Construction of AgCl/Ag/BiOCl with a concave-rhombicuboctahedron core–shell hierarchitecture and enhanced photocatalytic activity

Abstract

AgCl/Ag/BiOCl with a concave-rhombicuboctahedron hierarchitecture with excellent photocatalytic activity is obtained via a facile vapor diffusion strategy at room temperature without template or any additives. The AgCl/Ag/BiOCl shows considerably higher photocatalytic activity than pure Ag/AgCl and BiOCl under visible light irradiation, in which the main active species are holes and Cl atoms. The possible charge transfer mechanism for the enhanced visible light photocatalytic activity is proposed. The slow reaction rate of the vapor diffusion process could produce the hierarchical structure AgCl/Ag/BiOCl which consists of cubic AgCl as the core and BiOCl nanosheets on the surface. The heterojunction between AgCl and BiOCl could effectively promote the interfacial charge transfer and decrease the combination of photoinduced electrons and holes, thus produce a large number of holes and enhance photocatalytic activity. Furthermore, strong adsorption activity of BiOCl nanosheets on the surface of AgCl/Ag/BiOCl also promotes the photocatalytic activity. Finally, low consumption of Ag and higher photocatalytic efficiency are both achieved in the AgCl/Ag/BiOCl heterojunction photocatalyst. This novel photocatalyst demonstrates potential application for organic pollutant elimination and proposes insight for designing highly efficient heterojunction photocatalysts.

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1. Introduction

In the last decades, with the development of urbanization and industrialization, the environmental problems caused by industrial wastewater and toxic air pollutants have become an important issue. In this context, semiconductor photocatalysis has attracted much attention as a promising “green” solution.¹ The main obstacle that inhibits its practical application arises from the lack of photocatalysts with high efficiency and low cost.

Recently, BiOCl has been considered as a promising photocatalyst due to its excellent photocatalytic activity, nontoxicity and low cost.^2–7 BiOCl, as a ternary oxide semiconductor, has a layered crystal structure that consists of tetragonal [Bi₂O₂]²⁺ positive slabs interleaved by double negative slabs of chlorine atoms along the [001] direction. The layered structure can provide a space large enough to polarize the related atoms and orbital.^3,4,8–10 The induced internal static electric fields can effectively separate the photoinduced electron–hole pairs along the [001] direction efficiently, which is beneficial for enhancing photocatalytic activity. Therefore, BiOCl exhibited superior photocatalytic activity. However, the drawback of BiOCl photocatalyst is the requirement of UV light irradiation due to the wide band gap of 3.4 eV, since UV light accounts for a small part (less than 5%) of the solar spectrum. Until now, many efforts have been made to improve the photocatalytic activity of BiOCl under visible light.^3,11–15 Constructing heterojunction photocatalyst is one of the effective approaches to utilize visible light and promote the separation of photoinduced electrons and holes, thus enhance the photocatalytic activity.

Plasmonic photocatalysts, especially Ag/AgCl based photocatalysts have received much attention in the last decade because of their visible-light-driven photocatalytic activity.^16–23 As we know, nanoparticles of metal can absorb visible light because of their surface plasmon resonance (SPR),^24,25 and Ag nanoparticles formed on the surface of the AgCl could lead to strong absorption of light in the visible region. Ag/AgCl photocatalyst with various morphologies have been successfully synthesized and their photocatalytic activity was demonstrated in the degradation of organic pollutants under visible light irradiation.^{16,20,26–33} However, the application of Ag/AgCl photocatalyst was limited due to the high cost of Ag. To resolve this issue, much effort has been focused on coupling Ag/AgCl with other semiconductors for reducing the amount of Ag consumption.^34–38

Thus, constructing heterojunction photocatalyst of AgCl/Ag/BiOCl is a promising approach for reducing the cost and enhancing photocatalytic efficiency.^39,40 Usually, the preparation of this heterostructure is carried out via two strategies, which are based on one-step method (co-precipitation) and multi-step approach (synthesis and ion-exchange), respectively.^39–46 However, traditional one-step co-precipitation of AgCl/Ag/BiOCl in solutions inevitably leads to severe aggregation and poor dispersity, which consequently reduces the photocatalytic efficiency. And the multi-step approaches need complicated procedures and long reaction time. Furthermore, the size and morphology was difficult to control because of the fast growth kinetics between Bi³⁺, Ag⁺ ions and Cl⁻ ions. Photocatalysts with separate non-contacting particles of AgCl and BiOCl could be synthesized via these methods. The spatial gap between these non-contacting particles of photocatalysts will inevitably affect the transfer of photoinduced electrons and holes, and thus reduce the photocatalytic activity of photocatalyst. The reasons mentioned above usually lead to the heterojunction photocatalyst with unsatisfied performance.

