A0 Parameter Research Articles

An analysis of the dependence of the material length parameter a0 on the stress ratio

Safe life approaches in notch fatigue of metallic components rely on the knowledge of the material response to fatigue stresses at notches, which is typically quantified by a material-dependent length parameter. As a general material behaviour, such material parameter depends on several factors and one of the most important of them is the mean stress. The present study is focused on the El Haddad-Smith-Topper material length parameter a0 for analysing under which circumstances and to which extent it may vary with the applied mean stress or stress ratio. The analysis starts by considering the broader problem of the mean stress influence on the fatigue limit of plain material, blunt and sharp notches and cracks. Eventually, an analysis of previous sets of experimental data on wrought steels led to simple relations for estimating the a0 parameter at different stress ratios on the basis of the sole Vickers Hardness

Predicting the packing parameter for lipids in monolayers with the use of molecular dynamics

Lipid molecules form the backbone of biological membranes. Due to their amphiphilic structure, they can self-organize in a plethora of different structures when in contact with water. The type of self-assembled structure and its curvature depend on so-called shape factor or critical packing parameter, CPP, that can be derived knowing the molecular volume of a lipid (V), optimal surface area (a0) and critical chain length (lc) (see Intermolecular and Surface Forces by Jacob N. Israelachvili, Third Edition, 2011). The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. The greatest difficulties arise when calculating the a0 parameter, and although for some typical membrane lipids these values have been determined, there are a number of derivatives for which this parameter, and thus CPP, are unknown. The value of CPP allows not only to predict the type of self-assembled structure but also is a key factor for molecular interactions, which play a great role both in physiological and pathological conditions. So far, the determination of the packing parameter required the use of theoretical models with assumptions deviating from the physical conditions. Here we report a method based on molecular dynamics, which was applied to simulate lipid membranes consisting of cholesterol, oxysterols, sphingolipids, phosphatidylcholines, and phosphatidylethanolamines. For lipid molecules for which CPPs have already been determined, high compliance has been demonstrated. This proves that the method presented herein can be successfully used to determine packing parameters for other membrane lipids and amphiphilic molecules.

Sensitivity analysis of wind input parametrizations in the WAVEWATCH III spectral wave model using the ST6 source term package for Ireland

The performance of the third generation wave model WAVEWATCH III (version 6.07) using the ST6 source term package, developed by Zieger et al. (2015) and then updated by Liu et al. (2019), is investigated in the context of wave growth and dissipation in the west coast of Ireland. A sensitivity analysis is carried out to establish preliminary values of the parameters involved in the configuration of the wind input term Sin by tuning the CDFAC parameter to potentially eliminate a bias in the wind field and the a0 parameter that controls the strength of swell decay due to wind effects. A system of nested structured grids is used to model long-distance swells generated in the Atlantic Ocean that propagate all the way to the west coast of Ireland. The bias, the root-mean-square, the correlation coefficient and the scatter index statistical parameters, and the probability density function are used to validate the model by comparing the significant wave height from four local buoys measurements with numerical results. Comparisons between measurements and numerical data show a good overall agreement. The most appropriate value obtained for the drag coefficient CDFAC is 0.9, which represents a 10% decrease from the value proposed in the last versions of the package. Depending on the buoy selected for the analysis, the values tested for the second investigated parameter a0 lead to a reduction of the bias in the comparisons, together with a reduction of the other statistical parameters. These results confirm the values proposed in previous work for future developments.

A New Lithium‐Rich Zeolitic 10‐MR Zincolithosilicate MZS‐1 Hydrothermally Synthesized under High Pressure and Characterized by 3D Electron Diffraction

