Chemistry of Materials
DOI: 10.1021/acs.chemmater.3c01483
Ionic‐Liquid‐Based Nanofluids and Their Heat‐Transfer Applications: A Comprehensive Review
One of the emerging study areas to boost the heat transfer rates of the thermal devices is the further improvement of the thermophysical properties and thermal performance of ionic liquids (IL) by dispersing nanoparticles. This work provides a summary of the most recent research on the use of ionic liquid nanofluids as heat transfer fluids. Additionally, the methods for analyzing the thermophysical properties and creating IL nanofluids are discussed.
Abstract
Due to the improved thermophysical characteristics of ionic liquids (ILs), such as their strong ionic conductivity, negligible vapor pressure, and thermal stability at high temperatures, they are being looked at viable contender for future heat transfer fluids. Additionally, the dispersing nanoparticles can further improve the thermophysical characteristics and thermal performance of ionic liquids, which is one of the emerging research interests to increase the heat transfer rates of the thermal devices. The latest investigations about the utilization of ionic liquid nanofluids as a heat transfer fluid is summarized in this work. These summaries are broken down into three types: (a) the thermophysical parameters including thermal conductivity, viscosity, density, and specific heat of ionic liquids (base fluids), (b) the thermophysical properties like thermal conductivity, viscosity, density, and viscosity of ionic liquids based nanofluids (IL nanofluids), and (iii) utilization of IL nanofluids as a heat transfer fluid in the thermal devices. The techniques for measuring the thermophysical characteristics and the synthesis of IL nanofluids are also covered. The suggestions for potential future research directions for IL nanofluids are summarized.
Structural and Electronic Properties of Two‐Dimensional Materials: A Machine‐Learning‐Guided Prediction
For the purpose of predicting the structural and electronic properties of two-dimensional materials, a universal machine learning approach is reported.
Abstract
The growing number of studies and interest in two-dimensional (2D) materials has not yet resulted in a wide range of material applications. This is a result of difficulties in getting the properties, which are often determined through numerical experiments or through first-principles predictions, both of which require lots of time and resources. Here we provide a general machine learning (ML) model that works incredibly well as a predictor for a variety of electronic and structural properties such as band gap, fermi level, work function, total energy and area of unit cell for a wide range of 2D materials derived from the Computational 2D Materials Database (C2DB). Our predicted model for classification of samples works extraordinarily well and gives an accuracy of around 99 %. We are able to successfully decrease the number of studied features by employing a strict permutation-based feature selection method along with the sure independence screening and sparsifying operator (SISSO), which further supports the design recommendations for the identification of novel 2D materials with the desired properties.
Organometallic Allene [(μ‐C)(Fe(CO)4)2]: Bridging Carbon Showing Transformation from Classical Electron‐Sharing Bonding to Double σ‐Donor and Double π‐Acceptor Ligation
![Organometallic Allene [(μ-C)(Fe(CO)4)2]: Bridging Carbon Showing Transformation from Classical Electron-Sharing Bonding to Double σ-Donor and Double π-Acceptor Ligation](https://chemistry-europe.onlinelibrary.wiley.com/cms/asset/690d5856-85ca-4067-9925-eb138d459b33/cphc202300528-toc-0001-m.png)
Diversity in organometallic allenes: A structure-bonding study on two isomeric organometallic allenes [(μ-C)(Fe(CO)4)2] reveals a bis-pseudoallylic anionic delocalisation, similar to organic allene C(CH2)2, in the first case, and a typical three-center bis-allylic anionic delocalisation in the second one. A quantitative bonding analysis shows the transformation of the central carbon atom from a classical tetravalent coordinating center to a double σ-donor double π-acceptor ligand.
Abstract
Allenes (R2C=C=CR2) have been traditionally perceived to feature localized orthogonal π-bonds between the carbon centres. We have carried out quantum-mechanical studies of the organometallic allenes envisioned by the isolobal replacement of the terminal CH2 groups by the d8 Fe(CO)4 fragment. Our studies have identified two organometallic allenes viz. D2d symmetric [(μ-C)(Fe(CO)4)2] (2) and D3 symmetric [(μ-C)(Fe(CO)4)2] (3) with trigonal bipyramidal coordination at the Fe atoms. Compound 2 features the bridging carbon atom in an equatorial position with respect to the ligands on the TM centre, while 3 features the central carbon atom in an axial position. The bis-pseudoallylic anionic delocalisation proposed in the C2-C1-C3 spine of organic allene is retained in the organometallic allene 2, and is transformed to a typical three-centre bis-allylic anionic delocalisation in the organometallic allene 3. The topological analysis of electron density also indicates a bis-allylic anionic type delocalisation in the organometallic allenes. The quantitative bonding analysis using the EDA-NOCV method suggests a transition from classical electron-sharing bonding between the central carbon atom and the terminal groups in 1 to donor-acceptor bonding in 3. Meanwhile, both electron-sharing and donor-acceptor bonding models are found to be probable heuristic bonding representations in the organometallic allene 2.
Hydrogen‐induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations
Electronic states on the MoS2 basal plane due to the formation of sulfur vacancies while annealing in hydrogen are revealed using ambient pressure XPS and DFT calculations. The XPS spectra shows the development of new components in Mo 3d due to the formation of sulfur vacancies with increasing temperature. The DFT calculations with appropriate vacancy models reproduce the core-level shifts.
Abstract
Sulfur vacancy on an MoS2 basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS2 basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering.
Research Progress on Direct Contact Evaporation Heat Transfer between Two Immiscible Working Fluids
Simulation methods, experimental results, and enhancement pathways for direct contact vaporization heat transfer of organic workpieces in the past fifteen years are summarized, focusing on the dispersed phase of organic working fluids and the continuous phase of immiscible inorganic fluids. The changes in droplet population state and methods of enhanced heat transfer are discussed.
