Function-reversible facets enabling SrTiO₃ nanocrystals for improved photocatalytic hydrogen evolution

Abstract

It has been widely reported that, for faceted nanocrystals, the two adjacent facets with different band levels contribute to promoted charge separation, and provide active sites for photocatalytic reduction and oxidation reaction, respectively. In such cases, only one family of facets can be used for photocatalytic hydrogen evolution. Herein, by using SrTiO₃ nanocrystals enclosed by {023} and {001} facets as a model photocatalyst, this paper proposed a strategy to achieve the full-facets-utilization of the nanocrystals for photocatalytic hydrogen via chemically depositing Pt nanoparticles on all facets. The photo-deposition experiment of CdS provided direct evidence to demonstrate that the {023} facets which were responsible for photooxidation reaction can be function-reversed for photocatalytic hydrogen evolution after depositing Pt nanoparticles, together with the {001} facets. Thus, the full-facets-utilization led to a much-improved activity for photocatalytic hydrogen, in contrast to those SrTiO₃ nanocrystals with only {001} facets deposited by Pt nanoparticles via a photo-deposition method.

Graphical abstract

Keywords

SrTiO₃ nanocrystals / crystal facets / photocatalysis / hydrogen evolution

1 Introduction

Semiconductor-based photocatalysis can directly convert solar energy into chemical energy in hydrogen molecules via the water-splitting process, which has been widely accepted as a promising approach to meet the increasing energy demand [1–11]. Despite many processes made in recent years, the photocatalytic activity for H₂ evolution is still far from practical application, mainly due to the severe charge combination in the bulk and/or at the surface of semiconducting photocatalysts [12–15]. Thus, it is of great importance to make charge efficiently separate during the photocatalytic process [16–18].

To date, various strategies have been developed to promote charge separation in the bulk and/or at the surface of photocatalysts, such as constructing heterojunction [19–40], phase junction [41–45], and surface disordering engineering [46–49]. Among these approaches, the crystal-facet engineering has been widely reported to improve the separation of photo-generated charge carriers [41,50–52]. For the faceted semiconductor nanocrystal enclosed by two different families of facets, the photo-induced electrons would be accumulated on one family of facets with a lower conduction band bottom, while the photo-induced holes would be accumulated on the other family of facets, due to the band level difference of the adjacent facets, thus leading to the spatial electron and hole separation for photoactive reduction and oxidation reactions, respectively. For example, Li et al. synthesized a water-oxidation photocatalyst of BiVO₄ decahedron enclosed by {010} and {110} facets, and found that the photo-excited electrons and holes could be transferred to the {010} and {110} facets, respectively [53,54]. They further investigated the anisotropic charge distribution on different facets of BiVO₄ decahedron via the spatially resolved SPV spectroscopy with nanoscale spatial resolution and mV sensitivity, demonstrating that the built-in electric fields in this faceted BiVO₄ resulted in an anisotropic charge transfer [55]. The similar phenomenon was also reported on a facet-engineered chalcogenide photocatalyst [56,57]. Taking Cu₂WS₄ decahedra as model photocatalysts, Li et al. revealed that Pt nanoparticles were only deposited on the {001} facets of Cu₂WS₄ via the in-situ photo-deposition method, and the {101} facets were etched during the photocatalytic reaction, indicating that the photogenerated electrons and holes could be transferred to the {001} and {101} facets of Cu₂WS₄ decahedra, respectively [56].

Previously, cube and tetrahexahedron SrTiO₃ (STO) nanocrystals were synthesized enclosed with {023} and {001} facets [58]. By tracking the deposition positions of Pt and PbO₂ in the in-situ photo-deposition process, it was demonstrated that the photogenerated electrons and holes could be transferred to the low-indexed {001} facets and high-indexed {023} facets, respectively [58]. Moreover, this anisotropic charge distribution on {001} and {023} facets still maintained even after the surface reconstruction of STO by hydrogenation [49]. However, in these cases, only one family of facets was used for photocatalytic hydrogen evolution, while the other family of facets could not be involved in the hydrogen evolution reaction. As is known, photocatalytic water splitting is a heterogeneous catalysis process, which occurs only on the surface of photocatalyst. Thus, as the efficient facet utilization of the faceted photocatalyst for hydrogen evolution increases, the photocatalytic activity increases.

