Optimization of different wet chemical r

Ceramics International xxx (xxxx) xxx–xxx Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Optimization of different wet chemical routes and phase evolution studies of MnFe2O4 nanoparticles Mirza Mahmood Baiga,∗∗, Muhammad Asif Yousufa, Philips Olaleye Agboolab, Muhammad Azhar Khanc, Imran Shakird, Muhammad Farooq Warsia,∗ a Department of Chemistry, The Islamia University of Bahwalpur, 63100, Pakistan College of Engineering Al-Muzahmia Branch, King Saud University, PO-BOX 800, Riyadh, 11421, Saudi Arabia c Department of Physics, The Islamia University of Bahwalpur, 63100, Pakistan d Sustainable Energy Technologies Center, College of Engineering, King Saud University, Riyadh, Saudi Arabia b A R T I C LE I N FO A B S T R A C T Keywords: MnFe2O4 Monodisperse Dodecanol Single phase Micro-emulsion XRD Facile and low cost micro-emulsion method for the synthesis of single phase manganese ferrite (MnFe2O4) nanoparticles was explored In an attempt to synthesize monodisperse and single phase manganese ferrite (MnFe2O4) nanoparticles, micro-emulsion method using different oil phases such as dodecanol, toluene and low cost paraffin was adapted Simple co-precipitation method was also followed for comparison purpose In this facile approach, the strategy to control the particle size at nano-level has been explained in detail Formation mechanism of single phase manganese ferrite and appearance of different phases (such as goethite, manganite, hematite, hausmanite, maghemite, magnetite, etc) by these synthesis methods have been investigated and discussed The samples were annealed at various temperatures to probe the thermal stability Effect of annealing under air and under vacuum was studied Thermal gravimetric analysis (TGA) was used to study the phase transitions along with the investigation of appropriate annealing temperature for spinel ferrite formation X-ray Diffraction (XRD) analysis was used to study the crystal structure and phase identification Microstructural properties were studied using scanning electron microscopy (SEM) Fourier transform infrared spectroscopy (FTIR) was used to study the bond stretching (Metal-Oxygen) and cubic spinel structure of MnFe2O4 Introduction The state of the art magnetic materials i.e ferrites have become a considerable point of attraction because of comprising both electrical as well as magnetic properties [1] Among the nanostructured magnetic materials, spinel structure of ferrites has emerged as one of the interesting materials in the scientific research realm [2] Manganese Ferrite (MnFe2O4) that crystallizes in spinel structure found to be one of the versatile ferrites due to its distinctive physical and chemical properties [3] High magnetic permeability with high electric resistivity, low coercivity, moderate magnetic saturation, small magnetic anisotropy, mix valence states, high crystal symmetry and good chemical stability make it a promising candidate for application in sensors, transformers, filters, magnetic recordings, catalysis, biomedical, supercapacitors and many more [4] Preference of manganese ferrite to other ferrites like cobalt ferrite and nickel ferrite is due to its higher magnetic susceptibility along with ∗ its very low resistivity and consistency of its magnetic moment with Neel coupling scheme [5] High biocompatibility of manganese ferrite as compared to magnetite, hematite, cobalt ferrite and nickel ferrite make it very suitable for MRI based investigations [6] The morphology of spinel ferrites can be discussed on the basis of close-packed cubical arrangement of ions of oxygen, with manganese ions (+2) and iron ions (+3) located at two different A and B sites The A-site has tetrahedral (tetra) and B-site has octahedral (octa) oxygen ions coordination [7] Manganese ferrite in terms of the degree of inversion (fraction of divalent Manganese ions on Octahedral B-site represented by “i”) can be formulated as: [Mn1−i Fei]A-site(MniFe2−i)B-siteO4 When A-sites are occupied by all of Mn (2+) ions, it is referred as normal spinel having zero degree of inversion and when Mn (2+) ions are occupied on Bsites and Fe (3+) ions are divided equally between A (tetrahedral) and B (octahedral) sites, it is referred as inverse spinel having degree of inversion equal to one Typically, manganese based ferrites have a face Corresponding author Corresponding author E-mail addresses: farooq.warsi@iub.edu.pk (M.M Baig), mahmood.baig@iub.edu.pk (M.F Warsi) ∗∗ https://doi.org/10.1016/j.ceramint.2019.03.114 Received 13 December 2018; Received in revised form March 2019; Accepted 18 March 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l All rights reserved Please cite this article as: Mirza Mahmood Baig, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.03.114 Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Experimental work centered cubic (Fd3m) and partially inverted spinel structure having manganese (+2) ions on tetrahedral sites (predominantly) with degree of inversion equal to 0.20 Properties of ferrites are strongly interconnected with cations distribution [8–10] Properties of ferrites are tailored by synthetic strategies, stoichiometry, and the distribution of cations along with preference over tetrahedral A-site and octahedral Bsite [11] Ferrites have received/got importance, because their properties can be tuned