Hasil untuk "Physical and theoretical chemistry"

Chong TAN, Yuan QI, Yuhong YIN et al.

In this paper, composite nanostructures are constructed successfully by combining conductive carbon-based materials with MoS2. The MoS2/reduced Graphene Oxide (rGO) composite was synthesized by hydrothermal method, and its morphology, elemental composition and microstructure were characterized in detail. Then, the MoS2/rGO composite material was modified on the glass carbon electrode (GCE) to construct the methyl parathion (MP) electrochemical sensor. The experimental results show that compared with a single MoS2/GCE modified electrode, the MoS2/rGO modified electrode exhibits significantly improved electrochemical performance. This boost can be attributed to the rGO’s high electrical conductivity and its good interface combination with MoS2, which work together to facilitate electron transport and enhance catalytic activity. In the electrochemical detection of MP, the MoS2/rGO modified electrode shows excellent sensitivity, and its detection limit of MP reaches 11.92 ng/mL, providing an effective solution for the detection of MP with high sensitivity.

Sebastian Liebl, Josef M. Gallmetzer, Daniel Werner et al.

Igor V. Stiopkin, Champika N. Weeraman, P. Pieniazek et al.

Benjamin De Bari, James Dixon, D. Kondepudi et al.

The physical origin of behaviour in biological organisms is distinct from those of non-living systems in one significant way: organisms exhibit intentionality or goal-directed behaviour. How may we understand and explain this important aspect in physical terms, grounded in laws of physics and chemistry? In this article, we discuss recent experimental and theoretical progress in this area and future prospects of this line of thought. The physical basis for our investigation is thermodynamics, though other branches of physics and chemistry have an important role. This article is part of the theme issue 'Thermodynamics 2.0: Bridging the natural and social sciences (Part 1)'.

Nana Sun, Yuchen Jin, Hailong Wang et al.

: Incorporation of molecular switches with light, heat, and electricity responsibility into arti fi cial solids has been developed as a successful strategy to construct stimuli-responsive functional materials. However, precise manipulation of their molecular geometries and electronic structures to control the properties of macroscopic materials still remains a fundamental challenge. Herein, a photoresponsive covalent organic framework ( o -COF) with the square lattice was fabricated from the dynamic covalent chemistry reaction of ring-open dithienylethene − dialdehyde with 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (H 2 TAPP). UV irradiation of the dithienyle-thene-based units in o -COF a ff orded its reversible photoisomer ( c -COF) in the ring-closed form. In addition to a range of di ff raction, microscopic, and gas physical sorption characterizations, spectroscopic investigations with the help of theoretical simulations revealed di ff erent photocatalytic activities toward the evolution of singlet oxygen and corresponding photocatalytic oxidation of amines due to the di ff erent energy transfer pathways from the porphyrin unit to BBTP photoisomers in these two COFs. Most interestingly, such di ff erent photocatalytic behaviors for two COFs could be easily tuned in a reversible manner by adjusting the ring-closed/ open form of dithienylethene units by means of UV and visible light. mg) were added into 1.0 mL of CD 3 CN in a 5 mL quartz tube. The resultant mixture was stirred at room temperature upon irradiation with a 25 W blue LED light under air. Conversion of the product was determined by 1 H NMR in CD 3 CN. For the recycle test, the catalyst was separated by centrifugation, washed by CH 3 OH after every cycle, and dried at 25 ° C under vacuum for next use.

Bowen Jin, Jinguo Cao, Ruihan Yuan et al.

The perovskite lattice strain correlating to its physical chemistry not only impacts the optoelectronic properties but also the long‐term stability. The relaxation of perovskite lattice strain has been recognized as an important pathway to improve photovoltaic performance and broaden the application scope. With the growth of research interest and the thriving of synthetical approaches in strain engineering, it is particularly necessary to summarize the current strategies to give an in‐depth understanding of the relaxation of lattice strain. Herein, the milestones in strain relaxation studies are summarized and the theoretical simulation and methodological approach to correlate the crystal structure and physical properties at an atomic level is outlined. This perspective provides fundamentals to theoretically predict and experimentally measure the strain relaxation effect and suggests design principles and synthetical strategies for tackling the lattice strain issue for perovskites.

