Stable photocatalytic H₂ production and selective oxidation of phenylcarbinol via regulating charge separation over NiS₂/CdS under visible light

Abstract

The simultaneous development of highly efficient photocatalysts for organic oxidation and hydrogen production is crucial for sustainable energy conversion. In this study, we designed and synthesized a three-dimensional layered NiS₂/CdS ohmic junction photocatalyst capable of selectively oxidizing phenylmethanol (POL) to produce benzaldehyde (BDE) under visible light, accompanied by hydrogen (H₂) evolution. The NiS₂/CdS composite material was characterized using SEM, TEM, XPS, and XRD. Owing to the formation of an ohmic junction, it exhibited enhanced light absorption and charge separation, which facilitated the transfer of electrons from CdS to NiS₂. Photoelectrochemical and in situ XPS analyses confirmed that the photogenerated carriers were spatially separated, with holes on CdS driving POL oxidation and electrons on NiS₂ promoting H₂ production. The optimal 5% NiS₂/CdS achieved remarkable H₂ evolution (9.31 mmol g⁻¹ h⁻¹) as well as BDE generation (9.23 mmol g⁻¹ h⁻¹), with a 6-fold activity enhancement over pristine CdS. Additionally, the composite demonstrated excellent stability, retaining 97.96% activity after four cycles. This work highlighted the potential of ohmic junction photocatalysts for dual-functional redox reactions, offering a sustainable strategy for high-value chemical synthesis and clean energy production.

---

1. Introduction

With the global energy crisis and environmental pollution becoming increasingly serious, the development of cleaner and more sustainable energy conversion technologies has become a research hotspot. Hydrogen (H₂) is considered an ideal energy carrier for the future in view of its high energy density and zero carbon emissions.^1–4 Traditional hydrogen production methods (such as methane reforming and water electrolysis) rely on fossil fuels or are highly energy-consuming.⁵ Therefore, solar-driven photocatalytic hydrogen production technology has attracted much attention.^6–8 However, photocatalytic overall water splitting (OWS) for hydrogen production efficiency is relatively low, which was led by the rapid recombination of photogenerated electron–hole pairs and the slow kinetics of the oxygen evolution reaction (OER).^8–10 In recent years, the construction of bi-functional reaction systems—photocatalytic selective organic oxidation coupled with hydrogen production—has provided a new solution to this problem.^11–15 This strategy utilizes organic molecules (such as phenylcarbinol) as hole sacrificial agents to simultaneously achieve the synthesis of high-value chemicals and efficient hydrogen production during the photocatalytic process.^16–18 Among them, the coupling reaction of selective oxidation of phenylcarbinol (PhCH₂OH, POL) to benzaldehyde (PhCHO, BDE) and reduction of protons to produce hydrogen has become a research hotspot due to its high atom economy, environmentally friendly synthesis of highly valuable chemicals, and clean energy production.^19–21 The overall reaction of photocatalytic phenylcarbinol oxidation coupled with hydrogen production can be expressed as: PhCH₂OH + photocatalyst + light → PhCHO + H₂. This process involves the following key steps:^22,23 (I) light absorption and carrier separation: the semiconductor catalysts capture light energy to generate electron (e⁻)–hole (h⁺) pairs and enable the photogenerated electron–hole pairs to be effectively separated and migrate to the surface for reactions. (II) Phenylcarbinol oxidation: holes oxidize phenylcarbinol to benzaldehyde while releasing protons (H⁺). This process requires holes with appropriate oxidation ability. (III) Proton reduction to produce hydrogen: electrons on the conduction band reduce H⁺ to generate H₂. This process requires the catalyst to have an appropriate conduction band. (IV) Competition of side reactions: if holes are not effectively captured by phenylcarbinol, the OER or photocorrosion (such as CdS) may occur. If the oxidation ability of holes is too strong, it may further oxidize benzaldehyde to generate other by-products.²⁴ To enable effective photocatalytic selective phenylcarbinol oxidation coupled with hydrogen production, it is necessary to design photocatalysts that meet the above key steps.

