Unveiling Intrinsic Charge Transfer Dynamics in Bone-Joint S-Scheme Heterostructures for Promoting Photocatalytic Hydrogen Peroxide Generation

doi:10.21203/rs.3.rs-3351037/v1

Download PDF

Article

Unveiling Intrinsic Charge Transfer Dynamics in Bone-Joint S-Scheme Heterostructures for Promoting Photocatalytic Hydrogen Peroxide Generation

https://doi.org/10.21203/rs.3.rs-3351037/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Constructing compact direct Z- and S-scheme heterostructures is an efficient strategy for realizing highly efficient charge separation and photocatalytic performance. However, the driving charge source of the built-in electric field (BEF) for internal electron-hole complexation sites remains unknown, which is a barrier to rationally design heterojunctions. Here, experimental results and theoretical research unveiled that complicated internal charges can be directly transferred to an intermediate co-crystal plane for electron–hole complexation in compact S-scheme heterostructures, called “bone-joint” heterostructures. It acted as an inner source of BEF that compels charge directed migration and exciton dissociation. Moreover, those bone joint structures adjust the inherent chemical and energetic interactions that manipulate the reactant adsorption mode and surface reaction energy. As a result, a synthesized catalyst displayed remarkable hydrogen peroxide production performance and stability. This offers a new paradigm for intrinsic charge transfer dynamics in heterostructures and a guiding philosophy for designing efficient heterostructures.

Physical sciences/Chemistry/Catalysis/Photocatalysis

Physical sciences/Materials science/Materials for energy and catalysis/Photocatalysis

Hydrogen peroxide (H₂O₂) is a versatile and promising oxidant with extensive applications in the medical, chemistry, and environmental fields.^1,2 Currently, the industrial production of H₂O₂ employs the anthraquinone method, which requires high energy consumption, produces toxic byproduct emissions, and causes catalyst deactivation.^3,4 In contrast, photocatalytic technology is agreed to be a desirable alternative because of its advantages in terms of its economy, low carbon, green chemistry, and sustainable technology.^5,6 However, the application of photocatalytic H₂O₂ production is severely limited by the low quantum efficiency of charge recombination.^7,8 Therefore, it is crucial to overcome this bottleneck in semiconductors to enhance the photocatalytic performance.

Recently, constructing compact direct Z- and S-scheme heterostructures has become an efficient strategy for realizing charge separation and photocatalytic performance.^9,10 Moreover, to further enhance the photocatalytic performance, crafting a total contact interface within the heterostructure is desirable. That is, a compact two-phase interface that can construct electronic communication, a large internal electric field, and a charge channel to enhance charge transfer to surface reactive sites.^11,12 No matter how elaborate the atomic-level directional charge separation is, authentic charge transfer pathways in direct Z- and S-scheme heterostructures can be depicted, whereby external photoinduced electrons and holes are reserved in the conduction bands (CBs) of reduction photocatalysts and valence bands (VBs) of oxidation photocatalysts and transferred to the surface sites, respectively.^13,14 However, the interior complexation of photoinduced holes and electrons, an internal driving force of the internal electric field, has only been simply described at the interfacial VBs and CBs.¹⁵ Therefore, the source of a built-in electric field (BEF) for electron–hole complexation sites remains unknown, hindering the rational design of compact heterojunctions. However, only directional internal carrier complexation could result in a stronger internal electric field to form Z- or S-scheme heterostructures. Considerable evidence verifies that external photoinduced electrons and holes depend on certain facets;¹⁶ thus, internal complexation pathways may be related to different crystal orientations at the contact interface. Therefore, an in-depth understanding of the fundamental mechanism of the complexation pathways of photogenerated electron-hole pairs between direct Z- or S-scheme heterojunctions is desirable but currently remains challenging.

In this study, a ZnIn₂S₄-Zn₂In₂S₅ intermediate-crystal plane with a bone joint S-scheme heterostructure was first proposed and produced, providing a platform for internal charge complexation and driving a powerful BEF (Fig. 1a). As a result, this large BEF compels charge transfer and exciton dissociation. Furthermore, the semicoherent-interface bone joint adjusts the inherent chemical and energetic interactions that manipulate the reactant adsorption mode and surface reaction energy, resulting in exceptional photocatalytic H₂O₂ production rates. The results of this study offer a new model for intrinsic charge transfer dynamics in heterostructures and guide the design of efficient heterostructures.

Characterization of The Bone-joint Structure

The morphology of the as-synthesized ZIS was characterized using SEM, AFM, TEM, and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). As shown in Fig. 1b, ZIS-2 exhibits a hierarchical sheet-like morphology. The typical thicknesses of the ZnIn₂S₄, Zn₂In₂S₅, ZIS-2, and ZIS-R (random composite samples) were 11.39, 9.16, 6.62, and 7.49 nm (Supplementary Fig. 2), respectively. Based on the Brunauer-Emmett-Teller area method, the specific surface area of ZIS-2 was 31.62 m² g^− 1, which was greater than those of ZIS-R (22.25 m² g^− 1), Zn₂In₂S₅ (14.41 m² g^− 1), and ZnIn₂S₄ (7.63 m² g^− 1) (Supplementary Fig. 3). This indicates that ultrathin morphologies favor the diffusion of photogenerated carriers and high exposure of the active sites. The TEM elemental mapping (Fig. 1d–g) reveals that Zn, In, and S are uniformly distributed in ZIS, which suggests the successful synthesis of the ZIS heterostructure.