Zhengpeng Wang, Xuanhu Chen, F. Ren et al.

As an ultrawide bandgap semiconductor, gallium oxide (Ga2O3) has superior physical properties and has been an emerging candidate in the applications of power electronics and deep-ultraviolet optoelectronics. Despite numerous efforts made in the aspect of material epitaxy and power devices based on β-Ga2O3 with rapid progresses, the fundamental understanding of defect chemistry in Ga2O3, in particular, acceptor dopants and carrier compensation effects, remains a key challenge. In this focused review, we revisited the principles of popular approaches for characterizing defects in semiconductors and summarized recent advances in the fundamental investigation of defect properties, carrier dynamics and optical transitions in Ga2O3. Theoretical and experimental investigations revealed the microstructures and possible origins of defects in β-Ga2O3 bulk single crystals, epitaxial films and metastable-phased α-Ga2O3 epilayers by the combined means of first-principle calculation, deep level transient spectroscopy and cathodoluminescence. In particular, defects induced by high-energy irradiation have been reviewed, which is essential for the identification of defect sources and the evaluation of device reliability operated in space and other harsh environments. This topic review may provide insight into the fundamental properties of defects in Ga2O3 to fully realize its promising potential in practical applications.

W. Vallejo, Carlos Díaz-Uribe, Catalina Fajardo

Various studies have reported the versatility and great scope of programming tools in all areas of knowledge. Coding is generally of paramount importance to chemistry students regardless of whether they intend to work with theoretical chemistry. Google Colab notebooks can introduce students to programming concepts and could be a convenient tool to assist in the chemistry teaching process. In this article, we implemented Google Colab notebooks to aid in the teaching of thermodynamics in a physical chemistry class. We presented six notebooks, covering introductory concepts of both coding and thermodynamics as a set of learning objects that can be useful in a virtual learning environment. In addition, in some of the notebooks, we included a step-by-step guide on how to run virtual lab simulations. The Colab notebooks were created for students without previous experience in programming. All of the Colab notebooks contain exercises of the activities and the solutions of the proposed exercises. Furthermore, all of the Colab notebooks can be modified and downloaded from the Github repository. Finally, we used the Python programming language and Colab because they are free and widely used by the academic community.

Chunmei Li, Jinyuan Zhou, Di Wang et al.

Amide proton transfer (APT) magnetic resonance imaging (MRI) is an important molecular imaging technique at the protein level in tissue. Neurodegenerative diseases have a high likelihood of causing abnormal protein accumulation in the brain, which can be detected by APT MRI. This article briefly introduces the principles and image processing technology of APT MRI, and reviews the current state of research on Alzheimer's disease and Parkinson's disease using this technique. Early applications of this approach in these two neurodegenerative diseases are encouraging, which also suggests continued technical development and larger clinical trials to gauge the value of this technique.

Emil Vogt, H. Kjaergaard

The vibrational spectroscopy of the water dimer provides an understanding of basic hydrogen bonding in water clusters, and with about one water dimer for every 1,000 water molecules, it plays a critical role in atmospheric science. Here, we review how the experimental and theoretical progress of the past decades has improved our understanding of water dimer vibrational spectroscopy under both cold and warm conditions. We focus on the intramolecular OH-stretching transitions of the donor unit, because these are the ones mostly affected by dimer formation and because their assignment has proven a challenge. We review cold experimental results from early matrix isolation to recent mass-selected jet expansion techniques and, in parallel, the improvements in the theoretical anharmonic models. We discuss and illustrate changes in the vibrational spectra of complexes upon increasing temperature, and the difficulties in recording and calculating these spectra. In the atmosphere, water dimer spectra at ambient temperature are crucial. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Qiankui Zhang, Si Liu, Zeheng Lin et al.

