Adsorption of phosphate and photodegradation of cationic dyes with BiOI in phosphate-cationic dye binary system

Accepted Manuscript Adsorption of phosphate and photodegradation of cationic dyes with BiOI in phosphate-cationic dye binary system Jiaqian Zhu, Jiaying Li, Yuying Li, Jia Guo, Xiang Yu, Liang Peng, Boping Han, Yi Zhu, Yuanming Zhang PII: DOI: Reference:

S1383-5866(18)34465-4 https://doi.org/10.1016/j.seppur.2019.04.079 SEPPUR 15549

To appear in:

Separation and Purification Technology

Received Date: Revised Date: Accepted Date:

17 December 2018 23 April 2019 24 April 2019

Please cite this article as: J. Zhu, J. Li, Y. Li, J. Guo, X. Yu, L. Peng, B. Han, Y. Zhu, Y. Zhang, Adsorption of phosphate and photodegradation of cationic dyes with BiOI in phosphate-cationic dye binary system, Separation and Purification Technology (2019), doi: https://doi.org/10.1016/j.seppur.2019.04.079

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Adsorption of phosphate and photodegradation of cationic dyes with BiOI in phosphate-cationic dye binary system Jiaqian Zhu[a], Jiaying Li[a], Yuying Li[a], Jia Guo[c], Xiang Yu[b], Liang Peng[d], Boping Han*[d], Yi Zhu*[a], Yuanming Zhang*[a] a

Department of Chemistry, Jinan University, Guangzhou 510632, PR China

b

Analytical & Testing Center, Jinan University, Guangzhou 510632, PR China

c

Department of Ecology, Jinan University, Guangzhou 510632, PR China

d

Institute of Hydrobiology, Jinan University, Guangzhou 510632, PR China

*

Correspondence author: Tel: +86 20 85222756 (Y. Zhang and Y. Zhu); +86

02085220240 (B. Han) E-mail address: [email protected] (Y. Zhang); [email protected] (Y. Zhu); [email protected] (B. Han)

1

Abstract Bismuth oxyiodide (BiOI) with 3D microspheres structure was prepared and used for adsorption of phosphate and photodegradation of dyes in phosphate-dye binary system for the first time. BiOI exhibited excellent adsorption capacity of phosphate up to 55.80 mg P/L and outstanding photocatalytic activities for all the cationic dyes in phosphate-cationic dye binary system. RhB was 100% photodegraded within 50 minutes, and the photodegradation rates of MB and FB reached 92% and 95% within 100 minutes, respectively. But in phosphate-anionic/neutral dye binary system, BiOI displayed only good adsorption performance of phosphate but showed no photodegradation performance for anionic or neutral dyes. The mechanism was proposed as that PO43- adsorbed on the surface of BiOI, which changed from being neutral into being negatively charged, and then the cationic dyes were absorbed due to electrostatic attraction for photodegradation. The photodegradation was confirmed that the photogenerated electrons from the conduction band (CB) of BiOI which could reduce O2 to ·O2- and associate with h+ oxidized the cationic dyes. This work established a new approach of photodegrading organic dyes and adsorbing phosphate in waterbodies, and provided a new insight into wastewater treatment with two or more pollutants.

˖BiOI; adsorption of phosphate; photodegradation; cationic dyes Keyword˖

2

1. Introduction With the rapid development of urbanization and industrialization, the pollution of water gets gradually serious and has attracted tremendous attention from the whole world. There are many pollutants responsible for water pollution, among which phosphate and organic pollutants have been recognized as two of the main pollutants [1, 2]. Firstly, excessive phosphate in the runoff system, usually results in eutrophication which induces water-quality deterioration and algae bloom [3]. Various methods have been explored to remove phosphate from contaminated water prior to being released into environment, including chemical precipitation, electrolysis method, biological enrichment, ion-exchange and adsorption [4-9]. Owing to the advantages of cost-effectiveness, high selectivity and easy operation, adsorption is considered to be a promising method [10, 11]. Secondly, organic pollutants also deteriorate our water resources due to their wide applications in various fields, such as textile, food handling, cosmetics and printing [12, 13]. Many techniques have been applied in treating various dyes, such as membrane filtration [14], ion exchange [15], oxidation [16, 17], electrochemistry [18, 19], biological methods [20], adsorption [21] and photocatalysis [22]. Photocatalysis is regarded as one of the most effective technologies by degrading dyes because of its advantages of low cost, non-toxicity, strong stability and mild reaction condition [23, 24]. Currently, as a new class of layered photocatalyst, bismuth oxyhalides BiOX (X = Cl, Br, I) exhibit excellent photocatalytic activities due to their unique layered 3

