Miguel Angel Hernandez

Las zeolitas son minerales que pueden originarse a partir de formaciones rocosas o ser sintetizados en el laboratorio, y se caracterizan por una amplia diversidad de aplicaciones. Su composición química les confiere una alta capacidad de absorción y de intercambio iónico. Además, su estructura cristalina ordenada en una red tridimensional de microporos las convierte en excelentes materiales de soporte y vehículos para diversas sustancias. Estas propiedades han sido ampliamente aprovechadas en la industria y en la agricultura. No obstante, a pesar de ser materiales inorgánicos, su uso también se ha explorado en aplicaciones animales y humanas, particularmente en el ámbito de la salud y la biomedicina. El avance reciente en su estudio ha permitido evaluar su utilidad en el tratamiento de enfermedades crónicas como la diabetes. Algunos trabajos sugieren que puede contribuir con el control de la glucosa, y en el caso de las complicaciones asociadas, favorecer el proceso de cicatrización en úlceras por pie diabético, gracias a su efecto hemostático y de reparación tisular. A la luz de la evidencia disponible, las zeolitas se presentan como una alternativa prometedora para el desarrollo de nuevas herramientas terapéuticas con aplicaciones biomédicas diversas

This paper describes the isosteric enthalpy through narrow pores at low levels of coverage through adsorption of CO₂, CH₄, and H₂ on pores in natural chabazite exchanged with aqueous solutions of Na⁺, Mg²⁺, and Ca²⁺ salts at different concentrations, and with variable time and temperature of treatment. Experimental data of CO₂, CH₄, and H₂ adsorption were treated by the Freundlich and Langmuir equations. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric enthalpy of adsorption. The exchange with Mg²⁺ and Na+ favors an increase in the adsorption capacity for CO₂. while that of Ca²⁺ and Mg²⁺ favor adsorption through to H₂ and CH₄. These cations occupy sites in strategic positions S4 and S4’, which are located in the channels and nanocavities of these zeolites. The presence of Ca²⁺ and Mg²⁺ at S4 and S4′ sites causes increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. Depending on the conditions of the exchange treatment, Ca²⁺ and Mg²⁺, and Na+ were found to be most favorable, well distributed, and accessible for CO₂, CH₄, and H₂ adsorption.

This work reports, the obtainment and stabilization of organic nanoparticles (γ-sitosterol) and Ag cations on the external area of Ca-clinoptilolite zeolite (Z17) are presented. The novelty of the present study lies in the formation and stabilization of nanoparticle organic molecules (γ-sitosterol) and inorganic cations (Ag) on the external area of Ca-clinoptilolite zeolite. The γ-sitosterol nanoparticles were obtained using Tournefortia hirsutissima and were later stabilized on the external area of Ca-clinoptilolite. The Ca-clinoptilolite-rich mineral as well as silver zeolitic minerals was characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM); elementary composition of the zeolitic mineral was determined by microanalyses (EDS) and high-resolution adsorption (HRADS) using N₂ adsorption as a probe molecule. The EDS results about the exchange with Ag indicate the following sequence: Z17Ag03 > Z17Ag-09 > Z17Ag-06 > Z17Ag-01. The XRD studies indicate that only in the sample Z17Ag-03 there is an average crystal size of nanoparticles formed of 45.387 nm as determined by Sherrer’s equation. SEM images of clinoptilolite showed the presence of crystals with irregular and poorly defined box shapes that are typical for this type of zeolites. The nanoporosity of natural zeolites was studied by N₂ adsorption; external areas were estimated through the De Boer and BET equations. The specific surface area calculated by BET equation, , presents the following sequence: γ-SZ17 > Z17 > Z17Ag09 > Z17Ag03 > Z17Ag01 > Z17Ag06, while for the values of the external area obtained by the method, the sequence is : γ-Z17 > Z17 > Z17Ag03 > z17Ag09 > Z17Ag06 > Z17Ag01. For its part, the pore size distributions tell us that the sample Z17 exhibits a sharp multimodal distribution with pore size maxima happening at 1.262, 1.933, 3.824, and 4.282 nm. Z17Ag01 exhibits a bimodal distribution with pore size maxima occurring at 5.45 and 5.533 nm. The sample Z17Ag06 exhibits a sharp bimodal distribution with pore size maxima happening at 3.666 and 7.021 nm, and the sample Z17Ag09 exhibits a sharp trimodal distribution with pore size maxima happening at 1.853, 4.275 and 5.967 nm. Antibacterial activities of the exchanged samples with Ag on the external surface area were measured as a function of exchange level against Gram-positive bacteria (P. aureoginosa, K. pneumonie, and A. baumannii) and Gram-negative bacteria (E. coli, S. saprophyticcus, S. aureus, and E. feacalis); the selectivity sequence of the clinoptilolite and antibacterial activity results are presented. Z17Ag09 clinoptilolite seemed to be a promising antibacterial material.

