English

• Artificial photosynthesis based on semiconductors is considered to be a hopeful technology to solve the worldwide energy crisis and environmental pollution^[1-4]. However, a problem is that only ultraviolet (UV) light, which accounts for 5% of the total solar energy, can be harvested by some commonly used semiconductors, such as TiO₂, ZnO, and SnO₂. Compared with UV light, visible and NIR light has a strong penetrating capacity, which is of benefit for sufficient contact with substrates and solid-liquid photocatalytic process^[5-7]. Furthermore, the photocatalytic activity over most photocatalysts is only moderate due to the high recombination rate of photo - generated carriers in the semiconductor^[8-9]. Therefore, it must be of significance to explore high-efficiency photocatalysts with Vis-NIR response.

  Ternary metal oxide has been intensively investigated in the fields of fuel cells, DRM catalysis, and photocatalysis owing to their unique structures and high stability^[10-12]. However, there exist much fewer reports on the use of ternary metal oxide material as active photocatalysts for improving H₂ evolution under Vis-NIR light irradiation. Qin fabricated ZnO/ZnFe₂O₄ nanocomposite for organic dye degradation, which exhibits excellent photocatalytic performance due to the formation of heterojunction and the enhanced light absorption in the Vis-NIR region with the introduction of ZnFe₂O₄^[13]. Ding demonstrated that CdS/NiTiO₃ show superior photocatalytic activity for H₂ evolution in the Vis-NIR region because the NiTiO₃ show NIR light response which will contribute to H₂ evolution^[14]. The above research implies that the ternary metal oxide exhibits NIR light absorption which will contribute to photocatalysis, thus the ternary metal oxide may be an effective candidate for the development of wide - spectrum responsive photocatalysts^[15-16]. Ternary metal oxide lanthanum nickelate (LaNiO₃) has been demonstrated as an active photocatalyst for H₂ evolution. In the crystal structure of LaNiO₃, the La cation is 12-fold coordinated and the Ni cation is 6 - fold coordinated to the oxygen anions. The strong hybridization between the O2p and the transition-metal 3d orbitals in the [NiO₆] octahedra could induce structural distortions and/or Ni site valence transformations, thus modifying the physicochemical properties for enhanced performance^[17-19]. LaNiO₃ has a narrow band gap of 1.9 eV which can be excited by visible light. Moreover, LaNiO₃ shows intense light absorption during the Vis - NIR region and exhibits upconversion luminescence under NIR light irradiation which may endow LaNiO₃ with photocatalysis activity under Vis-NIR light irradiation. Metal sulfides have been extensively studied for photocatalytic H₂ under visible light irradiation due to their narrower band gaps and lower conduction band (CB) positions. Among various metal sulfides, CdS exhibit photocatalytic activity for H₂ evolution in the presence of a sacrificial agent under visible light irradiation^[20-22]. Unfortunately, the pure CdS still show lower activity and serious photocorrosion caused by the high recombination rate of the photoinduced electron-hole pairs. There are several methods to overcome its drawbacks, and the construction of direct Zscheme heterojunction is an effective approach to both improve photocatalytic activity and inhibit photocorrosion^[23-24].

  Compared with the common type-Ⅱ heterojunction, the direct Z-scheme heterojunction is more favorable which can not only accelerate the spatial separation efficiency of photoinduced electron -hole pairs but also maximize the higher reduction and oxidation potentials in hybrid photocatalysts. In the direct Z - scheme heterojunction system, the photoinduced electrons on the CB of component A will recombine with the holes on the valence band (VB) of component B (Fig. 1). Consequently, the photoinduced electrons and holes accumulated on the CB of component B and the VB of component A can be used for reduction and oxi - dation reaction, respectively. Hence, the direct Z - scheme photocatalytic heterojunction achieves high redox potential and effective spatial separation of photoinduced electron-hole pairs, contributing to photocatalytic reaction. The construction of direct Z - scheme heterojunction between CdS and suitable semiconductors has indeed been verified to be an effective way to achieve superior photocatalytic performance^[25-26]. The CB position of LaNiO₃ (0.21 V) is higher than the VB position of CdS, and thus photo-generated electrons in the CB of LaNiO₃ can recombine with the photo - generated holes in the VB of CdS in LaNiO₃/CdS composites, which makes it possible to construct the direct Z - scheme heterojunction. Thus, it can be anticipated that the hybridization of CdS with LaNiO₃ may form a direct Z - scheme heterojunction photocatalyst for solar energy conversion under Vis-NIR light irradiation.

