luffa fiber composite and its highly efficient visible light photocatalytic properties

Accepted Manuscript Preparation of recyclable BiOI/luffa fiber composite and its highly efficient visible light photocatalytic properties

Xue Yang, Xiaoyu Wang, Yan Zhao, Lei Xu, Tingting Wang, Xinyan Zhang PII:

S0959-6526(18)32319-9

DOI:

10.1016/j.jclepro.2018.07.324

Reference:

JCLP 13778

To appear in:

Journal of Cleaner Production

Received Date:

07 February 2018

Accepted Date:

31 July 2018

Please cite this article as: Xue Yang, Xiaoyu Wang, Yan Zhao, Lei Xu, Tingting Wang, Xinyan Zhang, Preparation of recyclable BiOI/luffa fiber composite and its highly efficient visible light photocatalytic properties, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro.2018.07.324

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ACCEPTED MANUSCRIPT Highlights

1. The novel recyclable BiOI/ luffa photocatalyst was prepared by deposition and hydrothermal method. 2. Flower-like BiOI microspheres with an average diameter of 7.0 μm anchor on the surface of luffa fiber. 3. Degradation rate of methyl orange by BiOI/ luffa could reach 83.7% after three cycles. 4. The enhanced visible light photocatalytic activity of BiOI/ luffa was discussed.

ACCEPTED MANUSCRIPT

Preparation of recyclable BiOI/luffa fiber composite and its highly efficient visible light photocatalytic properties Xue Yang a, Xiaoyu Wang b, Yan Zhao a*, Lei Xu a, Tingting Wang a, Xinyan Zhang a* a

School of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun 130022, China b School

of Environment Sciences, Northeast Normal University, Changchun 130117, China

ABSTRACT Water pollution has posed a serious threat to the environment and human health. There is an urgent need to develop highly efficient and application-convenient photocatalytic materials. To overcome this critical problem, the novel recyclable BiOI/luffa fiber photocatalyst was prepared by hydrothermal and deposition method, respectively. Several means, namely Scanning Electron Microscopy, X-ray power diffraction, Energy Dispersive Spectrometer, Specific Surface Area Analyzer and Ultraviolet– visible spectroscopy were applied to characterize the composite. The optimal pretreatment condition of (CH3)2CHOH and NaOH for luffa fiber was discussed. Further, the photocatalytic performance of BiOI/luffa was tested using methyl orange as target pollutant. The results showed that the composite prepared by deposition method had more uniform morphology and better properties. When the molar ratio of Bi:I in the reactants was adjusted to 2:5, the degradation rate of methyl orange by BiOI/luffa reached 98.86% for 70min under visible light. Importantly, the recycling test showed that the degradation rate still remained at 83.67% after three cycle usage. The obtained BiOI microspheres exhibited excellent visible light photocatalytic activity, and the luffa with high specific surface area could increase the adsorption of pollutants and facilitate the separation of BiOI. Keywords: BiOI

visible light catalysis

Luffa fiber

methyl orange

recycling

1. Introduction Wastewater is one of the most serious environmental problems due to the organic pollutants including industrial chemicals, dyes, pesticides and pharmaceuticals, which 1

