Polyaniline and its composites with zeolite ZSM-5 for efficient removal of glyphosate from aqueous solution

Nanostructured and granular polyanilines (PANIs) and their composites with zeolite ZSM-5, synthesized by the oxidative polymerization of aniline in water and aqueous solution of sulfuric acid, are evaluated as adsorbents of the organic herbicide glyphosate [N-(phosphonomethyl)glycine] in aqueous solution. The protonated and deprotonated forms of synthesized materials were characterized by elemental and thermogravimetric analysis, scanning electron microscopy, FTIR, Raman and UV-Vis spectroscopies, X-ray powder diffraction, and nitrogen physisorption measurements. The adsorption isotherms of glyphosate on studied materials were best fitted by Freundlich and Langmuir-Freundlich models. The adsorption characteristics of the investigated PANIs and PANI/ZSM-5 composites were found to be much more influenced by the oxidation state and protonation level of PANI in the adsorbents then by the textural and morphological properties of materials. The highest adsorption of glyphosate among all investigated PANI and PANI/ZSM-5 samples, as well as pure ZSM-5, exhibited the deprotonated granular PANI which was synthesized in sulfuric acid medium (98.5 mg/g). High adsorption capacity also showed the deprotonated PANI/ZSM-5 composite with similar to 50% of zeolite (61.9 mg/g) and the protonated nanostructured PANI (59.9 mg/g), both materials prepared in water without added acid.