Abstract Safety concerns impede the deployment of Li-metal batteries, while the highly flammable electrolytes make main contribution to the hazard caused by the reactive Li with electrolytes. Fire-extinguishing electrolytes do exist, but their introductions into the batteries have generally resulted in cycle performance trade-offs. In this work, we report a new electrolyte that consists of 1 M lithium hexafluorophosphate dissolved in a single solvent of vinylethylene carbonate (VEC), enabling Li-metal batteries with the most reliability in terms of high safety, long cycle life and practical scale-up among the up-to-date strategies. Combining theoretical calculations with physical and electrochemical characterizations, we demonstrate that this new electrolyte is highly flame-retardant, thanks to the strong combination of VEC with hydrogen and hydroxide radicals, and provides Li-metal anode with excellent cycle stability, attributed to easy desolvation of Li ions in VEC and unique interphase chemistry that consists of inorganic Li2CO3 underneath and organic –(CH2–CH2O)2- species on the top, originated from VEC reduction. Considering the low cost of VEC, this VEC-based electrolyte makes it possible for Li-metal batteries to be applied practically in large scale.

E. Stoffels, Y. Sakiyama, D. B. Graves

Christina Stangel, Eleni Nikoli, Nikos Tagmatarchis

The remarkable properties of transition metal dichalcogenides (TMDs), represented by molybdenum disulfide (MoS2), make them promising candidates as active nanomaterials for optoelectronics, electronic, and electrochemical applications. Different exfoliation methods can drastically alter the properties of TMDs, changing the metallic–semiconducting polytype or creating defects, while further chemical surface modification offers additional routes to tune the properties of TMDs by adding new functions. In this timely review, a general outlook on the most representative examples of TMD‐based materials interfacing photoactive components, such as porphyrins and phthalocyanines among others, yielding electron donor–acceptor hybrids and nanoensembles for energy conversion schemes, specifically for managing charge transfer events, is presented. The covalent and noncovalent approaches for the coupling of the aforesaid photoactive species with TMDs and their photophysical characterization are highlighted. Moreover, the properties, preparation methods, and characterization techniques of TMDs, mainly for MoS2, are also briefly discussed. Finally, perspectives and challenges of this emerging area are showcased, aiming to increase scientific attention and enhance not only the performance but also their applicability.

Cheng Chu, Song Ziwei, Wang Lingfeng et al.

The addition of microalloying elements improves the microstructure and properties of copper-based materials. In this study, WCu composites are synthesized in situ with Fe, Ni, or Mn as microalloying elements, and the effects of each element on the microstructural characteristics of the obtained composite are investigated. Fe, Ni, and Mn can be added in situ to WCu composites by thermite reduction. Increasing the temperature is not conducive to the reduction of MnO2 by Al. Ni, Fe, and Mn were well dissolved in the copper matrix, and their contents decreases in turn, while the Al content in the matrix increases in turn. Mn clearly reduces the size of tungsten particles, and the size reduction effect of the microalloying elements on tungsten particles follows the order Mn > Fe > Ni. The effect on the wettability of the interface follows the order Ni > Mn > Fe. Increasing the interfacial wetting is not conducive to the refinement of tungsten particles.

M. Pykal, P. Jurečka, F. Karlický et al.

Graphene has attracted great interest because of its remarkable properties and numerous potential applications. A comprehensive understanding of its structural and dynamic properties and those of its derivatives will be required to enable the design and optimization of sophisticated new nanodevices. While it is challenging to perform experimental studies on nanoscale systems at the atomistic level, this is the 'native' scale of computational chemistry. Consequently, computational methods are increasingly being used to complement experimental research in many areas of chemistry and nanotechnology. However, it is difficult for non-experts to get to grips with the plethora of computational tools that are available and their areas of application. This perspective briefly describes the available theoretical methods and models for simulating graphene functionalization based on quantum and classical mechanics. The benefits and drawbacks of the individual methods are discussed, and we provide numerous examples showing how computational methods have provided new insights into the physical and chemical features of complex systems including graphene and graphene derivatives. We believe that this overview will help non-expert readers to understand this field and its great potential.

