Nanoscale Porosity of High Surface Area Gadolinium Oxide Nanofoam Obtained With Combustion Synthesis

Abstract

water purification, as well as other fields of their implementation. Increasing the specific surface area is therefore an obvious pathway to increase the efficiency of materials used in these processes and technologies. This way, less material is needed making particular technology more costeffective and sustainable. An effective way of increasing the surface area of a material is by making its structure porous. An example of such porous materials are nano foams, which can be made with all kinds of materials including metals and metal oxides. [1] Gadolinium is a lanthanide with a partially filled 4f shell, giving it unique optical as well as magnetic properties. It is also known to have a large thermal-neutron capture cross-section which is exploited in various applications. [2,3] At room temperature, gadolinium(III) oxide (Gd 2 O 3 ) has a cubic crystal structure with space group 3 la . Above 1200 °C, the monoclinic structure (space group C2/m) takes over as being the most stable structure, and also a hexagonal phase (space group P4m2) exists at temperatures above 2100 °C. [4] Nanoscale Gd 2 O 3 can be applied in, among others, sensing applications, [5,6] in catalysis for the improvement of sulfur cathode materials for lithium-ion batteries, [7,8] and in the treatment of contaminated water. [9][10][11] For the latter, Nanoscale gadolinium oxide (Gd 2 O 3 ) is a promising nanomaterial with unique physicochemical properties that finds various applications ranging from biomedicine to catalysis. The preparation of highly porous Gd 2 O 3 nanofoam greatly increases its surface area thereby boosting its potential for functional use in applications such as water purification processes and in catalytic applications. By using the combustion synthesis method, a strong exothermic redox reaction between gadolinium nitrate hexahydrate and glycine causes the formation of crystalline nanoporous Gd 2 O 3 . In this study, the synthesis of Gd 2 O 3 nanofoam is achieved with combustion synthesis at large scale (grams). Its nanoscale porosity is investigated by nitrogen physisorption and its nanoscale 3D structure by electron tomography, and the formation process is investigated as well by means of in situ heating inside the transmission electron microscope. The bulk nanofoam product is highly crystalline and porous with a surface area of 67 m 2 g −1 as measured by physisorption, in good agreement with the electron tomographic 3D reconstructions showing an intricate interconnected pore network with pore sizes varying from 2 to 3 nm to tens of nanometers. In situ heating experiments point to many possibilities for tuning the porosity of the Gd 2 O 3 nanofoam by varying the experimental synthesis conditions.