Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO(2) Adsorbent - Interaction Mechanisms

Abstract

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.