Diatomite-immobilized BiOI hybrid photocatalyst: Facile deposition synthesis and enhanced photocatalytic activity

Accepted Manuscript Title: Diatomite-immobilized BiOI hybrid photocatalyst: Facile deposition synthesis and enhanced photocatalytic activity Author: Baoying Li Hongwei Huang Yuxi Guo Yihe Zhang PII: DOI: Reference:

S0169-4332(15)01615-3 http://dx.doi.org/doi:10.1016/j.apsusc.2015.07.049 APSUSC 30775

To appear in:

APSUSC

Received date: Revised date: Accepted date:

23-3-2015 7-7-2015 8-7-2015

Please cite this article as: B. Li, H. Huang, Y. Guo, Y. Zhang, Diatomiteimmobilized BiOI hybrid photocatalyst: Facile deposition synthesis and enhanced photocatalytic activity, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.07.049 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.

*Highlights (for review)

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Highlights

◆ A novel diatomite-immobilized BiOI hybrid photocatalyst has been prepared by a

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facile one-step deposition process for the first time.

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◆ The diatomite-immobilized BiOI hybrid photocatalyst exhibits much better photocatalytic performance.

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◆ This enhancement should be attributed to that diatomite can play as an excellent

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carrier platform to increase the reactive sites and promote the separation of photogenerated electron-hole pairs.

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on natural mineral.

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◆ This work shed new light on facile fabrication of novel composite photocatalyst based

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*Graphical Abstract (for review)

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Graphical abstract

Novel diatomite-immobilized BiOI hybrid photocatalyst with enhanced photocatalytic

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reactivity has been synthesized by a facile one-step deposition process for the first time.

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*Response to Reviewers

Dear Editors and Reviewers: Thank you for letter and for the reviewers’ comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with

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approval. The main corrections in the paper and the responds to the reviewer’s

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comments are as following:

Reviewer1:

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(1) RhB dye has some puzzlement to explain, such as its self-degraded, Please make it clear that the enhanced photocatalytic efficiency is due to as-prepared

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hybrid photocatalyst, not the RhB photosentization mechanism. What is the reason?

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Author reply: Thank you for this comment. In order to exclude the self-degradation and photosentization effect of RhB, methylene blue (MB) degradation over BiOI,

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diatomite and 7% D-BiOI was investigated. As shown in Fig. 3c, the photocatalytic activity of 7% D-BiOI was obviously higher than pure BiOI and diatomite, which is consistent with RhB decomposition results. Thus, the enhanced photocatalytic efficiency is ascribed to as-prepared hybrid photocatalyst instead of the RhB

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photosentization mechanism.

(2) Generally, with the large specific surface area of diatomite, it can enhance the photocatalytic efficiency. Thus, the comparison of N2 adsorption-desorption isotherms of pure diatomite, pure BiOI and the composites including surface area, pore diameter and pore volume should be provided. In addition, the particle size distribution graph should also be described. Author reply: Thank you for this advice. As discussed above, both loaded BiOI

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and diatomite carrier have porous features. Thus, the N2 adsorption–desorption isotherm tests were employed to investigate changes of the porous structures of resultant BiOI-diatomite. The results of BET surface area (SBET), pore volume and

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average pore diameter are summarized in Table 1. The specific surface area of 7%D-BiOI composite is 2.524 m2/g, which is a little higher than pure BiOI (1.567

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m2/g). Large surface area with mesoporous structure can promote adsorption,

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desorption and diffusion of reactants and products, which is favourable to obtain a high photocatalytic activity. Fig. 4 shows the particle size distribution graph of

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pure BiOI, pure diatomite and 7%D- BiOI. Their average particle size are 576nm，

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1123nm，856nm，respectively. The average particle size of 7%D- BiOI is slightly

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larger than the pure BiOI.

(3) In the XRD analysis, the saying of "the low content of diatomite and high

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intensity of BiOI diffraction peaks, the XRD diffraction peaks of diatomite are not detected". Please explain the reason? Author reply: We are sorry for the misleading. The intensity of XRD diffraction peaks is mainly proportional to the content of the phase. Due to the low content of

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diatomite, the XRD diffraction peaks of diatomite are hard to be detected. Now, the corrected explanation has been provided in the revised manuscript.