ACCEPTED MANUSCRIPT would result in the adverse effects on human health and natural resources. Photocatalysis is a promising water treatment technology for the degradation of organic pollutants (Mohanty et al., 2005; Lee et al., 2016; Ramezanalizadeh et al., 2017; Teh et al., 2017). However, highly efficient and easy recycling are the important limitation for practical application of photocatalysts. As a result, novel recyclable photocatalytic material has become one of the key solutions to alleviate water pollution problems. For example, Subramonian et al. synthesized a photocatalyst which could be reused up to five times without a significant drop in treatment efficiency of pulp and paper mill effluent (Subramonian et al., 2017). Bi-based semiconductor compounds are regarded as important photocatalysts due to their suitable energy gap, special layer structure and chemical stability (Xu et al., 2002; Zhang et al., 2008). Thereinto, bismuth oxyhalides BiOX (X = Cl, Br, I) have been reported to have visible light responding photocatalytic property. In previous researches, BiOI with narrow energy band gap 1.7-1.9 eV, was successfully used for photocatalytic degradation of pollutants such as dyes, phenol, pharmaceuticals and heavy metals (Hao et al., 2012; Hu et al, 2014; Wang et al.,2017; Yuan et al.,2017). Meanwhile, it is also applied in the elimination of NO and CO2 from air (Zhang et al., 2014; Montoya-Zamora et al., 2017). The hierarchical BiOI microspheres prepared using ethylene glycol as soft template were able to decompose 98.1% methylene blue under visible light (Wang et al., 2017). The BiOI sample (coprecipitation, 40% EDTA) could remove 98.5% of NO from air and displayed good stability (Montoya-Zamora et al., 2017). To be an effective catalyst for large-scale wastewater treatment, the BiOI need to be justified on the following two factors: (a) Enhanced visible light photocatalytic activity; (b) Easy separation and recycling after reaction. As is reported, photocatalyst with special morphology and structure is able to accelerate the absorbance and transfer of pollutant in photocatalytic process (Wang et al., 2017; Yuan et al., 2017). Moreover, the immobilization of photocatalyst on a specific support could be of great benefit. Several attempts have been already reported in the literatures and various techniques were successfully used to load catalyst on materials such as SiO2 glass beads, rings, reactor tubular walls, fiber-glass, quartz, zeolites, perlite and pumice (Elroz et al., 2013; Calia et al., 2017; Sudrajat, H., 2017). Natural fibers have attracted great interest as supporting material and adsorbent. The luffa sponge (Luffa cylindrica) has fibrous network, extensive surface area and therefore making it an ideal immobilization material. It has reported that the luffa fiber was composed of 60% cellulose, 30% hemicellulose and 10% lignin (Gianpietro et al., 2000). Recently, the luffa has been used to immobilize fungal hyphae (Tsai et al., 2012), dyeing water discoloration and reinforcing composites (Ghali et al., 2009). In this paper, the possibility to use luffa fiber as the carrier to support BiOI nanostructure was presented. Recyclable composites with advanced wastewater treatment capability is challenging and significant. It is in accordance with the “recycle” 2

ACCEPTED MANUSCRIPT of “3R” principle. Such innovative loading technological intention positively affects cleaner process and green production, thereby reducing or eliminating its potential harm to the environment. In addition, developing high efficiency, low energy consumption and wide applicability pholocatalyst can minimize pollutants and promote sustainable development. The novel BiOI/luffa composite could exhibit high visible light photocatalytic activity and easy recovery. Moreover, the physical and chemical properties of this adsorptive structure were characterized, and its sorption capacity and kinetic, mechanism were discussed. Also, the reusability of the adsorbent was examined for further application. It would give rise to a new recyclable material for deep photo degradation of organic pollutants. 2. Materials and methods 2.1. Materials Bismuth nitrate pentahydrate (Bi(NO3)3.5H2O) and potassium iodide (KI) were purchased from Aladdin Chemical Reagent Co. Ltd. Methyl orange (MO), (CH2OH)2, (CH3)2CHOH and NaOH were obtained from Sinopharm Chemical Reagent Beijing Co. Ltd. All the reagents used in this experiment were analytical grade and used as received. The luffa fiber was purchased from marketplace. 2.2. Preparation of recyclable BiOI/luffa (1) Pretreatment of luffa fiber: It was pretreated with (CH3)2CHOH and NaOH. Here the discussed optical treatment condition was: 2% (CH3)2CHOH, 7%NaOH , 60min pretreatment time and 40℃ for constant temperature shock. (2) Preparation of samples: (a) Deposition method. 0.486g Bi(NO3)3·5H2O was dissolved in 20mL (CH2OH)2, stirring for 30min, and 0.166g KI was dissolved in 20mL (CH2OH)2. The 0.5g pretreated luffa fiber was immersed in Bi(NO3)3·5H2O ethylene glycol solution and heated at 80℃ for 2 hours. Then the KI ethylene glycol solution was added into the mixture slowly and kept at 80℃for 2 hours. (b) Hydrothermal method. The steps were the same as those of deposition method except that the final mixture of all reactants was transferred into the Teflon-lined stainless steel autoclave at 160°C for 24 h to achieve hydrothermal process. After reaction, the samples were washed with distilled water，ethanol and then dried. Then the BiOI/luffa composite (S1) was obtained. For comparison, the samples (S2-S8) with different proportion of Bi:I:luffa were prepared according to the same process, respectively. The main parameters of experiment were listed in Table 1. 3

