Synthesis and characterization of analcime (ANA) zeolite using a kaolinitic rock

Abstract

Analcime is nowadays an important component in dental porcelain systems, in heterogeneous catalysis, in the nanoelectronic field, in selective adsorption and in stomatology (dental filling and prosthesis). Analcime synthesis from an impure, silica-rich kaolinite rock coming from Romana (Sassari, Italy) is here presented. A synthesis protocol is proposed that aims to make an improvement of synthesis conditions compared to the past. The hydrothermal treatment is in fact here achieved without aging times and without the use of sodium silicate or other additional silica source reported in the literature. Lower calcination temperature, synthesis temperature and crystallization time are verified in this work. The kaolin is subjected to calcination at the temperature of 650 °C and then mixed with NaOH. The experiment is performed at ambient pressure and 170 ± 0.1 °C. The degree of purity of analcime is calculated in 97.57% at 10 h. Analcime is characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, inductively coupled plasma optical emission spectrometry and thermal analysis. Density is also calculated. Cell parameters and the amount of amorphous phase in the synthesis powders is estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The experimental conditions make the synthesis protocol particularly attractive from an economic point of view. Also this work does not use a commercial kaolin but silica-rich impure kaolinitic rock from a disused quarry. This further reduces the costs of the experimental protocol. It also gives the protocol an added value, as the synthesis of a useful mineral is obtained through the valorization of an otherwise unused georesource. Both chemical and physical characterization of analcime is satisfactory making the experimental protocol very promising for an industrial transfer.

Silver Nanoclusters Loaded in Analcime Zeolite for Tunable Luminescence

“…Meanwhile, the reaction of TPA and Ag can also be clearly verified by the Fourier transform infrared (FT-IR) spectra in Figure ; the vibration bands attributed to ν s (COO – ) at 1585 cm –1 and ν as (COO – ) at 1427 cm –1 of sample ANA-TPA (ANA-TPA was prepared under the same synthetic conditions as those of Ag@ANA-TPA but without Ag) shift to lower wavenumbers at 1568 and 1421 cm –1 of sample Ag@ANA-TPA, suggesting that the COO – group assigned to TPA successfully coordinated with Ag + during the synthesis (Figure ). , Also, the vibration bands at 1008 cm –1 and 742, 687, and 621 cm –1 are assigned to the stretching mode of O–Na–O and the symmetric stretching mode of T–O–T (T = Al, Si), respectively, which are well matched with the reported of ANA and show almost no difference between different samples (Figure A). , The Raman diagram in Figure S14 also exhibits the characteristic bands attributed to TPA and the bands assigned to ANA, which are in good agreement with those previously reported. , Thus, it might be considered that TPA molecules effectively dispersed silver at the atomic level by coordinating with silver ions, causing the dissolution of some large Ag NPs. Moreover, very bright green light could be observed when the unwashed Ag@ANA-TPA was irradiated by a UV lamp in Figure S15a, which originated from the complexes formed between Ag + and TPA molecules in Figure S15b.…”

“…The XRD pattern is consistent with the standard data of ANA zeolites (JCPDS 41-1487), displaying intense diffraction peaks observed at 2θ = 15.8°, 25.9°, and 30.5°, which verifies a typical structure of ANA. , There are numerous irregular channels and cavities occupied by the exchangeable Na + ions in the crystal lattices in each crystal with an idealized unit cell of Na 16 Al 16 Si 32 O 96 · n H 2 O. The cavities in ANA, consisting of three distorted 8-rings and two 6-rings, are connected into “double” cavities that form irregular channels, as illustrated in Figure B,C . The Si/Al molar ratio of the synthesized zeolite was determined to be 2.1 by a X-ray photoelectron spectrometry (XPS) technique (Table S1), matching well with that of the idealized unit cells. , The ANA zeolite shows particle sizes in the range of 5–10 μm diameter with polyhedral morphology (Figure D).…”

“…The cavities in ANA, consisting of three distorted 8-rings and two 6-rings, are connected into “double” cavities that form irregular channels, as illustrated in Figure B,C . The Si/Al molar ratio of the synthesized zeolite was determined to be 2.1 by a X-ray photoelectron spectrometry (XPS) technique (Table S1), matching well with that of the idealized unit cells. , The ANA zeolite shows particle sizes in the range of 5–10 μm diameter with polyhedral morphology (Figure D). The lattice distance of 0.3493 nm can be observed from the aberration-corrected transmission electron microscopy (TEM) images shown in Figure A, in good agreement with the 0.3422 nm distance of the ANA (400) crystallographic plane .…”

A Short Review on the Utilization of Incense Sticks Ash as an Emerging and Overlooked Material for the Synthesis of Zeolites

“…Zeolites are present in nature and are mined in various parts of the world, but they are impure and less organized, so for smother work they have been synthesized commercially. Natural zeolites are formed in volcanic ashes, sedimentary rocks [37], clay-kaolins [38], red mud [39], coal fly ash (CFA) [6], bauxite minerals [1,40] and other earthy materials [41]. On the other hand, synthetic zeolites are synthesized in laboratory conditions by optimizing the conditions of various elements [42].…”

Synthesis of large single crystals of analcime in a template-free system

“…Usually, ANA is synthesized under hydrothermal conditions using aluminosilicate clear solutions or gels in the presence of different organic templates, [23][24][25][26][27][28] but the size and quality of the final crystals were not satisfactory. Besides, these studies showed a complex synthesis process, and the organic templates are not friendly to the environment.…”