(4) In this paper, the title of 3.2 should be "SEM analysis" Author reply: Thank you for this comment. Now, it has been corrected in the revised manuscript.

(5) The explanation for Fig.3 should be improved. In the manuscript, "The excessive diatomite would reduce the interfacial interaction between BiOI and

Page 4 of 36

diatomite", how does the interfacial interaction be reduced? Author reply: Thank you for this comment. When the amount of diatomite is too high (like 10% D-diatomite), only a fraction of diatomite was assembled by BiOI as shown in Fig. 3d. This is unfavourable for formation of effective interfacial

explanation for Fig. 3 has been provided in the revised manuscript.

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interaction for efficient charge transfer between BiOI and diatomite. The above

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(6) "Band gap" should be discussed in detail in order to help readers understand

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the photocatalysis process.

Author reply: Thank you for this good advice. It is well-known that the photocatalytic activities of photocatalysts depend on the generation, transfer and

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separation of photogenerated electron–hole pairs. The conduction band (CB) and

Butler and Ginley using eqs. EVB=X-Ee+0.5Eg

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ECB=EVB-Eg

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valence band (VB) potential of BiOI at the point of zero charge were calculated by

(2) (3)

where X is the absolute electronegativity of the semiconductors, which is defined as

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the geometric average of the absolute electronegativity of the constituent atoms; Ee is the energy of free electrons on the hydrogen scale (ca. 4.5 eV); E VB is the valence band (VB) potentials, ECB is the conduction band (CB) potential, and the Eg is the band gap of the semiconductor. The X value of BiOI is ca. 5.94 eV, and the top of the

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VB and the bottom of the CB of BiOI are calculated to be 2.39 and 0.49 eV, respectively, according to the above equations. Now, we have added the above discussions in the revised manuscript.

(7) Page 8, the "exceesive" should be "excessive". Author reply: It has been corrected in the revised manuscript.

(8) Recently, there are some other related manuscripts about removal of dyes via the photocatalyst under visible light irradiation should be cited in the

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introduction section. Author reply: According to your advice, we have added the above references (Ref 18 “H. Wang, X. Z. Yuan, Y. Wu, G. M. Zeng, X. H. Chen L. J. Leng, H. Li, Synthesis and applications of novel graphitic carbon nitride/metal-organic frameworks mesoporous photocatalyst for dyes removal, Applied Catalysis B: Environmental 174 L.

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(2015) 445-454.” Ref 19 “X. Z. Yuan, H. Wang, Y. Wu, X. H. Chen, G. M. Zeng,

J. Leng, Chen Zhang, A novel SnS2–MgFe2O4/reduced graphene oxide flower-like

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photocatalyst: Solvothermal synthesis, characterization and improved visible-light photocatalytic activity, Catalysis Communications 61 (2015) 62-66.” Ref 20 “H.

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Wang, X.Z. Yuan, Y. Wu, G. M. Zeng, X. H. Chen, L. J. Leng, Z. B. Wu, L. B. Jiang, H. Li , Facile synthesis of amino-functionalized titanium metal-organic frameworks

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and their superior visible-light photocatalytic activity for Cr(VI) reduction, Journal of

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Hazardous Materials 286 (2015) 187-194.”) in the revised manuscript.

Reviewer2:

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(1) For the different amounts of diatomite studied (0%, 3%, 5%, 7% and 10%), is this molar or weight percentage?

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Author reply: In our work, the different amounts of diatomite were weight percentage. Now, it has been corrected in the revised manuscript. (2) The authors state "a 300 W Xenon lamp served as the visible light" - to

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obtain visible light, a 420 nm cutoff filter should be used. Author reply: Thank you for this comment. In our work, to exclude the UV light, we used a 300W xenon lamp coupled with 420 nm cutoff filters as the visible light source. Now, the description has been corrected.

