Molecular Physics
Computational Chemistry
Thermodynamics
Spectoscopy
Materials Science
Solid State Physics
X-ray diffraction
Linear Algebra
Reduced Density Matrices
Materials Chemistry
48
Scopus Publications
Scopus Publications
Investigation of the surface charge behaviour of ettringite: Influence of pH, calcium, and sulphate ions Tiziana Missana, Oscar Almendros-Ginestà, Francisco Colmenero, Ana María Fernández, Miguel García-Gutiérrez Heliyon, 2024 . An electrostatic double layer model (DLM) was used to calculate the surface potential, considering the adsorption of both calcium and sulphate, as possible ions determining the potential (IDP), and formation of different complexes with ettringite surface functional groups (SOH). The variations of the ζ-potential could be satisfactorily predicted under the different chemical conditions of interest in a cementitious environment.
Density Functional Theory Study of the Crystal Structure and Infrared Spectrum of a Synthetized Ettringite Mineral Francisco Colmenero, Ana María Fernández, Oscar Almendros-Ginestà, Tiziana Missana Minerals, 2024 One of the most important hydration phases of Portland cement is ettringite, a calcium sulfo-aluminate mineral (Ca6Al2(OH)12(SO4)3·26H2O) showing a great capacity of adsorbing radionuclides and other contaminant cationic and anionic species, or incorporating them into its crystal structure. In this work, the X-ray diffraction pattern and infrared spectra of a synthetized ettringite sample are recorded and simulated, employing theoretical methods based on Density Functional Theory. Despite the complexity of this phase, the calculated structure, X-ray diffraction pattern and infrared spectrum are in excellent agreement with their experimental counterparts. Since the calculated and experimental spectra are consistent, the main infrared bands are assigned using a normal coordinate analysis, some of them being completely reassigned with respect to other experimental works. The good agreement found provides strong support for the computational methods employed towards their use for studying the surface adsorption properties and the incorporation of contaminations in its structure. The density of reactive groups at the surfaces of ettringite is reported, and the surface adsorption of water molecules is studied. These surfaces appear to be highly hydrophilic, in agreement with the experimental finding that the ettringite structure may include more water molecules, at least up to 27, one more than in its standard formula.
Theoretical Study of Copper Squarate as a Promising Adsorbent for Small Gases Pollutants Celia Adjal, Nabila Guechtouli, Vicente Timón, Francisco Colmenero, Dalila Hammoutène Molecules, 2024 Copper squarate is a metal–organic framework with an oxo-carbonic anion organic linker and a doubly charged metal mode. Its structure features large channels that facilitate the adsorption of relatively small molecules. This study focuses on exploring the potential of adsorbing small pollutants, primarily greenhouse gases, with additional investigations conducted on larger pollutants. The objective is to comprehend the efficacy of this new material in single and multiple molecular adsorption processes using theoretical methods based on density functional theory. Furthermore, we find that the molecular adsorption energies range from 3.4 KJ∙mol−1 to 63.32 KJ∙mol−1 depending on the size and number of adsorbed molecules. An exception is noted with an unfavorable adsorption energy value of 47.94 KJ∙mol−1 for 4-nitrophenol. More importantly, we demonstrate that water exerts an inhibitory effect on the adsorption of these pollutants, distinguishing copper squarate as a rare MOF with hydrophilic properties. The Connolly surface was estimated to give a more accurate idea of the volume and surface accessibility of copper squarate. Finally, using Monte Carlo simulations, we present a study of adsorption isotherms for individual molecules and molecules mixed with water. Our results point out that copper squarate is an efficient adsorbent for small molecular pollutants and greenhouse gases.
Complete Crystal Structures and Elastic Properties of the Uranyl Minerals Johannite, Pseudojohannite and Derriksite Francisco Colmenero, Jakub Plášil, Jiří Sejkora Crystals, 2022 Due to the high solubility of uranyl sulfate and selenite minerals, the investigation involving the determination of the crystal structures and physical properties of these minerals is essential in actinide environmental chemistry for the simulation of uranium migration from uraninite deposits and nuclear waste repositories. However, the determination of the complete crystal structures of the uranyl sulfate minerals johannite (Cu(UO2)2(SO4)2(OH)2 ·8H2O) and pseudojohannite (Cu3(UO2)4(SO4)2O4(OH)2 ·12H2O) and the uranyl selenite mineral derriksite (Cu4[((UO2)(SeO3)2(OH)6]) has not been feasible so far. In this work, the crystal structures of these minerals, including the positions of the hydrogen atoms, are determined using first principles solid-state methods based on periodic density functional theory using plane wave basis sets and pseudopotentials. The lattice parameters and associated geometrical variables as well as the corresponding X-ray diffraction patterns derived from the computed crystal structures are in excellent agreement with their experimental counterparts, derived from the corresponding experimental structures lacking the hydrogen atom positions. The complete crystal structure of derriksite is also determined by refinement from X-ray diffraction data, the resulting structure being consistent with the computed one. The knowledge of the positions of H atoms is of fundamental importance not only because they define the corresponding hydrogen bond networks holding together the atoms in the structures, but also because it allows for the efficient, inexpensive and safe determination of the physical properties using first principles methods. This feature is particularly important in the case of uranium-containing minerals due to their radiotoxicity, complicating the handling of the samples and experimental measurements. In this work, from the computed crystal structures, the elasticity tensors of these minerals are computed using the finite displacement method and a rich set of elastic properties including the bulk, Young’s and shear moduli, the Poisson’s ratio, ductility, anisotropy and hardness indices and bulk modulus derivatives with respect to pressure derivatives are determined.