  Figure 1

  

  Figure 1.  Schematic of the charge transfer in a direct Z-scheme photocatalytic system

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  Herein, a novel direct Z-scheme LaNiO₃/CdS nanohybrid with a wide spectrum response was fabricated via a refluxing method and employed as a novel photocatalyst for H₂ evolution under VisNIR light illumination. The LaNiO₃/CdS nanohybrid exhibited improved photocatalytic performance for photocatalytic performance due to the construction of direct Z-scheme heterojunction between LaNiO₃ and CdS, which was demonstrated by photoelectrochemical (PEC) tests. Moreover, LaNiO₃ exhibited luminescence at 406 and 628 nm when excited at 808 nm, which means that LaNiO₃ can generate electrons and holes under irradiation of NIR light for H₂ evolution.

  1.   Experimental

  All reagents were supplied by Aladdin Chemical Reagent Factory (Shanghai, China) and used without further purification. Deionized (DI) water was used in this work.

  1.1   Synthesis of LaNiO₃/CdS

  The LaNiO₃ nanoparticles were synthesized according to the reported literature^[27]. The LaNiO₃/CdS nanohybrid was synthesized from as - prepared LaNiO₃ nanoparticles, Cd(OAc)₂, and thiourea via a refluxing method, as shown in Fig. 2. Cd(OAc)₂ (0.2 mol·L^-1, 10 mL) were added to a suspension containing LaNiO₃ in DMF (70 ml) under continuous stirring. After that, a solution of thiourea in DMF (1.0 mol·L^-1, 6 mL) was added to the above suspension and the resultant suspension was refluxed at 160 ℃ for 6 h. The obtained product was filtrated, washed with ethanol, and dried at 60 ℃ in a vacuum overnight. The harvested samples were denoted as w% - LaNiO₃/CdS, where w (w=0, 10, 20, 30, 40, 50, 100) is the theoretical mass fraction value of LaNiO₃ in the LaNiO₃/CdS nanohybrid. For comparison, CdS were synthesized in a similar method. The used w% - LaNiO₃/CdS nanohybrid for characterization and photocatalytic evaluation is the 30% - LaNiO₃/CdS nanohybrid unless otherwise stated.

  Figure 2

  

  Figure 2.  Schematic preparation process for the LaNiO₃/CdS nanohybrid

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  1.2   Characterization

  The powder X - ray diffraction (XRD) patterns of the samples were obtained using a Bruker D8 Advance instrument (Cu Kα irradiation, λ =0.154 06 nm, U=40 kV, I=40 mA, 2θ =20° - 80°). Transmission electron microscope (TEM) images were obtained on a transmission electron microscope (JEM - 2100F, JEOL, Japan) with an accelerating voltage of 200 kV. The scanning electron microscope (SEM) images and Energy-dispersion X-ray analysis (EDX) spectra were captured using a Hitachi New Generation SU8010 field emission scanning electron microscope with an accelerating voltage of 15 kV. The nitrogen (N₂) adsorption - desorption isotherms of the LaNiO₃/CdS nanohybrid were obtained by using an ASAP 2020M apparatus (Micromeritics Instrument Co., USA) at 77 K. The X-ray photoelectron spectroscopy (XPS) spectra were acquired on a PHI Quantum 2000 XPS system equipped with a monochromatic Al Kα source and a charge neutralizer. Photoluminescence (PL) characterizations were conducted on an Edinburgh FL/FS900 spectrophotometer at room temperature. The fluorescence lifetime was measured by recording the time-resolved fluorescence emission spectra in a Deltapro Fluorescence Lifetime System. The upconversion spectrum was measured on a Hitachi F-7000 spectrometer equipped with a commercial 808 nm NIR laser. PEC characterization was performed on a ZENNIUM electrochemical workstation (Zahner, Germany), using a three electrodes cell with a Pt electrode and Ag/AgCl electrode as the counter electrode and reference electrode, respectively. Typically, the catalyst (5 mg) was dispersed in DMF (1 mL). Then, the mixture was spread on the FTO (fluorine-doped tin oxide) glass with an area of ca. 0.25 cm² and dried at room temperature. The detailed microstructures were observed on transmission electron microscopy (TEM, JEOL model JEM 2010 EX).

