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Article

Fabrication of Z-Scheme CeVO4/BiVO4 Heterojunction and Its Enhanced Photocatalytic Degradation of NFX

by
Zenan Liu
1,†,
Guang Lu
2,†,
Rongpeng Yang
1,
Zheng Li
1,* and
Fei Wang
3,*
1
School of Environmental & Safety Engineering, Liaoning Petrochemical University, Fushun 113001, China
2
School of Civil Engineering, Liaoning Petrochemical University, Fushun 113001, China
3
School of Petrochemical Engineering, Liaoning Petrochemical University, Fushun 113001, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Processes 2024, 12(8), 1614; https://doi.org/10.3390/pr12081614
Submission received: 26 June 2024 / Revised: 18 July 2024 / Accepted: 30 July 2024 / Published: 1 August 2024
(This article belongs to the Section Environmental and Green Processes)
Browse Figures
Versions Notes

Abstract

:
In this paper, BiVO4/CeVO4 composites were synthesized by hydrothermal method for photodegradation of norfloxacin (NFX) under visible light irradiation. The structure, morphologies, and optical properties of as-prepared samples were studied with XRD, SEM, BET, DRS, PL, XPS, EIS, and TPR. The results of the photocatalytic experiments demonstrated that the BiVO4/CeVO4 composites had more degradation performance of NFX compared with pure BiVO4 or CeVO4, which was attributed to the increased absorbance intensity of visible light, the reduced carrier coincidence rate, and the improved charge separation efficiency. Furthermore, the possible mechanism of the NFX degradation on BiVO4/CeVO4 composites under visible light irradiation was proposed according to the photocatalytic activity and free radicals trapping experiments.

1. Introduction

Recently, antibiotics have been widely used as therapeutic agents in clinical use to treat infections in humans and animals [1]. However, the indiscriminate use and abuse of antibiotics have also caused serious environmental issues, especially serious damage to animals and plants in the aquatic system [2]. Among antibiotics, norfloxacin (NFX), as a representative fluoroquinolone antibiotic, inhibits bacterial growth by hindering deoxyribonucleic acid gyrase and topo-isomerase IV [3] and increases antibiotic resistance under environmental conditions by causing genotoxicity and teratogenesis in humans and water-bound animals [4]. To remove NFX from water, many methods have been explored, including chemical oxidation, photocatalysis, biological treatment and others [5]. Among these methods, photocatalytic oxidation has drawn significant attraction for sustainable removal of NFX in wastewater due to its outstanding efficacy and ecologically friendly nature [6].
Bismuth vanadate (BiVO4) is widely studied as one of the most promising catalysts in the fields of photothermal catalysis, photo-electrocatalysis, and photocatalysis due to its suitable band gap, non-toxicity, strong light response capability, and strong chemical stability [7,8]. In addition, it has a large crystal size and controllable exposed crystal facets, providing the driving force for the formation of crystal facet heterojunctions [9]. Therefore, BiVO4 is suitable for the preparation of Z-type composite photocatalysts. For example, Yuan et al. constructed an HKUST-1@m-BiVO4 Z-type heterojunction and demonstrated high efficiency in photodegradation of tetracycline under visible light irradiation [10].
Cerium vanadate (CeVO4) is used in energy storage materials due to its abundance, non-toxicity, polyvalent state of vanadium, and good electrochemical and redox properties [11,12]. However, the photocatalytic activity of BiVO4 suffers from losses associated with its poor adsorptive performance and fast photogenerated electron–hole recombination [13]. Therefore, many researchers have employed various methods to improve the performance of CeVO4, such as improving synthesis methods, adding chelating agents, changing reaction temperature and time, and controlling the ratio of precursor particles. For example, Lu et al. synthesized cauliflower-like and flower-like CeVO4 via an ethylene glycol-aided hydrothermal method, which showed effective photodegradation performance of naphthalene in natural seawater under visible light [14]. Muhammad Jalil et al. synthesized Au@Al-CeVO4 photocatalysts for sustainable hydrogen production from water splitting and confirmed that gold cocatalysts and Al doping enhanced the catalytic sites and light harvesting ability of Au@Al-CeVO4 [15].
As far as our knowledge is concerned, no one ever reported the synthesis of a BiVO4/CeVO4 heterojunction photocatalyst for the removal of NFX. In this work, BiVO4/CeVO4 composites were successfully synthesized and characterized to analyze their structures and morphologies. The photocatalytic activity of BiVO4/CeVO4 composites was investigated in NFX degradation under visible light irradiation. Furthermore, the catalytic degradation mechanism of NFX was studied according to the results of capture experiments and related characterizations.

