# Photocatalytic NOx Removal Performance of TiO2-Coated Permeable Concrete: Laboratory Optimization and Field Demonstration

## TL;DR

Researchers developed permeable concrete with a TiO2 coating that effectively removes NOx pollutants from urban air, both in lab and real-world settings.

## Contribution

A durable, single-component TiO2 photocatalytic coating on permeable concrete is introduced for efficient and long-lasting NOx removal.

## Key findings

- The TiO2-coated permeable concrete achieved a maximum NOx removal efficiency of 77.5%.
- After 300 h of accelerated weathering, the coating retained approximately 80% of its initial performance.
- Outdoor tests confirmed NOx removal and nitrate by-product formation under natural light conditions.

## Abstract

Nitrogen oxides (NOx) emitted mainly from vehicle exhaust significantly contribute to urban air pollution, leading to photochemical smog and secondary particulate matter. Photocatalytic technology has emerged as a promising solution for continuous NOx decomposition under ultraviolet (UV) irradiation. This study developed an eco-friendly permeable concrete incorporating activated loess and zeolite to improve roadside air quality. The high porosity and adsorption capability of the concrete provided a suitable substrate for a TiO2-based photocatalytic coating. A single-component coating system was optimized by introducing colloidal silica to enhance TiO2 particle dispersibility and adding a binder to secure durable adhesion on the concrete surface. The produced permeable concrete met sidewalk quality standards specified in SPS-F-KSPIC-001-2006. Photocatalytic NOx removal performance evaluated by ISO 22197-1 showed a maximum removal efficiency of 77.5%. Even after 300 h of accelerated weathering, the activity loss remained within 13.8%, retaining approximately 80% of the initial performance. Additionally, outdoor mock-up testing under natural light confirmed NOx concentration removal and formation of nitrate by-products, demonstrating practical applicability in real environments. Overall, the integration of permeable concrete and a durable, single-component TiO2 photocatalytic coating provides a promising approach to simultaneously enhance pavement sustainability and reduce urban NOx pollution.