Fabrication of Bi2SiO5 hierarchical microspheres with an efficient photocatalytic performance for rhodamine B and phenol removal

Accepted Manuscript Title: Fabrication of Bi2 SiO5 hierarchical microspheres with an efficient photocatalytic performance for rhodamine B and phenol removal Authors: Lin Dou, Junbo Zhong, Jianzhang Li, Jieyue Luo, Ying Zeng PII: DOI: Reference:

S0025-5408(18)33900-X https://doi.org/10.1016/j.materresbull.2019.03.031 MRB 10436

To appear in:

MRB

Received date: Revised date: Accepted date:

8 December 2018 30 March 2019 31 March 2019

Please cite this article as: Dou L, Zhong J, Li J, Luo J, Zeng Y, Fabrication of Bi2 SiO5 hierarchical microspheres with an efficient photocatalytic performance for rhodamine B and phenol removal, Materials Research Bulletin (2019), https://doi.org/10.1016/j.materresbull.2019.03.031 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Fabrication of Bi2SiO5 hierarchical microspheres with an efficient photocatalytic performance for rhodamine B and phenol removal Lin Dou a, b, Junbo Zhong b*, Jianzhang Li b, Jieyue Luo b, Ying Zeng a* a

College of Materials and Chemistry & Chemical Engineering, Chengdu University

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of Technology, Chengdu 610059, PR China Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan,

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College of Chemistry and Environmental Engineering, Sichuan University of Science and Engineering, Zigong 643000, PR China

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*Corresponding author (E-mail: [email protected], [email protected])

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Graphical abstract

40 GLY-BSO

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H2O-BSO

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Intensity (a.u.)

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Research Highlights

>3D Bi2SiO5 hierarchical microspheres were successfully prepared.

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>Glycerol acts as a template to guide formation of the Bi2SiO5 hierarchical microspheres. >The solvents play an important role in influencing the growth of Bi2SiO5.

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>Bi2SiO5 microspheres have better photocatalytic performance than the nanoplates.

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Abstract Self-assembled three-dimensional (3D) Bi2SiO5 microspheres were synthesized via a solvothermal method using glycerol as reaction media and NH3•H2O as pH adjustment. The growth of Bi2SiO5 crystal was influenced by the solvothermal time.

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During the preparation process, glycerol acts as a soft template to guide the formation of the hierarchical microspheres. The photocatalytic activities of Bi2SiO5

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microspheres toward the degradation of Rhodamine B and phenol under light irradiation were evaluated. Bi2SiO5 microspheres display much higher photocatalytic

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activity than the Bi2SiO5 nanoplates. The high photocatalytic activity of hierarchical

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Bi2SiO5 microspheres can be ascribed to the enhanced light absorbance, the efficient

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separation of photo-generated electrons and holes and the large surface area. The main

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active species during the photocatalytic reaction are •OH and •O2-, proven by

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terephthalic acid photoluminescence probing technique and nitroblue tetrazolium (NBT) experiments. The Bi2SiO5 microspheres are stable during the photocatalytic

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reaction and can be used repeatedly.

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Keywords: Bi2SiO5; glycerol; microspheres; photocatalytic performance

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1. Introduction

Recently, as a new silicate-based ferroelectric oxide, Bi2SiO5 has been intensely

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investigated due to its nontoxicity, stability and excellent photocatalytic behaviors

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[1-3]. Aurivillius-phase Bi2SiO5 (BSO) crystallizes belong to the orthorhombic system and space group is Cmc21 [4-7]. Bi2SiO5 has a layered structure, which comprises a single layer of one dimensional (SiO3)2- pyroxene file layers sandwiched

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between (Bi2O2)2+ sheets [8-10]. The (Bi2O2)2+ layers and SiO4 tetrahedra are slightly distorted in the crystal structure of BSO. The distorted structure of SiO4 tetrahedra is favorable for the separation of the photo-generated holes and electrons. Therefore, it is anticipated that BSO will display high photocatalytic activity [11-13]. It would be 4

rather valuable to evaluate the photocatalytic activity of the BSO nanostructures. The photocatalytic activity of photocatalyst is tightly related to the preparation methods and the morphology [14-23]. In recent years, there have been increasing interests in the fabrication of three dimensional (3D) hierarchical microspheres

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assembled by nanoplatelets, because 3D nanostructured materials exhibit excellent physical/chemical properties in electrical conductivity [24], optical property [25-29],

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sensor [30-32] and magnetism [33-34]. The morphology-controlled fabrication of nano-/microstructured functional materials has opened up new possibilities to enhance

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their physical and chemical properties and remains a significant challenge.

