Macro- and Micronutrient Simultaneous Slow Release from Highly Swellable Nanocomposite Hydrogels Adriel Bortolin, †,‡ Andre ́ R. Serafim, † Fauze A. Aouada, †,§ Luiz H. C. Mattoso, †,‡ and Caue Ribeiro* ,†,‡ † National Nanotechnology Laboratory for Agribusiness, EMBRAPA-CNPDIA - Rua XV de Novembro, 1452, Sã o Carlos, SP 13560-970, Brazil ‡ PPGQ, Department of Chemistry, Federal University of Sã o Carlos - Rodovia, Washington Luís, Km 235, Sã o Carlos, SP 13566-905, Brazil * S Supporting Information ABSTRACT: Clay-loaded hydrogels have been arousing great interest from researchers and academics due to their unique properties and broad applicability range. Here we developed hydrogel-based nanocomposites intended for slow/controlled release of macro- and micronutrients into independent or concurrent systems. The produced nanocomposites underwent a hydrolysis treatment that improved their physicochemical properties. We obtained materials capable of absorbing water contents 5000 times greater than their weights, an outcome that makes them promising, particularly if compared with commercially available materials. Though swelling degree was affected by the presence of calcium montmorillonite (MMt), MMt has increased nutrient (urea and boron) loading capacity and, as a consequence of its interaction with the studied nutrients, has led to a slower release behavior. By evaluating the simultaneous release behavior, we observed that both the ionic (sodium octaborate) and the nonionic (urea) sources competed for the same active sites within the nanocomposites as suggested by the decreased loading and release values of both nutrients when administrated simultaneously. Because of its great swelling degree, higher than 2000 times in water, the nanocomposites formulated with high MMt contents (approximately 50.0% wt) as well as featuring high loading capacity and individual (approximately 74.2 g of urea g -1 of nanocomposite and 7.29 g of boron g -1 of nanocomposite) and simultaneous release denote interesting materials for agricultural applications (e.g., carriers for nutrient release). KEYWORDS: swelling degree, hydrolysis, nanocomposite, nanoclay, simultaneous release ■ INTRODUCTION Soil nutritional control plays, alongside other parameters, an essential role in assuring the efficiency of crops by affecting their yield and quality. Therefore, specific macro- and micronutrients must be spread in a controlled fashion in order for them to reach an ideal performance. The conventional means of nutrient spreading, however, present several draw- backs mostly related to their low efficiency and tough control, as well as high cost and waste. 1 To overcome these hurdles, scientific/technological strategies have been developed, such as slow/controlled release systems. Several materials have been used for this purpose, among which hydrogels stand out as a promising alternative to deliver agricultural nutrients. 2 Modified (e.g., clay-added) hydrogels have aroused growing interest because they feature improved key properties. 3 It is highly desirable to take advantage of the superior properties of hydrogel-based nanocomposites to manage essential nutrients in a rational manner. Furthermore, the addition of high clay loads may contribute to a cheaper product with increased feasibility for agricultural applications when compared to the commercially available polyacrylamide (PAAm)-based ones. 4 The nutrients commonly used in agriculture are classified as macronutrients (i.e., those required in high contents and that are responsible for plant physical structure) and micronutrients (i.e., those used in low contents, which control plant growth stages such as germination, root growth, and leaf force). 5 In previous works, 4 our group has analyzed hydrogels as delivery systems for the macronutrient nitrogen (from urea). Though urea is highly soluble in water, it did not form ions in solution. Micronutrients are generally administered as salts, 6 which means that they may irreversibly adsorb to hydrogel structure. There is little published data on the controlled release of micronutrients from hydrogels. Although some authors studied hydrogel interactions with boron, 7-9 no previous works dealing with hydrogels as boron carriers were found in the literature. This study therefore aimed to produce nanostructured hydrogels as well as to assess the slow/controlled release of boron from 3 basic sources: boric acid, borax, and commercially available sodium octaborate. The novelty of this work is the evaluation of the nanocomposites’ behavior upon the simultaneous desorption of boron and urea, a micro and a macronutrient, respectively. The nanocomposites comprised polyacrylamide (PAAm) and carboxymethylcellulose (CMC). The latter was modified with different calcium montmorillonite clay (MMt) contents in an effort to improve some of the nanocomposites’ properties (e.g., nutrient sorption and desorption capacities, mechanical resistance, and water absorption rate) and, as a consequence, reduce the production cost of the final product. 4 Received: January 16, 2016 Revised: March 20, 2016 Accepted: April 4, 2016 Article pubs.acs.org/JAFC © XXXX American Chemical Society A DOI: 10.1021/acs.jafc.6b00190 J. Agric. Food Chem. XXXX, XXX, XXX-XXX