Rapid and Eco-Friendly Synthesis of Mordenite Zeolite with Excellent Adsorption Ability to Wastewater Ammonium

A green one-step hydrothermal method was employed to prepare mordenite (MOR) zeolite for removing ammonium (NH4+) from wastewater, in which no organic template was used during the synthesis, while the hydrothermal time was effectively shortened to 12 h. Scanning electron microscopy images showed a prism-packed spherical structure of the synthesized MOR zeolite, with the NaOH/Si ratio being the main factor affecting the zeolite structure. The synthesized MOR zeolite with an adsorption capacity of 32.76 mg NH4+-N/g derived from the Langmuir isotherm could realize a quick establishment of the adsorption equilibrium within 5 min at a dosage of 2.0 g/L, and the adsorption kinetics were better described by the pseudo-second-order kinetic model. On the other hand, the MOR zeolite also demonstrated a stable performance and a reasonably good reusability under complex conditions, e.g., more than 90% of ammonium was removed after four cycles of reuse. Furthermore, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) revealed that the adsorption mechanism mainly included surface electrostatic interaction and ion exchange with the sodium ion. Consequently, the MOR zeolite prepared in this study can be considered a promising adsorbent for the fast and efficient removal of ammonium from wastewater.