structures consisting of [X-Bi-O-Bi-X] slabs stacked together to form internal static electric field which facilitated separating photogenerated carriers [25-27]. Among them, BiOI shows the smallest band-gap (~1.7 eV) and is an effective visible-light photocatalyst for photodegradating various pollutants [28-30]. Li et.al showed BiOI with 3D hierarchical structures applied in decomposition of methyl orange (MO) and phenol with the efficient photocatalytic activity [31]. Zan et.al demonstrated that the photodegradation activity of cationic Rhodamine B (RhB) with BiOI was enhanced highly due to its unique structure composed of single-crystal nanosheets with high symmetry [32]. Li et.al demonstrated that the enhanced photocatalytic activity of hollow microspheres-like BiOI for RhB was ascribed to the enhanced light absorption capacity, the shortened diffusion route of photogenerated carriers and the improved separation efficiency of interfacial charges [33]. Besides, it’s reported that BiOI with various structures exhibited high performance of adsorbing dyes. Ji et.al prepared flower-like BiOI nanoplates exhibiting excellent adsorption capacity (197 mg/g) for RhB via a simple EG-assisted solvothermal method[34]. Yang et.al synthesized microspheric BiOI with larger specific surface areas showing high removing efficiencies up to 80% towards RhB [35]. Zhu et.al testified that porous microspheres BiOI exhibited the rapid adsorption ability for both RhB and Cr(VI) on account of its ultrathin nanosheet structure [36]. But there are no reports on studying adsorption performance of BiOI for phosphate. Moreover, photodegradation of dyes and adsorption for phosphate in phosphate-dye binary system have not been reported either, which is very important for treatment of real waterbodies. 4

Herein, our work focused on photodegradation of dyes and adsorption for phosphate in phosphate-dye binary system. The microspheres-like BiOI was synthesized by a simple solvothermal method with high photodegradtion of cationic dyes and a high adsorption capacity of phosphate. The present study investigated the performances of adsorbing phosphate and photodegrading different types of dyes, including cationic dyes (RhB, methylene blue (MB), Fuchsin basic (FB)), anionic dyes (MO, salicylic acid) and nonionic dyes (phonel, disperse blue).

2. Experimental All the reagents were purchased from the Shanghai Aladdin Bio-Chem Technology Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd, and used without further purification.

2.1 Synthesis of BiOI BiOI in this work were fabricated by a facile solvothermal approach. Initially, 70 mL ethylene glycol solution containing 1.5 g Bi(NO3)3·5H2O was magnetically stirred for 30 min to obtain a uniform stable suspension. Secondly, 0.5 g KI was added to the as-prepared solution by stirring for another 30 min and ultrasonication for 10 min to form a uniformly dispersed solution. Then, the above solution was poured into a 100-mL Teflon-lined stainless steel autoclave and the reaction temperature was kept at 180 oC for 12 hours (h). Next, the fabricated materials were cooled to room temperature naturally and centrifuged three times with ethanol and deionized water, respectively. Lastly, after being dried in an oven at 60 oC for about 12 h, the orange 5

BiOI particles were obtained.

2.2 Characterization The structures and morphologies of BiOI samples were characterized by the X-ray diffraction (XRD, Bruker D8 Advance X-ray diffractometer, Cu Kα = 1.5406 Å) and the field emission scanning electron microscope (FE-SEM, Zeiss ULTRA 55). The elemental compositions and the chemical state and valence state of all the samples were analyzed by the transmission electron microscopy (TEM, JEOL 2010F), the energy dispersive spectroscopy (EDS, Bruker/Quanta 200) and X-ray photoelectron spectroscopy (XPS, ESCALab250). The zeta potential analyzer (Zetasizer NANO ZS 90, Malvin, UK) was used to analyze the potential values of various suspensions of the materials. The optical property of BiOI was obtained by the diffuse reflectance spectrum (DRS, Hitachi UV-3010). The concentrations of ions in the solution were examined by inductively coupled plasma mass spectrometry (ICP Spectrometer, ICAP 7000 SERIES).

