Pseudo-bottle-brush decorated thin-film composite desalination membranes with ultrahigh mineral scale resistance.

High water recovery is crucial to inland desalination but is impeded by mineral scaling of the membrane. This work presents a two-step modification approach for grafting high-density zwitterionic pseudo-bottle-brushes to polyamide reverse osmosis membranes to prevent scaling during high-recovery desalination of brackish water. Increasing brush density, induced by increasing reaction time, correlated with reduced scaling. High-density grafting eliminated gypsum scaling and almost completely prevented silica scaling during desalination of synthetic brackish water at a recovery ratio of 80%. Moreover, scaling was effectively mitigated during long-term desalination of real brackish water at a recovery ratio of 90% without pretreatment or antiscalants. Molecular dynamics simulations reveal the critical dependence of the membrane's silica antiscaling ability on the degree to which the coating screens the membrane surface from readily forming silica aggregates. This finding highlights the importance of maximizing grafting density for optimal performance and advanced antiscaling properties to allow high-recovery desalination of complex salt solutions.

Electrical and Optical Properties of γ-SnSe: A New Ultra-narrow Band Gap Material.

We describe the unusual properties of γ-SnSe, a new orthorhombic binary phase in the tin monoselenide system. This phase exhibits an ultranarrow band gap under standard pressure and temperature conditions, leading to high conductivity under ambient conditions. Density functional calculations identified the similarity and difference between the new γ-SnSe phase and the conventional α-SnSe based on the electron localization function. Very good agreement was obtained for the band gap width between the band structure calculations and the experiment, and insight provided for the mechanism of reduction in the band gap. The unique properties of this material may render it useful for applications such as thermal imaging devices and solar cells.

MXene-Based Ceramic Nanocomposites Enabled by Pressure-Assisted Sintering.

As MXenes become increasingly widespread, approaches to utilize this versatile class of 2D materials are sought. Recently, there has been growing interest in incorporating MXenes into metal or ceramic matrices to create advanced nanocomposites. This study presents a facile approach of mixing MXene with ceramic particles followed by pressure-assisted sintering to produce bulk MXene/ceramic nanocomposites. The effect of MXene addition on the densification behavior and properties of nanocomposites was explored through the Ti3C2Tz/alumina model system. We discovered that the presence of MXene altered the densification behavior and significantly enhanced the densification rate at low temperatures. In-depth microstructural characterization showed a homogeneous distribution of Ti3C2Tz MXene at the alumina grain boundaries. The Ti3C2Tz/alumina nanocomposites exhibited electrical conductivity but reduced hardness. We also demonstrated that using multilayered Ti3C2Tz as a precursor can produce composites with plate-like TiCx morphology. This work provides a conceptual approach for utilizing the diversity and versatility of MXenes in creating tunable advanced nanocomposites.

Single Molecule Study of the Polymerization of RecA on dsDNA: The Dynamics of Individual Domains.

In the Escherichia coli, RecA plays a central role in the recombination and repair of the DNA. For homologous recombination, RecA binds to ssDNA forming a nucleoprotein filament. The RecA-ssDNA filament searches for a homologous sequence on a dsDNA and, subsequently, RecA mediates strand exchange between the ssDNA and the dsDNA. In vitro, RecA binds to both ssDNA and dsDNA. Despite a wide range of studies of the polymerization of RecA on dsDNA, both at the single molecule level and by means of biochemical methods, important aspects of this process are still awaiting a better understanding. Specifically, a detailed, quantitative description of the nucleation and growth dynamics of the RecA-dsDNA filaments is still lacking. Here, we use Optical Tweezers together with a single molecule analysis approach to measure the dynamics of the individual RecA domains on dsDNA and the corresponding growth rates for each of their fronts. We focus on the regime where the nucleation and growth rate constants, k n and k g , are comparable, leading to a coverage of the dsDNA molecule that consists of a small number of RecA domains. For the case of essentially irreversible binding (using ATPγS instead of ATP), we find that domain growth is highly asymmetric with a ratio of about 10:1 between the fast and slow fronts growth rates.

Sample preparation induced phase transitions in solution deposited copper selenide thin films.

Thin films of CuSe were deposited onto GaAs substrate. XRD showed that the as-deposited films were of the Klockmannite (CuSe - P63/mmc 194) phase with lattice parameters a 0 = b 0 = 0.3939 nm, c 0 = 1.7250 nm; however, electron diffraction in the TEM surprisingly indicated the ß-Cu2-x Se phase (Cu1.95Se - R3̄m 166) with lattice parameters a 0 = b 0 = 0.412 nm, c 0 = 2.045 nm. The discrepancy originated from the specimen preparation method, where the energy of the focused ion beam resulted in loss of selenium which drives a phase transition to ß-Cu2-x Se in this system. The same phase transition was observed also upon thermal treatment in vacuum, as well as when the 200 keV electron beam was focused on a powder sample in the TEM. The initial phase can be controlled to some extent by changing the composition of the reactants in solution, resulting in thin films of the cubic α-Cu2-x Se (Cu1.95Se - Fm3̄m) phase co-existing together with the ß-Cu2-x Se phase.