(3) How did the authors obtain photocatalyst film on ITO glass? What method did they use? Author reply: The type of ITO conductive glasses we used in experiment was TIO-10-TN with size of 4 cm×2 cm, thickness of 1.1 mm and light transmittance of

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84%. The details of electrode deposition method are as follows: 5 mg of photocatalyst was added to 0.5 mL deionized water. After sonicating for 15 min, the suspension was deposited onto the ITO conductive glasses surface (the conductive side) with 5 mL plastic sucker. Afterwards, the electrode was dried and then calcined at 373 K for 10

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h. (4) Page 7, 3.1 & 3.2 use the same title.

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Author reply: Thank you for this comment. Now, it has been corrected in the revised

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manuscript.

(5) Page 16, in Figure caption of Fig.6, TBA should be IPA.

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Author reply: Thank you for this comment. Now, it has been corrected in the revised

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manuscript.

(6) Page 19, SEM images, there is no difference between Fig 3 (b) and (c), they are exactly the same.

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Author reply: We are sorry for this mistake. Now, it has been corrected in the revised

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manuscript.

Thank you for your good comments.

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Best regards

Hongwei Huang

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*Manuscript Click here to view linked References

Diatomite-immobilized BiOI hybrid photocatalyst: Facile deposition synthesis and enhanced photocatalytic activity

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Baoying Li, Hongwei Huang,* Yuxi Guo, Yihe Zhang*

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Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and

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Technology, China University of Geosciences, Beijing 100083, China

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Corresponding author：[email protected] (H.W. Huang); [email protected] (Y.H. +86-10-82332247.

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Zhang). Tel.:

1

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ABSTRACT: A novel diatomite-immobilized BiOI hybrid photocatalyst has been prepared by a facile one-step deposition process for the first time. The structure, morphology and optical property of the products were characterized by X-ray powder

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diffraction (XRD), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic performance of the as-prepared

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BiOI/diatomite photocatalysts was studied by photodegradation of Rhodamine B

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(RhB) and methylene blue (MB) and monitoring photocurrent generation under visible light (λ > 420 nm). The results revealed that BiOI/diatomite composites exhibit

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enhanced photocatalytic activity compared to the pristine BiOI sample. This

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enhancement should be attributed to that diatomite can play as an excellent carrier platform to increase the reactive sites and promote the separation of photogenerated

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electron-hole pairs. In addition, the corresponding photocatalytic mechanism was proposed based on the active species trapping experiments. This work shed new light

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on facile fabrication of novel composite photocatalyst based on natural mineral

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Keywords: BiOI, diatomite, Visible-light, composite, Photocatalytic; active species

2

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1 Introduction With the rapid development of industry, the environmental hazard caused by industry pollutant becomes more and more serious in recent years[1]. How to

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reduce and control the environmental pollution has become a global attention to the problem. Semiconductor photocatalysis as a new pollution treatment technology has

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shown great potential for application in the treatment of organic pollutants in water.

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Due to the low cost and non-toxity, TiO2 is widely investigate as a star photocatalyst[2-7]. However, the relatively large band gap determines TiO2 only to

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be used as UV light photocatalyst[8,9].

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BiOI is a new type of high efficient visible light photocatalyst with band gap of 1.7-1.9eV[10,11]. It can also be used as an excellent photocatalyst to decompose

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organic compounds into inorganic substances for purifying polluted wastewater. However, there exists some disadvantages when utilizing BiOI as individual

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photocatalyst, such as high recombination of photogenerated electron and hole, relatively high cost and easy aggregation[12]. Diatomite is a porous mineral with

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relatively pure chemical component that is mainly composed of amorphous SiO2[13,14]. It possesses large specific surface area, which is derived from the skeletons of single celled algae. Due to the advantages of diatomite, such as large specific surface area, high chemical stability, low cost and abundant resource, it may be a good catalyst carrier to promote the photoactivity[15,16]. Herein, BiOI/diatomite composite photocatalysts were synthesized for the first time by depositing BiOI microspheres on the surface of diatomite. It was found that 3

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the BiOI microspheres can be evenly distributed on diatomite, maximizely decreasing the aggregation effect of BiOI. The photocatalytic performance of the samples was examined by photocatalytic degradation of RhB solution. Compared to

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the pristine BiOI, the BiOI/diatomite composites display remarkably enhanced photocatalytic activity. The results demonstrated that diatomite can serve as a good

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photocatalyst-carrier[17] for efficient separation of photogenerated electron-hole

novel

graphitic

carbon

nitride/metal-organic

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pairs. Recently，lots of mesoporous photocatalysts have been reported，such as frameworks

mesoporous

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photocatalyst[18] and a novel SnS2–MgFe2O4/reduced graphene oxide flower-like

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photocatalyst[19]. Porous metal-organic frameworks have been arousing a great interest in exploring the application of MOFs as photocatalyst in environment

2 Experimental Section

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2.1. Materials

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remediation[20].

