Forming Nanoparticle Monolayers at Liquid–Air Interfaces by Using Miscible Liquids

One standard way of forming monolayers (MLs) of nanoparticles (NPs) is to drop-cast a NP dispersion made using one solvent onto a second, immiscible solvent; after this upper solvent evaporates, the NP ML can be transferred to a solid substrate by liftoff. We show that this previously universal use of only immiscible solvent pairs can be relaxed and close-packed, hexagonally ordered NP monolayers can self-assemble at liquid–air interfaces when some miscible solvent pairs are used instead. We demonstrate this by drop-casting an iron oxide NP dispersion in toluene on a dimethyl sulfoxide (DMSO) liquid substrate. The NPs are energetically stable at the DMSO surface and remain there even with solvent mixing. Excess NPs coagulate and precipitate in the DMSO, and this limits NPs at the surface to approximately 1 ML. The ML domains at the surface nucleate independently, which is in contrast to ML growth at the receding edge of the drying drop, as is common in immiscible solvent pair systems and seen here for the toluene/diethylene glycol immiscible solvent pair system. This new use of miscible solvent pairs can enable the formation of MLs for a wider range of NPs

Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering

The kinetics and intricate interactions governing the growth of 3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary NP SLs (BNSLs) in solution are understood by combining controlled solvent evaporation and <i>in situ</i>, real-time small-angle X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied here, the larger the NP, the farther apart are the NPs when the SNSLs begin to precipitate and the closer they are after ordering. This is explained by a model of NP assembly using van der Waals interactions between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker constant. When forming BNSLs of two different sized NPs, the NPs that are in excess of that needed to achieve the final BNSL stoichiometry are expelled during the BNSL formation, and these expelled NPs can form SNSLs. The long-range ordering of these SNSLs and the BNSLs can occur faster than the NP expulsion

Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering

The kinetics and intricate interactions governing the growth of 3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary NP SLs (BNSLs) in solution are understood by combining controlled solvent evaporation and <i>in situ</i>, real-time small-angle X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied here, the larger the NP, the farther apart are the NPs when the SNSLs begin to precipitate and the closer they are after ordering. This is explained by a model of NP assembly using van der Waals interactions between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker constant. When forming BNSLs of two different sized NPs, the NPs that are in excess of that needed to achieve the final BNSL stoichiometry are expelled during the BNSL formation, and these expelled NPs can form SNSLs. The long-range ordering of these SNSLs and the BNSLs can occur faster than the NP expulsion

Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering

The kinetics and intricate interactions governing the growth of 3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary NP SLs (BNSLs) in solution are understood by combining controlled solvent evaporation and <i>in situ</i>, real-time small-angle X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied here, the larger the NP, the farther apart are the NPs when the SNSLs begin to precipitate and the closer they are after ordering. This is explained by a model of NP assembly using van der Waals interactions between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker constant. When forming BNSLs of two different sized NPs, the NPs that are in excess of that needed to achieve the final BNSL stoichiometry are expelled during the BNSL formation, and these expelled NPs can form SNSLs. The long-range ordering of these SNSLs and the BNSLs can occur faster than the NP expulsion

Iodine Monochloride (ICl) as a Highly Efficient, Green Oxidant for the Oxidation of Alcohols to Corresponding Carbonyl Compounds

<div><p>ABSTRACT</p><p>Iodine monochloride (ICl) was discovered to be a highly efficient, green oxidant, which can oxidize aldose hemiacetals, diarylmethanols, arylalkylmethanols, anddialkylmethanols to the corresponding aldose lactones, diarylmethanones, arylalkylmethanones, and dialkylmethanones, respectively, in high yields. ICl as a green, metal-free oxidant is characterized by mild reaction condition, short reaction time, good yield, and broad scope.</p></div

Passivation of CdSe Quantum Dots by Graphene and MoS₂ Monolayer Encapsulation

The encapsulation of a monolayer of CdSe quantum dots (QDs) by one-to-three layer graphene and MoS₂ sheets protects the QDs from oxidation. Photoluminescence (PL) from the QD cores shows a much slower decrease in core diameter over time due to slower oxidation in regions where the QDs are covered by van der Waals (vdW) layers than in those where they are not, for chips stored both in the dark and in the presence of light. PL mapping shows that the CdSe QDs under the central part of the vdW sheet age slower than those near its edges, because oxidation of the covered QDs is limited by transport of oxygen from the edges of the vdW sheets and not transport across the vdW layers. The transport of oxygen to the covered QDs is analyzed by coupling the PL results and a model of QD core oxidation