2.3 Evaluation of photocatalytic activity To assess the photodegradation activity of the as-prepared materials in phosphate-dye binary system, the photodegradation of a series of dyes was carried out under visible light irradiation. 0.1g BiOI was put into 100 mL phosphate-dye binary system containing 100 mg P/L phosphate and a series of dyes (50 mg·L-1 RhB, 25 mg·L-1 MB, 50 mg·L-1 FB, 5 mg·L-1 MO, 5 mg·L-1 phenol), respectively. The system was stirred for 30 min in the dark at first to attain adsorption-desorption equilibrium, 6

and then under visible-light irradiation with 350 W Xe lamp. A proper amount of the reaction solution was taken out every 10 min (RhB, MB, FB) or 0.5 h (MO) or 1 h (phenol) interval, which was used to measure the absorbances on a uv-vis spectrophotometry. Finally, the degradation rates of the reactants were calculated according to the following formula:

K

ct u100% c0

(1)

where η was the degradation rate of dye, c0 was the initial concentration of dye, and ct was the concentration of dye at time of t. In addition, to seek the main active species during the photocatalytic process, the trapping experiments were also carried out in the same condition by adding different trapping agents, including p-benzoquinone (BQ), isopropanol (IPA), silver nitrate (AgNO3) as well as triethanolamine (TEOA).

2.4 Evaluation of adsorption capacityfor phosphate The adsorption capacity of BiOI for phosphate was studied by adding 0.1g BiOI into a series of 100 mL phosphate-dye binary system. The thermostatic oscillator was used for keeping the temperature of the above suspension in the triangle flasks (30 ± 1 °C, 24 h) constant. Additionally, ICP was used for calculation of all the phosphate concentration (including initial phosphate concentrations c0) in filtrate after the mixtures were filtrated and the below formula was used to determine the adsorption capacity of phosphate:

qt

Vu

(c0  ct ) m

(2) 7

where qt represented phosphate adsorption capacity at time of t (mg P/g), V stood for the volume of solution (mL), ct and c0 were the phosphate concentrations at time of t and initial time (mg P/L), respectively, and m was the weight of adsorbent (g). The phosphate adsorption study was done under the same operating condition with that of photocatalytic degradation during the photodegrading process. After or without the photodegradation process, the phosphate adsorption experiments were carried out in thermostatic oscillator without visible light. The demonstration of experimental set up was shown in Scheme S1 in supporting information.

3. Results and discussion As shown in Fig. 1, the adsorption capacity for phosphate in phosphate-RhB binary system was 55.80 mg/g, which was the same as that in only phosphate system without RhB. Moreover, the photodegradation rate of RhB with BiOI in phosphate-RhB binary system achieved 100% after 50 min. And the mineralization of RhB (Fig. S5) showed that the mineralization rate increased with time and reached 82% after 50 min. The above results indicated that BiOI had excellent performance in adsorbing phosphate and photodegrading RhB in phosphate-RhB binary system.

8

Fig. 1 The photocatalytic degradation rate of RhB with BiOI irradiated by visible light (inset represented the adsorption for PO43- with BiOI in phosphate single system in the dark, in phosphate-RhB binary system in the dark and under visible light irradiation , respectively).

For exploring the change of BiOI during the reaction process, XRD patterns of the as-fabricated BiOI during different reaction time were illustrated (Fig. 2). All the diffraction peaks of the as-prepared BiOI were indexed to BiOI with the tetragonal phase (Fig. S1). And it demonstrated that BiPO4 was indeed formed after adsoring PO43- for 30 min by swapping out BiOI due to the smaller Ksp of BiPO4 than that of BiOI [37], which was in good agreement with the standard card (PDF#45-1370) for the hexagonal BiPO4. As the reaction time went on, more and more PO43- adsorbed on BiOI surface formed BiPO4.