AbstractWe report the structure of a new high lithium content zincolithosilicate (MZS‐1) obtained after hydrothermal treatment under high pressure from a glass precursor. After synthesis microcrystalline mixture of phases was obtained among which the main phase was unknown. Due to the sub micrometric size of the crystallites its structure was determined from precession‐assisted 3D electron diffraction measured at 100 K and refined using the dynamical theory of diffraction. More accurate lattice parameters are obtained from Rietveld refinement of synchrotron powder data collected at the ambient temperature. The characteristic framework is described at the ambient temperature using an average unit cell a0=8.57999(5) Å, b0=14.12332(8) Å, c0=4.96827(3) Å in the space group Ccc2. The structure of the new zeolitic 10‐membered ring zincosilicate with chemical formula per unit cell (SiO2)2Zn0.408LiO(OH)2(Li,H)2.184 (Z=4) is composed of undulated silicate layers made of fused 6‐membered rings connected via vertices of (Zn,Li)O4 tetrahedra. A weak superstructure doubling the a0 parameter is observed and is explained by a Zn/Li ordering within the (Zn,Li)O4 layers.

Two new members of the Silica-X family of materials: RUB-5, a silica zeolite with a very high framework density and RUB-6, a hydrous layer silicate

The new zeolite RUB-5 and the new phyllo silicate RUB-6 were synthesized at temperatures between 130 °C and 200 °C from reaction mixtures consisting of SiO2/LiOH/B(OH)3/OA/H2O or SiO2/KOH/OA/H2O (OA = organic additive). Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and ATR-FTIR spectroscopy confirmed that RUB-5 is a framework silicate while RUB-6 is a layer silicate. The XRD powder patterns were indexed in monoclinic symmetry (space group: C2) with lattice parameters of a0 = 10.2699 (4) Å, b0 = 10.6556 (4) Å, c0 = 18.1551 (7) Å and β = 106.35 (1)° (RUB-5), and a0 = 10.1100 (43) Å, b0 = 10.6956 (51) Å, c0 = 20.5448 (44) Å and β = 105.79 (1)° (RUB-6). The chemical compositions of RUB-5 and RUB-6 are [Si42O84] (with a few silanol defects) and [Si40O76(OH)8] • C6H14N2, respectively. According to the XRD powder patterns, RUB-5 and RUB-6 have a disordered structure and belong to the Silica-X family of materials. The materials are structurally closely related and contain topologically identical, dense layer-like building units, named γ-layer. In the case of RUB-5 these building units are interconnected via additional Si atoms leading to a 2-dimensional pore system consisting of intersecting 8-ring channels. RUB-5 is a pure silica zeolite of very high density (2.20 g/cm3) which shows a negative thermal expansion between 20 °C and 470 °C. In the case of RUB-6, the layers are intercalated by organic cations which generate weak ionic bonds between cation and silicate layer. Formally, RUB-6 may be transformed into RUB-5 via a condensation reaction involving the γ-layers ([Si40O76(OH)8]) of RUB-6 and additional Si(OH)4 units from the reaction mixture to form the framework of RUB-5 ([Si42O84]) and water. In this sense, RUB-5 is the interlayer expanded zeolite based on the silicate layers of RUB-6.

Microstructural analysis of pitchblende in the Miaoershan area using TEM lattice imaging

This paper aims to reveal the formation process of pitchblende by analyzing its microstructural features on the nanoscale and atomic scale. Herein, we selected pitchblende samples from drilling cores from the Miaoershan area, southern China, as the research objects. The microstructural features of pitchblende particle cores were analyzed using high-resolution transmission electron microscopy (HRTEM), electron diffraction, energy spectrum (EDS) and electron microprobe analysis (EMPA), combined with density functional theory calculations. The results of this study reveal that the pitchblende grain boundaries are not clear, as they exhibit a cloudy distribution and some preferred orientations under HRTEM. The selected area electron diffraction (SAED) analyses show discontinuous ring patterns that are coherent with the presence of a preferred orientation. The HRTEM results reveal that pitchblende is a complex aggregate composed of nanocrystals with a diameter of 3–7 nm and unit cell parameters of a0 = 0.556 nm. The elements in the pitchblende are characterized by an irregular and scattered distribution of Ca, As, S, Fe, Mn, and Si. We assume that the formation of pitchblende is related to hard-base fluid in a reduced environment containing As and S. We used density functional theory calculations to obtain the pitchblende crystal structure model and simulated the positions of the U and O atoms to provide a reference for further analysis of the pitchblende crystal structure. We conjecture that uranium ions of U4+, U5+ and U6+ may coexist in pitchblende (stoichiometry U3O7).

