Super-high photocatalytic activity, stability and improved photocatalytic mechanism of monodisperse AgBr doped with In

Journal of Hazardous Materials 299 (2015) 570–576

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Super-high photocatalytic activity, stability and improved photocatalytic mechanism of monodisperse AgBr doped with In Limin Song a,∗ , Shujuan Zhang b,∗∗ , Shuna Zhang c a College of Environment and Chemical Engineering & State Key Laboratory of Hollow-Fiber Membrane Materials and Membrane Processes, Tianjin Polytechnic University, Tianjin 300387, PR China b College of Science, Tianjin University of Science & Technology, Tianjin 300457, PR China c College of Textile Engineering, Zhejiang Industry Polytechnic College, Shaoxing 312000, PR China

h i g h l i g h t s • In(III)-AgBr with higher photodegradation ability was synthesized successfully. • • OH radicals and Br0 were the main active species in the oxidation of MO. • In(III) substantially reduced the recombination rate of photon-generated carriers.

a r t i c l e

i n f o

Article history: Received 27 June 2015 Received in revised form 22 July 2015 Accepted 24 July 2015 Available online 28 July 2015 Keywords: In-AgBr Photodegradation Methyl orange Enhanced mechanism

a b s t r a c t Monodisperse In3+ doped AgBr (In-AgBr) nanoparticles were synthesized by a hydrothermal route. The pure AgBr and In-AgBr samples were investigated by X-ray powder diffraction, transmission electron microscopy, ultraviolet-visible absorption spectroscopy, X-ray photoelectron spectroscopy, measurement of total organic carbon, and electron paramagnetic resonance spectrometry. In-AgBr was more photocatalytically active than pure AgBr in photodegradation of 20 mg/L methyl orange under visible light irradiation ( > 420 nm). The 0.05 mol/L In-AgBr sample showed the highest photodegradation efficiency and high stability. The doped In3+ expanded the light absorption range, reduced the band gap of AgBr and improved the utilization of photons. The additional In3+ can inhibit the formation of Ag particles on the surface of AgBr, which can further stabilize AgBr. The doped In3+ in AgBr served as a temporary site for trapping of photoinduced electrons, and thereby obviously restrained the recombination of photoinduced electron-hole pairs on the surface of AgBr. The enhanced photocatalytic ability of In-AgBr may be mainly attributed to the improved separation efficiency of photogenerated charges. © 2015 Published by Elsevier B.V.

1. Introduction Semiconductor-based photocatalysts have attracted much attention owing to their ability and application in treatment of environmental pollution [1]. These semiconductors include metal oxides [2], metal sulfides [3], organic polymers [4], nonmetallic oxysalts [5], and metal halides [6]. The existing related works focus on designing the synthesis of semiconductors to improve the photocatalytic ability. Among the above semiconductors, AgBr is considered as an effective photocatalytic material. Since the

∗ Corresponding author. ∗∗ Corresponding author. Fax: +86 22 83955458. E-mail addresses: [email protected] (L. Song), [email protected] (S. Zhang). http://dx.doi.org/10.1016/j.jhazmat.2015.07.064 0304-3894/© 2015 Published by Elsevier B.V.

high efficiency and instability of AgBr particles under visible light radiation were reported in 2008 [7], intensive research has been devoted to searching for novel AgBr-based photocatalytic materials. The available strategies include fabrication of multicomposite [8], design of cocatalyst [9], formation of plasmonic photocatalyst [10–12], and control of morphology [13]. For example, the novel Ag3 VO4 /AgBr/Ag photocatalyst shows enhanced photocatalytic activity and stability [14]. AgBr/Ag3 PO4 shows an enhanced photocatalytic activity [15]. The photocatalytic activity of AgBr was improved using graphitic carbon nitride [16]. Fe3+ /AgBr can greatly photodecompose organic compounds [9]. However, improving photocatalytic activity of AgBr is still a huge challenge although AgBr is an excellent photocatalytic material. It is well-known that additional cation doping can enhance the photocatalytic activity of the main catalyst [17–19]. The main reason is as follows: cation doping can form a capturing center and

