Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Effect of EDTA organic coating on the spin canting behavior of maghemite nanoparticles for lead (II) adsorption Juan A. Ramos-Guivar a, ⁎ , Elvis O. López b , Jean-Marc Greneche c , F. Jochen Litterst b,d , Edson C. Passamani e a Departamento de Física del Estado Sólido (DAFES), Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, P. O. Box 14-0149, Lima 14, Peru b Brazilian Center for Physics Research (CBPF), Rio de Janeiro, RJ 22290-180, Brazil c Institut des Molécules et Matériaux du Mans (IMMM UMR CNRS 6283), Le Mans Université, 72085 Le Mans Cedex, France d Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, 38106 Braunschweig, Germany e Physics Department, Federal University of Espírito Santo, Vitória, ES 29075-910, Brazil ARTICLE INFO Keywords: EDTA Maghemite nanoparticles Spin canting Lead adsorption ABSTRACT EDTA functionalized γ-Fe 2 O 3 nanoparticles, with controlled-sizes between 4 and 8 nm and specific surface areas up to 272 m 2 /g, were prepared using modified co-precipitation routes and systematically characterized using local, surface and global experimental methods. The functionalized nanoparticles behave as a magnetic trilayer- like system formed by ferrimagnetic spinel-like grains, a spin-glass-like layer as a spacer, and a cover of iron hydroxide layer with antiferromagnetic interactions. The fraction of the Fe canted spins in the spacer layer and the specific surface area are directly related to the amount of the iron hydroxide thin layer. Small (large) amounts of the iron-hydroxide layer on the nanoparticle surfaces reduce (increase) the canted Fe spin fraction, decreasing (increasing) the exchange bias effect found in the functionalized NPs. The nanoparticles with the largest specific area were applied for Pb(II) adsorption and showed a reduction of Pb(II) concentration in contaminated water to a limit less than 10 μg L −1 for an equilibrium time of 7 h. The EDTA tailored γ-Fe 2 O 3 nanoparticles showed efficient Pb(II) adsorption, easy magnetic removal, and recycling properties, making this nanohybrid adsorbent a good potential candidate for a water cleaning process. 1. Introduction In functionalized Fe oxide-based nanoparticle systems, there are several issues that still need to be understood. For instance, in an as- sembly of magnetic nanoparticles (NPs), the chemical configuration of the surface depends on the hydrodynamic size of the NPs [1,2], and the point of zero charge is severely affected by agglomeration, surface oxidation, and functionalization [3,4]. These effects can strongly affect the NPs magnetization, the presence of an exchange bias (EB) effect and the adsorption process itself, reducing the magnetic separation prop- erties by the formation of a magnetic dead layer and related surface phenomena [5–7]. Therefore, the surface properties (magnetic dead layer, spin structure, valence state, surface phase, etc.) need to be thoroughly studied since the adsorption processes are based on surface phenomena. Thus, in Fe oxide-based NPs, 57 Fe Mössbauer spectrometry (a high-resolution method) is a good tool to get local information about the above issues, in particular, the Fe spin structures that occur in grain core as well as in grain surface [8]. More specifically, the spin canting effect in magnetic NPs is an in- teresting topic in the field of nanomagnetism [9–11], especially in magnetic NPs with a diameter smaller than 10 nm, where surface magnetic effects are noticeable due to translational symmetry breaking. Their canted spins can lead to a collective spin-glass-like (SGL) behavior and/or surface spin disorder [7,11–12], causing the exchange bias (EB) effect in magnetic NPs [10,11]. It has also been proposed to reduce the spin canting effect by functionalizing the magnetic NPs with organic molecules/layers [5,9,12]. Other authors have also shown the absence of the spin canting effect in 40 nm oxidized Fe 3 O 4 NPs functionalized by covalent bonding to phosphonate [6]. On the other hand, in a previous work [12], based on DC/AC magnetic measurements, the suppression of the EB effect was assumed to occur due to monodentate coordination between iron core atoms and carboxyl ethylenediaminetetraacetic acid (EDTA) groups. The presence of the surface spin canting effect was, however, not demonstrated so far in the configuration of chelating magnetic NPs, consequently the EB effect is still not clearly understood. The surface spin canting effect has been studied in several systems https://doi.org/10.1016/j.apsusc.2020.148021 Received 27 June 2020; Received in revised form 28 September 2020; Accepted 28 September 2020 ⁎ Corresponding author. E-mail address: juan.ramos5@unmsm.edu.pe (J.A. Ramos-Guivar). Applied Surface Science 538 (2021) 148021 Available online 01 October 2020 0169-4332/ © 2020 Elsevier B.V. All rights reserved. T