Simple glycerol-assisted and morphology controllable solvothermal synthesis of CeVO4/BiVO4 hierarchical hollow microspheres with enhanced photocatalytic activities

Miao Wang , Yingying Guo , Zedong Wang , Huihui Cui , Tongming Sun * and Yanfeng Tang *
College of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, P. R. China. E-mail: stm7314@ntu.edu.cn; tangyf@ntu.edu.cn

Received 25th May 2021 , Accepted 9th July 2021

First published on 9th July 2021


Abstract

CeVO4 hierarchical hollow microspheres with various morphologies have been synthesized via a simple glycerol (Gl)-assisted solvothermal route. They are constructed using different morphological nanoscaled units (nanoflakes, nanorods and nanowires) by adjusting the solvent ratio of the system. The Gl and L-aspartic acid (L-Asp) molecules act as structure–directing agents, meaning the CeVO4 hierarchical materials feature adjustable structural variations with 0D, 1D, and 2D structures. A possible formation mechanism is proposed based on the Gl content-dependent and time-dependent morphological evolution results. Under visible-light irradiation, the degradation results towards methylene blue (MB) indicate that the photocatalytic performance of the CeVO4/BiVO4 composites could be easily tuned by simply varying the Gl content ratio and the amount of BiVO4 NPs. Compared with pristine CeVO4, the photodegradation efficiency of the hierarchical nanowires-assembled CeVO4/BiVO4 hollow microspheres exhibit a two-fold increase after doping with 10% BiVO4 and the degradation rate reached 97.8% in 30 min. Owing to the easy fabrication, our strategy may provide broad possibilities for the future development of other hollow micro/nanostructures that exhibit an efficient performance.


1. Introduction

As one of the lanthanide vanadates, cerium vanadate (CeVO4) has attracted significant attention owing to its broad applications in supercapacitors, laser host and electrochromic materials, gas sensors and catalysts.1–5 In particular, with a wide band gap energy of around 3 eV, CeVO4 may offer a large number of opportunities for photocatalysis. Despite the significant progress that has been made in previous studies, the applications of CeVO4 photocatalysts are still restricted by many factors, such as their small surface area, fast charge recombination and limited light absorption under visible light.6–8 It is highly desirable to maximize the light absorption and efficiency of photocatalysis for practical applications. Therefore, significant efforts have been made to design and synthesize CeVO4 semiconductors for highly-efficient photocatalytic activities. Consequently, various micro/nanosized CeVO4 structures have been prepared (particles, rods, cube-like and microspheres).9–12 As is well known, the photocatalytic efficiency of CeVO4 is strongly reliant on the morphology and crystalline structure. However, to the best of our knowledge, hierarchical CeVO4 hollow microspheres organized by nanowires have not been reported and the relationship between the morphology and photocatalytic properties needs to be investigated further.

Nowadays, the designing of efficient hybrid visible-light responsive photocatalysts for the removal of organic contaminants from water has been considered as a great option for solving environmental crises.13–18 Among the visible-light-driven photocatalysts, the BiVO4-supported nanocomposite has been widely investigated owing to its excellent chemical stability and suitable electronic band structure (2.4 eV).19–21 On the other hand, owing to the superior characteristics (low density, large surface area, high permeability and countless active sites), the 3D hierarchical structures have received extensive attention owing to the excellent photocatalytic efficiency and adsorption performance towards organic contaminants.22–25 In this research, we explored the preparation of CeVO4 hierarchical hollow microspheres with various morphologies via a simple glycerol-assisted solvothermal route, in which glycerol (Gl) and L-aspartic acid (L-Asp) act as structure–directing agents. The influence of the Gl content and the reaction time on the morphology and crystalline structure of the products was examined. In addition, we proposed a possible growth mechanism of the hierarchical CeVO4 hollow microspheres assembled from different building units. Furthermore, the photocatalytic performance of the CeVO4 and CeVO4/BiVO4 hierarchical hollow microspheres towards methylene blue (MB) was thoroughly investigated under visible-light irradiation. When the molar ratio of CeVO4 and BiVO4 was 1[thin space (1/6-em)]:[thin space (1/6-em)]0.1, the MB degradation rate reached 97.8% within 30 min.

2. Experimental section

2.1. Synthesis of hierarchical nanowires-assembled CeVO4 hollow microspheres

All the regents used were of analytical grade. Typically, a mixture of Ce(NO3)3·6H2O (1.0 mmol) and L-Asp (1.0 mmol) was dissolved in a solution of Gl (6 mL) and H2O (18 mL), then 1.0 mmol NH4VO3 was added. After stirring vigorously for 20 min, the mixture was sealed in a 30 mL Teflon-lined stainless steel autoclave and heated at 150 °C for 24 h. After being cooled down to room temperature, the obtained precipitate was filtered, cleaned with distilled water and ethanol several times, and later dried at 80 °C for 3 h. Different morphological CeVO4 micro/nanostructures were prepared by comparative experiments including different reaction times (3, 6 and 12 h) and different volume ratios of Gl/H2O.

