- Email: [email protected]
One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB
Journal Pre-proof One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB Zhao Li, Baojin Ma, Xiaofei Zhang, Yuanhua Sang, Hong Liu PII:
S0013-9351(19)30873-4
DOI:
https://doi.org/10.1016/j.envres.2019.109077
Reference:
YENRS 109077
To appear in:
Environmental Research
Received Date: 28 September 2019 Revised Date:
28 November 2019
Accepted Date: 21 December 2019
Please cite this article as: Li, Z., Ma, B., Zhang, X., Sang, Y., Liu, H., One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB, Environmental Research (2020), doi: https://doi.org/10.1016/j.envres.2019.109077. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB Zhao Lia, Baojin Maa, Xiaofei Zhanga, Yuanhua Sanga* and Hong Liua,b
a
State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, PR China b Institute for Advanced Interdisciplinary Research, University of Jinan, Jinan 250022, Shandong, PR China * Corresponding Author. Email: [email protected]
Abstract: Water pollution from Rhodamine B (RhB) has become a challenging problem which human beings are urgent to confront. A high-efficiency photocatalysis system is required for the industrial application. A novel carbon doped bismuth oxychloride (C-BiOCl) composite photocatalyst with dual functional carbon was synthesized by one-pot hydrothermal process. The introduction of the carbon in the synthesis modified the morphology of BiOCl by suppressing the growing-up of the layered structures, which resulted in more active catalytic sites and shorter path of charge transfer. Moreover, the doped carbon would improve the utilization of light, and shift the band structures of the BiOCl. The as-synthesized C-BiOCl possesses a significant improvement (around 400%) on the photocatalytic degradation of RhB. Therefore, this efficient photocatalyst with dual functional carbon has been synthesized and would be regarded as a novel strategy for the design of high-performance photocatalysts. Keywords: Dual functional carbon; BiOCl nanosheets; Ultra-high efficiency; Doping; Heterostructure; Photocatalytic degradation 1
1. Introduction The energy crisis and environmental pollution have attracted much attention worldwide with the development of science and technology. Water pollution is one of the most intractable issues which threats our survival. The dyestuff is one of the most notorious contaminants in water ecosystem owing to their great output from industries, toxicity and difficulty of biodegradation (Aljerf, 2018). Rhodamine B (RhB), a kind of xanthene dye, is harmful to human beings resulting in irreversible irritation to the skin, eyes and respiratory tract (Dong et al., 2010). And the concentration of RhB in wastewater even exceeds 100 ppm in many conditions (Tao et al., 2017). However, the RhB removal efficiency of the counterpart three-dimensional electrochemical system and E-Fenton system are lower than 35% at neutral pH in 30 minutes (Liu et al., 2012). The basic strategies of removing RhB from water are the adsorption and oxidation processes. For instance, the activated carbon is used to adsorb the RhB molecular (Luan et al., 2016), however, after the adsorption, the activated carbon becomes a secondary pollution before further treatment. Essentially, this process is considered as a transfer of the pollution rather than degradation, which would be limited in the industrial application. The oxidation process could degrade the RhB molecules into non-toxic molecules, even into inorganic molecules and H2O (Nayak et al., 2019; Hong et al., 2016). A number of approaches have been researched, such as Fenton and photo-Fenton processes (Deng et al., 2019), photocatalytic oxidation (Yu et al., 2018; Liang et al., 2018), and photoelectrocatalytic oxidation (Pan et al., 2018). Among these approaches, photocatalytic oxidation is regarded as a promising 2
and operable direction to deal with organic dyes without further consumption material and energy (Zangeneh et al., 2015). The researches on dyes degradation are fabulous in amount, yet the photocatalytic efficiency is still too low to be applied industrially. Bismuth oxychloride (BiOCl) is an indirect band-gap semiconductor with negligible photocatalytic property (Jing et al., 2016). It possesses a tetragonal layered structure and contains [Cl-Bi-O-Bi-Cl] sheets with the Cl atoms along the c-axis by van der Waals force (Hu et al., 2014; Zhang et al., 2006; Mi et al., 2016). BiOCl also belongs to the family of main group multicomponent metal oxyhalides V-VI-VII, a significant category of ternary compounds because of the outstanding electrical, magnetic, optical, luminescent and catalytic properties (Lv et al., 2013). The bipyramidal crystal geometry of BiOCl usually grows in flakes or sheets regularly. This lamellar nanostructure with high crystallinity and ultrathin thickness can reduce the recombination of photogenerated electrons and holes (Kang et al., 2016). Thus, the photogenerated charge carriers can transfer to the surface quickly to react with the organic pollutant molecules. These properties imply it a good candidate as photocatalyst which is inconsistent with the weak photocatalytic property. Therefore, the improvement of the photocatalytic property of BiOCl has attracted extensive interests. And elemental doping is an effective and simple means to modify semiconductor photocatalysts (Li et al., 2015; Li et al., 2016; Zhang et al., 2018). For example, Song et al. reported that the crystal lattice and surface properties of BiOCl was modified by doping with fluorine ions and the as-obtained F-BiOCl degraded RhB in 30 minutes under visible light irradiation (Zhang et al., 2016). Huang et al. 3
proposed that the introducing of S element into BiOCl photocatalyst without forming any segregated impurity phase not only extended the light absorption range but also enhanced the separation efficiency of the photogenerated charge carriers. The photocatalytic O2 evolution of S-BiOCl was enhanced four times by that of BiOCl (Jiang et al., 2015). Song’s Group also found that with the doping of fluorine ions (F-), the size of the as-obtained BiOCl nanosheets reduced (Zhang et al., 2016). Besides that, carbon as a kind of vital nonmetallic element, has also attracted much attention. Combining TiO2 with carbonaceous species is regarded as a method to enhance photocatalytic activity by inhibiting charge carrier recombination and promoting the absorption of light. Thus, it will be interesting and meaningful to apply this idea into BiOCl material (Leary et al., 2011). In addition to the regulation of band gap and surface catalytic activity, the key point of doping mediated modification is to construct the composite material. As far as the heterostructure is constructed, the regulation of charge carriers would be more efficient, such as Ag/ZnO (Ren et al., 2010; Height et al., 2006) and CdS/TiO2 (Bai et al., 2011; Huo et al., 2011) heterojunctions, etc. As is well accepted, carbon nanoparticles would form during the acid/alkali-assisted hydrothermal process, and the precursor could be sodium citrate (Guo et al., 2013), glucose or sucrose (He et al., 2011). Once the carbon doping and the formation of heterostructure between C and BiOCl could achieve at the same time, the photocatalytic efficiency would be improved greatly. Herein, we synthesized a novel C-BiOCl composite photocatalyst via a one-pot 4
hydrothermal process. The photocatalytic property was evaluated via the photocatalytic degradation of RhB. The mechanism of the improvement was also discussed. The elemental doping and surface heterostructure construction should be the mean reasons. Thus, the dual functions of the carbon in the C-BiOCl photocatalyst was proposed. It is believed that this one-pot hydrothermal process for dual functional carbon synthesis will be beneficial to the study of high-efficiency photocatalyst.
2. Experimental procedures 2.1 Materials All the reagents in this work are analytic grade and commercially available. Bismuth nitrate (Bi(NO3)3·5H2O), potassium chloride (KCl), Glucose, ethanol and Rhodamine B (RhB) were purchased from Sinopharm Chemical Reagent Co., Ltd. All of the chemicals were used as purchased without further purification. 2.2 Synthesis The synthesis of BiOCl (BOC) and C-BiOCl (C-BOC) nanosheets were proceeded via the hydrothermal process, as illustrated in Scheme S1 in the Supporting Information. Typically, Bi(NO3)3 ·5H2O (1 mmol) was dissolved in 70 mL of deionized water, followed by the addition of KCl (1 mmol) under continuous stirring (300 r/min) for 30 minutes. Then added 0, 1, 2, and 4 mmol of glucose into the previous solutions, respectively. The solutions were transferred to the 100 mL Teflon-lined autoclaves and carried out the hydrothermal treatment at 120 oC for 10 h. After cooling down naturally, the products were washed with deionized (DI) water 5
and alcohol thoroughly. The samples of BOC and C-BOC (Figure S1 in the Supporting information) with different concentration of carbon were obtained after drying at 60 oC for 12h. 2.3 Characterization The X-ray powder diffraction patterns of the samples were measured by a Bruker D8 Advance powder X-ray diffractometer (XRD) with Cu Kα radiation (λ=0.1541 nm). The morphology was captured on a HITACHI S-4800 field emission scanning electron microscope (FESEM). The high-resolution transmission electron microscopic (HRTEM) images were scanned with a JEOL JEM 2100 microscope operated at 200 kV. The residual concentrations of RhB solution were tested by UV-Vis spectrophotometry (UV-2102PC). X-ray photoelectron spectroscopy (XPS) spectra and the valence band maximum (VBM) measurement were analyzed with an ESCALAB 250 instrument. Fourier Transform infrared spectra (FT-IR) was detected on a Thermo Nexus 670 spectrometer. A Renishaw 1000 microspectrometer with an excitation wavelength of 514.5 nm collected Raman spectra. UV-Vis diffuse reflectance spectra (DRS) was measured on a UV-Vis spectrophotometer (UV-2550) using BaSO4 as reflectance standard, an integrating sphere attachment with the range from 200 to 800 nm. 2.4 Evaluation of photocatalytic activity The photocatalytic activities of the BOC and various C-BOC samples were evaluated by the photocatalytic degradation of RhB solution (20 mg/L, concentration). To investigate clearly the degradation process, 20 mg/L of RhB (Zhang et al., 2010; 6
Cong et al., 2006; Cong et al., 2007) was adopted rather than 10 mg/L of RhB in view of the outstanding photocatalytic performance of C-BOC photocatalyst. First, 50 mL of RhB solution and 50 mg of as-prepared photocatalysts were placed in a 100 mL beaker. After ultrasonic treatment for 5 min, the suspension was magnetically stirred (300 r/min) in the dark for 30 min to establish the adsorption-desorption equilibrium of RhB on the surface of the catalysts. A 300 W Xe arc lamp was used as the light source with the light intensity of 30 mW·cm−2. The residual RhB concentrations in the supernatant were analyzed by UV-Vis spectrophotometry at the certain times. The maximum absorption wavelength of RhB is located at 554 nm and the scanning range is from 200 to 800 nm.
