-shift, reflecting that C 70 cannot change the band-gap of BiOCl. However, the absorption intensities of the C70/BiOCl photocatalysts are remarkably improved in the visible light region, which indicates that C70, as the visible light photosensitizer, is beneficial to enhance the absorption in visible light region. SPS is a direct and sensitive way to research the natures of the photogenerated charge pairs. As shown in Fig. 7a, C70/BiOCl photocatalysts display obvious SPS response from 300 nm to 355 nm, the SPS response intensity of 1% C70/BiOCl photocatalysts is about 25 times stronger than that of the bare BiOCl. The results further reveal that when the amount of C70 is excessive, the SPS signal is weaker. The excessive C70 will greatly block the light penetrate the interface between C70 and BiOCl, influencing the excitation of BiOCl, resulting in weak SPS signal accordingly. Usually, the stronger SPS signal, the higher separation rate of the charge pairs; the strong SPS responses of photocatalyst originates from high charge separation rate [68,69]. To further study the charge separation behavior after coupling with C70, the fluorescence 9
spectra of hydroxyl radicals (·OH) was performed. The 2-hydroxyterephthalic acid fluorescent method is a valid chemical way to characterize the separation of the photogenerated charge pairs， the more hydroxyl radicals (·OH) produced corresponds to the more efficient separation of photogenerated charges [70, 71]. As shown as Fig. 7b, for the bare BiOCl, the fluorescence signal intensity of ·OH is relative weak, the fluorescence signal intensity of ·OH over the composites gradually increases as the loading of C70 and the fluorescent response intensity of ·OH over the 1% C70/BiOCl photocatalysts is the strongest. The results fit well with the SPS response and the degradation of RhB over the photocatalysts. 3.2. Photocatalytic performance The RhB was used to evaluate the photocatalytic performance of the pure BiOCl and the C70/BiOCl photocatalysts under simulated sunlight irradiation. The black test indicates that the adsorption of RhB over all the C70/BiOCl photocatalysts after 1 h is below 25% (Fig.8a). The degradation of RhB solution without photocatalyst after 30 min is negligible. The results demonstrate that the degradation of RhB in this photocatalytic system originates from the presence of photocatalyst. As shown in Fig. 8b, about 49.7% and 66.4% of RhB can be decomposed over the bare BiOCl and P25 after 30 min. In comparison, after modification with C70, the photocatalytic activities of C70/BiOCl are greatly enhanced and the 1% C70/BiOCl photocatalysts holds the best photoactivity for the RhB degradation, 99.8% of RhB can be degraded under simulated sunlight irradiation for 30 min, benefiting from the improved separation rate of photogenerated charge pairs, which illustrates that C70 plays predominant role in boosting the performance of BiOCl. Compared with the 1% C70/BiOCl photocatalysts prepared in-situ by hydrothermal method, the physical mixture of 1% C70 and BiOCl shows poor photoactivity for the 10
RhB degradation (59.5%) under the same conditions, the result illustrates that the strong interaction between C70 and BiOCl is prerequisite for the enhanced photocatalytic performance of C70/BiOCl. The decay of RhB follows a first-order reaction kinetic equation, and rate constant of RhB over the 1% C70/BiOCl photocatalysts is the maximum (0.2028 min−1), the photocatalytic activity of 1% C70/BiOCl is 8 times higher than the pure BiOCl (Fig. 8c). In order to assess the stability of the C 70/BiOCl photocatalysts, we utilized a time-circle RhB photolysis experiment to evaluate the stability of 1% C70/BiOCl photocatalysts. As shown in Fig. 8d, it can be seen that photocatalytic activity decreases by 10% after the fifth cycle, implying the high stability of C70/BiOCl photocatalysts, therefore the photocatalysts have potential application in pollutants purification. 3.3. Mechanism In order to investigate the active species generated by the 1% C70/BiOCl photocatalysts during the photodegradation process under simulated solar irradiation, the ESR with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) technique was performed. As shown in the Fig.9, weak ESR signals of hydroxyl radicals (·OH) were observed and no superoxide radicals (O2•−) were detected for the pure BiOCl. Nevertheless, after modified by C70, much higher intensity of DMPO-superoxide radical (O2•−) and DMPO-hydroxyl radical (·OH) signals were observed for the 1% C70/BiOCl photocatalysts under the simulated sunlight irradiation, firmly confirming that C70 can quickly accept the photo-induced electrons to its surface and form O2•− by the reduction of O2. The band edge position of BiOCl can be calculated by using the equation: EVB = X − Ee + 0.5Eg, ECB = EVB − Eg [72]. The EVB and ECB are the valence band edge potential and conduction band edge potential respectively. X is the electronegativity of the semiconductor, the X is 6.33 for 11
BiOCl [73]. Ee is 4.5 eV, and Eg is 3.32 eV based on the DRS spectrogram (Fig. 6 inset). Therefore, the EVB and ECB of pure BiOCl are calculated to be 3.48 eV and 0.18 eV, respectively. The ECB (0.18 eV) of pure BiOCl is more positive than the potential of O2/O2•− (-0.33 eV vs NHE), the electrons from the CB of BiOCl cannot reduce O2 to generate O2•− [74]. This result is consistent with the ESR analysis of the pure BiOCl. However, when the C 70 was introduced, strong intensity of O2•− was determined by ESR analysis and scavenger experiments. To study the roles of the active species during the photocatalysis process, scavenger experiments were carried out by adding scavengers, benzoquinone (BQ) for O2•− radicals, disodium ethylene diamine inetetraacetic (EDTA-2Na) for holes (h+) and isopropanol (IPA) for ·OH radicals [75,76] into the C70/BiOCl photocatalytic system. From Fig. 10, the O2•− radicals and h+ plays main role during the photocatalysis process, while ·OH performs minor role. The scavenger experiments results agree well with the results of SPS、ESR and photocatalytic experiments, manifesting that the improved charge separation efficiency is the decisive factor for the enhanced photocatalytic activity of C70/BiOCl photocatalysts. As discussed above, a proposed enhancement mechanism for the excellent photocatalytic activity of C70/BiOCl photocatalysts was illustrated in Fig. 11. For the bare BiOCl, after exciting by the simulated sunlight, electrons can be jumped from valence band (VB) to conduction band (CB), leaving h+ at the valence band (VB). Usually, the bulk of photogenerated charge pairs recombine quickly, only a few charge carriers participate in the photocatalytic reaction, resulting in a low activity. While for the C70/BiOCl photocatalysts, the photocatalytic activity are greatly promoted (Fig. 8b), and the results of ESR experiments (Fig. 9a) demonstrate the modification of BiOCl by C70 results in more photogenerated h+ oxidize H2O or -OH to form ·OH. Since the 12
delocalized conjugated structure of C 70 makes it easier to transfer the photogenerated electrons, resulting in efficient photogenerated electron-hole pairs separation; the separated electrons with strong reduction ability on the surface of C70 can react with O2 to produce O2•− (Fig. 9b). The generated O2•− plays important role in the photodegradation process, resulting in excellent photocatalytic activity of C70/BiOCl [73].
4. Conclusion In conclusion, a novel C70 modified BiOCl photocatalyst with strong chemical interaction and closely integrated interface was successfully synthesized via a facile hydrothermal method. All the C70/BiOCl photocatalysts show improved photocatalytic activity for the degradation of RhB solution under the simulated sunlight irradiation, and the 1% C70/BiOCl photocatalysts show the best photocatalytic performance, which is attributed to the rapid photogenerated electron transfer ability of C70 and efficient separation of the photogenerated charge carriers. The main active species were determined to be O2•− radicals and h+ under the simulated sunlight irradiation by scavenger experiments. This work may offer a practical way to enhance the photocatalytic performance of BiOCl for pollutants degradation.
