Enhanced Hydrogen Purification in Nanoporous Phosphorene Membrane with Applied Electric Field

As a feasibility study for hydrogen purification, the mechanisms of H₂, CO₂, N₂, CO, and CH₄ penetrating through self-passivated porous phosphorene membranes with different pore sizes were systematically investigated by density functional theory. The thermal stability of porous phosphorene membranes with various pore sizes was studied by <i>ab initio</i> molecular dynamics. By applying an external electric field perpendicular to the porous phosphorene membrane, the diffusion of CO₂ and N₂ through the pores was remarkably suppressed due to the polarizability of these molecules, whereas the energy barrier and permeance of H₂ passing through the membrane is virtually unaffected. Thus, the application of the electric field improves the performance of hydrogen purification further. This finding opens up a new avenue to optimally tune the performance of 2D materials for gas separation by applying an external electric field

Label-Free LSPR Detection of Trace Lead(II) Ions in Drinking Water by Synthetic Poly(mPD-<i>co</i>-ASA) Nanoparticles on Gold Nanoislands

Using self-assembly gold nanoislands (SAM-AuNIs) functionalized by poly­(<i>m</i>-phenylenediamine-<i>co</i>-aniline-2-sulfonic acid) (poly­(mPD-<i>co</i>-ASA)) copolymer nanoparticles as specific receptors, a highly sensitive localized surface plasmon resonance (LSPR) optochemical sensor is demonstrated for detection of trace lead cation (Pb­(II)) in drinking water. The copolymer receptor is optimized in three aspects: (1) mole ratio of mPD:ASA monomers, (2) size of copolymer nanoparticles, and (3) surface density of the copolymer. It is shown that the 95:5 (mPD:ASA mole ratio) copolymer with size less than 100 nm exhibits the best Pb­(II)-sensing performance, and the 200 times diluted standard copolymer solution contributes to the most effective functionalization protocol. The resulting poly­(mPD-<i>co</i>-ASA)-functionalized LSPR sensor attains the detection limit to 0.011 ppb toward Pb­(II) in drinking water, and the linear dynamic range covers 0.011 to 5000 ppb (i.e., 6 orders of magnitude). In addition, the sensing system exhibits robust selectivity to Pb­(II) in the presence of other metallic cations as well as common anions. The proposed functional copolymer functionalized on AuNIs is found to provide excellent Pb­(II)-sensing performance using simple LSPR instrumentation for rapid drinking-water inspection

Initial Reduction of CO₂ on Pd‑, Ru‑, and Cu-Doped CeO₂(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO₂ reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO₂ on CeO₂(111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO₂(111) by weakening the adjacent Ce–O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO₂ adsorption, especially for Cu/CeO₂(111). The initial reductive dissociation CO₂ → CO* + O* on metal-doped CeO₂(111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO₂(111); the reductive hydrogenation CO₂ + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO₂(111), in which the most competitive route on Cu/CeO₂(111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO₂ + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO₂(111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO₂ reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO₂ on metal-doped CeO₂(111) surfaces

Methanol Oxidation on Pt₃Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition

PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt₃Sn­(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CH_<i>x</i>OH_<i>y</i>, <i>x</i> = 1–3, <i>y</i> = 0–1) were strongly adsorbed and preferred decomposition rather than desorption on Pt₃Sn­(111). The competitive methanol decomposition started with the initial O–H bond scission followed by successive C–H bond scissions, (i.e., CH₃OH → CH₃O → CH₂O → CHO → CO). The Brønsted–Evans–Polanyi relations and energy barrier decomposition analyses identified the C–H and O–H bond scissions as being more competitive than the C–O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt₃Sn­(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure