Improving visible-light-induced photocatalytic ability of TiO2 through coupling with Bi3O4Cl and carbon dot nanoparticles

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Improving visible-light-induced photocatalytic ability of TiO2 through coupling with Bi3O4Cl and carbon dot nanoparticles Aziz Habibi-Yangjeha, , Solmaz Feizpoora, Davod Seifzadeha, Srabanti Ghoshb,1 ⁎

a b

Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran Fuel Cell & Battery Division, CSIR-Central Glass and Ceramic Research Institute, 196, Raja S.C. Mullick Road, Kolkata 700032, India

ARTICLE INFO

ABSTRACT

Keywords: TiO2/Bi3O4Cl/carbon dots TiO2 Visible-light-induced photocatalyst Wastewater treatments

The fabrication of photocatalysts with considerable photocatalytic performance can be the main purpose for the researchers to substitute the traditional wastewater treatment processes. Accordingly, in this work, visible-lightresponsive TiO2/Bi3O4Cl/carbon dots (denoted as TO/BOC/CD) photocatalysts were synthesized via simple strategy. Multiple techniques including EIS, photocurrent, XPS, PL, UV–vis DRS, BET, FT-IR, EDX, XRD, HRTEM, and SEM were employed to explore electrochemical, chemical, and physical features of the nanocomposites. The photocatalytic ability of the samples for Cr (VI), methylene blue, fuchsine, and rhodamine B removals was examined to display their widespread capability in removing different pollutants. The optimal photocatalytic performance related to the nanocomposite with 20% of BOC and 1 mL of CD solution (TO/BOC/CD (1 mL) photocatalyst), which was 13.8, 25.9, 14.2, and 52.3-folds as high as the TiO2 and 2.84, 2.26, 2.57, and 5.25times higher than the TO/BOC (20%) nanocomposite in removals of Cr (VI), methylene blue, fuchsine, and rhodamine B, respectively. The impressive photocatalytic activity of the TO/BOC/CD photocatalysts is ascribed to the betterment of the optical property of the fabricated photocatalysts. With the enhancement CD content, the respective ternary nanocomposites displayed the highest optical absorption in the visible region. The other reasons in improving the photocatalytic activity are related to increased e−/h+ separation capability, and better textural properties. Additionally, trapping experiments demonstrated that the holes and superoxide anion radicals possess a substantial role during the photocatalytic reaction. Thus, this work could promote the potential utilization of TiO2-based photocatalysts for removal of hazardous contaminants under visible light.

1. Introduction The expanding world worries about growing environmental contamination and clean energy provision have turned into critical matters in recent years. Organic compounds and heavy metals have been recognized as a considerable part of water pollutions, which can lead to an unfavorable effect on the health of humans [1–4]. Plentiful approaches have been utilized to eliminate these toxic compounds from wastewater like biodegradation, adsorption, filtration, and photocatalytic processes. Between these approaches, photocatalytic technology has attracted much more attention because of its eco-friendly nature, simplicity of processing, and affordability [5–11]. Titanium dioxide (TiO2, abbreviated as TO) is realized to be the most favorable photocatalyst for environment protection and treatment of water, because of its abundance, chemical stability, nontoxic nature, and remarkable oxidation ability. Notwithstanding the extraordinary

properties of this semiconductor, the widespread utilization of this semiconductor is limited by the inherent defects including the short lifetime of charge carriers and a wide energy gap [12–18]. Hence, to overcome the obstacles and increase the absorption efficiency of TO in the visible region, various kinds of strategies have been suggested like doping of nonmetals and metals, dye-sensitization, and formation of heterojunctions with other semiconductors [19–31]. Nowadays, bismuth-based oxide semiconductors have also been studied as effective photocatalytic materials, like BiPO4 [32], Bi2WO6 [33], BiOX (Br, I, Cl) [34], and so on, which utilized in the field of sewage treatment technology. Wang et al. prepared CoO/BiVO4 composites with one-step hydrothermal-calcination method and showed that the degradation rate of Reactive Blue 19 solution could be up to 100% in 30 min under visible-light irradiation, because of enhancing visible-light absorption and separation efficiency of electron-hole pairs [35]. Very recently, PW12/CN@Bi2WO6 composites have been prepared

Corresponding author. E-mail address: [email protected] (A. Habibi-Yangjeh). 1 Present address: Department of Organic and Inorganic Chemistry, Universidad De Alcala, Madrid, Spain. ⁎

https://doi.org/10.1016/j.seppur.2019.116404 Received 8 October 2019; Received in revised form 5 December 2019; Accepted 6 December 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved.

Please cite this article as: Aziz Habibi-Yangjeh, et al., Separation and Purification Technology, https://doi.org/10.1016/j.seppur.2019.116404

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Scheme 1. The preparation process of the TiO2/Bi3O4Cl/CD photocatalysts.

Fig. 1. XRD patterns of the TO, TO/BOC, and TO/BOC/CD (1 mL) photocatalysts.