All the chemical reagents were purchased from Beijing Chemical Reagent Factory.

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They were analytical reagents and without further purification. Natural diatomite (D50=34.06μm, SBET=16.422m2/g, ω(SiO2)=86.82%) used in this study was provided by Changbai Mountain, Ltd. Diatomite was used after drying at 105 oC for 24 h and leaching with H2SO4. 2.2. Preparation of the samples Fig.1.shows the schematic illustration of preparation of BiOI immobilized on diatomite. In a typical experiment, 0.001mol Bi(NO3)3·5H2O was dissolved in 30 4

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ml ethanol solution, and 0.001mol KI was dissolved in 20 mL deionized water. Then different amounts of diatomite were dispersed in the KI solution. Next, the mixture was added drop wise into Bi(NO3)3·5H2O ethanol solution under strong

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magnetic stirring. Subsequently, the suspension was stirred for 30 mins at room temperature. After reaction, the reacted mixture was centrifugated, washed with

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distilled water and ethanol, and then dried in an oven at 60 °C for 4 h. The weight

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percentages of diatomite in the samples prepared by the above methods is 0%, 3%, 5%, 7%, 10%, respectively.

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2.3. Characterization

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Powder X-ray diffraction (XRD) was performed on an X/max-rA Advance diffractometer with Cu Kα radiation. The scanning step width of 0.02˚ and the

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scanning rate of 0.2o s-1 were applied to record the patterns in the 2θ range of 10-70o. The morphology and microstructure were obtained by a S-4800 scanning electron

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microscope (SEM). UV-vis spectra were performed with sample powder from Perkin Elmer Lambda 35 UV-vis spectrometer. The spectra was collected at

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200-1000nm referenced to BaSO4. The electrochemical experiments were performed

on

a

CHI660C

Electrochemical

Workstation

(Shanghai

ChenhuaInstrument Corporation, China). A three-electrode system was employed with a Platinum-aturated calomel electrode (SCE) as the reference electrode, a carbon electrode as the counter electrode, photocatalyst film electrodes on ITO served as the working electrode. A 300W xenon lamp with the 420 nm cutoff filters served as the visible light source. 0.1 M Na2SO4 was used as the supporting 5

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electrolyte. The applied voltage was 0 V for working electrode. All the potentials in this paper were respect to SCE. All measurements were carried out at room temperature.

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2.4. Measurement of photocatalytic activity Photocatalytic activities of BiOI/diatomite composites were evaluated by

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degradation of RhB (2×10-5 mol/L) and MB (2×10-5 mol/L) under visible light

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irradiation of a 500 W Xenon lamp with the 420 nm cutoff filters. A 25mg BiOI/diatomite composite was dispersed in an aqueous solution of the dyes (50 ml).

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Before illumination, the photocatalyst powder and dye solution were stirred in dark

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for 1 h to achieve the adsorption–desorption equilibrium of suspensions. After that, the light was turned on, and 3 ml of the suspension was taken at certain intervals and

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separated through centrifugation. The concentration of RhB and MB was analyzed by recording the absorbance at the characteristic band of 553 and 664 nm, respectively,

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on a Cary 5000 UV−vis spectrophotometer [21]. 2.5. Active species trapping experiments

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For detecting the active species in the photocatalytic system, 1mM ethylene diamine tetraacetic acid disodium salt (EDTA-2Na), 1 mM benzoquinone (BQ), and 1 mM iso-propanol (IPA) were added as the active species quenchers of the holes (h+), ·O2- ,and ·OH-, respectively[22,23]. The method was similar to the former photocatalytic activity experiment. 2.6. Photoelectrochemical measurements The photocurrent measurement and electrochemical impedance spectroscopy 6

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(EIS) were performed on an electrochemical analyzer (CHI-660B, China) consisting of a three-electrode quartz cell with the 0.1 M Na2SO4 electrolyte. Platinum wires and saturated calomel electrodes (SCE) were immersed in the reactor as the counter

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electrode and reference electrode, respectively. The BiOI and BiOI/diatomite composite film electrodes on ITO glass served as the working electrode. The

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electrochemical tests were measured at 0.0 V with a 300 W Xe lamp（a 420 nm cutoff

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filter was used）as the light source.

