RESUMO
A chabazite-type zeolite was prepared by the hydrothermal method. Before ion exchange, the chabazite was activated with ammonium chloride (NH4Cl). The ion exchange process was carried out at a controlled temperature and constant stirring to obtain ion-exchanged chabazites of Ti4+ chabazite (TiCHA), Zn2+ chabazite (ZnCHA), Cu2+ chabazite (CuCHA), Ag+ chabazite (AgCHA) and Au3+ chabazite (AuCHA). Modified chabazite samples were characterized by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), N2 adsorption methods and UV-visible diffuse reflectance spectroscopy (DRS). XRD results revealed that the chabazite structure did not undergo any modification during the exchange treatments. The photocatalytic activity of chabazite samples was evaluated by the degradation of methylene blue (MB) in the presence of H2O2 under ultraviolet (UV) light illumination. The photodegradation results showed a higher degradation efficiency of modified chabazites, compared to the synthesized chabazite. CuCHA showed an efficiency of 98.92% in MB degradation, with a constant of k = 0.0266 min-1 following a first-order kinetic mechanism. Then, it was demonstrated that the modified chabazites could be used for the photodegradation of dyes.
Assuntos
Azul de Metileno/química , Poluentes Químicos da Água/química , Zeolitas/química , Fotólise , Zeolitas/síntese químicaRESUMO
A combination of hard-templating (HT) and soft-templating (ST) approaches was studied to obtain MWW-type materials with intermediate physicochemical properties. The HT methodology involved the introduction of carbon particles as hard templates during gel synthesis to obtain a layered zeolitic precursor (LZP) with particles possessing a microspherical morphology. The LZP obtained was treated with surfactants as soft templates to expand the layers of the LZP, followed by a pillaring procedure. The materials were characterized by X-ray diffraction, transmission and scanning electron microscopy, elemental analysis and N2 adsorption. The results demonstrate that the obtained material possesses intermediate properties from both approaches, with interparticle mesopores/macropores and pore sizes between 18 and 46 Å. However, the ST procedure causes a partial disruption of some microspheres, forming small crystallite aggregates, and results in a decrease in the number of interparticle mesopores/macropores previously formed by the HT method. All synthesized solids presented catalytic activity, which was evaluated by the cracking of low-density polyethylene (LDPE) as a probe reaction.
Assuntos
Carbono/química , Zeolitas/síntese química , Adsorção , Dureza , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Nanopartículas , Porosidade , Difração de Raios X , Zeolitas/químicaRESUMO
The need for greener procedures is a fact to reduce residues, to decrease industrial costs, and to accomplish the environmental agreements. In an attempt to address this question, we propose the addition of a natural resource, Brazilian diatomite, to an MFI zeolite traditional synthesis. We have characterized the resulting product with different techniques, such as X-ray diffraction, microscopy, and gas sorption, and, afterwards, we evaluate the greenness of the process by the Green Star method. The results were promising: We obtained the desired topology in the form of small crystallites aggregated and a pore diameter of 0.8 nm. In conclusion, the product has the necessary characteristics for an adsorption or catalytic future tests and escalation to industrial production.
Assuntos
Terra de Diatomáceas/química , Zeolitas/síntese química , Brasil , Química Verde , Modelos Moleculares , Propriedades de Superfície , Difração de Raios X , Zeolitas/químicaRESUMO
Fly ash, a coal combustion residue produced by Termotasajero in Colombia, has been hydrothermally treated after an alkaline fusion to produce zeolite without addition of silicon or aluminum. The starting material was thoroughly mixed with NaOH, in a 1:1.2 mass ratio, to obtain a homogeneous mixture that was heated to 100 °C during different times (6, 8, and 10 h) and three zeolite samples were produced. The samples were characterized by XRD, SEM, XRF, Mössbauer spectroscopy, and N2 physisorption. According to characterization results (high surface area and appropriate morphological properties including crystallinity) and synthesis time, zeolitic catalyst synthesized with 8 h of hydrothermal treatment was selected to perform further analysis. This sample consisted of a mixture of zeolite X and zeolite A of high surface area (301 m2 g-1) and a Fe content of 6% wt/wt. The zeolite was used as a catalyst for the Fenton oxidation of Orange II. Experiments were performed in a laboratory batch reactor at 70 °C and constant pH = 3, using different concentrations of H2O2. When the stoichiometric amount of H2O2 was used, good mineralization (XTOC = 45%), complete discoloration, and oxidant consumption were obtained after 240 min of reaction. The sample retained activity after 16 h of usage. The presence of Fe in the reaction media was always detected and a homogeneous Fenton mechanism induced by surface-leached iron is suggested.