Acknowledgements The authors are particularly grateful to the support of Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education (LYJ14205), the program of State Key Laboratory Cultivation Base for Nonmetallic Composites and Functional Materials of Sichuan Province (14zxfk07) and Students Innovation Project of Sichuan Province (cx2017019). 13
References [1] X. Bai, C. Sun, D. Liu, X. Luo, D. Li, J. Wang, N. Wang, X. Chang, R. Zong, Y. Zhu, Photocatalytic degradation of deoxynivalenol using graphene/ZnO hybrids in aqueous suspension, Appl. Catal. B. 204 (2017) 11-20. [2] J. Hu, X. Wu, C. Huang, W. Fan, X. Qiu, Visible light photocatalytic activity induced by Rh (III) modification on the surface of BiOCl, Appl. Surf. Sci. 387 (2016) 45-50. [3] C. Li, Z. Sun, W. Zhang, C. Yu, S. Zheng, Highly efficient g-C3N4/TiO 2/kaolinite composite with novel three-dimensional structure and enhanced visible light responding ability towards ciprofloxacin and S. aureus, Appl. Catal. B. 220 (2018) 272-282. [4] P. Reddy, E. Kwon, K. Kim, T. Akter, S. Kalagara, Recent advances in photocatalytic treatment of pollutants in aqueous media, Environ. Int. 91 (2016) 94-103. [5] Z. Ai, J. Wang, L. Zhang, Substrate-dependent photoreactivities of BiOBr nanoplates prepared at different pH values, Chinese. J. Catal. 36 (2015) 2145-2154. [6] T. Giannakopoulou, I. Papailias, N. Todorova, N. Boukos, Y. Liu, J. Yu, C. Trapalis, Tailoring the energy band gap and edges’ potentials of g-C3N4/TiO2 composite photocatalysts for NOx removal, Chem. Eng. J. 310 (2017) 571-580. [7] D. Mao, A. Yu, S. Ding, F. Wang, S. Yang, C. Sun, H. He, Y. Liu, K. Yu, One-pot synthesis of BiOCl half-shells using microemulsion droplets as templates with highly photocatalytic performance for the degradation of ciprofloxacin, Appl. Surf. Sci. 389 (2016) 742-750. [8] S. Cao, F. Tao, Y. Tang, Y. Li, J. Yu, Size-and shape-dependent catalytic performances of oxidation and reduction reactions on nanocatalysts, Chem. Soc. Rev. 45 (2016) 4747-4765. [9] Q. Xiang, B. Cheng, J. Yu, Graphene-based photocatalysts for solar fuel generation, Angew. 14
Chem. Int. Ed. 54 (2015) 11350-11366. [10] R. He, S. Cao, J. Yu, Recent advances in morphology control and surface modification of Bi-based photocatalysts, Acta. Phys.-Chim. Sin. 12 (2016) 2841-2870. [11] S. Cao, J. Yu, Carbon-based H2-production photocatalytic materials, J. Photoch. Photobio. C 27 (2016) 72-99. [12] L. Yuan, Y. Xu, Photocatalytic conversion of CO2 into value-added and renewable fuels, Appl. Surf. Sci. 342 (2015) 154-167. [13] J. Wen, X. Li, H. Li, S. Ma, K. He, Y. Xu, Y. Fang, W. Liu, Q. Gao, Enhanced visible-light H2 evolution of g-C3N4 photocatalysts via the synergetic effect of amorphous NiS and cheap metal-free carbon black nanoparticles as co-catalysts, Appl. Surf. Sci. 358 (2015) 204-212. [14] M. Yang, Q. Yang, J. Zhong, J. Li, S. Huang, X. Li, PVA-assisted hydrothermal preparation of BiOF with remarkably enhanced photocatalytic performance, Mater. Lett. 201 (2017) 35-38. [15] L. Liu, L. Ding, Y. Liu, W. An, S. Lin, Y. Liang, W. Cui, Enhanced visible light photocatalytic activity by Cu2O-coupled flower-like Bi2WO6 structures, Appl. Surf. Sci. 364 (2016) 505-515. [16] C. Zhu, L. Zhang, B. Jiang, J. Zheng, P. Hu, S. Li, M. Wu, W. Wu, Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation, Appl. Surf. Sci. 377 (2016) 99-108. [17] W. Liu, G. Zhao, M. An, L. Chang, Solvothermal synthesis of nanostructured BiVO4 with highly exposed (010) facets and enhanced sunlight-driven photocatalytic properties, Appl. Surf. Sci. 357 (2015) 1053-1063. [18] Y. Su, L. Zhang, W. Wang, Internal polar field enhanced H 2 evolution of BiOIO3 nanoplates, 15
Int. J. Hydrogen Energ. 41 (2016) 10170-10177. [19] F. Li, Q. Wang, J. Ran, Y. Hao, X. Wang, D. Zhao, S. Qiao, Ionic liquid self-combustion synthesis of BiOBr/Bi24O31Br10 heterojunctions with exceptional visible-light photocatalytic performances, Nanoscale. 7 (2015) 1116-1126. [20] X. Liu, J. Zhong, J. Li, S. Huang, W. Song, PEG-assisted hydrothermal synthesis of BiOCl with enhanced photocatalytic performance, Appl. Phys. A. 119 (2015) 1203-1208. [21] Z. Zhao, W. Dai, Electronic structure and optical properties of BiOI ultrathin films for photocatalytic water splitting, Inorg. Chem. 54 (2015) 10732-10737. [22] M. Li, H. Huang, S. Yu, N. Tian, F. Dong, X. Du, Y. Zhang, Simultaneously promoting charge separation and photoabsorption of BiOX (X= Cl, Br) for efficient visible-light photocatalysis and photosensitization by compositing low-cost biochar, Appl. Surf. Sci. 386 (2016) 285-295. [23] J. Li, Y. Yu, L. Zhang, Bismuth oxyhalide nanomaterials: layered structures meet photocat -alysis, Nanoscale. 15 (2014) 8473-8484. [24] X. Wang, W. Bi, P. Zhai, X. Wang, H. Li, G. Mailhot, W. Dong, Adsorption and photocatalytic degradation of pharmaceuticals by BiOClxIy nanospheres in aqueous solution, Appl. Surf. Sci. 360 (2016) 240-251. [25] J. Hu, W. Fan, W. Ye, C. Huang, X. Qiu, Insights into the photosensitivity activity of BiOCl under visible light irradiation, Appl. Catal. B. 158 (2014) 182-189. [26] X. Yu, J. Shi, L. Feng, C. Li, L. Wang, A three-dimensional BiOBr/RGO heterostructural aerogel with enhanced and selective photocatalytic properties under visible light, Appl. Surf. Sci. 396 (2017) 1775-1782. 16
[27] R. He, J. Zhang, J. Yu, S. Cao, Room-temperature synthesis of BiOI with tailorable (001) facets and enhanced photocatalytic activity, J. Colloid. Interf. Sci. 478 (2016) 201-208. [28] H. Yu, C. Cao, X. Wang, J. Yu, Ag-modified BiOCl single-crystal nanosheets: dependence of photocatalytic performance on the region-selective deposition of Ag nanoparticles, J. Phys. Chem. C. 121 (2017) 13191-13201. [29] J. Di, J. Xia, Y. Ge, L. Xu, H. Xu, M. He, Q. Zhang, H. Li, Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity, J. Mater. Chem. A. 2 (2014) 15864-15874. [30] J. Wen, J. Xie, Z. Yang, R. Shen, H. Li, X. Luo, X. Chen, X. Li, Fabricating the robust g-C3N4 nanosheets/carbons/NiS multiple heterojunctions for enhanced photocatalytic H 2 generation: an insight into the trifunctional roles of nanocarbons, ACS. Sustain. Chem. Eng. 5 (2017) 2224-2236. [31] X. Wang, J. Cheng, H. Yu, J. Yu, A facile hydrothermal synthesis of carbon dots modified g-C3N4 for enhanced photocatalytic H2-evolution performance, Dalton Transactions. 46 (2017) 6417-6424. [32] Y. Sun, X. Xiao, X. Dong, F. Dong, W. Zhang, Heterostructured BiOI @ La(OH)3 nanorods with enhanced visible light photocatalytic NO removal, Chinese J. Catal. 38 (2017) 217-226. [33] W. Liu, L. Qiao, A. Zhu, Y. Liu, J. Pan, Constructing 2D BiOCl/C3N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation, Appl. Surf. Sci. 426 (2017) 897-905. [34] Y. Mi, H. Li, Y. Zhang, R. Zhang, W. Hou, One-pot synthesis of belt-like Bi2S3/BiOCl hierarchical composites with enhanced visible light photocatalytic activity, Appl. Surf. Sci. 423 17
(2017) 1062-1071. [35] Y. Li, K. Lv, W. Ho, Z. Zhao, Y. Huang, Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures, Chinese. J. Catal. 38 (2017) 321-329. [36] R. He, S. Cao, P. Zhou, J. Yu, Recent advances in visible light Bi-based photocatalysts, Chinese. J. Catal. 35 (2014) 989-1007. [37] D. Xu, Y. Hai, X. Zhang, S. Zhang, R. He, Bi2O3 cocatalyst improving photocatalytic hydrogen evolution performance of TiO2, Appl. Surf. Sci. 400 (2017) 530-536. [38] J. Zhang, J. Lu, K. Dai, C. Liang, Q. Liu, One-step growth of nanosheet-assembled BiOCl/BiOBr microspheres for highly efficient visible photocatalytic performance, Appl. Surf. Sci. 430 (2018) 639-646. [39] Y. Zhang, M. Park, H. Kim, B. Ding, S. Park, In-situ synthesis of nanofibers with various ratios of BiOClx/BiOBr y/BiOIz for effective trichloroethylene photocatalytic degradation, Appl. Surf. Sci. 384 (2016) 192-199. [40] Q. Yang, J. Li, J. Zhong, C. Cheng, Z. Xiang, J. Chen, Enhanced solar photocatalytic performance of (BiO)2CO3 prepared with the assistance of ionic liquid, Mater. Lett. 192 (2017) 157-160. [41] S. Zhu, T. Xu, H. Fu, J. Zhao, Y. Zhu, Synergetic effect of Bi 2WO6 photocatalyst with C60 and enhanced photoactivity under visible irradiation, Environ. Sci. Technol. 17 (2007) 62346239. [42] X. Li, R. Shen, S. Ma, X. Chen, J. Xie, Graphene-based heterojunction photocatalysts, Appl. Surf. Sci. 430 (2018) 53-107. 18
[43] X. Ma, X. Li, M. Li, X. Ma, L. Yu, Y. Dai, Effect of the structure distortion on the high photocatalytic performance of C 60/g-C3N4 composite, Appl. Surf. Sci. 414 (2017) 124-130. [44] K. Ozawa, S. Yamamoto, R. Yukawa, K. Akikubo, M. Emori, H. Sakama, I. Matsuda, Capturing transiently charged states at the C60/TiO2 (110) interface by time-resolved soft X-ray photoelectron spectroscopy, Org. Electron. 31 (2016) 98-103. [45] Y. Zhu, M. Pan, R. Zhu, T. Xu, J. Liu, J. Zhu, Y. Xi, G. Zhu, H. He, Enhanced photocatalytic activity of Zn/Ti-LDH via hybridizing with C60, Molecular Catalysis. 427 (2017) 54-61. [46] H. Tan, F. Denny, M. Hermawan, R. Wong, R. Amal, Y. Ng, Reduced graphene oxide is not a universal promoter for photocatalytic activities of TiO2, J. Materiomics. 3 (2017) 51-57. [47] T. Song, J. Huo, T. Liao, J. Zeng, J. Qin, H. Zeng, Fullerene [C60] modified Cr2−xFexO3 nanocomposites for enhanced photocatalytic activity under visible light irradiation, Chem. Eng. J. 287 (2016) 359-366. [48] X. Bai, L. Wang, Y. Wang, W. Yao, Y. Zhu, Enhanced oxidation ability of g-C3N4 photocatalyst via C60 modification, Appl. Catal. B. 152 (2014) 262-270. [49] R. Wakimoto, T. Kitamura, F. Ito, H. Usami, H. Moriwaki, Decomposition of methyl orange using C60 fullerene adsorbed on silica gel as a photocatalyst via visible-light induced electron transfer, Appl. Catal. B. 166 (2015) 544-550. [50] Q. Cai, Z. Hu, Q. Zhang, B. Li, Z. Shen, Fullerene (C60)/CdS nanocomposite with enhanced photocatalytic activity and stability, Appl. Surf. Sci. 403 (2017) 151-158. [51] F. Diederich, R. Ettl, Y. Rubin, R. Whetten, R. Beck, M. Alvarez, S. Anz, D. Sensharma, F. Wudl, K. Khemani, The higher fullerenes: isolation and characterization of C 76, C84, C90, C94, and C70O, an oxide of D5h-C70, Science. 252 (1991) 548-551. 19