Fig. 2. EDX spectra for the as-prepared photocatalysts. Table 1 Weight percentages of the components in the TO/BOC/CD (1 mL) nanocomposite.

by a hydrothermal method at 180 °C for 6 h and their photocatalytic activities for the degradation of tetracycline hydrochloride and reducing hexavalent chromium (Cr (VI)) were studied under the simulated xenon light [36]. Finally, Yang et al. prepared ternary Bi2MoO6/Ag/ AgCl nanocomposite. The photocatalytic efficiency of Bi2MoO6/Ag/ AgCl was evaluated by the degradation of Reactive Blue 19 dye. The results indicated that Bi2MoO6/Ag/AgCl photocatalyst exhibited higher photocatalytic activity than Bi2MoO6 [37]. More importantly, among

No. 1 2 3

2

Compounds

Weight %

TO BOC CD

76.84 18.96 4.30

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(a)

(b)

300 nm

5 nm

Fig. 3. SEM (a) and HRTEM (b) images of the TO/BOC/CD (1 mL) photocatalyst.

the Bi-based photocatalysts, especially Bi3O4Cl (denoted as BOC), as a Sillén family material, has been reached much attention, due to its unique layered structure and appropriate band gap (2.76 eV). The unique structure of BOC, which contains [Bi3O4] layers and double slabs of chlorine ions, could facilitate separation of photoinduced charge carriers and boost the photocatalytic performance of TO [38–42]. Besides, carbon dots (CD), as one of the photosensitizers, can be an outstanding candidate for boosting the photocatalytic efficiency of TO, due to easy preparation, broad solar spectrum absorption, optical stability, and biocompatibility [43–47]. Although several attempts have been made to prepare bismuth-based oxide photocatalysts, to the best of our knowledge, preparation of TO/BOC/CD nanocomposites and investigation of their photocatalytic activity have not been reported. In comparison with the reported works, we used a light source with a low power of 50 W for nearly complete removal of organic and inorganic pollutants. Therefore, the ternary TO/BOC/CD nanocomposite has substantial activity in photocatalytic removal of different environmental pollutants. Given these arguments, we synthesized ternary TO/BOC/CD photocatalysts, via a facile method. These nanocomposites demonstrated preeminent activities for eliminations of rhodamine B (RhB), fuchsine, and methylene blue (MB), and Cr (VI). The PL and photocurrent

experiments were used to verify the improved separation and migration of the charges in the TO/BOC/CD samples. The radicals trapping experiments revealed that the h+ and %O2− are the important reactive species in the elimination of RhB. The reusability tests for the optimum photocatalyst were also studied. At the end, a possible mechanism for the improvement of photocatalytic ability in the TO/BOC/CD samples was offered. 2. Experimental section 2.1. Preparation of photocatalysts The TO/BOC (20%) photocatalyst was prepared as follows: 0.3 g TO (P25) was added into 100 mL water with ultrasonication for 10 min. Thereafter, 0.4 g Bi(NO3)3·5H2O (Loba Chemie) and 20 mL ethylene glycol were appended into the TO suspension, which was stirred for 60 min. Next, the NH4Cl (Loba Chemie) solution (0.015 g, 30 mL) was dropped to the solution and stirred continuously for 10 min. Thereafter, the obtained solution was autoclaved at 160 °C for 12 h. After the hydrothermal reaction, the autoclave was cooled to reach room temperature and the precipitate was collected. The washed sample was dried at 60 °C. Finally, the achieved product was calcined at 500 °C for

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Fig. 4. XPS analysis of the TO/BOC/CD (1 mL) nanocomposite: (a) survey spectrum, (b) Ti, (c) O, (d) Bi, (e) Cl, and (f) C.

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300 min [41]. The TO/BOC/CD (1 mL) nanocomposite was fabricated through a simple method. The needed CD was obtained by a procedure explained previously [30]. Briefly, 3.0 g urea (Merck, 99%) and 3.0 g citric acid (Merck, 99%) were mixed with 10 mL of water. Thereafter, the solution was heated for 5 min in a domestic 750 W microwave oven. During the heating process, the solution changed from a colorless to a light brown solution and finally to a dark brown solid. Then, the resultant CD powder was dissolved in water. After that, the suspension was centrifuged. The produced brown aqueous solution remained stable for a long time. Finally, for preparation of the TO/BOC/CD (1 mL) nanocomposite, 0.4 g of the TO/BOC (20%) sample and 1 mL of the CD solution were appended into 100 mL water and sonicated for 10 min. Then, the resultant product was dried in an oven (Scheme 1). 2.2. Instruments The morphological features and elemental composition of the samples were probed via LEO 1430VP instrument. The HRTEM image was conducted by an EM-002B (TOPCON) microscope. X-ray diffraction (Philips Xpert, with Cu Kα radiation) was utilized to evaluate the crystal structures of the as-synthesized samples. A UV–vis spectrophotometer (Cecile 9000) was applied to study the optical characteristics of the materials. The PL and FT-IR spectra were taken on a fluorescence spectrophotometer and PerkinElmer Spectrum RX I instruments, respectively. The XPS spectra were recorded on JPS9010MC, JEOL instrument with mono-chromated Mg X-rays. The N2 adsorption–desorption isotherms were tested on a Belsorp Mini II apparatus. The ultrasonic treatment was applied with a Bandelin ultrasound generator HD 3100. The photoelectrochemical characterizations were realized by a µAutolabIII Potentiostat/Galvanostat in a standard three-electrode. The related information has been provided in our previous work [48]. 2.3. Evaluation of photocatalytic activity Photocatalytic reactions were carried out in a cylindrical glassy reactor upon LED lamp illumination (50 W). For this purpose, 100 mg of the sample was added in 250 mL of fuchsine (2.6 mg L−1), MB (3.2 mg L−1), RhB (4.8 mg L−1), and Cr (VI) (100 mg L−1) without adjusting solution pH (pH of the solutions was 5.4). Before starting the photocatalytic experiments, the solutions stored in the dark for 1 h to get an equilibrium. After exposing to the visible-light illumination, almost 3 mL of suspensions were withdrawn from the reaction systems at certain times. Eventually, the concentration of dyes was estimated at their characteristic wavelength via an UV–vis spectrophotometer.