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Tremendous methods have been developed to fabricate BSO hierarchical

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microspheres, such as using hexadecyl trimethylammonium bromide (CTAB) as

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template agent [9], a novel Bi2SiO5 flower-like microsphere via a phase junction [35],

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flower-like Bi2SiO5/Bi4Si3O12 heterostructures using CTAB-assisted preparation approach and TEOS as Si source [36]. However, successful synthetic strategies for the

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preparation of pure BSO nanocrystals, especially for the 3D hierarchical microspheres

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are still challenges.

As we know, solvothermal synthesis is widely used to prepare photocatalysts,

which is useful to form different conformations by self-assembly [37-39]. The

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viscosity of the solvent significantly influences the ion diffusion rate, which can regulate the crystal growth [40-43]. The morphologies of photocatalysts will be different if different solvents are used in a hydrothermal or solvothermal way. For example, BiOX with the 2D laminar structure or 3D hierarchitectures has been 5

reported by using different solvents, including water, ethanol, ethylene glycol and glycerol [44-46]. However, the effect of glycerol on the preparation and photocatalytic performance of Bi2SiO5 has seldom been concerned. In this study, 3D Bi2SiO5 microspheres assembled by nanoplatelets were

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synthesized via a solvothermal method using glycerol (GLY) as reaction media. The photocatalytic activities of the as-prepared Bi2SiO5 photocatalysts were evaluated by

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degradation of Rhodamine (RhB) and phenol aqueous solution under UV and Xe light

irradiation. The photocatalytic evaluation results demonstrate that the 3D Bi2SiO5

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microspheres display enhanced photocatalytic activity. Furthermore, the enhancement

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2.1 Preparation of samples

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2 Experimental sections

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in photocatalytic activity of 3D Bi2SiO5 microspheres was discussed.

All chemicals with analytical purity were purchased from Chengdu Kelong

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Chemical Reagent Factory (Chengdu, China) and used without further purification.

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3D Bi2SiO5 microspheres were synthesized through a hydrothermal process. Bismuth nitrate pentahydrate (4.8 mmol) was dissolved in 40 mL glycerol (GLY) under vigorous stirring until form transparent solution A. Sodium metasilicate

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nonahydrate (2.4 mmol) was dissolved in 12 mL 2.5% of NH3•H2O solution (1:9) under magnetic stirring to form solution B. Solution B was dropwise added into solution A, and the pH value of the mixture was adjusted to 9.0 by dropwise addition of 2.5% of the NH3•H2O solution. The mixture was further stirred for 30 min and then 6

poured into a 100 mL stainless-steel autoclave, which was maintained at 453 K for a different time under autogenous pressure and then cooled down to room temperature. The white precipitate was filtered, washed with deionized water for many times. The precipitate was dispersed in absolute ethanol and then dried in air at 333 K overnight.

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The powder was baked at 823 K for 4 hours to activate the Bi2SiO5. For comparison, Bi2SiO5 nanosheets were prepared according to the literature

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[10]. All the samples prepared by GLY-assisted solvothermal treatment were named as GLY-BSO and nanosheets-Bi2SiO5 prepared for comparison was marked as

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H2O-BSO.