ACCEPTED MANUSCRIPT Table 1 The reactant parameters of sample S

2.3. Characterization methods The morphology and size of luffa fiber and BiOI/luffa were characterized by scanning electron microscope (SEM, S4800, Hitachi, Japan). The surface elements of the sample were analyzed by energy dispersive spectrometer (EDS). The crystal structure of samples was recorded using Powder X-ray diffraction (XRD PANalytical, X’Pert). UV-vis diffuse reflectance spectrometer (DRS) of the samples were carried out by UV-vis spectrophotometer (UV-3101PC, Shimadzu) using BaSO4 as a reference. The BET surface area of BiOI material was measured via desorption data (BET Vsorb2802). The mineralization degree of MO solution was determined by total organic carbon analyzer (TOC-Vcpn, Shimadzu). 2.4. Photocatalytic experiments Methyl orange (MO) was used as simulated target pollutant to test the photocatalytic activity of the BiOI/luffa. In typical experiment, the sample S of BiOI/luffa (reaction amount shown in Table 1) was added into MO (10 mg/L, 50 mL). 10 mg/L of MO was used because many dyes are visible in water at concentrations as low as 1 mg/L, which is enough to present an aesthetic problem (Subramonian and Wu, 2014). A 300 W Xe lamp (PLS-SXE300, Beijing Perfect Light) with a cutoff filter (λ>420 nm) was used as visible light source, and the light intensity was set at 150 mW/cm2. Before irrigation, the reaction system was kept in the dark for 1h to ensure complete adsorption– desorption equilibrium. At set time interval, the solution was taken out and detected by spectrophotometer (UV-2600, Shimadzu) at the absorbance of 462 nm. 3. Results and discussion 3.1. Characterization of BiOI/luffa fiber 3.1.1. SEM analysis Fig. 1. SEM images of luffa fiber before (a) and after pretreatment (b), and BiOI/luffa prepared by deposition method (c, e, f) and hydrothermal method (d) Fig.1 shows the surface morphology of luffa fiber before (a) and after pretreatment (b) with (CH3)2CHOH and NaOH. It can be seen that the untreated luffa fiber has smooth and dry surface with thick waxiness. Pretreatment process resulted in a large number of grooves on the surface of luffa fiber due to the removal of hemicelluloses and lignin (Ghali et al,2009). Moreover, its specific surface area is also increased. This 4

ACCEPTED MANUSCRIPT feature may improve the adhesion between fibers and material when it is used in reinforced composites. The morphology and size of BiOI/luffa prepared by deposition and hydrothermal method were determined by SEM, shown in Fig.1. It reveals that the BiOI in both samples exhibits hierarchical microspheres structure. The flower-like microspheres with diameters ranging from 6 to 9 um anchor on the surface of luffa fiber. Microsphere is assembled by a large number of thin nanosheets and the accumulation of numerous nanolayer maintained staggered. As a result, this feature might endow BiOI with more actively photocatalytic properties because of its enhanced adsorbability. Fig. 2.

Histogram of diameters of BiOI microspheres

The histogram of the diameters of BiOI (prepared by deposition method) is indicated in Fig.2. The average diameter of

BiOI is 7.70 ± 0.03 μm under the 95% confidence

level，which shows that BiOI microspheres are uniformly distributed on the surface of luffa fiber. 3.1.2. X-ray diffraction patterns Fig. 3.

XRD patterns of BiOI prepared by hydrothermal and deposition method

Fig.3 shows the XRD patterns of as-prepared BiOI on luffa fiber. It can be found that the diffraction peaks of deposition and hydrothermal samples both accorded with the standard cards (JCPDS No.73-2062) of BiOI. Thereinto obvious peaks could be found at 2θ of 27.62°, 27.98°,45.06°, 51.12°, and 55.14°, assigned to the (102), (110), (200), (114) and (212) crystal faces (Zhang et al, 2013). The products synthesized by both methods were well crystallized. 3.1.3. EDS analysis Fig.4. EDS diagram of the BiOI/luffa prepared by deposition method (A) and hydrothermal method (B) Fig.5. EDS mapping images of BiOI/luffa prepared by deposition (c, d)

