Performance of photocatalytic oxidizing air cleaners in different experimental setups - a review

Photocatalytic oxidizing (PCO) air cleaners are offered for the abatement of gaseous pollutants (i.e., Volatile Organic Compounds or VOCs). However, due to a lack of testing standards, the overall characterization of the technology's effectiveness has been met with conflicting results. Different studies use varying experimental setups, test conditions, and different PCO air cleaner designs. According to the literature, the majority of testing has been in controlled laboratory setups with favorable conditions. As PCO air cleaner testing is scaled up to more realistic environments and conditions, the PCO removal efficiency tends to significantly decrease. The differences in removal efficiency can be attributed to a set of recurring factors including higher flowrates of air leading to less resident time of VOCs under PCO reaction, higher initial concentrations of VOCs leading to a saturation of the observed photocatalysts, variations in humidity which disrupts VOC oxidation, and a reduction in UV light uniformity in larger scale applications. Other factors include the generation of byproducts due to the incomplete oxidation of certain VOCs and the inability to abate certain VOCS depending on the PCO's photocatalyst. While noticeable advancements have been made in the overall design of PCO devices, the general opinion regarding the effectiveness of PCO technology is that it is not ready for home use. This review aims to bridge the gap on the lack of scalability in PCO testing and how that affects PCO commercialization. This is in addition to providing a general roadmap for real -world PCO testing, development, and factors related to it.