Fig. 5. (a) FT-IR spectra for the selected samples, (b) Optical properties for all of the samples.

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Fig. 6. Photodegradation of RhB over different as-prepared photocatalysts: (a) the TO, TO/BOC, TO/CD (1 mL), BOC/CD (1 mL), and TO/BOC/CD nanocomposites with various contents of CD.

3. Results and discussions

sample are displayed in Table 1. In order to study the morphological features of the TO/BOC/CD (1 mL) nanocomposite, HRTEM and SEM analysis were provided. The SEM image of the TO/BOC/CD (1 mL) nanocomposite has complied in Fig. 3a. It is evident that the ternary nanocomposite exhibited a spherical-like structure and nanoparticles are in aggregated state. Fig. 2b indicates the HRTEM image of this ternary nanocomposite. The fringes spacing of 0.320 and 0.298 nm are compatible with the (0 0 2) plane of CD and (4 1 1) plane of BOC, while the fringe spacing of 0.352 nm matches to the (1 1 1) plane of TO [40,48]. These results endorse that the CD and BOC nanoparticles have successfully combined with TO to form a heterojunction photocatalyst. To achieve a deeper insight into the composition and surface chemical states of the TO/BOC/CD (1 mL) nanocomposite, XPS analysis was carried out (Fig. 4). Fig. 4a shows that Ti, O, Cl, Bi, and C are the main elements in the TO/BOC/CD (1 mL) sample. As depicted in

To assign the crystalline phase of the samples, XRD measurements were performed and the outcomes are demonstrated in Fig. 1. The pattern of TO sample is accorded closely with the tetragonal phase [49]. The diffraction angles of TO/BOC and TO/BOC/CD (1 mL) samples are attributed to the tetragonal structure of TO and monoclinic BOC (JCPDS No. 36-0760) [40]. For the TO/BOC/CD photocatalyst, because of the low value and high dispersion of CD, no diffraction peaks of CD were observed [50]. EDX analysis was utilized to determine the elements presented in the materials and the outcomes are depicted in Fig. 2. The signals of Ti and O elements can be seen in the spectrum of the TO. The spectrum of the TO/BOC/CD (1 mL) nanocomposite illustrates that the ternary nanocomposite has constituted of Ti, O, Cl, Bi, and C atoms. In addition, weight percentages of the components in the TO/BOC/CD (1 mL)

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Fig. 4b, the binding energies at 458.4 and 464.3 eV are in good agreement with Ti 2p3/2 and Ti 2p1/2, proving the existence of Ti4+ [51]. In Fig. 4c, the O 1s spectrum indicates two peaks at 530.0 and 531.4 eV [52]. The existence of Bi3+ is proved by the Bi 4f5/2 and Bi 4f7/2 peaks at binding energies of 164.1 and 158.8 eV (Fig. 4d) [40]. The Cl 2p1/2 and Cl 2p3/2 transitions are located at the binding energies of 199.0 eV and 197.7 eV, which corroborates the existence of Cl− (Fig. 4e) [41]. The TO/BOC/CD (1 mL) sample also shows two C 1s characteristic peaks (Fig. 4f), which are ascribed to the C]O and CeC bonds at the binding energies of 288.5 and 284.9 eV [48]. To investigate the functional groups in the TO, TO/BOC, and TO/ BOC/CD (1 mL) samples, FT-IR spectroscopy was employed, as displayed in Fig. 5a. The absorption bands at 3400–3600 cm−1 and 400–600 cm−1 are attributed to the OeH and TieO groups, respectively [30]. For the TO/BOC and TO/BOC/CD (1 mL) materials, the absorption band at 540 cm−1 originated from the Bi-O bond [40]. Additionally, the C]C and C]O stretching vibrations, at 1400 and 1600 cm−1, are observed in the spectrum of TO/BOC/CD (1 mL) nanocomposite [48]. To evaluate the optical characteristics of the samples, the UV–Vis DR spectra were investigated. As observed in Fig. 5b, TO indicates a strong absorption in the ultraviolet light area. After incorporating TO with BOC, significant enhancement in absorption of visible light can be observed. Besides, combining the TO/BOC sample with CD leads to a noticeable increase in the visible light range. The absorption intensity for the ternary photocatalysts in the visible range enhances with the increased content of CD. The outcomes imply that the fabrication of TO/BOC/CD nanocomposites can remarkably boost the optical absorption response, which is useful to increase the photocatalytic activity. The photocatalytic performance of the materials was appraised by the removal of RhB under visible light (Fig. 6). Before the photocatalytic processes, the self-degradation of RhB under visible light was studied. It can be realized that RhB concentration has hardly altered in the absence of any photocatalyst upon visible light. As envisaged, the TO demonstrated low photocatalytic ability, with only 18.4% RhB degradation, after 60 min illumination. In comparison to TO, the TO/CD (1 mL), TO/BOC, and BOC/CD (1 mL) samples exhibited higher photodegradation ability and removal efficiency of 42.8, 36.1, and 47.8%, respectively. Meanwhile, after the introduction of CD in the TO/BOC sample, the removal efficiency of RhB was enhanced tremendously. By enhancing CD value from 0.5 mL to 1 mL, the photodegradation of RhB by the TO/BOC/CD photocatalysts was increased greatly, and then reduced when the CD value increased. The outcomes indicated that the TO/BOC/CD (1 mL) nanocomposite exhibited the best photocatalytic performance. Figures S1(a–c) represent the changes of UV–vis spectra for RhB during the photodegradation reaction. Diminish of RhB concentration by the TO and TO/BOC samples is merely 18.4% and 36.1% after 60 min, respectively. As seen, when the TO/BOC/CD (1 mL) photocatalyst was utilized as a photocatalyst, the RhB was quietly removed. The reaction kinetics of RhB removal was studied by a quasi-firstorder kinetics plot. The TO/BOC/CD (1 mL) sample represents notably higher reaction rate constant than the other as-prepared samples. The kobs value of TO/BOC/CD (1 mL) nanocomposite is 707 × 10−4 min−1, which is 52.3 and 5.25-folds faster than those of the TiO2 (13.5 × 10−4 min−1) and TO/BOC (134 × 10−4 min−1) photocatalysts, respectively. It can be concluded that the interactions

