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Article

Well-Defined Ultrasmall V-NiP2 Nanoparticles Anchored g-C3N4 Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H2 Evolution

by
Mengfan Niu
1,2,
Liyun Cao
1,2,*,
Qianqian Liu
3,
Xiaoyi Li
1,2,
Qian Chen
1,2,
Dinghan Liu
4,
Wenbin Li
1,
Jianfeng Huang
1,2,* and
Liangliang Feng
1,2,*
1
Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science and Technology, Xi’an 710021, China
2
School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China
3
School of Materials Science and Engineering, Xi’an University of Science and Technology, Xi’an 710021, China
4
School of Electronic Information and Artificial Intelligence, Shaanxi University of Science and Technology, Xi’an 710021, China
*
Authors to whom correspondence should be addressed.
Catalysts 2022, 12(9), 998; https://doi.org/10.3390/catal12090998
Submission received: 30 July 2022 / Revised: 31 August 2022 / Accepted: 1 September 2022 / Published: 5 September 2022
(This article belongs to the Special Issue Innovative Strategies for (Photo)Electrocatalytic Water Splitting and CO2 Reduction)
Browse Figures
Versions Notes

Abstract

:
Exploring low-cost and highly active, cost-effective cocatalysts is of great significance to improve the hydrogen evolution performance of semiconductor photocatalysts. Herein, a novel ultrasmall V-doped NiP2 nanoparticle, as an efficient cocatalyst, is reported to largely upgrade the photocatalytic hydrogen evolution reaction (HER) of g-C3N4 nanosheets under visible-light irradiation. Experimental results demonstrate that V-NiP2 cocatalyst can enhance the visible-light absorption ability, facilitate the separation of photo-generated electron-hole pairs and boost the transfer ability of electrons of g-C3N4. Moreover, the V-NiP2/g-C3N4 hybrid exhibits prominent photocatalytic HER activity 17 times higher than the pristine g-C3N4 counterpart, even outperforming the 1 wt.% platinum-loaded g-C3N4. This work displays that noble-metal-free V-NiP2 cocatalyst can serve as a promising and efficient alternative to Pt for high-efficiency photocatalytic H2 evolution.

Graphical Abstract

1. Introduction

The excessive dependence on non-renewable fossil fuels has largely promoted the research on sustainable clean energy [1,2,3]. Hydrogen energy is widely regarded as an ideal green fuel alternative to fossil ones, and thus it is highly urgent and significant to find an effective, environmentally friendly approach to producing H2 [4,5,6,7]. Photocatalytic water splitting holds great promise in terms of clean, large-scale and sustainable hydrogen production, whose hydrogen evolution efficiency extremely depends on the catalytic properties of photocatalysts [8,9,10,11]. In order to capture and utilize the visible light that dominates in the solar energy spectrum, it is quite imperative to explore the highly active and stable visible-light-driven photocatalysts for hydrogen evolution reaction (HER).
At present, a large number of photocatalysts are applied to hydrogen production from water under visible light. Graphitic carbon nitride (g-C3N4), a promising metal-free semiconducting polymer, has been given widespread attention in the realm of photocatalytic water splitting, photodegradation of pollutants and photocatalytic reduction in CO2 due to its advantages of being environmentally benign and low cost, with excellent chemical stability and a suitable band gap of about 2.7 eV [12,13,14,15]. However, the insufficient light absorption and rapid recombination of photo-generated electron-hole pairs have restricted the photocatalytic activity of pure g-C3N4 [11,16]. In recent years, researchers have made a lot of effort to improve the activity of g-C3N4, such as controlling its structure and morphology, coupling with other cocatalysts, and constructing the heterostructure [17,18,19,20,21]. Noble metal Pt is a brilliant cocatalyst of g-C3N4, but its scarce reserves and exorbitant price greatly hamper its practice applications [22,23]. In order to improve the photocatalytic HER performance of g-C3N4 under visible light, it has been an urgent task to develop cheap, efficient cocatalysts. It is reported that transition metal phosphide (TMP) catalysts are considered promising to replace precious metal-based cocatalysts to improve photocatalytic HER efficiency [24,25,26,27,28]. Thereinto, NiP2 possesses the characteristics of good electrical conductivity, corrosion resistance and stable chemical structure so that it can be applied as an electrode material for a metal ion battery and electrocatalysis [29,30,31]. Most recently, NiP2 as a cocatalyst has attracted a lot of attention in relation to photocatalytic hydrogen evolution. For example, Yan et al. reported a novel NiP2/Cu3P p-n heterojunction cocatalyst for improving the photocatalytic hydrogen evolution of g-C3N4; this material has good HER activity but unsatisfactory stability [32]. Yang et al. designed a novel NiP2/g-C3N4 heterojunction via a homogeneous precipitation method assisted by a thermal phosphorization reaction, in which NiP2 nanoparticles agglomerated severely, resulting in weak light absorption [33]. Thus, the incorporation of ultrasmall NiP2 nanoparticles into g-C3N4 for boosted photocatalytic HER performance is worthy of consideration. In addition, metal (Mn, Cr, V) doping is confirmed to be an effective route to improve the catalytic HER performance of semiconductors [34,35,36]. For instance, V-doped MoS2 material presented good HER activity because the V-doping is conducive to optimizing the electronic structure, increasing the active site, and accelerating the electronic transfer process of the pristine MoS2 [37]. Therefore, it is highly valuable to explore whether V-NiP2 can be an effective cocatalyst of g-C3N4 for photocatalytic HER.
In this work, V-NiP2 was reported, for the first time, as a cocatalyst of g-C3N4, and the as-synthesized V-NiP2/g-C3N4 material showed prominent photocatalytic HER under visible light (≥420 nm), even outperforming the 1 wt.% Pt-loaded g-C3N4. Such excellent photocatalytic activity of V-NiP2/g-C3N4 is mainly attributed to the enhanced absorption capability of visible light, fast electron transfer rate, and the depressed recombination of photogenerated electron-hole pairs, as well as abundant catalytic sites over the V-NiP2-loading g-C3N4 nanosheets.