9

Fig. 2 XRD patterns of BiOI in phosphate-RhB binary system for different reaction time.

The morphologies and microstructures of BiOI and BiOI absorbing PO43- after 24 hours (BiOI-24 h) were illustrated in Fig. 3 by SEM. The as-synthesized BiOI exhibited a 3D microsphere structure and then was converted to nanorods BiPO4 as more and more PO43- was adsorbed onto BiOI.

Fig. 3 SEM of BiOI for different reaction time: (a) the as-prepared BiOI (BiOI-0 min) and (b) the BiOI absorbing PO43- after 24 hours (BiOI-24 h).

Figs. 4a-d were the TEM and HR-TEM of BiOI-0 min and BiOI-24 h. The 0.285 nm lattice spacing of BiOI-0 min corresponded to the (110) planes of tetragonal BiOI. 10

The 0.228 nm and 0.605 nm lattice spacings of BiOI-24 h were, attributed to the (004) planes of tetragonal BiOI and the (100) planes of hexagonal BiPO4, respectively, indicating that BiPO4 and BiOI coexisted in BiOI-24 h. The EDS signals of elements Bi, O, I and P were clearly observed in Fig. 5e, respectively, suggesting that the coexistence of BiPO4 and BiOI which was in accordance with the results of XRD, SEM, TEM as well as HR-TEM.

Fig. 4 The TEM and HR-TEM s of BiOI-0 min and BiOI-24 h: (a-b) the as-prepared BiOI (BiOI-0 min) and (c-d) the BiOI absorbing PO43- after 24 hours (BiOI-24 h), (e) the corresponding EDS elemental mapping images of (c).

XPS was also used to detect the change during the adsorption and photocatalysis process in phosphate-RhB binary system Fig. 5. There was no difference between the Bi 4f images of BiOI-0 min and BiOI-30 min (Fig. S2a), indicating that the valence state of Bi didn’t change. The higher intensity of the adsorbed oxygen (Ads O) of BiOI-10 min than that of BiOI (Fig. 5a) and the appearance of P 2p of BiOI-10 min (Fig. 5b) demonstrated that PO43- was adsorbed onto BiOI in the beginning because the intensity of Ads O was ascribed to the O species adsorbed on the surface of 11

photocatalyst. However, for BiOI-30 min, the emergence of P-O in O 1s level spectrum and the much higher intensity of P 2p in P 2p level spectra, together with the results of XRD (Fig. 2), confirmed the formation of BiPO4. From BiOI-30min to BiOI-24h, the increase in the intensity of P-O and P 2p manifested that more and more BiPO4 was formed as time was increased. All the above results were in according with those of XRD.

Fig. 5 XPS of BiOI adsorbing PO43- for various time: (a) O 1s; (b) P 2p.

For detecting the major oxidative species during the photocatalytic process, the trapping experimentations were carried out. Among them, BQ was the superoxide radical (·O2-) capture agent, IPA was the hydroxyl radical (·OH) capture agent, silver nitrate was the electron capture agent and TEOA was the h+ scavenger. In Fig. 6, it demonstrated that ·O2- had an important impact on the photocatalytic reaction and followed by h+.

12

Fig. 6 Trapping experiments of active species during the photocatalytic process of RhB.

Besides, the UV-vis diffuse reflectance spectrum of BiOI was obtained for the optical absorption property (Fig. S3). The absorption edge of the as-prepared BiOI was at ~605 nm, and the bandgap of BiOI was calculated to be about 1.8 eV by the formula (1) in supporting information [38]. Furthermore, according to the formula (2) and (3) in supporting information, its conduction band (CB) and valence band (VB) were calculated to be 0.54 eV and 2.34 eV [39], respectively. In addition, due to its energy <2.95 eV, BiOI showed visible light (λ > 420 nm) response, causing that its photogenerated electrons could be excited to -0.61 eV, which was much higher than the CB of BiOI and much more negative than that of O2/·O2-. Consequently, a possible mechanism of BiOI adsorbing phosphate and photodegrading RhB in phosphate-RhB binary system was proposed. Before visible light irradiation, BiOI adsorbed PO43- and cationic dyes onto the surface at the same time which was confirmed by the simultaneous appearance of N 1s level spectrum (Fig. S2b) and P 2p (Fig. 5b) level spectrum, also demonstrating the adsorption of RhB onto BiOI was 13

