- Email: [email protected]
ACF photocatalyst
Applied Surface Science 488 (2019) 161–169
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full length article
Study on preparation and toluene removal of BiOI/Bi2WO6/ACF photocatalyst Yongqiang Wanga,b, a b
⁎,1
T
⁎
, Shan Jianga,1, Fang Liua,b, , Chaocheng Zhaoa, Dongfeng Zhaoa, Xinfu Lia
College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China State Key Laboratory of Petroleum Pollution Control, China University of Petroleum (East China), Qingdao 266580, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Photocatalysis Bi2WO6 Toluene Activated carbon fiber
The BiOI/Bi2WO6/ACF composite photocatalysts with different loads were prepared by hydrothermal method, and the catalysts were characterized by XRD, SEM, TEM, BET, XPS, DRS and photocurrent responses. The photocatalytic activity of the samples was studied with the toluene as model pollutant. The results showed that 20%mol BiOI/Bi2WO6 was uniformly loaded on the activated carbon fiber (ACF), and Bi2WO6 (133) orthorhombic crystal face and BiOI (012) tetragonal crystal face can be observed on the catalyst surface. The specific surface area of 20% mol BiOI/Bi2WO6/ACF is 787 m2·g−1, which is much higher than that of Bi2WO6/ACF. BiOI and Bi2WO6 exist simultaneously in the BiOI/Bi2WO6 according to the results of XPS, which corresponds to the results of TEM characterization, indicating that the composites were successfully prepared, and the absorption band edge and intensity of Bi2WO6 was enhanced greatly by the compositing of BiOI. The toluene removal efficiency could arrive at 76.3% for the concentration of 500 mg/m3 with the 20%mol BiOI/Bi2WO6/ACF.
1. Introduction In recent years, haze weather and ozone pollution are becoming more and more serious in china [1,2], volatile organic compounds (VOCs) is the main contributors of these problems, and toluene is a typical representative substance of VOCs [3]. There are many ways to escape toluene, which is harmful to people's production and life [4]. At present, the semiconductor photocatalysis technology cannot only be used in catalytic hydrolysis to produce H2 but also in pollution treatment. Photocatalytic technology has attracted much attention in the field of air purification because of its high degradation efficiency, no secondary pollution [5–8], economy and other advantages, and has broad application prospects [9–12]. Bi2WO6 is a new type of visible light non-titanium catalyst and was studied in recent years because of their nontoxicity, strong oxidizing power and visible light responsive. As a gap semiconductor material, its band gap width is about 2.7 eV [13–16]. However, the application of Bi2WO6 is greatly limited because of its high photoelectron recombination rate and its ability to absorb light less than 450 nm [17–20]. There are many ways to improve its photocatalytic performance, such as doping with CuO [21], ZnO [22] and C3N4 [23,24], and combining with narrow band gap semiconductor [25–29].
BiOI, as a highly anisotropic gap semiconductor, has a strong optical absorption ability in the 400–700 nm region, a narrow band gap width (1.7–1.9 eV), and a highly anisotropic layered structure of PbFCl type [30–32]. It has good adsorption and photocatalytic properties. In addition, the excited electrons must pass through a certain k-layer if they want to be excited by the valence band, so the recombination probability of BiOI photoinduced electron hole pairs is relatively low [33,34]. The photocatalytic performance of Bi2WO6 can be increased by the doping of BiOI because that BiOI improves the optical absorption characteristics in the visible region and the separation efficiency of photogenerated carriers, reduce the recombination probability of photoinduced electron hole pairs [35–39]. Up to now, there are many studies on the application of photocatalyst in the treatment of wastewater, but few researches on the treatment of VOCs, the literatures of using the activated carbon fiber (ACF) as the carrier to remove toluene is few. When ACF was used as a carrier to support BiOI/Bi2WO6 composite photocatalyst, ACF could adsorb low concentration organic pollutants quickly, then organic pollutants can be enriched on ACF and diffused to the interface of BiOI/Bi2WO6/ACF rapidly, so that the photocatalytic reaction could be accelerated. In this paper, BiOI/Bi2WO6/ACF photocatalysts with different loadings were prepared with hydrothermal method and characterized by XRD, SEM, TEM, BET, XPS, DRS and photocurrent responses, the
⁎
Corresponding authors at: College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China. E-mail addresses: [email protected] (Y. Wang), [email protected] (F. Liu). 1 Co-first authors; they have contributed equally to this work. https://doi.org/10.1016/j.apsusc.2019.05.228 Received 28 March 2019; Received in revised form 28 April 2019; Accepted 19 May 2019 Available online 20 May 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
photocatalytic activity of toluene as target pollutant was studied. The effects of BiOI loading, toluene concentration and light intensity on catalytic activity were discussed. 2. Experimental 2.1. Preparation of photocatalysts 2.1.1. Reagent Chemicals in the experiment were obtained from Sinopharm Chemical Reagent Co., Ltd. and without further purification. 2.1.2. Preparation of BiOI Bi(NO3)3·5H2O (1.36 g) was dissolved in 80 ml ethanol, stirred for 60 min, then 0.8 g PVP was added to the solution, stirred for several minutes and KI (0.4648 g) was added to obtain orange-yellow precipitation. After covering the film, stirred for 10 h, and then washed with absolute ethanol and deionized water until the supernatant was clear, then precipitated at the bottom of the centrifugal tube in a vacuum drying box and dried for 12 h.
Fig. 1. XRD patterns of Bi2WO6 and BiOI/Bi2WO6 samples.
2.1.3. Preparation of BiOI/Bi2WO6 Bi (NO3)3·5H2O (0.005 mol) was dissolved in 25 ml dilute nitric acid (including 5 ml concentrated nitric acid) to form A solution; Na2WO4·2H2O (0.0025 mol) was dissolved in 40 ml deionized water to form B solution; A and B solutions were mixed evenly to form C solution; According to the 0.05:1, 0.1:1, 0.2:1, 0.3:1 and 0.4:1 M ratio of BiOI to Bi2WO6, different amounts of BiOI were added into C solution, stirred for 30 min and then moved into 100 ml hydrothermal reactor. The filling ratio of BiOI/Bi2WO6 photocatalyst was 80%, and then heated at 160 °C for 20 h.
2.3. Activity evaluation of catalysts The catalytic activity of catalytic materials was evaluated by a selfmade photocatalytic reactor. The photocatalytic reactor was consisted of dynamic gas distribution part, photocatalytic reaction part and sampling part. In the gas distribution part, toluene mixtures with different concentrations were prepared by adjusting the total air flow rate and the intake of toluene. After mixing uniformly in the gas mixing bottle, both of them maintained a certain flow rate and passed through the quartz tube with BiOI/Bi2WO6/ACF composite material. The light source used 8 W ultraviolet lamp, and the main wavelength of light is 185 nm and the toluene was tested by Varian GC-3800.
2.1.4. Preparation of BiOI/Bi2WO6/ACF 2.1.4.1. ACF preprocessing. The ACF with the size of 100 ∗ 100 (mm) was immersed in 50% ammonia solution and cleaned by ultrasonic wave for 30 min. The ACF was washed three times with deionized water, and then immersed in 50% nitric acid solution. Then that was cleaned by ultrasonic wave for 30 min. Took out the ACF and washed it with deionized water for 3 times, then put it in oven and bake it at 100 °C to dry. The dried ACF was cut into 20 ∗ 20 (mm) spare parts.
3. Results and discussion 3.1. Characterization of catalysts 3.1.1. XRD The results of X ray diffraction (XRD) analysis of BiOI/Bi2WO6 with different loading capacity were shown in Fig. 1. It was shown that all the composite photocatalysts exhibited a coexistence of both tetragonal BiOI (JCPDS card No. 73-2062) and orthorhombic Bi2WO6 (JCPDS card No. 39-0256) phases, the characteristic peaks around 2ɵ of 28.31°, 32.83°, 47.13°, 55.6°, 58.5° and 68.8° were indexed to those of orthorhombic Bi2WO6, corresponding to (113), (002), (202), (133), (262) and (004) peaks, respectively [17,40–42]. The strong and sharp diffraction peaks indicated that all samples were highly crystalline. The characteristic peaks of BiOI can be observed at 29.6°, 31.77°, 45.51°, 55.15°, 66.4°, corresponding to (102), (110), (104), (212) and (220) peaks, respectively, and there was no other heterozygous peaks, which indicated that the purity of BiOI was higher. However, the characteristic peaks of BiOI did not appear at the low amount, which might be due to the relatively low diffraction intensity of the BiOI. The characteristic peak strength of Bi2WO6 decreased obviously, which may be due to the higher characteristic peak strength of Bi2WO6, which resulted in the relative obscurity or disappearance of the characteristic peak of the composite.
2.1.4.2. Loading on ACF. Used 1 ml epoxy resin solution which was diluted for 10 times and BiOI/Bi2WO6 (0.08 g) photocatalyst powder in a beaker. The photocatalyst solution was loaded on ACF by ultrasonic vibration. The composites were dried at 60 °C for 4 h and then the BiOI/ Bi2WO6/ACF composites were obtained by heat treatment for 2 h at 400 °C in a tubular furnace with N2 protection. 2.2. Catalysts characterization The X'Pert Pro MPD powder X-ray diffractometer (XRD) was made by Panalytical Company, which was used to analyze the crystallographic structure and chemical composition of the catalytic material, which used Cu-Ka radiation (40 kV, 50 mA) at a scanning rate of 4°min−1, 2θ ranges from 10° to 80°. The surface morphology and structure of the catalyst were observed and analyzed by scanning electron microscopy (SEM, S-4800) and high-resolution transmitting electron microscopy (HRTEM, JEM-2100f). X-ray photoelectron spectroscopy (XPS, Amicus Budget, Japan) was used to explore the chemical state of elements. Surface areas and porosity of photocatalysts were measured by the Brunauer–Emmett–Teller (BET) method (Tri Star3000). The optical properties of the prepared materials were analyzed by the UV–vis diffuse reflectance spectra (DRS) tested on a spectrometer (UV2550, Shimadzu, Japan), using BaSO4 as background reference. The photocurrent responses were measured on a CHI 660B electrochemical system.
