Fundamentally, the type-II and Z-scheme heterojunctions exhibit identical band alignments but diverge in the charge carriers transfer mechanisms. Here, we demonstrate that the Au-mediated heterojunction transition from type-II to Z-scheme dictates the subsequent photocatalytic NO reaction pathway to obtain excellent activity and selectivity. As proven by density functional theory (DFT) calculations, Kelvin probe force microscopy (KPFM), and in-situ X-ray photoelectron spectroscopy (XPS), the type-II to Z-scheme heterojunction transition is regulated by incorporating Au nanoparticles as electron bridges within in-situ fabricated NH₂-MIL-125/TiO₂ through controllable hydrolysis. This transition maintains robust redox potentials to generate more reactive active species through effectively separated charge carriers under the high-efficient built-in electric field. As a result, the Z-scheme (NH₂-MIL-125/Au/TiO₂) exhibits an impressive NO removal efficiency of 82.0%, surpassing the original NH₂-MIL-125 by 3.7 times and the type-II (NH₂-MIL-125/TiO₂) by 1.2 times, while shows a selectivity of almost 100% toward NO₂⁻/NO₃⁻. The in-situ Fourier transform infrared (FT-IR) and DFT reveal that, in comparison with the type-II favored NO⁺ intermediates, the Z-scheme favors NO⁻ intermediates with enhanced O₂/H₂O activation, enabling ideal Gibbs free energy for NO-to-NO₃⁻ conversion. This study achieves a metal-nanoparticle-mediated strategy for precisely engineering metal-organic framework (MOF)-based heterojunction architectures, which regulates the NO reaction pathways for efficient environmental purification.

Copper-based photocatalysts, featuring low cost, versatile valence states (Cu⁰, Cu⁺, Cu²⁺), and outstanding photophysical and photochemical properties, hold great promise for organic synthesis, environmental remediation, and energy conversion. This review systematically examines the pivotal role of variable-valence copper species in photocatalysis, establishing a dual-dimensional framework that spans valence evolution and catalytic systems. It highlights advances in Cu⁰ active sites, photoexcited Cu⁺ and Cu²⁺ species, and heterogeneous platforms such as polymer ligands, metal-organic frameworks, and single-atom catalysts. In homogeneous systems, Cu⁺ complexes achieve long-lived metal-to-ligand charge transfer states that drive single-electron transfer for C–C/C–X bond formation and alkene/alkyne bifunctionalization. Cu²⁺ participates in oxidation and radical cycles via ligand-to-metal charge transfer. In heterogeneous systems, Cu⁰ nanostructures enhance light absorption via localized surface plasmon resonance, while Cu⁺/Cu²⁺ semiconductors form Z/S-scheme heterojunctions to improve charge separation. Key strategies, including ligand engineering, defect control, interface design, and single-atom anchoring, are discussed to enhance carrier dynamics and stability. Despite challenges in in-situ characterization, mechanistic elucidation, and scalable synthesis, copper-based photocatalysts offer strong potential for light-driven synthesis, CO₂ valorization, and pollutant mineralization. Future efforts should focus on operando spectroscopy and theory-guided design of robust, selective catalysts to bridge fundamental research and industrial application.

Atmospheric pollutants such as volatile organic compounds (VOCs), nitrogen oxides (NO_x), and ozone (O₃) pose serious threats to health and ecological systems. As air pollution evolves toward multi-pollutant coexistence, synergistic control strategies have become increasingly important. This review systematically summarizes and compares three representative synergistic systems: VOCs–NO_x, VOCs–O₃, and multi-component VOCs. For VOCs–NO_x system, the key findings highlight the dominant role of coupled redox catalytic mechanisms, strongly governed by catalyst composition, active-site regulation, and reaction conditions. Synergistic VOCs–O₃ removal is mainly achieved through photocatalytic and O₃-assisted pathways, where interfacial charge transfer and reactive oxygen species generation are critical. In complex multi-component VOC systems, integrated catalytic strategies are required to address competitive adsorption and reaction coupling, giving rise to both synergistic and inhibitory effects. Distinct from previous surveys, this review offers a unified mechanistic framework to compare these systems, emphasizes multi-scale catalyst design principles, and elucidates competitive–synergistic behaviors in realistic mixed-pollutant environments. Remaining challenges include catalyst stability, selectivity, and efficiency under multi-pollutant conditions. Future research should focus on rational catalyst design, system-level optimization, and scalable engineering implementation to advance effective synergistic air pollution control.