C3N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation

Accepted Manuscript Title: Constructing 2D BiOCl/C3 N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation Authors: Wenwen Liu, Lulu Qiao, Anquan Zhu, Yi Liu, Jun Pan PII: DOI: Reference:

S0169-4332(17)32225-0 http://dx.doi.org/doi:10.1016/j.apsusc.2017.07.225 APSUSC 36759

To appear in:

APSUSC

Received date: Revised date: Accepted date:

3-7-2017 23-7-2017 24-7-2017

Please cite this article as: Wenwen Liu, Lulu Qiao, Anquan Zhu, Yi Liu, Jun Pan, Constructing 2D BiOCl/C3N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation, Applied Surface Sciencehttp://dx.doi.org/10.1016/j.apsusc.2017.07.225 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Highlights 1. 2D BiOCl/C3N4 layered composite with large contact surface was constructed. 2. The rate constant of optimal BiOCl/C3N4 was 6.05 time higher than that of C3N4. 3. Enhanced photocatalytic performance was mainly ascribed to large contact surface. 4. The photodegradation mechanism of 2D BiOCl/C3N4 to methyl orange was discussed.

Constructing 2D BiOCl/C3N4 layered composite with large contact surface for visible-light-driven photocatalytic degradation Wenwen Liu, Lulu Qiao, Anquan Zhu, Yi Liu, Jun Pan*

State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083, People’s Republic of China

*Corresponding author: E-mails: [email protected]

Abstract: The design and construction of a two-dimensional (2D) layered composite with large contact surface provide an efficient way for solving detrimental photoinduced carriers recombination. In this work, 2D layered composite coupling (001) facet of BiOCl nanoplates and (002) facet of C3N4 nanosheets was reasonable designed and successful constructed. In comparison with pure C3N4, the BiOCl/C3N4 hybrid structure with loading of 70% BiOCl exhibits the highest methyl orange photodegradation performance although BiOCl/C3N4 hybrid photocatalyst harvest less visible light. Obviously, enhanced photocatalytic performance is mainly ascribed to large contact surface of 2D layered hybrid structure, which is favorable for the interface electrons transfer and the separation of carriers between C3N4 and BiOCl. A probable degradation mechanism based on trapping experiments of active species, transient photocurrents, photoluminescence spectra, electrochemical impedance spectroscopy and energy band structures is proposed. This work may provide a further insight into the rational construction composites with large interface contact for high-efficiency light utilization.

Keywords: BiOCl/C3N4 photocatalyst, 2D layered composite, interface contact, photocatalytic activity, visible light, MO degration

1 Introduction The presence of organic pollutants in wastewater and their adverse effects on environment have sparked a widespread concern [1-3]. Among several promising strategies dealing with organic pollutants, semiconductor-based photocatalysis has attracted extensive interest in recent decades, which can utilize sunlight to remove them [4-6]. Graphite-like carbon nitride (C3N4) is a polymeric organic semiconductor material with good visible light response, and it possesses a layered structure similar to graphene [7-11]. To date, C3N4 has attracted a wide range of research interests in photocatalysis, such as hydrogen or oxygen evolution from water splitting [12,13], photocatalytic reduction of CO2 [14], and organic pollutants degradation [15-17]. However, detrimental rapid recombination of electrons and holes in C3N4 serious limits its enhancement of photocatalytic performance and practical applications. Therefore, continuous efforts have been tried, including mesoporous structures design [18], elements doping [19], co-catalyst coupling [20], composite construction [21-26]. Among these attempts, the composite construction via the combination of C3N4 with other semiconductors is one of the most effective strategy for separating photoinduced carriers, such as BiVO4/C3N4 [27], BiPO4/C3N4 [28], ZnO/C3N4 [29], and so forth. BiOCl has received great attention in the field of photocatalysis for its layered structure and high photocorrosion stability [30-35]. In our previous report, carriers regulation in BiOCl nanoplates with (001) and (110) crystal facets is demonstrated and it exhibits excellent photocatalytic efficiency for two kinds of pollutants