2. Experiment

2.1. Catalyst Preparation

The commercial material used in follow experiment were analytically grade and bought from Tianjin Opson Chemical Co., Ltd. (Tianjin, China).
Add 0.05 mol Ce(NO3)3·6H2O (or Bi(NO3)3·5H2O) to a mixture of 10 mL propanol and 10 mL ethylene glycol and stir for 60 min. Add 0.05 mol NH4VO4 to 50 mL distilled water at 80 °C and stir for 60 min. The latter is slowly added to the former while stirring for 30 min. Then, the mixed solution is transferred to a reaction vessel and kept at 180 °C for 4 h. Afterward, the mixture is cooled to room temperature, washed with water and ethanol, and dried at around 100 °C for 12 h. The CeVO4 (or BiVO4) sample is obtained.
Add NH4VO4 to 50 mL distilled water at 80 °C and stir for 60 min. Add Bi(NO3)3·5H2O and Ce(NO3)3·6H2O to a mixture of 10 mL propanol and 10 mL ethylene glycol and stir for 60 min. Then, the latter is slowly dripped into the former while stirring for 30 min. The obtained mixture is transferred to a reaction kettle and kept at 180 °C for 4 h. The composited sample can be obtained after being washed with water and ethanol and dried at around 100 °C for 12 h. The obtained composite material is named as 2Ce3Bi (Bi/Ce = 2:3) or 1Ce4Bi (Bi/Ce = 4:1).

2.2. Characterization of Catalyst

The samples were characterized using an X-ray diffractometer (XRD, XRD-7000) from Shimadzu Corporation, Kyoto, Japan; a scanning electron microscope (SEM, JSM-6700F) from JEOL Ltd., Tokyo, Japan; an X-ray photoelectron spectrometer (XPS, JEOL JPS-9010 MC) from JEOL Ltd., Tokyo, Japan; a UV–visible spectrophotometer (UV–vis, UV-5200PC) from China Yuanxi Instrument Co., Ltd., Beijing, China; a fluorescence spectrophotometer (PL, F-700) from Hitachi Ltd., Tokyo, Japan; and a Brunauer-Emmett-Teller (BET, ASAP 2020) from Quantachrome, Boynton Beach, FL, USA. In addition, the TPR and EIS measurements were carried out on an electrochemical workstation CHI-660E (Shanghai, China).

2.3. Photocatalytic Performance Test

The photocatalytic performance evaluation of the as-prepared composites was carried out by the photocatalytic degradation of NFX solution under visible light [16]. Before the photocatalytic reaction, 0.05 g of prepared photocatalytic material was placed in a 500 mL NFX solution. The glass tube containing the photocatalytic material and NFX-mixed solution was stirred under dark conditions for 30 min to achieve adsorption–desorption equilibrium of NFX on the surface of the photocatalytic material. During the photo reduction reaction, approximately 4 mL of reaction solution was taken at regular intervals and centrifuged at 9000 r/min for 3 min. The degradation rate of NFX in the supernatant was determined using a UV–visible spectrophotometer (278 nm) with the following Equation (1):
Degradation rate = (C0 − C)/C0
where C0 and C are the initial concentration of NFX before illumination and the concentration of NFX after a certain period of illumination, respectively.

2.4. Photocatalytic Performance Test

The instantaneous photocurrent response and electrochemical impedance spectroscopy (EIS) were measured on a CHI 600C electrochemical workstation produced by Shanghai Chenhua Company, Shanghai, China. A standard three-electrode electrochemical system was used with a Ag/AgCl electrode as the reference electrode and a platinum electrode as the counter electrode. The working electrode was prepared by spreading the synthesized catalysts on FTO conductive glass. The three electrodes were simultaneously placed in a beaker containing 0.2 mol/L Na2SO4 solution and all tests were conducted under ambient conditions.