2. Results and Discussion

The X-ray diffraction (XRD) patterns in Figure 1a are utilized to identify the crystal structure of pure g-C3N4 and V-NiP2/g-C3N4. As shown in Figure 1a, for the pure g-C3N4, two strong XRD diffraction peaks at 13.1° and 27.8° correspond to the (100) plane of the in-plane structural packing motif of tristriazine and the (200) plane of the interlayer stacking with aromatic systems, respectively (PDF#87-1526) [38,39,40]. In addition, some obvious diffraction peaks at 28.34°, 32.85°, 36.86°, 40.52, 47.14°, 55.92°, 58.64°, 61.25°, 63.87°, 76.08° and 78.43°, which are matched well with the (111), (200), (210), (211), (220), (311), (222), (320), (321) and (331) planes of NiP2 (JCPDS#21-0590), respectively [41]. The results indicate that the V-Ni2P/G-C3N4 composite is successfully prepared through the phosphating-calcination process. Figure 1b–d and Figure S1 record the surface chemical states of C, N, V, Ni and P for V-NiP2/g-C3N4 by using X-ray photoelectron spectroscopy (XPS). The C 1s spectra are shown in Figure S1a, three obvious deconvolution peaks at 284.6 eV, 286.02 eV and 288.25 eV can be observed, which correspond to the C–C and C–NH2 group, and the sp2-hybridized N–C=N in the aromatic ring, respectively [42]. The supreme deconvolution peaks of N 1 s in Figure S1b at 398.2 eV are assigned to the C–N=C structure from g-C3N4, the other peaks at 398.2 eV, 398.9 eV, 400.5 eV and 404.1 eV are attributed to C–N=C, N–(C)3, C–N–H and π excitations of the C=N conjugated structures in g-C3N4 [43]. Figure 1b demonstrates the presence of V, which has two deconvolution peaks at 516.9 eV for the V 2p3/2 and 524.4 eV for V 2p1/2 ascribed to the V–P bond [44]. As shown in Figure 1c, two peaks of Ni 2p3/2 (856.4 eV) and Ni 2p1/2 (874.4 eV) for V-NiP2/g-C3N4 can be attributed to Ni2+; the peaks at 862.6 eV and 880.6 eV correspond to Ni 2p3/2 and Ni 2p1/2, respectively [45], and the Ni-P binding energy is located at 853.7 eV [46]. For the P 2p XPS spectrum in Figure 1d, the peak appearing at 130 eV is attributed to the Ni-P bond, while the peak at 133.6 eV is due to the inevitable surface oxidation of P [47].
The SEM images in Figure S2a,b show the morphology and microstructure of g-C3N4 and V-NiP2/g-C3N4 samples. Pure g-C3N4 presents an irregular bulk morphology stacked by nanosheets in Figure S2a. While V-NiP2/g-C3N4 displays the crossed nanosheet structure attached with nanoparticles.
We further characterize the microstructure of the V-NiP2/g-C3N4, as shown in Figure 2. As shown in Figure 2a, it can be observed that a large number of nanoparticles grow on the nanosheets. As shown in Figure 2b, we have an in-depth observation of the nanoparticles, and it can be seen that the obvious lattice spacing of 0.27nm corresponds to the (200) interplanar spacing of cubic NiP2 (PDF#21-0590) [30]. To obtain the size distribution of the V-NiP2 cocatalyst, some more HRTEM images of V-NiP2/g-C3N4 photocatalyst were made (Figure S3), and the size of V-NiP2 nanoparticles was not considerably uniform and was examined to 3–8 nm due to the employed solid calcination method. The elemental mapping of V-NiP2/g-C3N4 is presented in Figure 2e, and C, N, Ni, V and P elements are uniformly distributed in the whole photocatalyst, illustrating that the V-Ni2P nanoparticles are dispersedly loaded on the surface of the g-C3N4 nanosheet surface. All these characterizations strongly indicate that the NiV-LDH precursor was successfully converted into V-NiP2 via a phosphorization reaction.
In order to determine the photocatalytic hydrogen evolution activity of all samples, photocatalytic tests were carried out with triethanolamine acid (TEOA) as a sacrificial agent under a 300 W lamp irradiation for 4 h. As presented in Figure 3a, pure g-C3N4 shows trace hydrogen evolution amounts due to the fast photogenerated carrier recombination and low-light absorption capacity [48]. However, V-NiP2/g-C3N4 composites present an obvious improved HER performance with a hydrogen production rate of 1426.82 µmol g−1, even higher than the 1%wt Pt/g-C3N4 (1116 µmol g−1). Furthermore, the as-prepared V-NiP2/g-C3N4 material exhibits much higher than most of the other g-C3N4-based photocatalysts (Table S1) [23,26,27,30,36,37,38,39]. The excellent catalytic HER activity can be mainly ascribed to the following three aspects: (i) the facilitated absorption of the visible-light region of g-C3N4 due to the incorporation of black V-NiP2 nanoparticles; (ii) the enhanced electron transfer