Advances in flexible and functional metal-organic frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009-2013 with reference to the early pertinent work since the late 1990s. Flexible MOFs combine the crystalline order of the underlying coordination network with cooperative structural transformability. These materials can respond to physical and chemical stimuli of various kinds in a tunable fashion by molecular design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host-guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallographic phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theoretical approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chemistry with the linker molecules controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-solution concept are included, and as well examples of possible applications of flexible metal-organic frameworks for separation, catalysis, sensing, and biomedicine.
We study the performance of classical and quantum machine learning (ML) models in predicting outcomes of physical experiments. The experiments depend on an input parameter x and involve execution of a (possibly unknown) quantum process E. Our figure of merit is the number of runs of E required to achieve a desired prediction performance. We consider classical ML models that perform a measurement and record the classical outcome after each run of E, and quantum ML models that can access E coherently to acquire quantum data; the classical or quantum data are then used to predict the outcomes of future experiments. We prove that for any input distribution D(x), a classical ML model can provide accurate predictions on average by accessing E a number of times comparable to the optimal quantum ML model. In contrast, for achieving an accurate prediction on all inputs, we prove that the exponential quantum advantage is possible. For example, to predict the expectations of all Pauli observables in an n-qubit system ρ, classical ML models require 2^{Ω(n)} copies of ρ, but we present a quantum ML model using only O(n) copies. Our results clarify where the quantum advantage is possible and highlight the potential for classical ML models to address challenging quantum problems in physics and chemistry.
Ana Maria Toader, Bogdan Frecus, Corneliu Ioan Oprea
et al.
We obtained thorough insight into the capabilities of various computational methods to account for the ligand field (LF) regime in lanthanide compounds, namely, a weakly perturbed ionic body and quasidegenerate orbital multiplets. The LF version of the angular overlap model (AOM) was considered. We intentionally took very simple idealized systems, the hypothetical [TbF]<sup>2+</sup>, [TbF<sub>2</sub>]<sup>+</sup> and [Tb(O<sub>2</sub>NO)]<sup>2+</sup>, in order to explore the details overlooked in applications on complex realistic systems. We examined the 4f and 5d orbital functions in connection to f–f and f–d transitions in the frame of the two large classes of quantum chemical methods: wave function theory (WFT) and density functional theory (DFT). WFT methods are better suited to the LF paradigm. In lanthanide compounds, DFT faces intrinsic limitations because of the frequent occurrence of quasidegenerate ground states. Such difficulties can be partly encompassed by the nonstandard control of orbital occupation schemes. Surprisingly, we found that the simplest crystal field electrostatic approximation, reconsidered with modern basis sets, works well for LF parameters in ionic lanthanide systems. We debated the largely overlooked <i>holohedrization</i> effect that inserts artificial inversion symmetry into standard LF Hamiltonians.
Abstract The proton transfer complex has been synthesized by mixing 1:1 ratio of 8-aminoquinoline (donor) and chloranilic acid (acceptor) in methanol. FTIR, 13C NMR, 1H NMR, Powder XRD and UV-visible studies confirmed the formation of the newly synthesized compound. These methods ascertain that cations and anions combine to form weak hydrogen bonds as N+–H----O–. The physical properties such as energy of interaction (ECT), resonating energy (RN), Ionization potential (ID), and oscillator strength (f), transition dipole strength (D) and free energy ( G) were estimated through UV-visible spectroscopy. The thermal stability of this complex and extensive erosion was analyzed by TGA/DTA study. Benesi-Hildebrand equation was used to determine 1:1 stoichiometry of this complex and to calculate the molar extinction coefficient (εCT ), the formation constant (KCT) and other physical parameters. The nature of transfer of charge relations plays a vital role in chemistry and in biological systems. The synthesized proton transfer complex has been screened for antibacterial activities against different bacteria and antifungal activities against different fungi. The proton transfer complex also displays outstanding interaction with the human protein (globulin) protein. The DFT calculations by B3LYP/6-311G** basis set gave theoretical establishment and HOMO (−5.468 eV) to LUMO (−3.328 eV) electronic energy gap ( as 2.140 eV. Theoretical analysis proves the biological characteristics as well. Molecular docking displays that CT complex is fully bound to the protein and determines the free binding energy value of −290.18 kcal/mol (FEB). A new organic charge transfer complex has been prepared, characterized and explored for antibacterial, antifungal and protein binding properties. The experimental results are supported by theoretical analysis. Communicated by Ramaswamy H. Sarma Highlights Charge transfer complex was synthesized and characterized by various techniques. Spectrophotometric studies were made in different polar solvents. KCT, ε CT and ECT of were determined using Benesi-Hildebrand equation. Structure and hydrogen-bonding network were also investigated by FT-IR and NMR (1H & 13C). Thermal analysis (TGA–DTA) was also used to confirm the thermal fragmentation and the stability of the CT-complex. Synthesized CT-complex was screened for its antimicrobial activity and protein (globulin) binding.