vital in the photodegrading reaction. Then, the photoinduced carriers of BiOI were excited by visible light and the photoinduced electrons on the CB of BiOI reduced O2 into ·O2-, which together with h+ oxidized the cationic dyes. The products from photodegradation of RhB was shown in Table S2, revealing that the conjugated structure of RhB was destroyed, which was then degraded into organic acids with low molecular weight and eventually mineralized into CO2 and H2O (Fig. S6). After the photodegradation of RhB, the more the absorption sites were, the more BiPO4 was formed by the exchange of adsorbed PO43- with the anions of BiOI.

Scheme 1 Mechanism of adsorption of phosphate and photodegradation of RhB in phosphate-RhB binary system.

In order to study the adsorption and photodegradation mechanism of BiOI in phosphate-dyes binary systems, other types of dyes were employed to construct phosphate-dye binary systems, such as cationic dyes (MB (methylene blue), FB (Fuchsin basic)), anionic dye (MO (Methyl Orange)) and neutral dye (phenol). As 14

shown in Fig. 7a all the cationic dyes were well photodegraded in phosphate-dye binary system. RhB was 100% photodegraded within 50 min, while the photodegradation rate of MB and FB were 92% and 95% within 100 min, respectively. But neither anionic nor neutral dyes were photodegraded (Fig. 7b). The adsorption performance of BiOI towards phosphate and dyes in phosphate-dye binary systems was shown in Figs. 7c and d. The adsorption capacity towards cationic dyes instantly increased to the maximum, but then decreased to the original value. While the adsorption capacities towards anionic and neutral dyes were insignificant. On the contrary, the adsorption capacity for PO43- increased continuously. In contrast, the adsorption performances of BiOI towards the three types of dyes were found to be excellent in the only dye system (Fig. 7e).

Fig. 7 BiOI adsorption capacity for phosphate and visible-light photodegradation of different types of dyes (a) and a series of cationic dyes (b) in phosphate-dye binary system; BiOI adsorption capacity for phosphate and different types of dyes(c) and 15

different cationic dyes (d) of in phosphate-dye binary system in the dark. BiOI adsorption for RhB, MO and phenol in dye system respectively (e).

In order to further reveal the mechanism, zeta potentials were measured (Table 1). The zeta potential of BiOI was almost zero (0.152 mV), and turned to be negative after the adsorption of PO43- (-6.51 mV), making it attractive for cationic dyes but repulsive for anionic and neutral dyes. Consequently, after adsorbing cationic dyes (MB, FB and MO), the zeta potentials approached zero and became less negative (-2.53 mV, -2.92 mV and -2.22 mV). But the zeta potentials got more negative (-9.17 mV and -6.89 mV) with the addition of MO and phenol respectively.

Table 1 Zeta potentials of BiOI, BiOI-P (BiOI in phosphate system), BiOI-RP (BiOI in phosphate-RhB binary system), BiOI-MBP (BiOI in phosphate-MB binary system), BiOI-FBP (BiOI in phosphate-FB binary system), BiOI-MOP (BiOI in phosphate-MB binary system), BiOI-PP (BiOI in phosphate- phenol binary system).

BiOI

BiOI-P BiOI-RP BiOI-MBP BiOI-FBP

BiOI-MOP

BiOI-PP

-9.17

-6.89

Zeta potential 0.152

-6.51

-2.53

-2.92

-2.22

(mV)

Therefore, it was proposed as follows: PO43- adsorbed on the surface of BiOI due to the smaller Ksp of BiPO4 than BiOI, which changed from being neutral into being negatively charged. In phosphate-dye binary systems, the cationic dyes were absorbed due to electrostatic attraction, but neither anionic dyes nor neutral dyes could be 16

absorbed resulting from the electrostatic repulsion. Instead, in only dye systems, all of the dyes could be adsorbed without the existence of phosphate, which further confirmed the above proposed adsorption process. Although the catalyst is far effective on adsorption of phosphate and photodegradation, the separation of catalyst from solution is a difficult job. There are two possible ways to separate BiOI from dye wastewater: 1) magnetic substances, such as Fe3O4, can be used to construct BiOI/Fe3O4 composites with magnetic properties, which can be separated from dye wasterwater after adsorption and photodegradation by exerting a magnet. 2) BiOI can be immobilized as films, which are easy to be recovered from dye wasterwater after adsorption and photo-degradation. The immobilization of BiOI as films is under way in our lab.