A multireflection and multiwavelength residual stress determination method using energy dispersive diffraction

The main focus of the presented work was the investigation of structure and residual stress gradients in the near-surface region of materials studied by X-ray diffraction. The multireflection method was used to measure depth-dependent stress variation in near-surface layers of a Ti sample (grade 2) subjected to different mechanical treatments. First, the multireflection grazing incidence diffraction method was applied on a classical diffractometer with Cu Kα radiation. The applicability of the method was then extended by using a white synchrotron beam during an energy dispersive (ED) diffraction experiment. An advantage of this method was the possibility of using not only more than one reflection but also different wavelengths of radiation. This approach was successfully applied to analysis of data obtained in the ED experiment. There was good agreement between the measurements performed using synchrotron radiation and those with Cu Kα radiation on the classical diffractometer. A great advantage of high-energy synchrotron radiation was the possibility to measure stresses as well as the a0 parameter and c0/a0 ratio for much larger depths in comparison with laboratory X-rays.

Investigation of the magnetic properties of Li0.8Na0.2FePO4 by using the Mössbauer spectroscopy

We have investigated Li0.8Na0.2FePO4, a cathode material for secondary battery applications, by using X-ray diffractometry (XRD), vibrating sample magnetometry (VSM) and Mossbauer spectroscopy. The crystal structure is found to be orthorhombic with lattice parameters of a0 = 10.333 A, b0 = 6.011 A and c0 = 4.700 A. From the temperature dependence of both the magnetization and the Mossbauer spectra, the Neel temperature is found to be TN = 51 K and the spin reorientation temperature to be TS = 20 K. The magnetic hyperfine field (Hhf), electric quadrupole splitting (ΔEQ) and isomer shift (δ) at 4.2 K are found to be Hhf = 130.50 kOe, ΔEQ = 2.63 mm/s and δ = 1.25 mm/s.

Structure and properties of ITQ-8: a hydrous layer silicate with microporous silicate layers.

ITQ-8 is a new hydrous layer silicate (HLS) with a chemical composition of [C4H8(C7H13N)2]8 [Si64O128(OH)16]·48H2O per unit cell. The synthesis of ITQ-8 was first described in 2002 by Díaz-Cabañas et al., the structure of this material, however, remained unsolved at that time. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and FTIR spectroscopy confirmed that ITQ-8 is a layer silicate. The XRD powder pattern was indexed in the monoclinic system with lattice parameters of a0 = 35.5168(5) Å, b0 = 13.3989(2) Å, c0 = 16.0351(2) Å, β = 106.74(2)°. The crystal structure was solved by simulated annealing. Rietveld refinement of the structure in space group C2/c converged to residual values of RBragg = 0.023, RF = 0.022 and chi(2) = 2.3 confirming the structure model. The structure of ITQ-8 contains silicate layers with a topology that resembles a (11-1) section of the framework of zeolite levyne. So far, this layer topology is unique among layer silicates. The layer can be regarded as made up of 4-, 6-, double-six and 8-rings which are interconnected to form cup-like "half-cages". Unlike other HLSs, which possess impermeable silicate layers, ITQ-8 contains 8-rings pores with a free diameter of 3.5 Å × 3.4 Å and can be regarded as a "small-pore layer silicate". In the crystal structure, the organic cations, 1,4-diquiniclidiniumbutane, used as structure directing agents during synthesis are intercalated between the silicate layers. Clusters (bands) of water molecules which are hydrogen bonded to each other and to the terminal Si-OH/Si-O(-) groups are located between the organic cations and interconnect the silicate layers. ITQ-8 is a very interesting material as precursor for the synthesis of microporous framework silicates by topotactic condensation or interlayer expansion reactions leading to 3D micro-pore systems which may be useful in applications as e.g. catalysts, catalyst supports and adsorbents of for separation.