In this work, taking SrTiO₃ nanocrystals enclosed by {023} and {001} facets as a model photocatalyst, a strategy was proposed to achieve the full-facets-utilization of the nanocrystal for photocatalytic hydrogen reaction by depositing Pt nanoparticles on all the exposed facets. The results of photo-deposition experiment of CdS demonstrated that the function of the {023} facets, which were used for oxidation reaction, could be reversed for photocatalytic hydrogen evolution after depositing Pt nanoparticles. Thus, the function-reversible {023} facets, together with the {001} facets, led to a higher activity of SrTiO₃ nanocrystal for photocatalytic hydrogen, in contrast to that of SrTiO₃ with Pt deposited by a photo-deposition method.

2 Materials and methods

2.1 Chemicals

Ethanolamine (EA) (NH₂CH₂CH₂OH), sodium hydroxide (NaOH), strontium nitrate (Sr(NO₃)₂), sodium borohydride (NaBH₄), methanol (CH₃OH), ethylene glycol (EG), surfer powder, toluene (C₇H₈), cadmium nitrate tetrahydrate (Cd(NO₃)₂·4H₂O) and tetrabutyl titanate (TBOT) (Ti(OC₄H₉)₄) were purchased from Sinopharm Chemical Reagent Co., Ltd. Ammonium hexachloroplatinate ((NH₄)₂PtCl₆) was offered by Alfa Aesar, A Johnson Matthey Company. All the materials were analytical grade and used without further purification, and the water used in all syntheses was deionized water with a resistivity of 18.25 MΩ·cm.

2.2 Synthesis of SrTiO₃ (STO) nanocrystals

The cube and tetrahexahedron STO nanocrystals enclosed with {023} and {001} facets were synthesized by solvothermal methods, as described in Refs. [49,58]. Briefly, 10 mmol of TBOT was dissolved into 20 mL of EA to form a transparent solution, and then a 50 mL of NaOH (3 mol/L) solution was dropped to obtain a suspension. An aqueous solution (10 mL) containing 10 mmol of Sr(NO₃)₂ was added to the suspension under stirring for 30 min. The reaction mixture was sealed in a 100 mL teflon lined stainless-steel autoclave, followed by heat treatment at 180 °C for 24 h. After cooling, the resulted white precipitate was centrifuged and washed with ethanol and deionized water five times. Finally, SrTiO₃ nanocrystals enclosed with {023} and {001} facets (STO) were obtained.

2.3 Photo-deposition (PD) of Pt and PbO₂ on STO

Photo-deposition of 2 wt.% (wt., mass fraction) Pt on the surface of STO was conducted by using (NH₄)₂PtCl₆ as the precursor. Briefly, the as-prepared STO sample (100 mg) was dispersed in an aqueous solution (220 mL) containing 20 vol.% (vol., volume fraction) methanol by a magnetic stirrer in a side irradiation Pyrex cell. A calculated (NH₄)₂PtCl₆ aqueous solution was added to the solution. After evacuation with N₂ gas, the suspension was irradiated by a 300 W Xe lamp for 5 h. Finally, the precipitate was centrifuged and washed with deionized water five times, and dried under vacuum at 80 °C overnight. The obtained sample was assigned as STO-PD. Similarly, photo-deposition of 5 wt.% PbO₂ on the surface of STO was performed by using Pb(NO₃)₂ as the precursor and KIO₃ as electron acceptor. The obtained sample was assigned as STO-PbO₂.

2.4 Chemical deposition (CD) of Pt on STO

100 mg of the as-prepared STO was dispersed in 17 mL of EG in a three-necked flask by using sonication, and a calculated EG solution containing (NH₄)₂PtCl₆ was then added into the three-necked flask under stirring for 30 min. Then, the three-necked flask was heated by an oil bath and maintained at 60 °C for 30 min. Finally, 167 mg of NaBH₄ was then added to the suspension and the suspension was stirred for 10 h. After cooling, the precipitate was centrifuged and washed with deionized water several times and dried under vacuum at 80 °C overnight. The obtained sample was assigned as STO-CD.

2.5 Photo-deposition of CdS on STO-CD

To investigate the role of Pt on {023} facets in the photocatalytic hydrogen reaction, CdS was selected to be deposited on STO-CD by a photo-deposition method. Briefly, 50 mg of STO-CD was dispersed in 200 mL of methanol. Then, 0.44 mL of toluene containing 0.44 mg of S powder and 3 mL of Cd(NO₃)₂ solution (2 mg/mL) was injected into the suspension. After evacuation with N₂ gas, the suspension was irradiated by a 300 W Xe lamp for 5 h. Finally, the precipitate was centrifuged and washed with toluene and methanol five times, and dried under vacuum at 80 °C overnight. The obtained sample was assigned as STO-CD-CdS.