2.2. Synthesis of CeVO4/BiVO4 nanocomposites

A typical CeVO4/BiVO4 nanocomposite was prepared as follows: 1 mmol as-prepared CeVO4 was dispersed in 24 mL deionized water with magnetic stirring. 0.1 mmol Bi(NO3)3·6H2O and 1 mmol NH4VO3 were subsequently added to the mixture, then the solution was stirred for 20 min. The mixture was sealed in a 50 ml Teflon-lined stainless-steel autoclave, heated at 150 °C for 3 h, and then naturally cooled to room temperature. The resulting solution was centrifuged and cleaned with distilled water and ethanol several times, and later dried at 80 °C for 3 h to gain a yellow powder. The molar ratios of CeVO4 and BiVO4 were 1[thin space (1/6-em)]:[thin space (1/6-em)]0.3, 1[thin space (1/6-em)]:[thin space (1/6-em)]0.5, 1[thin space (1/6-em)]:[thin space (1/6-em)]0.7 and 1[thin space (1/6-em)]:[thin space (1/6-em)]1. As a comparison, pure BiVO4 was prepared without the addition of CeVO4.

2.3. Characterization

The crystalline phase and structure of the products were analyzed using X-ray diffractometry (XRD) on a Bruker D8-Advance powder X-ray diffractometer (Cu Kα radiation λ = 0.15418 nm). The surface morphologies of the CeVO4 and CeVO4/BiVO4 were observed using scanning electron microscopy (SEM, Hitachi S-4800) and transmission electron microscopy (TEM, JEOL-2100F). The Brunauer–Emmett–Teller (BET) specific surface area was obtained from standard N2 adsorption–desorption isotherms measured using Micromeritics ASAP 2020C apparatus. X-ray photoelectron spectroscopy (XPS) spectra were collected on a ESCALAB MK II X-ray photoelectron spectrometer using a nonmonochrome Mg K-X-ray as an excitation source. UV-vis diffuse-reflectance spectra (DRS) was recorded with a Shimadzu UV-3600 spectrometer. An EMX-10/12 electronic paramagnetic resonance (EPR) spectrometer with a Xe lamp (Heraeus fur Strahler Q180, Bruker) was used to record the EPR spectra.

2.4. Photocatalytic degradation of MB

The visible-light photocatalytic activity of the samples was determined by irradiating MB solution under a Xe lamp (100 W) with a 420 nm cutoff filter, which was conducted in an XPA-7 photochemical reactor. Before irradiation, 24 mg of the CeVO4 sample was added into a series of quartz cuvettes containing 30 mL of MB solution (20 mg L−1) and this mixture was magnetically stirred for 30 min in the dark to achieve an adsorption–desorption equilibrium between the sample and the MB molecules. During irradiation, the quartz cuvette was carefully taken from the reactor at the given time. 3.5 mL of the solution was taken out and centrifuged to separate the samples. The UV-Vis absorption spectrum was then recorded on a Shimadzu UV-3600 spectrophotometer.

3. Results and discussion

Fig. 1a shows the XRD patterns of an as-prepared typical sample. All diffraction peaks are in good agreement with the tetragonal phase of CeVO4 (JCPDS No. 12-0757) and no impurities were detected. The strong diffraction peaks show that CeVO4 are well-crystallized. Fig. 1b and c shows the SEM images of the typical CeVO4. The low-magnification SEM image indicated that some hollow microspheres with an average diameter of about 2 μm were formed. The hollow interior and the shell outside are clearly observed in some broken spheres. The magnified SEM image from a single hollow sphere (Fig. 1c) reveals that it is self-assembled from a significant number of nanowires with an average length of about 400 nm. The hollow interiors of the CeVO4 microspheres were also directly reconfirmed using the TEM images, as shown in Fig. 1d and e, an obvious contrast between the edges and the center can be observed under the electric beam, evidently confirming the hollow nature of the CeVO4. The high magnification TEM image illustrates that the hollow microsphere is comprised of numerous nanowires, consistent with the SEM results. The high resolution transmission electron microscopy (HRTEM) image and the selected area electron diffraction (SAED) pattern (Fig. 1f and g) of a typical nanowire show that it is single-crystalline, and the spacing of approximately 0.35 nm between adjacent lattice planes corresponds to the distance between two (200) crystal planes. The BET specific surface area of the as-synthesized typical CeVO4 hollow microspheres was investigated using N2 adsorption–desorption measurements. As shown in Fig. 1h, the isotherm displays a typical H3 type hysteresis loop at a relative pressure (P/P0) of between 0.6 and 1.0. The presence of hysteresis revealed the existence of hollow structures in the sample, which is in agreement with the observations from SEM and TEM. The BET surface area of the nanowires-assembled CeVO4 hollow microspheres obtained using the typical procedure was 146.76 m2 g−1.
image file: d1qm00770j-f1.tif
Fig. 1 XRD (a), SEM (b and c), TEM (d and e), HRTEM (f), SAED pattern (g) and N2 adsorption–desorption isotherm (h) of a typical CeVO4 sample.