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3 Results and discussion 3.1. XRD analysis

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The XRD patterns of diatomite stabilized BiOI (Hereinafter referred to as D-BiOI)

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are shown in Fig. 2. According to the JCPDS card No. 10-445, the characteristic peaks can be observed at 2θ of 29.68◦, 31.71◦, 45.47◦, 51.45◦ and 55.23◦

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corresponding to the crystal planes of (101), (110), (200), (114) and (212) of BiOI, respectively. The intensity of XRD diffraction peaks is mainly proportional to the content of the phase. Due to the low content of diatomite, the XRD diffraction

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peaks of diatomite are hard to be detected. 3.2. SEM analysis

The morphology of the composites is investigated by SEM. Fig. 3a depicts the SEM images of the natural diatomite after drying at 105 oC for 24 h and leaching with H2SO4. It can be seen that the pore structure is cleaned well. When the impurities are removed from the diatomite by acidification, washing and calcination, the surface area and pore volume decrease while the average pore diameter 7

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increases[24]. The high porosity bodes well for its potential applications as a sorbent for heavy metals and a carrier for catalysts. The SEM images of the D-BiOI composites are shown in Fig. 3b-d. All the BiOI composites are immobilized on the

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natural diatomite well and there are scarcely any discrete particles. When diatomite content is 5% (Fig.3d), BiOI microspheres not only were loaded on the surface of

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diatomite, but also self-assembled together. As the diatomate content goes up to 7%,

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the BiOI microspheres were distributed evenly on it and no self-reunion was observed as shown in Fig. 3c. Fig. 3b shows the SEM image of BiOI/diatomite

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composite with the diatomite content of 10%. It can be found that the amount of

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diatomite is too high so that only a fraction of diatomite was assembled by BiOI. Too high or low diatomite contents are both unfavourable for effective interfacial

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interaction for efficient charge transfer between BiOI and diatomite. Thus, the 7% BiOI/diatomite may display an optimum photocatalytic activity.

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3.3. Specific surface area and particle size

As discussed above, both loaded BiOI and diatomite carrier have porous features.

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Thus, the N2 adsorption–desorption isotherm tests were employed to investigate changes of the porous structures of resultant BiOI-diatomite. The results of BET surface area (SBET), pore volume and average pore diameter are summarized in Table 1. The specific surface area of 7%D-BiOI composite is 2.524 m2/g, which is a little higher than pure BiOI (1.567 m2/g). Large surface area with mesoporous structure can promote adsorption, desorption and diffusion of reactants and products, which is favourable to obtain a high photocatalytic activity. Fig. 4 shows the 8

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particle size distribution graph of pure BiOI, pure diatomite and 7%D- BiOI. Their average particle size are 576nm，1123nm，856nm，respectively. The average particle size of 7%D- BiOI is slightly larger than the pure BiOI.

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3.4. UV− vis Diffuse Reflectance Spectroscopy The UV-visible diffuse reflectance spectra (DRS) of diatomite, BiOI and D-BiOI

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composites are shown in Fig. 5. We can see the absorption edge of the pristine

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diatomite is only about 350 nm. Nevertheless, the D-BiOI composites all exhibit comparative photo-absorption with BiOI with absorption edges around 650 nm. In

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semiconductors, different optical transitions can result in different types of band gap.