Obviously, an efficient photocatalyst for such a bifunctional redox reaction system should have the following features:^20–29 wide-spectrum absorption (visible light response); efficient carrier separation ability; appropriate band structure (the conduction band position should be more negative than the H⁺/H₂ potential, and the valence band position should be more positive than the oxidation potential of phenylcarbinol); and effective active sites. For individual photocatalysts, TiO₂, a classic photocatalyst, can catalyze various reactions, but it has a large band gap (∼3.2 eV) and responds only to ultraviolet light. Moreover, the selectivity of phenylcarbinol oxidation is relatively low due to its strong oxidation ability.²⁴ Another typical photocatalyst, CdS, is visible light responsive (∼2.4 eV) with suitable valence and conduction bands to selectively oxidise phenylcarbinol to benzaldehyde and reduce protons to hydrogen.^25,26 Nevertheless, the rapid recombination of photogenerated charges and its susceptibility to photocorrosion restrict its photocatalytic activity and stability.²⁷ Co-catalysts containing noble metals like Pt, PtO and Au are capable of significantly improving the activity and stability of the photocatalysts for hydrogen production.²⁸ The co-catalysts not only improve the photogenerated electron and hole separation and migration efficiencies,^29,30 but also act as active sites for hydrogen production, thereby reducing the over-potential for hydrogen evolution and accelerating H₂ generation.^31–33 However, the precious metals' rarity and high cost limit their large-scale application. Among various non-noble metal co-catalysts, nickel sulfides (NiS, NiS₂ and Ni₃S₄) with metallic properties have received extensive attention.^34–38 For example, Meng et al. designed and synthesized a 2D/2D–3D NiS/Zn₃In₂S₆ Schottky junction to promote the selective conversion of biomass alcohols and hydrogen production.³⁴ However, the barrier layer was formed on the NiS/Zn₃In₂S₆ interfaces due to the high work function of NiS. The improvement of the photocatalytic activity is limited. More recently, Yang et al. fabricated an ohmic contact Ni₃S₄/NiS₂/v-Zn₃In₂S₆ bi-functional photocatalyst, significantly enhancing the photocatalytic activity and stability of Zn₃In₂S₆ in the degradation of bisphenol A and hydrogen production.³⁷ Compared to NiS/Zn₃In₂S₆, the ohmic junctions of Ni₃S₄/NiS₂/v-Zn₃In₂S₆ exhibited cascading built-in electric fields consistent with the direction of photogenerated electron separation and migration, thereby significantly boosting photocatalytic performance. Constructing heterojunction photocatalysts with a built-in electric field that is consistent with the direction of photogenerated charge separation and migration is a frontier and hot topic in the design and preparation of photocatalysts.^39–41 It not only effectively separates and transfers photogenerated charges but also regulates the oxidation–reduction ability and active sites of photogenerated charges.

Inspired by the above analysis, we designed and synthesized a three-dimensional (3D) hierarchical NiS₂/CdS ohmic junction photocatalyst. The 3D hierarchical structure of CdS not only facilitated light absorption and catalyst recovery but also promoted the dispersion and loading of NiS₂. NiS₂ with a small work function forms an ohmic contact with CdS, and the built-in electric field drove the separation and migration of photogenerated electrons from CdS to the surface of NiS₂. Moreover, NiS₂ had a low over-potential for hydrogen evolution, achieving spatial separation in this dual-functional redox photocatalytic system—the selective oxidation of phenylcarbinol to benzaldehyde on CdS and the reduction of photogenerated electrons to hydrogen on NiS₂. The photocatalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The light absorption and band structure of the catalyst were analyzed by UV-vis diffuse reflectance spectroscopy (DRS) and Mott–Schottky tests. The photocatalytic mechanism was analyzed in detail through photoelectrochemical (PEC) measurements, in situ X-ray photoelectron spectroscopy (XPS), in situ electron paramagnetic resonance (EPR), active species trapping experiments, and theoretical calculations.

2. Experimental section

The detailed descriptions of the materials used in the experiment, the synthesis processes of CdS, NiS₂, and NiS₂/CdS photocatalysts, the photocatalytic activity test of NiS₂/CdS, the characterization of photocatalysts, and density functional theory (DFT) calculations are presented in the SI.

3. Results and discussion

3.1. Structure and morphology characterization

A self-assembly method was used to prepare NiS₂/CdS composites (Scheme 1). The XRD patterns of CdS, NiS₂ and NiS₂/CdS composites are displayed in Fig. 1a. The synthesized CdS exhibited a hexagonal phase (PDF #41-1049), while NiS₂ crystallizes in a cubic phase (PDF #89-1495). After the formation of the NiS₂/CdS composite, the diffraction peaks of NiS₂/CdS remained similar to those of pure CdS, demonstrating that the loading of NiS₂ did not alter the crystal structure of the host catalyst CdS or introduce any impurities. The absence of NiS₂ peaks might be attributed to its low loading amount (approximately 3.6% as determined by ICP-OES analysis) and uniform dispersion. SEM images (Fig. 1b and Fig. S1) revealed that CdS possessed a three-dimensional (3D) spherical morphology composed of aggregated nanoparticles with smooth surfaces, whereas NiS₂ exhibited a two-dimensional (2D) flexible sheet-like structure (Fig. S2). After NiS₂ loading, the NiS₂/CdS composite retained its 3D spherical architecture (Fig. 1c), but the nanoparticle surfaces displayed attached nanosheets (Fig. 1d). This observation was further corroborated by TEM analysis (Fig. 1e). HRTEM (Fig. 1f) revealed two different lattice fringes that were spaced at 0.35 nm and 0.23 nm, correlating with the (100) plane of CdS and the (211) plane of NiS₂, respectively. As shown in Fig. S3, the Ni, Cd and S elements were uniformly distributed, and the Ni element was mainly distributed on the outer surface. The NiS₂/CdS preparation method and the original TEM and HRTEM results all collectively indicated the presence of NiS₂.

