IR Absorption Research Articles

The influence of the volume concentration of hydrogen on the fine structure of the IR absorption spectra and conductivity features in congruent LiTaO3 crystals

A new method for changing the volume concentration of hydrogen in congruent LiTaO3 (lithium tantalate, LT) crystals has been studied. It has been established that pre-treatment of the sample in adipic acid significantly increases the volumetric concentration of hydrogen in the sample during subsequent annealing in a humid atmosphere at a relatively low annealing temperature. First of all, this preserves the LT single crystal in a single-domain state. In contrast to known methods for increasing the volumetric concentration of hydrogen, the proposed method affects the absorption coefficient of the sample in the optical range less than for a congruent LiNbO3 crystal. It has been shown that the type of IR absorption spectrum of OH− groups and the defect structure of the LT crystal significantly depend on the volume concentration of hydrogen in the sample. The study also analyzed the reasons for this effect. The temperature dependences of the electrical conductivity of LT samples with different hydrogen concentrations have been studied. It has been shown that the type of electronic conductivity of LT samples changes when the concentration of OH groups in the crystal increases significantly.

Cobalt(III) complexes with (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate. The influence of nature of alkali and alkaline earth metal counter cations on the supramolecular association of the complex

The coordination of hexadentate (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate (1,3-pndta) ligand with Co(III) has been investigated. Four octahedral [Co(1,3-pndta)]− complexes containing different counter cations, Li[Co(1,3-pndta)]⋅4H2O (1a), Li[Co(1,3-pndta)]⋅2H2O (1b), K[Co(1,3-pndta)]⋅H2O (1c) and Ca[Co(1,3-pndta)]2⋅5H2O (1d), were synthesized and structurally characterized. Single-crystal X-ray diffraction analysis, IR, NMR (1H and 13C) and electronic absorption spectroscopy were used for characterization of 1a − d. The influence of the ethyl substituent of 1,3-propanediamine chain in 1,3-pndta and the nature of metal counter cation on the structural modalities of carboxylate bridging groups in 1a − d were established by comparing with the analogous [M(1,3-pdta)] n − (1,3-pdta = 1,3-propanediamine-N,N,N’,N’-tetraacetate) and [M(1,3-pndta)] n − complexes (M = Co(III), Cr(III) and Ni(II)). Our studies have shown that the supramolecular association of the complexes is primarily governed by the size of the alkali or alkaline earth metal counter cation and its templating ability, while ethyl substituents, in most cases, prevent the formation of 3D polymeric frameworks.

Enricofrancoite, KNaCaSi4O10, a new Ca–K–Na silicate from Somma–Vesuvius volcano, southern Italy

Abstract Enricofrancoite (IMA2023–002), ideally KNaCaSi4O10, is a new litidionite-group member found as the product of high-temperature alteration of hosting silicates with the enrichment by Cu-bearing fluids at the rock–fumaroles interface related to the 1872 eruption of Somma–Vesuvius volcano, southern Italy. It occurs as euhedral and platy crystals or crusts together with litidionite, tridymite, wollastonite and Al- and Fe-bearing diopside, kamenevite, perovskite, rutile, Ti-rich magnetite and colourless Si-glass. Single crystals of enricofrancoite are transparent colourless or light blue with a vitreous lustre. Mohs hardness is 5.5. Dmeas is 2.63(3) g/cm3 and Dcalc is 2.63 g/cm3. The mineral is optically biaxial (−), α = 1.542(5), β = 1.567(5),γ = 1.575(5); 2V(meas) = 60(2)° and 2Vcalc = 58°. The mean chemical composition (wt.%, electron-microprobe data) is: SiO2 64.81, Al2O3 0.03, TiO2 0.08, FeO 0.07, MgO 1.71, CaO 10.64, CuO 2.22, Na2O 8.56, K2O 11.41, total 99.94. The empirical formula based on 10 O apfu is: K0.90Na1.03(Ca0.71Mg0.16Cu0.10)Σ0.97Si4.02O10. The Raman spectrum contains bands at 133, 248, 265, 290, 335, 400, 438, 510, 600, 690 and 1120 cm–1 and the wavenumbers of the IR absorption bands are: 424, 470, 492, 530, 600, 630, 690, 750, 788, 970, 1040 and 1160 cm–1. The eight strongest lines of the powder X-ray diffraction pattern are [d, Å (I, %) hkl]: 6.75 (42) 01 $\bar{1}$ , 3.65 (20) 11 $\bar{2}$ , 3.370 (100) 02 $\bar{2}$ , 3.210 (52) 102, 3.051 (18) 111, 3.033 (25) 2 $\bar{1}\bar{2}$ , 2.834 (22) 02 $\bar{3}$ and 2.411 (72) 03 $\bar{2}$ . Enricofrancoite is triclinic, space group P $\bar{1}$ , unit-cell parameters refined from the single-crystal data are a = 7.0155(4) Å, b = 8.0721(4) Å, c = 10.0275(4) Å, α = 104.420(4)°, β = 99.764(4)°, γ = 115.126(5)° and V = 472.74(5) Å3. The crystal structure has been refined from single-crystal X-ray diffraction data to R1 = 0.035 on the basis of 2078 independent reflections with Fo > 4σ(Fo). Enricofrancoite is an H2O-free analogue of calcinaksite with 5-coordinated Ca2+ at the M site.