Fig. 7. (a) The degradation rate constants of RhB over the different photocatalysts and (b) N2 adsorption/desorption curves for the TO, TO/BOC, and TO/ BOC/CD (1 mL) samples. Table 2 Textural properties of the TO, TO/BOC, and TO/BOC/COD (1 mL) photocatalysts. Sample

Surface area (m2 g−1)

Mean pore diameter (nm)

Total pore volume (cm3 g−1)

TO TO/BOC TO/BOC/CD (1 mL)

45.8 51.2 67.8

10.32 23.53 29.76

0.2327 0.2816 0.3241

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Fig. 8. (a) PL emission spectra, (b) On/off photocurrent responses and (c) Electrochemical impedance spectroscopy curves for the TO, TO/BOC, TO/CD (1 mL), BOC/ CD (1 mL), and TO/BOC/CD (1 mL) samples.

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Fig. 9. (a, b) Mott–Schottky curves for the TO and BOC samples. (c) Plots of (ahv)2 versus hv for the TO and BOC samples.

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samples, which corresponds to the high lifetime for the photogenerated e−/h+ pairs and great photocatalytic ability. The transient photocurrent curves of the samples are depicted in Fig. 8b. The higher photocurrent intensity reveals the lower recombination of charge carriers. Compared with the pristine TO, TO/CD (1 mL), BOC/CD (1 mL), and TO/BOC samples, the photocurrent density of TO/BOC/CD (1 mL) sample is clearly enhanced, which represents that incorporation of CD and BOC with TO can effectively diminish the recombination of charge carriers. Furthermore, these results can be well matched with the EIS Nyquist plots, as shown in Fig. 8c. The TO/BOC/CD (1 mL) photocatalyst exhibits the smallest arc radius relative to the other nanocomposites. Thereby, this can be related to the lowest e−/h+ recombination rate. In order to study the electronic properties of the TO and BOC samples, Mott–Schottky analyses were provided (Fig. 9(a, b)). The Mott-Schottky slope of TO is positive, suggesting that the TO is n-type semiconductor [28]. The negative slope of the M-S plot of BOC confirms that the BOC is p-type semiconductor [42]. The flat-band potential (Efb) for the TO and BOC were found to be −0.60 and +2.96 V vs. Ag/AgCl (−0.40 and +3.16 V vs. NHE). The conduction band potential (ECB) for n-type semiconductor is 0.1 eV below the Efb [53]. Whereas, the valence band position (EVB) for p-type semiconductor is 0.1 eV more positive potential than the Efb [54]. Hence, EVB for BOC is estimated to be +3.26 eV and ECB for TO be estimated to be −0.5 eV. Based on the Tauc's plots, the band gaps of TO and BOC are 3.20 and 2.76 eV, respectively. Accordingly, the EVB of TO is determined to be +2.70 eV. Also, the ECB of BOC is obtained to be +0.55 eV. To elucidate the probable degradation pathway, trapping experiments were applied. For this aim, 2-propanol (2-PrOH), benzoquinone (BQ), and ammonium oxalate (AO) are added to the photocatalytic reaction to trap the %OH, h+, and %O2− species, respectively. As manifested in Fig. 10, in the presence of 2-PrOH, the removal efficiency of RhB did not change expressively. However, the photocatalytic ability of the TO/BOC/CD (1 mL) sample was markedly diminished after BQ and AO were introduced, proposing that the %O2− and h+ are the prominent oxidative species for the degradation of RhB. According to the above data, a rational photocatalytic Z-scheme mechanism for the TO/BOC/CD nanocomposites is schematically depicted in Fig. 11. When TO/BOC/CD nanocomposite is illuminated by visible light, BOC is excited and produced electrons and holes, owing to its narrow energy gap. Besides, CD with upconversion feature converts longer wavelength lights to shorter wavelengths. Therefore, CD generates high-energetic photons for excitation of TO, and it can produce charge carriers upon visible-light irradiation [55,56]. The excited electrons in the CB of BOC can simply inject to the surface of CD and