4. Conclusion In brief, adsorption of phosphate and photodegradation of cationic dyes with photocatalysts in phosphate-cationic dye binary system were carried out for the first time. BiOI exhibited significant adsorption capacity of phosphate up to 55.80 mg P/L and excellent photocatalytic activities for all the cationic dyes in phosphate-cationic dye binary system. Photodegradation rate of RhB achieved 100% within 50 min, while those of MB and FB were 92% and 95% within 100 min, respectively. The mechanism was proposed as that PO43- adsorbed on the surface of BiOI, which changed from being neutral into being negatively charged, and then the cationic dyes were

absorbed

due

to

electrostatic

attraction

for

photodegradation.

The

photodegradation was confirmed that O2 was oxidized to •O2- by the photogenerated 17

electrons from the CB of BiOI, and •O2- associated with h+ oxidized the cationic dyes. This work not only demonstrated an excellent reference for a new approach of photodegrading organic dyes and adsorbing phosphate in waterbodies, but also promoteed wastewater treatment with two or more pollutants.

Conflicts of interest

There are no conflicts of interest to declare.

Acknowledgements This work was supported by National Natural Science Foundation of China (21706091), the Science and Technology Progam of Guangzhou, China (201804010400), Guangdong Provincial Department of Science and Technology Application

Research

and

Development

Supporting

Special

Fund

Project

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Environmental, 211 (2017) 252-257. [30] J. Di, J. Xia, Y. Ge, L. Xu, H. Xu, M. He, Q. Zhang, H. Li, Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity, Journal of Materials Chemistry A, 2 (2014) 15864-15874. [31] Y. Li, J. Wang, H. Yao, L. Dang, Z. Li, Efficient decomposition of organic compounds and reaction mechanism with BiOI photocatalyst under visible light irradiation, Journal of Molecular Catalysis A: Chemical, 334 (2011) 116-122. [32] L. Ye, L. Tian, T. Peng, L. Zan, Synthesis of highly symmetrical BiOI single-crystal nanosheets and their {001} facet-dependent photoactivity, Journal of Materials Chemistry, 21 (2011) 12479-12484. [33] J. Di, J. Xia, Y. Ge, L. Xu, H. Xu, M. He, Q. Zhang, H. Li, Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity, Journal of Materials Chemistry A, 2 (2014) 15864-15874. [34] W. Fan, H. Li, F. Zhao, X. Xiao, Y. Huang, H. Ji, Y. Tong, Boosting the photocatalytic performance of (001) BiOI: enhancing donor density and separation efficiency of photogenerated electrons and holes, Chemical Communications, 52 (2016) 5316-5319. [35] X. Wang, S. Yang, H. Li, W. Zhao, C. Sun, H. He, High adsorption and efficient visible-light-photodegradation for cationic Rhodamine B with microspheric BiOI photocatalyst, RSC Advances, 4 (2014) 42530-42537. 23

[36] J. Han, G. Zhu, M. Hojamberdiev, J. Peng, X. Zhang, Y. Liu, B. Ge, P. Liu, Rapid adsorption and photocatalytic activity for Rhodamine B and Cr (VI) by ultrathin BiOI nanosheets with highly exposed {001} facets, New Journal of Chemistry, 39 (2015) 1874-1882. [37] J. Cao, B. Xu, H. Lin, S. Chen, Highly improved visible light photocatalytic activity of BiPO4 through fabricating a novel p-n heterojunction BiOI/BiPO4 nanocomposite, Chemical engineering journal, 228 (2013) 482-488. [38] Y. Zhong, Y. Liu, S. Wu, Y. Zhu, H. Chen, X. Yu, Y. Zhang, Facile Fabrication of BiOI/BiOCl Immobilized Films With Improved Visible Light Photocatalytic Performance, Frontiers in chemistry, 6 (2018) 58. [39] T. Yan, M. Sun, H. Liu, T. Wu, X. Liu, Q. Yan, W. Xu, B. Du, Fabrication of hierarchical BiOI/Bi2MoO6 heterojunction for degradation of bisphenol A and dye under visible light irradiation, Journal of Alloys and Compounds, 634 (2015) 223-231.