2.6 Photocatalytic reaction

Photocatalytic hydrogen evolution was conducted in a Pyrex cell under full-wavelength irradiation. Briefly, 50 mg of photocatalyst powder was dispersed into 220 mL of 20 vol.% methanol solution by sonication for 30 min. After the reactor was purged with N₂ gas to eliminate air for 30 min, the suspension was irradiated by a 300 W Xe lamp for 5 h. The amount of H₂ gas was determined using an online thermal conductivity detector (TCD) gas chromatography (NaX zeolite column, TCD detector, N₂ carrier). The apparent quantum efficiency (AQE) was measured under visible light irradiation (λ = 350 ± 10 nm), and was calculated by the equation: AQE = N_e/N_p× 100%, where N_e is the number of reacted electrons and N_p is the number of incident photons.

2.7 Characterization

The optical properties of the samples were measured by a UV-vis-near-IR spectrophotometer (HITACHI U4100) equipped with a labsphere diffuse reflectance accessory within a 240−800 nm range, using BaSO₄ as the reference. The powder X-ray diffraction (XRD) characterization were conducted on a PANalytical X’pert MPD Pro diffractometer with Ni-filtered Cu Kα irradiation (λ = 1.5406 Å). The transmission electron microscopy (TEM) images, high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images, and high-resolution TEM (HRTEM) images were observed by a JEOL JEM-F200 transmission electron microscope. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Fisher ESCALAB Xi+ with monochromatic Al Kα radiation (hν = 1486.69 eV). All binding energies were referenced to the C 1s peak at 284.8 eV. The elemental analysis of the as-prepared samples was performed by an OXFORDMAX-80 energy-dispersive X-ray detector (EDX) which was mounted in the JEOL JEM-F200 transmission electron microscope.

3 Results and discussion

The cube and tetrahexahedron STO nanocrystals enclosed with {023} and {001} facets were synthesized by the solvothermal method, as shown in Fig. S1(a). Figures S1(b) and S1(c) show the scanning electron microscopy (SEM) image of STO loaded with Pt and PbO₂ nanoparticles by the photo-deposition method, respectively. It was clearly observed that Pt nanoparticles and PbO₂ nanoparticles were deposited on the surface of {001} and {023} facets of STO, respectively. This result revealed that the {023} and {001} facets provided active sites for photo-oxidation reaction and photo-reduction reaction (Fig. S1(d)), respectively. More details about the charge separation on the {001} and {023} facets of STO could be obtained in Refs. [49,58]. During the photocatalytic process, the photoexcited electrons would be trapped by the Pt nanoparticles deposited on the {001} facets of STO nanocrystals and take part in the photocatalytic hydrogen reaction (Fig.1(a)) [49,58]. As is known, the photocatalytic reaction occurs on the surface of photocatalyst. In the system of photocatalytic hydrogen evolution with hole scavengers (i.e., CH₃OH), the sacrificial agent would rapidly react with photo-generated holes, which was not the rate-determining step during the photocatalytic process, thus only leaving the photo-generated electrons in photocatalyst for hydrogen evolution. Consequently, the photocatalytic H₂ evolution reaction should be the rate-determining step in such a photocatalytic system. Hence, as the facets designed for the photocatalytic hydrogen evolution increase, the performance the photocatalyst possesses increases. Therefore, if the photo-reduction active sites (i.e., Pt cocatalyst) were constructed on all facets of STO, the {023} facets utilized for oxidation reaction would be reversibly activated for hydrogen evolution, together with the {001} facets, leading to the higher hydrogen evolution performance (Fig.1(b)).

Inspired by this assumption, Pt cocatalysts were deposited on both {001} and {023} facets of STO via a chemical deposition method (STO-CD). As a reference, the STO with Pt cocatalysts selectively deposited only on {001} facet (STO-PD) was synthesized by the photo-deposition method. XRD diffraction patterns in Fig. S2(a) revealed that both STO-PD and STO-CD possessed cubic-phase perovskite structure (JCPDS No. 00-035-0734, space group: Pm-3m), and no peaks for Pt were observed due to the relatively low content of Pt in these two samples. The SEM in Fig. S3 indicated that islanded Pt nanoparticles were distributed on both {001} and {023} facets of STO (Fig. S3), while for STO-PD, Pt nanoparticles were mainly deposited on the {001} facets of STO via the photo-deposition method (Fig. S1(b)), which was consistent with Refs. [49,58]. Furthermore, the XPS characterization in Fig. S4 revealed that the Pt nanoparticles deposited by both chemical deposition and photo-deposition methods were in the form of Pt(0), suggesting that the chemical states of Pt cocatalyst in these two samples should have no influence on their photocatalytic activities.