The chemical composition and electronic state of the as-prepared samples were further measured using XPS measurements. Fig. 2a displays the XPS survey spectra of the as-prepared samples, indicating that there are only Ce, V, O and C elements. In the high-resolution Ce 3d spectra (Fig. 2b), two characteristic peaks of Ce 3d5/2 are observed at about 885.7 and 881.5 eV, and those representing Ce 3d3/2 are observed at about 904.1 and 900.3 eV, implying the existence of Ce3+ ions.26 The V 2p spectra (Fig. 2c) of all samples are at approximately 516.9 eV (V 2p3/2) and 524.7 eV (V 2p1/2), ascribed to V5+. The fitted result of the O 1s spectrum in Fig. 2d displays two binding energies at 529.8 and 531.5 eV, indicating contributions from the two species of lattice oxygen (O2) in CeVO4.26,27


image file: d1qm00770j-f2.tif
Fig. 2 XPS spectra for the as-obtained CeVO4: (a) wide spectrum, (b) Ce 3d, (c) V 2p, and (d) O 1s.

To study the effects of the Gl content on the morphology and crystalline structure of the products, a series of contrast experiments were performed. Similar procedures were performed under the same reaction conditions, except for the use of different mixed solutions with Gl volumes of 0, 12, 18 and 24 mL instead of the previously used solution (6 mL Gl/18 mL H2O). Fig. 3a shows the XRD patterns of the as-prepared CeVO4 samples with various Gl dosages. All the diffraction peaks are indexed to pure tetragonal CeVO4. With a decrease in the amount of added Gl, the diffraction peaks of the samples become sharper and the growth rate of the (200) lattice plane is faster than that of the other lattice planes, suggesting the introduction of water is beneficial to the crystallinity and growth of CeVO4. The SEM images of the products obtained using different Gl contents are shown in Fig. 3b–f. There are many nanoflake-aggregated hollow microspheres in the absence of Gl (Fig. 3b), which is consistent with results reported in our previous work.12 As shown in Fig. 3c–f, nanowires, nanorods and nanoparticles-assembled microspheres are obtained when 6 mL Gl, 12 mL Gl and 24 mL Gl are used, respectively. Comparatively, the dimensions of the nanowires are much larger than those obtained with larger amounts of Gl, suggesting the addition of GL is unfavorable to the nuclei and the growth of CeVO4 nanostructures. Therefore, Gl molecules play a key role in the formation of CeVO4 with different morphologies and crystallinities. In a typical procedure, a suitable dosage of the Gl molecule will increase the opportunity for the formation of one-dimensional CeVO4 aggregated microspheres.


image file: d1qm00770j-f3.tif
Fig. 3 XRD (a), and SEM images of the CeVO4 samples obtained from different content of Gl: (b) 0 mL, (c) 6 mL, (d) 8 mL, (e) 12 mL, (f) 24 mL.

To better understand the formation process of the hierarchical structure, time-dependent experiments were conducted and the Gl volume was fixed as 8 mL. The intermediate products were measured using XRD and SEM analysis. As shown in Fig. 4a, the relative intensity of the samples is increased with an increase in the reaction time, revealing the crystallinity is improved. Detailed information on the corresponding microstructures is characterized and listed in Fig. 4b–f. After 3 h of reaction, many irregular tiny nanoparticles-assembled aggregates were prepared (Fig. 4b). After reacting for 6 h (Fig. 4c), the as-obtained nanoparticles further grew into one-dimensional nanorods, thus nanorods-assembled hierarchical CeVO4 microspheres were formed. With the reaction time increased from 9 to 24 h, as shown in Fig. 4d–f, the nanorods gradually evolved into nanowires, namely, the aspect ratio and particles sizes are larger than those of samples obtained within 3 h. Therefore, with the increasing reaction time, the as-obtained CeVO4 samples undergo a morphological evolution from nanoparticles-assembled spheres to nanowires-assembled hierarchical hollow microspheres. These results indicate that the reaction time is a crucial factor in controlling the morphology of the products.


image file: d1qm00770j-f4.tif
Fig. 4 XRD (a), and SEM images of the CeVO4 samples obtained from different reaction times: (b) 3 h, (c) 6 h, (d) 9 h, (e) 12 h, (f) 24 h.