  1.3   Photocatalytic H₂ evolution

  The photocatalytic H₂ evolution activity was performed in a 250 mL Pyrex reaction cell connected to a closed gas-circulation system. In a typical experiment, 20 mg of the catalyst powder was dispersed in 100 mL of an aqueous solution containing Na₂S and Na₂SO₃ as sacrificial reagents. Before the irradiation, the system was vacuumed for 30 min to remove the air. A Xe lamp (300 W) with a long-pass UV cutoff filter (λ > 420 nm) was used as the light source. The reaction temperature was controlled at 5 ℃ by cooling water during the reaction process. The produced H₂ was analyzed using a gas chromatograph (Agilent 7820A) equipped with a TDX - 01 packed column and a thermal conductivity detector (TCD).

  2.   Results and discussion

  2.1   Morphologies and structural characterization

  The crystalline phase of the samples was investigated by XRD. The XRD pattern of as - prepared LaNiO₃/CdS confirms the coexistence of CdS and LaNiO₃ (Fig. 3). In addition to peaks at 24.9°, 26.7°, 28.5°, 36.9°, 44.1°, 48.1°, and 52.2°, which can be ascribed to the (100), (002), (101), (102), (110), (103), and (112) plane of the hexagonal CdS phase (PDF No. 01 - 080 - 0006) ^[28-29], the XRD pattern of the as - prepared sample also shows diffraction peaks at 32.5°, 48.2°, and 58.6°, corresponding to the (110), (202), and (122) planes of orthorhombic LaNiO₃ (PDF No.00-033 - 0711) ^[30]. The results of powder XRD measurements demonstrate the successful formation of the LaNiO₃/CdS hybrid material.

  Figure 3

  

  Figure 3.  XRD patterns of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  The morphologies and structures of the asprepared samples were investigated by SEM and TEM. As shown in Fig. 4a, CdS presented a nanorod structure of 50 nm in diameter and 1 μm in length. Pure LaNiO₃ displayed irregular and aggregated blocks composed of agglomerated nanoparticles (Fig. 4b). For the LaNiO₃/CdS nanohybrid, LaNiO₃ was divided into nanoparti - cles and mixed with CdS nanorods (Fig. 4c). The high - resolution TEM (HRTEM) image showed lattice fringes of 0.316 and 0.384 nm, which can be assigned to the (101) and (101) planes of CdS and LaNiO₃, respectively (Fig. 4d). The clear interface of the LaNiO₃/CdS nanohybrid indicates the formation of heterojunction between LaNiO₃ and CdS component, promoting the migration of photoinduced electron-hole pairs and separation efficiency over the composites, contributing to the photocatalytic reaction. The presence of La, Ni, O, Cd, and S elements in the LaNiO₃/CdS nanohybrid is confirmed by energy - dispersive spectroscopy (EDS) spectra (Fig. S1, Supporting information). The ratio of LaNiO₃ and CdS was determined to be 1:2.1 based on the EDX results, which was comparable to the molar ratio in the starting material.