To directly observe the Pt distribution on the surface of STO by chemical deposition method in detail, the TEM image of a typical STO-CD nanocrystal was recorded (Fig.2(a)). Viewed from [100] direction, the STO-CD nanocrystal showed a dodecagon shape, consistent with Refs. [49,58]. It can be seen that there were some small particles with a size of less than 5 nm on both {023} and {001} facets of STO-CD nanocrystal, with the corresponding model of STO-CD illustrated by the inset i in Fig.2(a). To further investigate the small particles in detail, high-resolution TEM (HRTEM) images were recorded from the rectangle I, II, IV, and III regions, as shown in Fig.2(b)–Fig.2(e), respectively. The interplanar space of the nanoparticles shown in Fig.2(b)–Fig.2(e) was measured to be 2.27 Å, corresponding to the (111) plane of Pt metal. Fig.2(f) shows the energy-dispersive X-ray (EDX) spectrum of the point labeled in inset iii (Fig.2(a)), which was recorded from the rectangle V region in inset ii in Fig.2(a). The Cu signal came from the Cu grid, while the signals of Ti, Sr, and O came from SrTiO₃. The obvious Pt signal provided direct evidence confirming the existence of the Pt nanoparticles deposited on {023} facets of STO-CD nanocrystal. Therefore, it could be concluded that the Pt cocatalysts were successfully deposited on both {001} and {023} facets of STO by using the chemical deposition method. In addition, TEM and HRTEM images of STO-PD were also recorded to observe the Pt nanoparticles on the surface of STO-PD, as shown in Fig. S5. It can be seen that Pt nanoparticles are only deposited on the {001} facets of STO, and the size of Pt in STO-PD is less than 5 nm, which is similar to that of Pt in STO-CD, suggesting that the size of Pt nanoparticles should not contribute to the different photocatalytic activities of STO-PD and STO-CD. Moreover, without other variables introduced in the experiment, the only difference between these two samples is the position of deposited Pt, one only on {001} facets (STO-PD) and the other on both {001} and {023} facets (STO-CD).

Fig.3(a) shows the time-course photocatalytic hydrogen evolution of STO-PD and STO-CD, respectively. Obviously, the samples with Pt deposited on both {001} and {023} facets, i.e., STO-CD, exhibit a higher photocatalytic activity, which is ca. 2 times that of STO with Pt deposited on only {001} facets by the photo-deposition method (STO-PD) (Fig.3(b)). In addition, the AQE at 350 nm of the as-prepared STO-CD was calculated to be 0.83%. For the STO-PD sample, only {001} facets were used for the photocatalytic hydrogen evolution. In comparison, for STO-CD, Pt nanoparticles were deposited on both {001} and {023} facets, which may make all of the facets be activated for hydrogen evolution. Moreover, no obvious decay in photocatalytic H₂ evolution activity was observed for STO-CD over six consecutive cycles (Fig. S6), indicating the high stability of STO-CD.

To further demonstrate that the {001} and {023} facets deposited with Pt cocatalyst can be used for photocatalytic reduction reaction, i.e., hydrogen evolution, a series of ex-situ experiments were designed to identify the successful activation of {023} facets by Pt deposition. Briefly, the as-prepared STO-CD were dispersed in a methanol solution containing S powder and Cd(NO₃)₂ under the irradiation from a 300 W Xe lamp, and the obtained sample was assigned as STO-CD-CdS (Fig.4). As is known, photo-induced electrons and holes would be generated in SrTiO₃ when it is excited by the photons with an energy higher than its bandgap. During the photocatalytic process, the photo-excited electrons would be trapped by the Pt nanoparticles on the surface of photocatalyst to participate in the reduction reaction. Thus, in this designed ex-situ experiment, the electrons trapped by Pt nanoparticles are supposed to react with S to produce S²⁻ (S + 2e⁻→ S²⁻). The produced S²⁻ would then react with Cd²⁺ near Pt nanoparticles to generate CdS (S²⁻ + Cd²⁻→ CdS). Consequently, these CdS monomers would be nucleated on the surface of Pt nanoparticles to form a core-shell structured Pt@CdS on the surface of STO. Therefore, if both {023} and {001} facets deposited with Pt were used for photolytic hydrogen evolution, the CdS nanoshell would be deposited on the surface of Pt on both two facets of STO-CD (right top in Fig.4). In other words, if only the {001} facets deposited with Pt nanoparticles was used for photocatalytic hydrogen reaction, the CdS nanoshell would be only deposited on the surface of Pt on {001} facets (right bottom in Fig.4).