(a, b) and hydrothermal method

The EDS analysis indicates that both samples are comprised of Bi, O, I and C atoms, shown in Fig.4. The percentages of Bi atoms in composite prepared by precipitation and hydrothermal method are calculated to reach 51.07% and 32.47%, respectively. The high temperature in the hydrothermal process may affect the in-situ synthesis of BiOI on luffa fiber and lead to its dropping off. Fig.5 (a, b, c, d) display that Bi element 5

ACCEPTED MANUSCRIPT is well distributed on the luffa fiber. In general, Bi element is relatively uniform in the BiOI microsphere, especially observed in deposition sample. 3.1.4. Specific Surface Area Analysis Fig.6. N2 adsorption and desorption isotherms and corresponding pore-size distributions of BiOI/luffa prepared by deposition (A) and hydrothermal (B) method

The specific surface area and porosity properties of the BiOI/luffa were measured using nitrogen adsorption-desorption isotherms. The isotherms of the two kinds of samples can be classified as type IV with the observed hysteresis loop, seen in Fig.6 (A) and (B). The surface area of BiOI prepared by deposition (A) and hydrothermal (B) are 41.048 m2g-1and 21.961m2g-1, respectively. The BiOI samples contain mesopores with relatively wide pore size distributions, which might be arise from the aggregation of massive thin nanosheets (Liu et al, 2016). Different morphology of BiOI can be observed in correlation with their synthesis conditions. From Fig.2, the BiOI microspheres of deposition method have smoother nanolayers and maintain a relatively densified state. Here, numerous thinner sheets are assembled to form flower like structure. Therefore, the deposited sample owns more BiOI sheets and appropriate channel, which may contribute to its larger surface area. Moreover，it can be suspected that BiOI (A) could have the underlying excellent photocatalytic performance due to its larger specific surface area, providing more active site to accelerate reaction rate (Huang et al., 2012; Zeng et al., 2014; Yang et al., 2015). 3.1.5. UV-vis diffuse reflectance analysis Fig.7. UV-vis diffuse reflectance spectra and the plots of (αhv)1/2 vs the photon energy of BiOI

The band structure of semiconductors is one of the key factors for its photocatalytic activity. Fig.7 shows the UV visible diffuse reflectance spectra of the BiOI microspheres synthesized by deposition. The absorption edge of BiOI sample reaches 670 nm, illuminating that the photocatalyst is able to respond to visible light. Also, the band gap of the sample can be calculated according to the formula (1). α ( hv )=A ( hv-Eg) n/2

(1)

Where α , Eg, h, ν and A represent the adsorption coefficient, band gap energy, Planck’s constant, incident light frequency and the constant, respectively. For BiOI, the value of n is 4 due to its indirect bandgap transition (Zhang et al., 2006). Therefore, the band gap of BiOI is determined by the plot (αhv )1/2 versus energy (hv). The result 6

ACCEPTED MANUSCRIPT shows that the band gap of the prepared BiOI is 1.78 eV, which could facilitate the easy generation of active species and make the photocatalytic performance efficiently. 3.1.6. Profile and surface property of BiOI/luffa fiber Fig.8. Profile of BiOI/ luffa with different Bi:I molar ratio

It can been seen that the luffa fiber loaded BiOI still keeps its original structure and pattern. The color of samples color varies with the change of Bi:I molar ratio, shown in Fig.8. The luffa fiber without BiOI is primary color. With the increase of Bi:I molar ratio in the reactant（from S1 to S5）, the color of BiOI/luffa becomes deeper gradually and appears to be light yellow, yellow, orange and brown-red. With the continuous adding amount of Bi:I, the composite turns into deep red and the coated BiOI layer becomes thicker (S5-S8). 3.2. Photocatalytic properties test 3.2.1. Performance of different preparation methods Fig.9. Photocatalytic degradation of MO in the presence of BiOI/luffa prepared by different methods under visible light

Here, the degradation of MO under visible light irradiation was carried out to evaluate the photocatalytic activity of BiOI/luffa samples. Fig.9 displays that the degradation rate reaches 90.5% and 95.9% in 70 min by BiOI/luffa prepared by hydrothermal and deposition method, respectively. As above mentioned, BiOI prepared by deposition method has more regular spherical, homogeneous and dense surface compared with that of hydrothermal method. Further, its flower like microspheres structure with high specific surface area can enhance the effective contact with the pollutants and undergo photocatalytic reaction more actively. Fig.10. BiOI/luffa corresponding reactive constants towards the degradation of MO