3. Results and Discussion Figure 1 shows the XRD patterns of the BiOCl nanosheets synthesized with different amounts of glucose. The peaks of all obtained products are indexed to conventional BiOCl (JCPDS No. 06-0249) (Dong et al., 2016). It is noted that the diffraction intensity changes with the different amounts of glucose during the synthesis. For example, with the increase of glucose concentration, the diffraction intensity of the peak around 24o becomes higher than that around 26o. These peaks are corresponding to the (002) and (101) faces of BiOCl, respectively, which means the increased exposed ratio of the (002) faces and the decreased exposed ratio of the (101) faces. Moreover, compared to the intensity of the (001) face at 12o, the intensities of other peaks that are not assigned to the {001} group decreased. It implies that there 7
are more {001} faces exposed. It has been reported that BiOCl with {001} facet exposure possesses the enhanced photocatalytic ability of organic pollutant degradation (Li et al., 2015).
Figure 1. XRD patterns of BiOCl and three of C-BiOCl samples synthesized with various amount of glucose. Further, the full width at half-maximum (FWHM) of all peaks becomes larger gradually with much more glucose added during the synthesis process. It means that the crystalline grain size reduces according to the Scherrer equation D=Kλ/βcosθ (D-the average thickness of a grain perpendicular to the crystal face, K-the Scherrer constant, λ-the wavelength of X-Ray, β-the measured width at half intensity, θ-Bragg diffraction angle) (Holzwarth et al., 2011). The smaller size of the C-BOC photocatalyst would benefit the photocatalytic property due to the more catalytic active sites.
8
Figure 2. SEM images of BiOCl synthesized with (a) 0 mmol, (b) 1 mmol, (c) 2 mmol, and (d) 4 mmol Glucose. The morphology of the as-obtained BOC and C-BOC products are shown in Figure 2. All of samples are layered structure with high crystallinity. As depicted in Figure 2a, the BOC possesses the quadrate morphology with a surface area around 4 µm2. The general thickness is around 190 nm as demonstrated in the inset. By contrast, the surface areas of C-BOC samples obtained with 1, 2 and 4 mmol glucose are only approximately 0.09 µm2 measured by SEM images. Moreover, the corresponding thicknesses are about 55, 45 and 40 nm (Figure 2(b-d) and the insets). The smaller size of the C-BOC samples is consistent with the XRD analysis (Figure 1). The results indicate that the involving of carbon influences the growth of the BOC nanosheets. Evidently, carbon species impede the growth of BiOCl crystalline grain. It should be noted that the plates of bare BOC are smooth with good crystallinity, while those of 9
C-BOC possess the rough surfaces, suggesting higher accessible surface area for the tested process of RhB removal.
Figure 3. (a) TEM image and (b) HRTEM image of pristine BiOCl; (c) TEM image, (d) HRTEM image and (e-i) Elemental mapping of C-BOC nanosheets of Bi, Cl, O, C elements, and the merged image. Further analysis was performed based on the TEM images as shown in Figure 3. Figure 3a confirms that the surface of the pure BOC is clean and smooth. The lattice fringe image is clear and the crystal plane perpendicular to the surface is (110) plane (Lu et al., 2014; Yu et al., 2019) (Figure 3b). We marked the (110) plane in different position on the surface of the BOC. All the marked planes are in the same orientation, which indicates the high crystallinity in large area. We would like to propose the BOC nanocrystal as single crystal. With the carbon involved, the shape of the C-BOC 10
changes little but the size decreases obviously from ~2 µm to ~200 nm. Moreover, the lattice structure shows that there are many crystalline planes with different orientation (Figure 3d). It indicates that the C-BOC nanosheet is multicrystalline. Not only various orientations of planes but also some isolated carbon nanoclusters are detected on the surface of C-BOC nanosheets. The existence of the carbon nanoclusters might play an important role for the decrease of the sample size and the formation of the multicrytallization. The crystal growth of BOC is disturbed due to the existence of carbon. The elemental mapping of C-BOC (Figure 3(e-i)) shows the distribution of the Bi, Cl, O and C elements. It indicates the successful doping of carbon in the BOC nanosheets (Figure S2 in the Supporting information). The photocatalytic degradation of RhB over photocatalysts was performed by the illumination with the Xe arc lamp (Figure 4). Figure 4a shows the photocatalytic degradation of RhB with C-BOC nanosheets obtained from various addition of glucose. The surface adsorption property of RhB is obviously improved for different samples of C-BOC nanosheets. Without carbon involved, the adsorption of RhB is ~20%. With the involvement of carbon, the adsorption rates of RhB increase to ~40%, ~53%, and ~45% for the various addition of glucose of 1, 2, and 4 mmol. The more than one-fold improvement of adsorption can be assigned to the increase of surface area and improvement of adsorption property due to the modification of carbon clusters. After irradiated for 6 minutes by Xe arc lamp, the degradation rate of RhB with the BOC nanosheets is only 35%. With the involvement of carbon, the degradation rates increase to 80%, 100%, and 75% corresponding to various carbon 11
addition. The trend is consistent with the adsorption property. The relative low degradation rate with the highest carbon content should result from the thick covering of the BOC nanosheets which limits the light absorption and reduces the photocatalytic active sites. The C-BOC sample obtained with 2 mmol glucose is selected for the further study. The inset of Figure 4a displays the photos of the RhB supernatant extracted at 0, 2 and 4 minutes illumination with C-BOC nanosheets. Due to the high adsorption property of the C-BOC nanosheets of RhB, the reason of the RhB removal might be assigned to the adsorption instead of the degradation. The cyclic photocatalytic degradation process with BOC and C-BOC nanosheets is performed and shown in Figure 4b. The adsorption rates of RhB by BOC and C-BOC nanosheets decrease from ~20% and ~53% to ~10% and ~30%, respectively. Meanwhile, the degradation rates decrease. It indicates that the adsorption process contributes to the total rate of RhB removal. During the cyclic photocatalytic process with BOC nanosheets, the full degradation of RhB achieves at 40 minutes, however, it only approaches ~90% at 80 minutes for the second round, and merely approaches ~55% at 80 minutes for the third round. The significant decrease of the photocatalytic degradation property should be attributed to the adsorption along with a relatively low photocatalytic reaction rate. For the C-BOC nanosheets, during the cyclic photocatalytic process, the degradation of RhB at 10 minutes are all around 95%. The photocatalytic property of C-BOC nanosheets is much better than that of the BOC nanosheets. Inset of Figure 4b shows the adsorption of RhB by C-BOC and the compared illuminated area. Obviously, after the 5-minute illumination, the illuminated 12
area becomes decolorated. It indicates that the decoloring process can be assigned to the photocatalytic process of the C-BOC nanosheets (More details in Figure S3 in the Supporting information).