ZIF-75 under Pressure: Negative Linear Compressibility and Pressure-Induced Instability Francisco Colmenero, Vicente Timón Applied Sciences Switzerland, 2022 The behavior of the crystal structure of the zeolitic imidazolate framework ZIF-75 under pressure was studied by means of periodic density functional theory methods. Experimentally, it was shown that this material is tetragonal, space group I41/a at room temperature. However, according to the calculations, at zero temperature this material is monoclinic, space group C2/c. Irrespective of the symmetry of the material, the results show that ZIF-75 exhibits a negative linear compressibility effect and is unstable under relatively small applied pressures of the order of 0.1 GPa.
Mechanical Characterization of Anhydrous Microporous Aluminophosphate Materials: Tridimensional Incompressibility, Ductility, Isotropy and Negative Linear Compressibility Francisco Colmenero, Álvaro Lobato, Vicente Timón Solids, 2022 Here, a detailed mechanical characterization of five important anhydrous microporous aluminophosphate materials (VPI-5, ALPO-8, ALPO-5, ALPO-18, and ALPO-31) is performed using first principles methods based on periodic density functional theory. These materials are characterized by the presence of large empty structural channels expanding along several different crystallographic directions. The elasticity tensors, mechanical properties, and compressibility functions of these materials are determined and analyzed. All of these materials have a common elastic behavior and share many mechanical properties. They are largely incompressible at zero pressure, the compressibilities along the three crystallographic directions being frequently smaller than 5 TPa−1. Notably, the compressibilities of ALPO-5 and ALPO-31 along the three principal directions are smaller than this threshold. Likewise, the compressibilities of ALPO-18 along two directions are smaller than 5 TPa−1. All of the considered materials are shear resistant and ductile due to the large bulk to shear moduli ratio. Furthermore, all of these materials have very small mechanical anisotropies. ALPO-18 exhibits the negative linear compressibility (NLC) phenomenon for external pressures in the range P = 1.21 to P = 2.70 GPa. The minimum value of the compressibility along the [1 0 0] direction, ka=−30.9 TPa−1, is encountered for P = 2.04 GPa. The NLC effect in this material can be rationalized using the empty channel structural mechanism. The effect of water molecule adsorption in the channels of ALPO-18 is assessed by studying the hydrated ALPO-18 material (ALPO-18W). ALPO-18W is much more compressible and less ductile than ALPO-18 and does not present NLC effects. Finally, the effect of aging and pressure polymorphism in the mechanical properties of VPI-5 and ALPO-5 is studied. As hydration, aging leads to significant variations in the elastic properties of VPI-5 and increases substantially its compressibility. For ALPO-5, pressure polymorphism has a small impact in its elasticity at zero pressure but a large influence at high pressure.
Compressing the Channels in the Crystal Structure of Copper Squarate Metal-Organic Framework Francisco Colmenero, Álvaro Lobato, Vicente Timón Solids, 2022 The crystal structure of a copper squarate metal-organic framework is fully determined using first principles methods based in density functional theory. The compressibility of this material is studied by optimizing the structure under different isotropic pressures and uniaxial stresses directed along the direction of minimum compressibility, [1 0 0]. Under isotropic compression, channels become wider along [1 0 0], leading to negative linear compressibility, NLC. Under compression along [1 0 0], the unit-cell volume increases leading to negative volumetric compressibility.
Mechanical anomalies in mercury oxalate and the deformation of the mercury cube coordination environment under pressure Francisco Colmenero, Vicente Timón Applied Physics A Materials Science and Processing, 2021 In a recent work, the extremely anomalous mechanical behavior of the anhydrous zinc and cadmium oxalates was discovered. In this paper, the mechanical behavior of the anhydrous mercury oxalate containing the remaining transition metal element of the IIB group of periodic table is investigated. The crystal structure and elastic properties of $${\\text{HgC}}_{2} {\\text{O}}_{4}$$ HgC 2 O 4 are determined using first-principles solid-state methods. Although the structure of mercury oxalate and the coordination environment of mercury in this compound are radically different to those of the zinc and cadmium oxalates, a great degree of similarity in their mechanical behavior is unexpectedly found. The mechanical behavior of mercury oxalate is anomalous and exhibits the negative Poisson’s ratio (NPR) and the negative linear compressibility (NLC) phenomena. Under isotropic pressure, the compressibility along the [1,0,0] crystallographic direction is negative in the pressure range from − 2.50 to 0.25 GPa. For external pressures applied in the direction of minimum compressibility, which coincides with [1,0,0], mercury oxalate exhibits negative volumetric compressibilities from 0.22 to 1.40 GPa. The increase in volume in this material is significant for pressures larger than 1.0 GPa, and the compressibility becomes − 95.6 $${\\text{TPa}}^{ - 1}$$ TPa - 1 at P = 1.36 GPa. As for the zinc and cadmium oxalates, the increase in volume is so drastic that mercury oxalate becomes unstable for pressures larger than 1.4 GPa. The NLC effect in mercury oxalate is due to the highly deformable character of the cube coordination polyhedron of mercury. The coordination structure becomes octahedral near P = 1.3 GPa, just before its structural instability.