A possible formation mechanism was proposed based on the morphological evolution results, as shown in Fig. 5. Briefly, two key strategies are involved, namely, Gl content-dependent and time-dependent. With carboxyl and amino groups, the amino acid is a versatile, cheap and green complex agent and has been widely used as a morphology and structure directing agent in the nuclei, crystallization and aggregating process for inorganic nanomaterial synthesis.12,28,29 Firstly, the VO3− ions reacted with the Ce3+ ions to form CeVO4. In distilled water (Step I), the initial CeVO4 nanoparticles prefer to form 2D nanoflakes with the assistance of L-Asp and finally nanoflakes-assembled hollow microspheres are prepared, which have been reported in our previous work.12 On the other hand, as a simple and potentially tridentate ligand, Gl molecules can effectively coordinate with rare-earth cations resulting in the formation of numerous complexes.30 In the mixture of Gl and distilled water (step II), an extensive system of intermolecular hydrogen bonds between the OH–groups of the Gl kinetically control the anisotropic growth rates along the different crystal directions, which can lead to the formation of 1D micro/nanomaterials. Therefore, the formation of CeVO4 with different morphologies results from the combined effects of L-Asp, water and Gl. Driven by the surface energy of the nanoparticles, CeVO4 nanoparticles tend to grow along the 1D direction to form nanorods-assembled hollow microspheres and finally form nanowires-assembled hollow microspheres under suitable Gl conditions and longer reaction times, which are consistent with the Ostwald ripening (OR) mechanism.31


image file: d1qm00770j-f5.tif
Fig. 5 Schematic illustration of the formation process of CeVO4 hollow microspheres.

The XRD patterns of the typical CeVO4/BiVO4 composites (molar ratio as 1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) are shown in Fig. 6a. There are coexisting diffraction peaks for both CeVO4 and BiVO4. The SEM image shown in Fig. 6b demonstrates the particles of BiVO4 are well distributed on the surface of the CeVO4 hollow microspheres. In addition, the elemental distribution of the sample was studied using TEM line mapping and elemental mapping images (Fig. S1, ESI), proving that the elements Ce, V, O and Bi were homogeneously distributed through all the whole hollow microspheres. The energy band structure of a semiconductor is a crucial factor in determining its photocatalytic activity. The DRS spectra of the samples were measured. As shown in Fig. 6c, nanowires-assembled hollow microspheres of CeVO4 have an obvious absorption in the region of 250–700 nm, as for pure BiVO4, there is a broad absorption peak range from 200 to 500 nm. The band gaps of CeVO4 and BiVO4 are 1.00 and 2.06 eV (Fig. 6d), respectively, which are slightly lower than that of the previous reports.26 Furthermore, the band gaps of the CeVO4/BiVO4 composites increase gradually with the addition of the BiVO4, confirming the possible electronic transition between CeVO4 and BiVO4. Photoluminescence (PL) studies were performed to investigate the transfer and recombination process of the charge carriers in the samples. As presented in Fig. 6e, the broad emission peak centered at about 505 nm is ascribed to the radiative recombination process of self-trapped excitation. Compared with pure CeVO4, CeVO4/BiVO4 heterostructures exhibited a weaker emission peak, showing that the recombination efficiency of the photoinduced carrier reduced, thereby giving a higher photocatalytic performance. Interestingly, the lowest PL intensity was obtained for the sample CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1), revealing that the significantly weakened PL performance of CeVO4/BiVO4 was attributed to the synergistic effect of the electrons–holes transfer and BiVO4 nanoparticles.


image file: d1qm00770j-f6.tif
Fig. 6 (a) XRD patterns, (b) SEM image, (c) UV-vis DRS of the as-obtained samples, (d) the plots of (αhν)1/2versus hν and (e) PL of the typical CeVO4/BiVO4 composites (molar ratio as 1[thin space (1/6-em)]:[thin space (1/6-em)]0.1).