The TEM images confirm that the ZIS was assembled from multiple nanoflakes (Fig. 1h and i). A clear lattice fringe of 0.29 nm can be assigned to the (104) plane of hexagonal ZnIn₂S₄, and a distinct crystalline fringe of 0.32 nm can be assigned to the (104) plane of hexagonal Zn₂In₂S₅.^17,18 However, further lattice distortions and edge dislocations are clearly observed at the interfacial junction, which are attributed to the (006) plane of ZnIn₂S₄ and the (006) plane of Zn₂In₂S₅.^18,19 Based on the molecular models of ZnIn₂S₄ and Zn₂In₂S₅, the (006) plane in the two materials exhibits the same composition and configuration (Supplementary Fig. 4). This demonstrates that an interlaced interface was formed between the heterostructures, which is called as semicoherent interface. Moreover, an interlaced interface simulation was constructed to test this (detailed simulation method and interpretation are presented in the Supporting Information, see Supplementary Fig. 5). The results revealed that the terminal atoms of the (006) plane of ZnIn₂S₄ were rotated by an angle of 13° to form the (006) plane of Zn₂In₂S₅, which is produced from the interfacial strain that compelled the distortion of the lattice, suggesting that there are bone-joint links in the heterojunction because of the interatomic distances and different crystal symmetries (Fig. 1j). In addition, other interface inconsistencies were identified (Supplementary Fig. 5). HAADF-STEM was then performed to obtain the detailed information on the continuous semicoherent interfaces. No clear observable phase interface was observed (Fig. 1k–l), which was attributed to the atomic-level continuous interfaces. In addition, some atomic-level distortion exists in the semicoherent interfaces, corroborating the interfacial strain-induced sulfur vacancies (S_Vs), which was confirmed by the EPR results (Supplementary Fig. 7). These results confirmed the formation of a semicoherent interface bone joint in the ZIS heterojunction.

To further verify this, the crystallographic structures of the as-obtained samples were analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Despite the different XRD patterns of the ZnIn₂S₄, Zn₂In₂S₅, and ZIS composites, they present similar profiles, which is attributed to a repeating analogous structural unit (Fig. 1m).²⁰ Combining inductively coupled plasma mass spectrometry (ICP-MS) (Supplementary Fig. 9 and Supplementary Table 2) and XPS elemental content analyses (Supplementary Table 3) with the XRD and TEM results, the ZnIn₂S₄-Zn₂In₂S₅ heterojunction was confirmed (detailed explanation is provided in the Supporting Information). The sharped and shifted (006) XRD peak observed in ZIS-2 indicates that the compact interfacial heterostructure decreased the interplanar spacing and induced structural strain, contributing to the formation of bone-joint structures. This is confirmed by the HAADF-STEM results (Fig. 1l). The clearly distinguishable Raman peaks for the single ZIS are at approximately 128, 247, 302, and 355 cm^− 1, with 128 cm^− 1 being consistent with the featured layer structure and 247, 302, and 355 cm^− 1 corresponding to the LO₁, TO₂, and LO₂ modes of ZIS and associated with V(S-In-S)s (surface), V(S-In-S)i (interior), and V(S-Zn-S)s (surface), respectively (Supplementary Fig. 10).^21,22 Moreover, the ZIS-2 Raman peaks shift to a lower wavenumber, which is attributed to the interaction between the semicoherent interface bone joints, suggesting the rapid transition of charge carriers in the bone-joint areas.

Due to the geometry of the semicoherent interface bone joints, the results of the XPS can determine the electronic interactions. The Zn 2p, In 3d, and S 2p doublets were investigated in ZnIn₂S₄, Zn₂In₂S₅, ZIS-R (random composite heterojunction), and ZIS-2 (Supplementary Fig. 11). This demonstrated the existence of Zn²⁺, In³⁺, and S²⁻ in both samples.^23,24 Notably, the binding energies of S 2p (161.9 and 163.1 eV), In 3d (445.2 and 452.8 eV), and Zn 2p (1022.2 and 1045.2 eV) in ZIS-2 are negatively shifted compared to those of pristine ZnIn₂S₄. ZIS-R is in a similar scenario. However, they are still positive compared to Zn₂In₂S₅, suggesting the migration of electrons from ZnIn₂S₄ to Zn₂In₂S₅ following the contact between them, which is a typical characteristic of S-scheme heterojunctions.²⁵ Compared to ZIS-R, ZIS-2 exhibits a positive shift, suggesting that the semicoherent interface promotes internal electronic interactions. These results clearly show that the semicoherent interface bone joints introduce large interfacial strain and regulate the electron density of Zn₂In₂S₅ and ZnIn₂S₄, resulting in electronic interaction between the two components.²⁶ Therefore, the semicoherent interface bone joints adjust the inherent chemical and energetic interactions between the two components.