Scheme 1 Schematic illustration of the preparation of 3D CdS, NiS₂ and NiS₂/CdS.

Fig. 1 (a) XRD patterns of CdS, NiS₂/CdS and NiS₂. SEM images of (b) CdS and (c) and (d) NiS₂/CdS. (e) TEM and (f) HRTEM images of NiS₂/CdS. XPS spectra of (g) Cd 3d, (h) S 2p and (i) Ni 2p in NiS₂/CdS.

The surface chemical states and composition of the NiS₂/CdS composite were investigated by XPS. The survey spectrum (Fig. S4) indicated that Ni, S, and Cd were present in the composite. The peaks at 405.22 eV and 412.01 eV in the high-resolution Cd 3d spectrum (Fig. 1g) were assigned to Cd 3d_5/2 and Cd 3d_3/2, respectively, indicating that Cd was in the +2 oxidation state.²⁸ The peaks at 161.69 eV and 162.89 eV in the S 2p spectrum (Fig. 1h) were attributed to S 2p_3/2 and S 2p_1/2 for the divalent sulphide ions.²⁸ There were four distinct peaks in the Ni 2p spectrum (Fig. 1i) at 855.67 eV, 861.13 eV, 874.99 eV, and 881.50 eV, where the peaks at 855.67 eV and 874.99 eV were assigned to Ni 2p_3/2 and Ni 2p_1/2, respectively, whereas the remaining peaks were satellite features.³⁸ These characterisation results jointly confirmed the successful preparation of the NiS₂/CdS composite.

3.2. Optical and electrochemical analyses

Fig. 2a presents the UV-vis diffuse reflectance spectra (DRS) of pristine CdS and 5% NiS₂/CdS. Both materials exhibited strong visible-light absorption, with a slight enhancement observed after NiS₂ modification. On the basis of Tauc plot analysis (Fig. 2b), it was known that the band gap energy of CdS was 2.23 eV and that of NiS₂/CdS was 2.22 eV. Mott–Schottky (M–S) measurements (Fig. 2c) demonstrated that the flat-band potentials of CdS and NiS₂/CdS were −0.38 V and −0.44 V (vs. NHE), respectively, confirming that the n-type semiconductor nature of CdS remained unchanged after NiS₂ modification, as evidenced from the positive slopes of the M–S plots. It should be noted that the potential (E_Ag/AgCl) was converted into E_NHE (vs. normal hydrogen electrode (NHE)) according to the formula: E_NHE = E_Ag/AgCl + 0.197 V.^42–44 The conduction band (CB) of n-type semiconductors was negative by approximately 0.1 V compared to the flat band potential,^45,46 thereby estimating the CB positions of CdS and NiS₂/CdS to be −0.48 V and −0.54 V, respectively. Therefore, the valence band (VB) position of CdS was determined to be 1.75 V, and that of NiS₂/CdS to be 1.68 V (Fig. 2d). These results suggested that NiS₂ loading slightly enhanced the optical absorption and electron reduction capability of CdS. Although the hole oxidation ability of NiS₂/CdS was marginally reduced, it was still sufficient to selectively oxidize benzyl alcohol to benzaldehyde with no further over-oxidation (the oxidation potential of POL/BDE was about 1.6 V (vs. NHE)).⁴⁷

Fig. 2 (a) DRS spectra, (b) Tauc plots, (c) M–S plots and (d) electronic band structures of CdS and NiS₂/CdS.

The separation and migration efficiency of photogenerated charge carriers were critical factors influencing photocatalytic activity. The charge carrier dynamics of CdS and NiS₂/CdS were investigated using electron paramagnetic resonance (EPR) and photoelectrochemical (PEC) analyses.^48–50 TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) exhibited a characteristic triplet signal in both aqueous and acetonitrile solutions.⁵¹ In water, TEMPO scavenged photogenerated electrons, resulting in a sharp decrease in the triplet signal intensity, whereas in acetonitrile, it captured photogenerated holes, resulting in a weakened broad triplet signal. A more pronounced decrease in EPR signal intensity corresponded to higher charge carrier trapping efficiency, indicating improved charge separation and migration.⁵¹ As shown in Fig. 3a and b, NiS₂/CdS exhibited significantly lower EPR signals for both electrons and holes compared to pristine CdS, demonstrating superior charge separation and migration. This finding was further supported by PEC measurements, where NiS₂/CdS displayed a stronger photocurrent response (Fig. 3c). In addition, with the extension of the exposure time (Fig. S5), the photocurrent of CdS dropped sharply, while the photocurrent attenuation rate of NiS₂/CdS was relatively slow, indicating that the load of NiS₂ could inhibit the photocorrosion of CdS to a certain extent. Moreover, NiS₂/CdS showed an extended charge carrier lifetime, as evidenced by normalized current decay analysis (Fig. 3d). The transient time constant (τ) was determined from the slope of the linear region of a plot of ln D versus time. Here, D (normalized parameter) is defined by eqn (1):³⁸