degradation [36]. Besides, numerous studies reported by others indicate that composite construction between BiOCl and C3N4 also improved the photodegradation efficiency which benefits from its enhanced carriers separation and light absorption [37-42]. However, the interface in these composites is mainly point contact, endowing them with small contact surface and inefficient interfacial carriers transfer. Up to now, seldom research is focused on addressing this issue in BiOCl/C3N4 composite. Therefore, composite construction between BiOCl and C3N4 featuring large contact surface and efficient interfacial carriers transfer is still necessary to meet high photodegradation efficiency for various organic pollutants. In this work, 2D layered composite combining 2D BiOCl nanoplates and C3N4 nanosheets was synthesized using a simple calcination route. Its structure, composition, morphology and optical properties were characterized. The performance of BiOCl/C3N4 composite was evaluated through methyl orange (MO) degradation. As for BiOCl/C3N4 composite, face-to-face contact between 2D BiOCl and C3N4 can be achieved, resulting in large contact surface. Under visible light irradiation, the photoinduced electrons of C3N4 cross the interface between BiOCl and C3N4 and then reach the conduction band of BiOCl. Therefore, the large contact area of BiOCl/C 3N4 composite is beneficial to electrons interfacial transfer and separation. As a result, BiOCl/C3N4 2D layered composite shows an expected photocatalytic performance.

2 Experiment 2.1 Materials Urea, Bi(NO3)3·5H2O, mannitol and NaCl were analytical pure and used directly.

2.2 Synthesis Synthesis of C3N4 nanosheets: Firstly, the C3N4 bulk was prepared with urea at high temperature [43]. In detail, urea containing water with mass ratio of 2 was first heated to 550 °C (ramp rate: 2.3 °C/min) and then polymerized at this level for 4 h, followed by a natural cooling process. Then, the C3N4 nanosheets was obtained by thermal-oxidation etching. That is, C3N4 bulk was heated to 500 °C with a ramp rate of 5 °C/min and performed 4 h [44]. Finally, the powder was collected and washed for further use. Synthesis of BiOCl nanoplates: A previous reported hydrothermal method was used [36]. Firstly, 0.486 g of Bi(NO3)3·5H2O was added to 25 mL of mannitol aqueous solution (0.1 mol L-1). After that, 6.0 mL of NaCl aqueous solution (5.0 mol L-1) was dropped to the above solution with vigorous stirring. Then, the uniform suspension was poured into an autoclave. After being heated at 160 °C and 3 h, the obtained products were collected. Synthesis of BiOCl/C3N4 composites: 0.1 g of C3N4 nanosheets were ultrasonical immersed in 50 mL of water for 30 min. Then, an appropriate amount of BiOCl nanoplates was mixed with it and vigorous stirred. After the water existing in the mixture was evaporated at 80 °C, the mixture was further calcined at 250 °C for 3 h. According to this process, BiOCl-C3N4 composites with different mass ratios of 3:10, 5:10, 7:10 and 9:10 were prepared and signed as BOC/CN-0.3, BOC/CN-0.5, BOC/CN-0.7 and BOC/CN-0.9, respectively. 2.3 Characterization

The phase and composition were researched by X-ray diffraction (XRD) using D/max 2550 X-ray diffractometer manufactured by Rigaku Corporation. The morphology and structure were obtained by Nova Nano 230 scanning electron microscopy (SEM) manufactured by FEI Co. Ltd. and JEM-2100F transmission electron microscopy (TEM) manufactured by Japanese electronics Co. Ltd.. X-ray photoelectron spectroscopy (XPS) analysis taken on Thermo ESCAlab 250 spectrometer was used to test surface elemental composition. Fourier transform infrared spectra (FT-IR) were conducted on Nicolet 6700 spectrometer. An UV-Vis spectrometer (Evolution 220) was taken to gather UV-Vis diffuse reflectance spectra (DRS). Thermogravimetric (TG) analysis was obtained by a SDT Q600 analyzer. Surface area analyzer (TRISTAR-3000) was used to test the BET surface area. Photoluminescence (PL) spectra were carried on a Hitachi F-2700 spectrophotometer with 370 nm excitation wavelength. 2.4 Photoelectrochemical measurements A

Chenhua

CHI-660E

electrochemical

workstation

equipped

with

three-electrodes involving ITO electrode covered with samples, Pt and Ag/AgCl electrodes was used to perform the measurements. For the working electrode, 20 mg of samples were dispersed in a certain amount of dimethylformamide with 5 wt % Nafion solution to make a homogeneous solution. Then, 40 μL of above solution was dropped on ITO conducting glass (10 mm × 10 mm). After being dried at 100 °C for 1 h, three electrodes were immersed into a quartz cell containing 0.5 mol L-1 of Na2SO4 solution and exposed by Xe lamp (300 W, λ ≥ 420 nm).