Figure 4. (a) Photodegradation of RhB over BOC samples with different amounts of glucose, (b) Cyclic photodegradation of RhB with pure BOC and C-BOC (2 mmol glucose) illuminated by Xe arc lamp. To discuss thoroughly the effect of carbon-induced on the structure of BOC, the XPS spectra of Bi, O and C elements, and the Raman spectra of BOC and C-BOC are shown in Figure 5 (the native photocatalyst was analyzed without any treatment). The typical peaks of Bi observed at 159.2 and 164.7 eV (Figure 5a) are assigned to Bi 4f5/2 and Bi 4f7/2, respectively (Yan et al., 2016; Ouyang et al., 2018). There is no change of the binding energy of Bi after introducing carbon. Besides the Bi-O peak located at 530.3 eV, a peak at 529.8 eV is coherent with C-O bonding in the C-BOC nanosheets (Yu et al., 2016) (Figure 5b). Moreover, as shown in the XPS spectra of C 1s (Figure 5c), the peak of 284.6 eV is the extraneous signal which is used as the internal reference, while the peak lies at 286.8 eV also can be assigned to the bonding of C-O in C-BOC nanostructures (Yang et al., 2007). The results confirm the doping 13
condition of carbon in the C-BOC nanosheets. As shown in the Raman spectra (Figure 5d), the peaks at 143.3 cm-1 (A1g) and 199.1 cm-1 (Eg) of Bi-Cl stretching vibration mode in BOC sample shift to 141.6 and 192.8 cm-1 in the C-BOC sample, respectively (Wang et al., 2019). These shifts indicate that the doping of carbon species influences the Bi-Cl bonding. The weaker intensity of the Eg mode with carbon illustrates the doping of carbon restrains the Eg mode vibration. In addition, the G band peak of carbon materials at 1494.6 cm-1 is observed in C-BOC sample but not in BOC, which approves the existence of the carbon clusters.
Figure 5. High-resolution XPS spectra of (a) Bi 4f, (b) O 1s, (c) C 1s, and (d) Raman spectra of BOC and C-BOC (2 mmol glucose). The photo-response properties of semiconductors depend on the band structure, 14
which is characterized by the UV-Vis diffuse reflectance absorption spectra (Figure 6a) and VBM measurement (Figure 6b). The adsorption edge of BOC sample is about 370 nm, while the edge extends to 750 nm with carbon nanoclusters loaded, shown in Figure 6a. The carbonaceous species doping in the host lattice of nanosheets generate an impurity energy level in the band gap and promote the adsorption of visible light. However, these impurity energy levels influence the band structure little. According to the tangency of two curves, both BOC and C-BOC have the same band gap (3.4 eV). The UV light is still utilized mainly. In Figure 6b, the VBM of BOC sample is 3.68 eV, while that of C-BOC is 3.38 eV. The impurity energy level may cause a shoulder-like peak. It is calculated that the locations of conduction band are 0.28 and -0.02 eV, respectively, corresponding to BOC and C-BOC. The transfer of charge carriers in BOC and C-BOC nanosheets, as well as the proposed photocatalytic mechanism is presented in Figure 6c. When irradiated by Xe arc lamp, the photocatalyst could absorb enough energy, the electrons (e-) in the valence band can be excited to the conduction band. The dual function carbon results in the bands shift-up and the construction of the heterostructure. This shift would contribute to reducing O2 into ·O2 radicals. Compared to BOC, the shift of band structure of C-BOC enhances the reduction property of the photo-induced electrons. Meanwhile, carbon species as active sites could facilitate the separation and transfer of photogenerated charge carriers. The O2 molecules capture the electrons in the excited state and turn into ·O2 radicals and the holes (h+) migrate to the surface and react with H2O or OH- to produce ·OH radicals (Fu et al., 2019; Li et al., 2018; He et al., 15
2013). That would be the key reason for the significant improvement of the photocatalytic degradation of RhB with C-BOC. It also implies that the degradation of RhB with BOC might be more related to the generation of ·O2 radicals.
Figure 6. (a) UV-Vis diffuse reflectance absorption spectra, (b) Valence band maximum (VBM) and (c) The proposed photocatalytic mechanism of BOC and C-BOC samples.
4. Conclusions A new-type C-BiOCl photocatalyst was fabricated by a facile one-pot hydrothermal process. BiOCl was modified by introducing glucose as carbon source to construct a composite material and C-BiOCl exhibited higher photocatalytic activity and cyclic stability. The C-BOC photocatalyst possessed a highest 16
photocatalytic performance with the degradation of RhB molecules in only 6 minutes. The dual functional carbon species improved effectively the separation and transfer of photogenerated charge carriers, and increase the active sites. It is also proposed with the BOC photocatalyst that the · O2 radicals dominate photocatalytic degradation of RhB. This work not only introduces a simple and low-cost approach to fabricating an ultra-highly efficient photocatalyst, but also comes up with a new concept “dual functional carbon” for designing and synthesizing high-performance photocatalyst. The photocatalyst with high efficiency is required for the industrial application in water pollution treatment.
Acknowledgements This work was supported by the National Key Research and Development Program of China (2017YFE0102700), and National Natural Science Foundation of China (Grant No. 51732007), Major Innovation Projects in Shandong Province (2018YFJH0503), The Science Fund for Distinguished Young Scholars of Shandong Province (ZR2019JQ16) and the Fundamental Research Funds of Shandong University (2018WLJH64). The authors are thankful for the support from the Collaborative Innovation Center of Technology and Equipment for Biological Diagnosis and Therapy in Universities of Shandong.
Declaration of competing interest The authors declare no competing interests. 17
References Aljerf, L., 2018. High-efficiency extraction of bromocresol purple dye and heavy metals as chromium from industrial effluent by adsorption onto a modified surface of zeolite: kinetics and equilibrium study. J. Environ. Manage. 225, 120-132. Tao, P., Xu, Y., Song, C., Yin, Y., Yang, Z., Wen, S., Wang, S., Liu, H., Li, S., Li, C., Shao, M., Wang, T., 2017. A novel strategy for the removal of rhodamine B (RhB) dye from wastewater by coal-based carbon membranes coupled with the electric field. Sep. Purif. Technol. 179, 175-183. Liu, W., Ai, Z., Zhang, L., 2012. Design of a neutral three-dimensional electro-Fenton system with foam nickel as particle electrodes for wastewater treatment. J. Hazard. Mater. 243, 257-264. Dong, W., Lee, C. W., Lu, X., Sun, Y., Hua, W., Zhuang, G., Zhang, S., Chen, J., Hou, H., Zhao, D., 2010. Synchronous role of coupled adsorption and photocatalytic oxidation on ordered mesoporous anatase TiO2-SiO2 nanocomposites generating excellent degradation activity of RhB dye. Appl. Catal. B: Environ. 95 (3-4), 197-207. Luan, J., Hou, P. X., Liu, C., Shi, C., Li, G. X., Cheng, H. M., 2016. Efficient adsorption of organic dyes on a flexible single-wall carbon nanotube film. J. Mater. Chem. A 4 (4), 1191-1194. Nayak, S., Swain, G., Parida, K., 2019. Enhanced Photocatalytic Activities of RhB Degradation and H2 Evolution from in Situ Formation of the Electrostatic Heterostructure MoS2/NiFe LDH Nanocomposite through the Z-Scheme Mechanism via p-n Heterojunctions. ACS Appl. Mater. Interfaces 11 (23), 20923-20942. 18
Hong, Y., Jiang, Y., Li, C., Fan, W., Yan, X., Yan, M., Shi, W., 2016. In-situ synthesis of direct solid-state Z-scheme V2O5/g-C3N4 heterojunctions with enhanced visible light efficiency in photocatalytic degradation of pollutants. Appl. Catal. B: Environ. 180, 663-673. Deng, Y., Liao, Q., Zou, X., Luo, J., Tang, J., 2019. Hematite mesocrystals templated by hydrolyzed and aminolyzed glycidyl methacrylate, and their application in photocatalytic Fenton reaction. Cryst. Eng. Comm. 21 (10), 1579-1586. Yu, C., Yang, P., Tie, L., Yang, S., Dong, S., Sun, J., Sun, J., 2018. One-pot fabrication of β-Bi2O3@ Bi2S3 hierarchical hollow spheres with advanced sunlight photocatalytic RhB oxidation and Cr (VI) reduction activities. Appl. Surf. Sci. 455, 8-17. Liang, H., Liu, S., Zhang, H., Wang, X., Wang, J., 2018. New insight into the selective photocatalytic oxidation of RhB through a strategy of modulating radical generation. RSC Adv. 8 (24), 13625-13634. Pan, D., Ge, S., Zhang, X., Mai, X., Li, S., Guo, Z., 2018. Synthesis and photoelectrocatalytic activity of In2O3 hollow microspheres via a bio-template route using yeast templates. Dalton T. 47 (3), 708-715. Zangeneh, H., Zinatizadeh, A. A. L., Habibi, M., Akia, M., Isa, M. H., 2015. Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review. J. Ind. Eng. Chem. 26, 1-36. Jing, T., Dai, Y., Ma, X., Wei, W., Huang, B., 2016. The photocatalytic properties of ultrathin bismuth oxychloride nanosheets: a first principles study. Phys. Chem. Chem. 19
Phys. 18(10), 7261-7268. Hu, J., Fan, W., Ye, W., Huang, C., Qiu, X., 2014. Insights into the photosensitivity activity of BiOCl under visible light irradiation. Appl. Catal. B: Environ. 158, 182-189. Zhang, K. L., Liu, C. M., Huang, F. Q., Zheng, C., Wang, W. D., 2006. Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst. Appl. Catal. B: Environ. 68 (3-4), 125-129. Mi, Y., Wen, L., Wang, Z., Cao, D., Xu, R., Fang, Y., Zhou, Y., Lei, Y., 2016. Fe(III) modified BiOCl ultrathin nanosheet towards high-efficient visible-light photocatalyst. Nano Energy 30, 109-117. Lv, Y., Liu, H., Zhang, W., Ran, S., Chi, F., Yang, B., Xia, A., 2013. Room-temperature synthesis and high visible-light-induced photocatalytic activity of AgI/BiOI composites. J. Environ. Chem. Eng. 1(3), 526-533. Kang, S., Pawar, R. C., Lee, C. S., 2016. Decoration of Au nanoparticles onto BiOCl sheets for enhanced photocatalytic performance under visible irradiation for the degradation of RhB dye. J. Exp. Nanosci. 11(11), 853-871. Li, J., Zhao, K., Yu, Y., Zhang, L., 2015. Facet-Level Mechanistic Insights into General Homogeneous Carbon Doping for Enhanced Solar-to-Hydrogen Conversion. Adv. Funct. Mater. 25 (14), 2189-2201. Li, J., Cai, L., Shang, J., Yu, Y., Zhang, L., 2016. Giant enhancement of internal electric field boosting bulk charge separation for photocatalysis. Adv. Mater. 28 (21), 4059-4064.
