Rev. Chim. ♦ 71 ♦ no. 2 ♦ 2020 ♦ https://revistadechimie.ro 10 https://doi.org/10.37358/RC.20.2.7878 Influence of Precipitating Agent Concentration on Nanoparticles Size and Magnetic Properties of Zinc Ferrites ELENA VASILICA TRANDAFIR 1 *, RADU CIOCARLAN 2 , AUREL PUI 2 , ROLF HEMPELMANN 3 , OVIDIU FLORIN CALTUN 1 1 Alexandru Ioan Cuza University of Iasi, Faculty of Physics, 11 Blvd. Carol I, 700506, Iasi, Romania 2 Alexandru Ioan Cuza University of Iasi, Faculty of Chemistry, 11 Blvd. Carol I, 700506, Iasi, Romania 3 Physikalische Chemie, Universitaet des Saarlandes, Saarbruecken, Germany A series of Zn ferrite nanoparticles was prepared by varying the concentration of precipitating agent (NaOH) in the range of 1 – 5 M. Carboxymethylcellulose (CMC) was used as capping agent for stabilizing the particles and to prevent agglomeration. The synthesis done at low temperature was followed by a thermal treatment at 500ºC for 6 h in air. The crystallite size determined using Scherer formula ranged between 8 - 10 nm while the nanoparticles average size observed by Transmission Electron Microscopy varied in between 7-10 nm showing that the increase of coprecipitation agent concentration influences the particles growth. Vibrating sample magnetometry confirmed the strong influence that nanoparticles morphology and size play on superparamagnetic properties of Zn ferrite. Keywords: zinc ferrite; nanoparticle; coprecipitation; NaOH concentration; X-Ray diffraction New studies regarding zinc ferrites nanoparticles were developed for introducing the importance of small concentration of the precipitating agent during the synthesis step. In the last years Zn ferrite nanoparticles were reconsidered for different application such as hyperthermia [1], contrast agents [2 - 5], drug delivery [6], theranostic [7] due to their biocompatibility. Moreover this material is also being used for industrial application as waste water treatment [8], environmental protection [9] as well as gas sensing [10] and the list of possible application can continue. In bulk ZnFe2O4 has a normal spinel structure, in which all Zn 2+ ions occupy tetrahedral positions (A-sites) and all Fe 3+ ions octahedral positions (B-sites) being paramagnetic at room temperature, the transition to a magnetically ordered state occurs only at temperatures of about 10 K [11]. Magnetic properties of spinel ferrite nanoparticles are different from those of bulk materials and substantially depend on the particle size [12], [13]. The magnetic properties change significantly when the particle size decreases to a few tens of nanometers because at this scale cations’ inversion occurs, i.e. a part of zinc ions occupy the sites B, and part of iron ions the sites A [14] and the spinel structure become a mixed one and as consequence to the apparition of spontaneous magnetization [15]. Among the various preparation methods developed to produce Zn ferrite nanoparticles, such as reverse micelle [16], sol-gel [17], hydrothermal [11], the coprecipitation is the most used. A big part of literature reports the synthesis of ferrites from nitrate precursors [11, 18–29] but special attention is recently given to metallic chlorides precursors [30]–[40] due to the higher solubility in water of the resulted sodium chloride compared to the sodium nitrite [32, 33, 37, 38]. Depending on the synthesis media, aqueous or not, on the coprecipitation agent concentration or the pH of the solution or of the subsequent thermal treatment different grade of inversion is realized. The percentage of Fe ions in octahedral (Fe 3+ ) and tetrahedral (Fe 2+ ) sites varies and the magnetization of the two sub-lattice do not compensate and the nanoparticles behaves magnetic or superparamagnetic above room temperature. It is well known that the influence of the coprecipitation agent in the solution [41, 42] and the annealing treatment [38, 43–45] can influence dramatically the crystallite growth. The main goal of our study was to prepare ZnFe2O4 capped nanoparticles by simple aqueous coprecipitation of zinc (II) chloride and ferric (III) chloride solutions using NaOH as alkali and carboxymethylcellulose (CMC) as surfactant [34, 37]. By varying the concentration of NaOH, we expect to impose a certain particle shape which can lead to different grain size and consequently better tuning of magnetic properties. The variations in particle size and shape induced predominant changes in the magnetic behaviour of zinc ferrite powders. Experimental part Zinc ferrite nanoparticles were prepared by coprecipitation route using five mixed aqueous solutions of 0.2 M ZnCl2 and 0.4 FeCl3 • 6H2O, following the synthesis protocol described in [49]. The obtained samples are noted in this manuscript as ZFO nM, where n = 1÷5. Characterization Crystal phase formation of the annealed samples was checked by powder X-ray Diffraction (XRD) using the X-ray diffractometer type X’Pert Pro MPD diffractometer by PANalytical B. V. with Cu Kα radiation, λ = 0.15406nm. The *email: gafton.vasilica@gmail.com