3. Results and Discussion

3.1. XRD

As shown in Figure 1, the XRD pattern of pure BiVO4 matches perfectly with the monoclinic BiVO4 according to the standard card (JCPDS card number C4-0688). The characteristic peaks at 18.8°, 28.6°, 30.4°, 35.6°, 42.4°, 46.1°, and 52.8° correspond to the (020), (−121), (040), (200), (150), (240), and (−161) crystal planes, proving that the synthesized BiVO4 is a pure monoclinic phase without impurity phase generation and has good crystallinity [17]. The prepared pure CeVO4 sample shows characteristic peaks at 18.1°, 24.2°, 32.5°, 34.2°, 39.1°, 43.6°, and 47.9°, which correspond to the crystal planes (101), (200), (112), (220), (202), (103), and (321) in the standard PDF pattern (JCPDS12-0757), indicating high purity and high crystallinity of the tetragonal CeVO4 material [18]. When the Ce/Bi ratio is 1:4, the diffraction peaks in the BiVO4/CeVO4 composite are the same as those in pure BiVO4. When the Ce/Bi ratio is 2:3, new diffraction peaks appear at 2θ values of 18.2°, 24.3°, 32.5°, 43.5°, and 48.4°, belonging to the characteristic diffraction peaks of monoclinic CeVO4 (JCPDS12-0757), indicating the successful composition of BiVO4 and CeVO4. In addition, it can be seen that the intensity of the diffraction peaks of the BiVO4/CeVO4 composite increases gradually with the increase in CeVO4 content in the composite. The formed tetragonal-monoclinic phase structure is beneficial for the enhancement of the photocatalytic activity of the sample [19].

3.2. SEM and BET

The morphology of the prepared materials was studied using SEM images. As shown in Figure S1a, it is observed that the pancake-like BiVO4 is assembled by many small particles. As shown in Figure S1b, it is found that the CeVO4 samples are composed of many tiny nanoparticles. With the addition of BiVO4, it is obvious that the morphology of CeVO4 changes and the cross-sectional octahedral structures are formed (as shown in Figure S1c,d).
The surface areas of the prepared materials were conducted by the N2 absorption–desorption isotherms. As shown in Figure S2, the prepared samples exhibit the type IV isotherms with the H3 hysteresis loop, indicating the existence of macrospores. In addition, the specific surface areas are found to be 50.25, 32.05, 28.43, and 20.35 m2·g−1 for CeVO4, 2Ce3Bi, 1Ce4Bi, and BiVO4, respectively.