Tuning the Microenvironment of Water Confined in Ti3C2Tx MXene by Cation Intercalation.

The local microenvironment has recently been found to play a major role in the electrocatalytic activity of nanomaterials. Modulating the microenvironment by adding alkali metal cations into the electrolyte can be used to either suppress hydrogen or oxygen evolution, thereby extending the electrochemical window of energy storage systems, or to tune the selectivity of electrocatalysts. MXenes are a large family of two-dimensional transition metal carbides, nitrides, and carbonitrides that have shown potential for use in electrochemical energy storage applications. Due to their negatively charged surfaces, MXenes can accommodate cations and water molecules between the layers. Nevertheless, the nature of the aqueous microenvironment in the MXene interlayer space is poorly understood. Here, we apply Fourier transform infrared spectroscopy (FTIR) to probe the hydrogen bonding of intercalated water in Ti3C2Tx as a function of intercalated cation and relative humidity. Substantial changes in the FTIR spectra after cation exchange demonstrate that the hydrogen bonding of water molecules confined between the MXene layers is strongly cation-dependent. Furthermore, the IR absorbance of the confined water correlates with resistivity estimated by 4-point probe measurements and interlayer distance calculated from XRD patterns. This work demonstrates that cation intercalation strongly modulates the confined microenvironment, which can be used to tune the activity or selectivity of electrochemical reactions in the interlayer space of MXenes in the future.

Introduction of BaF2 to titanate-germanate glasses doped with rare-earth ions evidenced by NIR luminescence spectroscopy

A novel TiO2-GeO2-BaO-BaF2-Ga2O3 glasses doped with rare-earth were synthesized, and the impact of the substitution of BaF2 for BaO on properties has been investigated by luminescence spectroscopy. The IR absorption coefficient is extremely low, which is attractive for optical fibers emitting NIR radiation. Near-IR luminescence associated to the Er3+:4I13/2 → 4I15/2 (FWHM = 108 nm), Tm3+:3F4 → 3H6 (FWHM = 244 nm) and Ho3+:5I7 → 5I8 (FWHM = 179 nm) transitions are enhanced in the presence of BaF2. Luminescence lifetimes increase with increasing content of BaF2 in the glass composition. Fabricated optical materials with relatively high BaF2 content represent a good starting point for further investigations in the field of glass technology and modern photonics.