D = (I_t − I_st)/(I_in − I_st) (1)

where I_t, I_st, and I_in represent the photocurrent, at time t (s), the steady-state photocurrent, and the initial photocurrent, respectively. τ is obtained at ln D = −1. As presented in Fig. 3d, it could be clearly observed that NiS₂/CdS exhibited a longer charge carrier lifetime compared to pristine CdS. Open-circuit voltage (V_OC) measurements (Fig. 3e) confirmed that NiS₂/CdS exhibited a higher photovoltage response and slower decay kinetics compared to CdS. In addition, the electronic lifetime (τ_n) could be evaluated from the V_OC measurement value (eqn (2)).⁵¹

τ_n = (k_BT/e)/(dV_OC/dt) (2)

where k_B, T, e and t are the Boltzmann constant, temperature, single-electron charge and time, respectively. Further quantitative analysis (Fig. 3f) revealed that NiS₂ modification prolonged the charge carrier lifetime of CdS, which was beneficial for photocatalytic reactions. Moreover, linear sweep voltammetry (LSV) results (Fig. S6) revealed that NiS₂/CdS possessed a lower over-potential of H₂ production relative to pristine CdS, and the Tafel slope of NiS₂/CdS (mV dec⁻¹) was less than that of CdS (mV dec⁻¹). These results indicated that the surface of the NiS₂ co-catalyst was conducive to photocatalytic H₂ production. Notably, in situ XPS was utilized to elucidate the spatial separation and transfer of charge carriers. As shown in Fig. 3g–i, under light irradiation, the binding energies of Cd and S in NiS₂/CdS shifted positively, while that of Ni shifted negatively, indicating that photogenerated electrons migrated from CdS to NiS₂, whereas holes remained on CdS. This spatial charge separation effectively suppressed recombination and enhanced photocatalytic efficiency.

Fig. 3 EPR spectra for detecting photogenerated (a) electrons and (b) holes over CdS and NiS₂/CdS. (c) Photocurrent patterns and (d) the corresponding normalized plots of CdS and NiS₂/CdS. (e) Open circuit voltage decay patterns and (f) the corresponding electron lifetimes of CdS and NiS₂/CdS. In situ XPS spectra of NiS₂/CdS in the dark and under visible light: (g) Cd 3d, (h) S 2p and (i) Ni 2p.

3.3. Photocatalytic activity evaluation

The catalytic activity could be determined by the photocatalytic selective oxidation of phenylcarbinol (POL) to benzaldehyde (BDE) and the simultaneous release of hydrogen gas (H₂) under visible light irradiation. Control experiments confirmed that, in the absence of light or a catalyst, there was no H₂ production. In the presence of both a catalyst and visible light, simultaneous benzaldehyde production and H₂ evolution were detected (Fig. 4a). The separated BDE from the reaction solution was identified and quantified by NMR spectroscopy and gas chromatography (Fig. S7 and S8).⁴⁵ The BDE and H₂ release rates of pristine CdS were 1.51 and 1.55 mmol g⁻¹ h⁻¹, respectively. Upon NiS₂ modification, the photocatalytic activity significantly improved. The optimal performance was achieved with 5% NiS₂/CdS, resulting in release rates of 9.23 and 9.31 mmol g⁻¹ h⁻¹ for BDE and H₂, respectively—a 6-fold enhancement in H₂ production over pure CdS. The selectivity of BDE over 5% NiS₂/CdS was about 91.3%, and the estimated AQE of 5% NiS₂/CdS at 400 nm was around 1.2%.

Fig. 4 (a) Photocatalytic activities of CdS and NiS₂/CdS composites with different weight ratios of NiS₂ for selective oxidation of POL and H₂ production under visible light. (b) Photocatalytic H₂ production activity of NiS₂/CdS in different reaction solutions (H₂O, NaSO, LA and POL represent pure water, Na₂S/Na₂SO₃ solution, lactic acid, and PhCH₂OH, respectively). Cycling stability tests of (c) NiS₂/CdS and (d) CdS for selective oxidation of POL and H₂ production under visible light.

Furthermore, this bifunctional coupled reaction system outperformed conventional sacrificial-agent systems (Fig. 4b). For instance, the H₂ evolution rates of 5% NiS₂/CdS in Na₂S/Na₂SO₃ solution and lactic acid solution were 2.12 and 6.83 mmol g⁻¹ h⁻¹, respectively. Remarkably, its H₂ production rate in POL solution was 4.39 times and 1.36 times higher than that in Na₂S/Na₂SO₃ solution and lactic acid systems, confirming the superiority of this coupled reaction approach. It is worth noting that the NiS₂ loading not only enhanced the activity of CdS, but also markedly boosted its stability. After four consecutive cycles, 5% NiS₂/CdS retained 97.96% of its initial H₂ evolution activity (Fig. 4c), whereas pristine CdS suffered a 86.5% decline (Fig. 4d). Post-reaction characterization via XRD (Fig. S9) and SEM (Fig. S10) confirmed that 5% NiS₂/CdS maintained its original crystal phase and morphology, indicating excellent structural stability. These results demonstrated that NiS₂ modification effectively suppressed the photocorrosion of CdS while ensuring high recyclability and long-term stability. The poor stability of CdS mainly results from its photocorrosion.²⁷ After NiS₂ modification, the photogenerated charge separation–migration efficiency of CdS was significantly improved (Fig. 3), and the photogenerated charges were consumed in a timely manner (the photogenerated holes were used for the selective oxidation–dehydrogenation of POL, and the photogenerated electrons transferred to NiS₂ were used for H₂ production). As a result, the photocorrosion of CdS was suppressed to a certain extent, and NiS₂/CdS exhibited better stability.