3.3. XPS

To reveal the surface composition and oxidation state of the sample, measurements were performed with XPS. According to Figure 2a, the signal peaks of B, V, and O are shown in the XPS survey spectra of pure BiVO4. The signal peaks of V, O, and Ce are shown in the XPS survey spectra of pure CeVO4. The signal peaks of Bi, V, O, and Ce are shown in the XPS survey spectra of the composites with Ce/Bi ratios of 1:4 and 2:3.
Figure 2b shows the V 2p orbital spectra. It was found that the peaks at 517.42 eV and 524.68 eV are the characteristic peaks of V 2p3/2 and V 2p1/2 in pure BiVO4, while the peaks at 516.67 eV and 524.08 eV are the characteristic peaks of V 2p3/2 and V 2p1/2 in pure CeVO4. The peaks at 516.39 eV and 524.16 eV are the characteristic peaks of V 2p3/2 and V 2p1/2 in the composite with Ce/Bi ratio of 2:3, and the peaks at 516.59 eV and 523.75 eV are characteristic peaks of V 2p3/2 and V 2p1/2 in the composite with Ce/Bi ratio of 1:4. These results prove the presence of V5+ in the as-prepared samples [20].
Figure 2c shows the Bi 4f orbital spectrum. The peaks at 158.98 eV and 164.30 eV represent the characteristic peaks of Bi 4f5/2 and Bi 4f3/2 in pure BiVO4. The peaks at 158.69 eV and 163.99 eV represent the characteristic peaks of Bi 4f5/2 and Bi 4f3/2 in the composite with Ce/Bi ratio of 2:3. The peaks at 158.57 eV and 164.30 eV represent the characteristic peaks of Bi 4f5/2 and Bi 4f3/2 in the composite with Ce/Bi ratio of 1:4. There results indicate the presence of Bi3+ in the composite samples.
In Figure 2d, the peaks at 880.97 eV and 884.92 eV represent the characteristic peaks of Ce 3d5/2 in pure CeVO4. The peaks at 899.91 eV and 901.42 eV represent the characteristic peaks of Ce 3d3/2 in pure CeVO4. The peaks at 900.72 eV and 900.98 eV represent the characteristic peaks of Ce 3d5/2 in the 2:3 Ce/Bi composite. The peak at 902.63 eV represents the characteristic peak of Ce 3d3/2 in the 2:3 composite. The peaks at 881.13 eV and 885.12 eV represent the characteristic peaks of Ce 3d5/2 in the 1:4 Ce/Bi composite. The peaks at 900.18 eV and 903.93 eV represent the characteristic peaks of Ce 3d3/2 in the 1:4 composite. The Ce 3d results show the presence of Ce3+ in the composite [11,12,13,14].
In the O 1s spectrum shown in Figure 2e, the peaks at 529.48 eV and 531.05 eV are characteristic peaks of pure CeVO4. The peaks at 529.90 eV and 531.29 eV are characteristic peaks of pure BiVO4. The peaks at 529.42 eV and 531.60 eV are characteristic peaks of the Ce/Bi ratio 2:3 composite and the peaks at 529.36 eV and 531.29 eV are characteristic peaks of the Ce/Bi ratio 1:4 composite. The first peak is attributed to chemisorbed oxygen (Oads) and the second peak is attributed to hydroxyl oxygen (OOH) adsorbed with H2O. The presence of chemisorbed oxygen is beneficial for the generation of active oxygen species in photocatalytic reactions, thereby promoting the improvement of photocatalytic performance [21,22]. Based on the XPS results, the positions of the V 2p (Figure 2b) and Bi 4f (Figure 2c) peaks in the composites with Ce/Bi ratios of 2:3 and 1:4 slightly decrease compared to pure BiVO4. With the increase in CeVO4 proportion in the composite, the changes in V 2p and Bi 4f become more significant, which should be attributed to the Ce–Bi bonds in the composite material. The slight changes in binding energy indicate the presence of a BiVO4/CeVO4 heterojunction. The results in Figure 2d also show the presence of Ce3+ in the composites with Ce/Bi ratios of 2:3 and 1:4, further confirming the existence of Ce–Bi bonds in the composites and the successful formation of BiVO4/CeVO4 composites.

3.4. DRS

From the UV–vis DRS spectra in Figure 3a, it can be seen that the maximum absorption wavelengths of BiVO4, CeVO4, 1Ce4Bi, and 2Ce3Bi catalysts are 596, 1050, 780, and 867nm, respectively. In addition, the absorption intensity of the BiVO4/CeVO4 composite increases in the UV–vis light region and exhibits a significant blue shift with the content of CeVO4, indicating that the BiVO4/CeVO4 composite with a Ce/Bi ratio of 1:4 can more effectively utilize visible light and has an enhanced photocatalytic performance.
Based on the Tauc formula as in the following Equation (2) [12,13,14], Tauc plots are shown in Figure 3b.
(αhv) 1/n = k (hv − Eg)
where α represents the absorption coefficient, h represents the Planck constant, v represents the frequency related to the wavelength, and k is a proportionality constant. Since BiVO4 and CeVO4 are both direct band gap semiconductors, n is taken as 1/2 [4,5,6]. The band gaps of BiVO4, CeVO4, 1Ce4Bi, and 2Ce3Bi are calculated to be 2.18, 1.18, 1.59, and 1.43 eV, respectively.

