Solar-driven photocatalytic air purification for road infrastructure: Pollutant dynamics, material integration, and sustainable engineering

Road infrastructure provides a scalable platform for integrating photocatalytic technologies to mitigate urban air pollution. However, practical deployment remains uncertain because pollutants in road environments show substantial diversity and dynamic variation in their emission sources, exposure levels, and catalytic degradation processes. Although advances in materials science continue to expand the range and performance of photocatalysts, field applications remain constrained by insufficient solar energy utilization, mass transfer limitations, environmental durability, and selective pollutant conversion. This review establishes a framework linking target pollutants with photocatalytic application strategies in road infrastructure. It identifies low-concentration nitrogen oxides (NOx) and volatile organic compounds (VOCs), together with particulate matter (PM) associated with the secondary atmospheric transformation of these gaseous precursors, as key future targets for road air pollution control. The overall pathway through which photocatalysis reduces exposure to gaseous precursors and improves ambient air quality is further clarified. Progress across four representative engineering platforms is critically assessed, including cement concrete, asphalt pavements, aggregates, and roadside air purification installations. Different application strategies differ in catalyst immobilization, gas phase exposure, and environmental adaptability, and adopt distinct pathways for performance optimization. Understanding light response, charge separation, and interactions with engineering matrices provides a mechanistic basis for interpreting performance in engineering applications, including degradation efficiency, selectivity, durability, and feasibility. The review further identifies key challenges and future directions and highlights emerging opportunities in energy harvesting, multi field coupled catalysis, low carbon design, high value utilization of solid waste, multifunctionality, and long term durability.