20
Zhang, S., Wang, D., Song, L., 2016. A novel F-doped BiOCl photocatalyst with enhanced photocatalytic performance. Mater. Chem. Phys. 173, 298-308. Jiang, Z., Liu, Y., Jing, T., Huang, B., Wang, Z., Zhang, X., Qin, X., Dai, Y., 2015. One-pot solvothermal synthesis of S doped BiOCl for solar water oxidation. RSC Adv. 5 (58), 47261-47264. Leary, R., Westwood, A., 2011. Carbonaceous nanomaterials for the enhancement of TiO2 photocatalysis. Carbon 49(3), 741-772. Ren, C., Yang, B., Wu, M., Xu, J., Fu, Z., Yan, L., Guo, T., Zhao, Y., Zhu, C., 2010. Synthesis of Ag/ZnO nanorods array with enhanced photocatalytic performance. J. Hazard. Mater. 182 (1-3), 123-129. Bai, S., Li, H., Guan, Y., Jiang, S., 2011. The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes. Appl. Surf. Sci. 257 (15), 6406-6409. Zhang, A., He, R., Li, H., Chen, Y., Kong, T., Li, K., Ju. H., Zhu. J., Zhu. W., Zeng, J., 2018. Nickel doping in atomically thin tin disulfide nanosheets enables highly efficient CO2 reduction. Angew. Chem. Int. Edit. 57 (34), 10954-10958. Height, M. J., Pratsinis, S. E., Mekasuwandumrong, O., Praserthdam, P., 2006. Ag-ZnO catalysts for UV-photodegradation of methylene blue. Appl. Catal. B: Environ. 63 (3-4), 305-312. Huo, Y., Yang, X., Zhu, J., Li, H., 2011. Highly active and stable CdS-TiO2 visible photocatalyst prepared by in situ sulfurization under supercritical conditions. Appl. Catal. B: Environ. 106 (1-2), 69-75. 21
Holzwarth, U., Gibson, N., 2011. The Scherrer equation versus the'Debye-Scherrer equation'. Nat. nanotechnol. 6 (9), 534. Guo, Y., Wang, Z., Shao, H., Jiang, X., 2013. Hydrothermal synthesis of highly fluorescent carbon nanoparticles from sodium citrate and their use for the detection of mercury ions. Carbon 52, 583-589. He, X., Li, H., Liu, Y., Huang, H., Kang, Z., Lee, S. T., 2011. Water soluble carbon nanoparticles:
hydrothermal
synthesis
and
excellent
photoluminescence
properties. Colloids Surf. B 87(2), 326-332. Zhang, J., Wu, Y., Xing, M., Leghari, S. A. K., Sajjad, S., 2010. Development of modified N doped TiO2 photocatalyst with metals, nonmetals and metal oxides. Energy Environ. Sci. 3(6), 715-726. Cong, Y., Chen, F., Zhang, J., Anpo, M., 2006. Carbon and nitrogen-codoped TiO2 with high visible light photocatalytic activity. Chem. Lett. 35(7), 800-801. Cong, Y., Zhang, J., Chen, F., Anpo, M., He, D., 2007. Preparation, photocatalytic activity, and mechanism of nano-TiO2 co-doped with nitrogen and iron (III). J. Phys. Chem. C 111(28), 10618-10623. Dong, F., Xiong, T., Yan, S., Wang, H., Sun, Y., Zhang, Y., Huang. H., Wu, Z., 2016. Facets and defects cooperatively promote visible light plasmonic photocatalysis with Bi nanowires @ BiOCl nanosheets. J. Catal. 344, 401-410. Lu, H., Xu, L., Wei, B., Zhang, M., Gao, H., Sun, W., 2014. Enhanced photosensitization process induced by the p-n junction of Bi2O2CO3/BiOCl heterojunctions on the degradation of rhodamine B. Appl. Surf. Sci. 303, 360-366. 22
Yan, X., Zhu, X., Li, R., Chen, W., 2016. Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light. J. Hazard. Mater. 303, 1-9. Yu, L., Zhang, X., Li, G., Cao, Y., Shao, Y., Li, D., 2016. Highly efficient Bi2O2CO3/BiOCl
photocatalyst
based
on
heterojunction
with
enhanced
dye-sensitization under visible light. Appl. Catal. B: Environ. 187, 301-309. Yang, X., Cao, C., Hohn, K., Erickson, L., Maghirang, R., Hamal, D., Klabunde, K., 2007. Highly visible-light active C-and V-doped TiO2 for degradation of acetaldehyde. J. Catal. 252 (2), 296-302. Fu, S., Liu, X., Yan, Y., Li, L., Liu, H., Zhao, F., Zhou, J., 2019. Few-layer WS2 modified BiOBr nanosheets with enhanced broad-spectrum photocatalytic activity towards various pollutants removal. Sci. Total Environ. 133756. Yu, C., He, H., Fan, Q., Xie, W., Liu, Z., Ji, H., 2019. Novel B-doped BiOCl nanosheets with exposed (001) facets and photocatalytic mechanism of enhanced degradation efficiency for organic pollutants. Sci. Total Environ. 133727. Li, H., Li, J., Ai, Z., Jia, F., Zhang, L., 2018. Oxygen vacancy-mediated photocatalysis of BiOCl: reactivity, selectivity, and perspectives. Angew. Chem. Int. Edit. 57 (1), 122-138. Ouyang, W., Teng, F., Fang, X., 2018. High Performance BiOCl Nanosheets/TiO2 Nanotube Arrays Heterojunction UV Photodetector: The Influences of Self-Induced Inner Electric Fields in the BiOCl Nanosheets. Adv. Funct. Mater. 28 (16), 1707178.
23
He, Z., Shi, Y., Gao, C., Wen, L., Chen, J., Song, S., 2013. BiOCl/BiVO4 p-n heterojunction with enhanced photocatalytic activity under visible-light irradiation. J. Phys. Chem. C 118 (1), 389-398. Wang, L., Lv, D., Yue, Z., Zhu, H., Wang, L., Wang, D., Xu, X., Hao, W., Dou, S. X., Du, Y., 2019. Promoting photoreduction properties via synergetic utilization between plasmonic effect and highly active facet of BiOCl. Nano Energy 57, 398-404. Dukali, R. M., Radović, I. M., Stojanović, D. B., Šević, D. D., Radojević, V. J., Jocić, D. M., Aleksić, R. R., 2014. Electrospinning of laser dye Rhodamine B-doped poly (methyl methacrylate) nanofibers. J. Serb. Chem. Soc. 79(7), 867-880.
24
TOC One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB
25
One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB
Highlights
Carbon-modified BiOCl (C-BOC) photocatalyst was synthesized by one-pot method. The dual functions of carbon were proposed. C-BOC could degrade RhB completely in 6 minutes.
Dear Editors, We declare that we have no financial and personal relationships with any organizations or individuals that can inappropriately influence our work.