3.5. Electrochemical Performance Analysis

In order to study the effect of heterojunction structure on the efficiency of separating photogenerated electron–hole pairs, we studied the transient photocurrent response (TPR) of pure BiVO4, pure CeVO4, and BiVO4/CeVO4 composite samples with different Ce/Bi molar ratios. The efficiency of separating photogenerated charge carriers plays a very important role in photocatalytic activity. Generally, the higher the photocurrent density, the longer the time that photogenerated electrons and holes exist and the better the photocatalytic activity [23,24]. It can be clearly seen from Figure 4a that the BiVO4/CeVO4 composites with different Ce/Bi molar ratios exhibit significantly enhanced photocurrent density compared to the pure BiVO4 or CeVO4 samples. In addition, the BiVO4/CeVO4 composite with a Ce/Bi molar ratio of 2:3 has the highest photocurrent density, inhibiting the recombination of photogenerated electron carriers in the BiVO4/CeVO4 composite material. The above results indicate that CeVO4 can act as an electron acceptor to effectively transfer electrons and promote the separation of electron–hole pairs.
Electrochemical impedance spectroscopy (EIS) is also commonly used to study the migration impedance and separation efficiency of photogenerated charge carriers in semiconductors. The size of the interface resistance on the electrode surface can be reflected by the radius of the arc in the Nyquist curve [25]. In general, the smaller the radius of the arc, the smaller the interface resistance and the higher the charge transfer efficiency. As shown in Figure 4b, the Nyquist curves of all composite samples appear as semicircular arcs at high frequencies.
Moreover, BiVO4/CeVO4 composite samples with different Ce/Bi molar ratios compared to pure BiVO4 and CeVO4 samples exhibit a smaller Nyquist curve arc radius. And the BiVO4 /CeVO4 composite with a Ce/Bi molar ratio of 2:3 has the smallest arc radius, indicating that the migration resistance of photogenerated charge carriers in BiVO4/CeVO4 is the smallest and effectively avoiding the recombination of photogenerated charge carriers. According to the above photoelectrochemical analysis, it is found that the introduction of CeVO4 can effectively increase the number of photogenerated charge carriers in BiVO4 and reduce the migration resistance of charge carriers.

3.6. PL

The recombination of photogenerated carriers is manifested by fluorescence quenching as shown in Figure 5. Usually, the lower intensity of the photoluminescence peak indicates the lower recombination rate of photogenerated carriers [26]. As shown in Figure 5, the BiVO4/CeVO4 composite with a Ce/Bi ratio of 2:3 exhibits a higher fluorescence intensity than the others, suggesting that CeVO4 plays a key role in preventing the recombination of electron–hole pairs. This is because the formation of a Bi–Ce heterojunction after the combination of CeVO4 and BiVO4 introduces an internal electric field, which promotes the charge separation at the Bi–Ce interface and suppresses the recombination of electron–hole pairs.

3.7. Photocatalytic Results

The NFX degradation rates of pure CeVO4, pure BiVO4, and CeVO4/BiVO4 composites with different molar ratios are shown in Figure 6a. Without any catalysts, the degradation rates of NFX within 5 h are only 4.1%. And the degradation efficiency of NFX over the CeVO4 or BiVO4 catalysts is 19.5% and 64.3%, respectively. The CeVO4/BiVO4 composite with Ce/Bi ratio of 1:4 has a degradation rate of 70.1% for NFX, while the CeVO4/BiVO4 composite with Ce/Bi ratio of 2:3 has a degradation rate of 84.8% for NFX. From the results of XRD, XPS, and SEM, the CeVO4/BiVO4 composites are successfully prepared, and show higher degradation rates of NFX than those of the pure BiVO4 and CeVO4 samples. As shown with the results of DRS, PL, N2 adsorption–desorption, TPR and EIS, the visible light response, and BET, the separation and migration of photogenerated carriers are improved with the CeVO4/BiVO4 composite, resulting in the degradation efficiency of NFX gradually increasing with the increase in Ce/Bi ratio in the composite.
As shown in Figure 6b, there is a good linear relationship between -ln(C/C0) of all samples and the illumination time t, which indicates that the photocatalytic degradation of NFX is well accorded with the pseudo first-order kinetics. The reaction rate constant of the composite synthesized with a Ce/Bi ratio of 1:4 reaches 0.21702 h−1. And the NFX degradation rate constant of the composite synthesized with a Ce/Bi ratio of 2:3 is the highest (0.36177 h−1), which is 11.64 times and 2.16 times that of the pure CeVO4 sample (0.03106 h−1) and the pure BiVO4 sample (0.16756 h−1), respectively.
The results of this work, indeed, provide reference for researchers studying vanadate salts. However, the heterojunction interface of the prepared CeVO4/BiVO4 composites is not perfect (as shown in Figure S1), resulting in the NFX degradation rates of CeVO4/BiVO4 composites in our work being lower than BiVO4-rGO, g-C3N5/BiVO4/CoFe-LDH, BiVO4@LDHs, and CuO/{010}BiVO4 (as shown in Table S1) [3,4,5,6]. Therefore, the potential impact of impurities and the catalyst synthesis conditions need further optimization.