  Figure 4

  

  Figure 4.  SEM images of CdS nanorods (a), LaNiO₃ (b), and the LaNiO₃/CdS nanohybrid (c); HRTEM images of the LaNiO₃/CdS nanohybrid (d)

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  XPS analyses were conducted to determine the surface chemical composition and electronic state of the LaNiO₃/CdS nanohybrid. In the La3d core level spectra of the LaNiO₃/CdS nanohybrid (Fig. 5a), the splitting of the main peaks of La3d_5/2 and La3d_3/2 were at around 835.9 and 853.1 eV, respectively, and the shake -up satellite peaks of La3d_5/2 and La3d_3/2 were at 838.7 and 856.6 eV^[31]. As compared with pure LaNiO₃ (Fig. 5c, 835.6 and 852.6 eV, 838.2 and 855.5 eV), the binding energy of the La3d in the LaNiO₃/CdS nanohybrid shifted to a higher value by 0.4 eV, indicating an intimate interaction exists between CdS and LaNiO₃ component^[32-33]. In the meantime, the binding energy of Cd3d shifted to a lower value by 0.4 eV as compared with those of CdS (Fig. 5d, 411.6 and 404.8 eV), with Cd3d_5/2 and Cd3d_3/2 at 411.2 and 404.4 eV, respectively (Fig. 5b) ^[34]. The variation of binding energy implied that the electron transfer from LaNiO₃ to CdS. No obvious shift of the binding energy was observed for Ni, O, and S (Fig.S2a-S2c and Fig.S3a-S3c).

  Figure 5

  

  Figure 5.  XPS spectra of La3d (a) and Cd3d (b) for the LaNiO₃/CdS nanohybrid; XPS spectra of La3d (c) for LaNiO₃; XPS spectra of Cd3d (d) for CdS

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  The specific surface area and pore characteristics of the LaNiO₃/CdS nanohybrid were studied by N₂ physisorption measurements. Fig. 6 shows the obtained N₂ adsorption-desorption isotherms, which shape is categorized as the type Ⅳ isotherm with an H1 hysteresis loop. These findings indicate the presence of mesopores in the LaNiO₃/CdS nanohybrid. The BET (Brunauer-Emmett-Teller) specific surface area of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid were calculated to be approximately 14, 16, and 20 m²·g^-1, indicating the introduction of LaNiO₃ almost do not influence its surface areas. Furthermore, the existence of mesopores in the LaNiO₃/CdS nanohybrid will contribute to the mass transport for heterogeneous photoredox reactions.

  Figure 6

  

  Figure 6.  N₂ sorption isotherms of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  All the above characterization details indicate the formation of the LaNiO₃/CdS nanohybrid. Fig. 7 shows the optical absorption spectra for the obtained samples in a range of 200-1 600 nm. UV-Vis diffuse reflectance (DRS) spectra of the LaNiO₃/CdS nanohybrid showed a coupling of the light absorption of both CdS and LaNiO₃ by exhibiting an enhanced absorption in the visible light region. Moreover, the LaNiO₃/CdS nanohybrid exhibited intense light absorption in the NIR region due to the introduction of LaNiO₃, which may endow the LaNiO₃/CdS nanohybrid with photocatalytic activity under NIR light irradiation. The background noise at about 800 nm was caused by the variation of the detector.

  Figure 7

  

  Figure 7.  UV-Vis DRS spectra of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  2.2   Photocatalytic performances and mechanism discussion