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The band gap (Eg) can be determined by the Kubelka–Munk function[25,26] ahν=A(hν-Eg)n/2

(1)

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where a, h, v, Eg, and A are the absorption coefficient, Planck constant, these, n is determined by the type of optical transition of a semiconductor (n=1 for direct

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transition and n=4 for indirect transition). For BiOI, the n value is 4. The indirect band gaps estimated from the Kubelka–Munk functionare calculated to be 1.82 and

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2.11 eV for BiOI and 7% DB–BiOI, respectively. Though the band gap of D-BiOI is slightly larger than that of BiOI, the D-BiOI composite still holds the ability of responding to almost all of the visible light. 3.5. Photocatalytic activity The photocatalytic activity of BiOI/diatomite composites is evaluated by monitoring the decomposition of RhB in an aqueous solution under visible light irradiation (λ > 420 nm). As shown in Fig. 6a, the photocatalytic activity of BiOI has been improved 9

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steadily when the loading concentration of diatomite was below 7% (3%, 5%, and 7%) and reduced with continuous increase of the diatomite amount (10%). Among these, 7% BiOI/diatomite exhibits the highest degradation efficiency, and about 95% RhB

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was removed in 140 mins. The pseudo-first-order kinetic curves of RhB photodegradation were plotted to quantitatively compare the degradation rate. The

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experimental data (Fig. 6b) obviously show that the apparent rate constant k is

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0.01324, 0.01889, 0.01866, 0.02104 and 0.00979min −1 for D-BiOI composites with diatomite contents of 0%, 3%, 5%, 7%, and 10%, respectively. Namely, the

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photocatalytic activity of 7% D-BiOI is 1.59 times that of pristine BiOI. It is because

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BiOI microspheres were evenly distributed on diatomite when the diatomite content is 7%, which can maximizely decrease the aggregation effect of BiOI. It also can be

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explained that the largest interaction area between BiOI and diatomite occurs on 7% D-BiOI, thereby promoting the separation of photoinduced electron-hole pairs and

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greatly improving the photocatalytic efficiency. Fig.6c shows the methylene blue (MB) degradation curves over BiOI, diatomite and 7% D-BiOI. The photocatalytic activity

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of 7% D-BiOI was obviously higher than pure BiOI and diatomite, which is consistent with RhB decomposition results. Thus, the enhanced photocatalytic efficiency is ascribed to as-prepared hybrid photocatalyst instead of the RhB photosentization mechanism. 3.6. Photocatalytic Mechanism Fig. 7 shows the active species trapping results in photocatalytic process of D-BiOI. It was found that the photodegradation of RhB was almost not affected 10

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through adding 1 mM IPA as a quencher of •OH. In contrast, the photocatalytic activity of D-BiOI was largely suppressed by the addition of EDTA-2Na and BQ, and the inhibition efficiencies for degradation of RhB are about 22% and 85%,

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respectively. Thus, it could be inferred that superoxide radicals (•O2−) and holes (h+) serves as the main active species for the photodegradation of RhB over D-BiOI

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under visible light irradiation.

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The possible photocatalytic mechanism of D-BiOI composite was proposed as depicted in Fig. 8. Under visible light irradiation, the separation of electron and hole pairs occurred. Then, the photogenerated electrons were injected into the conduction

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band, and the holes were left in the valence band of BiOI. It is well-known that the photocatalytic activities of photocatalysts depend on the generation, transfer and

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separation of photogenerated electron–hole pairs. The conduction band (CB) and valence band (VB) potential of BiOI at the point of zero charge were calculated by

EVB=X-Ee+0.5Eg

(2) (3)

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ECB=EVB-Eg

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Butler and Ginley using eqs. [27,28]

where X is the absolute electronegativity of the semiconductors, which is defined as the geometric average of the absolute electronegativity of the constituent atoms; Ee is the energy of free electrons on the hydrogen scale (ca. 4.5 eV); E VB is the valence

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band (VB) potentials, ECB is the conduction band (CB) potential; and the Eg is the band gap of the semiconductor. The X value of BiOI is ca.5.94 eV, and the top of the VB and the bottom of the CB of BiOI are calculated to be 2.39 and 0.49 eV, respectively, according to the above equations. Here, the diatomite mainly plays an important part in two aspects. On one hand, diatomite can depress the self-reunion of BiOI and increase the specific surface area of composite, increasing the active sites photocatalsis reaction. On the other hand, diatomite serves as an excellent platform for the fast transfer of photogenerated electrons, thus greatly promoting the photocatalytic reactivity. 11