Formation of S-scheme Heterojunctions

Photon absorption is a thermodynamic factor of charge transfer. Therefore, the UV-Vis diffuse reflectance spectra of the prepared samples were determined (Supplementary Fig. 12).²⁷ As shown in Supplementary Fig. 13, the calculated CB locations for ZnIn₂S₄ and Zn₂In₂S₅ were − 0.66 and − 0.88 V, respectively. Thus, the VB potentials of ZnIn₂S₄ and Zn₂In₂S₅ were determined to be 1.48 and 1.44 V, respectively.²⁸ These results indicate the possibility of establishing an S-scheme heterojunction in ZIS and satisfying the thermodynamic requirements for H₂O₂ generation (Supplementary Fig. 14). To gain insight into the energy band structure, density functional theory (DFT) simulations were performed. Intriguingly, the band gap of ZIS was considerably decreased, suggesting that further charge carriers are produced (Supplementary Fig. 15). As shown in Supplementary Fig. 16, unlike ZnIn₂S₄, Zn₂In₂S₅, and ZIS-R, the PDOS of ZIS-2 overlaps Zn and In, implying strong electronic interactions in the bone-joint structure, which is conducive to the directional transfer of internal charges.

To confirm the S-scheme heterojunction in ZIS, several experiments were performed. First, DFT calculations were performed to predict the charge effective mass in the as-prepared samples (Supplementary Fig. 17). According to effective mass calculations, ZIS exhibits the smallest charge effective mass, indicating that the highest charge transfer rate can be expected in the heterojunction, suggesting that the tendency of charge carrier transfer follows the S-scheme mechanism.²⁹ To further demonstrate that photogenerated electrons at the interface of a ZnIn₂S₄-Zn₂In₂S₅ homojunction follow an S-scheme transfer mechanism, light-assisted KPFM was used to measure the change in the local potential of the homojunctions before and after illumination (Fig. 2a–f). Under dark conditions, ZIS-2 exhibited the largest surface potential (Supplementary Fig. 18). However, when integrated with Zeta potential results (Supplementary Fig. 19), ZIS-2 exhibited the strongest BEF (Supplementary Fig. 20), which can substantially encourage carrier migration and exciton dissociation. In addition, the surface potential of ZnIn₂S₄ increased from 53.86 to 65.22 mV after illumination, whereas that of Zn₂In₂S₅ decreased from 10.03 to 1.66 mV, which is consistent with the ZIS-R trend. This demonstrates that ZnIn₂S₄ loses electrons and the surface potential rises, whereas Zn₂In₂S₅ acquires electrons and the surface potential falls, further proving that the internal carrier migration follows the S-type heterojunction.³⁰

Intrinsic charge transfer dynamics

Despite the surface BEF charge transfer pathways being clearly observable, the complexation sites and internal driving force of the BEF are undefined. Based on the KPFM results, the surface potential of ZIS-2 increased by 19.73 eV under the light condition compared to the dark condition, which is more pronounced than the ZIS-R value (3.15 eV). This increase in surface potential can be explained by the intermediate-crystal plane hastening internal electron transport.³¹ Such a swinging carrier screening effect occurred in ZIS-2, indicating that the (006) transition layer of the bone-joint structure plays an important role in inward charge complexation. To determine the intrinsic charge transfer dynamics, first-principle calculations based on DFT were performed. As shown in Fig. 2g, the work functions of ZnIn₂S₄ and Zn₂In₂S₅ are 5.306 and 4.053 eV, respectively. This difference in work functions causes the transfer of electrons from Zn₂In₂S₅ to ZnIn₂S₄ to form a BEF. However, when the bone-joint structure is modified by vacancies, the work functions of ZnIn₂S₄-(006) and Zn₂In₂S₅-(006) are calculated as 4.405 and 4.227 eV, respectively. Thus, electrons are transferred from ZnIn₂S₄ to (006), while holes are transferred from Zn₂In₂S₅ to the (006) crystal plane, and the (006) crystal plane becomes a charge complexation site. In addition, the charge transfer path was determined using differential electron density (Supplementary Fig. 21) and surface charge distribution mapping (Supplementary Fig. 22). These results demonstrate that the (006) crystal plane accumulates a massive charge compared to the ZIS-R interface, which is derived from interface-vacancy-induced internal electronic structural changes that concentrate electrons and holes. This suggests that the semicoherent interface acts as the source of BEFs.

TA spectroscopy was used to determine the S-scheme internal complex site charge transfer mechanism (Fig. 2h–k). The electron delay of pure ZIS-R can be fitted by two exponential functions, and the time constants are τ₁ = 56.10 ps and τ₂ = 575.26 ps (Fig. 2j), where τ₁ reflects the stage where the electron goes from the CB to the trap state and τ₂ represents the migration to the VB.^32,33 While the ZIS-2 values τ₁ = 9.51 ps, τ₂ = 10.14 ps, and τ₃ = 550.72 ps (Fig. 2k) are assigned to the stage where the electron goes from the CB to the trap state, the charge complexation on the semicoherent interface, and migration to the VB, respectively. These results demonstrate that the intermediate transition state provides a composite platform for electrons and holes. To intuitively determine the complexation sites, a metal photodeposition experiment was performed. As shown in Supplementary Fig. 24, Pt and Mn₃O₄ nanoparticles are deposited on the edges of the (006) lattice transition layers, confirming that the (006) transition layer acts as the charge complexation site. This can be explained by the interfacial electric field being rooted in the bone-joint structure.