Scaling-up VPT2: A feasible route to include anharmonic correction on large molecules

Vibrational analysis plays a crucial role in the investigation of molecular systems. Though methodologies like second-order vibrational perturbation theory (VPT2) have paved the way to more accurate simulations, the computational cost remains a difficult barrier to overcome when the molecular size increases. Building upon recent advances in the identification of resonances, we propose an approach making anharmonic simulations possible for large-size systems, typically unreachable by standard means. This relies on the fact that, often, only portions of the whole spectra are of actual interest. Therefore, the anharmonic corrections can be included selectively on subsets of normal modes directly related to the regions of interest. Starting from the VPT2 equations, we evaluate rigorously and systematically the impact of the truncated anharmonic treatment onto simulations. The limit and feasibility of the reduced-dimensionality approach are detailed, starting on a smaller model system. The methodology is then challenged on the IR absorption and vibrational circular dichroism spectra of an organometallic complex in three different spectral ranges.

Optical constants of exoplanet haze analogs from 0.3 to 30 µm: Comparative sensitivity between spectrophotometry and ellipsometry

We report new optical constants (refractive index, n, and extinction coefficient, k) for exoplanet haze analogs from 0.3 to 30 µm. The samples were produced in a simulated N2-dominated atmosphere with two different abundance ratios of CO2 and CH4, using the PAMPRE plasma reactor at LATMOS. We find that our haze analogs present a significantly lower extinction coefficient in the optical and near-infrared (NIR) range compared to the seminal data obtained on Titan haze analogs. We confirm the stronger IR absorption expected for hazes produced in a gas mixture with higher CO2 abundances. Given the strong impact of the atmospheric composition on the absorbing power of hazes, these new data should be used to characterize early-Earth and CO2-rich exoplanet atmospheres. The data presented in this paper can be found in the Optical Constants Database. Using ellipsometry or spectrophotometry, the retrieved optical constants are affected by the sensitivity of the measurement and the accuracy of the calculations. A comparative study of both techniques was performed to identify limitations and better understand the discrepancies present in the previous data. For the refractive index n, errors of 1–3% are observed with both optical techniques and the different models, caused by the correlation with the film thickness. We find that UV-visible reflection ellipsometry provides similar n values, regardless of the model used; whereas the Swanepoel method on transmission is more subjected to errors in the UV. In the UV and mid-infrared (MIR), the different calculations lead to rather small errors on k. Larger errors of k arise in the region of weak absorption, where calculations are more sensitive to errors on the refractive index n.

Toward the IR Detection of Carbonic Acid: Absorption and Emission Spectra

With the recent radioastronomical detection of cis-trans-carbonic acid (H2CO3) in a molecular cloud toward the Galactic center, the more stable but currently unobserved cis-cis conformer is shown here to have strong IR features. While the higher-energy cis-trans-carbonic acid was detected at millimeter and centimeter wavelengths, owing to its larger dipole moment, the vibrational structure of cis-cis-carbonic acid is more amenable to its observation at micron wavelengths. Even so, both conformers have relatively large IR intensities, and some of these fall in regions not dominated by polycyclic aromatic hydrocarbons. Water features may inhibit observation near the 2.75 μm hydride stretches, but other vibrational fundamentals and even overtones in the 5.5–6.0 μm range may be discernible with JWST data. This work has employed high-level, accurately benchmarked quantum chemical anharmonic procedures to compute exceptionally accurate rotational spectroscopic data compared to experiment. Such performance implies that the IR absorption and even cascade emission spectral features computed in this work should be accurate and will provide the needed reference for observation of either carbonic acid conformer in various astronomical environments.

Dinuclear gold(I) pseudohalogen complexes bridged by a ferrocenyl bisphosphine ligand: synthesis, structure, and reactivity toward isothiocyanate