[52] D. Lu, G. Zhuang, H. Wu, S. Wang, S. Yang, P. Du, A large π‐ extended carbon nanoring based on nanographene units: bottom‐ up synthesis, photophysical properties, and selective complexation with fullerene C70, Angew. Chemie. 129 (2017) 164-168. [53] K. Zhang, H. Yu, X. Liu, Q. Dong, Z. Wang, Y. Wang, N. Chen, Y. Zhou, B. Song, Fullerenes and derivatives as electron transport materials in perovskite solar cells, Sci. Chi. Chem. 60 (2017) 144-150. [54] Y. He, G. Zhao, B. Peng, Y. Li, High‐ yield synthesis and electrochemical and photovoltaic properties of indene‐ C70 bisadduct, Adv. Funct. Mater. 20 (2010) 3383-3389. [55] R. Kumar, E. Gleißner, E. Tiu, Y. Yamakoshi, C70 as a photocatalyst for oxidation of secondary Benzylamines toimines, Org. Lett. 18 (2015) 184-187. [56] Z. Meng, L. Zhu, S. Ye, S. Liu, W. Oh, Detection of oxygen species generated of C70-Ag2Se heterojunction photocatalysts with excellent visible light driven photocatalytic performance, Fuller. Nanotub. Car. N. 24 (2016) 415-422. [57] P. Dallas, G. Rogers, B. Reid, R. Taylor, H. Shinohara, G. Briggs, K. Porfyrakis, Charge separated states and singlet oxygen generation of mono and bis adducts of C 60 and C70, Chem. Phys. 465 (2016) 28-39. [58] K. Moor, D. Valle, C. Li, J. Kim, Improving the visible light photoactivity of supported fullerene photocatalysts through the use of [C70] fullerene, Environ. Sci. Technol. 49 (2015) 61906197. [59] G. Yu, J. Gao, J. Hummelen, F. Wudl, A. Heeger, Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor/acceptor heterojunctions, Science. 270 (1995) 17891791. 20
[60] E. Cho, J. Ciou, J. Zheng, J. Pan, Y. Hsiao, K. Lee, J. Huang, Fullerene C 70 decorated TiO2 nanowires for visible-light-responsive photocatalyst, Appl. Surf. Sci. 355 (2015) 536-546. [61] M. Su, C. He, L. Zhu, Z. Sun, C. Shan, Q. Zhang, Y. Xiong, Enhanced adsorption and photocatalytic activity of BiOI-MWCNT composites towards organic pollutants in aqueous solution, J. Hazard. Mater. 229 (2012) 72-82. [62] M. Yang, Q. Yang, J. Zhong, S. Huang, J. Li, J. Song, C. Burda, Enhanced photocatalytic performance of Ag2O/BiOF composite photocatalysts originating from efficient interfacial charge separation, Appl. Surf. Sci. 416 (2017) 666-671. [63] J. Di, J. Xia, S. Yin, H. Xu, L. Xu, Y. Xu, H. Li, Preparation of sphere-like g-C3N4/BiOI photocatalysts via a react able ionic liquid for visible-light-driven photocatalytic degradation of pollutants, J. Mater. Chem. A. 15 (2014) 5340-5351. [64] S. Chen, R. Yan, X. Zhang, K. Hu, Z. Li, M. Humayun, Y. Qu, L. Jing, Photogenerated electron modulation to dominantly induce efficient 2, 4-dichlorophenol degradation on BiOBr nanoplates with different phosphate modification, Appl. Catal. B. 209 (2017) 320-328. [65] Z. Li, Y. Qu, K. Hu, M. Humayun, S. Chen, L. Jing, Improved photoelectrocatalytic activities of BiOCl with high stability for water oxidation and MO degradation by coupling RGO and modifying phosphate groups to prolong carrier lifetime, Appl. Catal. B. 203 (2017) 355-362. [66] B. Chase, N. Herron, E. Holler, Vibrational spectroscopy of fullerenes (C 60 and C70). Temperature dependant studies, J. Phys. Chem. 96 (1992) 4262-4266. [67] D. Garcia-hernandez, F. Cataldo, A. Manchado, About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)], Fuller. Nanotub. Car. N. 24 (2016) 225-233. 21
[68] A. Zada, M. Humayun, F. Raziq, X. Zhang, Y. Qu, L. Bai, C. Qin, L. Jing, H. Fu, Exceptional visible‐ light‐ driven cocatalyst‐ free photocatalytic activity of g‐ C3N4 by well designed nano-composites with plasmonic Au and SnO2, Adv. Energy. Mater. 6 (2016) 1601190-1601198 [69] R. Fazal, Y. Qu, X. Zhang, Enhanced cocatalyst-free visible-light activities for photocatalytic fuel production of g-C3N4 by trapping holes and transferring electrons, J. Phs. Chem. C. 120 (2016) 98-107. [70] J. Li, X. Zhang, F. Raziq, J. Wang, C. Liu, Y. Liu, J. Sun, R. Yan, B. Qu, C. Qin, Improved photocatalytic activities of g-C3N4 nanosheets by effectively trapping holes with halogen-induced surface polarization and 2, 4-dichlorophenol decomposition mechanism, Appl. Catal. B. 218 (2017) 60-67. [71] H. Wang, Y. Su, H. Zhao, H. Yu, S. Chen, Y. Zhang, X. Quan, Photocatalytic oxidation of aqueous ammonia using atomic single layer graphitic-C3N4, Environ. Sci. Technlo. 48 (2014) 11984-11990. [72] J. Chen, J. Zhong, J. Li, S. Huang, W. Hu, M. Li, Q. Du, Synthesis and characterization of novel Ag2CO3/g-C3N4 composite photocatalysts with excellent solar photocatalytic activity and mechanism insight, Molecular Catalysis. 435 (2017) 91-98. [73] J. Di, J. Xia, M. Ji, B. Wang, S. Yin, Q. Zhang, H. Li, Carbon quantum dots modified BiOCl ultrathin nanosheets with enhanced molecular oxygen activation ability for broad spectrum photocatalytic properties and mechanism insight, ACS. Appl. Mater. Inter. 36 (2015) 20111 -20123. [74] Y. He, L. Zhang, B. Teng, M. Fan. New application of Z-scheme Ag3PO4/g-C3N4 composite 22
in converting CO2 to fuel. Environ. Sci. Technol. 49 (2014) 649-656. [75] Z. Wan, G. Zhang, X. Wu, S. Yin, Novel visible-light-driven Z-scheme Bi12GeO20/g-C3N4 photocatalyst: oxygen-induced pathway of organic pollutants degradation and proton assisted electron transfer mechanism of Cr (VI) reduction, Appl. Catal. B. 207 (2017) 17-26. [76] W. Wang, D. Xu, B. Cheng, J. Yu, C. Jiang, Hybrid carbon @ TiO2 hollow spheres with enhanced photocatalytic CO2 reduction activity, J. Mater. Chem. A. 5 (2017) 5020-5029.
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Caption for Figures Fig. 1 N2 adsorption-desorption isotherms of BiOCl (a) and 1% C70/BiOCl (b) Fig. 2 XRD patterns of C70/BiOCl samples with different C70 contents Fig. 3 SEM of BiOCl (a), and 1.0% C70/BiOCl (b), (e), TEM of 1.0% C70/BiOCl (c) and (d), EDS of 1.0% C70/BiOCl (f), (g), (h) and (i) Fig. 4 XPS spectra of the photocatalyst: survey XPS spectrum of 1% C70/BiOCl (a), Bi 4f (b), O 1s (c), C 1s (d), High resolution XPS spectra of O 1s (e) and C 1s (f) region on the surfaces of 1% C70/BiOCl photocatalysts Fig. 5 FT-IR spectra of C70, BiOCl and 1% C70/BiOCl Fig. 6 UV-Vis DRS of C70/BiOCl samples with different C70 amount, inset is band energy level of pure BiOCl Fig. 7 SPS of the C70/BiOCl samples (a), FS spectra related to the amount of ·OH radical (b) Fig. 8 Adsorption of RhB on the different photocatalysts after 1h in dark (a), The decolorization efficiency with the irradiation time (b), Photocatalytic decolorization rate constants of RhB over the different photocatalysts(c), Five consecutive cycles of decolorization of RhB using the 1% C70/BiOCl (d) Fig. 9 DMPO spin-trapping ESR spectra recorded with BiOCl and 1% C70/BiOCl samples in aqueous dispersion (for DMPO-·OH) (a) and methanol dispersion (for DMPO-O2•−) (b) under simulated sunlight Fig. 10 The influence of different radical scavengers on photocatalytic activity of 1% C70/BiOCl samples 24
4
3
Quantity Adsorbed (cm /g)
Fig. 11 Photo-induced electron transfer between the excited BiOCl and C 70
a
Adsorption Desorption
3 2 1 0 0.0
0.2
0.4
0.6
0.8
1.0
60
3
Quantity Adsorbed (cm /g)
Relative Pressure (P/P0)
50
b
Adsorption Desorption
40 30 20 10 0 0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0) Fig. 1 N2 adsorption-desorption isotherms of BiOCl (a) and 1% C70/BiOCl (b)
25
C70
Intensity (a.u.)
3.0% 2.0% 1.0% 0.5% 0.1% [001]
BiOCl
10
20
30
40
50
60
2Theta (degree) Fig. 2 XRD patterns of C70/BiOCl samples with different C70 contents
26
Fig. 3 SEM of BiOCl (a), and 1.0% C70/BiOCl(b), (e), TEM of 1.0% C70/BiOCl (c) and (d), EDS of 1.0% C70/BiOCl (f), (g), (h) and (i)
27
120000
a
b
O(KLL)
Intensity (a.u)
Bi4f
60000
Intensity (a.u)
80000
Bi4p O1s Bi4d C1s
40000
Cl2p Bi5d
20000
O1s Bi4f5/2
Bi4f7/2
90000
1% C70/BiOCl
60000
30000
BiOCl
Cl2s Bi5p
1000
Intensity (a.u)
22000
800
600
400
Binding Energy (eV)
c
200
0
0
O1s
1% C70/BiOCl
16000
536
532
528
160
156
152
C1s
12000 1% C70/BiOCl
10000
BiOCl
BiOCl
14000 540
164
d
14000
20000 18000
168
Binding Energy (eV)
Intensity (a.u)
0
8000
524
292
Binding Energy (eV)
288
284
280
276
Binding Energy (eV)
21000
e
532.9 eV
Intensity (a.u)
Intensity (a.u)
20000 19000
11000
O 1s
f
C 1s
10000
530.4 eV
18000 17000
285.7 eV
9000
284.6 eV 288.6 eV
8000
16000 534
532
530
290
528
288
286
284
282
Binding Energy (eV)
Binding Energy (eV)
Fig. 4 XPS spectra of the photocatalyst: survey XPS spectrum of 1% C70/BiOCl (a), Bi 4f (b), O 1s (c), C 1s (d), High resolution XPS spectra of O 1s (e) and C 1s (f) region on the surfaces of 1% C70/BiOCl photocatalysts
28
Transmittance (%)
400 1% C70/BiOCl 300
200
BiOCl
100
C70
0 4000
3500
3000
2500
2000
1500 -1
Wavenumber (cm
1000
)
Fig. 5 FT-IR spectra of C70, BiOCl and 1% C70/BiOCl
29
500
1.0
0.6
1/2
(ahv) (ev)
0.8
Absorbance (a.u)
1/2
2.0
3.0% 2.0% 1.0% 0.5% 0.1% BiOCl
1.5 1.0 0.5 2.4
2.8
3.2
3.6
Energy (ev)
0.4
0.2
0.0
300
400
500
600
700
800
Wavelength (nm) Fig. 6 UV-Vis DRS of C70/BiOCl samples with different C70 amount, inset is band energy level of pure BiOCl
30
7
a
1.0% 2.0% 3.0% 0.5% 0.1% BiOCl
-3
Photovoltage (10 V)
6 5 4 3 2 1 0 300
310
320
330
340
350
360
370
Wavelength (nm) 40
Intensity/(a.u.)