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2.2 Characterization

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The phases of the products were identified by X-ray diffraction analysis (XRD)

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on a DX-2600 Discover (Cu Ka = 1.5406 Å) at a scan rate of 2° min-1. The

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microscopic surface structures of the samples were observed on a ZEISS SIGMA 500/VP scanning electron microscopy (FESEM). The specific surface areas were

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checked by the BET method on a QUADRASORB automatic surface analyzer

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(Quantachrome, America). The UV-Vis diffuse reflectance spectra (DRS) were recorded on a TU-1907 UV-Vis spectrophotometer and BaSO4 was used as a reference. Fourier transform infrared (FT-IR) spectra in pellets of the samples with

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KBr were recorded on an 8201PC spectrometer (Nicolet, US). The measurements of surface photovoltage spectroscopy (SPV) were carried out according to the procedures described in the Ref. [47-49]. The photoluminescence (PL) emission spectra were measured using Cary Eclipse (IEEE 488) with the excitation wavelength 7

of 312 nm. The surface composition and binding energy of the samples were determined by X-ray photoelectron spectroscopy (XPS, Perkin Elmer PHI 5500)，and the spectra were calibrated to the C 1s peak at 284.6 eV. 2.3 Photocatalytic activity evaluation

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Phenol and RhB were regarded as simulated target pollutants to evaluate the photocatalytic activity of Bi2SiO5 catalysts. A 300W Hg lamp (UV light) and a 500W

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Xe lamp (simulated solar light) were used as light sources. The measurements of RhB decay were performed in the ref. [50]. For degradation of phenol, 50 mg photocatalyst

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was added into 50 ml phenol solution (20 mg/L). At given time intervals, 4 mL

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aliquots were sampled and centrifuged to remove the photocatalysts. The

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chromatographic experiments with HPLC analysis were carried out using an

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ultraviolet absorbance detector (K 2501) operated at 270 nm coupled to a Venusil

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XBP-C18 (Agela Technologies Inc.) column. The mobile phase is a mixture of

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methanol and water (80:20, v/v) at a flow rate of 1 mL/min [51].

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3 Results and discussion

3.1. Characterization of the photocatalysts Fig.1 shows the XRD patterns and the crystal structure of Bi2SiO5. Fig.1 (a)

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shows that the XRD profiles of Bi2SiO5 prepared using different solvents; the entire diffraction peaks were observed, matching well with the orthorhombic Bi2SiO5 (JCPDS No.36-0287). There were no additional diffraction peaks of impurity were detected, indicating that pure Bi2SiO5 crystals were successfully prepared. According 8

to the Scherrer formula [52], D = Kλ/Bcosθ, where D is crystalline size, K is a constant (0.9), λ is 1.5406 Å, B is the full width at half maximum (FWHM) measured in radians on the 2θ scale, and θ is the Bragg angle for the diffraction peaks, the gradual broader diffraction peaks, and their lower intensity indicate the gradual

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smaller particle size. The FWHM and crystal size of Bi2SiO5 crystal were presented in Table 1, the average crystal sizes of H2O-BSO and GLY-BSO are estimated to be

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17.81 nm and 10.71 nm, respectively. Relative small crystal size results in high BET

surface area, according well with the results of the BET surface area. Fig.1(b) shows

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the XRD patterns of GLY-BSO treated by different solvothermal time. Pure Bi2SiO5

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product was obtained after 16 h, while the products were a mixture of Bi2O3 (JCPDS

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No.41-1449) and Bi2SiO5 below 12 h. Therefore, to obtain pure Bi2SiO5 product, the

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solvothermal time should be more than 12 hours. Fig.1(c) shows the crystal structure

(Bi2O2)2+ layers.

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of Bi2SiO5, which is composed of one dimension (SiO3)2- layers inserted between

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Fig.2 shows the SEM morphologies of the samples. Fig.2 (a) is a typical

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low-magnification SEM image of H2O-BSO, from which two-dimensional planar structure with an average length of 10 μm can be clearly observed. The high-magnification SEM image of H2O-BSO was shown in Fig.2(b). Fig.2(b) displays

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2D H2O-BSO layered structure, consisting of plenty of thin nanoplates. The SEM morphologies of GLY-BSO were shown in Fig.2(c) and Fig.2(d). As shown in Fig.2(c), numerous uniformly-sized spheres with an average diameter of 3 μm can be clearly observed. Moreover, no other morphologies can be detected, indicating a high 9

yield of the product with spherical morphology. Fig.2(d) exhibits the presence of hierarchical flower-like superstructures consisting of two-dimensional thin nanoplates, and the 3D flower-like structure was self-assembled by nanoplates. 3D Bi2SiO5 microspheres can remarkably enhance the adsorption of light because of