2.5 Photocatalytic activity evaluation MO (10 mg L-1) was selected as model pollutant to verify the activity of the as-prepared photocatalysts. The degradation process was executed by Xe lamp (300 W) equipped with 420 nm cut-off filter. Specifically, 10 mg of sample was uniform placed into a quartz glass tube containing of MO solution (15 mL). Before photocatalytic illumination, the solution kept stirring in the dark state for 1 h. Then the tube containing MO solution was irradiated with visible light. During the degradation, 5 mL of the solution was extracted at regular intervals. After centrifugation, the concentration of MO was calculated based on the absorbance at 463 nm recorded by a UV-Vis spectrophotometer. The same procedure was used to carry out trapping experiments of active species besides various trapping agents were injected.

3 Results and discussion 3.1 XRD analysis Fig. 1 shows the XRD of C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalysts with different mass ratios. As for C3N4, two characteristic peaks consisting a feeble (100) peak and a strong (002) peak are observed, respectively. For BiOCl, all diffraction peaks are corresponding to tetrahedral BiOCl phase. After hybridization, diffraction peaks of BiOCl/C3N4 hybrid photocatalysts are consistent with that of BiOCl besides the peaks intensity of C3N4 become less pronounced gradually with increasing content of BiOCl. The presence of this characteristic in BiOCl/C3N4 samples indicate that (002) peak of C3N4 is covered by BiOCl, confirming the

formation of large contact interface in BiOCl/C3N4 hybrid structures, which can also be discerned by SEM and TEM, as discussed later. 3.2 FT-IR spectra analysis The chemical structures of C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalysts with different mass ratios were studied by FT-IR spectra (Fig. 2). As for C3N4, the typical structure of C3N4 could be clearly observed, including feature breath of triazine units (809 cm-1), stretching modes of C−N and C=N (1200-1700 cm-1) and stretching vibration mode of N−H (3000-3600 cm-1). In the spectrum of BiOCl, characteristic peak at 524 cm-1 is observed, which can be indexed to Bi−O bond stretching vibration. When C3N4 combined with BiOCl, it can be found that the absorption peak intensity at 3436 cm-1 increases gradually from BOC/CN-0.3 to BOC/CN-0.9 with increasing content of BiOCl. In addition, all the characteristic absorption peaks of C3N4 and BiOCl are observed in the hybrid structures, which implies basic structure of composite after combination C3N4 and BiOCl is well maintained. 3.3 XPS analysis The surface chemical composition and chemical state of BOC/CN-0.7 hybrid structure can be obtained by XPS. The survey spectrum (Fig. 3a) of BOC/CN-0.7 displays the existence of Bi, O, Cl, C, N, well consistent with chemical composition of composite. For BOC/CN-0.7, the C1s features can be observed in Fig. 3b, two characteristic peaks at 284.8 eV and 288.3 eV attributes to C−C bonds and combination of C–N groups, respectively [45-47]. The binding energy value of N 1s

at 398.8 eV is assigned to N=C−N bonds. Additionally, two another peaks at 400.2 eV and 401.4 eV corresponds to N−C3 groups and N–H side groups. The peak at 404.6 eV originated from the charging effects (Fig. 3c) [48]. Fig. 3d shows two strong peaks of Bi 4f at 159.3 eV attributing to Bi 4f7/2 and 164.6 eV attributing to Bi 4f5/2 [49]. The O 1s (Fig. 3e) peak could be fitted to two locations at 530.0 eV and 531.6 eV, relating with the crystal lattice O and hydroxyl group, respectively [50]. The Cl 2p in Fig. 3f could be ascribed to Cl 2p1/2 (199.6 eV) and Cl 2p3/2 (198.0 eV), respectively [51]. 3.4 Morphology and structure The morphology and structure of BiOCl, C3N4 and BOC/CN-0.7 sample can be revealed by SEM and TEM. BiOCl sample shows square-like nanoplates structure and C3N4 appears as wrinkled nanosheets and rough slice (Fig. 4). As shown in Fig. 5a, BiOCl nanoplates marked by red outline are uniform anchored at the bearing surface of C3N4 and no single composition stacked together within the field of vision, resulting in the construction of 2D layered composite. TEM image of BOC/CN-0.7 depicted in Fig. 5b shows that the C3N4 nanosheets are acted as a substrate for compactly anchoring BiOCl nanoplates with face to face contact, further confirms the 2D layered structure (inset in Fig. 5b), which is corresponding to the SEM result. As indicated by HRTEM image (Fig. 5c), the fringes spacing of top surface in BiOCl is 0.273 nm, indexed to (110) lattice plane of tetragonal BiOCl, consistent with our previous results, that is, the top and bottom surfaces of BiOCl nanoplates are (001) facets [36]. As for C3N4 nanosheets, the large supporting surfaces are (002) facets