Due to the directional charge complexation platform, the high efficiency of carrier migration and exciton dissociation can be predicted. As shown in Supplementary Fig. 25a, the steady-state photoluminescence (PL) spectroscopy intensity of the ZIS-2 was considerably lower than that of the control sample, indicating that the development of the bone-joint structure is essential for the radiative complexation of charge carriers. As shown in Supplementary Fig. 25b, ZIS-2 exhibits the fastest PL decay, with an expected duration of 1.02 ns compared to ZnIn₂S₄ (1.65 ns) and Zn₂In₂S₅ (1.27 ns), indicating that the bone-joint structure is conductive to exciton dissociation. The Arrhenius equation [I_T = I₀/(1 + AExp(− E_b/K_BT))] can be used to obtain the exciton binding energy (E_b).³³ The calculated E_b of the ZIS-2 catalyst is 0.1 eV (Supplementary Fig. 26), which is much lower than that of ZIS-R (0.16 eV), ZnIn₂S₄ (0.37 eV), and Zn₂In₂S₅ (0.20 eV). This indicates a more straightforward and rapid disintegration of the excitons into a free charge in ZIS-2. To further evaluate the effectiveness of the photoexcited separation, photocurrent and electrochemical impedance spectroscopy were undertaken. According to Supplementary Fig. 27a, the decreasing photocurrent density intensity is in the order of ZIS-2 > ZIS-1 > ZIS-3 > ZIS-4 > ZIS-5 > ZIS-R > Zn₂In₂S₅ > ZnIn₂S₄, indicating that the "bone-joint" S-scheme heterojunctions enhances carrier separation. In addition, ZIS-2 has the shortest arc radius compared to the other samples (Supplementary Fig. 27b), suggesting a more effective capacity for charge transfer.

Above all, the semicoherent interface bone joint provides a platform for internal charge complexation and a powerful driving force for the BEF, which prevents the random migration of interface charges and thus enhances the carrier utilization rate. As expected, bone-joint S-scheme heterojunctions exhibit excellent photocatalytic activity.

Photocatalytic activity and mechanism

The photocatalytic conversion of H₂O and O₂ into H₂O₂ (PHH) is promising for the industrial production of H₂O₂. However, its use is often confined to the employment of sacrificial reagents. Here, the photocatalytic performance of the catalysts was evaluated using PHH under visible light without sacrificial reagents or cocatalysts. First, no product was produced in parallel studies conducted without light or O₂, suggesting that the PHH reaction is photocatalytic and requires O₂.

As shown in Fig. 3a, higher yield rates were observed in the ZIS-based S-scheme heterojunction. More importantly, ZIS-2 had the highest H₂O₂ production rate (5939 µmol g^− 1 h^− 1), almost 10 times greater than that of ZnIn₂S₄ (580 µmol g^− 1 h^− 1). Additionally, among the reported catalysts, it had the highest formation rates (Fig. 3b) (Supplementary Table 4).^34–51 As illustrated in Fig. 3c, the AQY of ZIS-2 at 420 nm reached 7.08% and continued to function even at wavelengths less than 600 nm. Furthermore, the stability of ZIS-2 over the course of eight subsequent runs indicated no loss of photoactivity or structural integrity (Fig. 3d), demonstrating the excellent stability of ZIS-2. According to the XRD (Supplementary Fig. 28a) and XPS (Supplementary Fig. 28b) spectra, no obvious damage to the ZIS-2 crystal surface was observed before or after the recycling test.

The bone-joint S-scheme heterojunctions had the highest charge carrier transfer capacity for enhancing photocatalytic activity. However, more importantly, surface properties can also affect photocatalytic performance. As shown in Supplementary Fig. 29, ZIS-2 exhibits the smallest H₂O contact angles, suggesting that it has a good affinity for H₂O. Moreover, H₂O₂ has a substantially larger contact angle with ZIS than it does with H₂O (Supplementary Fig. 30), indicating that the H₂O₂ molecules are difficult to break down in aqueous solutions. TPD studies on O₂ were subsequently undertaken. As shown in Supplementary Fig. 31, an obviously enhanced chemical O₂ activation capacity was observed in ZIS-2, suggesting that the bone-joint structure adjusts the inherent chemical and energetic interactions that enhance the activation of H₂O and O₂.