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multi-reflections [53]. The results of SEM are consistent with the results of the photocatalytic activity. Fig.2(e)-(j) show the time-dependent morphological evolution

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of the Bi2SiO5 samples treated by different solvothermal time. At the beginning of the solvothermal reaction, the morphology is spongy and amorphous. When the reaction

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time is 16 hours, the morphology of the Bi2SiO5 samples is spherical, as the

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solvothermal time is 24 hours, the morphology is hierarchical flower-like

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superstructures consisting of two-dimensional thin nanoplates.

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In light of the above results, it is reasonable to propose the formation process of

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hierarchical 3D Bi2SiO5 microspheres (Scheme 1). The physical chemistry features of the GLY solvent such as coordination and viscosity can influence the growth of

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Bi2SiO5. Firstly, Bi(NO3)3 can be dissolved in GLY solvent and forms bismuth

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alkoxide (BiIII-GLY alkoxide) [44]. Because of the relatively high temperature and pressure under solvothermal treatment, bismuth alkoxide gradually produces Bi2O22+, so the nucleating speed can be controlled [54]. Then these tiny nuclei grow up and

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gradually develop into nanosheets by Ostwald ripening process [55], then selfassembly nanosheets form microspheres in the GLY solvent. The viscosity of GLY solvent (934,293K) is higher than water (0.89, 293K), the assembled nanosheets are inclined to form hierarchical aggregations. Lastly, the regular hierarchical 10

microspheres were formed through a dissolution-recrystallization process of the preformed nanoparticles. GLY can act as complexion agents to form a polymer network, which plays a crucial role in directing the assembly and formation of Bi2SiO5 hierarchical structures.

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The BET surface areas of the Bi2SiO5 photocatalysts were evaluated by the N2 adsorption/desorption analysis (Fig.3). As shown in Fig.3, the typical type IV

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isotherm indicates that both samples possess mesoporous structures [56-58]. Remarkably, the cumulative amount of adsorption/desorption N2 in the H2O-BSO was

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reduced compared with the GLY-BSO sample. The specific surface area of

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GLY-BSO is determined to be 44.7 m2/g; it is much higher than that of H2O-BSO

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(14.7 m2/g). The inset of Fig.3 is the pore distribution plots of the obtained samples

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using the Barrett-Joyner-Halenda (BJH) method, indicating that GLY-BSO samples

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have large mesopores (20 nm). The large pores originate from the hollow mesoporous of GLY-BSO. For comparison, the pore size distribution of H2O-BSO mainly

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concentrates on 6.5 nm, which can be attributed to the small mesopores originated

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from the pores between the nanosheets. The specific surface parameters of two photocatalysts were presented in Table 2. The pore size of H2O-BSO is 42.1 nm, which is larger than that of GLY-BSO (28.8 nm). In general, smaller particle size and

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pore size leads to higher specific surface area, which agrees well with the results from XRD and adsorption/desorption N2. We further characterized the XPS spectrum of Bi2SiO5. Fig.4(a) shows that O, Bi, and Si elements were observed in the XPS spectrum, and no obvious impurities were 11

detected in the survey spectrum except for adventitious carbon. As shown in Fig.4(b), the peaks located at around 159.18 and 164.48 eV belong to the binding energies of the Bi 4f7/2 and Bi 4f5/2 peaks in the bare Bi2SiO5 [39]. High-resolution XPS spectra of the O 1s region on the surfaces of the photocatalysts were illustrated in Fig.4(c). Two

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oxygen signals situated at 530.17 eV and 532.21 eV were detected, which can be assigned to Bi-O and Bi-OH, respectively [5]. Fig.4(d) shows that the peak at 102.12

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eV can be assigned to Si 2p according to the previous report [59]. Fig.4(e) and Fig.4(f) display the content of surface hydroxyl oxygen on GLY-BSO is higher than that on

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H2O-BSO, implying that hydrothermal treatment of BSO using GLY solvent can

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significantly enhance the surface hydroxyl groups. Surface hydroxyl group exists in

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BSO is attributable to the chemically adsorbed H2O. Generally, high content of

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surface hydroxyl on the surface of BSO is conducive to the enhancement of

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photocatalytic activity, which can be further confirmed by the results of the photocatalytic evaluation [60-62].