L. Song et al. / Journal of Hazardous Materials 299 (2015) 570–576

restrain the recombination of photo-generated electrons and holes. The cation doping can also form an impurity band, which reduces the band gap and improves the utilization of photons. Cation doping can prolong the length of carrier diffusion and elongate the life of photogenerated charges. Cation doping can form lattice defects and produce more oxidized centers. Therefore, the cation-doped photocatalysts show enhanced photocatalytic oxidation ability. In addition to the above advantages of the cation doping in the sample, the In3+ ions have unique properties [20]. The In3+ ions are the main group element with a closed-shell electronic structure; therefore, In3+ ions are relatively stable in aqueous solution and air [20]. The In3+ compounds have excellent conductivity and light absorption properties [21]. Additional In3+ ions may promote the mobility rate of electrons and light absorption of AgBr, which can enhance the photocatalytic oxidation ability of AgBr [22]. In the present paper, In3+ was introduced as a doper to enhance the photocatalytic ability of AgBr. The effect of In3+ doping on the photocatalytic performance of AgBr was investigated in detail. The results show that In3+ effectively improved the photocatalytic activity of AgBr. The mechanism was also studied in detail. We hope this work provides a reference for exploring new AgBr-based photocatalytic materials. 2. Experimental 2.1. Synthesis of samples Preparation of AgBr: first, 0.9 g of AgNO3 and 0.55 g of NaBr were each dissolved in 52.5 mL of deionized water, and then the two solutions were mixed and stirred for 15 min. The mixture was poured into a stainless steel autoclave, which was kept at 60 ◦ C for 2 h. Finally, the resulting precipitate was collected, washed with deionized water and dried at 80 ◦ C for 6 h. Synthesis of In-AgBr photocatalyst: first, 0.2 g of AgBr was dispersed in 30 mL of In3+ aqueous solutions (0.001, 0.005, 0.01, 0.05, or 0.1 mol/L), and the mixtures were stirred for 15 min. The resulting suspensions were transferred to stainless steel autoclaves, and kept reacting at 60 ◦ C for 2 h. Finally, the products were collected, washed with deionized water and dried at 80 ◦ C for 6 h. 2.2. Characterization of samples The crystal phase of each sample was determined by powder X-ray diffraction (XRD, Rigaku D/max 2500, CuK␣,  = 1.5406 Å, 40 kV, 40 mA). The morphology of samples was characterized by transmission electron microscopy (TEM, Hitachi H-7650, 100 kV). Ultraviolet–visible (UV–vis) absorption spectra were recorded with an HP8453 spectrometer using BaSO4 as the reference. X-ray photoelectron spectroscopy (XPS) was conducted by a PerkinElmer PHI5300 XPS meter. The standard peak of adventitious carbon (C1s ) was used in calibration of BE. Total organic carbon contents (TOCs) of samples were measured by a Shimadzu-Toc-Vcph meter. Zeta potential at room temperature was measured with a Zetasizer nano ZS90 instrument. Electron spin resonance (ESR) spectra were recorded by a JES FA200 electron surface paramagnetic resonance (SPR) spectrometer. 2.3. Activity measurement Photodegradation of methyl orange (MO) proceeded in an outerirradiation quartz reactor vertically irradiated by a 300 W xenon lamp ( > 420 nm). About 100 mg of each sample was added to 100 mL of 20 mg/L MO aqueous solution. After stirring for 30 min in the dark to achieve adsorption equilibrium, the reaction proceeded under continuous stirring. Following the visible light radiation,

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Table 1 Cell parameters and volume of undoped and doped AgBr. Sample

Cell parameters a = b = c (Å)

Cell volume (Å3 )

AgBr 0.001 mol/L In-AgBr 0.005 mol/L In-AgBr 0.01 mol/L In-AgBr 0.05 mol/L In-AgBr 0.1 mol/L In-AgBr