The photocatalytic activities of the samples were evaluated by measuring the decoloration of the MB solution under visible-light irradiation. By using the different molar ratios of CeVO4/BiVO4 composites as catalysts, Fig. 7a presents the degradation efficiency of MB (C/C0) as a function of the irradiation time. Without any photocatalyst or in the presence of pristine CeVO4, the degradation of MB was very slow under visible-light irradiation. Moreover, BiVO4 had a significant effect on the photocatalytic process. Employing a 20 mg L−1 MB solution as a model pollutant, when CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) composites are introduced, the MB degradation reaches 97.8% within 30 min, which is higher than the other previously reported photocatalysts (Table 1). In addition, compared with pristine CeVO4, the photodegradation efficiency of CeVO4/BiVO4 demonstrated a two-fold increase after doping with 10% BiVO4. As the BiVO4 content increases or decreases, the photocatalytic efficiency of the CeVO4/BiVO4 composites declined gradually (Fig. S2, ESI), suggesting it follows the pseudo-first-order kinetic equation. Furthermore, the velocity constant value of CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) is 4.67 × 10−2 min−1, which is higher than that of the other molar ratio (Fig. 7b).35–37 Using fixed CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) as a typical catalyst, the photocatalytic degradation at different concentrations of MB was also investigated. Obviously, the higher the concentration of the MB solution, the lower the degradation rate (Fig. 7c). Fig. 7d shows the CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) photocatalytic recyclability towards the degradation of MB. The results indicated that CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) maintained its high MB degradation efficiency for up to five cycles. As shown in Fig. S3 (ESI), the SEM and TEM images of the recovered samples show that the morphology of CeVO4/BiVO4 remains the same, suggesting the photocatalysts are of excellent chemical stability. On the other hand, the photocatalytic activities of other different morphological CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) micro/nano-structures were also assessed (Fig. 7e). Compared with nanorods or nanoflakes-assembled CeVO4/BiVO4 hollow microspheres, nanowires-assembled CeVO4/BiVO4 porous microspheres exhibited the best efficiency, implying the unique hollow microspheres had an excellent photocatalytic activity under visible-light irradiation. Therefore, the photocatalytic performance of the CeVO4/BiVO4 composites can be easily modulated by simply changing the morphologies of the CeVO4 building units. As known, many factors including the size, crystallinity, morphology and BET surface area of the nanomaterials are key factors in achieving excellent photocatalytic performances. In this work, benefiting from the synergistic effects of the larger BET surface area, narrower energy gap, unique hierarchical structures and BiVO4 doping, the nanowires-assembled CeVO4/BiVO4 hollow microspheres achieved a significantly improved photocatalytic efficiency.


image file: d1qm00770j-f7.tif
Fig. 7 Comparison of the photodegradation efficiency of MB on the CeVO4/BiVO4 catalysts: (a) different molar ratios; (b) photocatalytic kinetic reaction rate constant values; (c) different concentrations of MB; (d) recyclability; (e) different morphologies; and (f) ESR spectra of DMPO–˙OH in a CeVO4/BiVO4 (1[thin space (1/6-em)]:[thin space (1/6-em)]0.1) sample.
Table 1 Comparison of MB degradation efficiency on CeVO4/BiVO4 hollow microspheres with other reported catalysts
Materials Light irradiation Amount of catalyst (mg) Degradable compounds Removal percentage
Z-scheme CeO2/CeVO4/V2O58 300 W Xe lamp 10 100 mL 10 mg L−1 MB 93.53% (240 min)
P-doped CeVO4 nanorods10 300 W Xe lamp 50 50 mL 20 mg L−1 MB 100% (180 min)
Hedgehog-like CeVO4–BiVO426 150 W Xe lamp 50 100 mL 50 mg L−1 levofloxacin 95.7% (300 min)
3% Dy doped CeVO4 nanorods32 UV light Irradiation 200 200 mL 1 mol L−1 MB 94% (80 min)
La2O3/CeVO4@halloysite nanotubes33 300 W Xe lamp 80 100 mL 20 mg L−1 tetracycline 61.9% (60 min)
InVO4/CeVO4 hollow nanobelts34 800 W Xe lamp 40 40 mL 20 mg L−1 tetracycline 92.4% (90 min)
CeVO 4 /BiVO 4 microspheres 100 W Xe lamp 24 30 mL 20 mg L −1 MB 97.8% (30 min)


Based on the above analysis, a schematic illustration for the photodegradation of MB by CeVO4/BiVO4 is proposed, as shown in Fig. 8. When exposed to light irradiation, CeVO4 and BiVO4 can be activated and produce electrons and holes. For BiVO4, the electrons in the valence band (VB) are excited to the conduction band (CB) by leaving a hole on the VB. However, for CeVO4, only part of the photoinduced electrons migrate from the VB to the CB. The photoinduced electrons on the CB of the CeVO4 flow to that of the BiVO4 and, in contrast, the holes on the VB of BiVO4 migrate to that of the CeVO4. The CB potential of the CeVO4 semiconductor (0.415 eV) is more positive than the standard reduction potential of O2/˙O2− (−0.046 eV).38 Thus, the electrons of CB on the CeVO4 surface cannot deoxidize O2 into ˙O2−. The VB potential of the BiVO4 semiconductor (2.689 eV) is more positive than that of ˙OH/H2O (2.27 eV).39 Thus, the photo-generated holes in the BiVO4 directly oxidize MB and react with the surface adsorbed OH group forming ˙OH radicals to oxidize the organic pollutants. To further confirm the existence of the active species ˙OH in the photodegradation process, the electron paramagnetic resonance (EPR) of CeVO4/BiVO4 was conducted (Fig. 7f). It can be seen that the characteristic signal of ˙OH is detected under visible light irradiation, and no signal is found in the dark. Meanwhile, the intensities of the characteristic signals are enhanced with the increasing irradiation time from 5 to 10 min, showing ˙OH has a primary effect on improving the degradation of MB, which is consistent with the previously reported literature.


image file: d1qm00770j-f8.tif
Fig. 8 Schematic illustration of MB degradation with CeVO4/BiVO4 composites under visible-light irradiation.