b
1.0% 2.0% 3.0% 0.5% 0.1% BiOCl
30
20
10
0 350
400
450
500
550
Emission wavelength (nm) Fig. 7 SPS of the C70/BiOCl samples (a), FS spectra related to the amount of ·OH radical (b) 31
30
1.0 b 19.3
20
21.7
23.1
RHB BiOCl mixture P25 0.1% 3.0% 0.5% 2.0% 1.0%
0.8 18.4
17.5
0.6
Ct/C0
Decolorization (%)
a
0.4
9.1
10
0.2 0.0 0
BiOCl 0.1% 0.5% 1.0%
2.0% 3.0%
-10 -5
Photocatalyst 1.2
c
10
15
20
25
30
d
0.20
2nd
1st
1.0
3rd
4th
5th
0.8 0.15
Ct/C0
-1
Rate constant (min
5
Time (min)
)
0.25
0
0.10
0.6 0.4
0.05
0.2
0.00 BiOCl 0.1% 0.5% 1.0% 2.0% 3.0% P25
0.0 0
30
60
90
120
150
Time (min)
Photocatalyst
Fig. 8 Adsorption of RhB on the different photocatalysts after 1h in dark (a), The decolorization efficiency with the irradiation time (b), Photocatalytic decolorization rate constants of RhB over the different photocatalysts (c), Five consecutive cycles of decolorization of RhB using the 1% C70/BiOCl (d)
32
210000
hydroxyl radical
a *
Intensity (a.u.)
*
*
*
180000
1% C70/BiOCl 150000
*
*
120000 90000
3360
*
*
3380
BiOCl
3400
3420
B/mT 560000
b
superoxide radical
Intensity (a.u.)
480000
*
*
* *
*
400000
*
320000
1% C70/BiOCl
240000 160000 BiOCl
80000 0 3345
3360
3375
3390
3405
3420
B/mT Fig. 9 DMPO spin-trapping ESR spectra recorded with BiOCl and 1% C70/BiOCl samples in aqueous dispersion (for DMPO-·OH) (a) and methanol dispersion (for DMPO-O2•−) (b) under simulated sunlight 33
120
Decolorization (%)
100 80 60 40 20 0
Blank
IPA
EDTA-2Na
BQ
Scavenger Fig. 10 The influence of different capture agents on photocatalytic activity of 1% C70/BiOCl
34
Fig. 11 Photo-induced electron transfer between the excited BiOCl and C70
35
Graphical abstract
Research Highlights
>C70 was used to couple with the BiOCl photocatalyst. >The enhanced photogenerated charges separation rate resulted from the modification of C70. >O2•− was formed in the C70/BiOCl photocatalytic system. >The photocatalytic performance has been apparently improved under simulate sunlight.
36
S0169-4332(18)30679-2 https://doi.org/10.1016/j.apsusc.2018.03.018 APSUSC 38766
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
11 December 2017 27 February 2018 2 March 2018
Please cite this article as: D. Ma, J. Zhong, J. Li, L. Wang, R. Peng, Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight, Applied Surface Science (2018), doi: https://doi.org/10.1016/j.apsusc. 2018.03.018
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Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight Dongmei Maa,b, Junbo Zhongb,*, Jianzhang Lib, Li Wangb, Rufang Penga,c,* a
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, 621010, P
R China b
Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan, College of
Chemistry and Environmental Engineering, Sichuan University of Science and Engineering, Zigong, 643000, P R China c
The State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials,
Southwest University of Science and Technology, Mianyang, 621010, P R China *Corresponding author (E-mail: [email protected], [email protected]) Dongmei Ma, E-mail address: [email protected] Junbo Zhong, E-mail address: [email protected] Jianzhang Li, E-mail address: [email protected] Li Wang, E-mail address: [email protected] Rufang Peng, E-mail address: [email protected]
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Enhanced photocatalytic activity of BiOCl by C70 modification and mechanism insight Abstract As an excellent photocatalyst which can compete with TiO 2, BiOCl has triggered increasing attention. However, the practical application of BiOCl has been significantly limited by the fast recombination of the photoinduced electron-hole charge pairs. In this study, to further enhance the separation efficiency of photoinduced electron-hole charge pairs of BiOCl, a series of efficient BiOCl photocatalysts were prepared by C 70 surface modification. The trapping experiments reveal that the main active species were determined to be superoxide radicals (O 2•−) and holes (h+) under simulated sunlight irradiation. The surface photovoltage spectroscopy (SPS) demonstrates that separation of the photoinduced electron-hole pairs has been significantly promoted, forming more ·OH, proven by terephthalic acid photoluminescence probing technique. The photocatalytic evaluation results display that the C70/BiOCl photocatalysts exhibit much higher photocatalytic activity in decolorization of rhodamine B (RhB) than that of the bare BiOCl under the simulated sunlight irradiation. The excellent electron acceptability of C70 is conducive to the separation of the photogenerated carriers and results in efficient formation of O2•−, proven by the results of SPS and electron spin-resonance (ESR), therefore the photocatalytic performance of C70/BiOCl has been greatly improved. Based on all these observations, an enhancement mechanism in photocatalytic performance of C70/BiOCl was proposed. Keywords: Photocatalysis; C70; BiOCl; O2•−; Charge separation
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1. Introduction With the rapid development of industrialization process, the environmental pollution caused by exhaust gases, organic and inorganic pollutants is becoming a great environmental crisis [1-9]. Among all the technologies developed, semiconductor photocatalytic technology has been regarded as an efficient and green approach to decompose the environmental contaminants, because this technology can effectively utilize the solar energy and completely eliminate the organic pollutants rapidly. Among the photocatalysts studied [10-14], bismuth oxychloride (BiOCl), known as one of the most important bismuth oxyhalides, endowed with nontoxicity, low cost and ease of preparation, has been widely investigated for its outstanding photocatalytic performance due to its unique layered structure [15-21]. However, the photocatalytic activity of BiOCl is greatly limited by its high recombination rate of photogenerated carriers [22-28]. Therefore, it is absolutely necessary to improve the separation efficiency of photogenerated carriers, promoting the photocatalytic performance of BiOCl. As well known, the photocatalysis process initiates from the separation of photogenerated carriers. The photogenerated electrons and holes transfer to the surfaces of photocatalysts, and then can form reactive species such as hydroxyl radical (·OH) and superoxide radicals (O2•−) by the redox reactions. Many studies have substantially shown that construction of composite photocatalyst can effectively enhance the separation of photogenerated carriers [29-40]. The photocatalysts modified by nanocarbon materials not only have low cost and high chemical stability, but also the synergistic effect between two materials can significantly improve the photocatalytic activity of the semiconductor photocatalyst [41-46]. Nanocarbon materials include carbon nanotubes, graphene, fullerenes and the like. Nanocarbon materials have special 3
electrical, physical and chemical properties, such as large specific surface area, high thermal stability as well as excellent ability to accept electrons [47-50]. Among the nanocarbon materials, C70, a less symmetrical fullerene, has drawn much attention for its novel properties due to the delocalized conjugated structure [51-58]. C70 has excellent electron acceptability [59]. Hsiao and coworkers prepared C70-TiO2 nanowire with chemical bonding. The results reveal that C70-TiO2 nanowire shows much better photocatalytic performance than TiO 2 under the UV illumination, originating from excellent electron acceptor ability of C70 [60]. Therefore, if couple C70 with BiOCl, then high separation efficiency of the photogenerated carriers will be anticipated, significantly enhancing the photocatalytic performance. Herrin, we reported in-situ preparation of C70/BiOCl for the first time. A series of experiments were carried out to investigate the relationship between the C 70 modification and the photocatalytic performance of BiOCl. Under simulated solar illumination, photocatalytic activities of the photocatalysts were evaluated using RhB as a model pollutant. The photocatalytic activities of the C70 modified BiOCl photocatalysts were significantly improved. The enhanced photocatalytic activity of C70/BiOCl was originated from the highly efficient separation of the photogenerated carriers, resulting in the efficient formation of O2•−.