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To examine whether there were any organic residues remaining on the surfaces

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of the samples when we use GLY as a solvent for synthesis. Fig.5 exhibits the IR spectra of H2O-BSO and GLY-BSO. In the IR region, the absorption peaks at 1625 and 3472 cm-1 are the δ (OH) bending vibration and v (OH) stretching vibrations of

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free water molecules on the photocatalyst surface. It is found that absorption peaks of the δ (OH) bending vibration and v (OH) stretching vibrations in GLY-BSO are stronger than H2O-BSO, which indicates that surface hydroxyl of GLY-BSO is more abundant than H2O-BSO. The results are consistent with the XPS results. The high 12

content of surface -OH is conducive to produce •OH，one of reactive species for photocatalytic degradation reaction [63-65]. The peak located around 1028 cm-1 is related with the v (Si-O) stretching vibration while the band located around 943 cm-1 is assigned to the stretching vibration mode of isolated (SiO5)6- groups forming a

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distorted tetrahedron [66]. The absorption band located around 857 cm-1 is due to absorption by the v (Bi-O-Si) stretching vibration. The sharp peak located around 450

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cm-1 could be associated with some vibration mode of the Bi-O bond [1]. The results

of IR are in agreement with previous studies, and the samples have an Aurivillius-like

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structure with [SiO4] tetrahedra and [BiO4] square pyramid.

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Fig.6(a) shows the UV-vis DRS of plate-like H2O-BSO and flower-like

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GLY-BSO microspheres. It can be observed that the flower-like GLY-BSO

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microspheres nanostructures exhibit stronger absorption intensity than that of 2D

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plate-like H2O-BSO, which is due to the special 3D flower-like structure of GLY-BSO. The hierarchical nanostructures can generate multiple lights reflecting and

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scattering, greatly increasing the effective optical path length of a photon and

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absorption probability [53]. Fig.6(b) is the band-gap of GLY-BSO and H2O-BSO, which was measured by a plot of (αhv)1/2 versus hv. Fig.6(b) shows that the band-gap of GLY-BSO is close to H2O-BSO. The band-gap of GLY-BSO is 3.16 eV. Eg is the

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band gap energy of the semiconductor, and ECBM can be determined by ECBM = EVBM – Eg [67]. Fig.6(b inset) is the VBM of GLY-BSO, which was measured by XPS, and the VBM is 1.8 eV vs vacuum level, so the EVB is 2.7 eV vs NHE, and the ECB is -0.46 eV. The reduction potential of O2/•O2- is -0.33 eV [68], therefore it is apparent that 13

the electrons from CB of GLY-BSO can reduce O2 to form •O2-. The result is consistent with the trapping measure. Fig.6(c) exhibits the SPV responses of the as-prepared samples. GLY-BSO sample has a stronger SPV response from 300-550 nm, which implies that the separation rate of photo-generated electron-hole is higher

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than H2O-BSO [69]. Terephthalic acid can effectively capture •OH radicals and generate a highly fluorescent product which can be easily detected in the fluorescence

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spectrometer [70-72]. To further investigate the formation of •OH, the fluorescence spectra of hydroxyl radicals (•OH) was performed. As displayed in Fig.6(d), the

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fluorescence signal intensity of •OH in GLY-BSO is stronger than that of H2O-BSO.

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As a strong oxidant, high level of •OH can accelerate the decay of pollutants,

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manifesting high photocatalytic performance. The results fit well with the SPV

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3.2. Photocatalytic performance

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responses and the degradation of RhB and phenol over the photocatalysts.

