Chemical Capture of Phosphine by a Sol−Gel-Derived Cu/TiO₂ Adsorbent − Interaction Mechanisms

In this study, a novel sol−gel-derived Cu/TiO 2 adsorbent has been demonstrated to exhibit exceptional capacities of 40.62, 49.52, and 108.48 mg PH 3 /g Cu/TiO 2 for the oxidative capture of phosphine (PH 3 ) in N 2, air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH 3 on the Cu/TiO 2 sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O 2 and water vapor on the capture capacity is discussed. The transformation of PH 3 followed the sequence of PH 2 → H 2 P−OH → HP(OH) 2 → P(OH) 3 → HO−P═O → H 3 PO 4 . At the same time, the CuO/Cu(OH) 2 moieties in the TiO 2 lattice were reduced to Cu 0 . The H 2 P−OH and HO−P═O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH 3 or the intermediates with adsorbed O 2 was not efficient. However, the Cu/TiO 2 sample catalyzed their interactions via reduction and then oxidation of the Cu 2+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H 3 PO 4, migrated to bound the TiO 2 support and free the CuO/Cu(OH) 2 for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO 2 in humidified air.