Title: Fabrication and photocatalytic performance of Bi <sub>24</sub> O <sub>31</sub> Br <sub>10</sub> nanosphere by a polyacrylamide gel method
Abstract: Micro & Nano LettersVolume 15, Issue 8 p. 499-502 ArticleFree Access Fabrication and photocatalytic performance of Bi24O31Br10 nanosphere by a polyacrylamide gel method Zuming He, Corresponding Author Zuming He [email protected] Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this authorJiangbin Su, Jiangbin Su Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this authorYongmei Xia, Corresponding Author Yongmei Xia [email protected] School of Materials and Engineering, Jiangsu University of Technology, Changzhou, 213001 People's Republic of ChinaSearch for more papers by this authorBin Tang, Bin Tang Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this author Zuming He, Corresponding Author Zuming He [email protected] Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this authorJiangbin Su, Jiangbin Su Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this authorYongmei Xia, Corresponding Author Yongmei Xia [email protected] School of Materials and Engineering, Jiangsu University of Technology, Changzhou, 213001 People's Republic of ChinaSearch for more papers by this authorBin Tang, Bin Tang Huaide School, Changzhou University, Jingjiang, 214500 People's Republic of China School of Mathematics & Physics, Changzhou University, Changzhou, 213164 People's Republic of ChinaSearch for more papers by this author First published: 22 July 2020 https://doi.org/10.1049/mnl.2020.0016Citations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract The authors have fabricated novel flower-like Bi24O31Br10 micro/nanospheres by a polyacrylamide gel method. The crystal structure, microstructure, bandgap, morphology, and optical property of the as-prepared Bi24O31Br10 micro/nanospheres were investigated by multiple techniques. The Bi24O31Br10 photocatalyst exhibits excellent photocatalytic performance for the degradation of methyl orange under visible light irradiation. Furthermore, the cycle experimental results show that the Bi24O31Br10 micro/nanospheres possess superior reusability. The possible photocatalytic work principle was proposed and discussed. 1 Introduction Semiconductor photocatalysis has been regarded as an application prospect in the degradation of organic pollutants [[1]]. TiO2 and ZnO are the best photocatalytic materials due to their non-toxic nature, chemical stability, and low cost [[2]]. Unfortunately, TiO2 and ZnO can only respond ultraviolet (UV) light because of their wide bandgaps [[3]]. To effectively utilise solar energy to drive photocatalytic reactions, therefore, it is essential to develop new visible-light-driven photocatalysts. In recent years, Bi24O31Br10 has attracted attention due to its hierarchical structure and excellent visible-light photocatalytic capability [[4]]. So far, the synthesis of Bi24O31Br10 mainly includes the calcining BiOBr method [[5]], solvothermal method [[6]], solvothermal method with the help of soluble starch [[7]], microwave-calcination route [[8]], and ion-exchange approach [[9]]. However, until now, there has been no research on the preparation of Bi24O31Br10 micro/nanospheres by a polyacrylamide gel method. In this work, Bi24O31Br10 nanospheres were prepared by a polyacrylamide gel method, and their photocatalytic performance was evaluated by removing methyl orange (MO). 2 Experimental 2.1 Fabrication of Bi24O31Br10 nanospheres All the chemical reagents were commercially available and used without further purification. The method to synthesise Bi24O31Br10 was similar to that in a previous publication [[10]]. The details are as follows: 2.4 mmol Bi(NO3)3 ·5H2 O was dissolved in 50 ml of deionised water with magnetic stirring for 30 min. Then 1 mmol cetyltrimethylammonium bromide was added into the above solution under magnetic stirring for 30 min. Then, the acrylamide monomer was added to the mixture solution and heated to 80°C to cause polymerisation reaction. The as-achieved gel was dried at 110°C for 24 h in a thermostat drier. The obtained dry gel was ground into a powder and further calcined at 450°C for 5 h to obtain Bi24O31Br10 micro/nanospheres. 