Paraquat adsorption on NaY zeolite at various Si/Al ratios: A combined experimental and computational study

NaY samples in the crystalline form with Si/Al ratios from 2.15 to 2.40 were synthesized as adsorbents for paraquat. Their surface areas, particle size, concentration of basic sites decreased with an increase of Al content in the synthesis gel. The interaction between paraquat molecule and NaY zeolite was investigated by periodic DFT calculations to understand the adsorption behavior. Paraquat adsorption by all samples fit with Langmuir model. The capacity of the adsorbents was in the range of 210-240 mg/g-adsorbent, higher than NaY in the previous reports. After paraquat adsorption, the surface areas of the samples decreased from around 800 to 30 m(2)/g indicating that paraquat adsorbed inside the zeolite pores. FAU samples with the highest Si/Al ratio (2.40) had the highest adsorption capacity in line with the results from the DFT calculations. The paraquat molecules located close to the negatively charged fragments of the zeolite framework, due to the electrostatic interaction with the positively charged ammonia groups of the organic molecule.