Improving structural features of nanoporous alumina using deuterated electrolytes

Abstract

Nanoporous anodic aluminum oxide (AAO) is a well-known nanoporous material with multiple applications. In the last years new experimental strategies have been developed to produce AAO in order to tune the pore morphology or ordering and discuss its growth mechanism. Here we describe an original approach to synthesize AAOs using deuterated electrolytes (i.e. sulfuric or oxalic acids in deuterated water D 2 O) leading to a pore diameter reduction of around 20 % and an increase in the pore ordering and pore growth. Better pore ordering in D 2 O is correlated to an increase in anion incorporation during the synthesis and the growth rate improvement is related to a decrease in the activation energy of the alumina formation. Moreover, the use of deuterated species allows to discuss the incorporation of hydroxyl groups during the AAO synthesis or the hydration after immersion in H 2 O or D 2 O by Small-Angle Neutron Scattering (SANS), a technique sensitive to deuteration. SANS reveals no changes between AAOs synthesized in H 2 O or D 2 O due to OH incorporation but shows differences after a long immersion time in water (H 2 O or D 2 O), indicating that the hydration is a slow process. This work shows that the use of deuterium is an interesting alternative for the synthesis of AAOs with well-controlled and specific morphologies and, from a fundamental point of view, can bring new general understanding about AAOs formation. • Nanoporous alumina have been synthesized using deuterated electrolytes. • The pore D p reached with deuterated electrolytes is as small as the smallest pore size obtained so far in the literature. • A better hexagonal pore ordering is observed and correlated to an increase in anion incorporation. • The pore growth rate is improved and related to a decrease in the activation energy of the alumina formation. • The use of deuterated electrolytes allows discussing the presence of OH groups within the material using SANS experiments.