The photocatalytic efficiency of photocatalysts prepared by these traditional method was usually not higher than pure Ag/AgCl.^40,44–46 Therefore, designing a rational synthetic strategy to produce AgCl/Ag/BiOCl heterostructure photocatalyst with high efficiency and low cost through simple and facile procedure is highly desirable for both scientific researches and practical applications.

We believe that heterojunction with good interface characteristic could be formed through vapor diffusion method in which the reaction rate between Bi³⁺, Ag⁺ ions and HCl molecules was slow. In this present study, AgCl/Ag/BiOCl heterojunction photocatalyst with concave-rhombicuboctahedron hierarchical morphology was synthesized via the proposed strategy. Comparing with traditional methods, this method was simple and can be completed at room temperature. The results demonstrated that the AgCl/Ag/BiOCl photocatalyst with uniform size and morphology showed higher photodegradation activity toward MO under visible light irradiation, comparing with pure Ag/AgCl and BiOCl. Finally, the photocatalytic mechanism during the photodegradation process was discussed in detail based on the measurements.

2. Experimental section

2.1 Materials

Bi(NO₃)₃·5H₂O, AgNO₃, isopropyl alcohol (IPA), ethylene diamine tetraacetic acid (EDTA), methyl orange (MO), hydrochloric acid (∼12 M) were analytically pure and used without further purification.

2.2 Synthesis of AgCl/Ag/BiOCl

In a typical synthesis, 0.1 mmol Bi(NO₃)₃·5H₂O and 0.1 mmol AgNO₃ were firstly ultrasonically dissolved into the 50 mL of deionized water at room temperature to form a homogeneous solution. Then the solution mentioned above and 1 mL HCl aqueous solution (∼12 M) in two separate beakers were both placed into a sealed vessel. The air-pressure in the sealed vessel was the same as air-pressure in the room. The scheme of vessel is shown in ESI.† During the process, the vaporized HCl molecules diffuse and react with the Bi(NO₃)₃ and AgNO₃ in the aqueous solution to form AgCl/BiOCl. After the growth process, sun light irradiation in the room in the middle of daytime causes the formation of plasmonic AgCl/Ag/BiOCl photocatalyst. After 1 hour, the resulting precipitate was collected by centrifugation, and washed using deionized water and absolute ethanol three times, respectively. Then, the product was transferred to an oven to dry at 60 °C overnight. For comparison, BiOCl and Ag/AgCl were synthesized using similar processes without adding AgNO₃ and Bi(NO₃)₃·5H₂O, respectively.

2.3 Characterization

X-ray diffraction patterns (XRD) of the samples were recorded with a D/max2600 (Rigaku, Japan) using the Cu-Kα radiation (λ = 0.154056 nm). Field emission scanning electron microscope (FESEM) images were obtained by a SU70 (Hitachi, Japan). Transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) images were obtained with a FEI, Tecnai TF20 field emission electron microscope operating at an accelerating voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) was performed on a Thermofisher K-Alpha X-ray spectrometer with Al source. UV-vis diffuse reflectance spectra (DRS) of the samples were obtained by UV-vis spectrometer (Perkin-Elmer, Lambda 850) using BaSO₄ as a reference and was converted from reflection to absorbance by the Kubelka–Munk method.

2.4 Photocatalytic activity test

The photocatalytic activity of the as-synthesized samples was evaluated by photodegradation of MO under visible light irradiation (λ ≥ 400 nm). The visible light was obtained by a 300 W xenon lamp with a 400 nm cutoff filter to ensure the needed irradiation light. In the photocatalytic degradation process, 30 mL aqueous solution of MO (10 mg L⁻¹) was placed in a glass beaker, and then 30 mg of photocatalysts was added. Before light irradiation, the mixture was first sonicated for 5 min and then kept in the dark for 30 min with stirring to reach the adsorption–desorption equilibrium between the organic molecules and the catalyst surface. At the given time an interval, 1 mL solution was taken from the suspension and immediately centrifuged. The concentration of MO was analyzed by a Perkin-Elmer Lambda 850 UV-vis spectrometer. All of the measurements were carried out at room temperature. To compare with photocatalytic activity of AgCl/Ag/BiOCl, the photocatalytic efficiency of BiOCl and Ag/AgCl were also performed under the identical conditions.