Abstract The rapid progress in the field of organic–inorganic halide perovskite (OIHP) has led to not only >24% power conversion efficiency for photovoltaics, but also provided breakthroughs in processing of materials with tailored functional behavior. This ability to design and synthesize engineered OIHP materials has opened the possibility to develop various other optoelectronic applications. In addition to that of photovoltaics, this includes photodetector, laser, light emitting diode, X-ray and gamma detector, photocatalyst, memory, transducer, transistor, and more. At this stage, the emphasis is on fundamental understanding of the underlying physics and chemistry of OIHP materials, which will assist the evaluation of device performance and provide explanations for some of the contradictory results reported in literature. This review discusses the theoretical and experimental analysis of the OIHP materials reported from various sources and considers the chemical and structural origin of their unique optoelectronic properties, correlated microstructures, and newly discovered extraordinary properties. In the first few sections, we summarize and discuss the crystallography, chemical bonding, and substitutional effects, followed by the discussion of correlated photophysics including the optical, electronic, excitonic, charge transport, and ion migration characteristics. Next, we revisit and discuss the in-depth behavior of films with unique defect structure, structural disorder, morphology, and crystallization thermodynamics. Novel thermal-electrical-optical properties including ferroelectricity, hot-carrier contribution, spin-orbit coupling effect, terahertz time response, edge-state discovery, etc., are rationalized considering the results debated in the community. We elaborate on the opportunities and challenges regarding stability, toxicity, and hysteresis. The viewpoint on commercialization of OIHP based solar module is presented with the goal of identifying near-term opportunities. Throughout this review, the overarching goal is to provide a simplified explanation for the complex physical effects and mechanisms, underlying interconnections between different mechanisms, uncertainties reported in literature, and recent important theoretical and experimental discoveries.
Chemical reaction dynamics are studied to monitor and understand the concerted motion of several atoms while they rearrange from reactants to products. When the number of atoms involved increases, the number of pathways, transition states and product channels also increases and rapidly presents a challenge to experiment and theory. Here we disentangle the dynamics of the competition between bimolecular nucleophilic substitution (SN2) and base-induced elimination (E2) in the polyatomic reaction F− + CH3CH2Cl. We find quantitative agreement for the energy- and angle-differential reactive scattering cross-sections between ion-imaging experiments and quasi-classical trajectory simulations on a 21-dimensional potential energy hypersurface. The anti-E2 pathway is most important, but the SN2 pathway becomes more relevant as the collision energy is increased. In both cases the reaction is dominated by direct dynamics. Our study presents atomic-level dynamics of a major benchmark reaction in physical organic chemistry, thereby pushing the number of atoms for detailed reaction dynamics studies to a size that allows applications in many areas of complex chemical networks and environments. As the number of atoms involved in a reaction increases, so do the experimental and theoretical challenges faced when studying their dynamics. Now, using ion-imaging experiments and quasi-classical trajectory simulations, the dynamics of the polyatomic reaction F– + CH3CH2Cl have been studied and the competition between bimolecular nucleophilic substitution and base-induced elimination has been disentangled.