Fig. 10. Effect of scavengers on the photodegradation rate constants of RhB on the TO/BOC/CD (1 mL) sample.

between TO, BOC, and CD and formation of heterojunctions between these nanoparticles have significantly promoted the photocatalytic activity of this ternary nanocomposite. To explore the pore characteristic and surface area of the as-prepared nanocomposites, nitrogen sorption analysis is used. As depicted in Fig. 7b, all of the samples possess type IV isotherms, which suggest the mesopore structures. The BET surface area of TO/BOC/CD is 67.8 m2/g, which is much larger than those of the TO (45.8 m2/g) and TO/BOC (51.2 m2/g) samples. Given these results, the TO/BOC/CD photocatalyst possesses more active sites, which are a clear reason for high photocatalytic performance. The total pore volume, mean pore diameter, and surface area of the samples are displayed in (Table 2). The EIS, photocurrent, and PL analyses were utilized to get knowledge about the separation and transmission the charge carriers. The PL spectra of TO, TO/BOC, TO/CD (1 mL), BOC/CD (1 mL), and TO/BOC/CD (1 mL) samples are shown in Fig. 8a. The TO/BOC/CD (1 mL) photocatalyst displayed weak photoluminescence intensity compared with the TO, TO/CD (1 mL), BOC/CD (1 mL), and TO/BOC

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Fig. 11. Schematic presentation for separation of charge carriers in the TO/BOC/CD nanocomposites.

further transfer and recombine with the photogenerated holes in the VB of TO, owing to good electron acceptor/donor properties of CD [57]. The CB potential of −0.50 eV for TO is more negative compared to the O2/%O2− (−0.33 eV), indicating that the photoinduced electrons accumulated in the CB of TO could react with O2 to generate %O2− radicals [58]. However, the holes left in the VB of BOC (+3.26 eV) can oxidize the adsorbed water molecules to give powerful active species

for decomposing the chromophores of RhB. As a result, the photogenerated electrons and holes are separated and led to the enhanced photocatalytic performance. To specify the potential applicability of the TO/BOC/CD (1 mL) nanocomposite in environmental applications, the reusable feature of the sample was examined, which are illustrated in Fig. 12a. The photocatalytic ability of the TO/BOC/CD (1 mL) photocatalyst did not

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diminish substantially after four runs. In order to prove this result, the XRD patterns of the photocatalyst before and after 4 photodegradation cycles are demonstrated in Fig. 12b. No observable changes were found before and after the cycling tests, demonstrating that the structure of TO/BOC/CD (1 mL) photocatalyst does not change during the photocatalytic reactions. The outcomes specified that this nanocomposite had sufficient stableness to be applied in practical applications. To illustrate the supremacy of the TO/BOC/CD (1 mL) photocatalyst, degradations of MB, fuchsine, phenol, and RhB, as organic contaminants, and photoreduction of Cr (VI), as an inorganic contaminant, were assayed, as elucidated in Fig. 13. These results indicate that the TO/BOC/CD (1 mL) sample has much better photocatalytic ability than the pristine TO and TO/BOC samples. The photocatalytic ability of this ternary sample is 19.4, 25.9, 14.2, 52.3, and 13.9 times faster than that of the bare TO and 2.3, 2.26, 2.57, 5.25, and 2.84 folds larger than the TO/BOC nanocomposite for eliminations of phenol, MB, fuchsine, RhB, and Cr (VI), respectively. 4. Conclusions Briefly, ternary TO/BOC/CD samples were fabricated and they characterized by several techniques. The TO/BOC/CD (1 mL) nanocomposite illustrated the substantial photocatalytic ability for degradations of phenol, MB, fuchsine, and RhB, and reduction of Cr (VI). Photocatalytic performance of this photocatalyst was 19.4, 25.9, 14.2, 52.3, and 13.9-folds larger than that of the TO and 2.3, 2.26, 2.57, 5.25, and 2.84-folds higher than the TO/BOC/CD sample for the eliminations of phenol, MB, fuchsine, and RhB, and Cr (VI), respectively. The photoluminescence and photocurrent tests were utilized to verify the effective charge separation and transfer in the ternary TO/BOC/CD (1 mL) nanocomposite. The radicals trapping experiments determined that %O2− and h+ are the crucially reactive species in the elimination of RhB. Therefore, the supremacy of the TO/BOC/CD (1 mL) photocatalyst for degradations of MB, fuchsine, and RhB, as organic contaminants, and photoreduction of Cr (VI), as an inorganic contaminant, was confirmed. Consequently, this work may provide the potential utilization of TiO2-based photocatalysts for photocatalytic removals of various contaminants under visible- light illumination. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 12. (a) Recycling runs for the TO/BOC/CD (1 mL) photocatalyst toward degradation of RhB. (b) XRD patterns of the TO/BOC/CD (1 mL) nanocomposite before and after photocatalysis.

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Fig. 13. The removal rate constants of the selected pollutants over the different photocatalysts.