Small Angle X‑ray Scattering of Iron Oxide Nanoparticle Monolayers Formed on a Liquid Surface

In situ small-angle X-ray scattering (SAXS) is used to show that iron oxide nanoparticles (NPs) of a range of sizes form hexagonally ordered monolayers (MLs) on a diethylene glycol liquid surface, after drop-casting the NPs in hexane and subsequent hexane evaporation. The formation of the ordered NP ML is followed in real time by SAXS when using a heptane solvent. During drying, the NPs remain in the hexane or heptane layer, and an ordered structure is not formed then. After drying, the NPs are farther apart than expected from only van der Waals attraction between the NP cores and Brownian motion considerations, which suggests the importance of ligand attraction in binding the NPs

Evolution and Size Distribution of Solid CO₂ Particles in Supercritical CO₂ Releases

CO₂ transportation safety is important for the successful implementation of carbon capture and storage (CCS) projects. The formation of solid CO₂ is a unique phenomenon in high-pressure CO₂ release. The evolution and size distribution of dry ice particles have a significant impact on assessment of the consequences of accidental release of supercritical CO₂ from a pipeline. The motivation is to investigate the particle behavior and size distribution and understand how the impact factors affect them. An experiment with various measurement methods was developed to carry out controllable CO₂ release from a high-pressure vessel. The macroparameters such as jet configuration, temperature, and velocity were recorded. Meanwhile, motion of the microparticles was also analyzed. In addition, the effects of initial pressure and temperature on the particle size distribution were investigated. The results showed that the agglomeration influenced the size distribution at different positions of the jet

Crystallographic Habit Tuning of Li₂MnSiO₄ Nanoplates for High-Capacity Lithium Battery Cathodes

Li₂MnSiO₄ has attracted significant attention as a cathode material for lithium ion batteries because of its high theoretical capacity (330 mA h g^–1 with two Li⁺ ions per formula unit), low cost, and environmentally friendly nature. However, its intrinsically poor Li diffusion, low electronic conductivity, and structural instability preclude its use in practical applications. Herein, elongated hexagonal prism-shaped Li₂MnSiO₄ nanoplates with preferentially exposed {001} and {210} facets have been successfully synthesized via a solvothermal method. Density functional theory calculations and experimental characterization reveal that the formation mechanism involves the decomposition of solid precursors to nanosheets, self-assembly into nanoplates, and Ostwald ripening. Hydroxyl-containing solvents such as ethylene glycol and diethylene glycol play a crucial role as capping agents in tuning the preferential growth. Li₂MnSiO₄@C nanoplates demonstrate a near theoretical discharge capacity of 326.7 mA h g^–1 at 0.05 C (1 C = 160 mA h g^–1), superior rate capability, and good cycling stability. The enhanced electrochemical performance is ascribed to the electrochemically active {001} and {210} exposed facets, which provide short and fast Li⁺ diffusion pathways along the [001] and [100] axes, a conformal carbon nanocoating, and a nanoscaled platelike structure, which offers a large electrode/electrolyte contact interface for Li⁺ extraction/insertion processes

Understanding the Improved Kinetics and Cyclability of a Li₂MnSiO₄ Cathode with Calcium Substitution

Limited practical capacity and poor cyclability caused by sluggish kinetics and structural instability are essential aspects that constrain the potential application of Li₂MnSiO₄ cathode materials. Herein, Li₂Mn_1–<i>x</i>Ca_<i>x</i>SiO₄/C nanoplates are synthesized using a diethylene-glycol-assisted solvothermal method, targeting to circumvent its drawbacks. Compared with the pristine material, the Ca-substituted material exhibits enhanced electrochemical kinetics and improved cycle life performance. In combination with experimental studies and first-principles calculations, we reveal that Ca incorporation enhances electronic conductivity and the Li-ion diffusion coefficient of the Ca-substituted material, and it improves the structural stability by reducing the lattice distortion. It also shrinks the crystal size and alleviates structure collapse to enhance cycling performance. It is demonstrated that Ca can alleviate the two detrimental factors and shed lights on the further searching for suitable dopants