2.2 Characterisation and photocatalytic activity test of Bi24O31Br10 nanospheres The crystal structures of the as-synthesised samples were characterised by using an X-ray diffraction (XRD) instrument with a scanning angle (2θ) range of 10–80° (Rigaku, D/max-2500, Cu Kα radiation λ = 0.15406). The elemental composition of the samples was detected by X-ray photoelectron spectroscopy (XPS) measurements with an Al Ka 150 W, 500 μm beam spot source (Thermo ESCALAB 250). The surface morphology of the sample was obtained by using a field-emission scanning electron microscope (FE-SEM, UAPR550, Zeiss, Germany). Transmission electron microscopy (TEM) images were measured using a JEM-300 TEM (JEOL, Japan). A spectrophotometer (Shimadzu UV 2550, Japan) with an integrating sphere was used to measure the UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) spectrum of the sample. Electron spin resonance (ESR) spectra were acquired on a Bruker model ESR JES-FA200 spectrometer. The functional groups on the surface of the sample were investigated by Fourier transform infrared spectroscopy on a Nicolet iS50 spectrometer (Thermo Fisher Scientific, USA). The specific surface area and particle size of the photocatalysts were obtained via the Brunauer–Emmett–Teller (BET) method based on the N2 adsorption–desorption isotherms (Micromeritics Instrument Corporation, USA). The photocatalytic performance of the sample was evaluated through the photodegradation of MO solution (20 ppm, pH = 6.8) under visible light irradiation. A 500 W xenon lamp with a UV cut-off filter (λ > 420 nm) was used as a visible light source. The distance between the light source and the photoreactor was 10 cm. The concentration of photocatalyst was 1000 ppm, the solution was sonicated for 30 min. Prior to irradiation, the mixture solution was stirred in the dark for 20 min to attain adsorption–desorption equilibrium. At intervals of 20 min, about 2.0 ml solution was withdrawn and the photocatalysts were separated from the suspension by filtration. Finally, the MO concentration was determined by using a UV–Vis spectrophotometer. The degradation rate η (%) was calculated according to (1) (1) where η (%) is the degradation rate of MO, A0 is the initial absorbance of the MO solution, and At is the absorbance of MO solution at degradation time t (min). 3 Results and discussion Fig. 1 illustrates the XRD patterns of Bi24O31Br10 before and after photocatalysis application. All the diffraction peaks can be well indexed according to the standard card of Bi24O31Br10 monoclinic phase (JCPDS 75-0888), which shows the material synthesised is fairly pure [[11]]. Furthermore, it is clearly found that all the diffraction peaks do not change after being photocatalytically used five times. This shows the fair stability of Bi24O31Br10. XPS was carried out to confirm the element oxidation states of Bi24O31Br10. Fig. 2a shows the Bi 4f7/2 and Bi 4f5/2 corresponding to the binding energies of 159.2 and 164.43 eV, respectively, which indicates that Bi3+ ion exists in the synthesised sample [[12]]. Fig. 2b displays the peaks at 529.66 and 531.04 eV, which are assigned to lattice oxygen (OL) and adsorbed oxygen (OA) [[13], [14]]. Fig. 2c illustrates the Br 3d spectrum, where the binding energy peaks at 68.5 and 69.4 eV are assigned to Br 3d3/2 and Br 3d5/2, respectively. The result indicates that the Br element is in the form of Br− [[7]]. Thus, the XPS analysis further confirms the formation of Bi24O31Br10. Fig. 1Open in figure viewerPowerPoint XRD patterns of Bi24O31Br10 before and after recycling experiment Fig. 2Open in figure viewerPowerPoint XPS spectra of a Bi 4f b O 1s c Br 3d of Bi24O31Br10 The FE-SEM and TEM images of Bi24O31Br10 are presented in Figs. 3a and b, respectively. It is clearly observed that Bi24O31Br10 exhibits flower-like micro/nanospheres with a mesoporous structure. Fig. 3c shows the high-resolution TEM (HRTEM) image of Bi24O31Br10, which clearly shows the lattice fringes with d117 = 0.27 nm. The UV–Vis DRS spectrum illustrating the optical property of Bi24O31Br10 is presented in Fig. 3d. The absorption edge of Bi24O31Br10 is located at ∼468 nm, indicating its excellent visible-light absorption capacity. The bandgap energy of Bi24O31Br10 is calculated to be ∼2.75 eV (inset). Therefore, Bi24O31Br10 can be responsive to visible light with high photocatalytic activity. Fig. 4 illustrates the FTIR spectrum of Bi24O31Br10 micro/nanospheres. It can be seen that two broad peaks centred at 1495.2 and 3379.5 cm−1 can be observed in the sample, which corresponds to the stretching vibrations of surface adsorbed hydroxyl groups and H–O–H molecules. In addition, the absorption peaks of Bi24O31Br10 are observed at around 702 and 851 cm−1, which are ascribed to the Bi–O stretching vibration. Fig. 3Open in figure viewerPowerPoint Morphology image and Uv-vis DRS spectrum of Bi24O31Br10 nanosphere a FE-SEM image b TEM image c HRTEM image d UV–Vis DRS spectrum of Bi24O31Br10 Fig. 4Open in figure viewerPowerPoint FTIR spectra of Bi24O31Br10 micro/nanospheres The BET specific surface area of the as-prepared samples was investigated by using nitrogen adsorption–desorption measurements. The BET specific surface areas of the Bi24O31Br10 samples obtained by various preparation methods are summarised in Table 