To evaluate the photocatalytic performance of Bi2SiO5 samples, 10 mg/L RhB

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dye and 20 mg/L phenol were used as target pollutants. Fig.7(a) exhibits the

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decolorization of RhB over different photocatalysts under different light source illumination. The degradation of RhB solution without photocatalyst after 30 min is negligible; the results demonstrate that the degradation of RhB in this photocatalytic

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system originates from the presence of a photocatalyst. It is apparent that GLY-BSO exhibits higher photocatalytic activity than H2O-BSO. Fig.7(b) shows the degradation of phenol, about 70% and 94.0% of phenol can be decomposed over the H2O-BSO and GLY-BSO after 80 min. As shown as in Fig.7(b) inset, the decay of phenol 14

follows a first-order reaction kinetic equation, and rate constant of phenol over GLY-BSO photocatalyst is 0.034 min-1. The photocatalytic activity of GLY-BSO is more than 2 times to H2O-BSO. To further ascertain the active species (h+, •OH and •O2-) during the

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photodegradation process, trapping experiments were carried out. Ammonium oxalate (AO) for h+, isopropanol (IPA) for •OH and benzoquinone (BQ) for •O2- [73] were

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dissolved in the reaction solution before the UV light irradiation. As shown in

Fig.7(c), the addition of h+ scavenger (AO) can decrease the phenol degradation

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efficiency from 44.07% to 43.29% over GLY-BSO, indicating that h+ performs a

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negligible role in the degradation of phenol. However, the degradation of phenol is

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significantly depressed by BQ and IPA, confirming that •O2- and •OH are the main

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active species during the photocatalytic process.

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To further investigate the photo-induced charge separation efficiency of all photocatalysts, nitroblue tetrazolium (NBT) experiments were studied [74]. As shown

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in Fig.7(d), it can be seen that the absorption peak of NBT in the GLY-BSO

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photocatalytic system at 259 nm is the lowest, indicating that •O2- in the GLY-BSO suspension sample is the highest. Combined with the results of scavenger and NBT experiments, it is apparent that increased content of •O2- can accelerate the decay of

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phenol, resulting in enhanced photocatalytic performance. 3.3. Photocatalysts stability For the photocatalytic reaction, photocatalyst stability is also an essential factor in the practical application. We utilize a time-circle phenol photolysis experiment to 15

evaluate the stability of GLY-BSO photocatalyst. As shown in Fig.8(a), the results show that GLY-BSO photocatalyst could be efficiently repeated and maintain its high activity after the fifth cycle, implying the high stability of GLY-BSO photocatalyst. Therefore the photocatalyst has a potential application in pollutants purification. In

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addition, Fig.8(b) shows the XRD patterns of GLY-BSO powders before and after photodegradation performance test. It is evident that the crystalline phase of

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GLY-BSO does not change after the photodegradation of RhB or phenol, indicating that the powders are stable. The results of the photodegradation performance test

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indicate that the GLY-BSO powders can be used in wastewater treatment due to the

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photocatalysis.

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4 Conclusions

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In summary, 3D Bi2SiO5 hierarchical microspheres were successfully prepared via a hydrothermal method. The solvents used in the solvothermal synthesis play an

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important role in affecting the growth and morphology of Bi2SiO5, Bi2SiO5 with the

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higher surface area in the form of 3D microspheres were obtained using glycerol as solvent whereas nanosheets were produced in the case of H2O solvent. During the preparation process, glycerol acts as a soft template to guide the formation of the

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hierarchical microspheres. The results also reveal that the presence of glycerol during synthesis also can tune the photodegradable property of Bi2SiO5 particles. Furthermore, according to the photocatalytic activity measurements, the as-prepared 3D Bi2SiO5 powders can be used as a potential material for the degradation of 16

environmental organic pollutants. This work offers a practical way to enhance the photocatalytic performance of Bi2SiO5 for pollutants degradation.

Acknowledgments

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This project was supported financially by the program of Education Department of Sichuan province (No.17ZB0301), the Opening Project of Key Laboratory of

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Green Catalysis of Sichuan Institutes of High Education (No.LYJ1601, LYJ1603), and

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Students Innovation Project of Sichuan Province (cx2017020).

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SC R

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SC R

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ED

M

A

N

U

SC R

IP T

91-98.