based on its crystal structure [52] and XRD results. After coupling BiOCl with C3N4, the BiOCl nanoplates exposed (001) facets lie on the (002) facets of C3N4. Therefore, we can deem that the large interface of 2D layered structure is constituted by (001) facets of BiOCl and (002) facets of C3N4 (Scheme 1). To verify the composition of 2D layered structure, Energy Dispersive X-ray (EDX) spectrum was utilized to collect the element information (Fig. 5d). EDX result shows the presence of Bi, O, Cl, C and N signal peak in composite structure, consistent with the result of XPS. These results indicate that BiOCl/C3N4 composite with 2D layered structure is indeed constructed. Therefore, the 2D layered structure with face to face contact is favorable for the interface electrons transfer and the separation of carriers between C3N4 and BiOCl, subsequently improving the photocatalytic performance. 3.5 TG analysis To obtain the actual content of BiOCl in the composite, TG analysis was adopted in air atmosphere (ramp rate: 10 °C/min). As depicted in Fig. 6, it is not stable and begins to decompose over 500 °C for C3N4 sample. The total decomposition temperature of C3N4 is about at 650 °C. The mass of BiOCl remains 73.91 % of the original mass over 860 °C. In the composite, the remained mass of BOC/CN-0.3, BOC/CN-0.5, BOC/CN-0.7 and BOC/CN-0.9 are 16.77 %, 23.84 %, 30.12 %, 34.95 % of the original mass, respectively. According to the measured results, the mass ratio of BiOCl to C3N4 in the composite are about 0.29, 0.48, 0.69, 0.90, which are little difference with the theoretical ratio. 3.6 N2 adsorption analysis

The N2 adsorption-desorption isotherm was measured to investigate the specific surface area and pore size distribution. The measured samples plots are regarded as type IV isotherms and have a hysteresis loop, revealing the formation of mesoporous (Fig. 7). Meanwhile, the pore size distribution of the C3N4, BiOCl and BOC/CN-0.7 is obtained in inset. The mesoporous peaks of both C3N4 and BOC/CN-0.7 at around 3.79 nm and 13.53 nm attributes to the porosity and stacking of C3N4 nanosheets, respectively. The BiOCl sample manifests a poor pore distribution. The specific surface area of C3N4 and BiOCl is 220.75 and 14.86 m2/g. The BOC/CN-0.7 composite shows a decreased specific surface area (86.15 m2/g) because of the introduction of BiOCl with low specific surface area. 3.7 Optical properties Fig. 8 presents UV-Vis DRS of BiOCl, C3N4 and BiOCl/C3N4 hybrid photocatalyst. As can be seen in Fig. 8a, BiOCl cannot be excited by visible light and the absorption edge is located at approximately 380 nm. Accordingly, band-gap energy (Eg) of BiOCl shown in Fig. 8b is 3.26 eV. C3N4 exhibits visible light response with absorption edge in approximately 460 nm, and the estimated Eg is 2.85 eV. As for BiOCl/C3N4 hybrid photocatalyst, it exhibits a composite absorption property of BiOCl and C3N4 with absorption edge in approximately 445 nm, harvesting less visible light to generate carriers in comparison with pure C3N4. 3.8 Photocatalytic performance The photocatalytic performance of C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalysts were tested using visible light by adopting MO as the model pollutant