With the model of STO-CD-CdS proposed in Fig.5(a), after the photodeposition reaction, there were many islanded nanoparticles on both {023} and {001} facets of STO (Fig.5(b)) in the size of ca. 10 nm, which was much larger than that of Pt on STO-CD (Fig. S3), suggesting that CdS nanoshells were deposited on the surface of Pt nanoparticles on both {023} and {001} facets. The TEM and HADDF-STEM images of STO-CD-CdS were recorded to investigate its crystal structure in detail, as shown in Fig.5(c) and Fig.5(d). The typical STO-CD-CdS particle showed a 12-side polygon with lots of nanoparticles attached on its outline viewed from [001] direction (Fig.5(c)). The dark contrast of the inside core (indicated by red arrow) and the light contrast of the shell (indicated by blue arrow) of the nanoparticles indicated the successful deposition of CdS nanoshell on the surface of Pt nanoparticles. Furthermore, HRTEM images were recorded from the rectangle I, II, IV, and III regions in Fig.5(c) to investigate the structure of the deposited Pt@CdS nanoparticles in STO-CD-CdS. As shown in Fig.5(e)–Fig.5(h), the interplanar spacings of 3.36 and 2.27 Å corresponded to the (111) plane of CdS shells and (111) plane of Pt nanoparticles, respectively, indicating that the Pt@CdS core@shell structure was successfully deposited on the surface of STO-CD. The obvious S and Cd signals in Fig.5(i) also confirmed the existence of CdS nanoshells deposited on the surface of Pt nanoparticles.

In the XRD pattern (Fig. S2(b)), a weak peak can be observed at 2θ = 26.5°, which can be indexed to the (111) plane of CdS, also confirming the existence in STO-CD-CdS. Furthermore, as shown in Fig. S7, the obvious absorption band in the range of ca. 400–550 nm for STO-CD-CdS should be ascribed to the light absorption from CdS shells on Pt nanoparticles, providing another evidence for the existence of CdS in STO-CD-CdS. The Cd 3d and S 2p XPS spectra (Fig. S8) revealed that the chemical states of Cd and S were +2 and −2, respectively, further verifying the existence of CdS in STO-CD-CdS. Based on these analysis results, it is convincing that the CdS nanoshells have been photo-deposited on the surface of Pt nanoparticles, which are chemically deposited on both {001} and {023} facets of STO. That is to say, the function of {023} facets, which are responsible for photooxidation reaction, can be reversibly activated by chemical deposition of Pt for photocatalytic reduction reaction for hydrogen evolution. Thus, the full utilization of {001} and {023} facets are believed to contribute to the great improvement in photocatalytic hydrogen activity for STO-CD, as compared to STO-PD. A plausible mechanism of charge transfer in STO-CD is proposed in Fig.6. During the photocatalytic process, photo-induced electrons and holes would be generated on both {001} and {023} facets of STO when it is excited by the photons with energy higher than its bandgap. For the STO-CD, Pt nanoparticles were deposited on all the {001} and {023} facets. The photoexcited electrons on both {001} and {023} facets would be trapped by the Pt nanoparticles, and take part in the hydrogen evolution, while the photoexcited holes would be transferred from the valence band maximum (VBM) of {001} facets to VBM of {023} facets, and participate in the CH₃OH oxidation reaction during the photocatalytic process.