To better understand the degradation of MO, the reaction kinetics for both different type BiOI/luffa was given in Fig.10. The degradation rate of the photocatalysts can be shown as BiOI/luffa (deposition, k=0.04464min-1)> BiOI/luffa (hydrothermal, k=0.02941min-1). Therefore, the BiOI/luffa prepared by deposition exhibits excellent photocatalytic activity. 3.2.2. TOC removal efficiency Fig.11. TOC removal for the photocatalytic degradation of MO over BiOI/luffa prepared by 7

ACCEPTED MANUSCRIPT deposition

The mineralization of the BiOI/luffa composite was evaluated by analyzing the MO degradation under identical reaction condition. As provided in Fig.11, the TOC removal efficiency is calculated to be 62.5% for 70 min visible light irradiation. It reveals that the BiOI/luffa could achieve the advanced treatment of MO wastewater with a relative desirable mineralization ability. 3.2.3. Influence of reactant ratio Fig.12. Photocatalytic degradation of MO in the presence of BiOI/luffa samples（A:S1-S6; B: S5,S7,S8）

The photocatalytic properties of as-prepared BiOI/luffa with different Bi:I proportion were measured by photodegrading of MO. In Fig.12(A), the photocatalytic efficiency of samples (S1 to S5) gradually increases with the decreasing mole ratio of Bi: I. The S5 sample has the best catalytic activity to remove the target pollutant. Moreover, in Fig.12(B), with the increase of loading amount , the degradation rates of MO by S5, S7 and S8are approximate to 96.7%，98.9% and 96.8% after irradiation for 70 min, respectively . The comparison suggests that the loading content and reactant ratio of BiOI/luffa composite have impact on its photocatalytic performance. 3.3. Stability of BiOI/ luffa fiber composite Fig.13. Recycling experiments over BiOI/ luffa for MO degradation under visible light irradiation

The stability of photocatalyst is very important for its practical application. Here the recycling experiments over BiOI/luffa for the degradation of MO were investigated. In Fig.13, the removal rates of three cycle photocatalytic degradation reactions is 98.5%, 90.8% and 83.7%, respectively. The result indicates that the luffa fiber has a strong load capacity and the prepared composite shows excellent recovery and utilization activity. 3.4. Possible mechanism of excellent visible light photocatalytic activity Fig.14. Capture experiments of photocatalytic active species

The possible enhanced photocatalytic mechanism of BiOI/luffa was investigated for its further understanding and application. Accordingly,

the capture experiment was

carried out to identify the active species in MO degradation process over BiOI/luffa. Here 1 mM isopropanol alcohol (IPA), 1,4-benzoquinone (BQ) and ammonium oxalate (AO) were added as •OH, •O2- and h+ scavengers, respectively. From Fig.14. it can be 8

ACCEPTED MANUSCRIPT seen that the presence of BQ and AO have great inhibition function on the MO degradation efficiency, while the existence of IPA has no obvious effect on MO degradation. This result indicates that •O2- and h+ play the major role in the photocatalytic oxidization of MO over BiOI/luffa, while ·OH minor role. Based on the above discussion, a possible enhanced photocatalytic mechanism of BiOI/luffa was proposed, shown in Fig.15. The hierarchical microstructure could facilitate BiOI microspheres to have more reactive sites, thus accelerating the transfer of photo excited carriers. Moreover, owing low bandgap (1.78eV) with estimated EVB=2.33eV and ECB=0.55eV, the prepared BiOI microspheres could respond to broader visible light, which displays high photocatalytic activity. Fig.15. Schematic diagram of MO degradation over BiOI/luffa under visible-light irradiation

On the other hand, as the carrier of BiOI, the luffa fiber has internal porous structure and rough surface. Active groups such as -OH, -COOH and -NH2 on luffa’s surface possess high affinity for polyvalent metal ions, dyes and other pollutants (Sulaymon et al., 2012; Hadjittofi et al., 2014). Such properties are helpful to improve the adsorption and transfer of catalytic reactant between the catalyst and the solution, which could promote the photocatalytic efficiency and separation of BiOI for its better recycling and comprehensive utilization.