2. Experimental section 2.1. Materials Fullerene (C70, 99.9%) was purchased from Yongxin Science and Technology Co., Ltd (Puyang China). All other chemical reagents (analytical grade) used in this work were purchased from Chengdu Kelong Chemical Reagents Factory and used as received. Deionized water was 4
utilized throughout the experimental part. All labware were cleaned by soaking in diluted HNO 3 solution for 24 h and washed by deionized water many times before the experiments. 2.2. Synthesis of C70/BiOCl photocatalysts For preparation of functional C70, desired C70 was ultrasonically dispersed in 3M HNO3 solution for 30 min, and then was refluxed for 72 h. The products were collected by centrifugation, washed with deionized water until pH =7.0 and dried at 353K overnight. C70/BiOCl photocatalysts were synthesized as the method reported in the Ref. [61]. Desired functionalized C70 and 5g Bi (NO3)3·5H2O were added into 20 mL glacial acetic acid with ultrasonic dispersion for 15 min, then 10 mL of KCl solution was slowly added into aforementioned solution with vigorous stirring (the molar of Cl- is equal to the molar of Bi3+), after intensely magnetic stirring for 30 min, the mixture was transferred into a 100 mL Teflon-lined stainless autoclave, maintained at 453K for 24 h, and then cooled to room temperature naturally. The solid was filtered, purified with deionized water/absolute ethanol many times, and dried at 80 ℃ overnight. A series of C70/BiOCl photocatalysts with different mass ratios of C70 (0.1%, 0.5%, 1.0%, 2.0% and 3.0%) were obtained and marked as 0.1%, 0.5%, 1.0%, 2.0% and 3.0%. The bare BiOCl was also prepared with the same procedure in the absence of C70. 2.3. Characterization of the samples The morphologies of the samples were observed on a FESEM UItra 55 scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). XRD patterns were conducted on a DX-2600 X-ray powder diffractometer with Cu Kα radiation. High-resolution transmission electron microscopy (HRTEM) was carried out on a Tecnai TEM G2 microscope at 300 kV. Specific surface area analysis was performed on a QUADRASORB automatic surface 5
analyzer (Quantachrome, America) using the Brunauer-Emmet Teller (BET) method. The UV-Vis diffuse reflectance spectra (DRS) of the samples were recorded in the range from 250 to 800 nm on a TU-1907 UV-vis spectrophotometer equipped with an integrated sphere attachment and BaSO4 was used as a reference. FT-IR spectra on pellets of the samples with KBr were recorded on a FT-IR 8201PC spectrometer (Nicolet, US). The SPS spectra of the samples were carried out on a home-made instrument. Photoluminescence (PL) emission spectra were measured using Cary Eclipse with the excitation wavelength of 312 nm. X-ray photoelectron spectroscopy (XPS) spectra were acquired on an ESCALAB MKII X-ray photoelectron spectrometer. The ESR spectra were performed on Bruker E 500 spectrometer. 2.4 Photocatalytic tests The photocatalytic activities of the as-prepared photocatalysts were investigated by the degradation of rhodamine B (RhB, 10 mg/L, pH = 7.0) under simulated solar irradiation. The photocatalytic experiments were conducted in a Phchem III photochemical reactor (Beijing NBET Technology Co., Ltd, China) with a 500 W Xe lamp under vigorously stirring. The dosage of catalysts was 1g/L, the volume of RhB solution was 50 mL. During the photolysis process, 4.0 mL suspension was collected and centrifuged to remove the photocatalyst at regular interval, the absorbance of RhB solution was measured at 554 nm. The blank test was also carried out as the same method without photocatalysts.
3. Results and discussion 3.1. Characterization of the C70/BiOCl photocatalysts The BET surface areas of the C70/BiOCl photocatalysts were evaluated by the N2 adsorption/ 6
desorption analysis (Fig. 1). According to the IUPAC, the adsorption-desorption isotherms of the bare BiOCl indicates that BiOCl has macropores, while the isotherms of the 1% C70/BiOCl can be readily identified as type IV with a type H2 hysteresis loop, indicating the presence of mesopore. It is clear that couple C70 with BiOCl alters the type of the pore, which can be further supported by the observation of SEM. Usually, macropores results in low specific surface area, while mesopore is beneficial to the high specific surface area, which accords well with the results of specific surface area. The specific surface area of the bare BiOCl is 1.5 m2/g, however, the surface area of 1% C70/BiOCl photocatalysts is 11.0 m2/g. It is evident that C70 increases the BET surface area of BiOCl, which can not only provide more surface active sites, but also make photogenerated charge transport easier [47,48], which is conducive to the photocatalytic activity. The XRD patterns of C70/BiOCl photocatalysts were shown in Fig.2. All the peaks of samples are in good consistent with the values of the standard XRD pattern of BiOCl (JCPDS Card No. 82-0485). No typical C70 peaks were observed due to the high dispersion and the low content of C70 in the C70/BiOCl photocatalysts. Moreover, the diffraction intensity of (001) peaks of BiOCl significantly decreases, indicating that C70 inhibits the growth of the (001) crystal face originated from the strong interaction between C70 with BiOCl. The SEM morphologies of the samples were shown in Fig. 3a and 3b. It is clear that the BiOCl has irregular sheet structure with the thickness of 100 nm. However, the C70/BiOCl photocatalysts are micro-spherical structure, the microspheres are constructed by numerous nanosheets, revealing that C70 could significantly affect the morphology of BiOCl and it can be inferred that the existence of C70 results in forming flower-like structure of C70/BiOCl as hard template. Furthermore, Bi, Cl, O and C were all observed on the basis of the EDS patterns 7
(Fig. 3 f, g, h, and i), further confirming the successful combination of C70 and BiOCl. TEM and HRTEM analysis give further details of the material. Fig. 3d presents the HRTEM image of 1% C70/BiOCl (Fig.3c). As demonstrated in Fig. 3d, the 1% C70/BiOCl photocatalyst is highly crystalline. The lattice fringes of 0.340 nm and 0.368 nm can be assigned to the (101) and the (002) plane of BiOCl, respectively. However, no lattice fringes of C70 were observed by HRTEM image due to the amorphous state of C70 in the C70/BiOCl photocatalysts. In addition, XPS was also conducted to further confirm the existence of C70. As expected, the elements of O, Bi, Cl, and C were observed in the XPS spectrum of 1% C70/BiOCl (Fig. 4a). As shown in Fig. 4b, the peaks located at around 159.0 and 164.3 eV belong to the binding energies of the Bi 4f7/2 and Bi 4f5/2 peaks in the bare BiOCl, respectively [62]. After coupling of C70, the Bi 4f peaks, O1s peaks and the C1s peak slightly shift to high binding energy due to the interaction between C70 and BiOCl (Fig. 4b, 4c, 4d) [63]. It should be noted that the C1s peak of 1% C70/BiOCl can be deconvoluted into three components as shown in Fig. 4e, the main peak at 284.6 eV can be attributed to adventitious carbon and the C-C bond with sp2 orbital, the peaks centered at 285.7 and 288.6 eV can be assigned to the oxygenated carbon and nitrous carbon [64], respectively. The O1s high-resolution XPS spectrum of 1% C70/BiOCl shows two peaks with binding energies at 530.4 eV and 532.9 eV, which can be ascribed to crystal lattice oxygen and chemisorbed oxygen (the hydroxyl groups) (Fig. 4f) [65]. All the above results indicate that BiOCl has been successfully modified by C70 with a strong interaction. The FT-IR was used to investigate the chemical structure of the 1% C70/BiOCl photocatalysts. Fig. 5 presents a comparison of the FT-IR spectra of C70, BiOCl and 1% C70/BiOCl photocatalysts. In the case of C70, the broad peak at 3429 cm−1 is assigned to the hydroxyl group and the 8
surface-adsorbed water. The peak located at 523.9 cm−1 can be attributed to the characteristic peaks of BiOCl and 1% C70/BiOCl photocatalysts. Both the spectra of C70 and 1% C70/BiOCl photocatalysts exhibit characteristic vibration peaks of C70 (532.6, 574.7, 671.2, 642.2, 793.8, 1075.4, 1134.8, 1429.4, 1631.1 and 1728.3 cm−1) [66,67], indicating that the prepared photocatalysts contain C70. As an eff ective photocatalyst, the optical absorption properties are very crucial for its photocatalytic performance. The UV-Vis absorption spectra of the samples were shown in the Fig. 6. The bare BiOCl only shows absorption at UV light region, and the absorption edge is around 360 nm, as compared to the BiOCl, the absorption edges of C70/BiOCl photocatalysts have no obvious red-shift, reflecting that C 70 cannot change the band-gap of BiOCl. However, the absorption intensities of the C70/BiOCl photocatalysts are remarkably improved in the visible light region, which indicates that C70, as the visible light photosensitizer, is beneficial to enhance the absorption in visible light region. SPS is a direct and sensitive way to research the natures of the photogenerated charge pairs. As shown in Fig. 7a, C70/BiOCl photocatalysts display obvious SPS response from 300 nm to 355 nm, the SPS response intensity of 1% C70/BiOCl photocatalysts is about 25 times stronger than that of the bare BiOCl. The results further reveal that when the amount of C70 is excessive, the SPS signal is weaker. The excessive C70 will greatly block the light penetrate the interface between C70 and BiOCl, influencing the excitation of BiOCl, resulting in weak SPS signal accordingly. Usually, the stronger SPS signal, the higher separation rate of the charge pairs; the strong SPS responses of photocatalyst originates from high charge separation rate [68,69]. To further study the charge separation behavior after coupling with C70, the fluorescence 9
spectra of hydroxyl radicals (·OH) was performed. The 2-hydroxyterephthalic acid fluorescent method is a valid chemical way to characterize the separation of the photogenerated charge pairs， the more hydroxyl radicals (·OH) produced corresponds to the more efficient separation of photogenerated charges [70, 71]. As shown as Fig. 7b, for the bare BiOCl, the fluorescence signal intensity of ·OH is relative weak, the fluorescence signal intensity of ·OH over the composites gradually increases as the loading of C70 and the fluorescent response intensity of ·OH over the 1% C70/BiOCl photocatalysts is the strongest. The results fit well with the SPS response and the degradation of RhB over the photocatalysts. 3.2. Photocatalytic performance The RhB was used to evaluate the photocatalytic performance of the pure BiOCl and the C70/BiOCl photocatalysts under simulated sunlight irradiation. The black test indicates that the adsorption of RhB over all the C70/BiOCl photocatalysts after 1 h is below 25% (Fig.8a). The degradation of RhB solution without photocatalyst after 30 min is negligible. The results demonstrate that the degradation of RhB in this photocatalytic system originates from the presence of photocatalyst. As shown in Fig. 8b, about 49.7% and 66.4% of RhB can be decomposed over the bare BiOCl and P25 after 30 min. In comparison, after modification with C70, the photocatalytic activities of C70/BiOCl are greatly enhanced and the 1% C70/BiOCl photocatalysts holds the best photoactivity for the RhB degradation, 99.8% of RhB can be degraded under simulated sunlight irradiation for 30 min, benefiting from the improved separation rate of photogenerated charge pairs, which illustrates that C70 plays predominant role in boosting the performance of BiOCl. Compared with the 1% C70/BiOCl photocatalysts prepared in-situ by hydrothermal method, the physical mixture of 1% C70 and BiOCl shows poor photoactivity for the 10