Yours sincerely, Yuanhua Sang Professor State Key Laboratory of Crystal Materials Shandong University Jinan, 250100, China
S0013-9351(19)30873-4
DOI:
https://doi.org/10.1016/j.envres.2019.109077
Reference:
YENRS 109077
To appear in:
Environmental Research
Received Date: 28 September 2019 Revised Date:
28 November 2019
Accepted Date: 21 December 2019
Please cite this article as: Li, Z., Ma, B., Zhang, X., Sang, Y., Liu, H., One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB, Environmental Research (2020), doi: https://doi.org/10.1016/j.envres.2019.109077. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB Zhao Lia, Baojin Maa, Xiaofei Zhanga, Yuanhua Sanga* and Hong Liua,b
a
State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, PR China b Institute for Advanced Interdisciplinary Research, University of Jinan, Jinan 250022, Shandong, PR China * Corresponding Author. Email: [email protected]
Abstract: Water pollution from Rhodamine B (RhB) has become a challenging problem which human beings are urgent to confront. A high-efficiency photocatalysis system is required for the industrial application. A novel carbon doped bismuth oxychloride (C-BiOCl) composite photocatalyst with dual functional carbon was synthesized by one-pot hydrothermal process. The introduction of the carbon in the synthesis modified the morphology of BiOCl by suppressing the growing-up of the layered structures, which resulted in more active catalytic sites and shorter path of charge transfer. Moreover, the doped carbon would improve the utilization of light, and shift the band structures of the BiOCl. The as-synthesized C-BiOCl possesses a significant improvement (around 400%) on the photocatalytic degradation of RhB. Therefore, this efficient photocatalyst with dual functional carbon has been synthesized and would be regarded as a novel strategy for the design of high-performance photocatalysts. Keywords: Dual functional carbon; BiOCl nanosheets; Ultra-high efficiency; Doping; Heterostructure; Photocatalytic degradation 1
1. Introduction The energy crisis and environmental pollution have attracted much attention worldwide with the development of science and technology. Water pollution is one of the most intractable issues which threats our survival. The dyestuff is one of the most notorious contaminants in water ecosystem owing to their great output from industries, toxicity and difficulty of biodegradation (Aljerf, 2018). Rhodamine B (RhB), a kind of xanthene dye, is harmful to human beings resulting in irreversible irritation to the skin, eyes and respiratory tract (Dong et al., 2010). And the concentration of RhB in wastewater even exceeds 100 ppm in many conditions (Tao et al., 2017). However, the RhB removal efficiency of the counterpart three-dimensional electrochemical system and E-Fenton system are lower than 35% at neutral pH in 30 minutes (Liu et al., 2012). The basic strategies of removing RhB from water are the adsorption and oxidation processes. For instance, the activated carbon is used to adsorb the RhB molecular (Luan et al., 2016), however, after the adsorption, the activated carbon becomes a secondary pollution before further treatment. Essentially, this process is considered as a transfer of the pollution rather than degradation, which would be limited in the industrial application. The oxidation process could degrade the RhB molecules into non-toxic molecules, even into inorganic molecules and H2O (Nayak et al., 2019; Hong et al., 2016). A number of approaches have been researched, such as Fenton and photo-Fenton processes (Deng et al., 2019), photocatalytic oxidation (Yu et al., 2018; Liang et al., 2018), and photoelectrocatalytic oxidation (Pan et al., 2018). Among these approaches, photocatalytic oxidation is regarded as a promising 2
and operable direction to deal with organic dyes without further consumption material and energy (Zangeneh et al., 2015). The researches on dyes degradation are fabulous in amount, yet the photocatalytic efficiency is still too low to be applied industrially. Bismuth oxychloride (BiOCl) is an indirect band-gap semiconductor with negligible photocatalytic property (Jing et al., 2016). It possesses a tetragonal layered structure and contains [Cl-Bi-O-Bi-Cl] sheets with the Cl atoms along the c-axis by van der Waals force (Hu et al., 2014; Zhang et al., 2006; Mi et al., 2016). BiOCl also belongs to the family of main group multicomponent metal oxyhalides V-VI-VII, a significant category of ternary compounds because of the outstanding electrical, magnetic, optical, luminescent and catalytic properties (Lv et al., 2013). The bipyramidal crystal geometry of BiOCl usually grows in flakes or sheets regularly. This lamellar nanostructure with high crystallinity and ultrathin thickness can reduce the recombination of photogenerated electrons and holes (Kang et al., 2016). Thus, the photogenerated charge carriers can transfer to the surface quickly to react with the organic pollutant molecules. These properties imply it a good candidate as photocatalyst which is inconsistent with the weak photocatalytic property. Therefore, the improvement of the photocatalytic property of BiOCl has attracted extensive interests. And elemental doping is an effective and simple means to modify semiconductor photocatalysts (Li et al., 2015; Li et al., 2016; Zhang et al., 2018). For example, Song et al. reported that the crystal lattice and surface properties of BiOCl was modified by doping with fluorine ions and the as-obtained F-BiOCl degraded RhB in 30 minutes under visible light irradiation (Zhang et al., 2016). Huang et al. 3
proposed that the introducing of S element into BiOCl photocatalyst without forming any segregated impurity phase not only extended the light absorption range but also enhanced the separation efficiency of the photogenerated charge carriers. The photocatalytic O2 evolution of S-BiOCl was enhanced four times by that of BiOCl (Jiang et al., 2015). Song’s Group also found that with the doping of fluorine ions (F-), the size of the as-obtained BiOCl nanosheets reduced (Zhang et al., 2016). Besides that, carbon as a kind of vital nonmetallic element, has also attracted much attention. Combining TiO2 with carbonaceous species is regarded as a method to enhance photocatalytic activity by inhibiting charge carrier recombination and promoting the absorption of light. Thus, it will be interesting and meaningful to apply this idea into BiOCl material (Leary et al., 2011). In addition to the regulation of band gap and surface catalytic activity, the key point of doping mediated modification is to construct the composite material. As far as the heterostructure is constructed, the regulation of charge carriers would be more efficient, such as Ag/ZnO (Ren et al., 2010; Height et al., 2006) and CdS/TiO2 (Bai et al., 2011; Huo et al., 2011) heterojunctions, etc. As is well accepted, carbon nanoparticles would form during the acid/alkali-assisted hydrothermal process, and the precursor could be sodium citrate (Guo et al., 2013), glucose or sucrose (He et al., 2011). Once the carbon doping and the formation of heterostructure between C and BiOCl could achieve at the same time, the photocatalytic efficiency would be improved greatly. Herein, we synthesized a novel C-BiOCl composite photocatalyst via a one-pot 4
hydrothermal process. The photocatalytic property was evaluated via the photocatalytic degradation of RhB. The mechanism of the improvement was also discussed. The elemental doping and surface heterostructure construction should be the mean reasons. Thus, the dual functions of the carbon in the C-BiOCl photocatalyst was proposed. It is believed that this one-pot hydrothermal process for dual functional carbon synthesis will be beneficial to the study of high-efficiency photocatalyst.
2. Experimental procedures 2.1 Materials All the reagents in this work are analytic grade and commercially available. Bismuth nitrate (Bi(NO3)3·5H2O), potassium chloride (KCl), Glucose, ethanol and Rhodamine B (RhB) were purchased from Sinopharm Chemical Reagent Co., Ltd. All of the chemicals were used as purchased without further purification. 2.2 Synthesis The synthesis of BiOCl (BOC) and C-BiOCl (C-BOC) nanosheets were proceeded via the hydrothermal process, as illustrated in Scheme S1 in the Supporting Information. Typically, Bi(NO3)3 ·5H2O (1 mmol) was dissolved in 70 mL of deionized water, followed by the addition of KCl (1 mmol) under continuous stirring (300 r/min) for 30 minutes. Then added 0, 1, 2, and 4 mmol of glucose into the previous solutions, respectively. The solutions were transferred to the 100 mL Teflon-lined autoclaves and carried out the hydrothermal treatment at 120 oC for 10 h. After cooling down naturally, the products were washed with deionized (DI) water 5
and alcohol thoroughly. The samples of BOC and C-BOC (Figure S1 in the Supporting information) with different concentration of carbon were obtained after drying at 60 oC for 12h. 2.3 Characterization The X-ray powder diffraction patterns of the samples were measured by a Bruker D8 Advance powder X-ray diffractometer (XRD) with Cu Kα radiation (λ=0.1541 nm). The morphology was captured on a HITACHI S-4800 field emission scanning electron microscope (FESEM). The high-resolution transmission electron microscopic (HRTEM) images were scanned with a JEOL JEM 2100 microscope operated at 200 kV. The residual concentrations of RhB solution were tested by UV-Vis spectrophotometry (UV-2102PC). X-ray photoelectron spectroscopy (XPS) spectra and the valence band maximum (VBM) measurement were analyzed with an ESCALAB 250 instrument. Fourier Transform infrared spectra (FT-IR) was detected on a Thermo Nexus 670 spectrometer. A Renishaw 1000 microspectrometer with an excitation wavelength of 514.5 nm collected Raman spectra. UV-Vis diffuse reflectance spectra (DRS) was measured on a UV-Vis spectrophotometer (UV-2550) using BaSO4 as reflectance standard, an integrating sphere attachment with the range from 200 to 800 nm. 2.4 Evaluation of photocatalytic activity The photocatalytic activities of the BOC and various C-BOC samples were evaluated by the photocatalytic degradation of RhB solution (20 mg/L, concentration). To investigate clearly the degradation process, 20 mg/L of RhB (Zhang et al., 2010; 6
Cong et al., 2006; Cong et al., 2007) was adopted rather than 10 mg/L of RhB in view of the outstanding photocatalytic performance of C-BOC photocatalyst. First, 50 mL of RhB solution and 50 mg of as-prepared photocatalysts were placed in a 100 mL beaker. After ultrasonic treatment for 5 min, the suspension was magnetically stirred (300 r/min) in the dark for 30 min to establish the adsorption-desorption equilibrium of RhB on the surface of the catalysts. A 300 W Xe arc lamp was used as the light source with the light intensity of 30 mW·cm−2. The residual RhB concentrations in the supernatant were analyzed by UV-Vis spectrophotometry at the certain times. The maximum absorption wavelength of RhB is located at 554 nm and the scanning range is from 200 to 800 nm.