Ferrocenyl bisphosphine-bridged dinuclear gold(I) complexes containing CF3COO as a pseudohalogen ligand were synthesized from the corresponding halides using CF3COOAg. The sequential treatment of gold(I) trifluoroacetates with aqueous NaN3 afforded the corresponding ferrocenyl bisphosphine-bridged dinuclear gold(I) azides. Isolated gold(I) pseudohalogen complexes were characterized through IR, NMR and X-ray crystallography. The characteristic IR absorption bands of ν(CO), ν(CF), and ν(N3) were at 1690, 1190, and 2040 cm−1, respectively, corresponding to the gold(I) trifluoroacetates and azides, verifying gold(I) pseudohalogen formation. The molecular structure of [Au2(η1-CF3CO2)2(µ-dippf)] (dippf = 1,1’-bis(diisopropylphosphino)ferrocene) through X-ray diffraction showed intermolecular Au⋅⋅⋅Au interactions with close contacts between molecules. The crystallographic images illustrate the polymeric chain of bis(phosphino)ferrocenyl gold(I) formed via intermolecular Au⋅⋅⋅Au bonds and layered packing arrays. In contrast, the molecular structures of [Au2(η1-CF3CO2)2(µ-dtbpf)] (dtbpf = 1,1’-bis(di-tert-butylphosphino)ferrocene) and Au2(N3)2(µ-dippf) showed intramolecular Au⋅⋅⋅Au aurophilic interactions, but the structures of [Au2(η1-CF3CO2)2(µ-dcpf)] (dcpf = 1,1′-bis(dicyclohexylphosphino)ferrocene) and Au2(N3)2(µ-dppf) revealed no direct interaction within the dinuclear gold(I) system. Gold(I) azides gradually react with isothiocyanates (allyl, (S)-(+)-1-phenylethyl, and benzyl) to afford the corresponding gold(I) tetrazole-thiolates [Au2X2(µ-dippf)] or [Au2X2(µ-dtbpf)] (X = S[CN4(Y)]) (Y = allyl, (S)-(+)-1-phenylethyl, and benzyl) via dipolar cycloaddition of the isothiocyanates into the Au-N3 bond.

Copper(II) coordination compounds based on bis-hydrazones of 2,6-diacetylpyridine: synthesis, structure, and cytotoxic activity.

By reacting a series of 2,6-diacetylpyridine bis-hydrazones containing pyrimidine (H2L1), benzimidazole (H2L2) and phthalazine (H2L3) heterocyclic fragments with copper(II) chloride and bromide, a variety of pentacoordinated complexes of the composition [Cu(H2L1)X]X, [Cu(HL2)X] and [Cu(HL3)X], where X = Cl-, Br-, are formed. The properties and structure of the compounds were studied by means of NMR, IR, UV-vis, ESR, and X-ray absorption spectroscopy, cyclic voltammetry and X-Ray single crystal diffraction methods. It was shown that complexes of the cationic type [Cu(H2L1)X]X have an asymmetric structure with a distorted square-pyramidal geometry of the coordination unit. The coordination polyhedron of metal chelates [Cu(HL2)X] and [Cu(HL3)X] is an almost ideal square pyramid. Investigations of the cytotoxic activity of the obtained compounds in vitro on human hepatocellular carcinoma (HepG2) and non-tumor human lung fibroblast (MRC-5) cell lines demonstrated that complexes show higher activity compared with the well-known anticancer agent cisplatin. In addition, metal chelates [Cu(H2L1)Cl]Cl, [Cu(HL2)Cl], [Cu(HL2)Br] and [Cu(HL3)Cl] were less toxic to non-tumor cells MRC-5. A study of the binding of complexes to bovine serum albumin (BSA) protein using fluorescence spectroscopy showed that copper complexes are strongly bound to BSA. To study the mechanism of interaction of the complexes with the DNA of cancer cells, molecular dynamics simulation of the compound [Cu(HL3)Cl] was carried out. It was shown that the complex enters into π-stacking interactions predominantly with adenine and thymine bases.

Transient IR spectroscopy of optically centrifuged CO2 (R186-R282) and collision dynamics for the J = 244-282 states.

