Fractal evolution of organic additive-assisted aluminosilicate sols and platelet-like growth of HEU-type clinoptilolites for selective adsorption of CO2 and CH4

Surfactant effect on the crystallization behavior of clinoptilolite is proposed. • Fractal evolution of the aluminosilicate sol is tracked via SAXS method. • Nucleation and growth behavior of clinoptilolite was clarified via DFT simulations. • Gas separation performance of the surfactant-assisted clinoptilolite was explored. The incorporation of organic additives into hydrothermal synthesis systems provides an effective strategy for regulating the crystallization and morphological evolution of HEU-type clinoptilolite (CP). Such organic additive-assisted regulation can modify platelet development, particle aggregation, interfacial characteristics, and pore accessibility, thereby influencing gas adsorption and transport behavior. Despite extensive studies on CP modification, the comparative effects of different organic additives on nucleation, growth, fractal evolution, and gas-separation behavior remain insufficiently understood. Herein, the influences of cetyltrimethylammonium bromide (CTAB), o -phenylenediamine (OPD), and polyethylene glycol (PEG) on CP crystallization were systematically investigated using X-ray diffraction (XRD), UV-Raman spectroscopy, solid-state 29 Si nuclear magnetic resonance, scanning electron microscopy, small-angle X-ray scattering (SAXS), gas adsorption measurements, and molecular simulations. In particular, SAXS patterns were employed to elucidate fractal evolution of aluminosilicate species during CP crystallization. The results revealed that organic additive-mediated interfacial interactions modified aluminosilicate evolution during the induction stage and delayed framework organization to different extents. During the growth stage, the CTAB-, OPD-, and PEG-containing systems exhibited formulation-dependent differences in crystallization retardation and anisotropic crystal growth. Gas adsorption and GCMC-MD simulations showed formulation-dependent changes in CO 2 , CH 4 , and N 2 adsorption and diffusion; notably, additive-containing samples generally exhibited lower absolute capacities, while mixed-gas breakthrough showed the strongest CO 2 /CH 4 kinetic separation for pure-CP, revealing a structure-transport trade-off rather than universal performance enhancement. These findings link additive-regulated crystallization and platelet-like morphological evolution with adsorption transport behavior, providing a mechanistic framework for tuning CP structure and CO 2 /CH 4 separation.