To further clarify the involvement of active species, free radical trapping studies were conducted. As shown in Supplementary Fig. 32, electrons play important roles in the photocatalytic production of H₂O₂. Despite the pathway of H₂O₂ production being a two-step 2e⁻ progress,⁵² it also consists of two typical steps (i.e., superoxide radicals as the intermediates or a one-step direct 2e⁻ process). In the system used herein, the generation of H₂O₂ over ZIS-2 is mainly dependent on the one-step direct 2e⁻ process. To better understand the mechanism, in situ FT-IR tests were carried out (Fig. 4a). Absorption bands at 910 cm^− 1, 1184.3–1413.2 cm^− 1, and 3200–3600 cm^− 1 were assigned to the adsorbed states of O₂, H₂O₂/–OH, and H₂O/–OH, respectively.^8,53 Surprisingly, a peak at 1115–1295 cm^− 1 belonging to Yeager-type –O–O–⁵³ indicates that the initial adsorption structure of O₂ on ZIS is primarily "bridged." Moreover, a (*OOH) signal derived from the superoxide radical was not found at 1258 cm^− 1.⁷ These results demonstrate that the reaction follows the double bond adsorption of the O₂ path, with the direct production of H₂O₂ without the production of intermediate *OOH.

To understand the underlying mechanisms, DFT calculations were conducted. As shown in Fig. 4b, the chemical bond lengths of –O–O– over ZIS are longer than those of –O–O, demonstrating that the activation of O₂ on bone-joint S-scheme heterojunctions leans toward the –O–O– configuration. Moreover, the more negative surface of the –O–O– molecule on the ZIS suggests that it is easier for bone-joint S-scheme heterojunctions to transfer electrons via the –O–O– configuration. Furthermore, the more efficient polarization of –O–O– adsorbed on ZIS proves that electronic interaction of O₂ with –O–O– models are likelier to appear. As shown in Fig. 4c, the free energy of the "bridge connection" is smaller, indicating that the O₂ adsorption follows the –O–O– type path.

The reaction pathways of the different catalysts were then further investigated. As shown in Supplementary Fig. 34, the chemical molecular charge polarization of –O–O– changed more prominently over ZIS-2. This was attributed to the semicoherent interface bone joint adjusting to the energetic interaction between the two components and guiding the electron transfer directly, resulting in a more rapid electron transfer from the surface to the absorbed O₂ molecule. Moreover, the smallest free energy of H₂O₂ production over ZIS, demonstrating a bone-joint configuration, is conducive to H₂O₂ generation (Fig. 4d). Based on this, the ZIS-2 photocatalytic H₂O₂ production mechanism is shown in Fig. 4e. When exposed to light, ZIS-2 is activated and generates relevant charge carriers. Following the bone-joint S-scheme heterojunction transfer mechanism, internal charges migrate to the "energy platform" of the (006) transition layer and generate a large BEF, while external electrons act on the Yeager-type –O–O– to produce H₂O₂.

A ZnIn₂S₄-Zn₂In₂S₅ intermediate-crystal plane with an S-scheme heterostructure bone joint was proposed and synthesized. At this junction, the bone-joint construction provides a platform that can guide internal charge complexation and thus drive a powerful BEF, which prevents the random migration of interface charges, thereby enhancing the carrier utilization rate. Moreover, this semicoherent interface bone joint can adjust the inherent chemical and energetic interactions between the two components, which greatly affects the reactant adsorption mode and surface reaction energy. The catalyst exhibits exceptionable photocatalytic H₂O₂ production rates. These findings demonstrate a new paradigm for intrinsic charge transfer dynamics in S-scheme heterostructures and offer a guiding philosophy for designing efficient heterostructures.

Preparation of ZnIn ₂ S ₄ and Zn ₂ In ₂ S ₅.

The series of Zn_mIn₂S_m+3 (m = 1, 2) was created using a low-temperature hydrothermal process. The following substances were dissolved in 160 mL of water: 2.0 mmol of InCl₃·4H₂O, m mmol of Zn(CH₃COO)₂·2H₂O, and (m + 3) mmol of thioacetamide. The mixture was rapidly agitated while being heated to 90^oC for 5 hours, and it was subsequently permitted to recede to the ambient temperature. After sonication of the suspension for one hour, the precipitate was centrifuged, washed with water that had been deionized and pure ethanol, and then dried under vacuum at 60^oC.

Preparation of ZIS.

The series ZIS-X (ZnIn₂S₄-Zn₂In₂S₅-1:X) was created using a low-temperature hydrothermal process. Take ZIS-2 as an example, 2.0 mmol of InCl₃·4H₂O, 1.66 mmol Zn(CH₃COO)₂·2H₂O and 4.66 mmol of thioacetamide were dissolved in 160 mL of water that had been deionized. The mixture was rapidly agitated while being heated to 90^oC for 5 hours, and it was subsequently permitted to recede to the ambient temperature. After sonication of the suspension for one hour, the precipitate was centrifuged, washed with water that had been deionized and pure ethanol, and then dried under vacuum at 60^oC.

Preparation of a composite sample of ZIS-R.

ZnIn₂S₄ and Zn₂In₂S₅ were mixed in 1 : 2 proportion and stirred vigorously at 90^oC for 5 hours and it was subsequently permitted to recede to the ambient temperature. After sonication of the suspension for one hour, the precipitate was centrifuged, washed with water that had been deionized and pure ethanol, and then dried under vacuum at 60^oC.

Characterization.

