Regulating the particle sizes of NaA molecular sieves toward enhanced heavy metal ion adsorption

Abstract

Heavy metal ions have a serious effect on humans and the ecosystem. Molecular sieves have attracted significant attention in heavy metal ion adsorption with distinct microporosity and uniform pore size. In this paper, we successfully synthesized nano-sized NaA molecular sieves in the presence of an organic templating agent while aluminum isopropoxide and silica sol were used as the aluminum and silica sources. To synthesize molecular sieves of the ideal size, the anionic cation concentration and templating agent were adjusted. The findings of Cu(II) and Pb(II) adsorption on NaA molecular sieves showed that under the ideal conditions of adsorption time at 90 minutes, pH = 5, adsorption temperature at 25 °C, and starting adsorbent concentration at 100 mg g⁻¹, the optimal adsorbing capacity could reach 230 mg g⁻¹ and 600 mg g⁻¹, respectively. Isotherm, kinetic, thermodynamic and reusability studies of heavy metal ion adsorption on NaA molecular sieves were carried out to investigate the adsorption kinetics. This work provides a new avenue to regulate the particle sizes of molecular sieves to enhance the adsorption capacity of heavy metal ions.