3. Results and discussion

3.1 Structural and morphological characterization

The crystalline structure of the as-prepared samples was investigated by X-ray diffraction. Fig. 1 shows the XRD patterns of the pure BiOCl, AgCl and AgCl/Ag/BiOCl heterojunction photocatalysts. Two series of XRD peaks can be observed in Fig. 1. All the diffraction peaks of these samples can be well indexed to the standard XRD data of tetragonal BiOCl (JCPDS no. 06-0249) and the cubic phase of AgCl (JCPDS file: 31-1238). The XRD data reveal the co-existence of BiOCl and AgCl phases in the as-prepared AgCl/Ag/BiOCl. The diffraction peaks of these samples are sharp and no other peaks of impurities could be observed, indicating the high quality and purity of the samples. It should be noted here that no characteristic peak that belong to Ag was detected. The reason may be that the amount of Ag NPs formed on the surface of Ag/AgCl and AgCl/Ag/BiOCl was too low to be detected.

Fig. 1 XRD patterns of BiOCl, Ag/AgCl and AgCl/Ag/BiOCl.

The morphology of the samples were characterized by SEM, TEM and HRTEM. Fig. 2 displays the SEM images of AgCl/Ag/BiOCl, BiOCl and AgCl photocatalysts. The BiOCl sample is composed of a large quantity of sheets with an in-plane size of 1–4 μm. The AgCl sample has an irregular spherical-like morphology with size of 0.5–1 μm. Interestingly, it can be clearly seen that the AgCl/Ag/BiOCl sample possesses regular concave-rhombicuboctahedron morphology with size of 1–4 μm. Obviously, from the high magnification FESEM images (inset of Fig. 2b), it can be seen that there are lots of nanosheets grown on the surface of AgCl/Ag/BiOCl sample. There are many gaps between these nanosheets, which is beneficial for reactant diffusion and transport.

Fig. 2 SEM images of AgCl/Ag/BiOCl (a, b), BiOCl (c) and Ag/AgCl (d).

The hierarchical structure of AgCl/Ag/BiOCl heterojunction photocatalyst is further studied via TEM. Fig. 3a shows the TEM image of the AgCl/Ag/BiOCl sample. It also reveals the rhombicuboctahedron-like structure of AgCl/Ag/BiOCl from the cross-section image. The AgCl/Ag/BiOCl sample contains nanosheets grown on the surface. To demonstrate the crystal structure of these nanosheets, the AgCl/Ag/BiOCl was studied by high-resolution TEM (HRTEM), and the images are shown in Fig. 3b and c. HRTEM image in Fig. 3b reveals the highly crystalline nature of the nanosheets. The clear lattice fringes with an interplanar lattice spacing of 0.27 nm correspond to the (110) planes. Furthermore, the HRTEM image of vertical nanosheet (Fig. 3c) shows clear and continuous lattice fringes with interplanar spacing of 0.74 nm which is assigned to the (001) planes of BiOCl.^47,48 The TEM images demonstrate that the BiOCl nanosheets on the surface of photocatalyst produced by vapor diffusion method have good crystallinity.

Fig. 3 TEM images and EDS spectrum of AgCl/Ag/BiOCl.

