This work evaluated the effect of Zn on the electronic state of copper in the Cu-Zn-mordenite binary system. The samples were prepared in two stages by sequential ion exchange of the initial sodium mordenite, using aqueous solutions of sulfate salts of these two metals, and changing the order of introduction of each of the cations, first Cu2+ and then Zn2+, or in the inverse order. The content of Zn and Cu changed within the 0.02-3.14 wt% interval at various Zn/Cu ratios. The prepared samples were characterized with UV-Vis spectroscopy in situ during temperature-programed oxidation (TPO) in oxygen, temperature-programed reduction (TPR) in hydrogen, and temperature-programed adsorption and desorption of NO (TPD). Cu and Zn have different affinities to mordenite, resulting in competition between them for zeolites sites, their redistribution, and formation of bimetallic Cu-O-Zn species. The order of ion-exchange makes it possible to modify the nature and the relative content of these metal species. Electronic properties of the resulting copper species strongly depend on both the Zn/Cu ratio and the order of exchange of metal ions. The knowledge we have obtained will be useful for designing of new effective catalysts based on copper-exchanged zeolites.

Density functional theory is the most used tool to predict the fundamental properties of crystalline and molecular systems. Here we present a study on the passivated oxidized graphene structures with hydrogen atoms at the edges (GO). A stability analysis was performed using the ground-state energies and first-principles thermodynamics. Initially, two stability pseudo-mappings were made on the GO structures, the first varying the position of an epoxide functional group and the second varying the position of a hydroxyl functional group. It was found that the adsorption of a hydroxyl group could occur at any position on the GO structure. The epoxy group has greater stability towards the nanostructure edges. Oxygen adsorption strengthens in Stone-Wales and C vacancy defects. Vacancies dominate the adsorption process. The O/C ratios were increased to 5%, 9%, 13%, and 16% with 27, 20, 19, and 4 oxidation configurations, respectively. All constructed GO structures are thermodynamically stable. For each selected coverage, the calculated bandgap follows the experimental trend. In addition, hydrogen bonds were observed at all coverages. At 13% and 16% O/C ratios, H2O formation happens without energy barriers, leaving epoxy and carbonyl groups as by-products. Our calculations suggest that hydroxyl groups can spontaneously promote the generation of water molecules together with epoxy and/or carbonyl groups. Hydrogen bridge interactions between the ligands in the hydroxyl group induce such an effect. The mechanism described here helps to understand the reactivity observed in experimental studies of GO nanostructures obtained from the bamboo Guadua Angustifolia ‘Kunth’.

Pt and Ir catalysts (3% w/w) supported on Ce0.97Ru0.03O(2) were synthesized and successfully tested in a low temperature CO oxidation process. The CO oxidation was followed in-operation, by FTIR spectroscopy. The catalysts were characterized by SEM-EDS, HTEM, XRD, DRS UV-vis, XPS techniques and BET isotherms. It was found that Pt and Ir nanoparticles on Ce0.97Ru0.03O2 drastically improved the CO oxidation in comparison to CeO2, showing the best performance the Pt/ Ce0.97Ru0.03O(2) system. From the FTIR studies, a route for CO oxidation was proposed. The CO oxidation pathway in Ce0.97Ru0.03O(2) considers that CO was adsorbed at the Ce and Ru sites, while O-2 is adsorbed on the surface oxygen vacancies, being activated by nearby Ru species. Subsequently, the activated oxygen reacts with CO linked to Ce and Ru to produce CO2. Also, Pt and Ir promotes oxygen vacancies, increasing the activation-adsorption of O-2 and, consequently, the activity of the catalyst was improved.

Functional materials that have a prominent place in high technology are not classified according to their origin (metals, ceramics, polymers, glass, etc.) or processing technology, but by the functions they can perform. Zeolites are an interesting and important raw material for preparing a variety of target substances. From a traditional point of view, they are aluminosilicate oxide with a nanoporous structure. However, zeolites are adsorbents, ion exchangers, catalysts, and can be used in medicine, agriculture, construction and many other applications. The availability of natural minerals, as well as methods of synthesis of their analogues, and modification of both natural and synthetic materials, developed in sufficient detail, allows to obtain a variety of substances with predetermined properties, which are tailored for specific purposes. This paper will discuss a wide range of existing and also possible applications of these materials, such as catalysis, photocatalysis and sensor design. The specified modifications are achieved through controlled changes in the chemical composition of the zeolite surface.

