Cold sintering yields first layered double hydroxides (LDH) monolithic materials

Abstract

Layered double hydroxides (LDHs) are key inorganic compounds relevant to a wealth of applicative purposes, by exploiting their layered structure allowing for ion/molecular sequestration or release. However, a technological barrier exists in the fabrication of cohesive LDH monoliths in link with their metastability. In this work, a series of cohesive monoliths of different LDH ionic compositions and structures (namely hydrotalcite, pyroaurite and hydrocalumite) were successfully obtained for the first time, using cold sintering via spark plasma sintering (SPS) at 130 degrees C. Thanks to the low temperature involved in this non-conventional consolidation approach, the structure and chemical stability of the LDHs are preserved and allow preparing densified LDH scaffolds with internal cohesion, as evidenced by densification rates often above 80 %, SEM microstructural observations and mechanical testing assessments, mainly due to a better alignment of adjacent layered particles. By way of water vapor sorption measurements, we demonstrate that the interfacial/interlayer spaces of the LDH structure remain accessible after cold sintering. Also, the porous network of the monoliths and related access to interfacial surface are shown to be tunable by adding a leachable pore-forming agent such as SiO2 beads. Possible sintering mechanisms are discussed by complementary experiments-simulations coupling, unveiling the role of LDH composition as in the case of Cl-bearing LDH. By overcoming the challenge of monolith fabrication out of LDH compounds, applications are expected to benefit from these findings, as in electronics, energy storage, catalysis, biomaterials and depollution.