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In order to understand the growth behaviors of the aluminosilicate species in the initial hydrothermal process and thereafter synthesis of clinoptilolites with high purity, the physicochemical characteristics of the aluminosilicate nanoparticles were elucidated by small angle X‐ray scattering (SAXS) and X‐ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images, Ultra‐Violet Raman (UV‐Raman) and Fourier transform infrared (FT‐IR) spectra. The results demonstrated that the aluminosilicate nanoparticles presented the first decreased surface fractal (Ds) values and then an increased Ds values in the initial reaction time of before 120 h. After that, the fractal transformations from Ds to mass fractal (Dm) occurred with the extensions of reaction time (120–144 h), but the decreased Dm values appeared after 144 h. Therefore, their growth mechanisms from uniform dispersions to aggregation, and even assembly were proposed. [ABSTRACT FROM AUTHOR]

The clinoptilolites (CPs) with high purity were prepared via structure directing agent (SDA) method combining with hydrothermal method using silica sol as the silica source and aluminum hydroxide as the aluminum source. Their structural features were characterized by X‐ray diffraction (XRD) patterns, Fourier transform infrared (FT‐IR) spectra, thermal gravimetric (TG) analysis, scanning electron micrograph (SEM) images, 29Si nuclear magnetic resonance (NMR) profiles. The effects of additive amount and aging time of used SDA, as well as synthetic parameters such as crystallization temperature and crystallization time on their structure and performance were emphasized. Particularly, the activation energies of their crystallization kinetics at different stages of induction period and growth period were calculated on the basis of Arrhenius equation. The results demonstrated that the obtained CPs presented the highest relative crystallinity when the additive amount of used SDA was 1 mL at aging periods of 2 d, otherwise, their relative crystallinity degree was low due to existences of a large number of heterocrystal impurities. Particularly, the apparent activation energy values for induction (En) and growth (Eg) profile were calculated by the Arrhenius equation. The En value (86.46 kJ/mol) of induction period was much higher than that Eg value (9.64 kJ/mol) of growth stage, suggesting that the induction period was the main controlling step during the synthetic CP. Finally, the synthetic CP was employed to preliminarily assess its performances for CH4/N2 separation. These demonstrations provide a promising method for the synthesis of CPs. [ABSTRACT FROM AUTHOR]

Nanosol precursor was obtained via hydrothermal pre-crystallization time periods of 6, 60 and 102 h at 423 K. Different amounts of nanosol precursor with different crystallization time periods were added to the hydrothermal synthesis system as structural promoter (SP) to synthesize clinoptilolite. The various characterizations such as XRD, SEM, BET, FT-IR, TG-DSC, ICP, UV-Raman, and element analysis were employed to investigate the structural and textural characteristics and potential applications of synthetic clinoptilolites in CH 4 /N 2 separation. Their activation energies of induction (E n) and growth (E g) periods during crystallization intervals were calculated according to Arrhenius equation, where the former being much larger than the latter proved that nucleation is the key in the synthesis of clinoptilolite. The E n value gradually decreased with increasing amount of the SP and its pre-crystallization time interval, which further revealed that the addition of SP with the shortened crystallization time is beneficial in the formation of crystal nuclei. However, the amount of SP significantly altered the particle size, extent of impurities (phillipsite), and thermal stability of the clinoptilolite. The results demonstrated that pure clinoptilolite could be successfully synthesized in a short time period at low temperature. Particularly, the ion exchange performance and CH 4 /N 2 separation capacity of clinoptilolite synthesized with the additive SP (3 wt %) in the pre-crystallization interval of 60 h were found almost in similarity with the clinoptilolite prepared without SP, showing a promising adsorbent for kinetic separation of CH 4 /N 2. Image 1 • Aluminosilicate sol as structural promoter for clinoptilolite was explored. • Crystalline kinetic for induction and growth stage in clinoptilolite was evaluated. • Potential application of Li-clinoptilolite in CH 4 /N 2 separation was investigated. • Adsorption heat for N 2 and CH 4 using Li-clinoptilolite as sorbent was calculated. • Nanosol precursor was an efficient structure promoter in synthesis of clinoptilolite. [ABSTRACT FROM AUTHOR]