Air-Exposed Nano-TiO₂ for Rapid and Sustainable Hydrolysis of Gaseous Phthalate Ester: The Remarkable Facet and Humidity Effects

The semivolatile nature of phthalate esters (PAEs) leads to their frequent detection in indoor air and agricultural plastic greenhouses, raising concerns about potential adverse effects to human health. The development of environmentally sustainable technologies for the degradation of gaseous PAEs presents a significant necessity. Herein, the facet-engineered nano-TiO₂ performed extremely strong catalytic hydrolysis activity toward gaseous dimethyl phthalate (DMP) in ambient air, suggesting a highly efficient and sustainable solution. The hydrolysis mechanism is attributed to bidentate-coordination-enhanced Lewis-acid catalysis regarding significant facet and humidity effects. First, the TiO₂'s {001} facet showed the highest catalytic hydrolysis activity under low relative humidity (RH ≤ 33%) conditions, ascribing to its higher surface bidentate Ti-Ti site density. Second, the inhibitory effect of surface water decreased significantly below 40-49% RH, where less than one hydration layer was present on nano-TiO₂, resulting in DMP hydrolysis rates 1-3 orders of magnitude faster than those at RH ≥ 76%. The facet hydroxylation property also affected its catalytic hydrolysis activity. A sequential hydrolysis-photocatalysis approach using facet-engineered nano-TiO₂ was demonstrated to effectively degrade gaseous DMP and its hydrolysis products. This study offers valuable insights for developing sustainable strategies for purifying airborne PAEs through designed nonaqueous surface catalysis.