rate resulting from the good electrical conductivity of V-NiP2; and (iii) the inhibited recombination rate of photogenerated electron-hole pairs on the g-C3N4 photocatalyst because the V-NiP2, as the electron trapping agent, can capture the photo-generated electron quickly. To evaluate the long-term stability of V-NiP2/g-C3N4, five cycles of H2 production experiments are shown in Figure 3b, no distinct decrease in the hydrogen evolution amount is observed, illustrating that V-NiP2/g-C3N4 maintains good stability. In order to verify the structure’s stability, the microstructure of V-NiP2/g-C3N4 after the test is characterized by HRTEM and elemental mapping, as shown in Figure S5. It can be seen that the NiP2 phase still exists in the used photocatalysts, and C, N, P, V and Ni elements are distributed in this material, indicating its structural stability during 20 h photocatalytic HER.
The light capture properties of pure g-C3N4 and V-NiP2/g-C3N4 samples were analyzed by the UV–vis diffuse reflection measurement. In Figure 4a, the pure g-C3N4 has weak absorption of visible light, but its absorption intensity gradually increases as the wavelength decreases from visible light to ultraviolet light, and its absorption edge is around 470 nm. As shown in Figure S4, the calculated pure g-C3N4 band gap is ~2.78 eV, which is consistent with the theoretical value of g-C3N4. The V-NiP2/g-C3N4 sample presents a considerably improved absorption in the UV–vis light region compared with pure g-C3N4, indicating that V-NiP2 is able to help g-C3N4 harvest more visible light [49]. As for V-NiP2/g-C3N4, the corresponding band gap is calculated to be 2.75 eV, as shown in Figure S3, and there is no obvious change compared with pure g-C3N4, implying that V-NiP2 did not dope into the g-C3N4 crystal lattice to change its band gap. This phenomenon indicates that V-NiP2 as a g-C3N4 cocatalyst, effectively promotes the visible-light absorption capacity of the V-NiP2/g-C3N4 photocatalyst.
In order to verify the interfacial charge separation of V-NiP2/g-C3N4, Figure 4b displays the photoluminescence spectra of g-C3N4 and V-NiP2/g-C3N4 samples. Under the examination wavelength of 363 nm, g-C3N4 exhibits an emission peak at 483nm. The PL intensity of V-NiP2/g-C3N4 is obviously lower than that of pure g-C3N4. To reveal the transfer and separation of the photogenerated electron-hole pairs, the transient photocurrent density vs. time curves are carried out at the turn on or off the light condition. Pristine g-C3N4 and V-NiP2/g-C3N4 are coated on FTO glass, respectively, as working electrodes to dry for 24 h in the air, measured in a mixed solution of 0.5 M Na2SO4 solution under discontinuous visible-light irradiation. The pure g-C3N4 shows a weak photocurrent response at each on-off light irradiation compared to V-NiP2/g-C3N4; the notably increased photocurrent intensity of the V-NiP2/g-C3N4 phenomenon demonstrates that V-NiP2 is effective in preventing the combination of the photogenerated electron-hole pairs, which is consistent with the prolonged photogenerated charges lifetime. The electrochemical impedance spectroscopy (EIS) Nyquist plots in Figure 4d show that V-NiP2/g-C3N4 displays a much smaller semicircle diameter compared to g-C3N4, illustrating the smaller charge transfer resistance, which contributes to the fast transfer of the photo-generated electron to the surface of V-NiP2/g-C3N4 for the improved HER.
Through discussion and analysis of the above experiment results, a plausible photocatalytic mechanism schematic in Figure 5 is carried out to help understand the specific photocatalytic hydrogen evolution reaction process of the V-NiP2/g-C3N4 photocatalyst. Under visible-light irradiation, the electrons of g-C3N4 on the valence band (VB) absorb the energy of photons, and then become excited and are transferred to the conduction band (CB), owing to the metallic character of V-NiP2. The photogenerated electrons are trapped by the V-NiP2 and easily and rapidly migrate to the V-NiP2 passing through the intimate interface, so the combination of photogenerated electron-hole pairs is retarded. Subsequently, the photo-generated electrons on the surface of V-NiP2 combine with H+ ions to form H2 molecules and are released from the water. Simultaneously, the photo-generated holes on the valence band of g-C3N4 will be timely depleted by the TEOA sacrificial reagent. Therefore, the photocatalytic hydrogen performance is greatly improved with the help of the V-NiP2 cocatalyst.