Interestingly, only BiOCl was detected by HRTEM, as shown in Fig. 3. To further confirm the composition of AgCl/Ag/BiOCl sample, AgCl/Ag/BiOCl was also characterized via energy-dispersive X-ray spectrum (EDS) and X-ray photoelectron spectroscopy (XPS). As shown in Fig. 3d, Bi, O, Cl and Ag elements all exist, and the C and Cu signals are ascribed to the substrate. Elements atomic ratio and XPS spectra were shown in Table S1† and Fig. 4. The peak positions in the XPS spectra were calibrated with C 1s at 284.6 eV. The XPS spectrum of AgCl/Ag/BiOCl sample shown in Fig. 4a indicates that the as-prepared sample consists of Bi, O, Cl, Ag and C elements. The high-resolution spectra of Bi 4f, Cl 2p, O 1s, and Ag 3d are shown in Fig. 4b–e. The two strong peaks at 159.3 and 164.6 eV shown in Fig. 4b are attributed to Bi 4f_7/2 and Bi 4f_5/2, respectively, which are characteristic of Bi³⁺ species in AgCl/Ag/BiOCl. Peaks with binding energies of 197.9 and 199.4 eV correspond to Cl 2p_3/2 and Cl 2p_1/2, respectively. Peak with binding energy of 530.4 eV corresponds to O 1s. Typical peaks of Ag 3d can be further divided into two different peaks. The peaks at 367.6 and 373.5 eV are attributed to Ag⁺ of AgCl, and the peaks at 368.5 and 374.4 eV are attributed to metallic Ag⁰ (Fig. 4e). On the base of XPS results, it could confirm the existence of both Ag and AgCl in the AgCl/Ag/BiOCl sample.

Fig. 4 XPS spectra of the sample of AgCl/Ag/BiOCl: (a) survey XPS spectrum, (b–e) high resolution XPS spectra of Bi 4f, O 1s, Cl 2p and Ag 3d.

Based on the XRD, EDS and XPS results, BiOCl and AgCl were both exist in AgCl/Ag/BiOCl heterostructure photocatalyst. But only BiOCl can be detected by HRTEM. To further confirm the structure and composition of AgCl/Ag/BiOCl sample, the elements mapping was characterized by TEM. The corresponding Bi, O, Cl and Ag elements images are shown in Fig. 5a–f, respectively. These EDX mapping images demonstrate that Bi and O were distributed on the out surface of AgCl/Ag/BiOCl sample, and Ag was only distributed in the inner core of AgCl/Ag/BiOCl sample, and Cl was distributed uniformly on the entire structure of AgCl/Ag/BiOCl sample. Base on the above measurements, the growth mechanism was proposed, as shown in Scheme 1. Hierarchical structure AgCl/Ag/BiOCl consists of cubic AgCl as core and BiOCl nanosheets on the surface, and the interface between AgCl and BiOCl could be clearly seen in elements mapping figures.

Fig. 5 EDX mapping of AgCl/Ag/BiOCl. TEM (left, a and b) and corresponding elemental distribution of Bi (yellow), Cl (orange), O (purple), and Ag (green).

Scheme 1 Illustration of possible formation mechanism of AgCl/Ag/BiOCl.

UV-vis diffuse reflectance spectra of Ag/AgCl, BiOCl and AgCl/Ag/BiOCl are shown in Fig. 6. BiOCl shows no absorbance in the visible light range. It is clear to see that the visible light absorption ability of AgCl/Ag/BiOCl is much increased compared to BiOCl, which could be ascribed to the characteristic absorption of the localized surface plasmon resonance.^49,50 And the Ag/AgCl shows the strongest absorption ability of visible light among three photocatalysts. However, the spectra of Ag/AgCl and AgCl/Ag/BiOCl does not show obvious peak in the visible light range, because the morphology and size of Ag nanoparticles are not uniform.

Fig. 6 DRS spectra of BiOCl, Ag/AgCl and AgCl/Ag/BiOCl.

3.2 Photocatalytic activity of AgCl/Ag/BiOCl photocatalysts

MO is one kind of organic dye that is often used as a model pollutant to study the photocatalytic activity of photocatalysts. In this experiment, the photocatalytic activity of pure BiOCl, pure Ag/AgCl, physical mixture of BiOCl and Ag/AgCl, and AgCl/Ag/BiOCl were evaluated by photodecomposition of MO under visible light irradiation, as shown in Fig. 7a. Before light irradiation, adsorption–desorption equilibrium between photocatalysts and MO molecules in solution was achieved in 30 min. There is obvious difference of the pollutant's concentration after dark adsorption for these photocatalysts, the adsorption activity follows an order of BiOCl > physical mixture > AgCl/Ag/BiOCl > Ag/AgCl. The characteristic absorption peak of MO at λ = 464 nm is used to monitor the photocatalytic degradation process. The degradation efficiency of all the samples is defined as C/C₀, where C and C₀ represent the remnant and initial concentration of MO, respectively.