The chemical structure and surface position of valence associated with the resultant samples were studied using the X-ray diffractograms (XRD; Bruker D8 Advance) and XPS (Thermo Fisher KAlpha Plus), among other techniques. The morphological structure of ZIS was examined utilising a SEM (Hitachi S-4800) and TEM (JEM-2100 F). The prepared ZIS's BET surface area was measured with Micrometrics ASAP 2020. A spectrophotometer with UV-vis (Shimadzu UV-3600 plus) was used to assess the optical absorption properties of ZnIn₂S₄, Zn₂In₂S₅, and ZIS. The apparatus AutoChem 2920 was used to carry out O₂ temperatures regulated adsorption (O₂-TPD). At ambient temperature and without the use of light irradiation, S-vacancies have been identified utilizing electron spin resonance (EPR) using a Bruker EMX-PLUS instrument. Measurements were performed using an electrochemical measurement workstation (CHI660E, Chenhua; test conditions: electrolyte: 0.05 mol L^− 1 Na₂SO₄, electrode: Ag/AgCl) photocurrent, EIS and even Mott-Schottky tests. Collection of chemical structures in reactions by FTIR spectrometer (Shimadzu).

Theoretical-calculation details.

All of the simulations made use of a CASTEP module. The limit of energy and vacuum separation were 450 eV and 20 Å, respectively. The Brillouin zone integrations consisted established to 3 × 3 × 1 for calculations on electrical performance and shape optimization. In addition, the ionic relaxation convergence was chosen at 0.01 eV Å⁻¹ and the atomic force was chosen at 10^− 5 eV. Each reactant molecule's Gibbs free energy was simulated throughout the reaction:

∆G = ∆E + ∆E_ZPE − T *∆S

where ∆E_ZPE, ∆E and ∆S stand for the zero-point energy, desorption energy, and entropy variations respectively. T is typically set to 298.15 K.

Photocatalytic H ₂ O ₂ production.

The photocatalytic generation of H₂O₂ was performed out in a glass vessel equipped with a reflux condenser. Typically, a 100 mL reactor received 20 mg of the material being tested together with 50 mL of pure water. The reactor had been continually supplied with oxygen at an inflation level of 119 mL min^− 1. To maintain the equilibrium between O₂ and water absorption and desorption, the reaction mixture has been stirred for 0.5 hours prior to illumination. The reaction was performed for 2 hours under appropriate conditions (a 300 W xe lamp, > 420 nm, light area: 18.47 cm^− 2). The H₂O₂ in water was determined spectrophotometrically using potassium titanium oxalate.⁵⁴ The calibration curve was created using 0.5 mL of quantitative hydrogen peroxide solution, 1 mL of water that had been deionized, and 1 mL of Titanium oxalate potassium liquid (0.05 mol L^− 1). Measurement of solution absorbance at 400 nm using UV-visible spectroscopy. If the amount of hydrogen peroxide is greater than 10 mmol L^− 1, the solution should be diluted to less than 10 mmol L^− 1 before detection. Finally, the reaction activity was assayed by replacing the hydrogen peroxide solution with an equal amount of reaction solution.

Data availability

All data that support the findings of this study are present in the paper and the Supplementary Information. Additional data related to the study are available from the corresponding author upon reasonable request.

Acknowledgements

This project was financially supported by Guizhou Provincial Science and Technology Foundation (No. ZK2021069 and 2023039), Young Science and Technology Talents Development Project of Education Department in Guizhou Province (No. KY2022144), National Natural Science Foundation of China (No. 22268015). The authors would like to thank Shiyanjia Lab (www.shiyanjia.com) for materials characterizations, and the computing support of the State Key Laboratory of Public Big Data, Guizhou University.

Author contributions

Y. Liu and X. Deng are equally to this work.

Competing interests

The authors declare no competing interests.