  The photocatalytic H₂ evolution experiments were performed over the as - prepared catalysts with Na₂S - Na₂SO₃ as a sacrificial agent under visible light irradiation. The CdS was coupled with LaNiO₃ to enhance the photocatalytic H₂ evolution furtherly (Fig. 8a). No H₂ was produced over LaNiO₃, demonstrating that LaNiO₃ alone is not active for photocatalytic H₂ evolution, which may be caused by the lower CB position of LaNiO₃ for H₂ evolution and the sluggish migration/separation kinetics of photoinduced electrons and holes. With the addition of LaNiO₃ into CdS, the H₂ evolution rate was increased from 32 to 46 μmol·h^-1 over the LaNiO₃/CdS nanohybrid (10% - LaNiO₃/CdS). When the LaNiO₃ content increased to 30%, 30% - LaNiO₃/CdS showed the optimal photocatalytic performance with an H₂ evolution rate of 147 μmol·h^-1. Such a noble metal - free H₂ evolution rate was much higher compared with those of other CdS-based photocatalysts in the literature (Table S1). However, with LaNiO₃ content in the hybrid increased to 40% (40% - LaNiO₃/CdS), a decrease in H₂ production was observed, which may be caused by the light shielding effect of excessive LaNiO₃ and the partial coverage of active sites on CdS. Fig. 8b depicts the H₂ evolution as a function of reaction time over 30%-LaNiO₃/CdS nanohybrid. 737 μmol H₂ was produced over the LaNiO₃/CdS nanohybrid in 5 h, which was about 4.3 times that of bare CdS (172 μmol). The photocatalytic performance of 30%-LaNiO₃/CdS nanohybrid was also higher than that of 1.0% Pt/CdS photocatalyst (371 μmol). The results demonstrate that LaNiO₃ is highly active in enhancing the photocatalytic H₂ evolution of CdS - based photocatalysts. Furthermore, the H₂ evolution increased to 996 μmol in the whole Vis-NIR region. The result implied that both visible and NIR irradiation can be harvested for photocatalytic H₂ evolution over the LaNiO₃/CdS nanohybrid. All these results demonstrate that the introduction of LaNiO₃ in the LaNiO₃/CdS nanohybrid can promote the photocatalytic performance for H₂ evolution in the Vis-NIR region.

  Figure 8

  

  Figure 8.  Photocatalytic H₂ evolution over a series of w%-LaNiO₃/CdS nanohybrid with different LaNiO₃ contents (a); Time-dependent H₂ evolution over LaNiO₃, CdS, Pt/CdS, and the LaNiO₃/CdS nanohybrid under visible light and Vis-NIR irradiation (b)

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  It is generally accepted that the combining of two semiconductors with suitable CB via the construction of a heterojunction is an effective strategy to facilitate charge transport and suppress the recombination of photoinduced electron - hole pairs in semiconductor-based photocatalysis^[35-37]. Therefore, the superior photocatalytic performance observed over the LaNiO₃/CdS nanohybrid may be ascribed to the construction of heterojunction between LaNiO₃ and CdS. To confirm the existence of LaNiO₃/CdS heterojunction and its important role in H₂ evolution, a physical mixture of LaNiO₃ and CdS with a comparable LaNiO₃/CdS ratio (3:7) was used for photocatalytic H₂ evolution. Compared with the LaNiO₃/CdS nanohybrid, the physical mixture of LaNiO₃ and CdS exhibited lower activity and only 198 μmol H₂ was produced in 5 h. This finding demonstrates that the heterojunction in the LaNiO₃/CdS nanohybrid is significant for photocatalytic H₂ evolution.

  The separation and transfer efficiency of the photoinduced electrons and holes has a great effect on photocatalytic performance, so PEC tests were performed to explore the migration and separation kinetics of photoinduced electrons and holes. The room temperature photoluminescence (PL) spectra were utilized to monitor the separation-recombination rate of photoinduced electrons and holes in photocatalysts to verify the charge separation effect. As shown in Fig. 9a, CdS displayed a strong band edge emission at ca. 530 nm, which can be attributed to the high recombination rate of photogenerated charge carriers in CdS^[38-39]. The formed LaNiO₃/CdS heterojunction can facilitate the transfer of the photoinduced electron - hole pairs, in accordance with the observation that the LaNiO₃/CdS nanohybrid displayed a PL peak with the lowest intensity. The time - resolved PL (TRPL) spectra (Fig. 9b) reveal that the fluorescence lifetime of LaNiO₃/CdS (4.2 ns) was much longer than that of CdS (1.0 ns), indicating that the population of surviving electrons was increased upon the combination of LaNiO₃, consistent with the PL quenching results. Moreover, the electrochemical impedance spectra (EIS) indicate that the LaNiO₃/CdS nanohybrid exhibited a smaller semicircle in the Nyquist plots compared with CdS (Fig. 9c). This finding indicates that a lower charge transfer resistance in the LaNiO₃/CdS nanohybrid, facilitating the migration and separation of photoinduced electron - hole pairs. In addition, the transient photocurrent spectra revealed that the photocurrent of the LaNiO₃/CdS nanohybrid was much higher than that of CdS (Fig. 9d), indicating the enhanced transfer behavior of charge carriers in the LaNiO₃/CdS nanohybrid. The above results demonstrate that LaNiO₃ could effectively promote transportation and inhibit the recombination of the photoinduced electrons and holes.