3.1.2. SEM and TEM images The morphological structure of as-prepared BiOI/Bi2WO6 samples was examined by SEM and HRTEM. It was shown that the surface of ACF without catalyst was smooth and free of impurities, arranged in a duct-like arrangement in Fig. 2a. It was shown that the surface of the ACF was covered with catalyst, but the catalyst had large particle size, 162
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 2. SEM images of ACF, Bi2WO6/ACF and BiOI/Bi2WO6/ACF: a ACF; b Bi2WO6/ACF; c, d 20%mol BiOI/Bi2WO6/ACF; e, f 10%mol BiOI/Bi2WO6/ACF.
3.1.3. XPS characterization The surface chemical composition and valence state of 20% mol BiOI/Bi2WO6/ACF were analyzed by XPS. As shown in Fig. 4a, the Bi in the sample consists of two peaks with binding energies of 158.8 and 164.1 eV, corresponding to Bi 4f7/2 and Bi 4f5/2, respectively. This indicated that the Bi element exists at positive trivalence in 20% mol BiOI/Bi2WO6/ACF. As shown in Fig. 4b, peaks at 37.2 eV and 35.1 eV corresponded to W 4f5/2 and W 4f7/2, respectively, indicating that W existed as a positive hexavalent in 20% mol BiOI/Bi2WO6/ACF. The peaks at 618.8 eV and 630.3 eV were characteristic peaks of I 3d5/2 and I 3d3/2 (Fig. 4c), indicating that element I exists in 20% mol BiOI/ Bi2WO6/ACF in the form of negative monovalent. The O 1s binding energy (Fig. 4d) of 530.1 eV can be attributed to the lattice oxygen in Bi2WO6 and BiOI.
uneven dispersion and agglomeration, and the binding strength with ACF was not high, and the load was small in Fig. 2b. It was shown that 20% mol BiOI/Bi2WO6 photocatalyst prepared by hydrothermal method was interlaced on ACF in clusters to form a dense film in Fig. 2c and d. The fiber rods were almost completely coated and dispersed uniformly without agglomeration. BiOI/Bi2WO6/ACF with uniform load and stable bonding strength was formed. Compared with Fig. 2b, the composite photocatalyst had higher dispersion and larger specific surface area than monomer photocatalyst. In Fig. 2e and f, 10% mol BiOI/Bi2WO6 photocatalyst was loaded on the surface of ACF unevenly, and no dense film was formed. Some areas of the fiber rod were not completely coated, and the load of the catalyst was less, which was consistent with the results of the activity test of the composite material. Fig. 3a showed that there are many regular spherical protrusions on the surface of the sample with large specific surface area, which improved the sample more adsorptive and has higher photocatalytic oxidation ability. The existence of discontinuous lattice can be clearly seen in Fig. 3b. The lattice fringe spacing was analyzed and measured accurately. The lattice fringe spacing was 0.305 nm and 0.320 nm, which corresponded to the Bi2WO6 (133) crystal face of orthorhombic system and BiOI (012) crystal face of tetragonal system respectively. BiOI and Bi2WO6 were effectively combined.
3.1.4. Brunauer-Emmett-Teller specific surface area The specific surface area of the composite was determined as shown in Table 1. The results showed that the specific surface area of ACF treated by activation is larger, up to 1575 m2·g−1, because the surface of blank ACF was clean and free of impurities, and the pores were not blocked. The specific surface area of Bi2WO6/ACF was the smallest. It was shown that Bi2WO6 had larger particle size and agglomeration phenomenon, 163
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 3. TEM images of 20% mol BiOI/Bi2WO6.
which blocked the pore structure of some ACF combining with SEM images. The specific surface area of 10% mol BiOI/Bi2WO6/ACF was the largest, because the particle size of the composite catalyst decreased with the addition of BiOI, and the particles were evenly distributed on the surface of ACF without agglomeration. The SEM images showed that 10% mol BiOI/Bi2WO6 was not completely coated on the surface of ACF, and less pore structure was blocked. The specific surface area of 20% mol BiOI/Bi2WO6/ACF was less than 10% mol BiOI/Bi2WO6/ACF, which may be due to the 20% mol BiOI/Bi2WO6 photocatalyst was more uniformly coated on the surface of ACF rod, more pore structure was blocked. The specific surface area of 30% mol BiOI/Bi2WO6/ACF and 20% mol BiOI/Bi2WO6/ACF was almost the same, which showed that the specific surface area of the composite was not a simple linear relationship with the loading of BiOI, but there was an optimum loading range. 3.1.5. DRS characterization The UV–Vis diffuse reflectance spectra of Bi2WO6, BiOI and BiOI/ Bi2WO6 composite photocatalysts with different loadings were shown in Fig. 5. It can be seen that all the photocatalysts had response in the ultraviolet and visible light region. The absorption band edge of Bi2WO6 was narrow, the absorption band edge of BiOI was about 420 nm and the composite showed enhanced absorption for visible light. The absorption band edge and absorption intensity of the composite expressed a trend of enhancement by compositing with BiOI. It was showed that there was obvious interaction between Bi2WO6 and BiOI. The band gap of photocatalyst were calculated according to the Kubelka-Muck function equations:
F (R) =
K (1 − R)2 = S 2R
(1)
The band gap energy of the photocatalyst can be obtained by plotting the [F(R) × hν]n/2 vs. hν and making tangent to it, K was the sample absorption coefficient, S was the sample reflection coefficient, R was the sample diffuse reflectance (%), h was the Planck constant
Fig. 4. XPS spectra of 20% mol BiOI/Bi2WO6/ACF: a Bi 4f; b W 4f; c I 3d; d O 1s.
164
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Table 1 BET, pore volume and size of composite materials prepared by different samples. Sample ACF 10% mol BiOI/Bi2WO6/ACF 20% mol BiOI/Bi2WO6/ACF 30% mol BiOI/Bi2WO6/ACF Bi2WO6/ACF
SBET/(m2·g−1)
Pore size/nm
Pore volume/(cm3·g−1)
1575 855 788 782 772
2.92 4.35 4.35 4.39 4.57
0.15 0.14 0.12 0.13 0.13
Fig. 6. Mott-Schottky conduction band curves of Bi2WO6 and BiOI.
and the E represented the voltage (eV). The valence band position can be calculated based on this formula
EVB = ECB + Eg
(2)
where the Eg represented the semiconductor band gap energy, EVB represented the valence band potential of semiconductors, and ECB represented the conduction band potential of semiconductors. According to the formula, the valence band position of Bi2WO6 and BiOI was 2.28 V and 0.9 V respectively. The schematic diagram of the band structure of Bi2WO6 and BiOI were shown in Fig. 7, according to the calculation results. The e− of Bi2WO6 and BiOI can transit from valence band to conduction band and generate holes in valence band under ultraviolet excitation, and the e− will move from BiOI to Bi2WO6 because that the conduction band of BiOI (−0.87 V) is lower than Bi2WO6 (−0.43 V). Moreover, the valence band of Bi2WO6 is more higher than that of BiOI, and the hole is transferred from the valence band of Bi2WO6 to the valence band of BiOI, so the photocatalytic reaction was improved because the effective separation of photogenerated electrons and holes. The photocatalytic activity of BiOI/Bi2WO6 is higher than that of pure Bi2WO6 and BiOI because the energy level matching of BiOI/Bi2WO6 heterojunction structure is beneficial to catalytic redox reaction. The electrons gathered at the CB are further transformed into %O2− with powerful oxidation ability, subsequent inducing the decomposition of various contaminants [43]. Reactive oxygen species, such as superoxide radicals (%O2−) and hydroxyl radicals (%OH) have strong oxidative ability and take crucial role in the photodegradation reactions.
Fig. 5. UV–vis spectra for the as-synthesized Bi2WO6 samples, BiOI samples, the photocatalyst of different proportion and plots of the [F(R) × hν]1/2 vs. hν curves of Bi2WO6 and BiOI catalyst.
(eV·s), ν was the optical frequency (Hz). When the sample was a direct semiconductor, n is 4 and when the sample was indirect semiconductor, n is 1, Because BiOI was an indirect semiconductor so n is 1. Fig. 5 showed the fitting band gap energy. The intercept between tangent and X axis was similar to the band gap energy of semiconductor. The band gap energies of Bi2WO6 and BiOI were 2.71 eV and 1.77 eV.
3.1.7. Photocurrent response analysis According to the periodic switch xenon lamp, the photocurrent response was tested. After illumination, the electrons in the Bi2WO6 and BiOI were transferred to conductive glass by the conduction band, resulting in the photocurrent response. The stronger the photocurrent response was, the higher the separation efficiency of the photogenerated electron hole pairs was. When the xenon lamp was turned on, the photocurrent response of the working electrode increased suddenly,
3.1.6. Band structure analysis The band gap energies of Bi2WO6 and BiOI were calculated to be 2.71 eV and 1.77 eV respectively by Kubelka-Muck equation. Referring to the calomel electrode, the positions of Bi2WO6 and BiOI conduction band (CB) were calculated by Mott-Schottky as −0.43 V and 0.87 V vs. NHE, respectively (Fig. 6). Where C represented the differential charge capacitance (F/cm2) of the space charge layer of the semiconductor, 165
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 9. Effect of different BiOI loading amount of active group on removal effect of toluene.