4 Conclusions

In summary, taking cube and tetrahexahedron STO nanocrystal enclosed with {023} and {001} facets as a model photocatalyst, full-facets-utilization of the nanocrystal for enhanced photocatalytic hydrogen reaction were achieved by depositing Pt nanoparticles on all the exposed facets. The activity of STO with Pt deposited on both {001} and {023} facets was ca. 2 times that of SrTiO₃ with Pt deposited on only {001} facets. The successful photodeposition of CdS shell on the surface of Pt deposited on all facets demonstrated that the function of the {023} facets, which were used for oxidation reaction, could be reversed for photocatalytic hydrogen evolution after depositing Pt cocatalyst. Thus, the function-reversible {023} facets, together with the {001} facets, led to the higher activity of SrTiO₃ nanocrystal for photocatalytic hydrogen evolution.

References

[1] Samanta B, Morales-GarcíaÁ, Illas F. . Challenges of modeling nanostructured materials for photocatalytic water splitting. Chemical Society Reviews, 2022, 51(9): 3794–3818

[2] Zhu Q, Xu Q, Du M. . Recent progress of metal sulfide photocatalysts for solar energy conversion. Advanced Materials, 2022, 34(45): 2202929

[3] Feng C, Wu Z P, Huang K W. . Surface modification of 2D photocatalysts for solar energy conversion. Advanced Materials, 2022, 34(23): 2200180

[4] Tao X, Zhao Y, Wang S. . Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts. Chemical Society Reviews, 2022, 51(9): 3561–3608

[5] Xue Z H, Luan D, Zhang H. . Single-atom catalysts for photocatalytic energy conversion. Joule, 2022, 6(1): 92–133

[6] Hisatomi T, Domen K. Reaction systems for solar hydrogen production via water splitting with particulate semiconductor photocatalysts. Nature Catalysis, 2019, 2(5): 387–399

[7] Wang Z, Hisatomi T, Li R. . Efficiency accreditation and testing protocols for particulate photocatalysts toward solar fuel production. Joule, 2021, 5(2): 344–359

[8] Ismael M. Environmental remediation and sustainable energy generation via photocatalytic technology using rare earth metals modified g-C₃N₄: A review. Journal of Alloys and Compounds, 2023, 931: 167469

[9] Zhang Y, Xu J, Zhou J. . Metal-organic framework-derived multifunctional photocatalysts. Chinese Journal of Catalysis, 2022, 43(4): 971–1000

[10] Zhou C, Wang T, Li D. . Flux-assisted low temperature synthesis of SnNb₂O₆ nanoplates with enhanced visible light driven photocatalytic H₂-production. Journal of Physical Chemistry C, 2021, 125(42): 23219–23225

[11] Wang J, Wang J, Shi R. . Facile fabrication of N-doped K₂Nb₂O₆ nanocrystals with defective pyrochlore structure for improved visible-light photocatalytic hydrogen production. Small Structures, 2023, 4(1): 2200105

[12] Guo L, Chen Y, Su J. . Obstacles of solar-powered photocatalytic water splitting for hydrogen production: A perspective from energy flow and mass flow. Energy, 2019, 172: 1079–1086

[13] Tang C, Cheng M, Lai C. . Recent progress in the applications of non-metal modified graphitic carbon nitride in photocatalysis. Coordination Chemistry Reviews, 2023, 474: 214846

[14] Wang N, Cheng L, Liao Y. . Effect of functional group modifications on the photocatalytic performance of g-C₃N₄. Small, 2023, 19(27): 2300109

[15] Tang Z R, Han B, Han C. . One dimensional CdS based materials for artificial photoredox reactions. Journal of Materials Chemistry. A, Materials for Energy and Sustainability, 2017, 5(6): 2387–2410

[16] Chen R, Chen J, Che H. . Atomically dispersed main group magnesium on cadmium sulfide as the active site for promoting photocatalytic hydrogen evolution catalysis. Chinese Journal of Structural Chemistry, 2022, 41: 2201014–2201018

[17] Yuan L, Han C, Yang M Q. . Photocatalytic water splitting for solar hydrogen generation: Fundamentals and recent advancements. International Reviews in Physical Chemistry, 2016, 35(1): 1–36

[18] Li S H, Zhang N, Xie X. . Stress-transfer-induced in situ formation of ultrathin nickel phosphide nanosheets for efficient hydrogen evolution. Angewandte Chemie International Edition, 2018, 57(40): 13082–13085

[19] Moon H S, Hsiao K C, Wu M C. . Spatial separation of cocatalysts on Z-scheme organic/inorganic heterostructure hollow spheres for enhanced photocatalytic H₂ evolution and in-depth analysis of the charge-transfer mechanism. Advanced Materials, 2023, 35(4): 2200172