Wu, Q. Y. et al. A metal-free photocatalyst for highly efficient hydrogen peroxide photoproduction in real seawater. Nat. Commun. 12, 483 (2021).
Zhao, Y. B. et al. Mechanistic analysis of multiple processes controlling solar-driven H₂O₂ synthesis using engineered polymeric carbon nitride. Nat. Commun. 12, 3701 (2021).
Liu, L.-L. et al. Edge electronic vacancy on ultrathin carbon nitride nanosheets anchoring O₂ to boost H₂O₂ photoproduction. Appl. Catal. B Environ. 302, 120845 (2022).
Luo, J. et al. Direct attack and indirect transfer mechanisms dominated by reactive oxygen species for photocatalytic H₂O₂ production on g-C₃N₄ possessing nitrogen vacancies. ACS Catal. 11, 11440–11450 (2021).
Oka, K. et al. Copolymer of phenylene and thiophene toward a visible-light-driven photocatalytic oxygen reduction to hydrogen peroxide. Adv. Sci. 8, 2003077 (2021).
Che, H. N. et al. Iodide-induced fragmentation of polymerized hydrophilic carbon nitride for high-performance quasi-homogeneous photocatalytic H₂O₂ production. Angew. Chem. Int. Ed. 60, 25546–25550 (2021).
Luo, J. J. et al. Photoredox-promoted Co-production of dihydroisoquinoline and H₂O₂ over defective Zn₃In₂S₆. Adv. Mater. 35, 2210110 (2023).
Yang, C. et al. Calcination-regulated microstructures of donor-acceptor polymers towards enhanced and stable photocatalytic H₂O₂ production in pure water. Angew. Chem. Int. Ed. 61, e202208438 (2022).
Du, C. et al. Fabricating S-scheme BiOBr/Zn₂In₂S₅ heterojunction for synergistic adsorption-photocatalytic degradation of tetracycline. Mat. Today Phys. 27, 100827 (2022).
Wang, P. et al. Piezotronic effect and hierarchical Z-scheme heterostructure stimulated photocatalytic H₂ evolution integrated with C-N coupling of benzylamine. Nano Energy 89, 106349 (2021).
Zhu, Z. J. et al. Chemically bonded alpha-Fe₂O₃/Bi₄MO₈Cl dot-on-plate Z-Scheme junction with strong internal electric field for selective photo-oxidation of aromatic alcohols. Angew. Chem. Int. Ed. 61, e202203519 (2022).
Gao, Z. et al. Interfacial Ti-S bond modulated S-scheme MOF/Covalent triazine framework nanosheet heterojunctions for photocatalytic C-H functionalization. Angew. Chem. Int. Ed., 62, e202304173 (2023).
Zhang, W. H. et al. Z-Scheme Photocatalytic Systems for Carbon Dioxide Reduction: Where Are We Now? Angew. Chem. Int. Ed. 59, 22894–22915 (2020).
Cheng, C. et al. An inorganic/organic S-Scheme heterojunction H₂-production photocatalyst and its charge transfer mechanism. Adv. Mater. 33, 2100317 (2021).
Cheng, C. et al. Verifying the Charge-Transfer mechanism in S-Scheme heterojunctions using femtosecond transient absorption spectroscopy. Angew. Chem. Int. Ed. 62, e202218688 (2023).
Li, R. G. et al. Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO₄. Nat. Commun. 4, 1432 (2013).
Ding, L. et al. 2D β-NiS as electron harvester anchors on 2D ZnIn₂S₄ for boosting photocatalytic hydrogen production. J. Alloys Compd. 853, 157328 (2021).
Du, C. et al. π-π conjugation driving degradation of aromatic compounds with in-situ hydrogen peroxide generation over Zn₂In₂S₅ grown on nitrogen-doped carbon spheres. Appl. Catal. B Environ. 310, 121298 (2022).
Dang, X. et al. The in situ construction of ZnIn₂S₄/CdIn₂S₄ 2D/3D nano hetero-structure for an enhanced visible-light-driven hydrogen production. J. Mater. Chem. A 9, 14888–14896 (2021).
Bai, P. et al. Junction of Zn_mIn₂S_3+m and bismuth vanadate as Z-scheme photocatalyst for enhanced hydrogen evolution activity: The role of interfacial interactions. J. Colloid Interface Sci. 628, 488–499 (2022).
Yang, W. et al. Minimized external electric field on asymmetric monolayer maximizes charge separation for photocatalysis. Appl. Catal. B Environ. 295, 120266 (2021).
Zhang, L. et al. Cr-metal-organic framework coordination with ZnIn₂S₄ nanosheets for photocatalytic reduction of Cr(VI). J. Clean. Prod. 341, 130891 (2022).
Zhang, G. et al. Preparation of ZnIn₂S₄ nanosheet-coated CdS nanorod heterostructures for efficient photocatalytic reduction of Cr(VI). Appl. Catal. B Environ. 232, 164–174 (2018).
Cao, S. et al. H₂-production and electron-transfer mechanism of a noble-metal-free WO₃@ZnIn₂S₄ S-Scheme heterojunction photocatalyst. J. Mater. Chem. A 10, 17174–17184 (2022).
Zhang, L. Y. et al. Emerging S-Scheme photocatalyst. Adv. Mater. 34, 2107668 (2022).
Huang, H. et al. Direct Z-Scheme heterojunction of semicoherent FAPbBr₃/Bi₂WO₆ interface for photoredox reaction with large driving force. ACS Nano 14, 16689–16697 (2020).
Song, M. et al. Edge- and bridge-engineering-mediated exciton dissociation and charge separation in carbon nitride to boost photocatalytic H₂ evolution integrated with selective amine oxidation. J. Mater. Chem. A 10, 16448–16456 (2022).
Wang, Q. et al. Steering rigidified nonplanar conjugation based perylene diimide supramolecular for enhancing photocatalytic activity. Mater. Today 61, 22–29 (2022).
Makarov, N. S. et al. Two-Photon absorption in CdSe colloidal quantum dots compared to organic molecules. ACS Nano 8, 12572–12586 (2014).
