The development of efficient, stable, and cocatalyst-free photocatalysts for solar-driven hydrogen production remains a critical challenge in sustainable energy research. This study introduces a novel class of metal-organic framework (MOF)/MOF heterojunctions designed to maximize visible-light absorption and promote spatial charge separation. The focus is on the MIL-167/MIL-125-NH2 system, where the formation of an interfacial junction between two distinct MOFs leads to significant enhancement in photocatalytic activity under visible light (λ ≥ 420 nm). The hybrid material achieves a hydrogen evolution rate of 455 mol h⁻¹ g⁻¹—nearly nine times higher than MIL-125-NH2 alone (51.2 mol h⁻¹ g⁻¹)—and over 500 times greater than pristine MIL-167 (0.8 mol h⁻¹ g⁻¹), all without any added cocatalysts or sacrificial agents. This performance underscores the effectiveness of engineered heterojunctions in overcoming inherent limitations of single-component MOF photocatalysts.
The synthesis protocol involves growing MIL-125-NH2 directly on pre-formed MIL-167 crystals, ensuring strong interfacial contact and electronic coupling. Structural characterization through powder X-ray diffraction (PXRD) confirms that both phases retain their crystallinity after composite formation, while scanning electron microscopy (SEM) reveals uniform coverage of small MIL-125-NH2 nanoparticles (~300–400 nm) on large MIL-167 microcrystals (20–60 μm). This hierarchical architecture facilitates rapid diffusion of reactants and products while maintaining high surface area and porosity. UV-vis diffuse reflectance spectroscopy shows a substantial extension of light absorption into the visible range, with a redshift extending beyond 700 nm—attributed to the enhanced π-conjugation and improved electronic delocalization across the interface. Photoluminescence (PL) analysis demonstrates a significant quenching of emission intensity in the heterojunction compared to the individual components, indicating suppressed radiative recombination due to efficient charge transfer across the junction.DNMT1 Antibody site Time-resolved PL measurements confirm that the excited-state lifetime of electrons in MIL-125-NH2 remains long (~3–5 ns), which is essential for enabling effective proton reduction before recombination occurs.
Electronic structure analysis via density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) reveals a type II band alignment: the conduction band (CB) of MIL-167 lies approximately 0.6 eV above that of MIL-125-NH2, while the valence band (VB) of MIL-167 is also positioned higher. This configuration enables directional electron transfer from MIL-167 to MIL-125-NH2 upon photoexcitation, effectively separating photogenerated charges and minimizing back-recombination. Furthermore, when irradiated with light above 515 nm—where MIL-125-NH2 has negligible absorption—the MIL-167/MIL-125-NH2 heterojunction still produces 197 mol g⁻¹ of H₂ after 8 hours, far exceeding the 5 mol g⁻¹ produced by MIL-125-NH2 alone. This result provides direct evidence of MIL-167 acting as a photosensitizer, harvesting low-energy photons and transferring electrons to the catalytic site.
The optimal performance is observed at 8 wt% MIL-167 loading, following a volcano-type trend, suggesting a balance between enhanced light absorption and potential shielding effects from excessive bulkier crystals. Physical mixtures of the two MOFs exhibit much lower activity (30–50 mol h⁻¹ g⁻¹), confirming that the synergy arises from true heterojunction formation rather than simple blending.NR6A1 Antibody Formula Stability tests show no loss in crystallinity or activity after multiple cycles, and ICP-MS analysis indicates minimal linker degradation.PMID:35073761 Apparent quantum yields (AQY) reach 2.5% at 450 nm and 0.7% at 500 nm—among the highest reported for MOF systems without cocatalysts—further validating the efficiency of this design. In contrast, UIO-66-NH2/MIL-125-NH2 heterojunctions, despite forming a similar type II structure, show no improvement due to overlapping absorption profiles and inefficient sensitization. These findings highlight the necessity of complementary optical properties and precise band engineering. This work establishes a foundational strategy for designing high-performance, multifunctional MOF heterojunctions capable of harnessing solar energy for clean hydrogen fuel production.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