3. Materials and Methods

3.1. Chemicals and Materials

Melamine was purchased from Tianjin Kermel Chemical Co., Ltd. Nickel (II) chloride hexahydrate (NiCl2·6H2O), vanadium chloride (III) (VCl3, ≥97%), Urea (CH4N2O, ≥98%), ammonium fluoride (NH4F, ≥96%) and ethanol absolute (CH3CH2OH, ≥99.8%) were purchased from Sinopharm Chemical Reagent Co., Ltd., (Shanghai, China). Sodium hypophosphite (NaH2PO2, ≥99%) and chloroplatinic acid hexahydrated (H2PtCl6·6H2O, ≥37%) were purchased from Aladdin Reagent Co., Ltd., (Shanghai, China). Triethanolamine (N(CH2CH2OH)3, ≥98%) was purchased from Tianli Chemical Reagent Co, Ltd., (Tianjin, China). All chemicals are analytical grade and used without further purification.

3.2. Synthesis of the V-NiP2/g-C3N4 Composite

3.2.1. Synthesis of Bulk g-C3N4

Bulk g-C3N4 was synthesized by calcining melamine in a muffle furnace with the temperature kept at 550 °C for 4 h with a heating rate of 5 °C min−1. After cooling down to room temperature, the yellow product of g-C3N4 was ground into power in an agate mortar for further use.

3.2.2. Synthesis of the NiV-LDH/g-C3N4 Precursor

The NiV-LDH/g-C3N4 precursor was prepared by a hydrothermal method. Specifically, 0.475 g of NiCl2·6H2O, 0.063 g of VCl3, 1 g of Urea and 0.24 g of NH4F were put into a clean beaker with 40 mL of deionized water, then 3 g of g-C3N4 was added into the beaker and stirred for 30 min. Then, it was transferred into a Teflon-lined Autoclave, maintained at 120 °C for 16 h. After cooling down to room temperature, the depositions were separated and washed with deionized water and absolute ethanol three times, separately. The obtained products were dried in an oven at 60 °C overnight, following which we obtained the 7.8%wt NiV-LDH/g-C3N4 precursor.

3.2.3. Synthesis of V-NiP2/g-C3N4 Composite

Firstly, 2 g of NaH2PO2 was placed upstream of a big porcelain boat, and 200 mg of prepared 7.8%wt NiV-LDH/g-C3N4 precursor was put downstream of the big porcelain boat, then transferred into a tube furnace and calcined in the Ar gas atmosphere at 500 °C for 2 h with a heating rate of 5 °C min−1.