Acknowledgement

Catal. B 225 (2017) 452–467. [4] S. Giannakis, S. Rtimi, C. Pulgarin, Light-assisted advanced oxidation processes for the elimination of chemical and microbiological pollution of wastewaters in developed and developing Countries, Molecules 22 (2017) 1070–1091. [5] D. Masih, Y. Ma, S. Rohani, Graphitic C3N4 based noble-metal-free photocatalyst systems: a review, Appl. Catal. B 206 (2017) 556–588. [6] X. Jin, L. Ye, H. Xie, G. Chen, Bismuth-rich bismuth oxyhalides for environmental and energy photocatalysis, Coord. Chem. Rev. 349 (2017) 84–101. [7] C. Sushma, S.G. Kumar, Advancements in the zinc oxide nanomaterials for efficient photocatalysis, Chem. Pap. 71 (2017) 2023–2042. [8] K. Qi, B. Cheng, J. Yu, W. Ho, A review on TiO2-based Z-scheme photocatalysts, Chin. J. Catal. 38 (2017) 1936–1955. [9] M. Pirhashemi, A. Habibi-Yangjeh, S. Rahim-Pouran, Review on the criteria anticipated for the fabrication of highly efficient ZnO-based visible-light-driven photocatalysts, J. Ind. Eng. Chem. 29 (2018) 1719–1747. [10] M. Mousavi, A. Habibi-Yangjeh, S. Rahim, Pouran, Review on magnetically separable graphitic carbon nitride-based nanocomposites as promising visible-lightdriven photocatalysts, J. Mater. Sci.: Mater. Electron. 29 (2018) 1719–1747. [11] M. Shekofteh-Gohari, A. Habibi-Yangjeh, M. Abitorabi, A. Rouhi, Magnetically separable nanocomposites based on ZnO and their applications in photocatalytic processes: a review, Crit. Rev. Environ. Sci. Technol. 48 (2018) 806–857. [12] M. Ge, J. Cai, J. Iocozzia, C. Cao, J. Huang, X. Zhang, J. Shen, S. Wang, S. Zhang, K.Q. Zhang, Y. Lai, Z. Lin, A review of TiO2 nanostructured catalysts for sustainable

The writers plenty appreciate the University of Mohaghegh Ardabili for financial support. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.seppur.2019.116404. References [1] Y. Zhang, B. Wu, H. Xu, H. Liu, M. Wang, Y. He, B. Pan, Nanomaterials-enabled water and wastewater treatment, NanoImpact 3 (2016) 22–39. [2] C.R. Holkar, A.J. Jadhav, D.V. Pinjari, N.M. Mahamuni, A.B. Pandit, A critical review on textile wastewater treatments: possible approaches, J. Environ. Manage. 182 (2016) 351–366. [3] Z. Xing, J. Zhang, J. Cui, J. Yin, T. Zhao, J. Kuang, Z. Xiu, N. Wan, W. Zhou, Recent advances in floating TiO2-based photocatalysts for environmental application, Appl.