[20] Zhang L, Zhang J, Yu H. . Emerging S-scheme photocatalyst. Advanced Materials, 2022, 34(11): 2107668

[21] Kosco J, Gonzalez-Carrero S, Howells C T. . Generation of long-lived charges in organic semiconductor heterojunction nanoparticles for efficient photocatalytic hydrogen evolution. Nature Energy, 2022, 7(4): 340–351

[22] Shen R, Zhang L, Li N. . W–N bonds precisely boost Z-scheme interfacial charge transfer in g-C₃N₄/WO₃ heterojunctions for enhanced photocatalytic H₂ evolution. ACS Catalysis, 2022, 12(16): 9994–10003

[23] Sun S, Gao R, Liu X. . Engineering interfacial band bending over bismuth vanadate/carbon nitride by work function regulation for efficient solar-driven water splitting. Science Bulletin, 2022, 67(4): 389–397

[24] Cai H, Wang B, Xiong L. . Orienting the charge transfer path of type-II heterojunction for photocatalytic hydrogen evolution. Applied Catalysis B: Environmental, 2019, 256: 117853

[25] Zhang T, Meng F, Cheng Y. . Z-scheme transition metal bridge of Co₉S₈/Cd/CdS tubular heterostructure for enhanced photocatalytic hydrogen evolution. Applied Catalysis B: Environmental, 2021, 286: 119853

[26] Liu D, Zhang J, Li C. . In-situ fabrication of atomic charge transferring path for constructing heterojunction photocatalysts with hierarchical structure. Applied Catalysis B: Environmental, 2019, 248: 459–465

[27] Wei D, Tan Y, Wang Y. . Function-switchable metal/semiconductor junction enables efficient photocatalytic overall water splitting with selective water oxidation products. Science Bulletin, 2020, 65(16): 1389–1395

[28] Hu J, Chen D, Mo Z. . Z-scheme 2D/2D heterojunction of black phosphorus/monolayer Bi₂WO₆ nanosheets with enhanced photocatalytic activities. Angewandte Chemie International Edition, 2019, 58(7): 2073–2077

[29] Faraji M, Yousefi M, Yousefzadeh S. . Two-dimensional materials in semiconductor photoelectrocatalytic systems for water splitting. Energy & Environmental Science, 2019, 12(1): 59–95

[30] Li J, Wu C, Li J. . 1D/2D TiO₂/ZnIn₂S₄ S-scheme heterojunction photocatalyst for efficient hydrogen evolution. Chinese Journal of Catalysis, 2022, 43(2): 339–349

[31] Li H, Sun B, Gao T. . Ti₃C₂ MXene co-catalyst assembled with mesoporous TiO₂ for boosting photocatalytic activity of methyl orange degradation and hydrogen production. Chinese Journal of Catalysis, 2022, 43(2): 461–471

[32] Yan T, Zhang X, Liu H. . CeO₂ particles anchored to Ni₂P nanoplate for efficient photocatalytic hydrogen evolution. Chinese Journal of Structural Chemistry, 2022, 41: 2201047–2201053

[33] Yang J, Wu X, Mei Z. . CVD assisted synthesis of macro/mesoporous TiO₂/g-C₃N₄ S-scheme heterojunction for enhanced photocatalytic hydrogen evolution. Advanced Sustainable Systems, 2022, 6(8): 2200056

[34] Mei Z, Wang G, Yan S, Wang J. Rapid microwave-assisted synthesis of 2D/1D ZnIn₂S₄/TiO₂ S-scheme heterojunction for catalyzing photocatalytic hydrogen evolution. Acta Physico-Chimica Sinica, 2021, 37(6): 2009097

[35] Wang P, Li H, Cao Y. . Carboxyl-functionalized graphene for highly efficient H₂-evolution activity of TiO₂ photocatalyst. Acta Physico-Chimica Sinica, 2021, 37(6): 2008047

[36] Han B, Liu S, Zhang N. . One-dimensional CdS@MoS₂ core-shell nanowires for boosted photocatalytic hydrogen evolution under visible light. Applied Catalysis B: Environmental, 2017, 202: 298–304

[37] Yang M Q, Han C, Xu Y J. Insight into the effect of highly dispersed MoS₂ versus layer-structured MoS₂ on the photocorrosion and photoactivity of CdS in graphene–CdS–MoS₂ composites. Journal of Physical Chemistry C, 2015, 119(49): 27234–27246