was the result of interaction and interaction of various factors. 3.2. Catalyst activity for toluene oxidation 3.2.1. Effect of BiOI loading on toluene removal The effect of BiOI loading on toluene removal was investigated by controlling the concentration of toluene gas at about 350 mg/m3. The results were shown in Fig. 9. As shown in Fig. 9, the removal ability of BiOI/Bi2WO6/ACF decreased gradually with the reaction proceeding, but the catalytic activity of Bi2WO6/ACF composites was lower than that of other composites. In the first 60 min of the reaction, the toluene removal rate of the composites can reached 100%, which was due to the combined effect of the adsorption of activated carbon fiber felt and the photocatalytic degradation of the catalyst. Subsequently, the activated carbon fiber felt gradually tended to adsorption saturation, the removal rate of toluene declined continuously, and the removal rate of toluene tended to be stable after 150 min. This was due to the adsorption saturation of activated carbon fiber felt, and the catalyst activity remained at a stable level. When the reaction duration was about 240 min, the removal rates of toluene by Bi2WO6/ACF, 5%mol BiOI/ Bi2WO6/ACF, 10%mol BiOI/Bi2WO6/ACF, 20%mol BiOI/Bi2WO6/ACF, 30%mol BiOI/Bi2WO6/ACF and 40%mol BiOI/Bi2WO6/ACF were 31.84%, 39.01%, 69.96%, 76.33%, 60.06% and 52.84% respectively. It was found that the activity of the composite photocatalyst was better than that of the monomer catalyst, and the 20%mol BiOI/Bi2WO6/ACF expressed the best catalytic activity. When the amount of BiOI was less than 20%, the number of active sites on the surface of Bi2WO6 monomer increased with the addition of BiOI, which increased the electron migration efficiency, thus reducing the recombination rate of electron-hole pairs and improving the quantum efficiency of materials [44,45]. This was also consistent with the SEM characterization results. It was also found that the synergistic effect of the heterostructures formed by the two compounds played an important role in enhancing the photocatalytic performance. The toluene removal rate decreased with the increased of BiOI content, which may be due to more BiOI aggregates on the surface of Bi2WO6 and covered the active sites, which hindered the electron migration. At the same time, the specific surface area of BiOI nanoparticles decreased due to the larger particle size of Bi2WO6, which leaded to the decrease of catalytic activity [46]. In order to better understand the change of toluene removal in BiOI/Bi2WO6/ ACF composites, the change curve of inlet and outlet concentration of 20%mol BiOI/Bi2WO6/ACF was drawn, as shown in Fig. 10. As shown in Fig. 10, the inlet concentration expressed a gradual
Fig. 7. Schematic illustration of the band gap structures of Bi2WO6 and BiOI.
Fig. 8. Photocurrent of Bi2WO6 samples and the photocatalyst of different proportion.
which was due to the rapid separation of the photogenerated carriers; when the xenon lamp was turned off, the photocurrent response will remain at a weak level, corresponding to the initial current intensity. It was found that BiOI/Bi2WO6 composite photocatalyst had stronger photocurrent response compared with Bi2WO6. The photocurrent response intensity of 20%mol BiOI/Bi2WO6 was obviously better than that of other BiOI composite photocatalysts, indicating that it had longer photogenerated electron hole survival time and higher photogenerated electron hole separation efficiency, which was more conducive to the effective transfer of interface electrons. As shown in Fig. 8 that the photocurrent response test were not completely consistent with the photocatalytic performance test, which showed that photocurrent response was not the only factor determining the activity of the catalyst. The process of photocatalytic reaction was very complicated. It
166
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 10. Changes in the concentration of import and export. Fig. 12. Effect of different light intensity on removal effect of toluene.
increasing trend, which was due to the longer experimental period in a day, the toluene concentration will increase slightly with the temperature rise. As the export concentration gradually increased with the gradual deactivation of the composites, the increase was more and more significant. It was found that the change rate of toluene removal had a decreasing trend.
device to change the light intensity, as shown in Fig. 12. As shown in Fig. 12, the stronger the light intensity was, the faster the degradation rate was. The removal rates of toluene for one, two and three lamps were 53.92%, 66.37% and 76.33%, when the reaction was about 240 min. Because the activation energy of photoreaction comes from the energy of photon, so the intensity of light had a significant effect on the reaction rate. However, the toluene removal rate did not double with the increase of light intensity, which may be due to the limited number of active sites indicated by the catalytic materials, resulting in the light intensity and toluene removal rate was not a simple multiple relationship.
3.2.2. Effect of toluene concentration on removal of toluene 20%mol BiOI/Bi2WO6/ACF was used to investigate the effect of different toluene concentrations on toluene removal. The results were shown in Fig. 11. As shown in Fig. 11, the toluene removal rates of 20% mol BiOI/ Bi2WO6/ACF were 76.33%, 72.39%, 57.92% and 31.37% at toluene concentrations of 385 mg/m3, 568 mg/m3, 846 mg/m3 and 2106 mg/ m3 after 240 min. With the increase of toluene concentration, the removal rate of toluene decreased and the removal rate decreases. This was due to the toluene tolerance range of the composite materials. Within the toluene tolerance range, the removal rate decreased with the increase of the toluene concentration. When the toluene concentration exceeds the tolerated range, the catalyst will lose its catalytic activity. 3.2.3. Effect of light intensity on toluene removal Light intensity affects the degradation rate of organic matters. The effect of light intensity on toluene removal was investigated by reducing the number of lamps in the reaction section of the experimental
3.2.4. Comparison of removal efficiency of toluene by adsorption photocatalytic oxidation and dark reaction adsorption As shown in Fig. 13, the removal capacity of ACF decreased with the reaction. However, when the lamp was not turned on, the adsorption capacity of composite materials was reduced, and the removal capacity of toluene decreased rapidly. When the lamp was turned on, the removal rate of toluene decreased slowly, indicating that the removal ability had been improved significantly and can be maintained at a relatively high level for a long time. It was proved that BiOI/Bi2WO6/ ACF composites combined the adsorption advantages of activated carbon and the photocatalytic degradation advantages of BiOI/Bi2WO6. The removal efficiency of toluene was more obvious than that of ACF or
Fig. 11. Effect of different toluene concentration on removal effect of toluene.
Fig. 13. Comparison of adsorption and photocatalytic degradation of toluene. 167
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
100
Declaration of Competing Interest The authors declare that they have no conflict of interest.
80
Removal/%
References 60
[1] J. Zhang, C. Zhang, H. He, Remarkable promotion effect of trace sulfation on OMS-2 nanorod catalysts for the catalytic combustion of ethanol, J. Environ. Sci. (China) 35 (2015) 69–75. [2] B. Giri, K. Kim, R. Pandey, J. Cho, H. Song, Y. Kim, Review of biotreatment techniques for volatile sulfur compounds with an emphasis on dimethyl sulfide, Process Biochem. 49 (2014) 1543–1554. [3] T. Jarangdet, K. Pratumyot, K. Srikittiwanna, W. Dungchai, W. Mingvanish, I. Techakriengkrai, M. Sukwattanasinitt, N. Niamnot N, A fluorometric paper-based sensor array for the discrimination of volatile organic compounds (VOCs) with novel salicylidene derivatives, Dyes Pigments, 159(2018), pp. 378–383. [4] M. Handa, Y. Lee, M. Shibusawa, M. Tokumura, Y. Kawase, Removal of VOCs in waste gas by the photo-Fenton reaction: effects of dosage of Fenton reagents on degradation of toluene gas in a bubble column, J. Chem. Technol. Biotechnol. 88 (2013) 88–97. [5] C. Chen, W. Ma, J. Zhao, Semiconductor-mediated photodegradation of pollutants under visible-light irradiation, J. Cheminf. 39 (2010) 4206–4219. [6] Y. Wang, W. Jiang, W. Luo, X. Chen, Y. Zhu, Ultrathin nanosheets g-C3N4 @Bi2WO6 core-shell structure via low temperature reassembled strategy to promote photocatalytic activity, Appl. Catal. B Environ. 237 (2018) 633–640. [7] J. Di, C. Chen, C. Zhu, et al., Bismuth vacancy mediated single unit cell Bi2WO6 nanosheets for boosting photocatalytic oxygen evolution, Appl. Catal. B Environ. 238 (2018) 119–125. [8] L. Yuan, K. Lu, F. Zhang, X. Fu, Y. Xu, Unveiling the interplay between light-driven CO2 photocatalytic reduction and carbonaceous residues decomposition: a case study of Bi2WO6-TiO2, binanosheets, Appl. Catal. B Environ. 237 (2018) 424–431. [9] H. Jiang, Q. Wang, S. Zang, J. Li, Q. Wang, Enhanced photoactivity of Sm, N, Ptridoped anatase-TiO₂ nano-photocatalyst for 4-chlorophenol degradation under sunlight irradiation, J. Hazard. Mater. 261 (2013) 44–54. [10] H. Lu, Q. Hao, T. Chen, L. Zhang, D. Chen, C. Ma, W. Yao, Y. Zhu, A high-performance Bi2O3/Bi2SiO5, p-n heterojunction photocatalyst induced by phase transition of Bi2O3, Appl. Catal. B Environ. 237 (2018) 59–67. [11] L. Yan, Y. Wang, H. Shen, Y. Zhang, J. Li, D, Wang, Photocatalytic activity of Bi2WO6/Bi2S3 heterojunctions: the facilitation of exposed facets of Bi2WO6 substrate, Appl. Surf. Sci. 393(2017), pp. 496–503. [12] Y. Fu, C. Chang, P. Chen, X. Chu, L. Zhu, Enhanced photocatalytic performance of boron doped Bi₂WO₆ nanosheets under simulated solar light irradiation, J. Hazard. Mater. 254 (2013) 185–192. [13] B. Li, X. Yang, F. Du, Hydrothermal synthesis and photocatalytic activities of Bi2WO6 with different surfactant, Appl. Mech. Mater. 395 (2013) 741–745. [14] Z. Zhu, Y. Yan, J. Li, One-step synthesis of flower-like WO3/Bi2WO6, heterojunction with enhanced visible light photocatalytic activity, J. Mater. Sci. 51 (2016) 2112–2120. [15] Y. Yang, J. Cui, H. Jin, F. Cao, A three-dimensional (3D) structured Bi2WO6-palygorskite composite and their enhanced visible light photocatalytic property, Sep. Purif. Technol. 205 (2018) 130–139. [16] Y. Zhu, Y. Wang, Q. Ling, Y. Zhu, Enhancement of full-spectrum photocatalytic activity over BiPO4/Bi2WO6, composites, Appl. Catal. B Environ. 200 (2017) 222–229. [17] T. Saison, N. Chemin, C. Chaneac, et al., Bi2O3, BiVO4, and Bi2WO6: impact of surface properties on photocatalytic activity under visible light, J. Phys. Chem. C 115 (2011) 5657–5666. [18] Z. Liu, F. Chen, Y. Gao, Y. Liu, P. Fang, S. Wang, A novel synthetic route for magnetically retrievable Bi2WO6 hierarchical microspheres with enhanced visible photocatalytic performance, J. Mater. Chem. A 1 (2013) 7027–7030. [19] A. Phuruangrat, P. Dumrongrojthanath, S. Thongtem, T. Thongtem, Hydrothermal synthesis of I-doped Bi2WO6, for using as a visible-light-driven photocatalyst, Mater. Lett. 224 (2018) 67–70. [20] Y. Su, G. Tan, T. Liu, et al., Photocatalytic properties of Bi2WO6/BiPO4 Z-scheme photocatalysts induced by double internal electric fields, Appl. Surf. Sci. 457 (2018) 107–114. [21] P. Kumar, M. Selvakumar, S. Babu, S. Induja, S. Karuthapandian, CuO/ZnO nanorods: an affordable efficient p-n heterojunction and morphology dependent photocatalytic activity against organic contaminants, J. Alloys Compd. 701 (2017) 562–573. [22] J. Ma, K. Wang, L. Li, T. Zhang, Y. Kong, S. Komarnenl, Visible-light photocatalytic decolorization of Orange II on Cu2O/ZnO nanocomposites, Ceram. Int. 41 (2015) 2050–2056. [23] J. Yuan, X. Liu, Y. Tang, et al., Positioning cyanamide defects in g-C3N4: engineering energy levels and active sites for superior photocatalytic hydrogen evolution, Appl. Catal. B Environ. 237 (2018) 24–31. [24] Y. Xu, Y. Chen, W. Fu, Visible-light driven oxidative coupling of amines to imines with high selectivity in air over core-shell structured CdS@C3N4, Appl. Catal. B Environ. 236 (2018) 176–183. [25] H. Li, Y. Cui, W. Hong, High photocatalytic performance of BiOI/Bi2WO6, toward toluene and Reactive Brilliant Red, Appl. Surf. Sci. 264 (2013) 581–588. [26] Y. Wang, Y. Zeng, X. Chen, et al., Tailoring shape and phase formation: rational synthesis of single-phase BiFeWOx nanooctahedra and phase separated Bi2WO6Fe2WO6 microflower heterojunctions and visible light photocatalytic performances,
40
20
20% molBiOI/Bi2WO6/ACF 0
100
200
300
400
500
600
Time/min Fig. 14. The stability of degradation of toluene by 20% mol BiOI/Bi2WO6/ACF composite.
