Mixed-Metal Oxides Latex Paints for Adsorptive Removal of Indoor Formaldehyde

Due to its presence in many consumer/household products, formaldehyde, at a normal boiling point of –19° C, is recognized as one of the most ubiquitous volatile organic indoor air pollutants. Adsorptive removal has become a well-accepted strategy in the abatement of formaldehyde. Previously, we demonstrated the applicability of mixed-metal oxides such as TiO₂/SiO₂ and ZrO₂/SiO₂ in abating formaldehyde vapor. In this follow-up work, we incorporated MMO solid sorbents into surface latex coatings in the form of thin films for passive control of indoor aldehydes. This novel surface coating strategy is a promising approach for designing the future smart buildings with less sick-building syndromes and building-related illnesses for the occupants. Two high-loading MMOs (TiO₂/SiO₂ and ZrO₂/SiO₂) were synthesized at two different weight ratios (75/25 and 85/15). The MMOs were formulated into paints, from which coatings were made. To optimize the effects of the pigments (sorbents), paints were prepared at critical pigment volume concentration (CPVC), a key parameter in preparing an effective latex paint. The formaldehyde removal performance of the surface coatings was evaluated in a lab-scale indoor air chamber and the results were compared with those of powder analogues. At 10 ppm_v formaldehyde concentration and 25° C, the chamber results revealed that ZrO₂/SiO₂-incorporated latex performed better than TiO₂/SiO₂-incorporated latex. In particular, 85/15 ZrO₂/SiO₂ coating exhibited a dynamic adsorption capacity of 0.82 mmol/g, about 10% more than that of TiO₂/SiO₂ coating, at 25° C using a formaldehyde vapor concentration of 10 ppm_v. Moreover, it was also observed that performance increased with loading, e.g., 75/25 ZrO₂/SiO₂ coating showed 25% lower dynamic adsorption capacity than that of the higher loading. Furthermore, it was observed that adsorbent coatings compared favorably with adsorbent powders. For instance, 85/15 ZrO₂/SiO₂ adsorbent powder showed 0.9 mmol/g in dynamic adsorption capacity relative to the 0.82 mmol/g of its coating counterpart. Moreover, chamber testing of cyclic sequential adsorption and desorption showed a minimal degree of performance degradation over cycles. Overall, this study highlights the potential of MMO latex paints for efficient abatement of indoor formaldehyde.