[38] Li Y H, Qi M Y, Li J Y. . Noble metal free CdS@CuS-Ni_xP hybrid with modulated charge transfer for enhanced photocatalytic performance. Applied Catalysis B: Environmental, 2019, 257: 117934

[39] Lu K Q, Qi M Y, Tang Z R. . Earth-abundant MoS₂ and cobalt phosphate dual cocatalysts on 1D CdS nanowires for boosting photocatalytic hydrogen production. Langmuir, 2019, 35(34): 11056–11065

[40] Wang Z, Wang L, Cheng B. . Photocatalytic H₂ evolution coupled with furfuralcohol oxidation over Pt-modified ZnCdS solid solution. Small Methods, 2021, 5(11): 2100979

[41] Adenle A, Zhou H, Tao X. . Crystal facet modulation of Bi₂WO₆ microplates for spatial charge separation and inhibiting reverse reaction. Chemical Communications, 2021, 57(88): 11637–11640

[42] Bai Y, Zhou Y, Zhang J. . Homophase junction for promoting spatial charge separation in photocatalytic water splitting. ACS Catalysis, 2019, 9(4): 3242–3252

[43] Scanlon D O, Dunnill C W, Buckeridge J. . Band alignment of rutile and anatase TiO₂. Nature Materials, 2013, 12(9): 798–801

[44] Liu M, Jing D, Zhou Z. . Twin-induced one-dimensional homojunctions yield high quantum efficiency for solar hydrogen generation. Nature Communications, 2013, 4(1): 2278

[45] Liu M, Wang L, (Max) Lu G. . Twins in Cd_1−xZn_xS solid solution: Highly efficient photocatalyst for hydrogen generation from water. Energy & Environmental Science, 2011, 4: 1372–1378

[46] Naldoni A, Altomare M, Zoppellaro G. . Photocatalysis with reduced TiO₂: From black TiO₂ to cocatalyst-free hydrogen production. ACS Catalysis, 2019, 9(1): 345–364

[47] Wang B, Shen S, Mao S S. Black TiO₂ for solar hydrogen conversion. Journal of Materiomics, 2017, 3(2): 96–111

[48] Chen X, Liu L, Yu P Y. . Increasing solar absorption for photocatalysis with black hydrogenated titanium dioxide nanocrystals. Science, 2011, 331(6018): 746–750

[49] Wang B, Shen S, Guo L. Surface reconstruction of facet-functionalized SrTiO₃ nanocrystals for photocatalytic hydrogen evolution. ChemCatChem, 2016, 8(4): 798–804

[50] Takata T, Jiang J, Sakata Y. . Photocatalytic water splitting with a quantum efficiency of almost unity. Nature, 2020, 581(7809): 411–414

[51] Ohno T, Sarukawa K, Matsumura M. Crystal faces of rutile and anatase TiO₂ particles and their roles in photocatalytic reactions. New Journal of Chemistry, 2002, 26(9): 1167–1170

[52] Tachikawa T, Yamashita S, Majima T. Evidence for crystal-face-dependent TiO₂ photocatalysis from single-molecule imaging and kinetic analysis. Journal of the American Chemical Society, 2011, 133(18): 7197–7204

[53] Li R, Zhang F, Wang D. . Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO₄. Nature Communications, 2013, 4(1): 1432

[54] Li R, Han H, Zhang F. . Highly efficient photocatalysts constructed by rational assembly of dual-cocatalysts separately on different facets of BiVO₄. Energy & Environmental Science, 2014, 7(4): 1369–1376

[55] Zhu J, Fan F, Chen R. . Direct imaging of highly anisotropic photogenerated charge separations on different facets of a single BiVO₄ photocatalyst. Angewandte Chemie International Edition, 2015, 54(31): 9111–9114

[56] Li N, Liu M, Zhou Z. . Charge separation in facet-engineered chalcogenide photocatalyst: A selective photocorrosion approach. Nanoscale, 2014, 6(16): 9695–9702

[57] Wang B, Liu M, Zhou Z. . Surface activation of faceted photocatalyst: When metal cocatalyst determines the nature of the facets. Advanced Science, 2015, 2(11): 1500153

[58] Wang B, Shen S, Guo L. SrTiO₃ single crystals enclosed with high-indexed {023} facets and {001} facets for photocatalytic hydrogen and oxygen evolution. Applied Catalysis B: Environmental, 2015, 166–167: 320–326

RIGHTS & PERMISSIONS

Higher Education Press 2023