Journal of Environmental Science and Health, Part B Pesticides, Food Contaminants, and Agricultural Wastes ISSN: 0360-1234 (Print) 1532-4109 (Online) Journal homepage: https://www.tandfonline.com/loi/lesb20 Adsorption of picloram on clays nontronite, illite and kaolinite: equilibrium and herbicide-clays surface complexes Jose L. Marco-Brown, Eric M. Gaigneaux, Rosa M. Torres Sánchez & María dos Santos Afonso To cite this article: Jose L. Marco-Brown, Eric M. Gaigneaux, Rosa M. Torres Sánchez & María dos Santos Afonso (2019): Adsorption of picloram on clays nontronite, illite and kaolinite: equilibrium and herbicide-clays surface complexes, Journal of Environmental Science and Health, Part B To link to this article: https://doi.org/10.1080/03601234.2018.1561055 View supplementary material Published online: 12 Feb 2019. Submit your article to this journal View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=lesb20 JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH, PART B https://doi.org/10.1080/03601234.2018.1561055 Adsorption of picloram on clays nontronite, illite and kaolinite: equilibrium and herbicide-clays surface complexes Jose L. Marco-BrownaÃ, Eric M. Gaigneauxb, Rosa M. Torres Sanchezc, and Marıa dos Santos Afonsoa aFacultad de Ciencias Exactas y Naturales, Departamento de Quımica Inorganica, Analıtica y Quımica Fısica, and CONICET-Universidad de Buenos Aires, Instituto de Quımica Fısica de los Materiales, Medio Ambiente y Energıa (INQUIMAE), Ciudad Universitaria Pabellon II 3er Piso, Int. Guiraldes€ 2160 (C1428EHA), Universidad de Buenos Aires, Buenos Aires, Argentina; bInstitute of Condensed Matter and Nanosciences (IMCN), Division Solids, Molecules and Reactivity (MOST), Universite Catholique de Louvain, Louvain-la-Neuve, Belgium; cCONICET-CCT La Plata-CIC, CETMIC (Centro de Tecnologıa en Recursos Minerales y Ceramica), M. B. Gonnet, Argentina ABSTRACT ARTICLE HISTORY The picloram (PCM) adsorption on nontronite, illite and kaolinite was studied at pH 3, 5 and 7. Received 12 July 2018 The adsorption isotherms had well-fitted to Langmuir and Freundlich models equations. The inter- Accepted 12 December 2018 actions of PCM with the clay mineral surfaces exhibited an anionic profile adsorption, with a KEYWORDS decrease in adsorption when the pH increases. The PCM adsorption capacity increases in the fol- lowing order: kaolinite < illite < nontronite. The X-ray diffraction (XRD) analysis of PCM-clay sam- Adsorption; picloram; herbicide; clays; XPS; ples revealed that the picloram molecule does not enter into the clays basal space. The surface complexes interaction of PCM with clays surface sites through nitrogen of the pyridine ring was confirmed by X-ray photoelectron spectroscopy (XPS). Due to the anionic form of PCM, the adsorption onto the external and edges surface sites of the clay minerals was proposed. Introduction The interaction between pesticides and clays takes singu- lar importance in processes related to the environmental dis- It is well know that the environmental behavior of raw and sipation of these compounds and in pollutants mitigation or synthetic chemicals is a dynamic phenomenon. After pesti- remediation process. cide application, the excess of pesticide, non-absorbed by Clays and clay-composites have been extensively proposed weeds, is partially vaporized to the atmosphere, runoff to as effective low cost absorbents for certain dyes and other surface water and also leached below root zone. These losses organic and inorganic pollutants.[6,7] However, given the in the amount of the applied pesticide would reach streams, enormous complexity of these adsorption processes in the rivers and lakes, or leach through soil with the possibility to environment, the use of simple pollutant-clay models acquires [1,2] contaminate subsurface water. great importance and interest to thoroughly understand the Picloram, 4-amino-3,5,6-trichloropyridine-2-carboxilic acid basic interactions between adsorbate and sorbate.[8] (PCM), is a synthetic organic chemical belong to the pyridine The edges and the faces of clay particles can adsorb anions, family with herbicide activity that regulates plant growth. It is cations, nonionic and polar contaminants from natural water. used to control unwanted broadleaf weeds, deeply rooted herb- Indeed, chemical groups in the surface of clay particles, and aceous weeds and woody plants in cereals such as barley, the pH value of the media, could play an important role in [2,3] wheat, sugarcane and oats. The maximum level of picloram adsorption processes.[9,10] To understand the active surface À1 contamination in drinking water is 0.5 mg L (2.07 lM), as sites of some clays (as montmorillonite, nontronite (N), illite was recommended by the EPA (Environmental Protection (I) and kaolinite (K)), it must be noted the following differen- Agency, USA). Picloram was recently detected in fresh water ces among them. Montmorillonite, nontronite and illite are 2:1 in a concentration of 0.3 lgLÀ1 (1.24 Â 10À3 lM) and its or TOT clay mineral, formed by layers constituted by two occurrences showed a seasonal pattern.