Collisions of optically centrifuged CO2 molecules with J = 244-282 (Erot = 22 800-30 300 cm-1) are investigated with high-resolution transient IR absorption spectroscopy to reveal collisional and orientational phenomena of molecules with hyper-thermal rotational energies. The optical centrifuge is a non-resonant optical excitation technique that uses ultrafast, 800 nm chirped pulses to drive molecules to extreme rotational states through sequential Raman transitions. The extent of rotational excitation is controlled by tuning the optical bandwidth of the excitation pulses. Frequencies of 30 R-branch ν3 fundamental IR probe transitions are measured for the J = 186-282 states of CO2, expanding beyond previously reported IR transitions up to J = 128. The optically centrifuged molecules have oriented angular momentum and unidirectional rotation. Polarization-sensitive transient IR absorption of individual rotational states of optically centrifuged molecules and their collision products reveals information about collisional energy transfer, relaxation kinetics, and dynamics of rotation-to-translation energy transfer. The transient IR probe also measures the extent of polarization anisotropy. Rotational energy transfer for lower energy molecules is discussed in terms of statistical models and a comparison highlights the role of increasing energy gap with J and angular momentum of the optically centrifuged molecules.

The Fabry-Perot effect suppression in gas cells used in THz absorption spectrometers

Gas cells are widely used in THz and IR absorption spectroscopy. However, reflections of an optical wave on cell input and output windows cause a gas sample measured spectrum distortion due to the Fabry-Perot effect. The hardware approach to decrease the Fabry-Perot effect in the THz spectral range is suggested. The approach is based on using a standard gas cell and the additional movable optically transparent window. To illustrate usefulness of the suggested approach, a simulation of registration of the sulfur dioxide absorption band near 660 GHz in the gas mixture consisted of 0.1 % SO2 and 99.9 % N2 was conducted. The absorption band profile fluctuations due to the Fabry-Perot effect were shown to be reduced by almost 4 times with the suggested approach implementation in relation to the default gas cell. This approach can be combined with other hardware and software variants of the Fabry-Perot effect suppression.

Spectroscopic and computational characterization of new promising donors – Manganese(III) porphyrins bearing carbazole groups

UV–vis, IR, MALDI-TOF, and femtosecond transient absorption spectroscopic techniques together with DFT and TDDFT computations have been employed to explore new manganese(III) porphyrins bearing [3,6-di-tert-butyl-carbazol-9-yl-benzoyloxy]- (MnP1) and [3,6-bis(3΄,6΄-di(tert-butyl)-9΄H-carbazol)-9H-carbazolbenzoyloxy]phenyl (MnP2) groups. MnP1 and MnP2 demonstrate the significant deviation of the macrocycle from planarity, which can be due to the high spin (S = 2) state of the manganese(III). By studying MnP1 and MnP2 excited states, the formation of the trip-quintet ones decaying in 13.7 ps and 17.3 ps, respectively, was established. The comparisons of MnP1 and MnP2 with the Co and Zn analogs have shown that both the number of generations and metal ion influence excited-state dynamics and electronic/structural properties.

Diffusion-controlled annealing kinetics of interstitial H in SnO2

SnO2 is a prototypical transparent conducting oxide that finds widespread applications as transparent electrodes, gas sensors, and transparent thin-film devices. Hydrogen impurities in SnO2 give rise to unintentional n-type behavior and unexpected changes to conductivity. Interstitial H (Hi) and H at an oxygen vacancy (HO) are both shallow donors in SnO2. An O–H vibrational line at 3155 cm−1, that can be produced by a thermal anneal at 500 °C followed by a rapid quench, has been assigned to the Hi center and is unstable at room temperature on a timescale of weeks. An IR absorption study of the decay kinetics of the 3155 cm−1 O–H line has been performed. The disappearance of Hi upon annealing has been found to follow second-order kinetics. Measurements of the decay rate for a range of temperatures have determined an activation energy for the diffusion of interstitial H in SnO2. These results provide fundamental information about how unintentional hydrogen impurities and their reactions can change the conductivity of SnO2 device materials in processes as simple as thermal annealing in an inert ambient.