Caption for Figures

PT

Fig.1 XRD patterns of Bi2SiO5 obtained using different solvents (a); XRD patterns of

CC E

GLY-BSO treated by different reaction time (b); the crystal structure of Bi2SiO5 (c). Fig.2 SEM of Bi2SiO5 using different solvents and different reaction time: (a-b) H2O, 24 h; (c-d) GLY, 24 h; (e) GLY, 4 h; (f) GLY, 8 h; (g) GLY, 12 h; (h) GLY, 16 h; (i)

A

GLY, 20 h; (j) GLY, 24 h. Fig.3 Nitrogen adsorption-desorption isotherms and the corresponding pore size distribution curve (inset) of different Bi2SiO5 samples: (a) H2O-BSO; (b) GLY-BSO. Fig.4 XPS spectra of the photocatalysts: survey XPS spectrum of Bi2SiO5 (a); Bi 4f 23

(b); O 1s (c); Si 2p (d); High resolution XPS spectra of O 1s GLY-BSO (e) and (f) H2O-BSO. Fig.5 FT-IR spectra of the Bi2SiO5 samples Fig.6 UV-Vis DRS of Bi2SiO5 samples (a); Bandgap of GLY-BSO, the inset is

IP T

XPS-VBM (b); SPV (c); PL spectra related to the amount of •OH radical (d). Fig.7 The decolorization of RhB using different light source (illumination time = 30

SC R

min) (a); The decolorization efficiency of phenol with the irradiation time, the inset is

rate constants (b); The influence of different capture agents on photocatalytic activity

U

of GLY-BSO, the reaction time is 20 min (c); Absorbance of NBT on different

N

photocatalysts, the reaction time is 20 min (d).

A

Fig.8 Five consecutive cycles of degradation of phenol using the GLY-BSO (a); XRD

CC E

PT

ED

M

patterns of GLY-BSO before and after five consecutive cycles (b).

Tables

Table 1 The FWHM and crystal size of Bi2SiO5 crystal (310)

(311)

A

Facet H2O-BSO GLY-BSO H2O-BSO GLY-BSO

2 Theta/degree

23.894

23.894

29.228

29.228

FWHM

0.474

0.709

0.491

0.951

crystal size/nm

17.71

11.84

17.90

9.59

24

Table 2 Effect of GLY on the specific surface parameters of Bi2SiO5 SBET (m2/g)

Pore volumes(mL/g)

Pore size (nm)

H2O-BSO

14.7

0.15

42.1

GLY-BSO

44.7

0.32

28.8

ED

M

A

N

U

SC R

IP T

Catalysts

PT

Scheme 1: Illustration of the possible formation mechanism of Bi2SiO5 Microspheres.

CC E

Bi(NO3 )3 5H2O

OH Coordination

Na2 SiO3 9H2O GLY

Bi O

O

O

OH OH

OH

SiO32-

Nucleation

OH

A

HO

Growth

Dissolution

Ostwald ripening Self-assembly

Recrystallization

25

IP T SC R U N

(a)

A M

H2O-BSO-24 h

PDF#36-0287

ED

PT

Intensity (a.u.)

GLY-BSO-24 h

20

30

40

50

2 Theta (degree)

A

CC E

10

PDF#41-1449

26

60

70







 





20 h





16 h

Bi2SiO5 Bi O  2 3 12 h 













 



8h

 



4h

 







10



20











30

40

50

ED

M

A

N

U

2 Theta (degree)

60

A

CC E

PT

Fig.1

27

70

IP T



SC R

Intensity (a.u.)



(b)

 

Fig.2

28

A ED

PT

CC E

IP T

SC R

U

N

A

M

IP T SC R U N A M ED

120

Adsorption Desorption

PT

(a)

A

-1 )

4

-1

5

3

3

80

dV/dD (dm /g nm

Va (cm3/g)

CC E

100

60 40

2 1 0 0

20

50

100 150 dp (nm)

200

0 0.0

0.2

0.4

0.6

P/P0

29

0.8

1.0

250

Adsorption Desorption

(b) 10 -1

6

3

100 50

4 2 0 0

0 0.0

50

0.2

100 150 dp (nm) 0.4

200

0.6

0.8

1.0

SC R

P/P0

IP T

Va (cm3/g)

150

8

-1

dV/dD (dm /g nm )

200

A

PT

H2O-BSO

GLY-BSO

164.48 eV Bi 4f7/2

Intensity (a.u.)