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Supporting information Adsorption of phosphate and photodegradation of cationic dyes with BiOI in phosphate-cationic dye binary system Jiaqian Zhu[a], Jiaying Li[a], Yuying Li[a], Jia Guo[c], Xiang Yu[b], Liang Peng[d], Boping Han*[d], Yi Zhu*[a], Yuanming Zhang*[a] a

Department of Chemistry, Jinan University, Guangzhou 510632, PR China

b

Analytical & Testing Center, Jinan University, Guangzhou 510632, PR China

c

Department of Ecology, Jinan University, Guangzhou 510632, PR China

d

Institute of Hydrobiology, Jinan University, Guangzhou 510632, PR China

*

Correspondence author: Tel: +86 20 85222756 (Y. Zhang and Y. Zhu); +86

02085220240 (B. Han) E-mail address: [email protected] (Y. Zhang); [email protected] (Y. Zhu); [email protected] (B. Han)

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Scheme S1 The pattern of experimental set up.

26

Fig. S1 XRD pattern of the as-prepared BiOI

27

Fig. S2 XPS images of the as-prepared BiOI and BiOI-30 min, (a): Bi 4f, (b): N 1s.

28

Fig. S3 UV-vis diffused reflectance spectra of the as-prepared BiOI; (inset: the plot of (αhυ) 1/2 versus (hυ) for BiOI.

Fig. S3 shows the band gaps of BiOI which are calculated from the spectra with the help of a Tauc plot using the following formula:

DhX

A(hX  Eg ) n / 2

(1)

where α, h, υ, A, Eg, and n are the absorption coefficient, Planck constant, frequency of light, proportionality constant, band gap, and the type of optical transition, respectively. If the type of optical transition is direct or indirect, n is the value of one or four. And the value of BiOI is four. It can be calculated that the bandgap of BiOI is about 1.8 eV. Furthermore, the corresponding valence band and conduction band position of BiOI can be calculated according to the following formula:

EVB

1 2

F  E e  Eg

(2) 29

ECB

EVB  Eg

(3)

In equations (2) and (3), EVB, Eg, χ, and Ee denote the valence band potential, band gap, absolute electronegativity and the energy of free electrons on the hydrogen scale (4.5 eV for standard hydrogen electrode), respectively. ECB represents the conduction band potential.

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Fig. S4 BiOI adsorption capacity for phosphate and visible-light photodegradation of salicylic acid and disperse blue.

31

Fig. S5 The decrease of TOC during photodegradation of RhB with BiOI in phosphate-RhB binary system under visible light irradiation.

32

Fig. S6 Photocatalytic degradation pathway of RhB with BiOI under visible light irradiation.

33

Table S1 BET specific surface areas of BiOI-0 min and BiOI-24 h. Surface area (m2/g) BiOI

24.17

BiOI-24 h

10.30

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Table. S2. Products from photocatalytic degradation of RhB detected by GC-MS m/z

Rt (min)

Name

46.01

6.556

Formic acid

45.06

8.668

ethanamine

62.04

11.346

ethane-1,2-diol

94.04

16.511

phenol

90.07

20.424

butane-1,4-diol

100.02

56.575

dihydrofuran-2,5-di one

110.04

27.431

pyrocatechol

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Structure

122.04

29.963

benzoic acid

146.06

37.450

adipic acid

166.03

42.120

phthalic acid

278.15

43.216

dibutyl phthalate

36

Highlights z

Adsorbing phosphate and photodegrading cationic dyes for the first time.

z

Excellent adsorption capacity for phosphate in all phosphate-dye binary system.

z

Excellent photocatalytic activities for cationic dyes in phosphate-cationic dye system.

z

No photocatalytic activities for anionic/neutral dye in phosphate-dye binary system.

z

The corresponding mechanism was proposed.

37

Graphical abstract

38