3.4. Photocatalytic mechanisms of the dual-function photoredox reactions

To elucidate the mechanism of efficient charge separation and migration in the NiS₂/CdS nanocomposites, the carrier concentration and work functions of NiS₂ and CdS were analyzed. The carrier concentration (N_D) was calculated from Mott–Schottky plots using eqn (3):^38,52

N_D = (2/εε₀e)(dU/dC⁻²) (3)

where ε₀ is the vacuum permittivity, ε is 8.7 for CdS,⁵² and C is the capacitance.

As shown in Fig. 5a, CdS and NiS₂/CdS had carrier concentrations of 6.76 × 10²⁰ cm⁻³ and 6.79 × 10²⁰ cm⁻³, respectively. After NiS₂ loading, the increase in carrier concentration implied that carriers were injected from NiS₂ into CdS. Subsequent theoretical calculations revealed that CdS and NiS₂ had work functions of 4.43 eV (Fig. 5b) and 5.12 eV (Fig. 5c), respectively. Consequently, the Fermi levels (E_F) relative to the vacuum level were −4.43 eV for CdS and −5.12 eV for NiS₂, suggesting that the Fermi level of CdS exceeded that of NiS₂ (Fig. 5d). Additionally, the calculated bandgap of NiS₂ was 0 eV (Fig. S11), consistent with literature reports describing NiS₂ as a metal-like cocatalyst.^35,37,38

Fig. 5 (a) Carrier densities of CdS and NiS₂/CdS. Work functions of (b) NiS₂ and (c) CdS. (d)–(f) Band diagrams of CdS and NiS₂ before and after the equilibrium, and photoexcited carriers’ separation and transfer mechanism.

The Fermi level disparity between NiS₂ and CdS facilitated the formation of an ohmic heterojunction upon contact. Due to the difference in Fermi levels, charge carriers (electrons) diffusely migrated from the material with a higher Fermi level (NiS₂) to the material with a lower Fermi level (CdS), increasing the carrier concentration in CdS—a finding corroborated by the carrier concentration. In the equilibrium state, an internal electric field was established from NiS₂ to CdS (Fig. 5e). Under illumination, this field drove the spatial separation of photogenerated electrons, enabling them to transition from the conduction band of CdS to NiS₂ (Fig. 5f), thereby suppressing recombination of photo-excited charge carriers and enhancing photocatalytic efficiency.

To clarify the reaction mechanism of photocatalytic selective oxidation of benzyl alcohol coupled with hydrogen evolution on NiS₂/CdS, we first performed the active species capture experiment. When triethanolamine (TEOA),^53,54 a hole scavenger, was incorporated into the reaction system, both BDE production and H₂ evolution rates were significantly inhibited (Fig. 6a). This observation indicated that the oxidation process of POL governed the proton reduction process for H₂ generation. On the other hand, upon the addition of an electron scavenger (CCl₄),^55,56 the H₂ production rate dramatically decreased, while the BDE yield remained largely unaffected. This suggested that the hole-mediated selective oxidation of POL to BDE proceeded independently of the electron-driven proton reduction process. Further insight was gained through in situ electron paramagnetic resonance (EPR) spectroscopy, which revealed that the selective dehydrogenation of POL followed a radical pathway. As shown in Fig. 6b, no EPR signal was detected in the dark. Nevertheless, a characteristic six-line EPR signal appeared when exposed to light, and it intensified with increasing exposure time. This sextet signal was attributed to carbon-centered radicals,⁵¹ confirming the radical-involved mechanism. Based on these results and pervious reports,^57–62 we proposed the following reaction mechanism for the NiS₂/CdS photocatalytic system (Fig. 6c): under visible light irradiation, CdS generated electron–hole pairs. Photogenerated electrons were driven by the internal electric field and spatially separated from CdS to NiS₂. The holes remaining on CdS oxidize POL through a radical-mediated pathway, selectively yielding BDE while releasing protons. The transferred electrons on NiS₂ subsequently reduced the protons to produce H₂. This process established an efficient bi-functional photocatalytic redox system, where the oxidation and reduction half-reactions were synergistically coupled while maintaining spatial separation of active sites. The radical-involved oxidation pathway accounts for the high selectivity toward BDE formation, while the effective charge separation ensured simultaneous proton reduction for H₂ evolution.

Fig. 6 (a) The trapping agent tests (TEOA and CCl₄ are the trapping agents for photogenerated holes and electrons, respectively), (b) in situ EPR spectra and (c) photocatalytic mechanism of NiS₂/CdS for selective oxidation of POL and H₂ production under visible light.