[2] tetrahedral (T) sheets with silicon atoms at the center of each PCM has an anionic character at the pH of most soils tetrahedron and one octahedral (O) sheet with aluminum and water environments (pKa 2.3), causing a very low atoms at the center of each octahedron, sandwiched within the sorption on soil particles. As a consequence PCM was classi- two tetrahedral sheets. Montmorillonite and nontronite present fied as a pesticide with a high leaching potential.[4,5] isomorphic substitutions in their structures; the permanent CONTACT Jose L. Marco-Brown [email protected], [email protected] Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Quımica Inorganica, Analıtica y Quımica Fısica, and CONICET-Universidad de Buenos Aires, Instituto de Quımica Fısica de los Materiales, Medio Ambiente y Energıa (INQUIMAE), Ciudad Universitaria Pabellon II 3er Piso, Int. Guiraldes€ 2160 (C1428EHA), Buenos Aires, Argentina ÃPresent address: Instituto de Investigacion e Ingenierıa Ambiental (3iA), Escuela de Ciencia y Tecnologıa, CONICET, Universidad Nacional de San Martın, Av. 25 de Mayo y Francia, 1650, General San Martın, Buenos Aires, Argentina Supplemental data for this article can be accessed here. ß 2019 Taylor & Francis Group, LLC 2 J. L. MARCO-BROWN ET AL. – À3 [11] charge of the structure has a non-zero value (0.2 0.6), so the water 430 ppm (1.78 Â 10 M), pKa ¼ 2.3. , M.W. ¼ 241. existence of hydrated cations in the interlayer compensates for 5 g.molÀ1) and used as received. All other chemical reagents the negative charge that the structure presents at typical envir- were provided by Merck PA and used without any further onmental pH. This property of montmorillonite and nontron- purification. Water was purified in a Milli-Q system from ite to house cations and their respective spheres of hydration Millipore Inc. in their interlayer give them the characteristic of being expand- Nontronite (hereafter labeled N) and illite (labeled I) able clay minerals, so the interlayer spacing depends on the were provided by Ward’s Natural Science Establishment, cations and the amount of water they can retain. The exchange Inc., USA, #49E5108 and #46E0315, respectively. Kaolinite of raw inorganic cations by organic ones at the interlayer ena- (labeled K), was provided by Georgia Kaolin, 6-Tile, 99%. N, bles these inner surface sites for adsorption. I and K were manually grinded in an agate mortar and Illite has more aluminum atoms in its tetrahedral layer sieved to a particle size less than 125 mm. than montmorillonite or nontronite, which gives it a higher The main properties for N, I and K were (i) cation permanent negative charge in its structure and can have a exchange capacity (CEC) of 112, 32 and 40 meq/100g deter- non-zero value of up to 0.8, so the charge compensation is mined by the ammonium method,[17] (ii) isoelectric point þ only given by the presence of K cations in its interlayer, (IEPpH) of 5.1, 7.1 and 2.8 determined by diffusion potential which are not available for ion exchange. These characteristics method[18] and (iii) purity >98% determined by XRD[19] for make it lose the capacity of expansion of the interlaminar all minerals. spacing by the entrance of other cations or water molecules. The structural formula, including isomorphic substitu- þ Kaolinite, a 1:1 or TO clay mineral, has very few iso- tions, as [(Si3,42Al0,58)(Al0,63Fe1,28Mg0,09)O10(OH)2]M 0,57 morphic substitutions, so the permanent charge of the struc- for N, and as [(Si3,94Al0,06)(Al1,43Fe0,27Mg0,26)O10(OH)2] þ ture tends to zero, which means that this mineral does not M 0,32 for I, were determined from the chemical analysis need the presence of ions in its interlayer as its structure following the method of Siguin et al.[20] Structural formula does not need to be charge-compensated. Consequently, the of the kaolinite was not determined due to it requires com- layers (TO) of the kaolinite are joined through hydrogen plementary analyzes to discern whether Fe and Ti (expressed bridges, so that this clay mineral does not exhibit interlayer as oxides) are components of the structure or are separated spacing as presented by some 2:1 minerals. from it as oxides. Pyridine-based and acidic pesticides have in their struc- The specific surface area SN2 was determined by nitrogen ture pyridine and carboxylate chemical groups with basic adsorption at 77 K on samples previously dried at 100 C for properties that can coordinate to the metal centers of the 6 h at high vacuum using a Micromeritis AccuSorb 2100 E adsorbent surface. PCM molecule (supporting information equipment. The SN2, calculated using the BET method, was Figure S1) could be used as pyridine-based or acidic pesti- 83, 6 and 3 m2/g for N, I and K, respectively.