Quartz crystal microbalances (QCMs) are devices that have been proven to function as sensors for detecting specific chemical species; this usually requires that the QCM is modified with a material that is capable to interact with the desired compound. Zeolites are an example of materials used as sensitive layer. This due to their capacity for selective adsorption and large surface area; moreover, they can grow directly on the QCM surface. After, the interaction between sensitive layer and analyte, there is a mass change on the QCM surface, which induces a frequency shift in the frequency generated by the QCM. However, the application of QCMs requires that some factors are considered, such as QCM functioning, wiring and surface functionalization. Even when there are commercial devices for QCM operation, a literature revision shows that some concepts are not understood, or some misconceptions are observed. In this work, the basics of QCM are discussed, from principles of operation to an application where a QCM was functionalized to work as sensor for water vapor.

On the basis of the density functional theory (DFT) calculations, the successive isomorphic substitution of one to six tetrahedrally coordinated Si cations by trivalent Al was systematically studied. As a result of exploring a significant number of configurations, without using a priori assumptions, it was found that the Al atoms are accommodated according to the ground state sequence in the tetrahedral sites TI - TIII - TIII - TI - TIII - TIII. The results in the general show: a) Al cations preferentially occupy TIII positions, b) the distribution of cations in the framework does not violate Loeurowenstein's rule, c) the distribution of cations in the framework does not satisfy Dempsey's rule, and d) only one Al cation is found per zeta-cage.

The population is constantly exposed to pathogenic infectious agents. Personal Protective Equipment (PPE) helps reduce the spread of disease among the population and prevent pandemic scenarios. There are nanoparticles (NPs) with biocidal properties that can improve the functionality of PPE. This article discusses the achievements in developing nanostructured biocides and methods for functionalizing textile materials using NPs from such kind of compounds. This will allow the production of PPE of a new generation with the capabilities of active health protection. The studies presented here suggest that incorporating nanoparticles in PPE could be of great help for the fight and containment of pathogens like the coronavirus SARS-CoV-2.

In this work, the integration of various elements was realized. This allowed the development of a measurement system for quantitative determination of the electrical response of the faujasite-modified QCM, which was caused by a change in mass during the adsorption and desorption processes. The nanostructured faujasite film was grown on the QCM surface, and water was used as a "model molecule" to test the ability of a measurement system to determine the change in mass associated with adsorption and desorption. It was shown that the sensitivity of the system is equal to 17 ng/Hz. The obtained sensitivity is sufficient to observe not only the adsorption and desorption process but even climate changes in the surrounding atmosphere.

The electronic properties of LTA-type zeolites in their siliceous, aluminized, and ferric frameworks compositions, all of which were selected in their sodium ion-exchange form and under anhydrous conditions, were studied through DFT computations. In the case of an aluminized framework, it was found that the non-Löwensteinian configuration is not only energetically more favorable but also has better electronic conductivity than the Löwensteinian framework. The two different ferric frameworks under consideration presented distinct magnetic nature and higher acidity compared to aluminized ones. Furthermore, it was observed that the purely siliceous LTA framework presented an inversion in the Löwdin charge trace behavior, suggesting that it is associated with its hydrophobic nature.

This work reports the facile synthesis of Pt-Mn nanoparticles supported on multiwall carbon nanotubes using the Brust–Schiffrin method and their electrochemical performance during methanol electro-oxidation reaction. According to the topographical and structural results, the Pt-Mn nanoparticles present high dispersion with a narrow size distribution of ~ 2.5 nm. Meanwhile, the electrochemical evaluation exhibits a greatly enhanced electrocatalytic activity. The electrocatalyst's performance improves as Mn increased up to 40 at.% in Pt nanoparticles, but it decreases as Mn reaches 50 at.%. The electrocatalytic activity fall could be attributed to a reduction on active sites favorable to the dissociation and dehydrogenation of methanol. Density functional theory computations reveal that the partial density of states (PDOS) associated with [Mn]3d orbitals could be directly correlated with the observed electrocatalytic behavior. The respective maximum PDOS contribution at the Fermi level also corresponds to the most active electrocatalyst, which contains Mn of ~ 40 at.%.

