Vol.:(0123456789) 1 3 Applied Physics A (2020) 126:641 https://doi.org/10.1007/s00339-020-03814-w PEG‑assisted synthesis and formation mechanism of Mg(OH) 2 nanostructures using natural brine Sadegh Yousef 1  · Behrooz Ghasemi 1  · Mohammad Tajally 1 Received: 7 April 2020 / Accepted: 16 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract In this study, magnesium hydroxide nanofakes (MHF) were synthesized using poly(ethylene glycol) (PEG 4000) sur- factant by exploiting chemical precipitation method from an impure brine enriched by large amounts of CaCl 2 for the frst time. Synthesized samples were characterized by X-ray Difraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and UV–Vis absorption spectroscopy. The efect of PEG on structural and morphological characteristics of synthesized samples, as well as the formation mechanism of MH nanostructures from the brine in the presence or absence of PEG (0, 5 and 10 mL), were precisely investigated. Obtained results implied the positive efect of the used surfactant on the uniformity of the morphology, the agglomeration behavior of MH nanoplates, and the decrease of the crystallite size (from 25.26 to 19.35 nm) of synthesized nanoparticles from the brine, which the optimum amount of this surfactant was 5 mL. In addition, UV–Vis spectroscopy results and investigation of optical properties showed that the presence of PEG led to an increasing in the value of the optical bandgap energy of MHF from 4.7 to 5 eV, indicating their ability to be used in optoelectronic nano-devices. Keywords Synthesis · Crystal growth · Mg(oh) 2  · Nanostructures · PEG · Brine 1 Introduction Magnesium hydroxide (MH) is an important inorganic material and is usually extracted from seawater or brine via precipitation process [1]. This chemical has attracted much attention due to its environmentally friendly, alka- linity, hydrophilicity, low fammability, nontoxic, noncor- rosive, and thermally stable behavior [2, 3] and has many applications due to its well-known physical and chemical properties. Besides that, nano-MH can be widely exploited in acidic waste neutralizer, papermaking industry, fertilizer additive [4, 5], chemical sensors [6], pharmacy [4], fame- retardants [7], nano-MgO production [8, 9], as a fller of polyurethane composite foams for improved sound absorp- tion [10], solar cells and submicron optoelectronics devices [11], several routes have been utilized to synthesize its nanostructures, such as sol–gel method [12], hydrothermal route [13], chemical precipitation method [14], microwave- assisted method [11], sonochemical method [15, 16]. Researchers believe that the shape and crystal size of nano- structures are strongly depended on the preparation process and the precursors [17]. The formation mechanism of MH nanostructures have been reported in several literature [5, 11, 14, 18, 19] and synthesize and study of its growth mechanism from impure precursors has been limited. In addition, several surfactants have been widely used to control the shape and crystal size of MH nanoparticles [19–23]. The surfactants such as poly(ethylene glycol) (PEG) are used as control of crystal growth, particle size and structure of nano-MH. An et al. [24] synthesized superfne ordered arrays of magnesium hydroxide (MH) nanoparticles via a direct precipitation method at room temperature through aging with a cationic surfactant, cetyl trimethylammonium bromide (CTAB) as crystal modifying agent. Pilarska et al. [25] studied the efect of type and con- centration of modifers (poly(ethylene glycol)s, PEG 200, PEG 8000 and PEG 20000) on the physicochemical and functional properties of magnesium hydroxide obtained by precipitation, and its calcinate magnesium oxide. They proved that the pres- ence of a modifer did not change the crystalline structure of * Sadegh Yousef s.yousef@semnan.ac.ir 1 Faculty of Metallurgy and Materials Science, Semnan University, Semnan, Iran