5.00175 5.00605 5.00592 5.00707 5.00488 5.01036

125.13 125.45 125.44 125.53 125.37 125.78

about 3 mL of the solution was extracted at a given time interval, withdrawn, centrifuged, and analyzed by the UV–vis spectrometer. 3. Results and discussion 3.1. Characterization of photocatalysts The phase structure and crystallite size of both AgBr and In-AgBr photocatalysts were investigated using XRD (Fig. 1). All the diffraction peaks of AgBr were assigned to the cubic phase of AgBr (JCPDS card no. 79-0149; a = b = c = 5.775 Å) (Fig. 1A), suggesting that pure AgBr phase was formed via our experimental route. The strong sharp peaks indicate good crystallization of AgBr. Both the shapes and positions of all diffraction peaks in the In-AgBr samples are similar to those of pure AgBr. No other In3+ compounds are found in Fig. 1A. The results show that the additional In3+ did not affect the composition of AgBr particles, which was proved by the enlarged XRD patterns in Fig. 1B. The positions of main diffraction peak in InAgBr changed slightly and regularly compared with those of AgBr (Fig. 1B). The peak positions shifted to left with increase of In3+ doping amount, indicating that additional In3+ was doped in the lattice of AgBr. The cell parameters and volumes of both pure AgBr and In-AgBr were calculated on Jade 6.0 to prove the change of AgBr lattice in Table 1. The cell parameters and volumes of In-AgBr lightly increased compared with those of AgBr. However, the radius of In3+ (0.08 nm) is smaller than that of Ag+ (1.13 nm), indicating that the doped In3+ mainly entered the lattice space, rather than replacing the Ag+ in AgBr. Moreover, the peak intensity of In-AgBr was improved compared with that of AgBr, which indicates an enhancement of crystallization. Herein, only the strongest peak (2 0 0) was used to calculate the crystal size of samples according to the Scherrer equation. The mean sizes of the 0, 0.001, 0.005, 0.01, 0.05, and 0.1 mol/L In-AgBr samples are 24.3, 22, 18.7, 19.6, 18.7, and 23.1 nm, respectively. Clearly, the In-AgBr samples show smaller crystallite sizes than AgBr. These results indicate that the additional In3+ not only improved the crystallization, but decreased the crystal size of In-AgBr samples. Additional In3+ adsorbed on the surface of AgBr particles inhibited the further growth of AgBr crystals; therefore, the sizes of the samples get smaller at first with the increasing of the concentration. However, the rising doping amount results in a part of doped In3+ entered the lattice space (gap); therefore, the sizes of the samples finally get larger. The crystallinity and size of particles are very important factors deciding its photocatalytic activity. Therefore, the additional In3+ in AgBr may enhance the photocatalytic ability of AgBr. Fig. 2 displays typical TEM images of pure AgBr and 0.05 mol/L In-AgBr. The two samples were first dispersed in ethanol, treated under ultrasonic radiation for 10 min and then dripped into 300 mesh copper grids for testing. As a result, the particles of AgBr and 0.05 mol/L In-AgBr were both monodisperse and did not congregate together (Fig. 2). The monodisperse structures can expose more surface active sites, which is helpful for the fulfillment of photocatalytic activity. Their shapes are similarly spherical-like (Fig. 2). Statistical calculation showed that the mean diameter of 0.05 mol/L In-AgBr particles was smaller than that of AgBr. This result indicates

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A 3+

0.1 mol/L In ions

3+

0.05 mol/L In ions

Intensity (a.u.)

3+

0.01 mol/L In ions

3+

0.005 mol/L In ions

3+

0.001 mol/L In ions

AgBr

10

20

30

40

50

60

70

80

2Theta/degree

B

3+

0.1 mol/L In ions

3+

Intensity (a.u.)

0.05 mol/L In ions

3+

0.01 mol/L In ions

3+

0.005 mol/L In ions

3+

0.001 mol/L In ions

Fig. 2. TEM images of (a) AgBr and (b) In-Ag3 PO4 (0.05 mol/L In3+ ions). AgBr

30

40

2Theta/degree

Fig. 1. X-ray diffraction patterns of pure and In-AgBr.

50

that the doped In3+ in AgBr can reduce the particle size, which is consistent with the XRD analysis. The UV–vis absorption spectra of AgBr and In-AgBr particles are shown in Fig. 3. A strong absorption within 350–470 nm in all samples can be assigned to the intrinsic bandgap absorption of AgBr (Fig. 3A), which is consistent with a previous report [9]. For pure AgBr, the obvious absorption at 450–800 nm can be assigned to the SPR of Ag, because the light-sensitive AgBr under light radiation forms Ag particles. However, the absorption in In-AgBr particles

L. Song et al. / Journal of Hazardous Materials 299 (2015) 570–576

2.0

573

200000

A

180000

367.8 eV

Ag3d

A

AgBr

160000

373.8 eV

1.5

Absorbtion (a.u.)

140000 120000

3+

0.001 mol/L In ions 1.0

367.9 eV

100000 3+

0.1 mol/L In ions

373.9 eV

80000

3+

0.05 mol/L In ions

60000

AgBr

40000

0.5

20000 3+

0.005 mol/L In ions

3+

0

3+

0.01 mol/L In ions

0.0

0.05 mol/L In AgBr 360

300

400

500

600

700

365

370

375

380

800

Wavelength (nm) 16500

B

B

445.4 eV

In3d

0.3 16000

AgBr 453.3 eV

3+

0.001 mol/L In ions

(a hv)

1/2

0.2

Intensity (a.u.)