RhB degradation (59.5%) under the same conditions, the result illustrates that the strong interaction between C70 and BiOCl is prerequisite for the enhanced photocatalytic performance of C70/BiOCl. The decay of RhB follows a first-order reaction kinetic equation, and rate constant of RhB over the 1% C70/BiOCl photocatalysts is the maximum (0.2028 min−1), the photocatalytic activity of 1% C70/BiOCl is 8 times higher than the pure BiOCl (Fig. 8c). In order to assess the stability of the C 70/BiOCl photocatalysts, we utilized a time-circle RhB photolysis experiment to evaluate the stability of 1% C70/BiOCl photocatalysts. As shown in Fig. 8d, it can be seen that photocatalytic activity decreases by 10% after the fifth cycle, implying the high stability of C70/BiOCl photocatalysts, therefore the photocatalysts have potential application in pollutants purification. 3.3. Mechanism In order to investigate the active species generated by the 1% C70/BiOCl photocatalysts during the photodegradation process under simulated solar irradiation, the ESR with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) technique was performed. As shown in the Fig.9, weak ESR signals of hydroxyl radicals (·OH) were observed and no superoxide radicals (O2•−) were detected for the pure BiOCl. Nevertheless, after modified by C70, much higher intensity of DMPO-superoxide radical (O2•−) and DMPO-hydroxyl radical (·OH) signals were observed for the 1% C70/BiOCl photocatalysts under the simulated sunlight irradiation, firmly confirming that C70 can quickly accept the photo-induced electrons to its surface and form O2•− by the reduction of O2. The band edge position of BiOCl can be calculated by using the equation: EVB = X − Ee + 0.5Eg, ECB = EVB − Eg [72]. The EVB and ECB are the valence band edge potential and conduction band edge potential respectively. X is the electronegativity of the semiconductor, the X is 6.33 for 11
BiOCl [73]. Ee is 4.5 eV, and Eg is 3.32 eV based on the DRS spectrogram (Fig. 6 inset). Therefore, the EVB and ECB of pure BiOCl are calculated to be 3.48 eV and 0.18 eV, respectively. The ECB (0.18 eV) of pure BiOCl is more positive than the potential of O2/O2•− (-0.33 eV vs NHE), the electrons from the CB of BiOCl cannot reduce O2 to generate O2•− [74]. This result is consistent with the ESR analysis of the pure BiOCl. However, when the C 70 was introduced, strong intensity of O2•− was determined by ESR analysis and scavenger experiments. To study the roles of the active species during the photocatalysis process, scavenger experiments were carried out by adding scavengers, benzoquinone (BQ) for O2•− radicals, disodium ethylene diamine inetetraacetic (EDTA-2Na) for holes (h+) and isopropanol (IPA) for ·OH radicals [75,76] into the C70/BiOCl photocatalytic system. From Fig. 10, the O2•− radicals and h+ plays main role during the photocatalysis process, while ·OH performs minor role. The scavenger experiments results agree well with the results of SPS、ESR and photocatalytic experiments, manifesting that the improved charge separation efficiency is the decisive factor for the enhanced photocatalytic activity of C70/BiOCl photocatalysts. As discussed above, a proposed enhancement mechanism for the excellent photocatalytic activity of C70/BiOCl photocatalysts was illustrated in Fig. 11. For the bare BiOCl, after exciting by the simulated sunlight, electrons can be jumped from valence band (VB) to conduction band (CB), leaving h+ at the valence band (VB). Usually, the bulk of photogenerated charge pairs recombine quickly, only a few charge carriers participate in the photocatalytic reaction, resulting in a low activity. While for the C70/BiOCl photocatalysts, the photocatalytic activity are greatly promoted (Fig. 8b), and the results of ESR experiments (Fig. 9a) demonstrate the modification of BiOCl by C70 results in more photogenerated h+ oxidize H2O or -OH to form ·OH. Since the 12
delocalized conjugated structure of C 70 makes it easier to transfer the photogenerated electrons, resulting in efficient photogenerated electron-hole pairs separation; the separated electrons with strong reduction ability on the surface of C70 can react with O2 to produce O2•− (Fig. 9b). The generated O2•− plays important role in the photodegradation process, resulting in excellent photocatalytic activity of C70/BiOCl [73].
4. Conclusion In conclusion, a novel C70 modified BiOCl photocatalyst with strong chemical interaction and closely integrated interface was successfully synthesized via a facile hydrothermal method. All the C70/BiOCl photocatalysts show improved photocatalytic activity for the degradation of RhB solution under the simulated sunlight irradiation, and the 1% C70/BiOCl photocatalysts show the best photocatalytic performance, which is attributed to the rapid photogenerated electron transfer ability of C70 and efficient separation of the photogenerated charge carriers. The main active species were determined to be O2•− radicals and h+ under the simulated sunlight irradiation by scavenger experiments. This work may offer a practical way to enhance the photocatalytic performance of BiOCl for pollutants degradation.
Acknowledgements The authors are particularly grateful to the support of Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education (LYJ14205), the program of State Key Laboratory Cultivation Base for Nonmetallic Composites and Functional Materials of Sichuan Province (14zxfk07) and Students Innovation Project of Sichuan Province (cx2017019). 13
References [1] X. Bai, C. Sun, D. Liu, X. Luo, D. Li, J. Wang, N. Wang, X. Chang, R. Zong, Y. Zhu, Photocatalytic degradation of deoxynivalenol using graphene/ZnO hybrids in aqueous suspension, Appl. Catal. B. 204 (2017) 11-20. [2] J. Hu, X. Wu, C. Huang, W. Fan, X. Qiu, Visible light photocatalytic activity induced by Rh (III) modification on the surface of BiOCl, Appl. Surf. Sci. 387 (2016) 45-50. [3] C. Li, Z. Sun, W. Zhang, C. Yu, S. Zheng, Highly efficient g-C3N4/TiO 2/kaolinite composite with novel three-dimensional structure and enhanced visible light responding ability towards ciprofloxacin and S. aureus, Appl. Catal. B. 220 (2018) 272-282. [4] P. Reddy, E. Kwon, K. Kim, T. Akter, S. Kalagara, Recent advances in photocatalytic treatment of pollutants in aqueous media, Environ. Int. 91 (2016) 94-103. [5] Z. Ai, J. Wang, L. Zhang, Substrate-dependent photoreactivities of BiOBr nanoplates prepared at different pH values, Chinese. J. Catal. 36 (2015) 2145-2154. [6] T. Giannakopoulou, I. Papailias, N. Todorova, N. Boukos, Y. Liu, J. Yu, C. Trapalis, Tailoring the energy band gap and edges’ potentials of g-C3N4/TiO2 composite photocatalysts for NOx removal, Chem. Eng. J. 310 (2017) 571-580. [7] D. Mao, A. Yu, S. Ding, F. Wang, S. Yang, C. Sun, H. He, Y. Liu, K. Yu, One-pot synthesis of BiOCl half-shells using microemulsion droplets as templates with highly photocatalytic performance for the degradation of ciprofloxacin, Appl. Surf. Sci. 389 (2016) 742-750. [8] S. Cao, F. Tao, Y. Tang, Y. Li, J. Yu, Size-and shape-dependent catalytic performances of oxidation and reduction reactions on nanocatalysts, Chem. Soc. Rev. 45 (2016) 4747-4765. [9] Q. Xiang, B. Cheng, J. Yu, Graphene-based photocatalysts for solar fuel generation, Angew. 14
Chem. Int. Ed. 54 (2015) 11350-11366. [10] R. He, S. Cao, J. Yu, Recent advances in morphology control and surface modification of Bi-based photocatalysts, Acta. Phys.-Chim. Sin. 12 (2016) 2841-2870. [11] S. Cao, J. Yu, Carbon-based H2-production photocatalytic materials, J. Photoch. Photobio. C 27 (2016) 72-99. [12] L. Yuan, Y. Xu, Photocatalytic conversion of CO2 into value-added and renewable fuels, Appl. Surf. Sci. 342 (2015) 154-167. [13] J. Wen, X. Li, H. Li, S. Ma, K. He, Y. Xu, Y. Fang, W. Liu, Q. Gao, Enhanced visible-light H2 evolution of g-C3N4 photocatalysts via the synergetic effect of amorphous NiS and cheap metal-free carbon black nanoparticles as co-catalysts, Appl. Surf. Sci. 358 (2015) 204-212. [14] M. Yang, Q. Yang, J. Zhong, J. Li, S. Huang, X. Li, PVA-assisted hydrothermal preparation of BiOF with remarkably enhanced photocatalytic performance, Mater. Lett. 201 (2017) 35-38. [15] L. Liu, L. Ding, Y. Liu, W. An, S. Lin, Y. Liang, W. Cui, Enhanced visible light photocatalytic activity by Cu2O-coupled flower-like Bi2WO6 structures, Appl. Surf. Sci. 364 (2016) 505-515. [16] C. Zhu, L. Zhang, B. Jiang, J. Zheng, P. Hu, S. Li, M. Wu, W. Wu, Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation, Appl. Surf. Sci. 377 (2016) 99-108. [17] W. Liu, G. Zhao, M. An, L. Chang, Solvothermal synthesis of nanostructured BiVO4 with highly exposed (010) facets and enhanced sunlight-driven photocatalytic properties, Appl. Surf. Sci. 357 (2015) 1053-1063. [18] Y. Su, L. Zhang, W. Wang, Internal polar field enhanced H 2 evolution of BiOIO3 nanoplates, 15
Int. J. Hydrogen Energ. 41 (2016) 10170-10177. [19] F. Li, Q. Wang, J. Ran, Y. Hao, X. Wang, D. Zhao, S. Qiao, Ionic liquid self-combustion synthesis of BiOBr/Bi24O31Br10 heterojunctions with exceptional visible-light photocatalytic performances, Nanoscale. 7 (2015) 1116-1126. [20] X. Liu, J. Zhong, J. Li, S. Huang, W. Song, PEG-assisted hydrothermal synthesis of BiOCl with enhanced photocatalytic performance, Appl. Phys. A. 119 (2015) 1203-1208. [21] Z. Zhao, W. Dai, Electronic structure and optical properties of BiOI ultrathin films for photocatalytic water splitting, Inorg. Chem. 54 (2015) 10732-10737. [22] M. Li, H. Huang, S. Yu, N. Tian, F. Dong, X. Du, Y. Zhang, Simultaneously promoting charge separation and photoabsorption of BiOX (X= Cl, Br) for efficient visible-light photocatalysis and photosensitization by compositing low-cost biochar, Appl. Surf. Sci. 386 (2016) 285-295. [23] J. Li, Y. Yu, L. Zhang, Bismuth oxyhalide nanomaterials: layered structures meet photocat -alysis, Nanoscale. 15 (2014) 8473-8484. [24] X. Wang, W. Bi, P. Zhai, X. Wang, H. Li, G. Mailhot, W. Dong, Adsorption and photocatalytic degradation of pharmaceuticals by BiOClxIy nanospheres in aqueous solution, Appl. Surf. Sci. 360 (2016) 240-251. [25] J. Hu, W. Fan, W. Ye, C. Huang, X. Qiu, Insights into the photosensitivity activity of BiOCl under visible light irradiation, Appl. Catal. B. 158 (2014) 182-189. [26] X. Yu, J. Shi, L. Feng, C. Li, L. Wang, A three-dimensional BiOBr/RGO heterostructural aerogel with enhanced and selective photocatalytic properties under visible light, Appl. Surf. Sci. 396 (2017) 1775-1782. 16
