Removal of gaseous formaldehyde by portable photocatalytic air purifier equipped with bimetallic Pt@Cu-TiO2 filter

In this research, a mini-scale air purifier (AP) system was built with a series of honeycomb (HC) ceramic filters coated with 1 wt% Pt@Cu/TiO2 (AP (PCT-x), where x = 1, 2, and 3 for Pt:Cu weight ratios). The designed AP (PCT-x) photocatalytic systems were investigated for the removal of formaldehyde (FA) vapor under varying operational conditions (e.g., FA concentration (0.5–5 ppm), AP-flow rate (100–160 L/min), and UV light intensity (0.004–0.982 W)). The enhanced photocatalytic activities of AP (PCT-x) system (e.g., compared to the monometallic analogues) are suspected to reflect the synergistic role of Pt metal sites (in terms of high work function (5.93 eV) for the 111 crystal plane) in the Pt@Cu bimetallic structures and the high electronic transitions between Pt and Cu sites on the TiO2 surface. Nonetheless, their photocatalytic activities tend to decrease at higher Pt content (e.g., PCT-3 relative to PCT-2) due possibly to the formation of Pt clusters and associated shielding effect. Overall, AP (PCT-2) exhibited the highest efficacy (over five reuse cycles) to attain 100% removal of FA (0.5 ppm) within 5 min at an AP-flow rate of 160 L/min and UV light intensity of 0.982 W (quantum yield (QY) of 1.94E-04 molecules/photon and figure of merit (FOM) of 1.21E-06 L∙mol/ (mg∙ J∙h)). According to the in-situ DRIFTS analysis, Pt2@Cu metal sites were favorable to promote the transfer of photo-induced charge carriers by TiO2 so as to accelerate the oxidation reaction of FA vapor (e.g., through the generation of OH• and O2•- radicals). This study offers practical insights into the potential of controlled tuning of redox dynamics (i.e., between Pt and Cu metal sites on TiO2) in the enhancement of the photocatalytic performance for air purification system.