Scott Simpson

Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes (NHCs) to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR and P NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron donating substituents tend to strengthen the interaction.

Xinyao Luo, Hangfu Yang, Nengjun Yu et al.

The structure, magnetic, and the magnetocaloric effecton the La0.7-xEuxSr0.3MnO3sample prepared by the solid-state reaction method had been investigated. The structure data obtained from X-ray powder diffraction and Rietveld refinement analysis show that all these samples have single-phase and a rhombohedra structure with R-3c space group. With the substitution of the Eu3+ content, the volume of unit cells and Mn-O-Mn bond angle increase monotonically as well as the Curie temperature TC, which is caused by the weakening of the double exchange interaction. A magnetic entropy change (-ΔSM)max of 2.21 J kg-1K-1 is obtained under a magnetic field change of 20 kOe for La0.66Eu0.04Sr0.3MnO3 sample. All samples exhibit the FM-PM phase transition with a second-order nature. In the electrochemistry corrosion experiment for the sample, the mass loss rate of the sample is small, so the material possesses optimal anticorrosion performance. The lattice structure and the Curie temperature of the material can be manipulated to some extend with Eu3+ substitution, which provides a method for magnetic refrigeration in an electrolyte solution environment.

V.V. Izmailov, M.V. Novoselova

The nanotopography of engineering surfaces of machine parts made of high alloy heat-treated steel and electric silver after finishing mechanical treatment was studied. The probability density functions of the nanotopography parameters – the heights of peaks and the radii of curvature of their vertices – were experimentally determined. These parameters are necessary for theoretical description of processes of the contact interaction of engineering surfaces (exemplifying on surfaces of silver and steel). It is established that the distributions of the above mentioned nanoroughness parameters are essentially asymmetrical and are far from normal ones. It has been proved that for the studied surfaces the probability densities of the above mentioned nanoroughness parameters are adequately described by the beta-distribution. The validity of this conclusion is confirmed by the fitting criteria such as χ^2 (K. Pearson’s criterion) and Romanovsky’s criterion.

Miriam Hauschild, Michal Borkowski, Pavlo O. Dral et al.

Abstract We report the synthesis of 5,7,12,14-tetraphenyl-substituted 6,13-dihydro-6,13-diazapentacene and its fully aromatic 6,13-diazapentacene congener. Both arylated diazapentacenes were characterized by X-ray crystallography to investigate their solid-state structures and by UV–vis spectroscopy and cyclic voltammetry to unveil their electronic properties. The experimental results are complemented with theoretical investigations. The semiconductor properties of both diazapentacene derivatives were assessed in organic field-effect transistors, whereby the fully aromatized compound showed comparably less abundant n-type behavior.

Lijiang Zhang, Xiaowen Zhang, Qian Lu et al.

Goethite is a stable and widespread mineral present in soil with many uses, and it affects the transportation and immobilization of heavy metals in solution. Nanogoethite was synthesized by a chemical precipitation method and used to batch adsorb U(VI) in solution. Adsorption experiments were used to understand the role of nanogoethite in controlling the U(VI) adsorption behavior in soil. The morphology and the crystallinity of nanogoethite were characterized by scanning electron microscopy and wide-angle X-ray powder diffractometry, respectively. The results showed that the crystallinity of nanogoethite after the adsorption of uranium did not change, but small particles appeared on the surface of the scales. The surface area was determined from N 2 adsorption–desorption experiments using the Brunauer–Emmett–Teller to be 81.86 m 2 /g. The effects of factors such as the contact time, pH, adsorbent dosage, and the initial concentration of uranium on the adsorption of U(VI) were investigated. The experimental results showed that nanogoethite removed over 85% of the U(VI) in an aqueous 5.0 mg/L U(VI) solution at pH 4.0 and at 298 K. The pseudo-second-order model was used to simulate the adsorption process. The results show that chemisorption plays a major role in the adsorption process. The results of this study suggest that nanogoethite may play a significant role in controlling the migration and transfer of U(VI) in the soil, thus controlling the presence of U(VI) in soil.