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3.7. Photoelectrochemical measurements Fig. 9 shows the photocurrent response of pristine BiOI and 7% D-BiOI samples with or without visible light illumination. Obviously, the current abruptly

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increases and decreases as switching the light source on and off. The photocurrent response of the pure BiOI was 3.79 μA, far behind that of 7% D-BiOI composites

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(8.07 μA). In other words, the photocurrent response of 7% D-BiOI composites was

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about 2.2 times higher than that of the pure BiOI. The results showed that the photogenerated electron–hole pairs of 7% D-BiOI could be separated more

charge carrier separation. This is consistent with the results from

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photogenerated

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effectively than that of pure BiOI, confirming the positive effect of diatomite on

the above photodegradation experiments.

In

summary,

we

ed

4. Conclusions for

the

first

time

successfully

prepared

the

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natural-diatomite-immobilized BiOI hybrid photocatalyst by a facile one-step deposition method. By controlling the content of diatomite, BiOI microspheres can be

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evenly distributed on the surface of diatomite and the photocatalytic activity can also be tuned. RhB photodegradation experiments demonstrated that 7% BiOI/diatomite composite exhibits the highest photocatalytic activity, far superior to that of the pristine BiOI. Diatomite can not only depress the self-aggregation of BiOI increasing the reactive sites, but also serve as an excellent platform for the separation and fast transfer of photogenerated electrons. It was confirmed by photocurrent response. Our findings may provide new insights into designing mineral-based photoelectrochemical 12

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materials by facile approach. Acknowledgements This work was supported by the National Natural Science Foundations of

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China (Grant No. 51302251), the Fundamental Research Funds for the Central

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ed

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Universities (2652013052).

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TiO2-diatomite, Appl. Surf. Sci. 303 (2014) 290-296. [2] J. M. Valtierra, E. Moctezuma, M. S. Cárdenas, C. F. Reyes, Global photonic

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efficiency for phenol degradation and mineralization in heterogeneous

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photocatalysis, J.Photochem Photobiol. A 174 ( 2005) 246-252.

[3] J. M. Valtierra, C. F. Reyes, J. R. Ortíz, E.Moctezuma, F. Ruiz, Preparation of

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Catal. B: Environ. 76 (2007) 264-274.

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Figures caption Table.1 Summary of surface characteristics of pure BiOI, diatomite and 7%D-BiOI samples determined from N2 sorption at −196 °C. Fig. 1 Schematic illustration of preparation of BiOI immobilized on diatomite.

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Fig. 2 XRD patterns of pure BiOI and D-BiOI. Fig. 3 SEM images of as-prepared samples, (a) diatomite (b)10% D-BiOI (c) 7%

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D-BiOI (d) 5% D-BiOI.

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Fig. 4 The particle size distribution graph. (a) pure BiOI, (b) pure diatomite (c) 7% D- BiOI.

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Fig. 5 UV−vis diffuse reflectance spectra of as-prepared samples obtained at

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different values of diatomite doped BiOI.

Fig. 6 Photocatalytic degradation curves of RhB over pure BiOI, 3%, 5%, 7%, and

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10% D–BiOI composites under the irradiation of visible light (l > 420 nm) (a,b). Photocatalytic degradation curves of MB over pure BiOI, Diatomite,

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and 7% D–BiOI composites (c).

Fig. 7 Photocatalytic degradation of RhB over D-BiOI photocatalysts aloneand with

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the addition of IPA, EDTA, or BQ. Fig.8 A schematic diagram of the possible pathways of BiOI immobilized on diatomite.

Fig. 9 Photocurrent generation in the BiOI and 7%D-BiOI under visible-light

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Table 1, Summary of surface characteristics of pure BiOI, diatomite and 7%D-BiOI samples determined from N2 sorption at −196 °C.

pore diameter (nm) 3.978 11.342 4.067

pore volume (cm3/g)b 0.001 0.054 0.002

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pure BiOI pure diatomite 7%D-BiOI

BET surface area (m2/g)a 1.567 16.422 2.524

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a Specific surface area data calculated from the multi-point BET method. b Pore diameter estimated from the desorption isotherm by the BJH model.

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