Síntese de zeólita tipo NaY utilizando casca de arroz como precursor de sílica: aspectos gerais

Abstract

Materials science is responsible for the study of the properties, structure and application of materials. Among the numerous properties, porosity stands out, since some solids have a degree of this characteristic. The International Union of Pure and Applied Chemistry (IUPAC) establishes a classification of porous materials based on the size of the pore diameter into: microporous, mesoporous and macroporous. Among the micro and mesoporous materials, zeolites stand out. Zeolites are crystalline aluminosilicates containing alkaline and alkaline earth elements as compensating ions (Na+, K+, Ca2+ e Ba2+). They are formed by a network of tetrahedrons of the type [SiO4]4- and [AlO4]5-, which are linked together by the four vertices, through oxygen. Many physicochemical properties are attributed to zeolites, both of natural and synthetic origin, allowing them to be applied in the most diverse areas, being used as catalysts, adsorbents, ion exchangers and molecular sieves. However, natural zeolites have a large amount of impurities in their composition, só that the composition of extracted minerals varies significantly between inorganic deposits. Thus, there is a need for research on the optimal conditions for zeolite synthesis. This work proposes a review on the synthesis of zeolite from the Faujasite family of the NaY type, a microporous material, through the presentation of the synthesis reaction parameters such as: temperature, reaction time, precursor gel aging, use of seeds, and the introduction of the possibility of substituting synthetic reagents for alternative sources. Thus, studies using silica obtained from rice husks for the synthesis of NaY-type zeolite were presented, in which the quality of the crystalline product obtained is characterized, mainly, through X-ray diffraction (XRD). As such, the NaY-type faujasite zeolite presents a characteristic and intense peak in X-ray diffraction at approximately 2θ equal to 6°. Other techniques become complementary for the characterization of zeolites, such as morphological analysis by scanning electron microscopy wit energy dispersive spectroscopy (SEM-EDS) and molecular analysis by Fourier transform infrared spectroscopy (FTIR). Then, through the review, it was possible to affirm that the best synthesis conditions for a Faujasite-type NaY zeolite occurs in a two-step reaction, with aging of the precursor gel and the use of seeds. Furthermore, the optimal reaction time occurs within 24 hours in hydrothermal synthesis.