Evolution of nucleation/growth kinetics for NaP zeolite crystals and the adsorption removal of phenol compound

Abstract

AbstractThe NaP zeolite with excellent crystallinity and adsorption performance was obtained by adopting the Na2SiO3 and NaAlO2 from coal fly ash as the raw materials. As the synthesis condition of aging for 0.5 h at 30°C and crystalizing for 8 h at 120°C with n(H2O)/n(SiO2) = 116, n(Na2O)/n(SiO2) = 1.4, and n(SiO2)/n(Al2O3) = 2.8, NaP zeolite owned higher crystallinity (98.98%) and spherical morphology (∼2.78 μm). During the crystallization, the nucleation/growth kinetics was calculated to survey the crystallization mechanism via the theoretical calculation and characterization methods. The diffusion of reactants in the solid–liquid‐phase interface was dominant, wherein the heterogeneous nucleation and solid‐phase transformation were also proposed based on the fitting results of Avarami–Erofeev and simple kinetic equations. The activation energy results of nucleation (En, 27.67 kJ/mol) and growth (Eg, 13.31 kJ/mol) demonstrated that the induced nucleation period was the critical step during the crystallization. Hence, the method of rapid nucleation was introduced and the induced nucleation time was shortened 50% (from ∼2.0 to ∼1.0 h) as the crystal seed was added. Moreover, the grain size of NaP‐Seed zeolite reduced to ∼2.02 μm. Meanwhile, the synthesized NaP zeolite adsorbent was employed for the removal of phenol compound from the aqueous solution. Under the synergistic effect of electrostatic interaction and pore filling effect, NaP zeolite exhibited better adsorption with the removal rate of 82.63% (pH = 5.0 and 40 min) and stability in the five consecutive cycles.