Topotactical Route to Multiwalled Cerium Oxide Nanotubes from MWCNTs

Abstract

biomedicine due to its ability to shift easily between Ce 4+ /Ce 3+ oxidation states, high oxygen storage capacity (OSC), increased oxygen ion conductivity, and excellent biocompatibility. [1,2] Over the years, extensive research efforts have been made to develop the controllable synthesis of CeO 2 nanomaterials with diverse structural morphologies owing to the importance of nano-size and geometrical effects. [3,4] Due to their inherent hollow structure, CeO 2 nanotubes possess a high surfaceto-volume ratio, which gives them active surface chemistry attributed to oxygen vacancies. Compared to 1D solid counterparts, CeO 2 nanotubes are more challenging to prepare since they demand a suitable strategy to develop the hollow structure. [5,6] Various soft-chemical methods have been investigated to prepare CeO 2 nanotubes. Methods include template-free and structural directingtemplate syntheses, the second being the most effective way to yield the hollow structure. Different growth mechanisms have been proposed by several research groups. Table S1 (Supporting Information) summarizes the synthesis methods, growth mechanisms, templates, and crystalline nature reported in the literature for CeO 2 nanotubes. Typical features of nanotubes include uniform wall thickness, diameters ranging from 10 to 500 nm, and lengths up to several micrometers. Often, nanotube walls are constituted by small crystallites with a random orientation. In some instances, however, crystalline regions show (111) preferred orientation, i.e., the stable CeO 2 (111) planes are preferentially exposed on nanotube-curved surfaces. The CeO 2 (111) is a Tasker type 2 surface, consisting of a repeating sequence of O-Ce-O trilayer units (3.1 Å in height) along [111] direction. [7,8] Atomistic simulations have demonstrated the structural stability of multiwalled CeO 2 nanotubes organized in a concentric circular configuration of OCeO units. [9] Moreover, simulations have indicated that the O vacancy cluster is more stable at the nanotube (111) outer surface than over a (111) flat surface. The presence of oxygen vacancies on the (111) surface is essential for enhancing the activity of CeO 2 . [10] However, continuous multiwalled arrangement along the tube axis to harness the benefits of a large curved CeO 2 ( 111) surface remains challenging. The MWCNTs as structural directing-template have been demonstrated to be effective in promoting uniform The development of new strategies for synthesizing 1D cerium oxide (CeO 2 ) hollow nanostructures has attracted much attention in recent years due to the importance of their superior properties and highly anisotropic geometry. This study reports an unpublished route of fabricating novel multiwalled CeO 2-δ nanotubes (CeO 2-δ NTs) in which the entire volume of functionalized multiwalled carbon nanotubes (f-MWCNTs) is converted into the CeO 2-δ pseudomorph through oxidation and dehydration topotactic reactions. The stable CeO 2-δ (111) planes are topotactically grown on the curved C (002) planes, preferentially expose...

Ce4+/Ce3+ Redox-Promoted Electron Transfer for Efficient Neutral H2O2 Electrosynthesis from Two-Electron Oxygen Reduction

“…Moreover, the intensities of the first-shell and higher-shell peaks increased with the CeO x contents, implying larger CeO x NPs. The weak long-range order for CeO x /CNT(0.4), combined with XPS and XANES results, suggested that CeO x /CNT(0.4) mainly consisted of atomically dispersed Ce 3+ –O x species . These spectroscopic results suggest a possible pathway for CeO x growth on the CNT.…”

“…The weak longrange order for CeO x /CNT(0.4), combined with XPS and XANES results, suggested that CeO x /CNT(0.4) mainly consisted of atomically dispersed Ce 3+ −O x species. 54 These spectroscopic results suggest a possible pathway for CeO x growth on the CNT. The Ce 3+ precursor ions first attach to surface oxygenate species on the CNT.…”