Batch adsorption of p-nitrophenol by ZSM-11: equilibrium, kinetic, and thermodynamic studies

In this study, ZSM-11 zeolite was successfully prepared by direct hydrothermal synthesis using silica sol as silicon source and tetrabutylammonium hydroxide as organic structure directing agent. X-ray diffraction confirmed the prepared product was well-crystalline ZSM-11 zeolite. Scanning electron microscopy showed that a single particle of the prepared product had a mean size of approximately 2.5mx6m. Batch adsorption experiments exhibited that solution pH, ZSM-11 dosage, and NaCl concentration had effects on PNP (p-nitrophenol) removal. A high adsorption capacity of 56.3mg/g was obtained at pH 4, 25 degrees C, ZSM-11 dosage of 0.3g/L, and initial PNP concentration of 20mg/L. The addition of NaCl (5.8-580mg/L) exerted a positive impact on PNP adsorption. Results of desorption experiments showed that a desorption percentage of 78.9% could be obtained in 120min using 1.44% NaOH solution as desorbent. The equilibrium adsorption data of PNP onto the as-prepared samples were well fitted by the Freundlich isothermal model in the temperature range 25-45 degrees C. The adsorption kinetics was found to obey the pseudo-second-order model. Thermodynamically, it was found that the adsorption of PNP onto ZSM-11 was spontaneous and enthalpy-driven with H degrees=-10.96kJ/mol. The ZSM-11 samples were found to be effective adsorbent for the removal of PNP from wastewater.