Poly(lactic acid) (PLA) biocomposites are usually plasticized to overcome the problem of poor ductility, which decreases the valuable tensile strength. In this study, novel nanofibrillated cellulose (NFC) was extracted to enhance the acetyl tributyl citrate (ATBC) plasticized PLA biocomposites. Interestingly, NFC not only exhibited an excellent strengthening effect but also showed a further toughening effect in the biocomposites. When 4 wt% NFC was added, the tensile strength, elongation at break, and impact strength of the biocomposites with 15 wt% ATBC and 20 wt% ATBC reached 52.6 MPa, 28.4%, 34.9 J/m and 35.8 MPa, 300.1%, 40 J/m, respectively. This is at least 1.1 folds higher in strength and 2.3 folds higher in impact toughness than the biocomposites without NFC. Glass transition and melting temperature slightly increased with NFC addition. More importantly, the mechanism of the strengthening and toughening effect was definitely elucidated, and the comprehensive performance of the application was evaluated. The findings of the study provide significant guidance for PLA application, such as in food packaging, medical engineering materials, and household products.
Abstract A series of BiOI doped with lanthanide metals (lanthanide metals = La, Ce, Eu) were synthesized by solvothermal method and calcination method. The physical and chemical state of the as-prepared BiOI doped with lanthanide metals were characterize by characterization methods. The Hg0 photocatalytic oxidation was performed under visible light to further evaluate the photocatalytic activity. The experimental results indicate that the introduction of lanthanide ions into the BiOI lattice has an important effect on the photocatalytic activity. Moreover, it was found that BiOI doped with different lanthanide ions have different effects on the separation efficiency of charge carriers and the prevention of photo-corrosion. Compared with BiOI doped with La and Eu ions, the results identified that the incorporation of Ce was of a significant role in promoting the photocatalytic activity BiOI. It is proposed that the incorporation of La and Eu ions could induce excessive electrons on the BiOI surface under visible light, which leads to photo-corrosion of the catalyst in contact with the surface H2O. More importantly, the enhanced photocatalytic activity of Ce-BiOI is attributable to the oxygen storage capacity of the Ce3+/Ce4 + redox pairs and surface defects that promote molecular oxygen activation to facilitate the photocatalytic oxidation reaction. This work can provide theoretical support for the future use of lanthanide metal substitution doped modified photocatalysts.
The need for high efficiency energy production, conversion, storage and transport is serving as a robust guide for the development of new materials. Materials with physical-chemical properties matching specific functions in devices are produced by suitably tuning the crystallographic- defect- and micro-structure of the involved phases. In this review, we discuss the case of Rare Earth doped Ceria. Due to their high oxygen diffusion coefficient at temperatures higher than ~500°C, they are very promising materials for several applications such as electrolytes for Solid Oxide Fuel and Electrolytic Cells (SOFC and SOEC, respectively). Defects are integral part of the conduction process, hence of the final application. As the fluorite structure of ceria is capable of accommodating a high concentration of lattice defects, the characterization and comprehension of such complex and highly defective materials involve expertise spanning from computational chemistry, physical chemistry, catalysis, electrochemistry, microscopy, spectroscopy, and crystallography. Results coming from different experimental and computational techniques will be reviewed, showing that structure determination (at different scale length) plays a pivotal role bridging theoretical calculation and physical properties of these complex materials.