(Fig. 9). The blank experiment demonstrates that MO is quite stable with illumination, ruled out self-degradation. As can be seen, the degradation of MO over pure BiOCl and C3N4 is 16.42% and 22.49% after 180 min irradiation. The photocatalytic performance displayed on pure BiOCl should be attribute to the MO photosensitization, consistent with the previous work [38]. Combination different content of BiOCl with C3N4 results in an improvement of the degradation of MO. Among these, BOC/CN-0.7 exhibits the highest photocatalytic performance, where about 84.28% MO is degraded after 180 mins (Fig. 9a). In addition, the degradation reaction of MO could be fitted as a pseudo-first-order kinetics and the rate constant of C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalyst is shown in Fig. 9b and Fig. 9c, respectively. The rate constant of BOC/CN-0.7 is 8.40 and 6.05 times higher than that of pure BiOCl and C3N4, respectively. Although BOC/CN-0.7 hybrid photocatalyst harvest less visible light in comparison with pure C3N4, photocatalytic degradation efficiency increases. These results reveal the key role of 2D layered structure with large contact surface in promoting transfer and separation of photoinduced electrons for enhanced photocatalytic performance. The stability of the BOC/CN-0.7 photocatalyst was conducted by recycling the photocatalyst to degrade MO. As shown in Fig. 9d, only a slight loss of activity is observed in degradation rate after 4 cycles of 180 mins, suggesting that the BOC/CN-0.7 photocatalyst proposed in this work exhibits good stability for organic contaminant photocatalytic oxidation. 3.9 Degradation mechanism analysis To investigate the active species in degradation reaction over the BOC/CN-0.7

composite, trapping experiments of active species were carried out. In this work, isopropanol (IPA) is selected as ·OH scavenger, p-benzoquinone (BQ) is used as ·O2scavenger and triethanolamine (TEOA) uses for holes scavenger. As depicted in Fig. 10a, the degradation efficiency of MO decreases dramatically in the presence of BQ and TEOA. On the contrary, the addition of IPA is not obvious affected for the MO photo-degradation. So, we infer that the active species in this work for MO photocatalysis are ·O2- and holes (Fig. 10b). To study the carriers transfer process and separation process in photocatalysts, the photocurrents were conducted. Fig. 11a shows the photocurrent curves of the C3N4, BiOCl and BOC/CN-0.7 composite. It could be seen that no photocurrent generates in BiOCl under visible light illumination as its wide bandgap. BOC/CN-0.7 composite shows a much larger photocurrent intensity than the C3N4, well agreement with the photocatalytic performance. The result confirms that the formation of large contact surface in BiOCl/C3N4 2D layered composite is high advanced for the transfer and separation of photoinduced electrons, which is further corroborated by PL spectra, the other efficient method used to study the carriers transfer process and separation process in photocatalysts. PL spectra of the C3N4 and BiOCl/C3N4 composite with different contents of BiOCl are shown in Fig. 11b. In comparison with C3N4, the emission intensities of BiOCl/C3N4 composites are greatly weakened, while BOC/CN-0.7 composite exhibits a lowest emission intensity in PL spectrum, consistent with the result of the transient photocurrents. Furthermore, electrochemical impedance spectroscopy (EIS) was also executed to further explore the carriers

transfer and separation. As seen in Fig. 12, the BOC/CN-0.7 composite have a small arc radius compare to the pure BiOCl and C3N4, implying the faster carriers transfer as the large contact surface between BiOCl and C3N4. To further find out the pathway of carriers transfer, the energy band structures of the catalysts were taken into consideration. First, the Mott-Schottky curve was applied to determine the type and the flat potential of catalysts [53]. As depicted in Fig. 13a and Fig. 13b, BiOCl and C3N4 are p-type and n-type semiconductor, respectively. Moreover, the flat potential (vs. Ag/AgCl) of BiOCl and C3N4 are 2.45 V and -1.45 V, respectively. The potential (vs. Ag/AgCl) can be converted into normal hydrogen electrode (NHE) according to the equation (1) [54]:

ENHE  E Ag/AgCl + E 0Ag/AgCl ……….(1) where E0Ag/AgCl = 0.197 V. Particularly, the valence band (VB) maximum is about 0.1 V below the flat potential for p-type semiconductor; the conduction band (CB) minimum is about 0.1 V above the flat potential for n-type semiconductor [55]. Thus, the VB position of BiOCl and the CB position of C3N4 are 2.75 V and -1.35 V (vs. NHE). Whereas, Eg of BiOCl nanoplates and C3N4 nanosheets are 3.26 eV and 2.85 eV, respectively (Fig. 8b). Therefore, according to equation (2) [36]: Eg = EVB - ECB

(2)

the position of CB and VB for BiOCl and C3N4 are -0.51 V and 1.50 V, respectively. Based on the above experiment results and inferred energy band data, a probable degradation mechanism occurring on the BOC/CN-0.7 composite is illustrated in Fig.

