Regulation of crystal growth process of NaP zeolite via the coupling effects of electrostatic interaction and steric hindrance.

Due to the rich pore structure, NaP zeolite adsorbent has been widely employed in the adsorption and separation fields. The NaP zeolite crystals with small size and good dispersion were generated with the addition of ionic surfactants using coal fly ash as the raw material. The effects of different types and concentrations of surfactants on the structure of NaP zeolites were investigated by various characterization methods. The optimal concentration of ionic surfactants was 0.5 cmc (critical micelle concentration) for NaP-CTAB and 0.125 cmc for NaP-SDBS. The NaP-SDBS zeolite at 0.125 cmc exhibited higher crystallinity (96.11%), the smallest grain size (2.20 ​μm), and the largest specific surface area (29.1 ​m2/g). The functional groups in the ionic surfactants exerted the electrostatic interaction (attraction and repulsion) and steric hindrance effects together with the negatively charged precursors of NaP zeolite, which provided a favorable foundation for broadening the application fields and improving the adsorption properties. And the introduction of ionic surfactants did not destroy the structure of NaP zeolites synthesized at optimal concentrations. Via the evaluation of Zn(II) adsorption, the NaP-SDBS zeolite showed the adsorption removal rate of 96.27% and the main adsorption manner was the ion exchange. Meanwhile, through the five times adsorption — desorption cycles, the adsorption properties of Zn(II) by NaP zeolites still reached above 95.30%, which demonstrated that NaP zeolite adsorbent is effective in treating industrial sewage. [Display omitted] • The grain size of NaP zeolite decreased by introducing the ionic surfactants. • The dispersion of NaP zeolite crystals was improved via the steric hindrance effect. • The steric hindrance and electrostatic interaction acted in synergy for NaP zeolite. [ABSTRACT FROM AUTHOR]