[27] R. He, J. Zhang, J. Yu, S. Cao, Room-temperature synthesis of BiOI with tailorable (001) facets and enhanced photocatalytic activity, J. Colloid. Interf. Sci. 478 (2016) 201-208. [28] H. Yu, C. Cao, X. Wang, J. Yu, Ag-modified BiOCl single-crystal nanosheets: dependence of photocatalytic performance on the region-selective deposition of Ag nanoparticles, J. Phys. Chem. C. 121 (2017) 13191-13201. [29] J. Di, J. Xia, Y. Ge, L. Xu, H. Xu, M. He, Q. Zhang, H. Li, Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity, J. Mater. Chem. A. 2 (2014) 15864-15874. [30] J. Wen, J. Xie, Z. Yang, R. Shen, H. Li, X. Luo, X. Chen, X. Li, Fabricating the robust g-C3N4 nanosheets/carbons/NiS multiple heterojunctions for enhanced photocatalytic H 2 generation: an insight into the trifunctional roles of nanocarbons, ACS. Sustain. Chem. Eng. 5 (2017) 2224-2236. [31] X. Wang, J. Cheng, H. Yu, J. Yu, A facile hydrothermal synthesis of carbon dots modified g-C3N4 for enhanced photocatalytic H2-evolution performance, Dalton Transactions. 46 (2017) 6417-6424. [32] Y. Sun, X. Xiao, X. Dong, F. Dong, W. Zhang, Heterostructured BiOI @ La(OH)3 nanorods with enhanced visible light photocatalytic NO removal, Chinese J. Catal. 38 (2017) 217-226. [33] W. Liu, L. Qiao, A. Zhu, Y. Liu, J. Pan, Constructing 2D BiOCl/C3N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation, Appl. Surf. Sci. 426 (2017) 897-905. [34] Y. Mi, H. Li, Y. Zhang, R. Zhang, W. Hou, One-pot synthesis of belt-like Bi2S3/BiOCl hierarchical composites with enhanced visible light photocatalytic activity, Appl. Surf. Sci. 423 17
(2017) 1062-1071. [35] Y. Li, K. Lv, W. Ho, Z. Zhao, Y. Huang, Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures, Chinese. J. Catal. 38 (2017) 321-329. [36] R. He, S. Cao, P. Zhou, J. Yu, Recent advances in visible light Bi-based photocatalysts, Chinese. J. Catal. 35 (2014) 989-1007. [37] D. Xu, Y. Hai, X. Zhang, S. Zhang, R. He, Bi2O3 cocatalyst improving photocatalytic hydrogen evolution performance of TiO2, Appl. Surf. Sci. 400 (2017) 530-536. [38] J. Zhang, J. Lu, K. Dai, C. Liang, Q. Liu, One-step growth of nanosheet-assembled BiOCl/BiOBr microspheres for highly efficient visible photocatalytic performance, Appl. Surf. Sci. 430 (2018) 639-646. [39] Y. Zhang, M. Park, H. Kim, B. Ding, S. Park, In-situ synthesis of nanofibers with various ratios of BiOClx/BiOBr y/BiOIz for effective trichloroethylene photocatalytic degradation, Appl. Surf. Sci. 384 (2016) 192-199. [40] Q. Yang, J. Li, J. Zhong, C. Cheng, Z. Xiang, J. Chen, Enhanced solar photocatalytic performance of (BiO)2CO3 prepared with the assistance of ionic liquid, Mater. Lett. 192 (2017) 157-160. [41] S. Zhu, T. Xu, H. Fu, J. Zhao, Y. Zhu, Synergetic effect of Bi 2WO6 photocatalyst with C60 and enhanced photoactivity under visible irradiation, Environ. Sci. Technol. 17 (2007) 62346239. [42] X. Li, R. Shen, S. Ma, X. Chen, J. Xie, Graphene-based heterojunction photocatalysts, Appl. Surf. Sci. 430 (2018) 53-107. 18
[43] X. Ma, X. Li, M. Li, X. Ma, L. Yu, Y. Dai, Effect of the structure distortion on the high photocatalytic performance of C 60/g-C3N4 composite, Appl. Surf. Sci. 414 (2017) 124-130. [44] K. Ozawa, S. Yamamoto, R. Yukawa, K. Akikubo, M. Emori, H. Sakama, I. Matsuda, Capturing transiently charged states at the C60/TiO2 (110) interface by time-resolved soft X-ray photoelectron spectroscopy, Org. Electron. 31 (2016) 98-103. [45] Y. Zhu, M. Pan, R. Zhu, T. Xu, J. Liu, J. Zhu, Y. Xi, G. Zhu, H. He, Enhanced photocatalytic activity of Zn/Ti-LDH via hybridizing with C60, Molecular Catalysis. 427 (2017) 54-61. [46] H. Tan, F. Denny, M. Hermawan, R. Wong, R. Amal, Y. Ng, Reduced graphene oxide is not a universal promoter for photocatalytic activities of TiO2, J. Materiomics. 3 (2017) 51-57. [47] T. Song, J. Huo, T. Liao, J. Zeng, J. Qin, H. Zeng, Fullerene [C60] modified Cr2−xFexO3 nanocomposites for enhanced photocatalytic activity under visible light irradiation, Chem. Eng. J. 287 (2016) 359-366. [48] X. Bai, L. Wang, Y. Wang, W. Yao, Y. Zhu, Enhanced oxidation ability of g-C3N4 photocatalyst via C60 modification, Appl. Catal. B. 152 (2014) 262-270. [49] R. Wakimoto, T. Kitamura, F. Ito, H. Usami, H. Moriwaki, Decomposition of methyl orange using C60 fullerene adsorbed on silica gel as a photocatalyst via visible-light induced electron transfer, Appl. Catal. B. 166 (2015) 544-550. [50] Q. Cai, Z. Hu, Q. Zhang, B. Li, Z. Shen, Fullerene (C60)/CdS nanocomposite with enhanced photocatalytic activity and stability, Appl. Surf. Sci. 403 (2017) 151-158. [51] F. Diederich, R. Ettl, Y. Rubin, R. Whetten, R. Beck, M. Alvarez, S. Anz, D. Sensharma, F. Wudl, K. Khemani, The higher fullerenes: isolation and characterization of C 76, C84, C90, C94, and C70O, an oxide of D5h-C70, Science. 252 (1991) 548-551. 19
[52] D. Lu, G. Zhuang, H. Wu, S. Wang, S. Yang, P. Du, A large π‐ extended carbon nanoring based on nanographene units: bottom‐ up synthesis, photophysical properties, and selective complexation with fullerene C70, Angew. Chemie. 129 (2017) 164-168. [53] K. Zhang, H. Yu, X. Liu, Q. Dong, Z. Wang, Y. Wang, N. Chen, Y. Zhou, B. Song, Fullerenes and derivatives as electron transport materials in perovskite solar cells, Sci. Chi. Chem. 60 (2017) 144-150. [54] Y. He, G. Zhao, B. Peng, Y. Li, High‐ yield synthesis and electrochemical and photovoltaic properties of indene‐ C70 bisadduct, Adv. Funct. Mater. 20 (2010) 3383-3389. [55] R. Kumar, E. Gleißner, E. Tiu, Y. Yamakoshi, C70 as a photocatalyst for oxidation of secondary Benzylamines toimines, Org. Lett. 18 (2015) 184-187. [56] Z. Meng, L. Zhu, S. Ye, S. Liu, W. Oh, Detection of oxygen species generated of C70-Ag2Se heterojunction photocatalysts with excellent visible light driven photocatalytic performance, Fuller. Nanotub. Car. N. 24 (2016) 415-422. [57] P. Dallas, G. Rogers, B. Reid, R. Taylor, H. Shinohara, G. Briggs, K. Porfyrakis, Charge separated states and singlet oxygen generation of mono and bis adducts of C 60 and C70, Chem. Phys. 465 (2016) 28-39. [58] K. Moor, D. Valle, C. Li, J. Kim, Improving the visible light photoactivity of supported fullerene photocatalysts through the use of [C70] fullerene, Environ. Sci. Technol. 49 (2015) 61906197. [59] G. Yu, J. Gao, J. Hummelen, F. Wudl, A. Heeger, Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor/acceptor heterojunctions, Science. 270 (1995) 17891791. 20
[60] E. Cho, J. Ciou, J. Zheng, J. Pan, Y. Hsiao, K. Lee, J. Huang, Fullerene C 70 decorated TiO2 nanowires for visible-light-responsive photocatalyst, Appl. Surf. Sci. 355 (2015) 536-546. [61] M. Su, C. He, L. Zhu, Z. Sun, C. Shan, Q. Zhang, Y. Xiong, Enhanced adsorption and photocatalytic activity of BiOI-MWCNT composites towards organic pollutants in aqueous solution, J. Hazard. Mater. 229 (2012) 72-82. [62] M. Yang, Q. Yang, J. Zhong, S. Huang, J. Li, J. Song, C. Burda, Enhanced photocatalytic performance of Ag2O/BiOF composite photocatalysts originating from efficient interfacial charge separation, Appl. Surf. Sci. 416 (2017) 666-671. [63] J. Di, J. Xia, S. Yin, H. Xu, L. Xu, Y. Xu, H. Li, Preparation of sphere-like g-C3N4/BiOI photocatalysts via a react able ionic liquid for visible-light-driven photocatalytic degradation of pollutants, J. Mater. Chem. A. 15 (2014) 5340-5351. [64] S. Chen, R. Yan, X. Zhang, K. Hu, Z. Li, M. Humayun, Y. Qu, L. Jing, Photogenerated electron modulation to dominantly induce efficient 2, 4-dichlorophenol degradation on BiOBr nanoplates with different phosphate modification, Appl. Catal. B. 209 (2017) 320-328. [65] Z. Li, Y. Qu, K. Hu, M. Humayun, S. Chen, L. Jing, Improved photoelectrocatalytic activities of BiOCl with high stability for water oxidation and MO degradation by coupling RGO and modifying phosphate groups to prolong carrier lifetime, Appl. Catal. B. 203 (2017) 355-362. [66] B. Chase, N. Herron, E. Holler, Vibrational spectroscopy of fullerenes (C 60 and C70). Temperature dependant studies, J. Phys. Chem. 96 (1992) 4262-4266. [67] D. Garcia-hernandez, F. Cataldo, A. Manchado, About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)], Fuller. Nanotub. Car. N. 24 (2016) 225-233. 21
[68] A. Zada, M. Humayun, F. Raziq, X. Zhang, Y. Qu, L. Bai, C. Qin, L. Jing, H. Fu, Exceptional visible‐ light‐ driven cocatalyst‐ free photocatalytic activity of g‐ C3N4 by well designed nano-composites with plasmonic Au and SnO2, Adv. Energy. Mater. 6 (2016) 1601190-1601198 [69] R. Fazal, Y. Qu, X. Zhang, Enhanced cocatalyst-free visible-light activities for photocatalytic fuel production of g-C3N4 by trapping holes and transferring electrons, J. Phs. Chem. C. 120 (2016) 98-107. [70] J. Li, X. Zhang, F. Raziq, J. Wang, C. Liu, Y. Liu, J. Sun, R. Yan, B. Qu, C. Qin, Improved photocatalytic activities of g-C3N4 nanosheets by effectively trapping holes with halogen-induced surface polarization and 2, 4-dichlorophenol decomposition mechanism, Appl. Catal. B. 218 (2017) 60-67. [71] H. Wang, Y. Su, H. Zhao, H. Yu, S. Chen, Y. Zhang, X. Quan, Photocatalytic oxidation of aqueous ammonia using atomic single layer graphitic-C3N4, Environ. Sci. Technlo. 48 (2014) 11984-11990. [72] J. Chen, J. Zhong, J. Li, S. Huang, W. Hu, M. Li, Q. Du, Synthesis and characterization of novel Ag2CO3/g-C3N4 composite photocatalysts with excellent solar photocatalytic activity and mechanism insight, Molecular Catalysis. 435 (2017) 91-98. [73] J. Di, J. Xia, M. Ji, B. Wang, S. Yin, Q. Zhang, H. Li, Carbon quantum dots modified BiOCl ultrathin nanosheets with enhanced molecular oxygen activation ability for broad spectrum photocatalytic properties and mechanism insight, ACS. Appl. Mater. Inter. 36 (2015) 20111 -20123. [74] Y. He, L. Zhang, B. Teng, M. Fan. New application of Z-scheme Ag3PO4/g-C3N4 composite 22
in converting CO2 to fuel. Environ. Sci. Technol. 49 (2014) 649-656. [75] Z. Wan, G. Zhang, X. Wu, S. Yin, Novel visible-light-driven Z-scheme Bi12GeO20/g-C3N4 photocatalyst: oxygen-induced pathway of organic pollutants degradation and proton assisted electron transfer mechanism of Cr (VI) reduction, Appl. Catal. B. 207 (2017) 17-26. [76] W. Wang, D. Xu, B. Cheng, J. Yu, C. Jiang, Hybrid carbon @ TiO2 hollow spheres with enhanced photocatalytic CO2 reduction activity, J. Mater. Chem. A. 5 (2017) 5020-5029.