Abstract Aerosol nanoclusters (AN), defined here as molecular aggregates suspended in a gas with dimensions between 2 and 10 nm, are the link between substances that we think of as molecules, or the “gas phase,” and those that we consider as particles, or the “condensed phase.” The ability to measure and model the physical and chemical properties of size-resolved AN, which at present is rudimentary at best, is crucial for understanding how particles form and evolve in a number of environments that are natural or influenced by human activities. This review describes the current state-of-the-art for measuring and modeling the size-resolved composition of atmospheric AN. We focus specifically on instruments, many relying on mass spectrometry, that show promise for closing the measurement gap under atmospherically relevant conditions by increasing the size of measurable gas-phase clusters (bottom-up approaches) and by decreasing the size of measurable nanoparticles (top-down approaches). Theoretical methods for predicting AN composition have similarly relied on bottom-up approaches that extend the accuracy of quantum chemistry calculations to larger molecular systems, as well as top-down approaches that correct bulk composition aerosol models for size-dependent properties such as viscosity and volatility. Current measurement and modeling challenges that must be overcome in order to close the gap are discussed.
Nanostructured materials have attained incredible interest in recent days due to their distinctive chemical, physical, mechanical, magnetic and optoelectronic properties. In the present study, metal nano particle (SnO2) was doped with graphite, graphene oxide (GO) and reduced graphene oxide (rGO) with various composition (1:100), (1:1) and (100:1) by weight ratio. The citrate-nitrate gel combustion method was used to prepare nanocrystalline SnO2 while GO and rGO were synthesized through modified Hummer’s method. The preparation of SnO2-rGO composites was done using a one-step hydrothermal process. The electrical and structural behaviour of the composites of graphite, GO and rGO mixed with SnO2 were elucidated by the impedance analyzer in the frequency range from 10Hz to 1MHz. It is observed that the composite of SnO2 with graphite and reduced graphene oxide have similar broad characteristics while SnO2 mixed with GO is exhibiting different properties which could be attributed to the presence of oxygen functionaries.
Industrial electrochemistry, Physical and theoretical chemistry
Li metal provides an ideal anode for the highest energy density batteries, but its reactivity with electrolytes brings poor cycling stability. Electrolyte additives have been employed to effectively improve the cycling stability, often with the underlying mechanism poorly understood. In this work, applying lithium bis(oxalate)borate (LiBOB) as a chemical source for a dense and protective interphase, we investigate this issue with combined techniques of electrochemical/physical characterizations and theoretical calculations. It was revealed that the solid electrolyte interphase (SEI) formed by Li and the carbonate electrolyte is unstable and responsible for the fast deterioration of the Li anode. When LiBOB is present in the electrolyte, a reinforced SEI was formed, enabling significant improvement in cycling stability due to the preferential reduction of the BOB anion over the carbonate molecules and the strong combination of its reduction products with the species from the electrolyte reduction. The effectiveness of such new SEI chemistry on the Li anode supports excellent performance of a Li/LiFePO4 cell. This approach provides a pathway to rationally design an interphase on the Li anode so that high energy density batteries could be realized.
Electro-osmosis technology is an effective method for slurry dewatering, and the voltage gradient, electrode spacing and electrode radius have a large effect on electro-osmosis dewatering. In this paper, a series of tests are conducted to study the effects of those factors on slurry dewatering. The results indicate that a higher voltage gradient can improve electro-osmosis dewatering. Under the same voltage gradient, a smaller electrode spacing leads to a lower discharge rate and less energy consumption, but the water content is also smaller than that with a larger electrode spacing. A larger electrode radius has a good effect on electro-osmosis dewatering, but its energy consumption is also increased. When the slurry is dewatered by electro-osmosis, the water content will be maldistributed after dewatering, with the lowest water content in the anode and the highest in the cathode, and the factors that affect electroosmosis are also analyzed theoretically. In engineering applications, the voltage gradient and electrode radius should be increased appropriately, and the electrode spacing should be reduced to obtain a lower water content.
