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.