14. Under visible light irradiation, the C3N4 is excited and immediately generates electron-hole pairs, whereas BiOCl cannot be excited as its wide band gap. The straddling energy band structure and 2D large contact interface in BOC/CN-0.7 composite make the photoinduced electrons derived from the CB of C3N4 direct inject into that of BiOCl. Since of the CB position of BiOCl is more negative than the standard potential of O2/·O2-, it can reduce the adsorbed O2 to produce ·O2-, contributed to degrade the MO [56]. Meanwhile, the holes generated in VB of C3N4 can direct oxidize the MO as the oxidation potential of MO (+0.94 V vs. NHE) is smaller than VB potential [57]. For ·OH, it can not be generated because the fact that VB potential of C3N4 is smaller than redox potential of OH-/·OH (+1.99 V vs. NHE), consistent with our trapping experiments of active species [58]. Therefore, the ·O2acts as active specie can attack the MO and thus degrade MO effectively together with holes.

4 Conclusion In summary, a 2D layered structure photocatalyst has been successful constructed, in which 2D BiOCl nanoplates is coupled with C3N4 nanosheets by using a facile calcination method. Compared to pure C3N4, the photocatalytic activity of BiOCl/C3N4 composite is great improved although the light absorption is relatively inferior. The BiOCl/C3N4 composite with loading of 70% BiOCl exhibits the highest photocatalytic activity in degrading MO model pollutant. The rate constant of optimal BiOCl/C3N4 composite is 8.40 and 6.05 times higher than that of pure BiOCl and

C3N4, respectively. The improved ability of BiOCl/C3N4 composite should be main benefited from the large interface contact of 2D layered structure for the efficient interface electrons transfer and electrons and holes separation between C3N4 and BiOCl. This study may provide some valuable information for the construction of 2D layered composite to improve photocatalytic activity.

Acknowledgement The authors gratefully acknowledge financial support from the Science Fund for Distinguished Young Scholars of Hunan Province (2015JJ1016), National Science Foundation of China (51302325).

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Scheme 1. Schematic diagram of interface composition in BiOCl-C3N4 2D layered structure.

Fig. 1. XRD of C3N4, BOC/CN-0.3, BOC/CN-0.5, BOC/CN-0.7, BOC/CN-0.9 and BiOCl.

Fig. 2. FT-IR curves of C3N4, BOC/CN-0.3, BOC/CN-0.5, BOC/CN-0.7, BOC/CN-0.9 and BiOCl.

Fig. 3. XPS spectra of BOC/CN-0.7: (a) survey spectrum, high resolution spectra of (b) C 1s, (c) N 1s, (d) Bi 4f, (e) O 1s and (f) Cl 2p.

Fig. 4. SEM images of pure C3N4 (a) and BiOCl (b).

Fig. 5. (a) SEM, (b) TEM, (c) HRTEM images and (d) EDX of analysis BOC/CN-0.7.

Fig. 6. TG images of C3N4, BOC/CN-0.3, BOC/CN-0.5, BOC/CN-0.7, BOC/CN-0.9 and BiOCl.

Fig. 7. The N2 adsorption-desorption isotherm and pore size distribution plots of C3N4, BOC/CN-0.7 and BiOCl.

Fig. 8. (a) UV-Vis DRS of C3N4, BOC/CN-0.7 and BiOCl. (b) The measured band gap of C3N4 and BiOCl.

Fig. 9. (a) The photodegradation of MO over pure C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalysts. (b) The kinetics plots and (c) rate constant of C3N4, BiOCl and BiOCl/C3N4 hybrid photocatalysts with MO photodegradation. (d) The recycling tests of BOC/CN-0.7 for four successive experiments.

Fig. 10. Trapping experiments of the active species (a) and degradation efficiency of BOC/CN-0.7.

Fig. 11. The photocurrent responses and the PL spectra of the as-prepared samples.

Fig. 12. EIS images of C3N4, BOC/CN-0.7 and BiOCl.

Fig. 13. The Mott-Schottky plots of BiOCl and C3N4.

Fig. 14. The probable degradation mechanism of MO over BiOCl/C3N4 composite under visible light irradiation.