Industrial electrochemistry, Physical and theoretical chemistry
As steel reinforced concrete is exposed to marine environments, chloride ions penetrate the concrete structures and lead to corrosion of the reinforced bars, which causes serious destruction of the bridge structures. In order to decrease the cost of repairs and the durability of reinforced bars, use of admixtures in concrete structures has attracted the attention of engineers and researchers around the world. In this work, the effect of Kaolin admixtures as partial replacement of ordinary Portland cement on the corrosion resistance of duplex 2205 stainless steel rebar were considered by open circuit potential, electrochemical impedance spectroscopy and polarization analysis after immersion to the marine environment. The electrochemical results indicated that the specimen with 8 kg/m3 Kaolin had higher corrosion resistance and potential than all the others. The surface morphologies of the samples revealed that corrosion products on the surface of DS steel rebar were reduced by addition of Kaolin. The results show that the Kaolin as additives enhance the durability of the concrete and prevent corrosive ions from reaching the surface of metal rebars, which may be an alternative material for development of the construction industry.
Industrial electrochemistry, Physical and theoretical chemistry
A large number of oxides has been investigated in the last twenty years as possible new materials for various applications ranging from opto-electronics to heterogeneous catalysis. In this context, ferroelectric oxides are particularly promising. The electric polarization plays a crucial role at many oxide surfaces, and it largely determines their physical and chemical properties. Ferroelectrics offer in addition the possibility to control/switch the electric polarization and hence the surface chemistry, allowing for the realization of domain-engineered nanoscale devices such as molecular detectors or highly efficient catalysts. Lithium niobate (LiNbO3) is a ferroelectric with a high spontaneous polarization, whose surfaces have a huge and largely unexplored potential. Owing to recent advances in experimental techniques and sample preparation, peculiar and exclusive properties of LiNbO3 surfaces could be demonstrated. For example, water films freeze at different temperatures on differently polarized surfaces, and the chemical etching properties of surfaces with opposite polarization are strongly different. More important, the ferroelectric domain orientation affects temperature dependent surface stabilization mechanisms and molecular adsorption phenomena. Various ab initio theoretical investigations have been performed in order to understand the outcome of these experiments and the origin of the exotic behavior of the lithium niobate surfaces. Thanks to these studies, many aspects of their surface physics and chemistry could be clarified. Yet other puzzling features are still not understood. This review gives a résumé on the present knowledge of lithium niobate surfaces, with a particular view on their microscopic properties, explored in recent years by means of ab initio calculations. Relevant aspects and properties of the surfaces that need further investigation are briefly discussed. The review is concluded with an outlook of challenges and potential payoff for LiNbO3 based applications.
Carbon nanocages with a hierarchical structure have attracted increasing attention in recent years due to the high rate capability of supercapacitors based on such materials. In this study, cubic carbon nanocages (CNCs) with a hierarchical porous structure were prepared by using cubic magnesium oxide as a template and sucrose as the carbon source. The carbon nanocages interconnect to form 3D nanoparticles, when used as the electrode material for supercapacitors, exhibit a high specific capacitance and excellent rate capability. The specific capacitance at a current density of 50 A g-1 can reach 135 F g-1. The excellent capacitive performance of carbon nanocages is attributed to the macropores formed by the cavity inside the cages and interparticle voids, which provide a fast pathway for ion transportation by shortening the diffusion pathway for electrolyte ions. Moreover, CNCs possess good cycling stability with a capacitance retention of 96.2% after 10000 cycles.
Industrial electrochemistry, Physical and theoretical chemistry
A bipolar plate is an important component of proton exchange membrane fuel cells (PEMFC). The fabrication of multiple slots is a key part in preparation of metallic bipolar plates. They can be produced by electrochemical machining (ECM). During the ECM process, high flow resistance occurs with the increase of slots length and depth, which will make metal hydroxide and other by-products accumulate in the outlet of electrolyte and limit the maximum feed rate of cathode. Therefore, a flow channels contraction cathode structure with variable cross-section has been proposed. It can make the flow velocity of electrolyte increase gradually in the inter-electrode gap and take away electrolysis products better. In order to remove electrolysis products further, tool vibration is applied. The flow channels contraction cathode has been determined with numerical simulations, and the comparison experimental results show that the way is effective in improving the feed rate and ensuring the uniformity of slots depth.
Industrial electrochemistry, Physical and theoretical chemistry