Silicon nanowires in photocatalytic water treatment: From a critical review to a conceptual band-diagram framework for radical generation and design of Si-based heterostructures

Silicon nanowires (Si NWs ) have emerged as versatile nanostructures that enhance light harvesting and charge carrier dynamics in advanced photocatalytic systems. Originating in photovoltaic research, Si NWs have high potential for wastewater remediation, particularly for treating persistent organic pollutants (POPs) and emerging contaminants (ECs) that are resistant to conventional methods. This review critically synthesizes the current state of the art in Si NW -based photocatalysts, highlighting the interplay between synthesis strategies, such as metal-assisted chemical etching (MACE), and structural factors, including doping level, crystalline orientation, and aspect ratio. This review proposes a conceptual design framework based on an effective band-diagram window for radical generation in Si-based photocatalysts. Integrating band energetics, charge-transport constraints, and interfacial barriers (native SiO₂), this work delineates the subset of carrier energies and locations that actually contribute to H₂O₂ and • OH formation. This framework is used to reinterpret reported Si NW /metal and Si NW /semiconductor heterostructures and to formulate design rules and research priorities for scalable Si NW -based AOPs. Special attention is given to hybrid junction architectures, including semiconductor–metal and Z-scheme assemblies, which optimize charge separation and broaden the generation of reactive species under visible light irradiation. Key factors affecting photocatalytic performance are systematically discussed and benchmarked through comparative tables and figures, highlighting trends in pollutant degradation efficiencies and rate constants. Ultimately, this review identifies existing knowledge gaps and outlines future directions for integrating Si NWs into scalable, solar-driven oxidation processes that aim to achieve sustainable water treatment solutions. The insights are for the rational design of next-generation hybrid photocatalysts for the reduction of emerging contaminants. • Effective band-diagram window shows why nominal band edges may not yield ROS in water. • Design-to-endpoints map links design levers to ROS fingerprints/performance metrics. • Design rules/checklist prioritize oxide/passivation, cocatalysts & junction selection. • Cross-platform benchmark sites Si NWs vs . common photocatalysts for water treatment. • Expanded application scope: dyes, antibiotics/antibacterial, and disinfection cases.