Abstract
The direct contact evaporation heat transfer of two immiscible fluids can realize low-temperature differential heat transfer, which is an important method to improve the heat transfer coefficient. This article focuses on the dispersed phase of organic working fluids and the continuous phase of immiscible inorganic fluids and summarizes the research on direct contact evaporation heat transfer in the past 15 years. The main research methods include theoretical analysis, numerical models, and experimental research. The evaporation process of a single droplet mainly involves bubble droplet growth, droplet configuration and discriminant, droplet shape change, rising speed and path, etc. In practice, dispersed phases mostly exist in populations, and the research mainly focuses on collisions, coalescence, and rupture between droplets and bubbles, as well as on the number and size distribution. The volumetric heat transfer coefficient is used to reflect the heat transfer capacity of the heat exchanger. The factors affecting evaporation heat transfer performance are complex, and increasing the uniform mixing of bubbles is an important method to improve the heat transfer coefficient. In the future, direct contact evaporation heat transfer is expected to be promoted to multiple fields.
Flow‐Integrated Preparation of Norbornadiene Precursors for Solar Thermal Energy Storage
Molecular solar thermal (MOST) energy storage systems are getting increased attention related to renewable energy storage applications. Particularly, 2,3-difunctionalized norbornadiene-quadricyclane (NBD-QC) switches bearing a nitrile (CN) group as one of the two substituents are investigated as promising MOST candidates thanks to their high energy storage densities and their red-shifted absorbance. Moreover, such NBD systems can be prepared in large quantities (a requirement for MOST-device applications) in flow through Diels-Alder reaction between cyclopentadiene and appropriately functionalized propynenitriles. However, these acetylene precursors are traditionally prepared in batch from their corresponding acetophenones using reactive chemicals potentially leading to health and physical hazards, especially when working on a several-grams scale. Here, we develop a multistep flow-chemistry route to enhance the production of these crucial precursors. Furthermore, we assess the atom economy (AE) and the E-factor showing improved green metrics compared to classical batch methods. Our results pave the way for a complete flow synthesis of NBDs with a positive impact on green chemistry aspects.
Synthesis and Wittig olefination of (2-methyl-3-oxoisoindolin-1-yl)triphenylphosphonium tetrafluoroborate: facile access to 3-alkylidene-2-methylisoindolin-1-ones
.
Mechanisms of CH4 activation over oxygen‐preadsorbed transition metals by ReaxFF and AIMD simulations
Methane catalytic oxidation has been extensively studied for its huge potential for energy and industrial synthesis. Oxygen atoms adsorbed on transition metal surfaces often change the catalytic activity to activate methane. The dynamic processes of methane oxidation are vital for the understanding of the effects of pre-adsorbed oxygen atoms on transition metal surfaces. This article reports the CH4 dissociation pathways on Au, Cu, Ni, Pt, and Pd surfaces using reactive force field molecular dynamic simulations.
Abstract
The chemisorbed oxygen usually promotes the CH bond activation over less active metals like IB group metals but has no effect or even an inhibition effect over more active metals like Pd based on the static electronic structure study. However, the understanding in terms of dynamics knowledge is far from complete. In the present work, methane dissociation on the oxygen-preadsorbed transition metals including Au, Cu, Ni, Pt, and Pd is systemically studied by reactive force field (ReaxFF). The ReaxFF simulation results indicate that CH4 molecules mainly undergo the direct dissociation on Ni, Pt, and Pd surfaces, while undergo the oxygen-assisted dissociation on Au and Cu surfaces. Additionally, the ab initio molecular dynamics (AIMD) simulations with the umbrella sampling are employed to study the free-energy changes of CH4 dissociation, and the results further support the CH4 dissociation pathway during the ReaxFF simulations. The present results based on ReaxFF and AIMD will provide a deeper dynamic understanding of the effects of pre-adsorbed oxygen species on the CH bond activation compared to that of static DFT.
Synthesis of Chrysanthemum‐Like BiOBr Microspheres by Structure Induction of Chitosan for Enhancing Photocatalytic Activity
Chrysanthemum-like BiOBr microspheres (CLB0.45) were designed and prepared by using chitosan (CS) as a soft template/structure inducer. CLB0.45 demonstrated efficient performance for the degradation of organic pollutants (dyes and antibiotics) due to suitable lattice plane exposure and band gap. The material also exhibited good cyclic stability.
Abstract
Photocatalysis is a green technology with important application prospects in environmental fields such as wastewater treatment. Herein, we synthesized chrysanthemum-like BiOBr microspheres (CLB0.45) by introduction of structure guide and soft-template. Natural biomass chitosan (CS) in the precursor of BiOBr successfully suppressed the growth of both (001) and (102) lattice planes through the solvent effect, and promoted the exposure of (110) lattice planes that dominated the photocatalytic performance. Significantly, the polymer chains regulated the nanosheets of BiOBr to accurately self-assemble. The obtained CLB0.45 had narrower band gap and more active sites due to surface defects, and the photocatalysts have higher photo-electron hole pairs separation efficiency. Additionally, the degradation performance towards rhodamine B (RhB; 99.7 %, 30 min) of the CLB0.45 was increased, which was 4.6 times higher than that of pure BiOBr. The degradation rate of tetracycline (TC) was also excellent (85.3 %). The photodegradation mechanism of CLB0.45 was proposed and verified. In summary, the prepared CLB0.45, obtained through structure guiding and using a soft template, have a promising future in the photocatalytic purification of organic pollutants.