Synthesis and characterization of Zn-doped LiFePO4 cathode materials for Li-ion battery

Synthetic LiFe1-xZnxPO4 (0 ≤ x ≤ 0.26) samples have been prepared using wet chemistry method. The samples have been characterized by means of Rietveld structure refinement of Powder-XRD data and by Mössbauer spectroscopy. Impurities such as Li3PO4 and Fe2P have been detected in small amount and quantified by Rietveld analysis. No Zn-bearing impurity has been detected up to x=0.15, but significant amounts of LiZnPO4 have been observed in the samples with x ≥ 0.2. The unit cell volume of LiFePO4 decreases anisotropically with increasing Zn content (−0.7% of initial volume of 291.343Å3). Cell parameter (orthorhombic Pbnm space group, #62) b0 and c0 decrease with increasing Zn content, whereas a0 parameter is almost constant. The average <Li–O> and <Fe–O> interatomic distances in the M1 and M2 sites are almost constant, whereas the <P–O> distance slightly decreases (−1.4% of the initial value). Interestingly, O2–O1–O2 bond angle along the [001] direction decreases with increasing Zn-content, thus resulting in a marked decrease of the c0 axis length although the <M1-O> distance remains essentially constant. Mössbauer analyses show the majority of Fe to be divalent and located in an octahedral site similar to available literature data for LiFePO4. The Fe3+/(Fe3++Fe2+) ratio ranges from 0.10 to 0.17, and is not related to the Zn content. Preliminary electrochemical analyses of Zn doped samples in comparison to pristine LiFePO4 are reported.

Structure of β-AgGaO2; ternary I–III–VI2 oxide semiconductor with a wurtzite-derived structure

The structure of the wurtzite-derived β-AgGaO2 was refined by Rietveld analysis of high-resolution powder diffraction data obtained using synchrotron X-ray radiation. The space group of the crystal is Pna21 with lattice parameters of a0=5.56175Å, b0=7.14749Å, and c0=5.46875Å. The deviation of O–Ag–O and M–O–M bond angles from the regular tetrahedral angle of 109.5° was very large at ~8° and ~11°, respectively. The electronic structure of β-AgGaO2 is discussed based on its structure, and the indirect band gap of β-AgGaO2 was related to significant tetrahedral distortion. Although β-AgGaO2 decomposes into metallic silver and Ga2O3 at a high temperature in any atmosphere, β-AgGaO2 is stable up to 690°C under an O2 atmosphere. No direct transformation from the wurtzite-derived phase to a delafossite phase occurs in β-AgGaO2.

Theoretical estimation of the critical packing parameter of amphiphilic self-assembled aggregates

The estimating of critical packing parameter (p) of amphiphilic compounds is considered as a hypothetical rather than an empirical. Consequently, an attempt has been made for determining such a dimensionless parameter for homologous series of sodium p-n-alkyl benzoates (n=0–8) hydrotropes using quantum mechanical calculations that depend on density functional theory (DFT). The calculations were based on the following well-defined model, p=v/a0lc, where v is the volume of the hydrotrope tail, a0 is the effective head group area and lc is the length of the extended hydrotrope tail. It was found that the magnitude of both v and lc parameters can be estimated directly from quantum mechanical calculations. While the investigations found that the a0 parameter is parallel to the Connolly solvent accessible surface area (Csa) which could also be determined through theoretical computations. The obtained results were in good agreement with published data using small angle neutron scattering (SANS) technique. Hence, the theoretical model for predicting p of amphiphilic at critical micelle- or aggregation-concentration (cmc or cac) is p=v/Csalc. An apparent success was observed through applying this simple model to some randomly selected surfactants. It has been concluded that the theoretical calculations that based on quantum mechanical (DFT) method can be considered as a powerful tool for estimating the critical packing parameter of amphiphilic molecules. Finally, the results strongly suggest the employment of the presented model for estimating p of amphiphilic molecules at cmc or cac by computational chemistry software.