Assuntos
Compostos Azo/química , Benzenossulfonatos/química , Cinza de Carvão/química , Zeolitas/síntese química , Catálise , Colômbia , Peróxido de Hidrogênio/química , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura , Oxidantes/química , Oxirredução , Peróxidos/química , Espectroscopia de Mossbauer , Difração de Raios X , Zeolitas/químicaRESUMO
Zeolite synthesis is a wide area of study with increasing popularity. Several general reviews have already been published, but they did not summarize the study of imidazolium species in zeolite synthesis. Imidazolium derivatives are promising compounds in the search for new zeolites and can be used to help understand the structure-directing role. Nearly 50 different imidazolium cations have already been used, resulting in a variety of zeolitic types, but there are still many derivatives to be studied. In this context, the purpose of this short review is to help researchers starting in this area by summarizing the most important concepts related to imidazolium-based zeolite studies and by presenting a table of recent imidazolium derivatives that have been recently studied to facilitate filling in the knowledge gaps.
Assuntos
Cátions/química , Imidazóis/química , Zeolitas/síntese química , Técnicas de Química Sintética , Modelos Moleculares , Estrutura MolecularRESUMO
Several researchers have reported zeolite synthesis using coal ash for a wide range of applications. However, little attention has been given to green processes, including moderate synthesis conditions, using waste as raw material and effluent reuse or reduction. In this study, Brazilian coal fly ashes were used for integrated synthesis of zeolites 4A and Na-P1 by two different routes and under moderate operating conditions (temperature and pressure). Both procedures produced zeolites with similar conversions (zeolite 4A at 82% purity and zeolite Na-P1 at 57-61%) and high CEC values (zeolites 4A: 4.5meqCa(2+)g(-1) and zeolites Na-P1: 2.6-2.8meqNH4(+)g(-1)). However, process 1 generated less effluent for the zeolite mass produced (7mLg(-1)), with low residual Si and Al levels and 74% of the Si available in the coal fly ash incorporated into the zeolite, while only 55% is used in process 2. For use as a builder in detergents, synthetic zeolite 4A exhibited conformity parameters equal to or greater than those of the commercial zeolite adopted as reference. Treatment of swine wastewater with zeolite Na-P1 resulted in a high removal capacity for total ammoniacal nitrogen (31mgg(-1)).
Assuntos
Compostos de Amônio/isolamento & purificação , Cinza de Carvão/química , Detergentes/síntese química , Química Verde , Zeolitas/síntese química , Animais , Suínos , Purificação da ÁguaRESUMO
Coal-fired plants in Coahuila (Mexico) produce highly reactive fly ash (MFA), which is used in a one-step process as a raw material in producing zeolite. We explored two routes in the synthesis of zeolite: (a) direct MFA zeolitization, which resulted in the formation of W zeolite with KOH and analcime with NaOH and (b) a MFA fusion route, which resulted in the formation of zeolite W or chabazite with KOH and zeolite X or P with NaOH. No residual crystalline phases were present. When LiOH was employed, ABW zeolite with quartz and mullite were obtained. For both zeolitization routes, the nature of the alkali (KOH, NaOH, LiOH), the alkali/MFA ratio (0.23-1.46), and the crystallization temperature and time (90-175 degrees C; 8-24 h) were evaluated. Additionally, the effect of temperature and time on MFA fusion was studied. W zeolite was obtained by both zeolitization methods. The direct route is preferred because it is a straightforward method using soft reaction conditions that results in a high yield of low cost zeolites with large crystal agglomerates. It was demonstrated that aluminum modified W zeolite has the ability to remove 99% of the arsenic (V) from an aqueous solution of Na(2)HAsO(4).7H(2)O originally containing 740 ppb.