15500 15000 14500 14000

3+

0.005 mol/L In ions

13500

0.1

13000

3+

0.05 mol/L In ions 3+

0.1 mol/L In ions

12500 435

3+

0.01 mol/L In ions

0.0 1.5

2.0

2.5

440

445

450

455

460

Bing energy (eV) 3.0

3.5

4.0

Wavelength (nm)

4.5

5.0

5.5

Fig. 4. XPS spectra of the as-synthesized AgBr and In-AgBr (0.05 mol/L In3+ ions). (A) Ag3d, (B) In3d.

Fig. 3. UV–vis absorption spectra of the as-synthesized AgBr and In-AgBr.

In3+

disappears, suggesting that additional can inhibit the formation of Ag particles under natural light radiation. Therefore, the doped In3+ can further stabilize AgBr. Compared with pure AgBr, the absorption edges of In-AgBr particles shift to red (Fig. 3A), indicating the bandgap was smaller than that of AgBr. The indirect bandgaps of the samples were estimated from the plot of “(␣h␯)1/2 versus photon energy (h␯)” (Fig. 3B). The bandgaps for 0, 0.001, 0.005, 0.01, 0.05, and 0.1 mol/L In-AgBr samples are 2.22, 2.16, 2.16, 2.19, 2.2, and 2.2 eV, respectively. The bandgap reduction is helpful for absorption of lower-energy photons, which will improve the efficiency of photons. To study the surface valence and composition of the samples, AgBr and 0.05 mol/L In-AgBr were analyzed by XPS. Fig. 4A shows the binding energies and intensities of the surface element of Ag 3d in AgBr and 0.05 mol/L In-AgBr. The Ag 3d peaks of AgBr are at about 367.8 and 373.8 eV, which are in accordance with another report [9]. The position of the Ag 3d peak in the In-AgBr sample shifts to higher energy compared with AgBr, suggesting that the electron density of Ag+ was somewhat decreased in In-AgBr. This phenomenon could be ascribed to the doped In3+ in AgBr, and suggests the strong interaction or new bonds of Ag-Br-In between In3+ and AgBr, which results in a slight transfer of electron density of In3+ . The XPS of the In3+ in In-AgBr is shown in Fig. 4B. The peaks at about 445.4 and 453.3 eV can be assigned to In3+ [23]. The peak position is slightly lower than that of the binding energy of In3+ of In(NO3 )3 , which results from the strong interaction or new bonds

of Ag-Br-In between the doped In3+ and AgBr. The new XPS peaks of In in Fig. 4B further suggests that In3+ was doped into AgBr. 3.2. Photocatalytic activity of photocatalysts To study the potential applicability of the test samples, we investigated the photodegradation of 20 mg/L MO aqueous solution over AgBr or In-AgBr under visible light irradiation. The pure AgBr was used as the reference. The mixed catalyst and MO solution was stirred in dark to reach adsorption equilibrium before photodegradation. The adsorbed amount is shown in Fig. 5. The adsorption ratios on 0, 0.001, 0.01, 0.05, and 0.1 mol/L In-AgBr samples are 6.7%, 4.1%, 8.25%, 6.37%, and 3.4%, respectively. The adsorbed amount is so small that it does not affect the photodegradation ratio. The MO photodegradation ratio after 12 min is 71% (Fig. 5). However, all the In-AgBr (0.001, 0.01, 0.05, and 0.1 mol/L In3+ ) samples were remarkably and highly active after 12 min, with photodegradation ratios of 83.5%, 91.5%, 93.4%, and 79.1%, respectively. These results suggest that the doped In3+ can largely improve the photodegradation performance of AgBr. The photodegradation activities of In-AgBr samples were improved first, and then reduced with the increasing amount of In3+ (Fig. 5). Moreover, the 0.05 mol/L In-AgBr sample was the most active in removal of MO, indicating that the appropriate In3+ concentration in AgBr to obtain the optimal photodegradation ability is 0.05 mol/L. The increase of doping amount can significantly decrease the thickness of the space charge layer on AgBr surface. The absorbed photons can be effectively separated

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100

6.0

20mg/L MO solution 5.5

AgBr 3+ 0.001 mol/L In ions 3+ 0.01 mol/L In ions 3+ 0.05 mol/L In ions 3+ 0.1 mol/L In ions

60

40

5.0

TOC (mg/L)

MO concentration removal (%)

80

AgBr

4.5 4.0 3.5

in dark

20

3.0 3+

In-AgBr (0.05 mol In ions)

0

2.5 -35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

0

1

2

Irradiation time (min) Fig. 5. The photocatalytic activity over AgBr and In-AgBr. The concentration of catalysts is 1.0 g/L.