SYNTHESES AND PROPERTIES OF COBALT AND NICKEL HYDROXIDE NANOSHEETS

Nanosheets of cobalt and nickel hydroxides nanosheets were prepared by delamination of layered compounds, Co II( OH )1.73( DBS )0.27·0.87 H 2 O ( Co - DBS , DBS = dodecylbenzene sulfonate) and Ni II( OH )1.63( DBS )0.37·1.24 H 2 O ( Ni - DBS ), respectively. Powder X-ray diffraction analyses of the layered compounds revealed lattice parameters of a0 = 3.07 Å and c0 = 30 Å ( Co - DBS ) and a0 = 3.09 Å and c0 = 30 Å ( Ni - DBS ) in the hexagonal system. Dispersions of Co - DBS and Ni - DBS in 1-butanol produced colloidal solutions of nanosheets, [ Co - DBS ] delam and [ Ni - DBS ] delam , respectively. Poly(vinylpyrrolidone) ( PVP ) was dissolved in [ Co - DBS ] delam and [ Ni - DBS ] delam and the mixtures were dried to yield Co - PVP and Ni - PVP , respectively. These nanosheets measured 150-500 nm for [ Co - DBS ] delam and 135-400 nm for [ Ni - DBS ] delam by means of dynamic light scattering. Atomic force microscopy images showed lateral dimensions of 100-500 nm for [ Co - DBS ] delam and 50-100 nm for [ Ni - DBS ] delam . In the former image, the cobalt hydroxide nanosheets had a fairly flat terrace structure with thickness of 3.1-3.6 nm and with aspect ratios of 30-150, whereas in the latter image dome-like nanosheets of nickel hydroxide with height of 2.2-2.3 nm were confirmed. These nanosheets were regarded as monolayer. Magnetization experiments at 1.8 K showed hysteresis loops for Co - DBS , Co - PVP , Ni - DBS , and Ni - PVP .

Structure, Bonding, and Relative Stability of the Ground and Low-Lying Electronic States of CuO2. The Role of Exact Exchange

The C(2v) and C(s) ground and low-lying states of doublet CuO2 are examined for a series of different density functionals (pure, hybrid, and meta-hybrid) and CCSD(T) methods. The effect of changing the B3LYP functional a0 parameter is also explored. CCSD(T) results at the complete basis set limit show that the relative stability of the different electronic states is 2A(2)(C(2v)) < 2A''(Cs) < 2B(2)(C(2v)) < 2A'(C(s)) 2A(1)(C(2v)) < 2B(1)(C(2v)). Unlike CCSD(T), all DFT methods analyzed in this work erroneously predict the end-on 2A'' state as the ground state for CuO2 irrespective of the type of functional and percentage of Hartree-Fock (exact) exchange included in the B3LYP-like functional. Among the different functionals tested, B3LYP gives the best geometries and relative energies for the different electronic states when compared to CCSD(T) results. As for the effect of the a0 parameter, it is found that the B3LYP-like functional yielding better geometries contains 20% of exact exchange, although somewhat unexpectedly, the B3LYP-like functional with a larger contribution of exact exchange (90%) is the one that gives the smaller standard deviation for relative energies.

Synthesis of magnetite nanoparticles by thermal decomposition of ferrous oxalate dihydrate

Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C2O4) · 2H2O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and pO2 = 10−25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a0 = 8.39 A. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature.

Reconciling φ radiative decays with other data for a0(980), f0(980), ππ→KK and ππ→ηη

Data for φ→γ(ηπ0) are analysed using the KK loop model and compared with parameters of a0(980) derived from Crystal Barrel data. The ηπ mass spectrum agrees closely and the absolute normalisation lies just within errors. However, BES parameters for f0(980) predict a normalisation for φ→γ(π0π0) at least a factor 2 lower than is observed. This discrepancy may be eliminated by including constructive interference between f0(980) and σ. The magnitude required for σ→KK is consistent with data on ππ→KK. A dispersion relation analysis by Buttiker, Descotes-Genon and Moussallam of ππ→KK leads to a similar conclusion. Data on ππ→ηη also require decays of σ to ηη. Four sets of ππ→KK data all require a small but definite f0(1370) signal.

