Substrate (chemistry)

About: Substrate (chemistry) is a research topic. Over the lifetime, 35902 publications have been published within this topic receiving 740722 citations. The topic is also known as: enzyme substrate.

Engineering Substrate Interactions for High Luminescence Efficiency of Transition-Metal Dichalcogenide Monolayers

Abstract: It is demonstrated that the luminescence efficiency of monolayers composed of MoS2, WS2, and WSe2 is significantly limited by the substrate and can be improved by orders of magnitude through substrate engineering. The substrate affects the efficiency mainly through doping the monolayers and facilitating defect-assisted nonradiative exciton recombinations, while the other substrate effects including straining and dielectric screening play minor roles. The doping may come from the substrate and substrate-borne water moisture, the latter of which is much stronger than the former for MoS2 and WS2 but negligible for WSe2. Using proper substrates such as mica or hexagonal boron nitride can substantially mitigate the doping effect. The defect-assisted recombination depends on the interaction between the defect in the monolayer and the substrate. Suspended monolayers, in which the substrate effects are eliminated, may have efficiency up to 40% at room temperatures. The result provides useful guidance for the rational design of atomic-scale light emission devices.

Covalent organic framework-modulated interfacial polymerization for ultrathin desalination membranes

Abstract: The demand for thin-film composite nanofiltration membranes bearing unprecedented water permeance and desirable salt rejection is ever increasing in desalination. Conventional interfacial polymerization usually generates a thick (∼100 nm) skin layer on hydrophobic substrate having low-porosity, leading to limited water permeance. Herein, we engineered a highly porous and superhydrophilic composite substrate to modulate the interfacial polymerization and generate an ultrathin polyamide skin layer, even below 10 nm. The composite substrate was constructed by depositing covalent organic framework nanosheets (CONs) on a microfiltration membrane via vacuum-assistant assembly. Owing to the highly porous structure and superhydrophilic nature of CONs, the composite substrate favored a high storage capacity and uniform distribution of the amine monomers. We manipulated the monomer storage capacity of the substrate by varying the loading content of CONs and demonstrated that higher amino monomer concentration could accelerate the self-sealing and self-termination of the interfacial polymerization, thus generating a thinner skin layer from ∼70 nm to sub-10 nm. Moreover, the highly porous structure of CONs imparted little additional water transport resistance. The sub-10 nm film composite membrane exhibited a superior water permeance of 535.5 L m−2 h−1 MPa−1 with a high rejection of 94.3% for Na2SO4, which was about 2–8 times higher than that of state-of-the-art nanofiltration membranes with comparable rejection.

Deposition by adsorption under an electrical field

Abstract: A method for depositing a material by adsorption onto a substrate, includes a step of exposing the substrate to a precursor molecule in the gaseous phase These precursor molecules present a non-zero dipole moment An electrical field is applied during the substrate exposing step to cause a reactive branch of the precursor molecules to adsorb into the surface of the substrate in a manner such that the precursor molecules have essentially a same orientation Next, the substrate is exposed to reagent molecules in the gaseous phase which react with the adsorbed precursor molecules so that organic branches of the adsorbed precursor molecules other than the reactive organic branch are replaced by elements of the reagent molecules This process results in the formation of a monoatomic layer

Mechanistic Rationalization of Unusual Kinetics in Pd-Catalyzed C–H Olefination

Abstract: Detailed kinetic studies and novel graphical manipulations of reaction progress data in Pd(II)-catalyzed olefinations in the presence of mono-N-protected amino acid ligands reveal anomalous concentration dependences (zero order in o-CF3-phenylacetic acid concentration, zero order in oxygen pressure, and negative orders in both olefin and product concentrations), leaving the catalyst concentration as the sole positive driving force in the reaction. NMR spectroscopic studies support the proposal that rate inhibition by the olefinic substrate and product is caused by formation of reversible off-cycle reservoirs that remove catalyst from the active cycle. NMR studies comparing the interaction between the catalyst and substrate in the presence and absence of the ligand suggest that weak coordination of the ligand to Pd prevents formation of an inactive mixed acetate species. A fuller understanding of these features may lead to the design of more efficient Pd(II) catalysts for this potentially powerful C–H func...