Fig. 7 (a) The comparisons of photocatalytic activities among the samples BiOCl, Ag/AgCl, physical mixture of BiOCl and Ag/AgCl, and AgCl/Ag/BiOCl. (b–d) Trapping experiments of active species during the photocatalytic reaction.

It is worth noting that, under visible light irradiation, the AgCl/Ag/BiOCl displays superior photocatalytic activity. The MO molecules were almost completely decomposed after 15 min irradiation in the presence of AgCl/Ag/BiOCl photocatalyst. In the case of Ag/AgCl and physical mixture, about 57% and 49% of MO were decomposed after 15 min, respectively. While in the case of BiOCl, the decrease of MO concentration was attributed to the adsorption.

The order of photocatalytic activity is AgCl/Ag/BiOCl > Ag/AgCl > physical mixture > BiOCl. AgCl/Ag/BiOCl shows much better photocatalytic activity than that of Ag/AgCl, BiOCl, or physical mixture. Furthermore, the photocatalytic experiment was also carried out under sunshine irradiation in the middle of daytime, and 76% of the MO molecules were decomposed after 1 hour in the presence of AgCl/Ag/BiOCl photocatalyst, as shown in Fig. 7a. This demonstrates potential practical application of AgCl/Ag/BiOCl photocatalyst for organic pollutant elimination.

3.3 Mechanism of photocatalytic activity of AgCl/Ag/BiOCl

To demonstrate the photocatalytic mechanism of AgCl/Ag/BiOCl, the active species in photocatalytic reactions were studied in detail. In the photocatalytic process, a series of active species will be involved in the photocatalytic reaction. In order to clarify the photocatalytic mechanism of AgCl/Ag/BiOCl, a series of sacrificial agents were utilized to trap the active species during the photocatalytic process. Fig. 7b exhibits the trapping experiments of active species during the photocatalytic process. 10 mM isopropyl alcohol (IPA) was employed for quenching ˙OH, and 10 mM ethylene diamine tetraacetic acid (EDTA) for h⁺. N₂ was introduced to expel the O₂ for decreasing ˙O₂⁻. The photodegradation of MO over AgCl/Ag/BiOCl was almost not affected by the addition of IPA and N₂. On the contrary, the photodegradation efficiency of MO over AgCl/Ag/BiOCl obviously decreased by the addition of EDTA. Therefore, it can be concluded that holes are the main active species of AgCl/Ag/BiOCl in photocatalytic reaction under visible light irradiation, instead of ˙O₂⁻ or ˙OH.

Furthermore, in order to demonstrate that why the photocatalytic efficiency of AgCl/Ag/BiOCl is higher than that of Ag/AgCl, different concentrations of EDTA were employed in the photodegradation process of Ag/AgCl and AgCl/Ag/BiOCl. As shown in Fig. 7c, the photodegradation efficiency of MO over AgCl/Ag/BiOCl did not decreased obviously by the addition of 1 mM EDTA, compared to the addition of 10 mM EDTA. However, the photocatalytic degradation efficiency of MO over Ag/AgCl decreased obviously by the addition of 1 mM EDTA. Therefore, it can be concluded that a large number of holes were produced in AgCl/Ag/BiOCl under visible light irradiation, comparing with Ag/AgCl. When the concentration of EDTA is 1 mM, only a part of holes produced by AgCl/Ag/BiOCl will be trapped. AgCl/Ag/BiOCl could still photodegrade the MO efficiently. Furthermore, even 10 mM EDTA was added into the solution, almost all the MO molecules were photodecomposed after 1 hour, as shown in Fig. 7d, which demonstrated that AgCl/Ag/BiOCl could produced holes efficiently under visible light irradiation.

To explain the enhanced photocatalytic activity of AgCl/Ag/BiOCl, a photocatalytic mechanism was proposed according to the above experiments, and the mechanism scheme is shown in Fig. 8. The conduction band minimum (CBM) and valence band maximum (VBM) have been calculated to be −0.09 and 3.16 eV for AgCl, and 0.11 and 3.55 eV for BiOCl.³⁹ It was known that BiOCl and AgCl cannot absorb visible light irradiation because of their wide band gap. However, Ag nanoparticle can absorb visible light due to the surface plasmon resonance. Under visible light irradiation, the absorbed photons would be separated to electrons and holes. The photogenerated holes transfer to the AgCl surface, leading to the formation of Cl atoms from the oxidation of Cl⁻ ions.⁵¹ The Cl atoms are reactive radical species that can oxidize MO efficiently, and Cl atoms are reduced to Cl⁻ ions again.

