Removal of herbicide from aqueous solution: evidence of 2-ethyl-6-methylaniline adsorption in synthetic ZSM-12 zeolite

In the last decades, the widespread use of pesticides in modern agriculture is becoming an important environmental problem due to their persistence in the aquatic systems for many years after their application [1]. Chloroacetanilides and their degradation products are frequently detected in surface and subsurface water due to the relatively high water solubility, high potential to leach and migrate through the soil and contaminate ground water. In this study the capability of ZSM-12 zeolite for 2-ethyl-6-methylaniline (C2H5C6H3(CH3)NH2, labelled EMA) removal from water was evaluated by combining chromatographic, thermogravimetric and synchrotron X-ray powder diffractometric techniques. The adsorption isotherm was determined using the batch method. The EMA concentration in the aqueous solution was determined by Headspace Gas Chromatography coupled to Mass Spectrometry (HS-GC-MS). XRD patterns of ZSM-12 containing 6-azonia-spiro-[5,5]-undecane as structure directing agent (ZSM-12-SDA), calcined ZSM-12 (ZSM-12-c) and calcined and EMA loaded ZSM-12 (ZSM-12-EMA) were collected at the MCX beamline of Elettra-Sincrotrone Trieste (0.827Å fixed wavelength). Thermal analyses (TG and DTA) of all samples were performed in air at up to 900 °C (10°C/min heating rate). Rietveld refinement revealed the incorporation of about 4 EMA molecules per unit cell, in very good agreement with the weight loss given by TG analyses and with the saturation capacity determined by the adsorption isotherms. The rapid kinetic combined with the good adsorption capacity suggested that ZSM-12 represent a promising future candidate as an environmentally friendly alternative in the removal of acetanilides compounds from water. [1] Otero R., Fernández J. M., Ulibarri M. A., Celis R., & Bruna F. (2012). Adsorption of non-ionic pesticide S-metolachlor on layered double hydroxides intercalated with dodecylsulfate and tetradecanedioate anions. Applied Clay Science, 65, 72-79.