3.3. Characterizations

The crystal phases of the materials were examined by Rigaku, D/max-2200pc X-ray diffractometer (XRD) with Cu Kα irradiation at a scanning rate of 8° min−1. The morphology and microstructures were investigated using field emission scanning electron microscopy (Hitachi, S4800) and transmission electron microscopy (Tecnai G2 F20S-TWIN), respectively. The surface elemental composition and chemical state were analyzed by X-ray photoelectron spectroscopy (XPS) of a Surface Science Instruments Spectrometer with monochromatic Al Kα source. The Ultraviolet–visible (UV-vis) absorption spectra were obtained on Cary 5000 UV–vis spectrometer (Agilent). The photoluminescence (PL) spectra and time-resolved photoluminescence decay spectra were measured on Edinburgh FS5 spectrophotometer.

3.4. Photocatalytic Hydrogen Evolution Measurements

The photocatalytic hydrogen generation performance of the as-prepared V-NiP2/g-C3N4 was evaluated by an automatic online photocatalytic test system (Labsolar-6A, Beijing Perfectlight Co., Ltd., Beijing, China). An amount of 50 mg of photocatalyst was firstly dispersed with strong stirring for 0.5 h in the 80 mL of slurry solution containing 15 mL of triethanolamine (TEOA, 15 vol%) at room temperature. Before the photocatalytic experiment, the slurry was transferred into a quartz flask and then a continuous magnetic stirrer was applied. Before light irradiation, the Labsolar-6A reaction system was bubbled with N2 to remove the air. Using Agilent gas chromatography (GC-7890B, America) with N2 as the carrier gas and TCD (Thermal Conductivity Detector) as the detector.

3.5. Photoelectrochemical Measurements

Transient photocurrent response and electrochemical impedance spectroscopy (EIS) measurements were performed on an electrochemical workstation (CHI 660E, Shanghai Chenhua Instruments, Shanghai, China) using three standard electrodes with Pt wire, Hg/HgCl2 and 0.5 M Na2SO4 solution as a reference electrode, counter electrode and electrolyte, respectively. The working electrode was prepared on a clean FTO glass (2 cm × 2 cm). Specifically, 10 mg of photocatalyst was dispersed in 150 μL of isopropanol and 10 μL of Nafion solution, followed by sonication for 30 min. Finally, the slurry was homogenized, coated on FTO glass, and dried naturally for 24 h. The visible-light source was a 300 W Xe lamp (PLS-SXE 300 D, Beijing Perfect Light Technology Co., Ltd., Beijing, China) with a UV-cut filter (λ ≥ 420 nm).

4. Conclusions

In conclusion, a novel well-defined ultra-small V-NiP2 nanoparticle was successfully developed as an effective cocatalyst of g-C3N4 to improve photocatalytic HER activity under visible-light irradiation (≥420 nm). Benefitting from the enhanced visible-light absorption ability, the separation of photo-generated carriers was facilitated, the recombination of photogenerated electron-hole pairs was weakened, and the electron transfer ability was boosted, with the resulting V-NiP2/g-C3N4 hybrid exhibiting prominent photocatalytic HER activity 17 times higher than the pristine g-C3N4 counterpart, even outperforming the 1 wt.% platinum-loaded g-C3N4. Our work shown here injects new impetus to develop transition metal phosphides as low-cost and high-performance cocatalysts of g-C3N4 for efficient photocatalytic HER.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal12090998/s1, Figure S1: The XPS spectra of (a) C 1s, (b) N 1s for V-NiP2/g-C3N4; Figure S2: SEM of (a) g-C3N4, (b) V-NiP2/g-C3N4; Figure S3: HRTEM of V-NiP2/g-C3N4; Figure S4:The banding energy of pure g-C3N4 and V-NiP2/g-C3N4; Figure S5: HRTEM and elemental mapping of V-NiP2/g-C3N4 after test; Table S1: Summary of the Photocatalytic H2 Evolution on g-C3N4-Based Photocatalysts.