3.8. Free Radical Capture Experiment

In order to investigate the main active substances generated by the 2Ce3Bi composite in the photocatalytic process, TEOA, BQ, AgNO3, or IPA was added to the experiment of NFX photodegradation to capture ·O2−, h+, e−, or ·OH, respectively [27]. As shown in Figure 7, the removal rate of NFX with the composite was 86% without adding any active substances. After adding AgNO3, the removal rate of NFX decreased from 86% to 78%, indicating that e- played a minor role in the photocatalytic process. After adding TEOA, the removal rate of NFX decreased from 86% to 60%, indicating that ·O2− also played a relatively minor role in the photocatalytic process. After adding BQ, the removal rate of NFX decreased from 86% to 32%, indicating that h+ played an important role in the photocatalytic process. With the addition of IPA, the removal rate of NFX decreased from 86% to 18%, indicating that ·OH is the main active substance in the photocatalytic process of CeVO4/BiVO4 composite material.

3.9. Analysis of Photocatalytic Mechanism

It is generally believed that semiconductor heterojunction composites with matched band structures can promote the separation of charge carriers, thereby enhancing photocatalytic activity [28]. Under zero charge point conditions, the band edge positions of the semiconductor conduction band (ECB) and the valence band (EVB) can be calculated by the following empirical formula:
ECB = χ − Ee − 1/2Eg
EVB = Eg + ECB
where χ is the absolute electronegativity of the semiconductor (the χ values of BiVO4 and CeVO4 are 6.035 and 5.56 eV, respectively), Ee is the free electron energy scale (approximately 4.5 eV), and Eg is the band gap width of the semiconductor (the band gap width values of the pure BiVO4 and the pure CeVO4 samples are 2.18 eV and 1.26 eV according to UV–vis DRS calculation results, respectively). Therefore, the conduction band bottom and valence band top potentials of BiVO4 are calculated as 0.45 eV and 2.63 eV, and those of CeVO4 are calculated as 0.43 eV and 1.69 eV.
When two semiconductor materials (BiVO4 and CeVO4) are combined, a heterojunction structure can be formed at the interface of the two materials. When the BiVO4/CeVO4 composite system is exposed to visible light, the electrons in the valence band of BiVO4 can be excited and transitioned to the conduction band (as shown in Figure 8). At the same time, an equal number of holes are left in the valence band position. The same process can also occur in CeVO4. Due to the relatively large band gap width of the BiVO4 sample, the amount of photogenerated charge carriers produced in BiVO4 is less than that in CeVO4. Since the conduction band edge potential of BiVO4 (0.45 eV) is higher than that of CeVO4 (0.43 eV) and the valence band edge potential of CeVO4 (1.69 eV) is lower than that of BiVO4 (2.63 eV), the photogenerated electrons in the conduction band of CeVO4 can migrate to the conduction band of BiVO4 and the photogenerated holes in the valence band of BiVO4 can migrate to the valence band of CeVO4. This migration process greatly inhibits the recombination probability of photogenerated charge carriers and enhances the separation efficiency of electron–hole pairs, which is consistent with the results of PL spectra and transient photocurrent response. On the other hand, NFX molecules can also be excited to generate NFX* radicals under visible light irradiation. The excited state NFX* radicals adsorbed on the catalyst’s surface can transfer electrons to the conduction band of BiVO4 and then migrate to the conduction band of CeVO4.