Li, F. et al. Understanding the unique S-scheme charge migration in triazine/heptazine crystalline carbon nitride homojunction. Nat. Commun. 14, 3901 (2023).
Yang, C. et al. Effects of Illumination Direction on the Surface Potential of CH₃NH₃PbI₃ Perovskite Films Probed by Kelvin Probe Force Microscopy. ACS Appl. Mater. Interfaces 11, 14044–14050 (2019).
Jiao, X. et al. Defect-mediated electron–hole separation in one-unit-cell ZnIn₂S₄ layers for boosted solar-driven CO₂ reduction. J. Am. Chem. Soc. 139, 7586–7594 (2017).
Peng, H. et al. Oxygen vacancy and Van der Waals heterojunction modulated interfacial chemical bond over Mo₂C/Bi₄O₅Br₂ for boosting photocatalytic CO₂ reduction. Appl. Catal. B Environ. 318, 121866 (2022).
Chen, X. et al. Visible-light-driven hydrogen peroxide production from water and dioxygen by perylenetetracarboxylic diimide modified titanium-based metal–organic frameworks. J. Mater. Chem. A 9, 26371–26380 (2021).
Shiraishi, Y. et al. Resorcinol-formaldehyde resins as metal-free semiconductor photocatalysts for solar-to-hydrogen peroxide energy conversion. Nat. Mater. 18, 985–993 (2019).
Lin, S. et al. Piezocatalytic and photocatalytic hydrogen peroxide evolution of sulfide solid solution nano-branches from pure water and air. Small 18, 2200914 (2022).
Zeng, X. et al. Simultaneously tuning charge separation and oxygen reduction pathway on graphitic carbon nitride by polyethylenimine for boosted photocatalytic hydrogen peroxide production. ACS Catal. 10, 3697–3706 (2020).
Chen, X. et al. Sacrificial agent-free photocatalytic H₂O₂ evolution via two-electron oxygen reduction using a ternary α-Fe₂O₃/CQD@g-C₃N₄ photocatalyst with broad-spectrum response. J. Mater. Chem. A 8, 18816–18825 (2020).
Chen, L. et al. Acetylene and diacetylene functionalized covalent triazine frameworks as metal-free photocatalysts for hydrogen peroxide production: a new two-electron water oxidation pathway. Adv. Mater. 32, 1904433 (2020).
Zheng, Y. et al. Photocatalytic production of H₂O₂ over facet-dependent Ti-MOF. Catal. Sci. Technol. 12, 969–975 (2022).
Li, X. et al. Boosting photocatalytic H₂O₂ production in pure water over a plasmonic photocatalyst with polyethylenimine modification. J. Mater. Chem. A 11, 1503–1510 (2023).
Yang, C. et al Calcination-regulated microstructures of donor-acceptor polymers towards enhanced and stable photocatalytic H₂O₂ production in pure water. Angew. Chem. Int. Ed. 61, e202208438 (2022).
Zhang, J. et al. Efficient photocatalytic H₂O₂ production from oxygen and pure water over graphitic carbon nitride decorated by oxidative red phosphorus. Appl. Catal. B Environ. 298, 120522 (2021).
Chu, C. et al. Photocatalytic H₂O₂ production driven by cyclodextrin-pyrimidine polymer in a wide pH range without electron donor or oxygen aeration. Appl. Catal. B Environ. 314, 121485 (2022).
Liu, Y. et al. Substoichiometric covalent organic frameworks with uncondensed aldehyde for highly efficient hydrogen peroxide photosynthesis in pure water. Appl. Catal. B Environ. 331, 122691 (2023).
Wu, C. B. et al. Polarization engineering of covalent triazine frameworks for highly efficient photosynthesis of hydrogen peroxide from molecular oxygen and water. Adv. Mater. 34, 2110266 (2022).
Xu, L. et al. Fabrication of a photocatalyst with biomass waste for H₂O₂ synthesis. ACS Catal. 11, 14480–14488 (2021).
Yang, T. et al. Covalent furan-benzimidazole-linked polymer hollow fiber membrane for clean and efficient photosynthesis of hydrogen peroxide. Adv. Funct. Mater. 33, 2300714 (2023).
Zhang, Y. et al. Water flow induced piezoelectric polarization and sulfur vacancy boosting photocatalytic hydrogen peroxide evolution of cadmium sulfide nanorods. Appl. Catal. B Environ. 331, 122714 (2023).
Fu, C. et al. Unraveling the dual defect effects in C₃N₅ for piezo-photocatalytic degradation and H₂O₂ generation. Appl. Catal. B Environ. 332, 122752 (2023).
Zhang, X. et al. Unraveling the dual defect sites in graphite carbon nitride for ultra-high photocatalytic H₂O₂ evolution. Energy Environ. Sci. 15, 830–842 (2022).
Liu, L. et al. Linear conjugated polymers for solar-driven hydrogen peroxide production: the importance of catalyst Stability. J. Am. Chem. Soc. 143, 19287–19293 (2021).
Luo, Y. et al. Sulfone-modified covalent organic frameworks enabling efficient photocatalytic hydrogen peroxide generation via one-step two-electron O₂ reduction. Angew. Chem. Int. Ed. 62, e202305355 (2023).
Xu, Z. et al. Trace water triggers high-efficiency photocatalytic hydrogen peroxide production. J. Energy Chem. 64, 47–54 (2022).

There is NO Competing Interest.

SI.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

Unveiling Intrinsic Charge Transfer Dynamics in Bone-Joint S-Scheme Heterostructures for Promoting Photocatalytic Hydrogen Peroxide Generation

Status:

Version 1

Abstract

Figures

Introduction

Results

Characterization of The Bone-joint Structure

Formation of S-scheme Heterojunctions

Intrinsic charge transfer dynamics

Photocatalytic activity and mechanism

Conclusion

Methods

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1