4. Conclusions

Employing Gl and L-Asp as morphology-directing agents, a simple solvothermal method was developed to prepare CeVO4 hierarchical hollow microspheres assembled using different building units (nanowires, nanorods, nanoflakes and nanoparticles). Benefiting from the synergistic effects of the unique hierarchical hollow microspheres and BiVO4 doping, nanowires-assembled CeVO4/BiVO4 heterostructures have achieved a significantly improved photocatalytic efficiency towards MB under visible-light irradiation. The content ratio of Gl/H2O and the reaction time play crucial roles in the formation of products with different morphologies. The photocatalytic performance of the CeVO4/BiVO4 composites can be easily modulated by simply changing the morphologies of CeVO4, and the photodegradation of MB demonstrates a two-fold increase after doping with 10% BiVO4. Therefore, this simple Gl-assisted and morphology-controllable solvothermal route will provide an effective strategy for designing other hollow micro/nanostructures and the obtained hierarchical CeVO4/BiVO4 hollow microspheres are promising candidates for use in the photocatalytic field.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 22075152, 21776140, 22073052) and the Science and Technology Projects Fund of Nantong City (JC2020134, JC2020133). We are very grateful to the Nantong University Analytical Testing Center for its support for testing.

References

  1. J. Z. He, J. H. Zhao, Z. Run, M. J. Sun and H. Pang, Ultrathin cerium orthovanadate nanobelts for high-performance flexible all-solid-state asymmetric supercapacitors, Chem. – Asian J., 2015, 10, 338–343 CrossRef CAS PubMed.
  2. M. Y. Chang, M. F. Wang, Y. Q. Chen, M. M. Shu, Y. J. Zhao, B. B. Ding, Z. Y. Hou and J. Lin, Self-assembled CeVO4/Ag nanohybrid as photoconversion agents with enhanced solar-driven photocatalysis and NIR-responsive photothermal/photody-namic synergistic therapy performance, Nanoscale, 2019, 11, 10129 RSC.
  3. J. M. Hou, H. H. Huang, Z. Z. Han and H. B. Pan, A role of oxygen adsorption and gas sensing mechanism for cerium vanadate (CeVO4) nanorods, RSC Adv., 2016, 6, 14522–14558 RSC.
  4. C. Wang, B. Yang, J. L. Xu, F. Xia and J. Z. Xiao, Effects of CeVO4 electrode morphology and oxygen content on ammonia sensing properties for potentiometric sensor, Sens. Actuators, B, 2019, 299, 126863 CrossRef CAS.
  5. T. Kokulnathan, T. S. Priya and T. J. Wang, Surface engineering three-dimensional flowerlike cerium vanadate nanostructures used as electrocatalysts: real time monitoring of clioquinol in biological samples, ACS Sustainable Chem. Eng., 2019, 7, 16121–16130 CrossRef CAS.
  6. M. Wang, X. M. Hu, Z. Y. Zhan, T. M. Sun and Y. F. Tang, Facile fabrication of CeVO4 hierarchical hollow microspheres with enhanced photocatalytic activity, Mater. Lett., 2019, 253, 259–262 CrossRef CAS.
  7. P. Babu, S. Mohanty, B. Naik and K. Parida, Serendipitous assembly of mixed phase BiVO4 on B-doped g-C3N4: an appropriate p–n heterojunction for photocatalytic O2 evolution and Cr(VI) reduction, Inorg. Chem., 2019, 58, 12480–12491 CrossRef CAS PubMed.
  8. X. Cui, Z. Y. Liu, G. S. Li, M. Zhang, Y. T. Song and J. Wang, Self-generating CeVO4 as conductive channel within CeO2/CeVO4/V2O5 to induce Z-scheme charge-transfer driven photocatalytic degradation coupled with hydrogen production, Int. J. Hydrogen Energy, 2019, 44, 23921–23935 CrossRef CAS.
  9. K. Ye, X. H. Niu, H. W. Song, L. J. Wang and Y. X. Peng, Combining CeVO4 oxidase-mimetic catalysis with hexametaphosphate ion induced electrostatic aggregation for photometric sensing of alkaline phosphatase activity, Anal. Chim. Acta, 2020, 1126, 16–23 CrossRef CAS PubMed.