BiOI/Bi2WO6. Therefore, the ability to remove toluene was more obvious when activated carbon fiber felt and BiOI/Bi2WO6 were combined.
3.2.5. Stability of the photocatalyst As shown in Fig. 14, After 600 min of toluene removal reaction, the toluene removal efficiency of 20% mol BiOI/Bi2WO6/ACF can still reach 72.75%. Among them, the loss of removal may be due to the complex pore structure of the composites, and the toluene molecules adsorbed in these channels are not easy to be resolved. At the same time, it can also be explained that the composite material has a strong toluene removal ability and is a good composite material.
4. Conclusions (1) Using activated carbon fiber (ACF) as the carrier, BiOI/Bi2WO6/ ACF with different loads was prepared by hydrothermal method. The introduction of BiOI did not change the main phase of Bi2WO6, and the composite formed the orthorhombic crystal structure. BiOI was dispersed on the surface of Bi2WO6. The well conductivity of BiOI increased the number of active sites and promotes the separation of photogenerated carriers. It was shown that 20% mol BiOI/Bi2WO6 was uniformly distributed on the surface of ACF and increased the specific surface area of the composite photocatalytic materials. BiOI and Bi2WO6 existed in the composites and kept their original structures. There was a synergistic effect between them and the BiOI and Bi2WO6 composite can broaden the spectral response range and had high activity according to the results of various characterization and analysis. (2) The photocatalytic removal of toluene showed that the activity of composite photocatalyst was better than that of Bi2WO6. When the concentration of toluene was about 568 mg/m3 and the light intensity was 24 W, 20% mol BiOI/Bi2WO6/ACF had the best removal effect, and the removal rate arrived at 76.33%, which was 2.4 times of the Bi2WO6.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (51202294), Shandong Province Natural Science Foundation of China (ZR2019MEE112) and the Fundamental Research Funds for the Central Universities of China (18CX02123A). 168
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
[37] D. Jiang, L. Chen, J. Zhu, M. Chen, W. Shi, J. Xie, Novel p-n heterojunction photocatalyst constructed by porous graphite-like C3N4 and nanostructured BiOI: facile synthesis and enhanced photocatalytic activity, Dalton Trans. 42 (2013) 15726–15734. [38] H. An, B. Lin, C. Xue, X. Yan, Y. Dai, J. Wei, G. Yang, Formation of BiOI/g-C3N4 nanosheet composites with high visible-light-driven photocatalytic activity, Chin. J. Catal. 39 (2018) 654–663. [39] J. Wang, L. Tang, G. Zeng, et al., Atomic scale g-C3N4/Bi2WO6, 2D/2D heterojunction with enhanced photocatalytic degradation of ibuprofen under visible light irradiation, Appl. Catal. B Environ. 209 (2017) 285–294. [40] K. Zhang, J. Wang, W. Jiang, W. Yao, H. Yang, Y. Zhu, Self-assembled perylene diimide based supramolecular heterojunction with Bi2WO6 for efficient visiblelight-driven photocatalysis, Appl. Catal. B Environ. 232 (2018) 175–181. [41] J. Sheng, X. Li, Y. Xu, Effect of sintering temperature on the photocatalytic activity of flower-like Bi2WO6, Acta Phys. -Chim. Sin. 30 (2014) 508–512. [42] G. Zhang, L. Fan, M. Li, J. Yang, X. Zhang, B. Huang, Synthesis of nanometer Bi2WO6, synthesized by sol–gel method and its visible-light photocatalytic activity for degradation of 4BS, J. Phys. Chem. Solids 71 (2010) 579–582. [43] H. Huang, K. Xiao, Y. He, et al., In situ assembly of BiOI@Bi12O17Cl2 p-n junction: charge induced unique front-lateral surfaces coupling heterostructure with high exposure of BiOI {001} active facets for robust and nonselective photocatalysis, Appl. Catal. B Environ. 199 (2016) 75–86. [44] Z. Lin, W. Wang, S. Liu, L. Zhang, H. Xu, W. Zhu, A sonochemical route to visiblelight-driven high-activity BiVO4 photocatalyst, J. Mol. Catal. A Chem. 252 (2006) 120–124. [45] M. Gotic, S. Music, M. Ivanda, M. Soufek, M. Popovic, Synthesis and characterisation of bismuth(III) vanadate, J. Mol. Struct. 744 (2005) 535–540. [46] X. Zhang, Z. Ai, F. Jia, L. Zhang, Generalized one-pot synthesis, characterization, and photocatalytic activity of hierarchical BiOX (X = Cl, Br, I) nanoplate microspheres, J. Phys. Chem. C 112 (2008) 747–753.
Chem. Eng. J. 351 (2018) 295–303. [27] W. He, Y. Sun, G. Jiang, H. Huang, X. Zhang, F. Dong, Activation of amorphous Bi2WO6 with synchronous Bi metal and Bi2O3 coupling: photocatalysis mechanism and reaction pathway, Appl. Catal. B Environ. 232 (2018) 340–347. [28] J. Wang, W. Shi, D. Liu, Z. Zhang, Y. Zhu, D. Wang, Supramolecular organic nanofibers with highly efficient and stable visible light photooxidation performance, Appl. Catal. B Environ. 202 (2017) 289–297. [29] F. Xu, H. Chen, C. Xu, D. Wu, Z. Gao, Q. Zhang, K. Jiang, Ultra-thin Bi2WO6 porous nanosheets with high lattice coherence for enhanced performance for photocatalytic reduction of Cr(VI), J. Colloid Interface Sci. 525 (2018) 97–106. [30] M. Hojamberdiev, Z. Kadirova, Y. Makinose, G. Zhu, N. Matsushita, J. Rodriguez, S. Aldabe Bilmes, M. Hasegawa, K. Okada K, Influence of BiOI content on the photocatalytic activity of Bi2WO6/BiOI/allophane composites and molecular modeling studies of acetaldehyde adsorption, J Taiwan Inst Chem E, 81(2017), pp. 258–264. [31] G. Zhu, M. Hojamberdiev, S. Zhang, et al., Enhancing visible-light-induced photocatalytic activity of BiOI microspheres for NO removal by synchronous coupling with Bi metal and graphene, Appl. Surf. Sci. 467-468 (2019) 968–978. [32] Y. Chen, J. Fang, S. Lu, W. Xu, Z. Liu, X. Xu, Z. Fang, One-step hydrothermal synthesis of BiOI/Bi2WO6 hierarchical heterostructure with highly photocatalytic activity, J. Chem. Technol. Biotechnol. 90 (2015) 947–954. [33] Y. Huang, Y. Gao, Q. Zhang, et al., Biocompatible FeOOH-carbon quantum dots nanocomposites for gaseous NOx, removal under visible light: improved charge separation and high selectivity, J. Hazard. Mater. 354 (2018) 54–62. [34] Y. Cui, W. Hong, H. Li, X. Wu, X. Fan, L. Zhu, Photocatalytic degradation and photocatalytic mechanism of methyl orange and phenol by BiOI/Bi2WO6, Inorg. Chim. Acta 30 (2014) 431–441. [35] X. Meng, Z. Zhang, New insight into BiOX(X = Cl, Br, and I) hierarchical microspheres in photocatalysis, Mater. Lett. 225 (2018) 152–156. [36] H. Huang, C. Liu, et al., Self-sacrifice transformation for fabrication of type-I and type-II heterojunctions in hierarchical BixOyIz/g-C3N4 for efficient visible-light photocatalysis, Appl. Surf. Sci. 470 (2019) 1101–1110.
