Re ECF Project: 2015-18

Project Title: Development and demonstration of photocatalytic asphalt for removal of roadside air pollutants

Applicant: Professor Michael K H Leung, School of Energy and Environment, City University of Hong Kong

Total Approved Grant: $499,680 (ECF & WWGF: 50/50)

Duration: 1/4/2016 to 30/9/2017

Project Status/Remarks: Completed

Recent overseas and Mainland investigations have shown that photocatalytic-asphalt-paved road can effectively remove roadside nitrogen oxides (NOx) and sulphur oxides (SOx) emitted by motor vehicles. The nitrogen dioxide (NO2) reduction is so significant that the photocatalytic asphalt could reduce our roadside NO2 below the air quality objective in Hong Kong. Since photocatalytic performance depends on not only the functional properties of the photocatalyst, but also the surrounding conditions, such as solar irradiance, humidity, temperature, precipitation, etc., it is necessary to investigate and demonstrate the effectiveness of photocatalytic asphalt on enhancement of our air quality. The project aims to:

(a). develop commercially viable photocatalytic asphalts that can be activated by ultra-violate (UV) and visible (Vis) light; and
(b). obtain their performance characteristics in removal of NOx and SOx as well as their functional durability and the cost effectiveness.

Summary of the Findings/Outcomes:
This project has demonstrated the feasibility of the photocatalytic asphalt developed. A novel visible-light-active carbon modified titanium dioxide (C-TiO2) functionalized asphalt for photocatalytic removal of vehicular emissions is developed. The C-TiO2 photocatalyst demonstrated superior photocatalytic activities to the conventional P25. The C-TiO2 loaded photocatalytic asphalt has demonstrated outstanding NOx removal performance under laboratory simulated environment. The optimal sample can degrade 400 ppb of NOx within 1.5 hours. Different implementation methods were compared and the spray-coating method was found to be most effective. Field tests were conducted to study the performance in real-world conditions. The NOx concentration around the photocatalyst modified area was remarkably lower. A post heat treatment technique was found effective in enhancing the durability of the coating. The cost of the spray-coating method for real world applications is estimated as USD$1-3 per square meter. Mass production of the C-TiO2 might possibly further reduce the cost. However, road test results are highly dependent on the surrounding environment, weather, etc., so that a long term of observation is needed. The findings were presented in the World Energy Summit held in Singapore 2017. One conference paper and one journal paper were published.