  Figure 9

  

  Figure 9.  Steady-state PL spectra (a), TRPL spectra (b), EIS spectra (c), transient photocurrent responses (d) of CdS and the LaNiO₃/CdS nanohybrid

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  Based on the band structures of LaNiO₃ and CdS as well as the PEC characterizations, two possible reaction mechanisms of the photocatalytic H₂ evolution are proposed: type Ⅱ heterojunction and direct Z-scheme. The CB potential of CdS and LaNiO₃ was investigated by Mott - Schottky plots (Fig. S4), and the flat band potentials of CdS and LaNiO₃ were about -0.53 and 0.21 V (vs NHE, pH=7.0), respectively. Combined with their band - gap energies, the band structures of CdS and LaNiO₃ can be illustrated in Fig 10. According to conventional type Ⅱ heterojunction (Fig. 10a), the photoinduced electrons on the CB of CdS can transfer to the CB of LaNiO₃ for H₂ evolution. However, the potential of the photogenerated electron in the CB of LaNiO₃ is too high for H₂ evolution, which is conflicted with the enhanced photocatalytic activity of the LaNiO₃/CdS nanohybrid. Therefore, the direct Z-scheme may be the most possible mechanism for photocatalytic H₂ evolution over the LaNiO₃/CdS nanohybrid. As shown in the direct Z-scheme LaNiO₃/CdS system (Fig. 10b), the photoinduced electrons on the CB of LaNiO₃ will recombine with the photoinduced holes on the VB of CdS under visible light irradiation. In the meantime, the accumulated electrons on the CB of CdS have sufficient reduction potential for H₂ evolution, while the holes on the VB of LaNiO₃ can react with Na₂S-Na₂SO₃ to com - plete the photocatalytic redox cycle. Such a direct Z - scheme charge transfer can efficiently promote the separation of photoinduced electrons and holes, prolonging the lifetime of the electrons for boosting H₂ evolution over the LaNiO₃/CdS nanohybrid^[40-42].

  Figure 10

  

  Figure 10.  Proposed mechanism for H₂ evolution over direct Z-scheme LaNiO₃/CdS heterojunction photocatalysts

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  Fig. 11 shows the upconversion PL spectra of LaNiO₃ while excited by an 808 nm laser. The PL spectra exhibited two luminescence bands located at 406 and 628 nm, which demonstrated that LaNiO₃ could be excited by NIR light. As a result, the photoinduced electrons in CB of LaNiO₃ can recombine with the photoinduced holes in VB of CdS under Vis - NIR irradiation, facilitating the separation of the charge carrier. Moreover, the emission fluorescence at 406 nm can be absorbed by CdS in the LaNiO₃/CdS nanohybrid, which will contribute to photocatalytic H₂ evolution. This result was in accordance with the activity test results that the introduction of NIR could enhance the photocatalytic performance of the LaNiO₃/CdS nanohybrid.

  Figure 11

  

