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In recent years, climate change has attracted the attention of the scientific community. These changes are attributed to human action, which is responsible for the emission of polluting gases, mainly through the burning of fossil fuels, deforestation, and industrial processes that are responsible for the greenhouse effect. Post-combustion CO₂ capture using solid adsorbents is a technology that is currently gaining prominence as an alternative and viable form of capture to other industrial processes used. Zeolites are adsorbents capable of capturing CO₂ selectively due to their properties such as textural properties, high surface area, and active sites. In this context, this work developed materials with a zeolite structure with an alternative low-cost silica source from beach sand, called MPI silica, to make the process eco-friendly. Crystallization time studies were carried out for materials containing MFI-type zeolites with MPI silica with a time of 15 h (ZM 15 h) and 3 days (SM 3 d), with relative crystallinities of 92.90% and 111.90%, respectively. The synthesized materials were characterized by several techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), the textural analysis of N₂ adsorption/desorption isotherms, absorption spectroscopy in the infrared region with Fourier transform (FTIR), scanning electron microscopy (SEM), and thermal analysis. The evaluation of the experimental adsorption isotherms showed that the best results were for the zeolites synthesized in the basic medium, namely ZMP 3 d, ZM 10.5 h, and ZM 15 h, with capacities of 3.72, 3.10, and 3.22 mmol/g of CO₂, respectively, and in the hydrofluoric medium, namely SP 9 d, SM 3 d, and SM 6 d, with capacities of 3.94, 3.78, and 3.60 mmol/g of CO₂, respectively. The evaluation of the mathematical models indicated that the zeolites in the basic medium best fitted the Freündlich model, namely ZMP 3 d, ZM 10.5 h, and ZM 15 h, with capacities of 2.56, 1.68, and 1.87 mmol/g of CO₂, respectively. The zeolites in the hydrofluoric medium are adjusted to the Langmuir model (SP 9 d and SM 3 d) and Temkin model (SM 6 d), with capacities of 3.79, 2.23, and 2.11 mmol/g of CO₂, respectively. Full article

Emissions caused by polluting gases, such as carbon dioxide, are one of the main contributors to the generation of the greenhouse effect that leads to global warming, responsible for climate change. An alternative to mitigating these emissions is the use of adsorbents capable of capturing CO₂. Zeolites are considered one of the most effective adsorbents in gas adsorption and separation technologies due to their high specific area and pore size and, consequently, greater adsorption capacity when compared to other commonly used materials. Despite this, reagents used in syntheses as the source of silica often make obtaining these materials more expensive. Seeking to overcome this limitation, in this work, materials (for CO₂ capture) were developed with a zeolitic structure using a low-cost alternative source of silica from beach sand called MPI silica to make the synthesis process eco-friendly. The crystallization time of the materials was studied, obtaining an LTA zeolite with MPI silica in a period of 1 h (ZAM 1 h), with a relative crystallinity of 74.26%. The materials obtained were characterized using the techniques of X-ray diffraction (XRD), X-ray fluorescence (XRF), absorption spectroscopy in the infrared region with Fourier transform (FTIR), scanning electron microscopy (SEM), and thermal analysis. The evaluation of the experimental adsorption isotherms showed that the zeolite LTA Aerosil^®200 (standard zeolite) and MP had adsorption capacities of 5.25 mmol/g and 4.83 mmol/g of CO₂, respectively. The evaluation of mathematical models indicated that the LTA zeolites fit the Temkin model best and had the same trend, with calculated adsorption capacities of 3.97 mmol/g and 3.75 mmol/g, respectively. Full article

The effects of flame retardant silica (SiO₂) and magnesium hydroxide (Mg(OH)₂) on the thermal decomposition process of polyimide (PI) are discussed in this paper. Firstly, the decomposition process of PI in a nitrogen and oxygen atmosphere was studied by thermogravimetric analysis and differential scanning calorimetry methods, and the kinetic parameters were calculated by the nonlinear fitting method. In an inert atmosphere, PI decomposition consists of a three-step endothermic reaction, whereas in an oxygen atmosphere, PI decomposition consists of two steps, in which the first step does not change, and the second step changes to a violent exothermic peak. The effects of 3 wt % SiO₂ (SPI) and 3 wt % Mg(OH)₂ (MPI) on the degradation kinetics of PI are discussed. The results show that under an oxygen atmosphere, SiO₂ and Mg(OH)₂ hydroxide mainly delayed the second-step oxidation exothermic peak temperature of PI by 5 °C. In summary, the first step of the PI degradation is not affected by oxygen, and the flame retardant mainly acts in the second step, which can delay the oxidation heat release. In addition, the addition of SiO₂ could prevent PI from aging whereas Mg(OH)₂ has barely effect on the aging of PI. Full article

Chemical interactions between metal particles (Ag or Ni) dispersed in a low-cost MCM-41^M produced from beach sand amorphous silica and sulfur compounds were evaluated in the deep adsorptive desulfurization process of real diesel fuel. N₂ adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy (STEM-EDX) were used for characterizing the adsorbents. HRTEM and XPS confirmed the high dispersion of Ag nanoparticles on the MCM-41 surface, and its chemical interaction with support and sulfur compounds by diverse mechanisms such as π-complexation and oxidation. Thermodynamic tests indicated that the adsorption of sulfur compounds over Ag(I)/MCM-41^M is an endothermic process under the studied conditions. The magnitude of ΔH° (42.1 kJ/mol) indicates that chemisorptive mechanisms govern the sulfur removal. The best fit of kinetic and equilibrium data to pseudo-second order (R² > 0.99) and Langmuir models (R² > 0.98), respectively, along with the results for intraparticle diffusion and Boyd’s film-diffusion kinetic models, suggest that the chemisorptive interaction between organosulfur compounds and Ag nanosites controls sulfur adsorption, as seen in the XPS results. Its adsorption capacity (q_m = 31.25 mgS/g) was 10 times higher than that obtained for pure MCM-41^M and double the q_m for the Ag(I)/MCM-41^C adsorbent from commercial silica. Saturated adsorbents presented a satisfactory regeneration rate after a total of five sulfur adsorption cycles. Full article