4. Conclusion

Overall, this study succeeded in developing a NiS₂/CdS ohmic junction photocatalyst suitable for the effective coupling of selective phenylcarbinol oxidation and hydrogen production under visible light irradiation. The Fermi level difference between NiS₂ and CdS created an ohmic junction that generated an internal electric field, leading to the spatial separation of photogenerated electrons and holes. Not only did this design enhance charge carrier separation, it also optimized the redox processes, with holes on CdS selectively oxidizing POL to BDE and electrons on NiS₂ reducing protons to H₂. The 5% NiS₂/CdS composite exhibited superior photocatalytic activity, achieving H₂ and BDE production rates of 9.31 and 9.23 mmol g⁻¹ h⁻¹, respectively, significantly outperforming pristine CdS. Furthermore, the composite displayed outstanding stability, retaining 97% of the initial activity during multiple cycles, which was attributed to the suppression of photocorrosion by NiS₂. Mechanistic studies revealed a radical-involved oxidation pathway for POL and confirmed the synergistic coupling of the two half-reactions. This work provided a novel strategy to construct efficient and stable dual-functional redox photocatalysts, which was beneficial to the development of sustainable energy conversion and green chemical synthesis. The findings underscore the importance of ohmic junctions in photocatalysis and pave the way for future research on non-precious metal-based cocatalysts for multifunctional applications.

Author contributions

Zhenyu Liu: conceptualization, data curation, formal analysis, investigation, methodology, software, validation, visualization, writing – original draft, writing – review and editing. Zhenyu Zhang: conceptualization, funding acquisition, investigation, resources, project administration, supervision, writing – review and editing. Yaming Zhao: software, supervision, validation. Cheng Xue: supervision, validation. Chenggong Gong: supervision, validation. Canghao Li: supervision, validation. Weisheng Liu: conceptualization, funding acquisition, investigation, resources, project administration, supervision, writing – review and editing. Felipe de Jesus Silerio-Vázquez: supervision.

Conflicts of interest

The authors declare that they have no competing interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Supplementary information (SI) is available. See DOI: https://doi.org/10.1039/d5nj02951a.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 21871122), the Lanzhou Institute of Technology Doctoral Research Start-up Fund (Grant No. 1204000423) and the Lanzhou Institute of Technology Youth Science and Technology Innovation Project in 2025 (Grant No. 2025-KJ-30).