Fig. 8 Photocatalytic mechanism scheme of AgCl/Ag/BiOCl under visible light irradiation (λ ≥ 400 nm).

The slow reaction rate of vapor diffusion process could produce AgCl/Ag/BiOCl with good crystallinity, which consists of cubic AgCl as core and BiOCl nanosheets on the surface. Owing to the well-defined interface between BiOCl and AgCl, this could produce a lower energy barrier that a carrier charge has to overcome when crossing an interface, the plasmon-induced electrons in Ag nanoparticles could easily transfer to the conduction band of BiOCl. Therefore, the heterojunction between AgCl and BiOCl increases the separation efficiency of photoinduced electrons and holes. And AgCl/Ag/BiOCl shows higher photocatalytic activity comparing with Ag/AgCl photocatalyst, even the Ag/AgCl exhibits the best absorption ability in visible light range (shown in Fig. 6).

Furthermore, since photocatalytic processes occur on the surface of photocatalysts, the dye molecules should first adsorbed on the surface of photocatalysts before it was photodecomposed. Therefore, the BiOCl with strong adsorption activity (as shown in Fig. 7a) grown on the surface of AgCl could enhance photocatalytic activity of AgCl/Ag/BiOCl, comparing with Ag/AgCl. This is also one reason that the photocatalytic efficiency of physical mixture is lower than that of pure Ag/AgCl (as shown in Fig. 7a).

In addition, the stability of a photocatalyst is also one of the most important factors in practical applications. Therefore, the photocatalytic stability of the AgCl/Ag/BiOCl photocatalyst was studied by recycling photocatalytic reaction with four cycles, as shown in Fig. 9a. It can be seen that there was no evident decrease of photocatalytic efficiency of the AgCl/Ag/BiOCl photocatalyst after four cycles of photodegradation of MO. And the small decrease in photocatalytic activity is attributed to the slight loss of samples in the recycling experiments.

Fig. 9 (a) Four cycles of recycling photodegradation experiments of AgCl/Ag/BiOCl. (b) XRD patterns of AgCl/Ag/BiOCl before and after recycling experiments.

Fig. 9b shows the XRD pattern of the AgCl/Ag/BiOCl photocatalyst after four cycles of recycling photodegradation experiments, which is almost identical to that of the as-prepared AgCl/Ag/BiOCl sample, except for the diffraction peaks with mark of blue cycle, which can be indexed to the cubic phase of Ag (JCPDS file: 65-2871). These results demonstrate that the AgCl/Ag/BiOCl could be used as a stable and efficient photocatalyst during practical applications.

4. Conclusions

In summary, an efficient and facile one-step vapor diffusion approach was developed to prepare hierarchical AgCl/Ag/BiOCl heterojunction photocatalyst at room temperature. A series of characterizations demonstrated the formation of AgCl/Ag/BiOCl heterojunction photocatalyst. The AgCl/Ag/BiOCl consists of AgCl as core and BiOCl nanosheets on the surface, and the interface between AgCl and BiOCl could be clearly seen in elements mapping figure. The AgCl/Ag/BiOCl photocatalyst exhibited excellent visible light photocatalytic performance, which is even higher than that of Ag/AgCl photocatalyst. The photocatalytic mechanism was revealed via active species trapping experiments. The holes and Cl atoms played important roles in the photodegradation of MO. Owing to the well-defined interface between BiOCl and AgCl, which could produce a lower energy barrier that an carrier charge has to overcome when crossing an interface, the heterojunction between BiOCl and AgCl effectively promoted the separation of photogenerated electron–hole pairs and resulting in enhancement of photocatalytic activity. In addition, the BiOCl on the surface with strong adsorption activity, and the gaps between BiOCl nanosheets are beneficial for reactant diffusion and could enhance photocatalytic activity of AgCl/Ag/BiOCl, comparing with Ag/AgCl. Finally, low consumption of Ag and higher photocatalytic efficiency were both achieved in the AgCl/Ag/BiOCl heterojunction photocatalyst.

Acknowledgements

This work was partially supported by the National Natural Science Foundation of China (no. 21401034), the Natural Science Foundation of Heilongjiang Province (QC2015008).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra14170f

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