Stress-field in Sputtered Mo Thin Films and Mo/Ni Superlattices: Origin and Evolution after Ion-Irradiation

ABSTRACTIn the present study the ion irradiation technique is used to investigate the origin of the stress-field in Mo layers grown by ion beam sputtering. Strain measurements were performed by X- ray Diffraction (XRD) using the sin2ψ method. The evolution of the sin2ψ plots with ion irradiation shows that the usual assumption of a biaxial stress state is not adequate to determine the true stress-free lattice parameter a0 of the film. A new stress model based on a triaxial state of stress, which includes a hydrostatic component linked to point defects induced volume distortions, is derived to interpret the XRD results. For pure Mo films, the obtained a0 parameter is close to the bulk value, while for Mo sublayers in Mo/Ni superlattices, the a0 value is lower due to intermixing between Ni and Mo. These results demonstrate that ion irradiation is a powerful tool for stress relaxation, which allows to obtain additional information on the respective contribution of chemical effects and growth defects to the a0 value.

Analysis of the effect of changing the a0 parameter of the Becke3-LYP hybrid functional on the transition state geometries and energy barriers in a series of prototypical reactions

A series of eleven gas-phase chemical reactions have been examined to assess the dependence of transition state geometries and energy barriers, as well as energy differences between reactants and products, on the a0 B3LYP functional parameter. Throughout the study we have changed the a0 parameter from 0.1 to 0.9 and for the ac and ax parameters we have followed the relationships ax = 1 − a0 and ac = ax. By comparing with the QCISD transition state geometries and energy barriers, our systematic study allows us to identify the influence of the a0 parameter in the reactions studied. In general, B3LYP calculations with the original parameters underestimate energy barriers, this trend being corrected when the a0 parameter increases. Our study also shows that the fraction of Hartree–Fock exchange needed to predict accurate barrier heights differs from the optimal fraction needed to predict thermochemical properties and geometries.

Parametrization of the Becke3‐LYP hybrid functional for a series of small molecules using quantum molecular similarity techniques

AbstractThe a0, ax, and ac semiempirical parameters of the original Becke three‐parameter method have been optimized by minimizing the difference between the density given by this method and the singles and doubles quadratic configuration interaction (QCISD) generalized density using quantum molecular similarity measures. The optimization is performed including the hybrid energy functional in a self‐consistent fashion and employing the relaxed geometry at each set of a0, ax, and ac parameters. This method has been applied to a series of 16 small molecules with different bonding patterns. Results show that, at least in diatomic molecules, it is possible to obtain a set of parameters that reproduces almost exactly the QCISD electron density. The optimized parameters for the studied molecules follow two main general trends: (a) the parameters governing the amount of gradient corrections for exchange and correlation have similar values (ac≈ax); and (b) the larger the exact exchange included, the smaller the gradient correction for exchange needed (a0≈1−ax). Especially interesting are the values obtained for the a0 parameter, which reflect how much exact exchange should be included in the description of a particular system. Finally, for H2 and LiH, we have carried out a search for other possible local minima on the quadratic error integral surface concluding that for these molecules there is not a unique set of parameters that produces a B3LYP density of QCISD quality. © 2001 John Wiley &amp; Sons, Inc. J Comput Chem 22: 1666–1678, 2001

Hydrotalcites with an extended Al3+-substitution: Synthesis, simultaneous TG-DTA-MS study, and their CO2 adsorption behaviors

A maximum Al3+-substitution has been demonstrated to be 45 mole% of (M + Al) in the brucite layer of hydrotalcites. The chemical composition of the highly substituted hydrotalcites can be typically represented by [M0.55Al0.45(OH)2] [(CO3)0.225 · 0.50H2O] where M = Mg, Ni, Zn, and Co. It showed the small lattice parameters of a0 3.05–2.98 A in the hexagonal lattice, which corroborates Al3+-substitution in the brucite layer. The simultaneous thermal analyses (TG and DTA) and mass spectrometry (MS) study have been performed. The highly Al3+-substituted hydrotalcites also showed quite different isotherms for the CO2 adsorption. These materials adsorbed CO2 gas by removing water within the interlayer and showed the selectivity for CO2 adsorption: Cu–Al ∼Zn—Al &lt; Co—Al &lt; Mg—Al &lt; Ni—Al. The Mg—Al and Co—Al hydrotalcite-like compounds showed a doubled amount of CO2 by removing carbonate ions within the interlayer.