  10. Z. D. Liu, K. Sun, M. Z. Wei and Z. Ma, Phosphorus-doped cerium vanadate nanorods with enhanced photocatalytic activity, J. Colloid Interface Sci., 2018, 531, 618–627 CrossRef CAS PubMed.
  11. Y. Q. Shen, Y. C. Huang, S. J. Zheng, X. F. Guo, Z. X. Chen, L. M. Peng and W. P. Ding, Nanocrystals of CeVO4 doped by metallic heteroions, Inorg. Chem., 2011, 50, 6189–6194 CrossRef CAS PubMed.
  12. J. J. Ding, X. Liu, M. Wang, Q. Liu, T. M. Sun, G. Q. Jiang and Y. F. Tang, Controlled synthesis of CeVO4 hierarchical hollow microspheres with tunable hollowness and their efficient photocatalytic activity, CrystEngComm, 2018, 20, 4499–4505 RSC.
  13. M. Moniruddin, E. Oppong, D. Stewart, C. McCleese, A. Roy, J. Warzywoda and N. Nuraje, Designing CdS-based ternary heterostructures consisting of Cometal and CoOx cocatalysts for photocatalytic H2 evolution under visible light, Inorg. Chem., 2019, 58, 12325–12333 CrossRef CAS PubMed.
  14. Y. R. Lv, R. Huo, S. Y. Yang, Y. Q. Liu, X. J. Li and Y. H. Xu, Self-assembled synthesis of PbS quantum dots supported on polydopamine encapsulated BiVO4 for enhanced visible-light-driven photocatalysis, Sep. Purif. Technol., 2018, 197, 281–288 CrossRef CAS.
  15. T. K. Jia, F. Fua, J. L. Li, Z. Deng, F. Long, D. S. Yu, Q. Cui and W. M. Wang, Rational construction of direct Z-scheme SnS/g-C3N4 hybrid photocatalyst for significant enhancement of visible-light photocatalytic activity, Appl. Surf. Sci., 2020, 499, 143941 CrossRef CAS.
  16. X. L. Zhu, P. Wang, M. M. Li, Q. Q. Zhang, E. A. Rozhkova, X. Y. Qin, X. Y. Zhang, Y. Dai, Z. Y. Wang and B. B. Huang, Novel high-efficiency visible-light responsive Ag4(GeO4) photocatalyst, Catal. Sci. Technol., 2017, 7, 2318–2324 RSC.
  17. S. Mohanty, P. Babu, K. Parida and B. Naik, Surface-plasmon-resonance-induced photocatalysis by core–shell SiO2@Ag NCs@Ag3PO4 toward water-splitting and phenol oxidation reactions, Inorg. Chem., 2019, 58, 9643–9654 CrossRef CAS PubMed.
  18. P. Babu, S. Mohanty, B. A. Naik and K. Parida, Synergistic effects of boron and sulfur codoping into graphitic carbon nitride framework for enhanced photocatalytic activity in visible light driven hydrogen generation, ACS Appl. Energy Mater., 2018, 1, 5936–5947 CrossRef.
  19. M. Ganeshbabu, N. Kannan, P. S. Venkatesh, G. Paulraj, K. Jeganathan and D. MubarakAli, Synthesis and characterization of BiVO4 nanoparticles for environmental applications, RSC Adv., 2020, 10, 18315–18322 RSC.
  20. P. Babu, S. Mohanty, B. Naik and K. Parida, Serendipitous assembly of mixed phase BiVO4 on B-Doped g-C3N4: an appropriate p–n heterojunction for photocatalytic O2 evolution and Cr(VI) reduction, Inorg. Chem., 2019, 58, 12480–12491 CrossRef CAS PubMed.
  21. N. A. Mohamed, J. Safaei, A. F. Ismail, M. N. Khalid, M. F. Jailani, M. F. Noh, N. A. Arzaee, D. Zhou, J. S. Sagu and M. A. Teridi, Boosting photocatalytic activities of BiVO4 by creation of g-C3N4/ZnO@BiVO4 heterojunction, Mater. Res. Bull., 2020, 125, 110779 CrossRef CAS.
  22. M. Wang, T. M. Sun, Y. J. Shi, G. Q. Jiang and Y. F. Tang, 3D hierarchical ZnOHF nanostructures: synthesis, characterization and photocatalytic properties, CrystEngComm, 2014, 16, 10624–10630 RSC.
  23. H. Salari and H. Yaghmaei, Z-Scheme 3D Bi2WO6/MnO2 heterojunction for increased photoinduced charge separation and enhanced photocatalytic activity, Appl. Surf. Sci., 2020, 532, 147413 CrossRef CAS.
  24. J. L. Zhou, M. Wu, Y. J. Zhang, C. G. Zhu, Y. W. Fang, Y. F. Li and L. Yu, 3D hierarchical structures MnO2/C: a highly efficient catalyst for purification of volatile organic compounds with visible light irradiation, Appl. Surf. Sci., 2018, 447, 191–199 CrossRef CAS.
