COVID-19 pandemic has transformed our social behaviors. Regular disinfection actions using conventional disinfectants could be one most effective way to suppress the virus transmission. While frequent spraying operation could be compulsory. Photocatalytic coatings technology provides a reliable, safe, and continuously effective surface disinfection solution which becomes more widely used both in Hong Knog and globlely. However, there has not been any testing protocols or standard developed to evaluate the long-term performance of the photocatalyst coating in actual environment. 

In this thesis, I present the process of evaluating the anti-microbial performance of photocatalytic wall paint. The evaluation was conducted through an onsite study for at least 100 days in two primary schools in Hong Kong, using adenosine triphosphate (ATP) bioluminescence assay. About 500 sqm of wall areas are painted in both primary schools and samples are collected on both painted and unpainted area adopting a randomized controlled trials for the measurement. The selected locations include different type of surfaces and location that are in frequent contact with students and staffs. By comparing the measured values from the experimental group (locations with the photocatalytic paint) and the control group (locations without the photocatalytic paint) with long-term monitoring, the painted area shows consistently lower in microbial activities, reflected in lower RLU values, with 0.5 log to 2.5 log difference in various locations in both schools. The results confirm that the photocatalytic paint is effective in reducing microbial activities on wall surfaces in both indoor and semi-outdoor settings. Meanwhile, these results also demonstrate that the ATP bioluminescence assay conducted in a systematic approach can serve as a reference to the quick evaluation of the microbial activity following a general data processing protocol as discussed in this thesis.

I also demonstrate the inhibitory activity of a novel visible light active photocatalyst, boron-doped bismuth oxybromide (B-BiOBr), towards SARS-CoV-2 in 10% fetal bovine serum without light or under irradiation at 426 nm by a light emitting diode (LED). SARS-CoV-2 inactivation in the presence of B-BiOBr with LED irradiation achieved > 99.999% (5.32-log) in less than 5 minutes, which is 400 to 10,000 times higher than those achieved with conventional photocatalysts of tungsten or titanium oxide nanomaterials, respectively. Even without LED irradiation, B-BiOBr in the dark inactivated >99.9% (3.32-log) of SARS-CoV-2. LED irradiation at 426 nm alone, without the photocatalyst, achieved about 71% (0.54-log) inactivation. The remaining 1.46-log inactivation came from the photocatalytic-induced reactive oxygen species. This three-pronged approach that leverages different modes of action to engineer disinfection strategies shows the potential to mitigate environmental transmission of emerging pathogens.

Last but not least, a potential technology development routine for photocatalysis-based long-lasting disinfection solotion is proposed. Results from a few ongoing research is supplemented.

Meeting Link: To request for meeting link, please write to phsywu@ust.hk.