In terms of a method based on Cauchy integrals, we have obtained a robust analytic expression to predict a unique physical solution for the Scholte slowness in all range of possible elastic and isotropic media. Proper analysis of the discontinuities of the secular Scholte equation allows the identification of the velocity of the evanescent wave in one of three possible regimes. When the liquid phase tends to vanish, it was observed: a) the Rayleigh wave solution or the free surface limit, and b) the rarefied fluid medium limit, where there exists a gradual extinction of the Scholte wave as both the density and velocity of the fluid decrease. In general terms, the results show that the propagation speed of a Scholte wave is less than or equal to that of a Rayleigh wave.

Asymmetric Janus transition metal dichalcogenide MoSSe is a promising catalytic material due to the intrinsic in-plane dipole of its opposite faces. The atomic description of the structures observed by experimental techniques is relevant to tuning and optimizing its surface reaction processes. Furthermore, the experimentally observed triangular morphologies in MoSSe suggest that an analysis of the chemical environment of its edges is vital to understand its reactivity. Here we analyze the size-shape stability among different triangular structures-quantum- dots proposed from the ideal S(-1010) and Mo(10-10) terminations. Our stability analysis evidenced that the S-Se termination is more stable than Mo; moreover, as the size of the quantum dot increases, its stability increases as well. Besides, a trend is observed, with the appearance of elongated Mo-S/Se bonds at symmetric positions of the edges. Tersoff-Hamann scanning tunneling microscopy images for both faces of the stablest models are presented. Electrostatic potential isosurfaces denote that the basal plane on the S face of both configurations remains the region with more electron density concentration. These results point toward the differentiated activity over both faces. Finally, our study denotes the exact atomic arrangement on the edges of MoSSe quantum dots corresponding with the formation of S/Se dimers who decorates the edges and their role along with the faces as catalytic sites.

A functional material is a term used for a material with properties that fit a specific application. These properties can be intrinsic to a material, or the material can be tuned for obtaining the desired properties. Some materials can be used by themselves as functional materials, while others support functional materials. Zeolites are nanostructured porous materials that can be used as functional materials or used as supports for other functional materials. Quantum dots are luminescent materials with plenty of applications such as biomarkers, photocatalytic degradation, or biocides. However, the use of quantum dots is limited by the effect of moisture or heat on them. The applications of quantum dots can be improved if proper support is used. In this work, a brief overview of the use of zeolites as supports for quantum dots is offered, and their applications in optical devices are discussed.

Metal-organic frameworks (MOFs) are versatile materials that are of interest due to their application and properties. MOFs are highly crystalline and porous materials; they are composed of organic bridging ligands, acting as linkers, and a three-dimensional (3D) network of metal ions that are secondary building units. Since the MOFs have a high surface area, high porosity, tunable topography, and their structures are quite diverse, these materials are used in process of separation/purification, gas/energy storage, drug delivery, catalysis, and chemical sensors. Since the MOFs can be modified to selectively adsorb chemical species, they can be used as sensitive layer for modification of sensors. This process allows the sensor to detect the target analyte. Quartz crystal microbalances (QCMs) are highly sensitive mass sensors. In this chapter, the authors review the literature related to QCMs modified with MOFs. In particular, the relationship between target analyte, class of MOF, and instrument used for measurement of frequency variations.

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite plates were introduced by diffusion the TEOS molecules which were further hydrolyzed, and finally the material was annealed to remove the organic phase, leaving the 2D zeolite plates separated by pillars of silicon dioxide. To monitor the successive structural changes and the state of the atoms of the zeolite framework and organic compounds at all the steps of the synthesis of pillared MOR and MFI zeolites, the nuclear magnetic resonance method (NMR) with magic angle spinning (MAS) was applied. The 27Al and 29Si MAS NMR spectra confirm the regularity of the zeolite frameworks of the as synthetized materials. Analysis of the 1H and 13C MAS NMR spectra and an experiment with variable contact time evidence a strong interaction between the charged “heads” –[N(CH3)3]+ of CTAB and the zeolite framework at the place of [AlO4]− location. According to 27Al and 29Si MAS NMR the evacuation of organic cations leads to a partial but not critical collapse of the local zeolite structure.

