Metal-loaded polyol-montmorillonite with improved affinity towards hydrogen

Abstract

Metal-organoclays (MOC) were prepared through incorporation of Boltorn polyol dendrimer H30 in Na+-exchanged montmorillonite (NaMt), followed by in-situ dispersion of Cu0 and Pd0 nanoparticles (CuNPs and PdNPs). The organoclays displayed high CO2 retention capacity (CRC) of 3.6–11.1 μmol/g, but metal incorporation induced a significant increase of hydrogen uptake up to 51.8–508.2 micmol/g at the expense of the CRC. Thermal programmed desorption and FT-IR investigations revealed strong interactions with CO2 before metal incorporation. These interactions markedly depleted in the presence of CuNPs and PdNPs. This was regarded as a precise indicator of the appreciable metal stabilization within the organic entanglement, due to enhancements of HO:Cu0 and HO:Pd0 interactions at the expense of HO:CO2 carbonate-like association. The CO2 and H2 retention capacities (CRC and HRC, respectively) were found to strongly correlate to the number of OH groups of the dendritic moiety incorporated. Hydrogen retention appears to involve mainly physical interactions as supported by easy gas release between 20 °C and 75 °C or even at room temperature under vacuum. This demonstrates unequivocally the reversible capture of hydrogen. The increase of the hydrogen uptake with increasing contact time provides evidence of the occurrence of diffusion phenomena. This was not observed with CO2 before metal incorporation, suggesting a structure compaction that improves metal stabilization. This opens new prospects for hydrogen storage via truly reversible capture on low cost clay materials and biodegradable hyperbranched macromolecules deriving from plants.