3. Results and Discussion Figure 1 shows the XRD patterns of the BiOCl nanosheets synthesized with different amounts of glucose. The peaks of all obtained products are indexed to conventional BiOCl (JCPDS No. 06-0249) (Dong et al., 2016). It is noted that the diffraction intensity changes with the different amounts of glucose during the synthesis. For example, with the increase of glucose concentration, the diffraction intensity of the peak around 24o becomes higher than that around 26o. These peaks are corresponding to the (002) and (101) faces of BiOCl, respectively, which means the increased exposed ratio of the (002) faces and the decreased exposed ratio of the (101) faces. Moreover, compared to the intensity of the (001) face at 12o, the intensities of other peaks that are not assigned to the {001} group decreased. It implies that there 7
are more {001} faces exposed. It has been reported that BiOCl with {001} facet exposure possesses the enhanced photocatalytic ability of organic pollutant degradation (Li et al., 2015).
Figure 1. XRD patterns of BiOCl and three of C-BiOCl samples synthesized with various amount of glucose. Further, the full width at half-maximum (FWHM) of all peaks becomes larger gradually with much more glucose added during the synthesis process. It means that the crystalline grain size reduces according to the Scherrer equation D=Kλ/βcosθ (D-the average thickness of a grain perpendicular to the crystal face, K-the Scherrer constant, λ-the wavelength of X-Ray, β-the measured width at half intensity, θ-Bragg diffraction angle) (Holzwarth et al., 2011). The smaller size of the C-BOC photocatalyst would benefit the photocatalytic property due to the more catalytic active sites.
8
Figure 2. SEM images of BiOCl synthesized with (a) 0 mmol, (b) 1 mmol, (c) 2 mmol, and (d) 4 mmol Glucose. The morphology of the as-obtained BOC and C-BOC products are shown in Figure 2. All of samples are layered structure with high crystallinity. As depicted in Figure 2a, the BOC possesses the quadrate morphology with a surface area around 4 µm2. The general thickness is around 190 nm as demonstrated in the inset. By contrast, the surface areas of C-BOC samples obtained with 1, 2 and 4 mmol glucose are only approximately 0.09 µm2 measured by SEM images. Moreover, the corresponding thicknesses are about 55, 45 and 40 nm (Figure 2(b-d) and the insets). The smaller size of the C-BOC samples is consistent with the XRD analysis (Figure 1). The results indicate that the involving of carbon influences the growth of the BOC nanosheets. Evidently, carbon species impede the growth of BiOCl crystalline grain. It should be noted that the plates of bare BOC are smooth with good crystallinity, while those of 9
C-BOC possess the rough surfaces, suggesting higher accessible surface area for the tested process of RhB removal.
Figure 3. (a) TEM image and (b) HRTEM image of pristine BiOCl; (c) TEM image, (d) HRTEM image and (e-i) Elemental mapping of C-BOC nanosheets of Bi, Cl, O, C elements, and the merged image. Further analysis was performed based on the TEM images as shown in Figure 3. Figure 3a confirms that the surface of the pure BOC is clean and smooth. The lattice fringe image is clear and the crystal plane perpendicular to the surface is (110) plane (Lu et al., 2014; Yu et al., 2019) (Figure 3b). We marked the (110) plane in different position on the surface of the BOC. All the marked planes are in the same orientation, which indicates the high crystallinity in large area. We would like to propose the BOC nanocrystal as single crystal. With the carbon involved, the shape of the C-BOC 10
changes little but the size decreases obviously from ~2 µm to ~200 nm. Moreover, the lattice structure shows that there are many crystalline planes with different orientation (Figure 3d). It indicates that the C-BOC nanosheet is multicrystalline. Not only various orientations of planes but also some isolated carbon nanoclusters are detected on the surface of C-BOC nanosheets. The existence of the carbon nanoclusters might play an important role for the decrease of the sample size and the formation of the multicrytallization. The crystal growth of BOC is disturbed due to the existence of carbon. The elemental mapping of C-BOC (Figure 3(e-i)) shows the distribution of the Bi, Cl, O and C elements. It indicates the successful doping of carbon in the BOC nanosheets (Figure S2 in the Supporting information). The photocatalytic degradation of RhB over photocatalysts was performed by the illumination with the Xe arc lamp (Figure 4). Figure 4a shows the photocatalytic degradation of RhB with C-BOC nanosheets obtained from various addition of glucose. The surface adsorption property of RhB is obviously improved for different samples of C-BOC nanosheets. Without carbon involved, the adsorption of RhB is ~20%. With the involvement of carbon, the adsorption rates of RhB increase to ~40%, ~53%, and ~45% for the various addition of glucose of 1, 2, and 4 mmol. The more than one-fold improvement of adsorption can be assigned to the increase of surface area and improvement of adsorption property due to the modification of carbon clusters. After irradiated for 6 minutes by Xe arc lamp, the degradation rate of RhB with the BOC nanosheets is only 35%. With the involvement of carbon, the degradation rates increase to 80%, 100%, and 75% corresponding to various carbon 11
addition. The trend is consistent with the adsorption property. The relative low degradation rate with the highest carbon content should result from the thick covering of the BOC nanosheets which limits the light absorption and reduces the photocatalytic active sites. The C-BOC sample obtained with 2 mmol glucose is selected for the further study. The inset of Figure 4a displays the photos of the RhB supernatant extracted at 0, 2 and 4 minutes illumination with C-BOC nanosheets. Due to the high adsorption property of the C-BOC nanosheets of RhB, the reason of the RhB removal might be assigned to the adsorption instead of the degradation. The cyclic photocatalytic degradation process with BOC and C-BOC nanosheets is performed and shown in Figure 4b. The adsorption rates of RhB by BOC and C-BOC nanosheets decrease from ~20% and ~53% to ~10% and ~30%, respectively. Meanwhile, the degradation rates decrease. It indicates that the adsorption process contributes to the total rate of RhB removal. During the cyclic photocatalytic process with BOC nanosheets, the full degradation of RhB achieves at 40 minutes, however, it only approaches ~90% at 80 minutes for the second round, and merely approaches ~55% at 80 minutes for the third round. The significant decrease of the photocatalytic degradation property should be attributed to the adsorption along with a relatively low photocatalytic reaction rate. For the C-BOC nanosheets, during the cyclic photocatalytic process, the degradation of RhB at 10 minutes are all around 95%. The photocatalytic property of C-BOC nanosheets is much better than that of the BOC nanosheets. Inset of Figure 4b shows the adsorption of RhB by C-BOC and the compared illuminated area. Obviously, after the 5-minute illumination, the illuminated 12
area becomes decolorated. It indicates that the decoloring process can be assigned to the photocatalytic process of the C-BOC nanosheets (More details in Figure S3 in the Supporting information).