Bismuth molybdate low-temperature γ-phase (γ-Bi2MoO6) has been widely studied as catalytic compound, and a recent experimental study demonstrated that Ruthenium (Ru) doping on γ-Bi2MoO6 enhanced their CO to CO2 conversion capacity at low temperature. To elucidate the effect of Ru-doping on γ-Bi2MoO6 electronic properties, in the present work are calculated the electronic structure and optical properties of γ-Bi2MoO6 and Ru-doped γ-Bi2MoO6 (γ-Bi2MoO6:Ru) compounds, in terms of the Density Functional Theory (DFT), using the modified Becke-Johnson (mBJ) approximation to the exchange-correlation potential. The electronic band structure, the total and projected density of states (DOS and PDOS, respectively), the real and imaginary part of dielectric function, ε, and the absorption spectra of both γ-Bi2MoO6 and γ-Bi2MoO6:Ru compounds, were obtained after the structural optimization of its crystalline lattices. The results show that Ru doping contributes to the generation of electronic states into the forbidden region of γ-Bi2MoO6, leading to a band-gap reduction, increasing their absorption along the visible-light regime. Our results provide insights for the development of novel ruthenium doped bismuth semiconductors for catalytic-related applications.

Measurement of time-frequency parameters is a task required in quite diverse applications, which include clock synchronization, radar systems, sensors, etc. This is the reason why frequency measurement is one of the key processes in many systems. Accordingly, approximation of a signal frequency has been actively researched and plenty of measurement techniques have been proposed. In the last years, the principle of rational approximations has been evaluated for frequency measuring, particularly for sensors. In this work, we examine the effect of phase in input signals during measurement, when the principle of rational approximations is applied. Data from an experimental measurement system is analyzed and conclusions are drawn.

Optoelectronic oscillators (OEO) based sensors generate low-phase-noise signals, whose frequency is in the order of GHz. These sensors are highly sensitive to parameters like strain, transverse load or temperature. Particularly, an OEO transforms a wavelength change into a frequency shift in the order of MHz. This creates a particular challenge for measuring instruments used in OEO, where novel mathematical methods for advanced processing of their signals is required. The principle of rational approximations is a frequency measurement technique based on number theory, with the fundamental property of measurement time dependent on the frequency value of input signals. This means that if the frequency of input signals increases, less time for measuring is required. This is quite useful for time-frequency measurement systems, where if more accuracy is needed, more time is required for measuring. This paper shows how the principle of rational approximations can be used in OEO based sensors, this allows to estimate the frequency shifts in a bandwidth from 6 to 600 MHz, with a maximum uncertainty of 2.5 MHz. Such an accuracy is achieved in a time as short as $0.2~\mu \text{s}$ .

In order to understand the electronic properties that $$\gamma $$(L)-$${\text {Bi}}_{2}{\text {MoO}}_{6}$$ and $$\gamma $$(H)-$${\text {Bi}}_{2}{\text {MoO}}_{6}$$ crystalline phases present, theoretical calculations were performed under the density functional theory (DFT) method. The computed PDOS for both phases shows that although these present a difference in bandgap values (larger for $$\gamma $$(H)-$${\text {Bi}}_{2}{\text {MoO}}_{6}$$ phase), the same type of orbitals is found at the HOMO and LUMO levels. The Löwdin charge values obtained from a population analysis suggest that the $$\gamma $$(H)-$${\text {Bi}}_{2}{\text {MoO}}_{6}$$ phase presents a larger number of both acid and basic sites at the free surface. We also observe that the occupation degree of the valence orbitals in this phase is greater than that in the $$\gamma $$(L)-$${\text {Bi}}_{2}{\text {MoO}}_{6}$$ phase.