Author Contributions

Conceptualization, L.C. and J.H.; Data curation, M.N.; Formal analysis, Q.L. and L.F.; Investigation, M.N., X.L., W.L. and Q.C. Methodology, L.C.; L.F. and D.L. Supervision, L.C.; L.F. and J.H. Writing—original draft preparation, M.N.; Writing—review and editing, M.N. and Q.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (Nos. 22179074, 52073166), Natural Science Basic Research Program of Shaanxi (Program No. 2022JQ-481), the Xi’an Key Laboratory of Green Manufacture of Ceramic Materials Foundation (No. 2019220214SYS017CG039), the Key Program for International S&T Cooperation Projects of Shaanxi Province (2020KW-038, 2020GHJD-04), Science and Technology Program of Xi’an, China (2020KJRC0009), Science and Technology Resource Sharing Platform of Shaanxi Province (2020PT-022), Science and Technology Plan of Weiyang District, Xi’an (202009), Open foundation of Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry, Ministry of Education (KFKT2020-01).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) XRD patterns of g-C3N4 and V-NiP2/g-C3N4; The XPS spectra of (b) V 2p. (c) Ni 2p, and (d) P 2p for V-NiP2/g-C3N4.
Figure 1. (a) XRD patterns of g-C3N4 and V-NiP2/g-C3N4; The XPS spectra of (b) V 2p. (c) Ni 2p, and (d) P 2p for V-NiP2/g-C3N4.
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Figure 2. (a,c) TEM of V-NiP2/g-C3N4, (b) HRTEM of V-NiP2/g-C3N4; (d,e) elemental mapping of C, N, Ni, V, and P, respectively.
Figure 2. (a,c) TEM of V-NiP2/g-C3N4, (b) HRTEM of V-NiP2/g-C3N4; (d,e) elemental mapping of C, N, Ni, V, and P, respectively.
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Figure 3. (a) Photocatalytic H2 evolution rate of g-C3N4, V-NiP2/g-C3N4 and 1%wt Pt/g-C3N4; (b) The cycling stability experiments of photocatalytic H2 evolution for V-NiP2/g-C3N4 under visible light irradiation for 20 h.
Figure 3. (a) Photocatalytic H2 evolution rate of g-C3N4, V-NiP2/g-C3N4 and 1%wt Pt/g-C3N4; (b) The cycling stability experiments of photocatalytic H2 evolution for V-NiP2/g-C3N4 under visible light irradiation for 20 h.
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Figure 4. (a) UV–vis diffuse reflection spectra of pure g-C3N4 and V-NiP2/g-C3N4; (b) The photoluminescence (PL) spectra of g-C3N4 and V-NiP2/g-C3N4; (c) Transient photocurrent responses of g-C3N4 V-NiP2/g-C3N4; (d) EIS Nyquist plots of g-C3N4 and V-NiP2/g-C3N4 in 0.5M Na2SO4 solution visible light irradiation.
Figure 4. (a) UV–vis diffuse reflection spectra of pure g-C3N4 and V-NiP2/g-C3N4; (b) The photoluminescence (PL) spectra of g-C3N4 and V-NiP2/g-C3N4; (c) Transient photocurrent responses of g-C3N4 V-NiP2/g-C3N4; (d) EIS Nyquist plots of g-C3N4 and V-NiP2/g-C3N4 in 0.5M Na2SO4 solution visible light irradiation.
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Figure 5. Photocatalytic mechanism schematic of V-NiP2/g-C3N4 photocatalyst for H2 evolution under visible-light irradiation.
Figure 5. Photocatalytic mechanism schematic of V-NiP2/g-C3N4 photocatalyst for H2 evolution under visible-light irradiation.
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Niu, M.; Cao, L.; Liu, Q.; Li, X.; Chen, Q.; Liu, D.; Li, W.; Huang, J.; Feng, L. Well-Defined Ultrasmall V-NiP2 Nanoparticles Anchored g-C3N4 Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H2 Evolution. Catalysts 2022, 12, 998. https://doi.org/10.3390/catal12090998

AMA Style

Niu M, Cao L, Liu Q, Li X, Chen Q, Liu D, Li W, Huang J, Feng L. Well-Defined Ultrasmall V-NiP2 Nanoparticles Anchored g-C3N4 Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H2 Evolution. Catalysts. 2022; 12(9):998. https://doi.org/10.3390/catal12090998

Chicago/Turabian Style

Niu, Mengfan, Liyun Cao, Qianqian Liu, Xiaoyi Li, Qian Chen, Dinghan Liu, Wenbin Li, Jianfeng Huang, and Liangliang Feng. 2022. "Well-Defined Ultrasmall V-NiP2 Nanoparticles Anchored g-C3N4 Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H2 Evolution" Catalysts 12, no. 9: 998. https://doi.org/10.3390/catal12090998

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