Figure 4. (a) Photodegradation of RhB over BOC samples with different amounts of glucose, (b) Cyclic photodegradation of RhB with pure BOC and C-BOC (2 mmol glucose) illuminated by Xe arc lamp. To discuss thoroughly the effect of carbon-induced on the structure of BOC, the XPS spectra of Bi, O and C elements, and the Raman spectra of BOC and C-BOC are shown in Figure 5 (the native photocatalyst was analyzed without any treatment). The typical peaks of Bi observed at 159.2 and 164.7 eV (Figure 5a) are assigned to Bi 4f5/2 and Bi 4f7/2, respectively (Yan et al., 2016; Ouyang et al., 2018). There is no change of the binding energy of Bi after introducing carbon. Besides the Bi-O peak located at 530.3 eV, a peak at 529.8 eV is coherent with C-O bonding in the C-BOC nanosheets (Yu et al., 2016) (Figure 5b). Moreover, as shown in the XPS spectra of C 1s (Figure 5c), the peak of 284.6 eV is the extraneous signal which is used as the internal reference, while the peak lies at 286.8 eV also can be assigned to the bonding of C-O in C-BOC nanostructures (Yang et al., 2007). The results confirm the doping 13
condition of carbon in the C-BOC nanosheets. As shown in the Raman spectra (Figure 5d), the peaks at 143.3 cm-1 (A1g) and 199.1 cm-1 (Eg) of Bi-Cl stretching vibration mode in BOC sample shift to 141.6 and 192.8 cm-1 in the C-BOC sample, respectively (Wang et al., 2019). These shifts indicate that the doping of carbon species influences the Bi-Cl bonding. The weaker intensity of the Eg mode with carbon illustrates the doping of carbon restrains the Eg mode vibration. In addition, the G band peak of carbon materials at 1494.6 cm-1 is observed in C-BOC sample but not in BOC, which approves the existence of the carbon clusters.
Figure 5. High-resolution XPS spectra of (a) Bi 4f, (b) O 1s, (c) C 1s, and (d) Raman spectra of BOC and C-BOC (2 mmol glucose). The photo-response properties of semiconductors depend on the band structure, 14
which is characterized by the UV-Vis diffuse reflectance absorption spectra (Figure 6a) and VBM measurement (Figure 6b). The adsorption edge of BOC sample is about 370 nm, while the edge extends to 750 nm with carbon nanoclusters loaded, shown in Figure 6a. The carbonaceous species doping in the host lattice of nanosheets generate an impurity energy level in the band gap and promote the adsorption of visible light. However, these impurity energy levels influence the band structure little. According to the tangency of two curves, both BOC and C-BOC have the same band gap (3.4 eV). The UV light is still utilized mainly. In Figure 6b, the VBM of BOC sample is 3.68 eV, while that of C-BOC is 3.38 eV. The impurity energy level may cause a shoulder-like peak. It is calculated that the locations of conduction band are 0.28 and -0.02 eV, respectively, corresponding to BOC and C-BOC. The transfer of charge carriers in BOC and C-BOC nanosheets, as well as the proposed photocatalytic mechanism is presented in Figure 6c. When irradiated by Xe arc lamp, the photocatalyst could absorb enough energy, the electrons (e-) in the valence band can be excited to the conduction band. The dual function carbon results in the bands shift-up and the construction of the heterostructure. This shift would contribute to reducing O2 into ·O2 radicals. Compared to BOC, the shift of band structure of C-BOC enhances the reduction property of the photo-induced electrons. Meanwhile, carbon species as active sites could facilitate the separation and transfer of photogenerated charge carriers. The O2 molecules capture the electrons in the excited state and turn into ·O2 radicals and the holes (h+) migrate to the surface and react with H2O or OH- to produce ·OH radicals (Fu et al., 2019; Li et al., 2018; He et al., 15
2013). That would be the key reason for the significant improvement of the photocatalytic degradation of RhB with C-BOC. It also implies that the degradation of RhB with BOC might be more related to the generation of ·O2 radicals.
Figure 6. (a) UV-Vis diffuse reflectance absorption spectra, (b) Valence band maximum (VBM) and (c) The proposed photocatalytic mechanism of BOC and C-BOC samples.
4. Conclusions A new-type C-BiOCl photocatalyst was fabricated by a facile one-pot hydrothermal process. BiOCl was modified by introducing glucose as carbon source to construct a composite material and C-BiOCl exhibited higher photocatalytic activity and cyclic stability. The C-BOC photocatalyst possessed a highest 16
photocatalytic performance with the degradation of RhB molecules in only 6 minutes. The dual functional carbon species improved effectively the separation and transfer of photogenerated charge carriers, and increase the active sites. It is also proposed with the BOC photocatalyst that the · O2 radicals dominate photocatalytic degradation of RhB. This work not only introduces a simple and low-cost approach to fabricating an ultra-highly efficient photocatalyst, but also comes up with a new concept “dual functional carbon” for designing and synthesizing high-performance photocatalyst. The photocatalyst with high efficiency is required for the industrial application in water pollution treatment.
Acknowledgements This work was supported by the National Key Research and Development Program of China (2017YFE0102700), and National Natural Science Foundation of China (Grant No. 51732007), Major Innovation Projects in Shandong Province (2018YFJH0503), The Science Fund for Distinguished Young Scholars of Shandong Province (ZR2019JQ16) and the Fundamental Research Funds of Shandong University (2018WLJH64). The authors are thankful for the support from the Collaborative Innovation Center of Technology and Equipment for Biological Diagnosis and Therapy in Universities of Shandong.
Declaration of competing interest The authors declare no competing interests. 17
References Aljerf, L., 2018. High-efficiency extraction of bromocresol purple dye and heavy metals as chromium from industrial effluent by adsorption onto a modified surface of zeolite: kinetics and equilibrium study. J. Environ. Manage. 225, 120-132. Tao, P., Xu, Y., Song, C., Yin, Y., Yang, Z., Wen, S., Wang, S., Liu, H., Li, S., Li, C., Shao, M., Wang, T., 2017. A novel strategy for the removal of rhodamine B (RhB) dye from wastewater by coal-based carbon membranes coupled with the electric field. Sep. Purif. Technol. 179, 175-183. Liu, W., Ai, Z., Zhang, L., 2012. Design of a neutral three-dimensional electro-Fenton system with foam nickel as particle electrodes for wastewater treatment. J. Hazard. Mater. 243, 257-264. Dong, W., Lee, C. W., Lu, X., Sun, Y., Hua, W., Zhuang, G., Zhang, S., Chen, J., Hou, H., Zhao, D., 2010. Synchronous role of coupled adsorption and photocatalytic oxidation on ordered mesoporous anatase TiO2-SiO2 nanocomposites generating excellent degradation activity of RhB dye. Appl. Catal. B: Environ. 95 (3-4), 197-207. Luan, J., Hou, P. X., Liu, C., Shi, C., Li, G. X., Cheng, H. M., 2016. Efficient adsorption of organic dyes on a flexible single-wall carbon nanotube film. J. Mater. Chem. A 4 (4), 1191-1194. Nayak, S., Swain, G., Parida, K., 2019. Enhanced Photocatalytic Activities of RhB Degradation and H2 Evolution from in Situ Formation of the Electrostatic Heterostructure MoS2/NiFe LDH Nanocomposite through the Z-Scheme Mechanism via p-n Heterojunctions. ACS Appl. Mater. Interfaces 11 (23), 20923-20942. 18
Hong, Y., Jiang, Y., Li, C., Fan, W., Yan, X., Yan, M., Shi, W., 2016. In-situ synthesis of direct solid-state Z-scheme V2O5/g-C3N4 heterojunctions with enhanced visible light efficiency in photocatalytic degradation of pollutants. Appl. Catal. B: Environ. 180, 663-673. Deng, Y., Liao, Q., Zou, X., Luo, J., Tang, J., 2019. Hematite mesocrystals templated by hydrolyzed and aminolyzed glycidyl methacrylate, and their application in photocatalytic Fenton reaction. Cryst. Eng. Comm. 21 (10), 1579-1586. Yu, C., Yang, P., Tie, L., Yang, S., Dong, S., Sun, J., Sun, J., 2018. One-pot fabrication of β-Bi2O3@ Bi2S3 hierarchical hollow spheres with advanced sunlight photocatalytic RhB oxidation and Cr (VI) reduction activities. Appl. Surf. Sci. 455, 8-17. Liang, H., Liu, S., Zhang, H., Wang, X., Wang, J., 2018. New insight into the selective photocatalytic oxidation of RhB through a strategy of modulating radical generation. RSC Adv. 8 (24), 13625-13634. Pan, D., Ge, S., Zhang, X., Mai, X., Li, S., Guo, Z., 2018. Synthesis and photoelectrocatalytic activity of In2O3 hollow microspheres via a bio-template route using yeast templates. Dalton T. 47 (3), 708-715. Zangeneh, H., Zinatizadeh, A. A. L., Habibi, M., Akia, M., Isa, M. H., 2015. Photocatalytic oxidation of organic dyes and pollutants in wastewater using different modified titanium dioxides: A comparative review. J. Ind. Eng. Chem. 26, 1-36. Jing, T., Dai, Y., Ma, X., Wei, W., Huang, B., 2016. The photocatalytic properties of ultrathin bismuth oxychloride nanosheets: a first principles study. Phys. Chem. Chem. 19
Phys. 18(10), 7261-7268. Hu, J., Fan, W., Ye, W., Huang, C., Qiu, X., 2014. Insights into the photosensitivity activity of BiOCl under visible light irradiation. Appl. Catal. B: Environ. 158, 182-189. Zhang, K. L., Liu, C. M., Huang, F. Q., Zheng, C., Wang, W. D., 2006. Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst. Appl. Catal. B: Environ. 68 (3-4), 125-129. Mi, Y., Wen, L., Wang, Z., Cao, D., Xu, R., Fang, Y., Zhou, Y., Lei, Y., 2016. Fe(III) modified BiOCl ultrathin nanosheet towards high-efficient visible-light photocatalyst. Nano Energy 30, 109-117. Lv, Y., Liu, H., Zhang, W., Ran, S., Chi, F., Yang, B., Xia, A., 2013. Room-temperature synthesis and high visible-light-induced photocatalytic activity of AgI/BiOI composites. J. Environ. Chem. Eng. 1(3), 526-533. Kang, S., Pawar, R. C., Lee, C. S., 2016. Decoration of Au nanoparticles onto BiOCl sheets for enhanced photocatalytic performance under visible irradiation for the degradation of RhB dye. J. Exp. Nanosci. 11(11), 853-871. Li, J., Zhao, K., Yu, Y., Zhang, L., 2015. Facet-Level Mechanistic Insights into General Homogeneous Carbon Doping for Enhanced Solar-to-Hydrogen Conversion. Adv. Funct. Mater. 25 (14), 2189-2201. Li, J., Cai, L., Shang, J., Yu, Y., Zhang, L., 2016. Giant enhancement of internal electric field boosting bulk charge separation for photocatalysis. Adv. Mater. 28 (21), 4059-4064.