Bi 5d

Si 2p

159.18 eV Bi 4f5/2

(b) Bi 4f

O 1s3 Bi 4d 5 Bi 4d

Bi 4p

Bi 4f

C 1s

Intensity (a.u.)

CC E

(a)

O KLL

ED

M

A

N

U

Fig.3

GLY-BSO

H2O-BSO

1200

1000

800

600

400

200

0

168

Binding energy (eV)

166

164

162

160

Binding energy (eV)

30

158

156

(c) O 1s

(d) Si 2p

530.17 eV 532.21 eV

102.12 eV Si 2p

Bi-O

Intensity (a.u.)

Intensity (a.u.)

-OH

GLY-BSO

GLY-BSO

H2O-BSO

H2O-BSO 534

533

532

531

530

529

108

528

106

104

Binding energy (eV)

(e) O 1s

102

100

Binding energy (eV)

535

534

533

532

531

530

529

H2O-BSO

535

528

SC R

49.05%

534

U

Intensity (a.u.)

Intensity (a.u.)

57.84%

GLY-BSO

533

532

531

530

Binding energy (eV)

N

Binding energy (eV)

PT

ED

M

A

Fig.4

160

H2O-BSO GLY-BSO

0

450

1028 857

40

583

80

943

120

1625

T (%)

A

CC E

200

-40 4000

3500

3000

2500

2000

1500 -1

Wavenumber (cm ) 31

96

50.95%

(f) O 1s

42.16%

98

IP T

535

1000

500

529

528

PT

ED

M

A

N

U

SC R

IP T

Fig.5

A

2.5 1/2

H2O-BSO GLY-BSO

0.6 0.4 0.2

2.0

2000

(b)

1500

Intensity (a.u.)

(a)

1/2

Absorbance (a.u.)

CC E

0.8

3.0

(Ahv) (eV)

1.0

1.5

XPS-VBM

1000 500 0 -500 4

3 2 1 Binding energy (eV)

0

1.0

H2O-BSO GLY-BSO

0.5

3.16 eV 0.0 200

250

300

350

400

450

0.0 2.0

500

Wavelength (nm)

2.5

3.0

3.5

Energy (eV)

32

4.0

4.5

50

50

H2O-BSO

40

GLY-BSO

40

Intensity (a.u.)

GLY-BSO

-7

30 20

30 20 10

10 0 300

350

400

450

500

550

0 350

600

400

Wavelength (nm)

450

500

Emission wavelength (nm)

CC E

PT

ED

M

A

N

U

SC R

Fig.6

550

IP T

Photovoltage (10 V)

(d)

(c)

H2O-BSO

Simulated solar

0.8

B

100

A H2O-BSO A

75

(a)

0.04

BSO (GLY)

-1

UV

B GLY-BSO

0.6

(b)

0.03 0.02

BSO (H2O)

0.01 0.00

Ct/C0

A

Decolorization of RhB (%)

Light off

Rate constant (min )

1.0

125

Photocatalysts

0.4

50

H2O-BSO

B 25 A

B

GLY-BSO

0.2

A

0.0

0

Different light sources

0

20

40

60

Irradiation of time (min)

33

80

50

2.5

32.5% 30 20 10 0

Blank

BQ

AO

Black H2O-BSO

2.0

GLY-BSO 1.5 1.0 0.5 0.0 200

IPA

300

400

Wavelength (nm)

Scavenger

A

CC E

PT

ED

M

A

N

U

SC R

Fig.7

500

34

600

IP T

39.27%

40

(d)

(c)

43.29%

Absorbance (a.u.)

Degradation of phenol (%)

44.07%

1.2

(a) 1.0 1 2 3 4 5

Ct/C0

0.8 0.6

IP T

0.4 0.2

60

120

180

240

300

Irradiation of time (min)

420

(b)

10

ED

U

M

A

N

(402)

(022)

(311) (020)

After Fresh

(310)

Intensity (a.u.)

360

SC R

0

(313)

0.0

20

30

40

A

CC E

Fig.8

PT

2 Theta (degree)

35

50

60

70