169
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full length article
Study on preparation and toluene removal of BiOI/Bi2WO6/ACF photocatalyst Yongqiang Wanga,b, a b
⁎,1
T
⁎
, Shan Jianga,1, Fang Liua,b, , Chaocheng Zhaoa, Dongfeng Zhaoa, Xinfu Lia
College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China State Key Laboratory of Petroleum Pollution Control, China University of Petroleum (East China), Qingdao 266580, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Photocatalysis Bi2WO6 Toluene Activated carbon fiber
The BiOI/Bi2WO6/ACF composite photocatalysts with different loads were prepared by hydrothermal method, and the catalysts were characterized by XRD, SEM, TEM, BET, XPS, DRS and photocurrent responses. The photocatalytic activity of the samples was studied with the toluene as model pollutant. The results showed that 20%mol BiOI/Bi2WO6 was uniformly loaded on the activated carbon fiber (ACF), and Bi2WO6 (133) orthorhombic crystal face and BiOI (012) tetragonal crystal face can be observed on the catalyst surface. The specific surface area of 20% mol BiOI/Bi2WO6/ACF is 787 m2·g−1, which is much higher than that of Bi2WO6/ACF. BiOI and Bi2WO6 exist simultaneously in the BiOI/Bi2WO6 according to the results of XPS, which corresponds to the results of TEM characterization, indicating that the composites were successfully prepared, and the absorption band edge and intensity of Bi2WO6 was enhanced greatly by the compositing of BiOI. The toluene removal efficiency could arrive at 76.3% for the concentration of 500 mg/m3 with the 20%mol BiOI/Bi2WO6/ACF.
1. Introduction In recent years, haze weather and ozone pollution are becoming more and more serious in china [1,2], volatile organic compounds (VOCs) is the main contributors of these problems, and toluene is a typical representative substance of VOCs [3]. There are many ways to escape toluene, which is harmful to people's production and life [4]. At present, the semiconductor photocatalysis technology cannot only be used in catalytic hydrolysis to produce H2 but also in pollution treatment. Photocatalytic technology has attracted much attention in the field of air purification because of its high degradation efficiency, no secondary pollution [5–8], economy and other advantages, and has broad application prospects [9–12]. Bi2WO6 is a new type of visible light non-titanium catalyst and was studied in recent years because of their nontoxicity, strong oxidizing power and visible light responsive. As a gap semiconductor material, its band gap width is about 2.7 eV [13–16]. However, the application of Bi2WO6 is greatly limited because of its high photoelectron recombination rate and its ability to absorb light less than 450 nm [17–20]. There are many ways to improve its photocatalytic performance, such as doping with CuO [21], ZnO [22] and C3N4 [23,24], and combining with narrow band gap semiconductor [25–29].
BiOI, as a highly anisotropic gap semiconductor, has a strong optical absorption ability in the 400–700 nm region, a narrow band gap width (1.7–1.9 eV), and a highly anisotropic layered structure of PbFCl type [30–32]. It has good adsorption and photocatalytic properties. In addition, the excited electrons must pass through a certain k-layer if they want to be excited by the valence band, so the recombination probability of BiOI photoinduced electron hole pairs is relatively low [33,34]. The photocatalytic performance of Bi2WO6 can be increased by the doping of BiOI because that BiOI improves the optical absorption characteristics in the visible region and the separation efficiency of photogenerated carriers, reduce the recombination probability of photoinduced electron hole pairs [35–39]. Up to now, there are many studies on the application of photocatalyst in the treatment of wastewater, but few researches on the treatment of VOCs, the literatures of using the activated carbon fiber (ACF) as the carrier to remove toluene is few. When ACF was used as a carrier to support BiOI/Bi2WO6 composite photocatalyst, ACF could adsorb low concentration organic pollutants quickly, then organic pollutants can be enriched on ACF and diffused to the interface of BiOI/Bi2WO6/ACF rapidly, so that the photocatalytic reaction could be accelerated. In this paper, BiOI/Bi2WO6/ACF photocatalysts with different loadings were prepared with hydrothermal method and characterized by XRD, SEM, TEM, BET, XPS, DRS and photocurrent responses, the
⁎
Corresponding authors at: College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China. E-mail addresses: [email protected] (Y. Wang), [email protected] (F. Liu). 1 Co-first authors; they have contributed equally to this work. https://doi.org/10.1016/j.apsusc.2019.05.228 Received 28 March 2019; Received in revised form 28 April 2019; Accepted 19 May 2019 Available online 20 May 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
photocatalytic activity of toluene as target pollutant was studied. The effects of BiOI loading, toluene concentration and light intensity on catalytic activity were discussed. 2. Experimental 2.1. Preparation of photocatalysts 2.1.1. Reagent Chemicals in the experiment were obtained from Sinopharm Chemical Reagent Co., Ltd. and without further purification. 2.1.2. Preparation of BiOI Bi(NO3)3·5H2O (1.36 g) was dissolved in 80 ml ethanol, stirred for 60 min, then 0.8 g PVP was added to the solution, stirred for several minutes and KI (0.4648 g) was added to obtain orange-yellow precipitation. After covering the film, stirred for 10 h, and then washed with absolute ethanol and deionized water until the supernatant was clear, then precipitated at the bottom of the centrifugal tube in a vacuum drying box and dried for 12 h.
Fig. 1. XRD patterns of Bi2WO6 and BiOI/Bi2WO6 samples.
2.1.3. Preparation of BiOI/Bi2WO6 Bi (NO3)3·5H2O (0.005 mol) was dissolved in 25 ml dilute nitric acid (including 5 ml concentrated nitric acid) to form A solution; Na2WO4·2H2O (0.0025 mol) was dissolved in 40 ml deionized water to form B solution; A and B solutions were mixed evenly to form C solution; According to the 0.05:1, 0.1:1, 0.2:1, 0.3:1 and 0.4:1 M ratio of BiOI to Bi2WO6, different amounts of BiOI were added into C solution, stirred for 30 min and then moved into 100 ml hydrothermal reactor. The filling ratio of BiOI/Bi2WO6 photocatalyst was 80%, and then heated at 160 °C for 20 h.
2.3. Activity evaluation of catalysts The catalytic activity of catalytic materials was evaluated by a selfmade photocatalytic reactor. The photocatalytic reactor was consisted of dynamic gas distribution part, photocatalytic reaction part and sampling part. In the gas distribution part, toluene mixtures with different concentrations were prepared by adjusting the total air flow rate and the intake of toluene. After mixing uniformly in the gas mixing bottle, both of them maintained a certain flow rate and passed through the quartz tube with BiOI/Bi2WO6/ACF composite material. The light source used 8 W ultraviolet lamp, and the main wavelength of light is 185 nm and the toluene was tested by Varian GC-3800.
2.1.4. Preparation of BiOI/Bi2WO6/ACF 2.1.4.1. ACF preprocessing. The ACF with the size of 100 ∗ 100 (mm) was immersed in 50% ammonia solution and cleaned by ultrasonic wave for 30 min. The ACF was washed three times with deionized water, and then immersed in 50% nitric acid solution. Then that was cleaned by ultrasonic wave for 30 min. Took out the ACF and washed it with deionized water for 3 times, then put it in oven and bake it at 100 °C to dry. The dried ACF was cut into 20 ∗ 20 (mm) spare parts.
3. Results and discussion 3.1. Characterization of catalysts 3.1.1. XRD The results of X ray diffraction (XRD) analysis of BiOI/Bi2WO6 with different loading capacity were shown in Fig. 1. It was shown that all the composite photocatalysts exhibited a coexistence of both tetragonal BiOI (JCPDS card No. 73-2062) and orthorhombic Bi2WO6 (JCPDS card No. 39-0256) phases, the characteristic peaks around 2ɵ of 28.31°, 32.83°, 47.13°, 55.6°, 58.5° and 68.8° were indexed to those of orthorhombic Bi2WO6, corresponding to (113), (002), (202), (133), (262) and (004) peaks, respectively [17,40–42]. The strong and sharp diffraction peaks indicated that all samples were highly crystalline. The characteristic peaks of BiOI can be observed at 29.6°, 31.77°, 45.51°, 55.15°, 66.4°, corresponding to (102), (110), (104), (212) and (220) peaks, respectively, and there was no other heterozygous peaks, which indicated that the purity of BiOI was higher. However, the characteristic peaks of BiOI did not appear at the low amount, which might be due to the relatively low diffraction intensity of the BiOI. The characteristic peak strength of Bi2WO6 decreased obviously, which may be due to the higher characteristic peak strength of Bi2WO6, which resulted in the relative obscurity or disappearance of the characteristic peak of the composite.
2.1.4.2. Loading on ACF. Used 1 ml epoxy resin solution which was diluted for 10 times and BiOI/Bi2WO6 (0.08 g) photocatalyst powder in a beaker. The photocatalyst solution was loaded on ACF by ultrasonic vibration. The composites were dried at 60 °C for 4 h and then the BiOI/ Bi2WO6/ACF composites were obtained by heat treatment for 2 h at 400 °C in a tubular furnace with N2 protection. 2.2. Catalysts characterization The X'Pert Pro MPD powder X-ray diffractometer (XRD) was made by Panalytical Company, which was used to analyze the crystallographic structure and chemical composition of the catalytic material, which used Cu-Ka radiation (40 kV, 50 mA) at a scanning rate of 4°min−1, 2θ ranges from 10° to 80°. The surface morphology and structure of the catalyst were observed and analyzed by scanning electron microscopy (SEM, S-4800) and high-resolution transmitting electron microscopy (HRTEM, JEM-2100f). X-ray photoelectron spectroscopy (XPS, Amicus Budget, Japan) was used to explore the chemical state of elements. Surface areas and porosity of photocatalysts were measured by the Brunauer–Emmett–Teller (BET) method (Tri Star3000). The optical properties of the prepared materials were analyzed by the UV–vis diffuse reflectance spectra (DRS) tested on a spectrometer (UV2550, Shimadzu, Japan), using BaSO4 as background reference. The photocurrent responses were measured on a CHI 660B electrochemical system.