Benzene, toluene, ethylbenzene, and p-xylene (BTEX) are hazardous volatile organic compounds mostly released from fuel combustion, paint gas emissions, and biomass burning. In this work, it is studied the BTEX sorption influence on the surface reactivity of a new kind of nanoporous composite, prepared via an in situ functionalization of SBA-15 with a Mg–Al calcined hydrotalcite (HTC). During its preparation, Mg/Al mixed oxides are indeed formed and dispersed on the SBA-15 surface with non-blockage porosity. Furthermore, the physicochemical surface properties are exalted from its precursors and it is synergistically favorable for the BTEX sorption at low pressure and temperature.

The nanoporosity in zeolite ZSM-5 was analyzed as a function of SiO2/Al2O3 molar ratio (MR). The internal pore structure was studied by high-resolution adsorption. Surface areas, microporous volume, characteristic energy of sorption, and pore-size distributions were calculated from N2 sorption isotherms by the BET, Langmuir, t-method of de Boer, αS-plot of Sing, direct comparative plots of Lee, Newnham, Dubinin-Astakhov, differential adsorption curves, and nonlocal density functional theory methods. The results indicated that MR dependence in these zeolites caused structural defects through micropore opening and widening as well as the emergence of further slit-like mesopores.

Emissions of carbon dioxide (CO₂) and nitrogen dioxide (NO₂) in recent years has been increased considerably. One way to reduce the concentration of these greenhouse gases in the atmosphere is adsorptive capture. This paper describes the main results of adsorption of N₂, NO₂, and CO₂ on epistilbite, both natural and on samples that were chemically treated at various concentrations of HCl. Data on the adsorption of CO₂ and NO₂ were evaluated by the Freundlich and Langmuir equations. Additionally, the thermodynamic parameters of adsorption were calculated, including the degree of interaction of the zeolite samples with gases by gradually changing the isosteric heat capacities of adsorption. The acid treatment improves the adsorption capacity of epistilbite with respect to NO₂ and CO₂, due the replacement of large extra-framework cation by small H⁺ ions. The improvement in the distribution of pore sizes in epistilbite samples was calculated by the method of Barrett-Joyner-Halenda. The sample H1 that was prepared in a moderately concentrated acid showed the best behavior in the CO₂ adsorption processes, while the natural EPIN material preferably adsorbs NO₂.

Carbon dioxide (CO₂) is considered one of the most important greenhouse gases in the study of climate change. CO₂ adsorption was studied using the gas chromatography technique, while the Freundlich and Langmuir adsorption models were employed for processing isotherm data in the temperature range of 473–573 K. The isosteric heat of adsorption was calculated from the Clausius–Clapeyron equation. Moreover, the thermodynamic properties ΔG, ΔU, and ΔS were evaluated from the adsorption isotherms of Langmuir using the Van’t Hoff Equation. The four soil samples were recollected from San Juan Amecac, Puebla, Mexico, and their morphologies were investigated through X-ray diffraction (XRD) and N₂ adsorption at 77 K. The SJA4 soil has a crystalline Kaolinite phase, which is one of its non-metallic raw materials, and N₂ isotherms allowed for the determination of pore size distributions and specific surface areas of soil samples. The Barrett–Joyner–Halenda (BJH) distribution of pore diameters was bimodal with peaks at 1.04 and 3.7 nm, respectively. CO₂ adsorption showed that the SJA1 soil afforded a higher amount of adsorbed CO₂ in the temperature range from 453 to 573 K followed by SJA4 and finally SJA2, classifying this process as exothermic physisorption.

Our research group has developed a group of hybrid biomedical materials potentially useful in the healing of diabetic foot ulcerations. The organic part of this type of hybrid materials consists of nanometric deposits, proceeding from the Mexican medicinal plantTournefortia hirsutissimaL., while the inorganic part is composed of a zeolite mixture that includes LTA, ZSM-5, clinoptilolite, and montmorillonite (PZX) as well as a composite material, made of CaCO₃and montmorillonite (NABE). The organic part has been analyzed by GC-MS to detect the most abundant components present therein. In turn, the inorganic supports were characterized by XRD, SEM, and High Resolution Adsorption (HRADS) of N₂at 76 K. Through this latter methodology, the external surface area of the hybrid materials was evaluated; besides, the most representative textural properties of each substrate such as total pore volume, pore size distribution, and, in some cases, the volume of micropores were calculated. The formation and stabilization of nanodeposits on the inorganic segments of the hybrid supports led to a partial blockage of the microporosity of the LTA and ZSM5 zeolites; this same effect occurred with the NABE and PZX substrates.

This paper deals with the emergence of pores in natural erionite zeolite during ion-exchange treatment with aqueous Na