Study on formation of Pd nanocatalyst in self-reducing silica nanotube produced by using sacrificial Fe3O4 template and its efficacy in Cr(VI) reduction

Palladium is extensively used for catalyzing various organic and inorganic reactions. The nanostructures of Pd are expected to exhibit an improved catalytic efficacy. However, their uses have several issues which could be addressed by encapsulating the Pd nanostructures in the appropriate host matrices without affecting the accessibility of catalytic sites. In the present work, the silica nanotubes were formed by coating of the (3-glycidyloxypropyl)trimethoxysilane and tetraethoxysilane on the Fe3O4 NPs template, which was subsequently leached out. The reducing groups on the silica nanotubes were incorporated by the grafting of hydrazine using 3-glycidyloxypropyl linkers on the silica nanotubes and subsequently reacting with hydrazine. Thus formed silica nanotubes were loaded with the Pd NPs using self-reducing route and also using the external agent for further reduction of Pd2+ ions loaded by the ion-exchange mechanism, which increased the Pd loading from 43 mg g−1 to 128 mg g−1. Thus, formed Pd NPs loaded silica nanotubes were characterized by various techniques such as EDS, FESEM, HRTEM and SAXS to understand the formation of Pd NPs embedded silica nanotubes and their physical properties. The HRTEM images showed the formation of silica nanotubes having ≈10 nm diameter and varying length (20–60 nm). The SAXS studies suggested the Pd NPs were having 6 nm sizes irrespective of the reducing routes or the loading capacity. The Pd NPs loaded silica nanotubes were found to possess a remarkable efficiency for catalyzing the representative oxyions reduction of CrO42− to Cr(III) with formic acid at room temperature. Based on room temperature reduction, the transport of Cr(VI) across the anion-exchange membrane and subsequent reduction to Cr(III) in the receiver compartment was studied to develop a new Cr(VI)-separation process having the potentials applications for a variety of feeds.