3.1.2. SEM and TEM images The morphological structure of as-prepared BiOI/Bi2WO6 samples was examined by SEM and HRTEM. It was shown that the surface of ACF without catalyst was smooth and free of impurities, arranged in a duct-like arrangement in Fig. 2a. It was shown that the surface of the ACF was covered with catalyst, but the catalyst had large particle size, 162
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 2. SEM images of ACF, Bi2WO6/ACF and BiOI/Bi2WO6/ACF: a ACF; b Bi2WO6/ACF; c, d 20%mol BiOI/Bi2WO6/ACF; e, f 10%mol BiOI/Bi2WO6/ACF.
3.1.3. XPS characterization The surface chemical composition and valence state of 20% mol BiOI/Bi2WO6/ACF were analyzed by XPS. As shown in Fig. 4a, the Bi in the sample consists of two peaks with binding energies of 158.8 and 164.1 eV, corresponding to Bi 4f7/2 and Bi 4f5/2, respectively. This indicated that the Bi element exists at positive trivalence in 20% mol BiOI/Bi2WO6/ACF. As shown in Fig. 4b, peaks at 37.2 eV and 35.1 eV corresponded to W 4f5/2 and W 4f7/2, respectively, indicating that W existed as a positive hexavalent in 20% mol BiOI/Bi2WO6/ACF. The peaks at 618.8 eV and 630.3 eV were characteristic peaks of I 3d5/2 and I 3d3/2 (Fig. 4c), indicating that element I exists in 20% mol BiOI/ Bi2WO6/ACF in the form of negative monovalent. The O 1s binding energy (Fig. 4d) of 530.1 eV can be attributed to the lattice oxygen in Bi2WO6 and BiOI.
uneven dispersion and agglomeration, and the binding strength with ACF was not high, and the load was small in Fig. 2b. It was shown that 20% mol BiOI/Bi2WO6 photocatalyst prepared by hydrothermal method was interlaced on ACF in clusters to form a dense film in Fig. 2c and d. The fiber rods were almost completely coated and dispersed uniformly without agglomeration. BiOI/Bi2WO6/ACF with uniform load and stable bonding strength was formed. Compared with Fig. 2b, the composite photocatalyst had higher dispersion and larger specific surface area than monomer photocatalyst. In Fig. 2e and f, 10% mol BiOI/Bi2WO6 photocatalyst was loaded on the surface of ACF unevenly, and no dense film was formed. Some areas of the fiber rod were not completely coated, and the load of the catalyst was less, which was consistent with the results of the activity test of the composite material. Fig. 3a showed that there are many regular spherical protrusions on the surface of the sample with large specific surface area, which improved the sample more adsorptive and has higher photocatalytic oxidation ability. The existence of discontinuous lattice can be clearly seen in Fig. 3b. The lattice fringe spacing was analyzed and measured accurately. The lattice fringe spacing was 0.305 nm and 0.320 nm, which corresponded to the Bi2WO6 (133) crystal face of orthorhombic system and BiOI (012) crystal face of tetragonal system respectively. BiOI and Bi2WO6 were effectively combined.
3.1.4. Brunauer-Emmett-Teller specific surface area The specific surface area of the composite was determined as shown in Table 1. The results showed that the specific surface area of ACF treated by activation is larger, up to 1575 m2·g−1, because the surface of blank ACF was clean and free of impurities, and the pores were not blocked. The specific surface area of Bi2WO6/ACF was the smallest. It was shown that Bi2WO6 had larger particle size and agglomeration phenomenon, 163
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 3. TEM images of 20% mol BiOI/Bi2WO6.
which blocked the pore structure of some ACF combining with SEM images. The specific surface area of 10% mol BiOI/Bi2WO6/ACF was the largest, because the particle size of the composite catalyst decreased with the addition of BiOI, and the particles were evenly distributed on the surface of ACF without agglomeration. The SEM images showed that 10% mol BiOI/Bi2WO6 was not completely coated on the surface of ACF, and less pore structure was blocked. The specific surface area of 20% mol BiOI/Bi2WO6/ACF was less than 10% mol BiOI/Bi2WO6/ACF, which may be due to the 20% mol BiOI/Bi2WO6 photocatalyst was more uniformly coated on the surface of ACF rod, more pore structure was blocked. The specific surface area of 30% mol BiOI/Bi2WO6/ACF and 20% mol BiOI/Bi2WO6/ACF was almost the same, which showed that the specific surface area of the composite was not a simple linear relationship with the loading of BiOI, but there was an optimum loading range. 3.1.5. DRS characterization The UV–Vis diffuse reflectance spectra of Bi2WO6, BiOI and BiOI/ Bi2WO6 composite photocatalysts with different loadings were shown in Fig. 5. It can be seen that all the photocatalysts had response in the ultraviolet and visible light region. The absorption band edge of Bi2WO6 was narrow, the absorption band edge of BiOI was about 420 nm and the composite showed enhanced absorption for visible light. The absorption band edge and absorption intensity of the composite expressed a trend of enhancement by compositing with BiOI. It was showed that there was obvious interaction between Bi2WO6 and BiOI. The band gap of photocatalyst were calculated according to the Kubelka-Muck function equations:
F (R) =
K (1 − R)2 = S 2R
(1)
The band gap energy of the photocatalyst can be obtained by plotting the [F(R) × hν]n/2 vs. hν and making tangent to it, K was the sample absorption coefficient, S was the sample reflection coefficient, R was the sample diffuse reflectance (%), h was the Planck constant
Fig. 4. XPS spectra of 20% mol BiOI/Bi2WO6/ACF: a Bi 4f; b W 4f; c I 3d; d O 1s.
164
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Table 1 BET, pore volume and size of composite materials prepared by different samples. Sample ACF 10% mol BiOI/Bi2WO6/ACF 20% mol BiOI/Bi2WO6/ACF 30% mol BiOI/Bi2WO6/ACF Bi2WO6/ACF
SBET/(m2·g−1)
Pore size/nm
Pore volume/(cm3·g−1)
1575 855 788 782 772
2.92 4.35 4.35 4.39 4.57
0.15 0.14 0.12 0.13 0.13
Fig. 6. Mott-Schottky conduction band curves of Bi2WO6 and BiOI.
and the E represented the voltage (eV). The valence band position can be calculated based on this formula
EVB = ECB + Eg
(2)
where the Eg represented the semiconductor band gap energy, EVB represented the valence band potential of semiconductors, and ECB represented the conduction band potential of semiconductors. According to the formula, the valence band position of Bi2WO6 and BiOI was 2.28 V and 0.9 V respectively. The schematic diagram of the band structure of Bi2WO6 and BiOI were shown in Fig. 7, according to the calculation results. The e− of Bi2WO6 and BiOI can transit from valence band to conduction band and generate holes in valence band under ultraviolet excitation, and the e− will move from BiOI to Bi2WO6 because that the conduction band of BiOI (−0.87 V) is lower than Bi2WO6 (−0.43 V). Moreover, the valence band of Bi2WO6 is more higher than that of BiOI, and the hole is transferred from the valence band of Bi2WO6 to the valence band of BiOI, so the photocatalytic reaction was improved because the effective separation of photogenerated electrons and holes. The photocatalytic activity of BiOI/Bi2WO6 is higher than that of pure Bi2WO6 and BiOI because the energy level matching of BiOI/Bi2WO6 heterojunction structure is beneficial to catalytic redox reaction. The electrons gathered at the CB are further transformed into %O2− with powerful oxidation ability, subsequent inducing the decomposition of various contaminants [43]. Reactive oxygen species, such as superoxide radicals (%O2−) and hydroxyl radicals (%OH) have strong oxidative ability and take crucial role in the photodegradation reactions.
Fig. 5. UV–vis spectra for the as-synthesized Bi2WO6 samples, BiOI samples, the photocatalyst of different proportion and plots of the [F(R) × hν]1/2 vs. hν curves of Bi2WO6 and BiOI catalyst.
(eV·s), ν was the optical frequency (Hz). When the sample was a direct semiconductor, n is 4 and when the sample was indirect semiconductor, n is 1, Because BiOI was an indirect semiconductor so n is 1. Fig. 5 showed the fitting band gap energy. The intercept between tangent and X axis was similar to the band gap energy of semiconductor. The band gap energies of Bi2WO6 and BiOI were 2.71 eV and 1.77 eV.
3.1.7. Photocurrent response analysis According to the periodic switch xenon lamp, the photocurrent response was tested. After illumination, the electrons in the Bi2WO6 and BiOI were transferred to conductive glass by the conduction band, resulting in the photocurrent response. The stronger the photocurrent response was, the higher the separation efficiency of the photogenerated electron hole pairs was. When the xenon lamp was turned on, the photocurrent response of the working electrode increased suddenly,
3.1.6. Band structure analysis The band gap energies of Bi2WO6 and BiOI were calculated to be 2.71 eV and 1.77 eV respectively by Kubelka-Muck equation. Referring to the calomel electrode, the positions of Bi2WO6 and BiOI conduction band (CB) were calculated by Mott-Schottky as −0.43 V and 0.87 V vs. NHE, respectively (Fig. 6). Where C represented the differential charge capacitance (F/cm2) of the space charge layer of the semiconductor, 165
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 9. Effect of different BiOI loading amount of active group on removal effect of toluene.