4. Conclusions

The BiVO4/CeVO4 composites were successfully synthesized by hydrothermal method and were confirmed by XRD, SEM, and XPS. The BiVO4/CeVO4 composite with a molar ratio of 2:3 exhibited the highest photodegradation rate of 84.8% for NFX under visible light irradiation. The improved performance was attributed to the increased absorbance intensity of visible light, the reduced carrier coincidence rate, and the improved charge separation efficiency. The active free radical capture experiments confirmed that ·OH was the main active species in the photocatalytic process. Furthermore, a plausible mechanism of the NFX degradation in BiVO4/CeVO4 photocatalysts under visible light irradiation was proposed according to the photocatalytic activity and radical species trapping experiments. This research will promote the further purification of wastewater by sunlight.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/pr12081614/s1. Figure S1: SEM pattern of prepared samples: (a) BiVO4, (b) CeVO4, (c) 1Ce4Bi and (d) 2Ce3Bi; Figure S2: Adsorption-desorption isotherm of prepared samples; Table S1: The results in comparison with literatures.

Author Contributions

Investigation, R.Y.; Resources, F.W.; Writing—original draft, Z.L. (Zenan Liu); Writing—review & editing, G.L.; Supervision, Z.L. (Zheng Li). All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the National Science Foundation of China (Grant No. 41701364), the Natural Science Foundation of Liaoning Province (Grant No. LJKMZ20220722, LJKMZ20220716, and LJKZ0379) and the Fushun Talent Plan project (Grant No. FSYC202107006).

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Processes 12 01614 g001
Figure 1. XRD pattern of prepared samples.
Figure 1. XRD pattern of prepared samples.
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Figure 2. Wide XPS spectra of different samples (a) and HR-XPS spectrum of V2p (b), Bi 4f (c), Ce 3d (d), and O1s (e).
Figure 2. Wide XPS spectra of different samples (a) and HR-XPS spectrum of V2p (b), Bi 4f (c), Ce 3d (d), and O1s (e).
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Figure 3. UV–vis diffuse reflectance spectra (a) and the (αhν)1/2 vs. hν (b) of as-prepared samples.
Figure 3. UV–vis diffuse reflectance spectra (a) and the (αhν)1/2 vs. hν (b) of as-prepared samples.
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Figure 4. TPR (a) and EIS (b) of different samples.
Figure 4. TPR (a) and EIS (b) of different samples.
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Figure 5. Photoluminescence spectra of different samples.
Figure 5. Photoluminescence spectra of different samples.
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Figure 6. NFX photodegradation of different samples under visible light (a) and the corresponding pseudo first-order kinetics of NFX degradation (b).
Figure 6. NFX photodegradation of different samples under visible light (a) and the corresponding pseudo first-order kinetics of NFX degradation (b).
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Figure 7. Effect of the scavengers on the degradation rate of NFX.
Figure 7. Effect of the scavengers on the degradation rate of NFX.
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Figure 8. Diagram of the possible photocatalytic mechanism of the decomposition of NFX with the 2Ce3Bi sample under visible light irradiation.
Figure 8. Diagram of the possible photocatalytic mechanism of the decomposition of NFX with the 2Ce3Bi sample under visible light irradiation.
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MDPI and ACS Style

Liu, Z.; Lu, G.; Yang, R.; Li, Z.; Wang, F. Fabrication of Z-Scheme CeVO4/BiVO4 Heterojunction and Its Enhanced Photocatalytic Degradation of NFX. Processes 2024, 12, 1614. https://doi.org/10.3390/pr12081614

AMA Style

Liu Z, Lu G, Yang R, Li Z, Wang F. Fabrication of Z-Scheme CeVO4/BiVO4 Heterojunction and Its Enhanced Photocatalytic Degradation of NFX. Processes. 2024; 12(8):1614. https://doi.org/10.3390/pr12081614

Chicago/Turabian Style

Liu, Zenan, Guang Lu, Rongpeng Yang, Zheng Li, and Fei Wang. 2024. "Fabrication of Z-Scheme CeVO4/BiVO4 Heterojunction and Its Enhanced Photocatalytic Degradation of NFX" Processes 12, no. 8: 1614. https://doi.org/10.3390/pr12081614

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