References

1. B. Xia, B. He, J. Zhang, L. Li, Y. Zhang, J. Yu, J. Ran and S. Z. Qiao, Adv. Energy Mater., 2022, 12, 2201449.
2. Y. Che, K. Wang, C. Wang, B. Weng, S. Chen and S. Meng, J. Mater. Sci. Technol., 2026, 243, 228–236.
3. X. Yan, J. H. Dong, J. Y. Zheng, Y. Wu and F. X. Xiao, Chem. Sci., 2024, 15, 2898–2913.
4. R. Chen, G. Liu, B. Xia, T. Liu, Y. Xia, S. Liu, A. Kiakalaieh and J. Ran, Chem. Commun., 2024, 60, 10989–10999.
5. C. Anand, B. Chandraja, P. Nithiya, M. Akshaya, P. Tamizhdurai, G. Shoba, A. Subramani, R. Kumaran, K. K. Yadav, A. Gacem, J. K. Bhutto, M. A. Alreshidi and M. W. Alam, Int. J. Hydrogen Energy, 2025, 111, 319–341.
6. H. Nishiyama, T. Yamada, M. Nakabayashi, Y. Maehara, M. Yamaguchi, Y. Kuromiya, Y. Nagatsuma, H. Tokudome, S. Akiyama, T. Watanabe, R. Narushima, S. Okunaka, N. Shibata, T. Takata, T. Hisatomi and K. Domen, Nature, 2021, 598, 304–307.
7. W. H. Lee, C. W. Lee, G. D. Cha, B. H. Lee, J. H. Jeong, H. Park, J. Heo, M. S. Bootharaju, S. H. Sunwoo, J. H. Kim, K. H. Ahn, D. H. Kim and T. Hyeon, Nat. Nanotechnol., 2023, 18, 754–762.
8. T. S. Teitsworth, D. J. Hill, S. R. Litvin, E. T. Ritchie, J. S. Park, J. P. C. Jr, A. D. Taggart, S. R. Bottum, S. E. Morley, S. Kim, J. R. McBride and J. M. Atkin, Nature, 2023, 614, 270–274.
9. C. Bie, L. Wang and J. Yu, Chem, 2022, 8, 1567–1574.
10. P. Zhou, I. A. Navid, Y. Ma, Y. Xiao, P. Wang, Z. Ye, B. Zhou, K. Sun and Z. Mi, Nature, 2023, 613, 66–70.
11. J. Wan, L. Liu, Y. Wu, J. Song, J. Liu, R. Song, J. Low, X. Chen, J. Wang, F. Fu and Y. Xiong, Adv. Funct. Mater., 2022, 32, 2203252.
12. J. Luo, C. Zhu, J. Li, J. Jin, N. E. Soland, P. W. Smith, Y. Shan, A. M. Oddo, A. L. Maulana, L. Jayasinghe, X. Chen, T. Wang, J. A. Lin, E. Lu, B. Schaefer, M. Schmalzbauer, R. Zhang, F. Seeler, C. Lizandara-Pueyo, J. Guo and P. Yang, J. Am. Chem. Soc., 2025, 147, 3428–3437.
13. Y. Che, B. Weng, K. Li, Z. He, S. Chen and S. Meng, Appl. Catal., B, 2025, 361, 124656.
14. X. Bao, M. Liu, Z. Wang, D. Dai, P. Wang, H. Cheng, Y. Liu, Z. Zheng, Y. Dai and B. Huang, ACS Catal., 2022, 12, 1919–1929.
15. Y. W. Han, Y. X. Zhang, L. Ye, T. J. Gong, X. B. Lu, N. Yan and Y. Fu, Adv. Funct. Mater., 2025, 2425473.
16. N. Luo, W. Nie, J. Mu, S. Liu, M. Li, J. Zhang, Z. Gao, F. Fan and F. Wang, ACS Catal., 2022, 12, 6375–6384.
17. T. Zhou, Z. Luo, M. Shi, Y. Zhang, Q. Lu, M. Chen, H. Sun, T. He, J. Zhang and Q. Liu, Appl. Catal., B, 2025, 370, 125190.
18. B. Sun, M. Ye, Y. Xu, Y. Jiang, D. Hou, X. Q. Qiao, M. Wang, Y. Du and D. S. Li, Adv. Sci., 2025, 2501931.
19. Z. Huang, P. Sun, H. Zhang, H. Zhang, S. Zhang, Z. Chen, S. Xie and S. Xie, ACS Catal., 2024, 14, 4581–4592.
20. R. Pan, X. Ge, Q. Liu, H. Yin, Y. Guo, J. Shen, D. Zhang, P. Chen, J. Yuan, H. Xie and C. Liu, Adv. Funct. Mater., 2024, 34, 2315212.
21. M. Ma, R. Wang, L. Shi, R. Li, J. Huang, Z. Li, P. Li, E. Y. Konysheva, Y. Li, G. Liu and X. Xu, Adv. Funct. Mater., 2024, 34, 2405922.
22. Q. Lin, Y. H. Li, M. Y. Qi, J. Y. Li, Z. R. Tang, M. Anpo, Y. M. A. Yamada and Y. J. Xu, Appl. Catal., B, 2020, 271, 118946.
23. O. Savateev, J. Zhuang, S. Wan, C. Song, S. Cao and J. Tang, Chin. J. Catal., 2025, 70, 44–114.
24. M. Zhang, C. Chen, W. Ma and J. Zhao, Angew. Chem., Int. Ed., 2008, 47, 9730–9733.
25. J. Xiang, J. Li, X. Yang, S. Gao and R. Cao, Acta Phys. Chim. Sin., 2023, 39, 2205039.
26. M. Zhang, K. Li, C. Hu, K. Ma, W. Sun, X. Huang and Y. Ding, Chin. J. Catal., 2023, 47, 254–264.
27. H. Yang, Y. Xia, J. Guo, L. Xue, S. A. Carabineiro, K. Lv, L. Wen and S. Ouyang, Appl. Catal., B, 2025, 362, 124700.
28. X. Wang, M. Huang, M. Xu, X. Pan and S. Liang, Mater. Lett., 2024, 361, 136126.