20
Zhang, S., Wang, D., Song, L., 2016. A novel F-doped BiOCl photocatalyst with enhanced photocatalytic performance. Mater. Chem. Phys. 173, 298-308. Jiang, Z., Liu, Y., Jing, T., Huang, B., Wang, Z., Zhang, X., Qin, X., Dai, Y., 2015. One-pot solvothermal synthesis of S doped BiOCl for solar water oxidation. RSC Adv. 5 (58), 47261-47264. Leary, R., Westwood, A., 2011. Carbonaceous nanomaterials for the enhancement of TiO2 photocatalysis. Carbon 49(3), 741-772. Ren, C., Yang, B., Wu, M., Xu, J., Fu, Z., Yan, L., Guo, T., Zhao, Y., Zhu, C., 2010. Synthesis of Ag/ZnO nanorods array with enhanced photocatalytic performance. J. Hazard. Mater. 182 (1-3), 123-129. Bai, S., Li, H., Guan, Y., Jiang, S., 2011. The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes. Appl. Surf. Sci. 257 (15), 6406-6409. Zhang, A., He, R., Li, H., Chen, Y., Kong, T., Li, K., Ju. H., Zhu. J., Zhu. W., Zeng, J., 2018. Nickel doping in atomically thin tin disulfide nanosheets enables highly efficient CO2 reduction. Angew. Chem. Int. Edit. 57 (34), 10954-10958. Height, M. J., Pratsinis, S. E., Mekasuwandumrong, O., Praserthdam, P., 2006. Ag-ZnO catalysts for UV-photodegradation of methylene blue. Appl. Catal. B: Environ. 63 (3-4), 305-312. Huo, Y., Yang, X., Zhu, J., Li, H., 2011. Highly active and stable CdS-TiO2 visible photocatalyst prepared by in situ sulfurization under supercritical conditions. Appl. Catal. B: Environ. 106 (1-2), 69-75. 21
Holzwarth, U., Gibson, N., 2011. The Scherrer equation versus the'Debye-Scherrer equation'. Nat. nanotechnol. 6 (9), 534. Guo, Y., Wang, Z., Shao, H., Jiang, X., 2013. Hydrothermal synthesis of highly fluorescent carbon nanoparticles from sodium citrate and their use for the detection of mercury ions. Carbon 52, 583-589. He, X., Li, H., Liu, Y., Huang, H., Kang, Z., Lee, S. T., 2011. Water soluble carbon nanoparticles:
hydrothermal
synthesis
and
excellent
photoluminescence
properties. Colloids Surf. B 87(2), 326-332. Zhang, J., Wu, Y., Xing, M., Leghari, S. A. K., Sajjad, S., 2010. Development of modified N doped TiO2 photocatalyst with metals, nonmetals and metal oxides. Energy Environ. Sci. 3(6), 715-726. Cong, Y., Chen, F., Zhang, J., Anpo, M., 2006. Carbon and nitrogen-codoped TiO2 with high visible light photocatalytic activity. Chem. Lett. 35(7), 800-801. Cong, Y., Zhang, J., Chen, F., Anpo, M., He, D., 2007. Preparation, photocatalytic activity, and mechanism of nano-TiO2 co-doped with nitrogen and iron (III). J. Phys. Chem. C 111(28), 10618-10623. Dong, F., Xiong, T., Yan, S., Wang, H., Sun, Y., Zhang, Y., Huang. H., Wu, Z., 2016. Facets and defects cooperatively promote visible light plasmonic photocatalysis with Bi nanowires @ BiOCl nanosheets. J. Catal. 344, 401-410. Lu, H., Xu, L., Wei, B., Zhang, M., Gao, H., Sun, W., 2014. Enhanced photosensitization process induced by the p-n junction of Bi2O2CO3/BiOCl heterojunctions on the degradation of rhodamine B. Appl. Surf. Sci. 303, 360-366. 22
Yan, X., Zhu, X., Li, R., Chen, W., 2016. Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light. J. Hazard. Mater. 303, 1-9. Yu, L., Zhang, X., Li, G., Cao, Y., Shao, Y., Li, D., 2016. Highly efficient Bi2O2CO3/BiOCl
photocatalyst
based
on
heterojunction
with
enhanced
dye-sensitization under visible light. Appl. Catal. B: Environ. 187, 301-309. Yang, X., Cao, C., Hohn, K., Erickson, L., Maghirang, R., Hamal, D., Klabunde, K., 2007. Highly visible-light active C-and V-doped TiO2 for degradation of acetaldehyde. J. Catal. 252 (2), 296-302. Fu, S., Liu, X., Yan, Y., Li, L., Liu, H., Zhao, F., Zhou, J., 2019. Few-layer WS2 modified BiOBr nanosheets with enhanced broad-spectrum photocatalytic activity towards various pollutants removal. Sci. Total Environ. 133756. Yu, C., He, H., Fan, Q., Xie, W., Liu, Z., Ji, H., 2019. Novel B-doped BiOCl nanosheets with exposed (001) facets and photocatalytic mechanism of enhanced degradation efficiency for organic pollutants. Sci. Total Environ. 133727. Li, H., Li, J., Ai, Z., Jia, F., Zhang, L., 2018. Oxygen vacancy-mediated photocatalysis of BiOCl: reactivity, selectivity, and perspectives. Angew. Chem. Int. Edit. 57 (1), 122-138. Ouyang, W., Teng, F., Fang, X., 2018. High Performance BiOCl Nanosheets/TiO2 Nanotube Arrays Heterojunction UV Photodetector: The Influences of Self-Induced Inner Electric Fields in the BiOCl Nanosheets. Adv. Funct. Mater. 28 (16), 1707178.
23
He, Z., Shi, Y., Gao, C., Wen, L., Chen, J., Song, S., 2013. BiOCl/BiVO4 p-n heterojunction with enhanced photocatalytic activity under visible-light irradiation. J. Phys. Chem. C 118 (1), 389-398. Wang, L., Lv, D., Yue, Z., Zhu, H., Wang, L., Wang, D., Xu, X., Hao, W., Dou, S. X., Du, Y., 2019. Promoting photoreduction properties via synergetic utilization between plasmonic effect and highly active facet of BiOCl. Nano Energy 57, 398-404. Dukali, R. M., Radović, I. M., Stojanović, D. B., Šević, D. D., Radojević, V. J., Jocić, D. M., Aleksić, R. R., 2014. Electrospinning of laser dye Rhodamine B-doped poly (methyl methacrylate) nanofibers. J. Serb. Chem. Soc. 79(7), 867-880.
24
TOC One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB
25
One-pot synthesis of BiOCl nanosheets with dual functional carbon for ultra-highly efficient photocatalytic degradation of RhB
Highlights
Carbon-modified BiOCl (C-BOC) photocatalyst was synthesized by one-pot method. The dual functions of carbon were proposed. C-BOC could degrade RhB completely in 6 minutes.
Dear Editors, We declare that we have no financial and personal relationships with any organizations or individuals that can inappropriately influence our work.
Yours sincerely, Yuanhua Sang Professor State Key Laboratory of Crystal Materials Shandong University Jinan, 250100, China