4

5

6

Fig. 7. TOC evolution in the process of the photocatalytic degradation of 20 mg/L MO on AgBr and In-AgBr (0.05 mol/L In3+ ions).

0.55

100

0.50

3rd run

1st run

0.45

0.35 0.30 0.25 0.20 0.15 0.10

MO concentration removal (%)

20 mg/L MO after adsorption 2 min 4 min 6 min 8 min 10 min 12 min 14 min 16 min

0.40

Intensity (a.u.)

3

Time (min)

0.05

2nd run

4th run

80

5th run

60

40

20

0.00 -0.05 300

400

500

600

700

Wavelength (nm) Fig. 6. The UV–vis absorption spectra of solution in the process of the photocatalytic degradation of 20 mg/L MO on In-AgBr (0.05 mol/L In3+ ions). The concentration of catalysts is 1.0 g/L.

when the thickness of the space charge layer is equal to the depth of incident light into the sample. At that time, the doping amount is the optimal. The appropriate In3+ concentration in AgBr can largely improve the photocatalytic ability of AgBr. Fig. 6 shows the temporal spectral evolution of MO over 0.05 mol/L In-AgBr under visible light irradiation. The strong characteristic absorption peak at 465 nm was assigned to the n → p* electronic transition from the hydrazone structure of MO. Therefore, the characteristic absorption peaks were gradually weakened with time. After 16 min, the absorption peak at 465 nm almost disappeared, which probably means that MO molecules were degraded or converted. To confirm the degraded products, the removal of TOC was measured and the results are showed in Fig. 7. The TOCs during the photodegradation of 20 mg/L MO over AgBr and 0.05 mol/L In-AgBr (1.0 g/L) are shown in Fig. 7. Clearly, the TOC removal efficiency of MO after 6 min were 39.68 and 55.7% for AgBr and 0.05 mol/L In-AgBr, which further proved that the doped In3+ can promoted the photodegradation of MO, and MO molecules can be removed efficiently. However, the removal ratios are not consistent with the activity ratios for AgBr and 0.05 mol/L In-AgBr. This result suggests that only a part of MO molecules can be destroyed and converted to CO2 , H2 O, and other small molecules, but the other

0

20

40

60

80

100

Recycling time Fig. 8. Recycling tests of degradation of 20 mg/L MO over In-AgBr (0.05 mol/L In3+ ions). The concentration of catalysts is 1.0 g/L.

part may be converted to intermediate products. The durability of 0.05 mol/L In-AgBr was tested by MO photodegradation for five recycles (Fig. 8). The MO photodegradation ratios after five recycles were still up to 90% and almost did not change, suggesting that the In-AgBr sample was stable during the MO photoegradation. Fig. 9A exhibits the XRD pattern of the fresh and used 0.05 mol/L In-AgBr. For the used In-AgBr, the strong action of MO molecules and AgBr surface in the photocatalytic reaction leaded to a significant reduction of the peak intensity of In-AgBr. However, we did not find Ag or Ag2 O particles in Fig. 9A. Therefore, the doped in3+ can suppress the formation of Ag or Ag2 O particles on the surface of AgBr, and enhance the stability of AgBr. Fig. 9B shows the XPS spectra of the fresh and used 0.05 mol/L In-AgBr. Compared with two XPS spectra, the peak intensity of the used In-AgBr became lower than that of the fresh sample because of the effect of the MO molecules in the photocatalytic process. However, the Ag3d and Br3d peak positions of the two samples were identical, indicating that the phase composition and surface valence of AgBr did not change before and after the photocatalytic reaction. The conclusion showed that the In-AgBr was very stable. This result is consistent with the XRD results.

L. Song et al. / Journal of Hazardous Materials 299 (2015) 570–576

575

2000

A

A

3+

In-AgBr (0.05 mol In ions)

AgBr 16 min

1800

Intensity (a.u.)

1600

12 min

Fresh

1400

1200

8 min Intensity (a.u.)