was the result of interaction and interaction of various factors. 3.2. Catalyst activity for toluene oxidation 3.2.1. Effect of BiOI loading on toluene removal The effect of BiOI loading on toluene removal was investigated by controlling the concentration of toluene gas at about 350 mg/m3. The results were shown in Fig. 9. As shown in Fig. 9, the removal ability of BiOI/Bi2WO6/ACF decreased gradually with the reaction proceeding, but the catalytic activity of Bi2WO6/ACF composites was lower than that of other composites. In the first 60 min of the reaction, the toluene removal rate of the composites can reached 100%, which was due to the combined effect of the adsorption of activated carbon fiber felt and the photocatalytic degradation of the catalyst. Subsequently, the activated carbon fiber felt gradually tended to adsorption saturation, the removal rate of toluene declined continuously, and the removal rate of toluene tended to be stable after 150 min. This was due to the adsorption saturation of activated carbon fiber felt, and the catalyst activity remained at a stable level. When the reaction duration was about 240 min, the removal rates of toluene by Bi2WO6/ACF, 5%mol BiOI/ Bi2WO6/ACF, 10%mol BiOI/Bi2WO6/ACF, 20%mol BiOI/Bi2WO6/ACF, 30%mol BiOI/Bi2WO6/ACF and 40%mol BiOI/Bi2WO6/ACF were 31.84%, 39.01%, 69.96%, 76.33%, 60.06% and 52.84% respectively. It was found that the activity of the composite photocatalyst was better than that of the monomer catalyst, and the 20%mol BiOI/Bi2WO6/ACF expressed the best catalytic activity. When the amount of BiOI was less than 20%, the number of active sites on the surface of Bi2WO6 monomer increased with the addition of BiOI, which increased the electron migration efficiency, thus reducing the recombination rate of electron-hole pairs and improving the quantum efficiency of materials [44,45]. This was also consistent with the SEM characterization results. It was also found that the synergistic effect of the heterostructures formed by the two compounds played an important role in enhancing the photocatalytic performance. The toluene removal rate decreased with the increased of BiOI content, which may be due to more BiOI aggregates on the surface of Bi2WO6 and covered the active sites, which hindered the electron migration. At the same time, the specific surface area of BiOI nanoparticles decreased due to the larger particle size of Bi2WO6, which leaded to the decrease of catalytic activity [46]. In order to better understand the change of toluene removal in BiOI/Bi2WO6/ ACF composites, the change curve of inlet and outlet concentration of 20%mol BiOI/Bi2WO6/ACF was drawn, as shown in Fig. 10. As shown in Fig. 10, the inlet concentration expressed a gradual
Fig. 7. Schematic illustration of the band gap structures of Bi2WO6 and BiOI.
Fig. 8. Photocurrent of Bi2WO6 samples and the photocatalyst of different proportion.
which was due to the rapid separation of the photogenerated carriers; when the xenon lamp was turned off, the photocurrent response will remain at a weak level, corresponding to the initial current intensity. It was found that BiOI/Bi2WO6 composite photocatalyst had stronger photocurrent response compared with Bi2WO6. The photocurrent response intensity of 20%mol BiOI/Bi2WO6 was obviously better than that of other BiOI composite photocatalysts, indicating that it had longer photogenerated electron hole survival time and higher photogenerated electron hole separation efficiency, which was more conducive to the effective transfer of interface electrons. As shown in Fig. 8 that the photocurrent response test were not completely consistent with the photocatalytic performance test, which showed that photocurrent response was not the only factor determining the activity of the catalyst. The process of photocatalytic reaction was very complicated. It
166
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
Fig. 10. Changes in the concentration of import and export. Fig. 12. Effect of different light intensity on removal effect of toluene.
increasing trend, which was due to the longer experimental period in a day, the toluene concentration will increase slightly with the temperature rise. As the export concentration gradually increased with the gradual deactivation of the composites, the increase was more and more significant. It was found that the change rate of toluene removal had a decreasing trend.
device to change the light intensity, as shown in Fig. 12. As shown in Fig. 12, the stronger the light intensity was, the faster the degradation rate was. The removal rates of toluene for one, two and three lamps were 53.92%, 66.37% and 76.33%, when the reaction was about 240 min. Because the activation energy of photoreaction comes from the energy of photon, so the intensity of light had a significant effect on the reaction rate. However, the toluene removal rate did not double with the increase of light intensity, which may be due to the limited number of active sites indicated by the catalytic materials, resulting in the light intensity and toluene removal rate was not a simple multiple relationship.
3.2.2. Effect of toluene concentration on removal of toluene 20%mol BiOI/Bi2WO6/ACF was used to investigate the effect of different toluene concentrations on toluene removal. The results were shown in Fig. 11. As shown in Fig. 11, the toluene removal rates of 20% mol BiOI/ Bi2WO6/ACF were 76.33%, 72.39%, 57.92% and 31.37% at toluene concentrations of 385 mg/m3, 568 mg/m3, 846 mg/m3 and 2106 mg/ m3 after 240 min. With the increase of toluene concentration, the removal rate of toluene decreased and the removal rate decreases. This was due to the toluene tolerance range of the composite materials. Within the toluene tolerance range, the removal rate decreased with the increase of the toluene concentration. When the toluene concentration exceeds the tolerated range, the catalyst will lose its catalytic activity. 3.2.3. Effect of light intensity on toluene removal Light intensity affects the degradation rate of organic matters. The effect of light intensity on toluene removal was investigated by reducing the number of lamps in the reaction section of the experimental
3.2.4. Comparison of removal efficiency of toluene by adsorption photocatalytic oxidation and dark reaction adsorption As shown in Fig. 13, the removal capacity of ACF decreased with the reaction. However, when the lamp was not turned on, the adsorption capacity of composite materials was reduced, and the removal capacity of toluene decreased rapidly. When the lamp was turned on, the removal rate of toluene decreased slowly, indicating that the removal ability had been improved significantly and can be maintained at a relatively high level for a long time. It was proved that BiOI/Bi2WO6/ ACF composites combined the adsorption advantages of activated carbon and the photocatalytic degradation advantages of BiOI/Bi2WO6. The removal efficiency of toluene was more obvious than that of ACF or
Fig. 11. Effect of different toluene concentration on removal effect of toluene.
Fig. 13. Comparison of adsorption and photocatalytic degradation of toluene. 167
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
100
Declaration of Competing Interest The authors declare that they have no conflict of interest.
80
Removal/%
References 60
[1] J. Zhang, C. Zhang, H. He, Remarkable promotion effect of trace sulfation on OMS-2 nanorod catalysts for the catalytic combustion of ethanol, J. Environ. Sci. (China) 35 (2015) 69–75. [2] B. Giri, K. Kim, R. Pandey, J. Cho, H. Song, Y. Kim, Review of biotreatment techniques for volatile sulfur compounds with an emphasis on dimethyl sulfide, Process Biochem. 49 (2014) 1543–1554. [3] T. Jarangdet, K. Pratumyot, K. Srikittiwanna, W. Dungchai, W. Mingvanish, I. Techakriengkrai, M. Sukwattanasinitt, N. Niamnot N, A fluorometric paper-based sensor array for the discrimination of volatile organic compounds (VOCs) with novel salicylidene derivatives, Dyes Pigments, 159(2018), pp. 378–383. [4] M. Handa, Y. Lee, M. Shibusawa, M. Tokumura, Y. Kawase, Removal of VOCs in waste gas by the photo-Fenton reaction: effects of dosage of Fenton reagents on degradation of toluene gas in a bubble column, J. Chem. Technol. Biotechnol. 88 (2013) 88–97. [5] C. Chen, W. Ma, J. Zhao, Semiconductor-mediated photodegradation of pollutants under visible-light irradiation, J. Cheminf. 39 (2010) 4206–4219. [6] Y. Wang, W. Jiang, W. Luo, X. Chen, Y. Zhu, Ultrathin nanosheets g-C3N4 @Bi2WO6 core-shell structure via low temperature reassembled strategy to promote photocatalytic activity, Appl. Catal. B Environ. 237 (2018) 633–640. [7] J. Di, C. Chen, C. Zhu, et al., Bismuth vacancy mediated single unit cell Bi2WO6 nanosheets for boosting photocatalytic oxygen evolution, Appl. Catal. B Environ. 238 (2018) 119–125. [8] L. Yuan, K. Lu, F. Zhang, X. Fu, Y. Xu, Unveiling the interplay between light-driven CO2 photocatalytic reduction and carbonaceous residues decomposition: a case study of Bi2WO6-TiO2, binanosheets, Appl. Catal. B Environ. 237 (2018) 424–431. [9] H. Jiang, Q. Wang, S. Zang, J. Li, Q. Wang, Enhanced photoactivity of Sm, N, Ptridoped anatase-TiO₂ nano-photocatalyst for 4-chlorophenol degradation under sunlight irradiation, J. Hazard. Mater. 261 (2013) 44–54. [10] H. Lu, Q. Hao, T. Chen, L. Zhang, D. Chen, C. Ma, W. Yao, Y. Zhu, A high-performance Bi2O3/Bi2SiO5, p-n heterojunction photocatalyst induced by phase transition of Bi2O3, Appl. Catal. B Environ. 237 (2018) 59–67. [11] L. Yan, Y. Wang, H. Shen, Y. Zhang, J. Li, D, Wang, Photocatalytic activity of Bi2WO6/Bi2S3 heterojunctions: the facilitation of exposed facets of Bi2WO6 substrate, Appl. Surf. Sci. 393(2017), pp. 496–503. [12] Y. Fu, C. Chang, P. Chen, X. Chu, L. Zhu, Enhanced photocatalytic performance of boron doped Bi₂WO₆ nanosheets under simulated solar light irradiation, J. Hazard. Mater. 254 (2013) 185–192. [13] B. Li, X. Yang, F. Du, Hydrothermal synthesis and photocatalytic activities of Bi2WO6 with different surfactant, Appl. Mech. Mater. 395 (2013) 741–745. [14] Z. Zhu, Y. Yan, J. Li, One-step synthesis of flower-like WO3/Bi2WO6, heterojunction with enhanced visible light photocatalytic activity, J. Mater. Sci. 51 (2016) 2112–2120. [15] Y. Yang, J. Cui, H. Jin, F. Cao, A three-dimensional (3D) structured Bi2WO6-palygorskite composite and their enhanced visible light photocatalytic property, Sep. Purif. Technol. 205 (2018) 130–139. [16] Y. Zhu, Y. Wang, Q. Ling, Y. Zhu, Enhancement of full-spectrum photocatalytic activity over BiPO4/Bi2WO6, composites, Appl. Catal. B Environ. 200 (2017) 222–229. [17] T. Saison, N. Chemin, C. Chaneac, et al., Bi2O3, BiVO4, and Bi2WO6: impact of surface properties on photocatalytic activity under visible light, J. Phys. Chem. C 115 (2011) 5657–5666. [18] Z. Liu, F. Chen, Y. Gao, Y. Liu, P. Fang, S. Wang, A novel synthetic route for magnetically retrievable Bi2WO6 hierarchical microspheres with enhanced visible photocatalytic performance, J. Mater. Chem. A 1 (2013) 7027–7030. [19] A. Phuruangrat, P. Dumrongrojthanath, S. Thongtem, T. Thongtem, Hydrothermal synthesis of I-doped Bi2WO6, for using as a visible-light-driven photocatalyst, Mater. Lett. 224 (2018) 67–70. [20] Y. Su, G. Tan, T. Liu, et al., Photocatalytic properties of Bi2WO6/BiPO4 Z-scheme photocatalysts induced by double internal electric fields, Appl. Surf. Sci. 457 (2018) 107–114. [21] P. Kumar, M. Selvakumar, S. Babu, S. Induja, S. Karuthapandian, CuO/ZnO nanorods: an affordable efficient p-n heterojunction and morphology dependent photocatalytic activity against organic contaminants, J. Alloys Compd. 701 (2017) 562–573. [22] J. Ma, K. Wang, L. Li, T. Zhang, Y. Kong, S. Komarnenl, Visible-light photocatalytic decolorization of Orange II on Cu2O/ZnO nanocomposites, Ceram. Int. 41 (2015) 2050–2056. [23] J. Yuan, X. Liu, Y. Tang, et al., Positioning cyanamide defects in g-C3N4: engineering energy levels and active sites for superior photocatalytic hydrogen evolution, Appl. Catal. B Environ. 237 (2018) 24–31. [24] Y. Xu, Y. Chen, W. Fu, Visible-light driven oxidative coupling of amines to imines with high selectivity in air over core-shell structured CdS@C3N4, Appl. Catal. B Environ. 236 (2018) 176–183. [25] H. Li, Y. Cui, W. Hong, High photocatalytic performance of BiOI/Bi2WO6, toward toluene and Reactive Brilliant Red, Appl. Surf. Sci. 264 (2013) 581–588. [26] Y. Wang, Y. Zeng, X. Chen, et al., Tailoring shape and phase formation: rational synthesis of single-phase BiFeWOx nanooctahedra and phase separated Bi2WO6Fe2WO6 microflower heterojunctions and visible light photocatalytic performances,
40
20
20% molBiOI/Bi2WO6/ACF 0
100
200
300
400
500
600
Time/min Fig. 14. The stability of degradation of toluene by 20% mol BiOI/Bi2WO6/ACF composite.