Enhancing the performance of the solar thermoelectric generator in unconcentrated and concentrated light

The solar thermoelectric generator is undoubtedly an important candidate to convert solar into electric energy. The current efficiency of the thermoelectric generator is low, but recent research indicates an improvement in efficiency. The paper presents a method that leads to performance enhancement of the solar thermoelectric generator. An absorbent layer comprising of metallic oxides and additives was deposited by the spray deposition technique on the hot side of the solar thermoelectric generator to increase irradiance absorption. The main properties of the absorbent layer consist of an optimized IR absorption, good thermal transmission to the contact material, and thermal resistance. The absorbent layer deposited on the hot side of the STEG has low thermal emittance 0.073, high absorbance 0.98 and high stability, which makes it a very good candidate for use as an absorbent layer for improving the performance of the STEG. The new solar thermoelectric generator is studied in two environmental situations: artificial light in the lab, from 600 W/m2 to 1200 W/m2 and in concentrated light from 20 suns to 80 suns. Analysis of the results obtained shows an increase in power generation more than 25 % for the irradiance around 1 sun and up to 82 % for the concentration light.

K4ZnV5O15Cl: A Congruent‐Melting Mid‐Infrared Nonlinear Optical Crystal Combined with Strong Second‐Harmonic Generation and High Laser‐Induced Damage Threshold

AbstractIt is extremely challenging to accomplish second‐harmonic generation (SHG) in the whole mid‐infrared (MIR) region for oxide crystals due to their short IR absorption cutoff wavelengths. Herein, a new MIR nonlinear optical (NLO) crystal of K4ZnV5O15Cl (KZVC) is designed and synthesized by the aliovalent substitution of [VIIIO5] with [ZnIIO4Cl] based on the K2(VO)(V2O7) matrix. KZVC features an ordered 2D [ZnV5O15Cl]∞ layered structure comprising [ZnO4Cl] / [VO5] square pyramids and [VO4] tetrahedron as functional units. Importantly, KZVC shows excellently balanced performances of strong SHG responses (12 × KDP @ 1064 nm, 1.1 × AgGaS2 @ 2.05 µm), broad IR transparency range (0.52‒10 µm), congruent‐melting behavior, and highest laser‐induced damage threshold (LIDT) (60 × AgGaS2 @ 1064 nm) among the reported vanadates. Most remarkably, KZVC represents the first example in the oxide‐based IR NLO crystals that can achieve phase matching in a wide wavelength range extending from 1.8 to 10 µm, fully covering the important MIR atmospheric windows (3‒5 µm).

Combined Surface-Enhanced Raman and Infrared Absorption Spectroscopies for Streamlined Chemical Detection of Polycyclic Aromatic Hydrocarbon-Derived Compounds.

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of universally prevalent carcinogenic environmental contaminants. It is increasingly recognized, however, that PAHs derivatized with oxygen, sulfur, or nitrogen functional groups are frequently more dangerous than their unfunctionalized counterparts. This much larger family of chemicals─polycyclic aromatic compounds─PACs─is far less well characterized than PAHs. Using surface-enhanced Raman and IR Absorption spectroscopies (SERS + SEIRA) combined on a single substrate, along with density functional theoretical (DFT) calculations, we show that direct chemical detection and identification of PACs at sub-parts-per-billion concentration can be achieved. Focusing our studies on 9,10-anthraquinone, 5,12-tetracenequinone, 9-nitroanthracene, and 1-nitropyrene as model PAC contaminants, detection is made possible by incorporating a hydroxy-functionalized self-assembled monolayer that facilitates hydrogen bonding between analytes and the SERS + SEIRA substrate. 5,12-Tetracenequinone was detected at 0.3 ppb, and the limit of detection was determined to be 0.1 ppb using SEIRA alone. This approach is straightforwardly extendable to other families of analytes and will ultimately facilitate fieldable chemical detection of these dangerous yet largely overlooked environmental contaminants.

Bathochromically shifted absorption and near IR emission in bismuth(III) porphyrins with meso-fluorophenyl and methoxyphenyl substitutions

A series of bismuth(III) porphyrins with varying degrees of electron-donating and electron-withdrawing groups in their meso-positions have been synthesized. All the porphyrins were synthesized successfully and characterized spectroscopically. The absorption studies reveal bathochromically shifted spectra, up to [Formula: see text]60 nm, compared to their corresponding free-base porphyrins which is common for [Formula: see text]-type hyperporphyrins. Interestingly, all the samples exhibited broad near-IR phosphorescence at room temperature. The spectroscopic studies indicate that the demetallation occurs in both solution and solid states to form corresponding free-base porphyrin and this process is much faster in meso-trimethoxyphenyl substituted bismuth(III) porphyrin. Nevertheless, the study reveals interesting optical properties of bismuth(III) porphyrins, particularly red-shifted absorption and near IR emission bands.