29. S. Li, S. Meng, H. Zhang, A. R. Puente-Santiago, Z. Wang, S. Chen, M. J. Muñoz-Batista, Y. Zheng and B. Weng, Adv. Funct. Mater., 2025, e13682,  DOI:10.1002/adfm.202513682.
30. F. M. Yap, G. Z. S. Ling, B. J. Su, J. Y. Loh and W.-J. Ong, Nano Res. Energy, 2024, 3, e9120091.
31. Q. Yang, T. Wang, Z. Zheng, B. Xing, C. Li and B. Li, Appl. Catal., B, 2022, 315, 121575.
32. R. Wang, L. Shi, E. Y. Konysheva and X. Xu, Adv. Funct. Mater., 2025, 35, 2418074.
33. Y. Feng, S. Gong, Y. Wang, C. Ban, X. Qu, J. Ma, Y. Duan, C. Lin, D. Yu, L. Xia, X. Chen, X. Tao, L. Gan and X. Zhou, Adv. Mater., 2025, 37, 2412965.
34. S. Meng, H. Wu, Y. Cui, X. Zheng, H. Wang, S. Chen, Y. Wang and X. Fu, Appl. Catal., B, 2020, 266, 118617.
35. S. Liu, B. Zhang, Z. Yang, Z. Xue and T. Mu, Green Chem., 2023, 25, 2620–2628.
36. S. Meng, Y. Cui, H. Wang, X. Zheng, X. Fu and S. Chen, Dalton Trans., 2018, 47, 12671–12683.
37. L. Yang, J. Guo, J. Tang, Z. Zhang and S. Li, Sep. Purif. Technol., 2025, 354, 129031.
38. Z. Zhang, C. Chen, M. Tayyab, Z. Wei, X. Zheng, W. Shangguan, S. Zhang, S. Chen and S. Meng, Chem. Eng. J., 2025, 509, 161409.
39. J. Li, J. Yao, Q. Yu, X. Zhang, S. A. Carabineiro, X. Xiong, C. Wu and K. Lv, Appl. Catal., B, 2024, 351, 123950.
40. B. B. Luan, X. Chu, Y. Wang, X. Qiao, Y. Jiang and F. M. Zhang, Adv. Mater., 2024, 36, 2412653.
41. L. Yuan, C. Zhang, Y. Zou, T. Bao, J. Wang, C. Tang, A. Du, C. Yu and C. Liu, Adv. Funct. Mater., 2023, 33, 2214627.
42. H. Derikvand, N. Tahmasebi and S. Barzegar, J. Phys. Chem. Solid, 2023, 181, 111528.
43. H. Derikvand, N. Tahmasebi and S. Barzegar, Chemosphere, 2024, 355, 141879.
44. Y. Poursam, N. Tahmasebi, H. Derikvand and H. Moayeri, ACS Appl. Nano Mater., 2025, 8, 6465–6478.
45. H. Zhang, Y. Gao, S. Meng, Z. Wang, P. Wang, Z. Wang, C. Qiu, S. Chen, B. Weng and Y. M. Zheng, Adv. Sci., 2024, 11, 2400099.
46. S. Meng, C. Chen, X. Gu, H. Wu, Q. Meng, J. Zhang, S. Chen, X. Fu, D. Liu and W. Lei, Appl. Catal., B, 2021, 285, 119789.
47. Y. Wang, J. Pu, J. An, X. Liang, W. Li, Y. Huang, J. Yang, T. Chen and Y. Yao, Inorg. Chem., 2024, 63, 5269–5280.
48. J. Lei, N. Zhou, S. Sang, S. Meng, J. Low and Y. Li, Chin. J. Catal., 2024, 65, 163–173.
49. E. Zhao, J. Shan, P. Yin, W. Wang, K. Du, C. C. Yang, J. Guo, J. Mao, Z. Peng, C. H. Wang and T. Ling, ACS Catal., 2024, 14, 14711–14720.
50. S. Li, C. You, K. Rong, C. Zhuang, X. Chen and B. Zhang, Adv. Powder Mater., 2024, 3, 100183.
51. J. Lei, H. Yang, B. Weng, Y. M. Zheng, S. Chen, P. W. Menezes and S. Meng, Adv. Energy Mater., 2025, 2500950.
52. H. Wu, S. Meng, J. Zhang, X. Zheng, Y. Wang, S. Chen, G. Qi and X. Fu, Appl. Surf. Sci., 2020, 505, 144638.
53. M. Y. Qi, X. N. Shao, Z. R. Tang and Y. J. Xu, ACS Mater. Lett., 2025, 7, 1533–1539.
54. J. Xu, Q. Zhang, X. Gao, P. Wang, H. Che, C. Tang and Y. Ao, Angew. Chem., Int. Ed., 2023, 135, e202307018.
55. B. Liu, Y. Li, Y. Guo, Y. Tang, C. Wang, Y. Sun, X. Tan, Z. Hu and T. Yu, ACS Nano, 2024, 18, 17939–17949.
56. M. Y. Qi, Q. Lin, Z. R. Tang and Y. J. Xu, Appl. Catal., B, 2022, 307, 121158.
57. B. Weng, M. Zhang, Y. Lin, J. Yang, J. Lv, N. Han, J. Xie, H. Jia, B. Su, M. Roeffaers, J. Hofkens, Y. Zhu, S. Wang, W. Choi and Y. Zheng, Nat. Rev. Clean Technol., 2025, 1, 201–215.
58. Y. Wei, Y. Wu, J. Wang, Y. Wu, Z. Weng, W. Huang, K. Yang, J. Zhang, Q. Li, K. Lu and B. Han, J. Mater. Chem. A, 2024, 12, 18986–18992.
59. K. Valencia, A. Hernández-Gordillo, L. Cerezo and S. E. Rodil, Dalton Trans., 2025, 54, 8483–8497.
60. C. Jiang, Y. Ding, J. Lin, Y. Sun, W. Zhou, X. Zhang, H. Zhao, W. Cao and D. Cheng, Dalton Trans., 2025, 54, 2460–2470.
61. Z. Chen, J. Deng, Y. Zheng, W. Zhang, L. Dong and Z. Chen, Chin. J. Catal., 2024, 61, 135–143.
62. S. Li, F. Chen, Q. An, R. Tang and H. Huang, Adv. Funct. Mater., 2024, 34, 2409035.

---