BiOI/Bi2WO6. Therefore, the ability to remove toluene was more obvious when activated carbon fiber felt and BiOI/Bi2WO6 were combined.
3.2.5. Stability of the photocatalyst As shown in Fig. 14, After 600 min of toluene removal reaction, the toluene removal efficiency of 20% mol BiOI/Bi2WO6/ACF can still reach 72.75%. Among them, the loss of removal may be due to the complex pore structure of the composites, and the toluene molecules adsorbed in these channels are not easy to be resolved. At the same time, it can also be explained that the composite material has a strong toluene removal ability and is a good composite material.
4. Conclusions (1) Using activated carbon fiber (ACF) as the carrier, BiOI/Bi2WO6/ ACF with different loads was prepared by hydrothermal method. The introduction of BiOI did not change the main phase of Bi2WO6, and the composite formed the orthorhombic crystal structure. BiOI was dispersed on the surface of Bi2WO6. The well conductivity of BiOI increased the number of active sites and promotes the separation of photogenerated carriers. It was shown that 20% mol BiOI/Bi2WO6 was uniformly distributed on the surface of ACF and increased the specific surface area of the composite photocatalytic materials. BiOI and Bi2WO6 existed in the composites and kept their original structures. There was a synergistic effect between them and the BiOI and Bi2WO6 composite can broaden the spectral response range and had high activity according to the results of various characterization and analysis. (2) The photocatalytic removal of toluene showed that the activity of composite photocatalyst was better than that of Bi2WO6. When the concentration of toluene was about 568 mg/m3 and the light intensity was 24 W, 20% mol BiOI/Bi2WO6/ACF had the best removal effect, and the removal rate arrived at 76.33%, which was 2.4 times of the Bi2WO6.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (51202294), Shandong Province Natural Science Foundation of China (ZR2019MEE112) and the Fundamental Research Funds for the Central Universities of China (18CX02123A). 168
Applied Surface Science 488 (2019) 161–169
Y. Wang, et al.
[37] D. Jiang, L. Chen, J. Zhu, M. Chen, W. Shi, J. Xie, Novel p-n heterojunction photocatalyst constructed by porous graphite-like C3N4 and nanostructured BiOI: facile synthesis and enhanced photocatalytic activity, Dalton Trans. 42 (2013) 15726–15734. [38] H. An, B. Lin, C. Xue, X. Yan, Y. Dai, J. Wei, G. Yang, Formation of BiOI/g-C3N4 nanosheet composites with high visible-light-driven photocatalytic activity, Chin. J. Catal. 39 (2018) 654–663. [39] J. Wang, L. Tang, G. Zeng, et al., Atomic scale g-C3N4/Bi2WO6, 2D/2D heterojunction with enhanced photocatalytic degradation of ibuprofen under visible light irradiation, Appl. Catal. B Environ. 209 (2017) 285–294. [40] K. Zhang, J. Wang, W. Jiang, W. Yao, H. Yang, Y. Zhu, Self-assembled perylene diimide based supramolecular heterojunction with Bi2WO6 for efficient visiblelight-driven photocatalysis, Appl. Catal. B Environ. 232 (2018) 175–181. [41] J. Sheng, X. Li, Y. Xu, Effect of sintering temperature on the photocatalytic activity of flower-like Bi2WO6, Acta Phys. -Chim. Sin. 30 (2014) 508–512. [42] G. Zhang, L. Fan, M. Li, J. Yang, X. Zhang, B. Huang, Synthesis of nanometer Bi2WO6, synthesized by sol–gel method and its visible-light photocatalytic activity for degradation of 4BS, J. Phys. Chem. Solids 71 (2010) 579–582. [43] H. Huang, K. Xiao, Y. He, et al., In situ assembly of BiOI@Bi12O17Cl2 p-n junction: charge induced unique front-lateral surfaces coupling heterostructure with high exposure of BiOI {001} active facets for robust and nonselective photocatalysis, Appl. Catal. B Environ. 199 (2016) 75–86. [44] Z. Lin, W. Wang, S. Liu, L. Zhang, H. Xu, W. Zhu, A sonochemical route to visiblelight-driven high-activity BiVO4 photocatalyst, J. Mol. Catal. A Chem. 252 (2006) 120–124. [45] M. Gotic, S. Music, M. Ivanda, M. Soufek, M. Popovic, Synthesis and characterisation of bismuth(III) vanadate, J. Mol. Struct. 744 (2005) 535–540. [46] X. Zhang, Z. Ai, F. Jia, L. Zhang, Generalized one-pot synthesis, characterization, and photocatalytic activity of hierarchical BiOX (X = Cl, Br, I) nanoplate microspheres, J. Phys. Chem. C 112 (2008) 747–753.
Chem. Eng. J. 351 (2018) 295–303. [27] W. He, Y. Sun, G. Jiang, H. Huang, X. Zhang, F. Dong, Activation of amorphous Bi2WO6 with synchronous Bi metal and Bi2O3 coupling: photocatalysis mechanism and reaction pathway, Appl. Catal. B Environ. 232 (2018) 340–347. [28] J. Wang, W. Shi, D. Liu, Z. Zhang, Y. Zhu, D. Wang, Supramolecular organic nanofibers with highly efficient and stable visible light photooxidation performance, Appl. Catal. B Environ. 202 (2017) 289–297. [29] F. Xu, H. Chen, C. Xu, D. Wu, Z. Gao, Q. Zhang, K. Jiang, Ultra-thin Bi2WO6 porous nanosheets with high lattice coherence for enhanced performance for photocatalytic reduction of Cr(VI), J. Colloid Interface Sci. 525 (2018) 97–106. [30] M. Hojamberdiev, Z. Kadirova, Y. Makinose, G. Zhu, N. Matsushita, J. Rodriguez, S. Aldabe Bilmes, M. Hasegawa, K. Okada K, Influence of BiOI content on the photocatalytic activity of Bi2WO6/BiOI/allophane composites and molecular modeling studies of acetaldehyde adsorption, J Taiwan Inst Chem E, 81(2017), pp. 258–264. [31] G. Zhu, M. Hojamberdiev, S. Zhang, et al., Enhancing visible-light-induced photocatalytic activity of BiOI microspheres for NO removal by synchronous coupling with Bi metal and graphene, Appl. Surf. Sci. 467-468 (2019) 968–978. [32] Y. Chen, J. Fang, S. Lu, W. Xu, Z. Liu, X. Xu, Z. Fang, One-step hydrothermal synthesis of BiOI/Bi2WO6 hierarchical heterostructure with highly photocatalytic activity, J. Chem. Technol. Biotechnol. 90 (2015) 947–954. [33] Y. Huang, Y. Gao, Q. Zhang, et al., Biocompatible FeOOH-carbon quantum dots nanocomposites for gaseous NOx, removal under visible light: improved charge separation and high selectivity, J. Hazard. Mater. 354 (2018) 54–62. [34] Y. Cui, W. Hong, H. Li, X. Wu, X. Fan, L. Zhu, Photocatalytic degradation and photocatalytic mechanism of methyl orange and phenol by BiOI/Bi2WO6, Inorg. Chim. Acta 30 (2014) 431–441. [35] X. Meng, Z. Zhang, New insight into BiOX(X = Cl, Br, and I) hierarchical microspheres in photocatalysis, Mater. Lett. 225 (2018) 152–156. [36] H. Huang, C. Liu, et al., Self-sacrifice transformation for fabrication of type-I and type-II heterojunctions in hierarchical BixOyIz/g-C3N4 for efficient visible-light photocatalysis, Appl. Surf. Sci. 470 (2019) 1101–1110.
169