1000

Used

10

20

30

40

50

60

70

800

80 4 min

600

2Theta/degree 120000

400

B

110000

Fresh

0.05 mol/L In-AgBr

100000

200

Intensity (a.u.)

in dark

90000 80000

0

70000 60000

-200 318.1

50000

318.2

318.3

318.4

318.5

318.6

318.7

318.8

Magnetic Field (G)

Ag3d

40000

3000 3+

30000

In-AgBr (0.05 mol In ions)

B

20000 10000

16 min

Used

0

2500

360

365

370

375

380

Bing energy (eV) 20000

C

Fresh

0.05 mol/L In-AgBr

18000

2000

12 min

14000

Intensity (a.u.)

Intensity (a.u.)

16000

12000 10000

1500

Br3d

8000

8 min 1000

6000 4000 2000

Used

500

0 60

62

64

66

68

70

72

74

76

4 min

78

Bing energy (eV) Fig. 9. XRD and XPS spectra of the fresh and used In-AgBr (0.05 mol/L In3+ ions).

0

in dark

3.3. Photocatalytic process and mechanism The ESRs under visible light radiation for AgBr and 0.05 mol/L In-AgBr were measured to detect the main active species in MO photoegradation (Fig. 10). As a result, we only detected DMPO-• OH signals, but no DMPO-• O2 - or DMPO-• OOH signals. Therefore, • OH is the main active species during the MO photoegradation over InAgBr. Moreover, there are DMPO-• OH signals in dark for both AgBr and 0.05 mol/L In-AgBr (Fig. 10A and B), which suggests that AgBr is very sensitive to even weak natural light. • OH does not obviously

318.1

318.2

318.3

318.4

318.5

318.6

318.7

318.8

Magnetic Field (G)

Fig. 10. DMPO spin-trapping ESR spectra for DMPO-• OH in the presence of AgBr and In-AgBr (0.05 mol/L In3+ ions) under visible light irradiation ( > 420 nm) and in dark.

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attenuate with time (Fig. 10B), suggesting that the doped In3+ can further stabilize AgBr under visible light radiation. The intensity of DMPO-• OH signals is around 2.98 times higher than that of AgBr (Fig. 10A), indicating that the doped In3+ can greatly increase the amount of • OH under visible light radiation. Therefore, the doped In3+ severely improved the photocatalytic ability during the MO photoegradation. AgBr can produce photoinduced electrons and holes, and form Ag particles under visible light radiation. The photoinduced electrons rapidly transfer from AgBr to Ag particles via the SPR effect, while the photoinduced holes transfer onto the surface of AgBr [9]. The photoinduced electrons can be trapped by the adsorbed O2 to produce • O2 − . Meanwhile, the photoinduced holes can combine with OH− to form • OH. According to the ESR result in Fig. 10, • OH is the main active species during the MO photoegradation. Therefore, we conclude that • O2 − may be finally converted to • OH by a series of changes. In addition, Br− can trap photogenerated holes to form Br0 [6,11,12], and Br0 can oxidize MO into small molecules. Finally, • OH and Br0 are the active species responsible for the MO photoegradation. In-AgBr + h → h+ + e− OH− + h+ → • OH O2 + e− → • O2 − → • OOH → H2 O2 → • OH • OH

+ MO → products

Br− + h+ → Br0 Br0 + MO → products Then, we propose the mechanism of In-AgBr improvement according to the above analysis and other references [24,25]. Doped In3+ expanded the light absorption range, reduced the band gap of AgBr and improved the utilization of photons. The doped In3+ can obviously change the thickness of the space charge layer on AgBr surface, which will significantly affect the separation efficiency of photogenerated charges. The doped In3+ contains multiple positive charges, and exists on the surface of AgBr particles. Therefore, it serves as a temporary site for trapping of photoinduced electrons, which obviously restrain the recombination of photoinduced electron–hole pairs on the surface of AgBr [24]. The above aspects result in an enhancement of stability and photocatalytic ablity. 4. Conclusions In3+ -doped AgBr was successfully prepared by a hydrothermal route. Under the mild condition, In3+ mainly enters the lattice space of AgBr. The strong attraction of photogenerated electrons and In3+ allowed In3+ to severely improve the optical property of AgBr and separation efficiency of photogenerated charges. In short, the doped In3+ in AgBr largely improved the photocatalytic performance of AgBr. Finally, we hope this work provides a novel method for construction of highly efficient AgX photocatalysts. Acknowledgements This work was supported by Natural Science Foundation of Tianjin of China (14JCYBJC20500) and Students Innovation and Entrepreneurship Training Program (201510058039).

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