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A. Habibi-Yangjeh, et al. H2 generation, Int. J. Hydrogen Energy 42 (2017) 8418–8449. [13] J. Lowa, B. Chenga, J. Yu, Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2: a review, Appl. Surf. Sci. 392 (2017) 658–686. [14] N.R. Khalid, A. Majid, M.B. Tahir, N.A. Niaz, S. Khalid, Carbonaceous-TiO2 nanomaterials for photocatalytic degradation of pollutants: a review, Ceram. Int. 43 (2017) 14552–14571. [15] C.S. Uyguner-Demirel, N.C. Birben, M. Bekbolet, Elucidation of background organic matter matrix effect on photocatalytic treatment of contaminants using TiO2: A review, Catal. Today 284 (2017) 202–214. [16] K.M. Reza, A.S.W. Kurny, F. Gulshan, Parameters affecting the photocatalytic degradation of dyes using TiO2: A review, Appl. Water Sci. 7 (2017) 1569–1578. [17] Z. Shayegan, C.-S. Lee, F. Haghighat, TiO2 photocatalyst for removal of volatile organic compounds in gas phase–A review, Chem. Eng. J. 334 (2017) 2408–2439. [18] M. Humayun, F. Raziq, A. Khan, W. Luo, Modification strategies of TiO2 for potential applications in photocatalysis: a critical review, Green Chem. Lett. Rev. 11 (2018) 86–102. [19] H. Hou, F. Gao, M. Shang, L. Wang, J. Zheng, Z. Yang, J. Xu, W. Yang, Enhanced visible-light responsive photocatalytic activity of N-doped TiO2 thoroughly mesoporous nanofibers, J. Mater. Sci.: Mater. Electron. 28 (2017) 3796–3805. [20] L. Ji, Y. Zhang, S. Miao, M. Gong, X. Liu, In situ synthesis of carbon doped TiO2 nanotubes with an enhanced photocatalytic performance under UV and visible light, Carbon 125 (2017) 544–550. [21] M. Malligavathy, S. Iyyapushpam, S.T. Nishanthi, D.P. Padiyan, Photoreduction synthesis of silver on Bi2O3/TiO2 nanocomposites and their catalytic activity for the degradation of methyl orange, J. Mater. Sci.: Mater. Electron. 28 (2017) 18307–18321. [22] M. Zalfani, Z.-Y. Hu, W.-B. Yu, M. Mahdouani, R. Bourguiga, M. Wu, Y. Li, G.V. Tendeloo, Y. Djaoued, B.-L. Su, BiVO4/3DOM TiO2 nanocomposites: effect of BiVO4 as highly efficient visible light sensitizer for highly improved visible light photocatalytic activity in the degradation of dye pollutants, Appl. Catal. B 205 (2017) 121–132. [23] S. Feizpoor, A. Habibi-Yangjeh, S. Vadivel, Novel TiO2/Ag2CrO4 nanocomposites: efficient visible-light-driven photocatalysts with n–n heterojunctions, J. Photochem. Photobiol. A 341 (2017) 57–68. [24] D. Sánchez-Rodríguez, M.G.M. Medrano, H. Remita, V. Escobar-Barrios, Photocatalytic properties of BiOCl-TiO2 composites for phenol photodegradation, J. Environ. Chem. Eng. 6 (2018) 1601–1612. [25] S. Yaparatne, C.P. Tripp, A. Amirbahman, Photodegradation of taste and odor compounds in water in the presence of immobilized TiO2-SiO2 photocatalysts, J. Hazard. Mater. 346 (2018) 208–217. [26] J. Chun-Te Lin, K. Sopajaree, T. Jitjanesuwan, M.-C. Lu, Application of visible light on copper-doped titanium dioxide catalyzing degradation of chlorophenols, Sep. Purif. Technol. 191 (2018) 233–243. [27] H. Zangeneh, A.A. Zinatizadeh, M. Feyzi, S. Zinadini, D.W. Bahnemann, Application of a novel triple metal-nonmetal doped TiO2 (KBN-TiO2) for photocatalytic degradation of Linear Alkyl Benzene (LAB) industrial wastewater under visible light, Mater. Sci. Semicond. Process. 75 (2018) 193–205. [28] S. Feizpoor, A. Habibi-Yangjeh, Ternary TiO2/Fe3O4/CoWO4 nanocomposites: Novel magnetic visible-light-driven photocatalysts with substantially enhanced activity through p-n heterojunction, J. Colloid Interface Sci. 524 (2018) 325–336. [29] V. Moradi, M.B.G. Jun, A. Blackburn, R.A. Herring, Significant improvement in visible light photocatalytic activity of Fe doped TiO2 using an acid treatment process, Appl. Surf. Sci. 427 (2018) 791–799. [30] S. Feizpoor, A. Habibi-Yangjeh, K. Yubuta, Integration of carbon dots and polyaniline with TiO2 nanoparticles: substantially enhanced photocatalytic activity to removal various pollutants under visible light, J. Photochem. Photobiol., A 367 (2018) 94–104. [31] S. Feizpoor, A. Habibi-Yangjeh, K. Yubuta, S. Vadivel, Fabrication of TiO2/ CoMoO4/PANI nanocomposites with enhanced photocatalytic performances for removal of organic and inorganic pollutants under visible light, Mater. Chem. Phys. 224 (2019) 10–21. [32] D. Kai, Y. Dan, W. Wei, P. Gao, B. Liu, Fabrication of multiple hierarchical heterojunction Ag@AgBr/BiPO4/r-GO with enhanced visible-light-driven photocatalytic activities towards dye degradation, Appl. Surf. Sci. 445 (2018) 39–49. [33] M. Hojamberdiev, Z.C. Kadirova, Y. Makinose, G.Q. Zhu, S. Emin, N. Matsushita, M. Hasegawa, K. Okada, Involving CeVO4 in improving the photocatalytic activity of a Bi2WO6/allophane composite for the degradation of gaseous acetaldehyde under visible light, Colloids Surf. A 529 (2017) 600–612. [34] H.B. Song, R.Y. Wu, Y.M. Liang, H.L. Xiong, G.J. Ji, Facile synthesis of 3D nanoplate-built CdWO4/BiOI heterostructures with highly enhanced photocatalytic performance under visible-light irradiation, Colloids Surf. A: Physicochem. Eng. Aspects 522 (2017) 346–354. [35] Y. Wang, D. Yu, W. Wang, P. Gao, L. Zhang, S. Zhong, B. Liu, The controllable

[36] [37]

[38] [39] [40] [41]

[42] [43] [44] [45] [46] [47] [48] [49]

[50] [51]

[52] [53] [54] [55] [56] [57] [58]