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Caption for Figures Fig. 1 N2 adsorption-desorption isotherms of BiOCl (a) and 1% C70/BiOCl (b) Fig. 2 XRD patterns of C70/BiOCl samples with different C70 contents Fig. 3 SEM of BiOCl (a), and 1.0% C70/BiOCl (b), (e), TEM of 1.0% C70/BiOCl (c) and (d), EDS of 1.0% C70/BiOCl (f), (g), (h) and (i) Fig. 4 XPS spectra of the photocatalyst: survey XPS spectrum of 1% C70/BiOCl (a), Bi 4f (b), O 1s (c), C 1s (d), High resolution XPS spectra of O 1s (e) and C 1s (f) region on the surfaces of 1% C70/BiOCl photocatalysts Fig. 5 FT-IR spectra of C70, BiOCl and 1% C70/BiOCl Fig. 6 UV-Vis DRS of C70/BiOCl samples with different C70 amount, inset is band energy level of pure BiOCl Fig. 7 SPS of the C70/BiOCl samples (a), FS spectra related to the amount of ·OH radical (b) Fig. 8 Adsorption of RhB on the different photocatalysts after 1h in dark (a), The decolorization efficiency with the irradiation time (b), Photocatalytic decolorization rate constants of RhB over the different photocatalysts(c), Five consecutive cycles of decolorization of RhB using the 1% C70/BiOCl (d) Fig. 9 DMPO spin-trapping ESR spectra recorded with BiOCl and 1% C70/BiOCl samples in aqueous dispersion (for DMPO-·OH) (a) and methanol dispersion (for DMPO-O2•−) (b) under simulated sunlight Fig. 10 The influence of different radical scavengers on photocatalytic activity of 1% C70/BiOCl samples 24
4
3
Quantity Adsorbed (cm /g)
Fig. 11 Photo-induced electron transfer between the excited BiOCl and C 70
a
Adsorption Desorption
3 2 1 0 0.0
0.2
0.4
0.6
0.8
1.0
60
3
Quantity Adsorbed (cm /g)
Relative Pressure (P/P0)
50
b
Adsorption Desorption
40 30 20 10 0 0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0) Fig. 1 N2 adsorption-desorption isotherms of BiOCl (a) and 1% C70/BiOCl (b)
25
C70
Intensity (a.u.)
3.0% 2.0% 1.0% 0.5% 0.1% [001]
BiOCl
10
20
30
40
50
60
2Theta (degree) Fig. 2 XRD patterns of C70/BiOCl samples with different C70 contents
26
Fig. 3 SEM of BiOCl (a), and 1.0% C70/BiOCl(b), (e), TEM of 1.0% C70/BiOCl (c) and (d), EDS of 1.0% C70/BiOCl (f), (g), (h) and (i)
27
120000
a
b
O(KLL)
Intensity (a.u)
Bi4f
60000
Intensity (a.u)
80000
Bi4p O1s Bi4d C1s
40000
Cl2p Bi5d
20000
O1s Bi4f5/2
Bi4f7/2
90000
1% C70/BiOCl
60000
30000
BiOCl
Cl2s Bi5p
1000
Intensity (a.u)
22000
800
600
400
Binding Energy (eV)
c
200
0
0
O1s
1% C70/BiOCl
16000
536
532
528
160
156
152
C1s
12000 1% C70/BiOCl
10000
BiOCl
BiOCl
14000 540
164
d
14000
20000 18000
168
Binding Energy (eV)
Intensity (a.u)
0
8000
524
292
Binding Energy (eV)
288
284
280
276
Binding Energy (eV)
21000
e
532.9 eV
Intensity (a.u)
Intensity (a.u)
20000 19000
11000
O 1s
f
C 1s
10000
530.4 eV
18000 17000
285.7 eV
9000
284.6 eV 288.6 eV
8000
16000 534
532
530
290
528
288
286
284
282
Binding Energy (eV)
Binding Energy (eV)
Fig. 4 XPS spectra of the photocatalyst: survey XPS spectrum of 1% C70/BiOCl (a), Bi 4f (b), O 1s (c), C 1s (d), High resolution XPS spectra of O 1s (e) and C 1s (f) region on the surfaces of 1% C70/BiOCl photocatalysts
28
Transmittance (%)
400 1% C70/BiOCl 300
200
BiOCl
100
C70
0 4000
3500
3000
2500
2000
1500 -1
Wavenumber (cm
1000
)
Fig. 5 FT-IR spectra of C70, BiOCl and 1% C70/BiOCl
29
500
1.0
0.6
1/2
(ahv) (ev)
0.8
Absorbance (a.u)
1/2
2.0
3.0% 2.0% 1.0% 0.5% 0.1% BiOCl
1.5 1.0 0.5 2.4
2.8
3.2
3.6
Energy (ev)
0.4
0.2
0.0
300
400
500
600
700
800
Wavelength (nm) Fig. 6 UV-Vis DRS of C70/BiOCl samples with different C70 amount, inset is band energy level of pure BiOCl
30
7
a
1.0% 2.0% 3.0% 0.5% 0.1% BiOCl
-3
Photovoltage (10 V)
6 5 4 3 2 1 0 300
310
320
330
340
350
360
370
Wavelength (nm) 40
Intensity/(a.u.)
b
1.0% 2.0% 3.0% 0.5% 0.1% BiOCl
30
20
10
0 350
400
450
500
550
Emission wavelength (nm) Fig. 7 SPS of the C70/BiOCl samples (a), FS spectra related to the amount of ·OH radical (b) 31
30
1.0 b 19.3
20
21.7
23.1
RHB BiOCl mixture P25 0.1% 3.0% 0.5% 2.0% 1.0%
0.8 18.4
17.5
0.6
Ct/C0
Decolorization (%)
a
0.4
9.1
10
0.2 0.0 0
BiOCl 0.1% 0.5% 1.0%
2.0% 3.0%
-10 -5
Photocatalyst 1.2
c
10
15
20
25
30
d
0.20
2nd
1st
1.0
3rd
4th
5th
0.8 0.15
Ct/C0
-1
Rate constant (min
5
Time (min)
)
0.25
0
0.10
0.6 0.4
0.05
0.2
0.00 BiOCl 0.1% 0.5% 1.0% 2.0% 3.0% P25
0.0 0
30
60
90
120
150
Time (min)
Photocatalyst
Fig. 8 Adsorption of RhB on the different photocatalysts after 1h in dark (a), The decolorization efficiency with the irradiation time (b), Photocatalytic decolorization rate constants of RhB over the different photocatalysts (c), Five consecutive cycles of decolorization of RhB using the 1% C70/BiOCl (d)
32
210000
hydroxyl radical
a *
Intensity (a.u.)
*
*
*
180000
1% C70/BiOCl 150000
*
*
120000 90000
3360
*
*
3380
BiOCl
3400
3420
B/mT 560000
b
superoxide radical
Intensity (a.u.)
480000
*
*
* *
*
400000
*
320000
1% C70/BiOCl
240000 160000 BiOCl
80000 0 3345
3360
3375
3390
3405
3420
B/mT Fig. 9 DMPO spin-trapping ESR spectra recorded with BiOCl and 1% C70/BiOCl samples in aqueous dispersion (for DMPO-·OH) (a) and methanol dispersion (for DMPO-O2•−) (b) under simulated sunlight 33
120
Decolorization (%)
100 80 60 40 20 0
Blank
IPA
EDTA-2Na
BQ
Scavenger Fig. 10 The influence of different capture agents on photocatalytic activity of 1% C70/BiOCl
34
Fig. 11 Photo-induced electron transfer between the excited BiOCl and C70
35
Graphical abstract
Research Highlights
>C70 was used to couple with the BiOCl photocatalyst. >The enhanced photogenerated charges separation rate resulted from the modification of C70. >O2•− was formed in the C70/BiOCl photocatalytic system. >The photocatalytic performance has been apparently improved under simulate sunlight.
36