  Figure 11.  Upconversion PL spectra of LaNiO₃ while excited by an 808 nm laser

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  The cycling reactions were conducted to confirm direct Z - scheme charge transfer over the LaNiO₃/CdS nanohybrid for photocatalytic H₂ evolution, which will suppress the accumulation of photoinduced holes on CdS and consequently inhibit the photo corrosion of CdS for enhancing the photostability. As shown in Fig. 12a, the XRD pattern of the used CdS showed a new peak, ascribing to the elemental S (PDF No. 72-2402), and the CdS lost 26.7% of its original photocatalytic activity in the fourth run (Fig. 13). On the contrary, the LaNiO₃/CdS nanohybrid exhibited enhanced stability in cycling reaction. No obvious change was observed in the XRD pattern of the used LaNiO₃/CdS nanohybrid and 91.9% of its original photocatalytic activity was maintained after four runs (Fig. 12b and Fig. 13). Based on type Ⅱ heterojunction, the photoinduced electrons and holes will accumulate in LaNiO₃ and CdS, respectively, and the photoinduced holes on CdS will accelerate the photo corrosion of CdS. However, the LaNiO₃/CdS nanohybrid exhibited enhanced stability in the cycling reaction. In addition, the detected Cd²⁺ in the filtrate from the CdS suspension was 3.2 - fold that from the LaNiO₃/CdS nanohybrid. This result implies that photoinduced holes are transferred away from the CdS sites more effectively, inhibiting the oxidation of lattice S^2-. Consequently, the direct Z-scheme photocatalytic reaction mechanism can elucidate the enhanced photostability of the LaNiO₃/CdS nanohybrid.

  Figure 12

  

  Figure 12.  XRD patterns of the used and fresh CdS (a) and the LaNiO₃/CdS nanohybrid (b)

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  Figure 13

  

  Figure 13.  Cycling test of the LaNiO₃/CdS nanohybrid and CdS for photocatalytic H₂ evolution

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  3.   Conclusions

  In summary, the Vis-NIR light-responsive direct Z-scheme LaNiO₃/CdS nanohybrid was successfully synthesized and fully characterized. The as-obtained LaNiO₃/CdS nanohybrid showed superior photocatalytic activity for H₂ evolution due to the construction of LaNiO₃/CdS heterojunction as well as the enhanced light absorption in the Vis - NIR region, which was demonstrated by PEC and upconversion spectrum test. The LaNiO₃/CdS nanohybrid exhibited improved stability relative to CdS, which may be ascribed to the transfer away of photoinduced holes from CdS according to the direct Zscheme heterojunction. This work provides an effective way of enhancing NIR photocatalytic H₂ evolution based on the direct Z-scheme heterojunction photocatalyst, which will be conducive to making full use of solar energy in the future.

  Supporting information is available at http://www.wjhxxb.cn

  
  
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  Figure 1  Schematic of the charge transfer in a direct Z-scheme photocatalytic system

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  Figure 2  Schematic preparation process for the LaNiO₃/CdS nanohybrid

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  Figure 3  XRD patterns of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  Figure 4  SEM images of CdS nanorods (a), LaNiO₃ (b), and the LaNiO₃/CdS nanohybrid (c); HRTEM images of the LaNiO₃/CdS nanohybrid (d)

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  Figure 5  XPS spectra of La3d (a) and Cd3d (b) for the LaNiO₃/CdS nanohybrid; XPS spectra of La3d (c) for LaNiO₃; XPS spectra of Cd3d (d) for CdS

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  Figure 6  N₂ sorption isotherms of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  Figure 7  UV-Vis DRS spectra of LaNiO₃, CdS, and the LaNiO₃/CdS nanohybrid

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  Figure 8  Photocatalytic H₂ evolution over a series of w%-LaNiO₃/CdS nanohybrid with different LaNiO₃ contents (a); Time-dependent H₂ evolution over LaNiO₃, CdS, Pt/CdS, and the LaNiO₃/CdS nanohybrid under visible light and Vis-NIR irradiation (b)

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  Figure 9  Steady-state PL spectra (a), TRPL spectra (b), EIS spectra (c), transient photocurrent responses (d) of CdS and the LaNiO₃/CdS nanohybrid

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  Figure 10  Proposed mechanism for H₂ evolution over direct Z-scheme LaNiO₃/CdS heterojunction photocatalysts

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  Figure 11  Upconversion PL spectra of LaNiO₃ while excited by an 808 nm laser

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  Figure 12  XRD patterns of the used and fresh CdS (a) and the LaNiO₃/CdS nanohybrid (b)

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  Figure 13  Cycling test of the LaNiO₃/CdS nanohybrid and CdS for photocatalytic H₂ evolution

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