  25. Y. Y. Guo, Y. X. Mo, H. H. Cui, M. Wang, Y. F. Tang and T. M. Sun, Green and facile synthesis of hierarchical ZnOHF microspheres for rapid and selective adsorption of cationic dyes, J. Mol. Liq., 2021, 329, 115529 CrossRef CAS.
  26. G. Lu, Z. S. Lun, H. Y. Liang, H. Wang, Z. Li and W. Ma, In situ fabrication of BiVO4–CeVO4 heterojunction for excellent visible light photocatalytic degradation of levofloxacin, J. Alloys Compd., 2019, 772, 122–131 CrossRef CAS.
  27. I. Othman, J. H. Zain, M. A. Haija and F. Banat, Catalytic activation of peroxymonosulfate using CeVO4 for phenol degradation: an insight into the reaction pathway, Appl. Catal., B, 2020, 266, 118601 CrossRef.
  28. T. A. King, J. M. Kandemir, S. J. Walsh and D. R. Spring, Photocatalytic methods for amino acid modification, Chem. Soc. Rev., 2021, 50, 39–57 RSC.
  29. Y. X. Guo, S. W. Lin, X. Li and Y. P. Liu, Amino acids assisted hydrothermal synthesis of hierarchically structured ZnO with enhanced photocatalytic activities, Appl. Surf. Sci., 2016, 384, 83–91 CrossRef CAS.
  30. N. G. Naumov, M. S. Tarasenko, A. V. Virovets, Y. Kim, S. J. Kim and V. E. Fedorov, Glycerol as ligand: the synthesis, crystal structure, and properties of compounds [Ln2(H2L)2(H3L)4][Re6Q8(CN)6], Ln = La, Nd, Gd, Q = S, Se, Eur. J. Inorg. Chem., 2006, 298–303 CrossRef CAS.
  31. H. W. Liu and J. M. Chang, CeVO4 yolk–shell microspheres constructed by nanosheets with enhanced lithium storage performances, J. Alloys Compd., 2020, 849, 156682 CrossRef CAS.
  32. A. Phuruangrat, T. Thongtem and S. Thongtem, Hydrothermal synthesis and characterization of Dy-doped CeVO4 nanorods used for photodegradation of methylene blue and rhodamine B, J. Rare Earths, 2020 DOI:10.1016/j.jre.2020.11.005.
  33. J. R. Guan, J. Z. Li, Z. F. Ye, D. Y. Wu, C. Y. Liu, H. Q. Wang, C. C. Ma, P. W. Huo and Y. S. Yan, La2O3 media enhanced electrons transfer for improved CeVO4@halloysite nanotubes photocatalytic activity for removing tetracycline, J. Taiwan Inst. Chem. Eng., 2019, 96, 281–298 CrossRef CAS.
  34. W. C. Ding, X. Lin, G. H. Ma and Q. F. Lu, Designed formation of InVO4/CeVO4 hollow nanobelts with Z-scheme charge transfer: synergistically boosting visible-light-driven photocatalytic degradation of tetracycline, J. Environ. Chem. Eng., 2020, 8, 104588 CrossRef CAS.
  35. X. B. Li, S. W. Yang, J. Sun, P. He, X. G. Xu and G. Q. Ding, Tungsten oxide nanowire-reduced graphene oxide aerogel for high-efficiency visible light photocatalysis, Carbon, 2014, 78, 38–48 CrossRef CAS.
  36. P. Babu and B. Naik, Cu–Ag bimetal alloy decorated SiO2@TiO2 hybrid photocatalyst for enhanced H2 evolution and phenol oxidation under visible light, Inorg. Chem., 2020, 59, 10824–10834 CrossRef CAS PubMed.
  37. S. W. Yang, C. C. Ye, X. Song, L. He and F. Liao, Theoretical calculation based synthesis of a poly(p-phenylenediamine)–Fe3O4 composite: a magnetically recyclable photocatalyst with high selectivity for acid dyes, RSC Adv., 2014, 4, 54810 RSC.
  38. N. Li, Z. T. Liu, M. Liu, C. R. Xue, Q. Chang, H. Q. Wang, Y. Li, Z. C. Song and S. L. Hu, Facile synthesis of carbon dots@2D MoS2 heterostructure with enhanced photocatalytic properties, Inorg. Chem., 2019, 58, 5746–5752 CrossRef CAS.
  39. G. Lu, F. Wang and X. J. Zou, Hydrothermal synthesis of m-BiVO4 and m-BiVO4/BiOBr with various facets and morphologies and their photocatalytic performance under visible light, J. Alloys Compd., 2017, 697, 417–426 CrossRef.

Footnote

Electronic supplementary information (ESI) available. See DOI: 10.1039/d1qm00770j

This journal is © the Partner Organisations 2021