Dealloyed
nanoporous metals made of very-reactive elements have rarely been
reported. Instead, reactive materials are used as sacrificial components
in dealloying. The high chemical reactivity of nonprecious nanostructured
metals makes them suitable for a broad range of applications such
as splitting water into H2 gas and metal hydroxide. On
the other hand, the same high chemical reactivity hinders the synthesis
of nanostructured metals. Here we use a pH-controlled dealloying strategy
to fabricate bulk nanoporous Zn with bulk dimensions in the centimeter
range via the selective removal of Al from metastable face-centered
cubic bulk Zn20Al80 at. % parent alloys. The
corresponding bulk nanoporous Zn exhibits a hierarchical ligament/pore
architecture characterized by primary ligaments and pores with an
average feature size in the submicrometer range. These primary structures
are made of ultrafine secondary ligaments and pores with a characteristic
feature size in the range of 10–20 nm. Our bulk nanoporous
Zn can split water into H2 and Zn(OH)2 at ambient
temperature and pressure and continuously produce H2 at
a constant rate of 0.08 mL/min per gram of Zn over 8 h. We anticipate
that in this hierarchical bulk architecture, the macropores facilitate
the flow of water in the bulk of the material, while the mesopores
and ultrafine ligaments provide a high surface area for the reaction
of water with Zn. The bulk nanoporous Zn/water system can be used
for on-board or on-demand H2 applications, during which
H2 is produced when needed, without prior storage of this
gas compressed in cylinders as it is currently the case.
The crossing of environmental barriers poses major adaptive challenges. Rareness of freshwater-marine transitions separates the bacterial communities, but how these are related to brackish counterparts remains elusive, as do the molecular adaptations facilitating cross-biome transitions. We conducted large-scale phylogenomic analysis of freshwater, brackish, and marine quality-filtered metagenome-assembled genomes (11,248). Average nucleotide identity analyses showed that bacterial species rarely existed in multiple biomes. In contrast, distinct brackish basins cohosted numerous species, but their intraspecific population structures displayed clear signs of geographic separation. We further identified the most recent cross-biome transitions, which were rare, ancient, and most commonly directed toward the brackish biome. Transitions were accompanied by systematic changes in amino acid composition and isoelectric point distributions of inferred proteomes, which evolved over millions of years, as well as convergent gains or losses of specific gene functions. Therefore, adaptive challenges entailing proteome reorganization and specific changes in gene content constrains the cross-biome transitions, resulting in species-level separation between aquatic biomes.
The crossing of environmental barriers poses major adaptive challenges. Rareness of freshwater-marine transitions separates their bacterial communities, but how these are related to brackish counterparts remains elusive, as are molecular adaptations facilitating cross-biome transitions. Here, we conduct large-scale phylogenomic analysis of freshwater, brackish, and marine quality-filtered metagenome-assembled genomes (11,276 MAGs). Average nucleotide identity analyses showed that bacterial species rarely existed in multiple biomes. Distinct brackish basins co-hosted numerous species despite differences in salinity and geographic distance, the latter having stronger intra-species population structuring effects. We further identified the most recent cross-biome transitions, which were rare, ancient, and most commonly directed towards the brackish biome. Transitions were accompanied by changes in isoelectric point distribution and amino acid composition of inferred proteomes, as well as convergent gains or losses of specific gene functions. Therefore, adaptive challenges entailing proteome reorganization and specific changes in gene content result in species-level separation between aquatic biomes.
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