4. Conclusion In summary, the novel recyclable BiOI/luffa fiber composite with high visible light photocatalytic activity was prepared by deposition and hydrothermal method, respectively. It is confirmed that the high specific surface area of luffa improved the adsorption of pollutants and realized the separation of BiOI for its recyclable utilization. After pretreated with (CH3) 2CHOH and NaOH, the surface area of luffa became larger and made it easier to combine with BiOI. Compared with hydrothermal method, the BiOI/ luffa prepared by deposition has more uniform morphology and excellent properties. Meanwhile, the ratio of Bi:I:luffa in the composite also has impact on its catalytic activity. Because of the low band gap (1.78eV) and strong adsorption property, BiOI/luffa composite has exhibited excellent visible light catalytic performance, in which the •O2- and h+ play a major role. Importantly，its degradation rate of MO reaches 83.67% by three cycle usage. The luffa fiber has strong carrier capacity and the prepared BiOI/ luffa fiber exhibits advanced recovery and treatment efficiency.

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Acknowledgements The authors appreciate the financial support of National Natural Science Foundation of China [grant number 51678122]; the Education Department of Jilin province "13th Five-Year" Science and Technoloogy Research project [grant number 2016-382] and [grant number 2016-360]; the Youth Science Foundation of Changchun University of Science and Technology University [ grant number XQNJJ-2016-07].

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ACCEPTED MANUSCRIPT Zheng, J., Jiao, Z.,2017. Magnetic recyclable bismuth oxyiodide/polyacrylic anion exchange resin composites with enhanced photocatalytic activity under visible light. J. Colloid Interface Sci., 504, 620.

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ACCEPTED MANUSCRIPT Table and Figure Captions Table 1 The reactant parameters of sample S

Fig. 1. SEM images of luffa fiber before (a) and after pretreatment (b), and BiOI/luffa prepared by deposition method (c, e, f) and hydrothermal method (d) Fig. 2. Histogram of diameters of BiOI microspheres Fig. 3. XRD patterns of BiOI prepared by hydrothermal and deposition method Fig.4. EDS diagram of the BiOI/luffa prepared by deposition method (A) and hydrothermal method (B) Fig.5. EDS mapping images of BiOI/luffa prepared by deposition hydrothermal method (c, d).

(a, b) and

Fig.6. N2 adsorption and desorption isotherms and corresponding pore-size distributions of BiOI/luffa prepared by deposition (A) and hydrothermal (B) method Fig.7. UV-vis diffuse reflectance spectra and the plots of (αhv)1/2 vs the photon energy of BiOI Fig.8. Profile of BiOI/ luffa with different Bi:I molar ratio Fig.9. Photocatalytic degradation of MO in the presence of BiOI/luffa prepared by different methods under visible light Fig.10. Fig.10. BiOI/luffa corresponding reactive constants towards the degradation of MO Fig.11. TOC removal for the photocatalytic degradation of MO over BiOI/luffa prepared by deposition Fig.12. Photocatalytic degradation of MO in the presence of BiOI/luffa samples （A:S1-S6; B: S5,S7,S8） Fig.13. Recycling experiments over BiOI/ luffa for MO degradation under visible light irradiation Fig.14. Capture experiments of photocatalytic active species Fig.15. Schematic diagram of MO degradation over BiOI/luffa under visible-light irradiation

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Table 1

The reactant parameters of sample S

Sample

Bi(NO3)3·5H2O (g)

KI (g)

Luffa fiber (g)

molar ratio (Bi:I)

S1

0.486

0.166

0.5

1:1

S2

0.486

0.332

0.5

1:2

S3

0.486

0.498

0.5

1:3

S4

0.486

0.664

0.5

1:4

S5

0.486

0.830

0.5

1:5

S6

0.486

0.996

0.5

1:6

S7

0.972

0.830

0.5

2:5

S8

1.458

0.830

0.5

3:5

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Fig. 1. SEM images of luffa fiber before (a) and after pretreatment (b), and BiOI/luffa prepared by deposition method (c, e ,f ) and hydrothermal method (d)

15

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Fig. 2.