IR, Raman spectroscopic, DFT, AIM and NCI characterization of O-H‧‧‧O/π‧‧‧π bonds in dimer and trimer species as computed from MD simulations in water for Protocatechuic acid

In the present work we report a study of the O-H‧‧‧O dimer, bifurcated dimer and O-H‧‧‧O/π‧‧‧π bonded trimer species as determined by Molecular Dynamics simulations for Protocatechuic acid. Multiple O-H‧‧‧O bond interactions are correlated to the unsymmetrical broad band structure observed in the experimental IR absorption spectrum near 3400 cm−1. To gain an understanding of the O-H‧‧‧O/π‧‧‧π bond interactions and its resultant structures referred above, we carried out MD simulations using ten monomer species in water solvent of 1000 molecules for 1 ns. We have identified different O-H‧‧‧O bonds between hydroxyl-hydroxyl, carboxyl-hydroxyl and carboxyl-carboxyl groups in the dimer and bifurcated dimer species, whereas in the trimer, there are O-H‧‧‧O bonds and π‧‧‧π bonds in ring-to-ring interactions. Computed radial distribution functions confirm that (i) the O-H‧‧‧O/π‧‧‧π bonds exist in all the dimer/trimer species; (ii) the donor-acceptor bond lengths in O-H‧‧‧O bonds are less than the sum of van der Waals radii of the H and O atoms. Lifetimes of the O-H‧‧‧O bonds at 5.0 to 13.5 ps correspond to the association/dissociation of those bonds. Stabilization energies for both intra- and inter-molecular O-H‧‧‧O bonds in the dimer and trimer lie in the range 0.93 – 11.20 kcal/mol. Stabilization energies of the six π‧‧‧π bonded trimer species lie in the range 0.13 – 0.44 kcal/mol. Geometry, vibrational modes and other electronic properties for the most stable dimer computed at B3LYP/6-311++G (d, p) level has been shown to be a satisfactory model.

Enhanced radiation heat transfer performance of Alumina-Spinel composite sphere with hollow structure for rapidly ultra-high temperature thermal storage/release process

Heat storage technologies for high temperatures have recently been gaining increasing attention. For heat storage applications at high temperatures, such as industrial regenerative burner systems, the impact of radiant heat transfer on the efficiency of rapid heat storage and release cannot be ignored. Hence, the development of heat storage materials with high infrared radiation absorption is of great significance for energy saving and CO2 emission reduction. Consequently, this study innovatively proposes an advanced composite heat storage material, composited by alumina and a Fe-Co-Mn-Al spinel, with the aim of improving absorptivity. A medium-entropy approach is employed to improve IR absorptivity of alumina. Through the strategic adding of various transition metal oxides, the radiative absorptivity of the alumina material in the 600–1200 °C range increased from an initial 0.2 to an impressive 0.8, provided that doping additives remain below 10 wt%. The high-temperature heat storage material balances cost, heat recovery efficiency and thermal stability. In addition, the heat storage material is prepared as a hollow sphere to further enhance the heat storage density of rapid heat storage/release and reduce cost. Multi-scale numerical simulations are carried out to reveal the heat transfer enhancement mechanisms of modified materials and hollowing. radiative modification can significantly increase the heat storage and release capacity, especially at ultra-high temperatures above 1000 °C. Experimental evaluations using an actual regenerative burner further confirmed the heat recovery performance of this novel heat storage sphere. Comparing with conventional regenerative burner system, heating power remarkably increased by 24.6 %, and the heat storage density of packed bed improved by 16.7 %. This study promises to significantly improve the efficiency of rapid heat recovery at high temperature.