4 Search Results

Rare earth elements (REEs), critical to modern industry, are difficult to separate and purify, given their similar physicochemical properties originating from the lanthanide contraction. Here, we systematically study the transport of lanthanide ions (Ln³⁺) in artificially confined angstrom-scale two-dimensional channels using MoS₂-based building blocks in an aqueous environment. The results show that the uptake and permeability of Ln³⁺ assume a well-defined volcano shape peaked at Sm³⁺. This transport behavior is rooted from the tradeoff between the barrier for dehydration and the strength of interactions of lanthanide ions in the confinement channels, reminiscent of the Sabatier principle. Molecular dynamics simulations revealmore » that Sm³⁺, with moderate hydration free energy and intermediate affinity for channel interaction, exhibit the smallest dehydration degree, consequently resulting in the highest permeability. Our work not only highlights the distinct mass transport properties under extreme confinement but also demonstrates the potential of dialing confinement dimension and chemistry for greener REEs separation.« less

Emulating angstrom-scale dynamics of the highly selective biological ion channels is a challenging task. Recent work on angstrom-scale artificial channels has expanded our understanding of ion transport and uptake mechanisms under confinement. However, the role of chemical environment in such channels is still not well understood. Here, we report the anomalously enhanced transport and uptake of ions under confined MoS2-based channels that are ~five angstroms in size. The ion uptake preference in the MoS2-based channels can be changed by the selection of surface functional groups and ion uptake sequence due to the interplay between kinetic and thermodynamic factors that dependmore » on whether the ions are mixed or not prior to uptake. Our work offers a holistic picture of ion transport in 2D confinement and highlights ion interplay in this regime.« less

Controlling the ion transport through graphene oxide (GO) membrane is challenging, particularly in the aqueous environment due to its strong swelling tendency. Fine-tuning the interlayer spacing and chemistry is critical to create highly selective membranes. We investigate the effect of single-site divalent cations in tuning GO membrane properties. Competitive ionic permeation test indicates that Cu²⁺ cations dominate the transport through the 2D channels of GO membrane over other cations (Mg²⁺/Ca²⁺/Co²⁺). Without/With the single-site M²⁺ modifications, pristine GO, Mg-GO, Ca-GO, and Cu-GO membranes show interlayer spacings of ~13.6, 15.6, 14.5, and 12.3 Å in wet state, respectively. The Cu-GO membrane showsmore » a two-fold decrease of NaCl (1 M) permeation rate comparing to pristine GO, Mg-GO, and Ca-GO membranes. In reverse osmosis tests using 1000 ppm NaCl and Na₂SO₄ as feeds, Cu-GO membrane shows rejection of ~78% and ~94%, respectively, which are 5%–10% higher than its counterpart membranes.« less

Identifying highly selective catalysts and accurately measuring NH₃ yield without false-positives from contaminations remain two challenges in electrochemical nitrogen reduction reaction (NRR). Here, we report N-defective carbon nitride grown on carbon paper (CN/C) as a highly selective electrocatalyst. The NH₃ yield was determined reliably by the slope of mNH₃-time plot rather than averaging the accumulated amount over time. Results showed the as-synthesized CN/ C₆₀₀ (synthesized at 600 °C) with a higher density of C=N-C N2C vacancies achieved an NH₃ production of 2.9 μg mgcat. ^-1 h^-1 at -0.3 V (versus RHE), ~5.7-fold higher than CN/C₅₀₀. The Faradaic efficiency for CN/more » C₆₀₀ is among the highest of 62.1%, 33.9%, and 16.8% at -0.1 V, -0.2 V, and -0.3 V, respectively. The NH₃ production was verified by isotope ¹⁵N₂ experiments. Further increase of N-defects on CN/C₆₀₀ using plasma etching led to higher NH₃ yield than comparably larger current, pointing to N-defects sites for promoting NRR.« less