Histogram of diameters of BiOI microspheres

16

(102) (110)

30

40

50

60

(302) (310) (302) (310)

(114) (212) (213) (204) (220)

(200)

Deposition (112) (004)

20

(114) (212) (213) (204) (220)

(200)

Hydrothermal (112) (004)

Intensity (a.u.)

(102) (110)

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70

80

2-Theta (degree) Fig. 3.

XRD patterns of BiOI prepared by hydrothermal and deposition method

17

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A

B

Fig.4. EDS diagram of the BiOI/luffa prepared by deposition method (A) and hydrothermal method (B)

18

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Fig.5. EDS mapping images of BiOI/luffa prepared by deposition (a, b) and hydrothermal method (c, d)

19

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60

0.001

80

0.000 0

40

20

40

60

80

100

Pore size(nm)

20

A

0 0.0

0.2 0.4 0.6 0.8 Relative Pressure(P/P0)

60

0.002

3

100

0.003

Volume (cm /g)

0.002

3

120

3

80

0.003

Volume(cm /g)

3

Volume(cm /g)

100

Volume(cm /g)

120

0.001

0.000 0

40

20

40

60

80

100

Pore size(nm)

20

B

0 0.0

1.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure(P/P0)

Fig.6. N2 adsorption and desorption isotherms and corresponding pore-size distributions of BiOI/luffa prepared by deposition (A) and hydrothermal (B) method

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1.8

6 5

(ahv) /(eV)

1/2

1.6

1/2

1.4

Abs

1.2 1.0

4 3 2 1 0

1.6

2.0

BiOI

2.4

2.8

3.2

3.6

4.0

hv/eV

0.8 0.6 0.4 0.2 0.0 200

400

600

800

Wavelength(nm) Fig.7. UV-vis diffuse reflectance spectra and the plots of (αhv)1/2 vs the photon energy of BiOI

21

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Fig.8. Profile of BiOI/ luffa with different Bi:I molar ratio

22

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deposition hydrothermal

1.0

C /C t 0

0.8 0.6 0.4 0.2 0.0 -60

-40

-20

0

20

40

60

80

Time (min) Fig.9. Photocatalytic degradation of MO in the presence of BiOI/luffa prepared by different methods under visible light

23

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3.5

deposition hydrothermal

3.0

-1

k=0.04464min

ln (C0/Ct)

2.5 2.0 1.5 -1

k=0.02941min

1.0 0.5 0.0 -10

0

10

20

30

40

50

60

70

80

Time (min) Fig.10. BiOI/luffa corresponding reactive constants towards the degradation of MO

24

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1.0

TOC removal efficiency (100%)

TOC/TOCo

0.8 0.6 0.4 0.2 0.0 0

10

20

30

40

50

60

70

80

Time（min)

Fig.11. TOC removal for the photocatalytic degradation of MO over BiOI/luffa prepared by deposition

25

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(S1)1:1 (S2)1:2 (S3)1:3 (S4)1:4 (S5)1:5 (S6)1:6

1.0

Ct/C0

0.8 0.6 0.4 0.2 0.0 -60

-40

-20

0

20

40

60

Time (min) A

1.0

(S5)1:5 (S7)2:5 (S8)3:5

Ct/C0

0.8 0.6 0.4 0.2 0.0 -60

-40

-20

0

20

40

60

Time (min) B

Fig.12. Photocatalytic degradation of MO in the presence of BiOI/luffa samples （A:S1-S6; B: S5,S7,S8）

26

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1.0 0.8

Ct/C0

0.6 0.4 0.2 0.0 1st

2nd

3rd

Fig.13. Recycling experiments over BiOI/ luffa for MO degradation under visible light irradiation

27

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NO scavenger

1.0

IPA AO BQ

Ct/C0

0.8 0.6 0.4 0.2 0.0 -60 -40 -20 0 20 Time (min)

40

60

80

Fig.14. Capture experiments of photocatalytic active species

28

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O2

·O2H2O

eVisible light

CB

e-

e-

0.55V BiOI 1.78eV 2.33V

h+

H+ H

h+

h+

·OH H

MO

VB

·O H

H2O/OH-

H2O + CO2

Fig.15. Schematic diagram of MO degradation over BiOI/luffa under visible-light irradiation

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