1. It is found that the BET specific surface area of the Bi24O31Br10 micro/nanosphere is measured to be 70.12 m2/g, which is much larger than the other reported results of Bi24O31Br10. The much larger surface area facilitates the contaminant contact with the catalyst and enhances the photocatalytic performance. Table 1. BET specific surface areas of Bi24O31Br10 samples obtained by various preparation methods Preparation methods BET, m2/g Reference polyacrylamide gel method 70.12 in this Letter solvothermal method with the help of soluble starch 12.8 [[7]] ion-exchange approach to the fabrication 67.16 [[9]] solvothermal method 36.0 [[6]] microwave-calcination route 16.3 [[8]] Fig. 5a shows the time-dependent photocatalytic removing of MO under visible light irradiation. Self-photolysis of MO in the absence of any catalyst can be neglected. The Bi24O31Br10 displays an excellent photocatalytic activity and ∼96.3% of MO is decomposed after irradiation for 120 min. Fig. 5b shows the first-order kinetic simulation of MO degradation with the Bi24O31Br10 sample. There is a nice linear correlation between ln(Ct/C0) and the reaction time (t), and the k value is obtained as 1.41 × 10−2 min−1. Moreover, the photocatalytic stability experiment was carried out under the same condition. As can be seen from Fig. 5c, the degradation rate of Bi24O31Br10 has no obvious decrease after recycling five times, which indicates that the Bi24O31Br10 catalyst possesses superior reusability. To explore the active species on the degradation of MO, the isopropyl alcohol (IPA), disodium ethylene-diaminetetraacetate (EDTA-2Na) and benzoquinone were selected as the scavengers of hydroxyl radicals (•OH), holes (h+), and superoxide radicals (), respectively [[15], [16]]. The result of the free radical capturing experiments is shown in Fig. 5d. It is clearly observed that when 0.1 mM IPA and EDTA-2Na are separately added into the photocatalytic system, the corresponding degradation rate is significantly inhibited. This indicates that •OH and h+ are the predominant reactive species in this photocatalytic systems. The electron paramagnetic resonance (EPR) technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to further confirm the presence of •OH radicals. As shown in Fig. 5e, no EPR signal related to •OH can be observed in the dark. Nevertheless, the EPR signal peaks of the DMPO–•OH are observed under visible light irradiation, indicative of the existence of •OH radicals in the photocatalytic systems. The possible photocatalytic principle of Bi24O31Br10 can be explained as follows (Fig. 5f). According to the literature, the conduction band (CB) and valance band (VB) of Bi24O31Br10 are −0.46 and +2.29 eV, respectively [[17]]. Under visible light irradiation, electrons are excited from the VB of Bi24O31Br10 to the CB, meanwhile generating h+ in the VB. The photoelectrons on the CB of Bi24O31Br10 react with O2 to form , and then reacts with H+ to generated •OH due to the sufficiently negative CB potential compared to the standard redox potential of Eθ (O2/) (−0.33 eV versus normal hydrogen electrode (NHE)) [[18], [19]]. Finally, the •OH radicals remove MO. Simultaneously, the standard redox potential of Eθ (•OH/OH−) is +2.38 eV versus NHE [[20]], which is positive to the VB potential of Bi24O31Br10 (+2.29 eV). Therefore, h+ can directly oxidise MO. Fig. 5Open in figure viewerPowerPoint Photocatalytic performance and mechanism of Bi24O31Br10 nanosphere a Photo-degradation rate of MO under visible light irradiation using Bi24O31Br10 b Kinetic plot of the MO degradation c Cycling degradation efficiency of Bi24O31Br10 d Active species trapping experiments for the degradation of MO over Bi24O31Br10 under visible light irradiation e Spin-trapping ESR spectra of Bi24O31Br10 under dark or visible light irradiation f Proposed photo-degradation mechanism of Bi24O31Br10 photocatalyst 4 Conclusions In conclusion, flower-like Bi24O31Br10 micro/nanospheres were prepared by a polyacrylamide gel method. They exhibit excellent photocatalytic performance for removing MO under visible light irradiation. •OH and h+ are the predominant active species in the photocatalytic system. Moreover, recycling experiments indicate that the Bi24O31Br10 micro/nanospheres exhibit stability. 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Yi Z. et al.: 'NaBH4-reduction induced evolution of Bi nanoparticles from BiOCl nanoplates and construction of promising Bi@BiOCl hybrid photocatalysts', Catalysts., 2019, 9, p.795 (doi: 10.3390/catal9100795) Citing Literature Volume15, Issue8July 2020Pages 499-502 FiguresReferencesRelatedInformation
Publication Year: 2020
Publication Date: 2020-07-01
Language: en
Type: article
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