14

synthesis of novel heterojunction CoO/BiVO4 composite catalysts for enhancing visible-light photocatalytic property, Colloids Surf. A 578 (2019) 123608. R. Yang, S. Zhong, L. Zhang, B. Liu, PW12/CN@Bi2WO6 composite photocatalyst prepared based on organic-inorganic hybrid system for removing pollutants in water, Sep. Purif. Technol. 235 (2019) 116270. R. Yang, F. Dong, X. You, M. Liu, Z. Shan, Z. Lishan, B/ Liu, Facile synthesis and characterization of interface charge transfer heterojunction of Bi2MoO6 modified by Ag/AgCl photosensitive material with enhanced photocatalytic activity, Mater. Lett. 252 (2019) 272–276. S. Ning, L. Ding, Z. Lin, Q. Lin, H. Zhang, H. Lin, J. Long, X. Wang, One-pot fabrication of Bi3O4Cl/BiOCl plate-on-plate heterojunction with enhanced visible-light photocatalytic activity, Appl. Catal. B 185 (2016) 203–212. Y. Huang, Y. He, M. Cui, Q. Nong, J. Yu, F. Wu, X. Meng, Synthesis of AgCl/Bi3O4Cl composite and its photocatalytic activity in RhB degradation under visible light, Catal. Commun. 76 (2016) 19–22. Y. Ma, Y. Chen, Z. Feng, L. Zeng, Q. Chen, R. Jin, Y. Lu, Y. Huang, Y. Wu, Y. He, Preparation, characterization of Bi3O4Cl/g-C3N4 composite and its photocatalytic activity in dye degradation, J. Water Process Eng. 18 (2017) 65–72. H. Che, G. Che, E. Jiang, C. Liu, H. Dong, C. Li, A novel Z-Scheme CdS/Bi3O4Cl heterostructure for photocatalytic degradation of antibiotics: mineralization activity, degradation pathways and mechanism insight, J. Taiwan Inst. Chem. Eng. 91 (2018) 224–234. G. Gupta, S.K. Kansal, Novel 3-D flower like Bi3O4Cl/BiOCl p-n heterojunction nanocomposite for the degradation of levofloxacin drug in aqueous phase, Process Saf. Environ. Prot. 128 (2019) 342–352. H. Li, X. He, Z. Kang, H. Huang, Y. Liu, J. Liu, S. Lian, C.H.A. Tsang, X. Yang, S.T. Lee, Water-soluble fluorescent carbon quantum dots and photocatalyst design, Angew. Chem. Int. Ed. 49 (2010) 4430–4434. H. Zhang, L. Zhao, F. Geng, L.-H. Guo, B. Wan, Y. Yang, Carbon dots decorated graphitic carbon nitride as an efficient metal-free photocatalyst for phenol degradation, Appl. Catal. B 180 (2016) 656–662. W. Liu, C. Li, Y. Ren, X. Sun, W. Pan, Y. Li, J. Wang, W. Wang, Carbon dots: Surface engineering and applications, J. Mater. Chem. B 4 (2016) 5772–5788. M. Tuerhong, X.U. Yang, Y.I.N. Xue-Bo, Review on carbon dots and their applications, Chin. J. Anal. Chem. 45 (2017) 139–150. M. Pirsaheb, A. Asadi, M. Sillanpää, N. Farhadian, Application of carbon quantum dots to increase the activity of conventional photocatalysts: a systematic review, J. Mol. Liq. 271 (2018) 857–871. S. Feizpoor, A. Habibi-Yangjeh, I. Ahadzadeh, K. Yubuta, Oxygen-rich TiO2 decorated with C-Dots: Highly efficient visible-light-responsive photocatalysts in degradations of different contaminants, Adv. Powder Technol. 30 (2019) 1183–1196. Y. Zhang, Z.-R. Tang, X. Fu, Y.-J. Xu, TiO2-graphene nanocomposites for gas-phase photocatalytic degradation of volatile aromatic pollutant: is TiO2-graphene truly different from other TiO2-carbon composite materials? ACS Nano 4 (2010) 7303–7314. Q. Que, Y. Xing, Z. He, Y. Yang, X. Yin, W. Que, Bi2O3/Carbon quantum dots heterostructured photocatalysts with enhanced photocatalytic activity, Mater. Lett. 209 (2017) 220–223. N. Parveen, M.O. Ansari, T.H. Han, M.H. Cho, Simple and rapid synthesis of ternary polyaniline/titanium oxide/graphene by simultaneous TiO2 generation and aniline oxidation as hybrid materials for supercapacitor applications, J. Solid State Electrochem. 21 (2017) 57–68. Q. Wang, J. Huang, H. Sun, K.-Q. Zhang, Y. Lai, Uniform carbon dots@TiO2 nanotube arrays with full spectrum wavelength light activation for efficient dye degradation and overall water splitting, Nanoscale 9 (2017) 16046–16058. A. Ishikawa, T. Takata, J.N. Kondo, M. Hara, H. Kobayashi, K. Domen, Oxysulfide Sm2Ti2S2O5 as a stable photocatalyst for water oxidation and reduction under visible light irradiation (k 650 nm), J. Am. Chem. Soc. 124 (2002) 13547–13553. Z. Li, M. Wang, J. Shen, Z. Zhu, Y. Liu, Synthesis of BiOI nanosheets/coarsened TiO2 nanobelts heterostructures for enhancing visible light photocatalytic activity, RSC Adv. 6 (2016) 30037–30047. Z. Zhang, S. Lin, W. Cui, X. Li, H. Li, Enhanced photocatalytic activity of Ag/CQDs/ Bi2O2CO3 composite photocatalyst under full-spectrum light, Mater. Lett. 234 (2019) 264–268. Y. Zhang, L. Wang, M. Yang, J. Wang, J. Shi, Carbon quantum dots sensitized ZnSn (OH)6 for visible light-driven photocatalytic water purification, Appl. Surf. Sci. 466 (2019) 515–524. X. Wu, J. Zhao, L. Wang, M. Han, M. Zhang, H. Wang, H. Huang, Y. Liu, Z. Kang, Carbon dots as solid-state electron mediator for BiVO4/CDs/CdS Z-scheme photocatalyst working under visible light, Appl. Catal. B 206 (2017) 501–509. J. Wen, J. Xie, X. Chen, X. Li, A review on g-C3N4-based photocatalysts, Appl. Surf. Sci. 391 (2017) 72–123.