by chemical manipulation easily by facile strategies [12] Tuning the size of ferrites to nano-scale further enhances the magnetic properties considerably [13] Magnetic properties, such as Neel temperature, magnetic anisotropy, and magnetization depend on the inversion degree which is re3+ sponsible for normal and inverse spinel structure as the Fe3+ (tetra)-Fe(octa) 2+ 3+ exchange interaction is dominant over Mn(tetra)- Fe(octa) interaction Different synthesis methods lead to the partial oxidation of Mn 2+ to Mn 3+ ions (having magnetic moment μB less than for Fe3+ ion i.e, μB) which shows preference towards octahedral sites and hence enhances the inversion degree that decreases the magnetization Low inversion degree is the key feature for enhancement in magnetization has been an experimental challenge for the scientists which strongly associated with way of synthesis and oxidation state of Manganese ions [14] Science and technology need advanced strategies for improving the physical, chemical and other properties of materials [15] In the near past, extreme keens have been disseminated to tailor the shapes and size of nano-materials and explaining the interconnection between the shapes and properties of materials Synthesis of shape-restrained system has been an experimental challenge for the scientists Achievements have been made in shape-control of nanomaterials It is obvious to develop the scientific routes to produce complex metallic oxides by shaping-reshaping process to enhance their electric and magnetic properties The most functional routes of synthesis of nanomaterials are co-precipitation, micro-emulsion, sol-gel (auto-combustion mechanism), hydrothermal and utilization of solvothermal and bio-mimetic [16] Despite, these methods are practiced to fabricate the nano-scale ferrites, overall the quality of the ferrites is poor with the large size distribution and size control is unapprised in many of these methods Mostly size variation is controlled by using post-synthesis annealing treatment at various temperatures, which affects the cations distribution [17] In addition, the major drawback is formation of αFe2O3 and decomposition of ferrites at high annealing temperature [18,19] In many of the above discussed methods, mostly the complication is at elevated temperature i.e especially coarsening and aggregation of particles [20] The utilization of micro-emulsion technique proved to be the best research process to control size of particles, their morphology, shape or geometry, surface area and homogeneity This method endorses the single-phase synthesis at very low temperature due to homogeneous mixing of primary precursor particles [21] In many of the above-discussed methods, mostly the complication observed at elevated temperature i.e especially coarsening and aggregation of particles [20] To synthesize de-agglomerated, monodisperse (narrow size distribution), porous, stable with high surface area nanoparticles, micro-emulsion technique is the most versatile preparatory technique [22–25] One of the advantages of micro-emulsion method over other methods is it facilitation for the formation of nano-environment (i.e nano-reactors) which leads monodisperse nanoparticles [26] To synthesize the single phase (by controlling the oxidation state of manganese ions), monodisperse, low cost, environmental friendly, porous and nano-sized manganese ferrite, we adopted several routes and finally achieved our goal as finding a new and cheap route i.e water in paraffin oil (micro-emulsion method) To the best of our knowledge, this optimized route to obtain single phase nanocrystalline MnFe2O4 has not reported previously 2.1 Chemicals All chemicals and solvents involved were of analytical grade and used without further purification Ferric nitrate (Fe(NO3)3.9H2O (Sigma-Aldrich ≥ 99%)), Manganese acetate Mn(CH3COO)2.4H2O (Merck, 99%), n-Hexadecyl trimethyl ammonium bromide (CTAB) C19H42NBr (Fisher Scientific UK 99%), 1-butanol (Merck, ˃98%), 1dodecanol (Sigma Aldrich), Sodium hydroxide (Merck, 99.98%), Methanol and ethanol(Merck, 98%), Ammonia 32% (BDH Chemicals), Paraffin oil (Merck), Triton X-100 (Sigma-Aldrich, 99%), Sodium dodecyl sulphate (Merck, 98.5%), Toluene (BDH, anhydrous 99.8%), Tetra butyl ammonium bromide (TBAB) (Sigma-Aldrich, 98%) 2.2 Synthesis by micro-emulsion method Sample-1: Manganese Ferrites (MnFe2O4) nanoparticles were prepared using CTAB/H2O/1-dodecanol weight ratio of 14:7:79 1-dodecanol (a long chain alcohol) was used as oil phase, CTAB used as a surfactant respectively In first step, metal salt solutions [0.1M Mn (CH3COO) and 0.2M Fe (NO3)3] were prepared in deionized water The required volumes of freshly prepared metal salt solutions were used These solutions were mixed with vigorous stirring The reaction mixtures were heated at 60 °C for 10 After that, micro emulsion (CTAB/H2O/1-dodecanol) were added in the reaction mixtures, and mixed up homogeneously for 20 35% NH3 solution was added drop wise to all six reaction mixtures to maintain pH at 11 All reaction mixtures were stirred vigorously for 90 The precipitates were washed with ethanol and then water several times and dried in oven at 150 °C The dried samples annealed at various temperatures in air for h Sample-2: Manganese Ferrites (MnFe2O4) nanoparticles were prepared using CTAB/H2O/(1- dodecanol+1-butanol) with weight ratio of 14:7: (39.5 + 39.5) 1-dodecanol (a long chain alcohol) was used as oil phase, CTAB used as a surfactant and 1-butanol as co-surfactant respectively In first step, metal salt solutions [0.1 M Mn (CH3COO) and 0.2 M Fe (NO3)3] were prepared in deionized water The required volumes of freshly prepared metal salt solutions were used The required appropriate volumes were mixed and these reaction mixtures were kept on vigorous stirring The reaction mixtures were heated at 60 °C for 10 After that, micro-emulsion CTAB/H2O/(1- dodecanol+1-butanol) were added in the reaction mixtures, and mixed up homogeneously for 20 35% NH3 solution was added drop wise to all six reaction mixtures to maintain pH at 11 All reaction mixtures were stirred vigorously for 90 The precipitates were washed with ethanol and then water several times and dried in oven at 150 °C The dried samples annealed at various temperatures in air for h Sample-3: Manganese ferrites (MnFe2O4) nanoparticles were prepared using SDS/H2O/Toluene SDS was used as surfactant and toluene as oil phase In first step, metal salt solutions [0.1M Mn (CH3COO) and 0.2M Fe (NO3)3] were prepared in deionized water The required volumes of freshly prepared metal salt solutions were used The solutions were mixed according to required stoichiometric ratio These solutions were mixed with vigorous stirring The reaction mixtures were heated at 60 °C for 10 After that, micro emulsion SDS/H2O/Toluene were added in the reaction mixtures, and mixed up homogeneously for 20 Fresly prepared NaOH solution was added drop wise to all six reaction mixtures to maintain pH at 11 All reaction mixtures were stirred vigorously for 90 The precipitates were washed with ethanol and then water several times and dried in oven at 150 °C The dried samples annealed at various temperatures under vacuum and in air for h Sample-4: Manganese ferrites (MnFe2O4) nanoparticles were prepared via low cost, micro emulsion system using Triton X-100/1-butanol/Paraffin (weight ratio of 10:25:40) Triton X-100, 1-butanol, Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Table Synthesis scheme for preparation of MnFe2O4 nanoparticles using various micro emulsion methods Samples Salt solution Micro emulsion Precipitating agent (To maintain pH = 11) Washing solvent Annealing temperature +0.2M Fe 3+ CTAB/H2O/1-dodecanol NH3 Ethanol/Water +0.2M Fe 3+ NH3 Ethanol/Water NaOH Ethanol/water NaOH Ethanol/water 900 °C(in air), 950 °C(in air) 900 °C(in air), 950 °C(in air) 400 °C(vacuum), 600 °C(in air) 400 °C(vacuum), 600 °C(in air), 800 °C(in air) 0.1M Mn 2+ M-2 0.1M Mn 2+ M-3 0.1M Mn2+ +0.2M Fe3+ CTAB/H2O/(1-butanol+ 1-dodecanol) SDS/H2O/Toluene M-4 0.1M Mn2+ +0.2M Fe3+ Triton X-100/1-butanol/paraffin oil M-1 of particles while the non-polar hydrocarbon tail gets attached with oil [29] Dodecanol being more hydrophobic and a long chain alcohol stabilizes the particles by adsorbing on the colloid at the smaller size which prevents and suppresses further growth of colloid that results in reduction of particle size [30] It was suggested that suppression of the nucleation of nanoparticles was done by the penetration of long chain alcohol into the palisade layer (i.e in the vicinity of hydrophilic heads of reverse micelle) of reverse micelle Penetration of alcohol in the surfactant micelles actually decreases the rate of molecular exchange among monomers and micelles which results in the suppression of growth of particle size [31] Another possible mechanism for reduction of particle size may be the tightening of the molecular packing which slows the rate of molecular swapping among monomers and micelles by addition of dodecanol into the vicinity of hydrophilic heads of reverse micelle(Fig 2) The Following are the proposed reaction equations for formation of ferrites Paraffin oil were used as surfactant, co-surfactant and oil phase respectively In first step, metal salt solutions [0.1M Mn (CH3COO) and 0.2M Fe (NO3)3] were prepared in de-ionized water The required volumes of freshly prepared metal salt solutions were used The solutions were mixed according to required stoichiometric ratio These solutions were mixed with vigorous stirring The reaction mixtures were heated at 60 °C for 10 After that, micro emulsion (TritonX-100/1-butanol/ Paraffin mixture) were added in the reaction mixtures, and mixed up homogeneously for 20 Freshly prepared 1M NaOH solution was added drop wise to all six reaction mixtures to maintain pH at 11 All reaction mixtures were stirred vigorously for 90 The precipitates were washed with ethanol and then water several times and dried in oven at 150 °C The resultant product was annealed at various temperatures under vacuum and in air (Table 1) 2.3 Synthesis by Co-precipitation method Four different types of samples were prepared using co-precipitation method and surfactant assisted co-precipitation method (using different surfactants such as CTAB, SDS and TBAB), First we prepared metal salt solutions [0.1M Mn (CH3COO)2 and 0.2M Fe (NO3)3] in de-ionized water The required volumes of freshly prepared metal salt solutions were used These solutions were mixed with vigorous stirring The reaction mixtures were heated at 60 °C for 10 Then prepare 0.1 M solution of various surfactants and add in four different beakers Maintaining the pH at 11 by using ammonia solution, the reaction was continued for hours with vigorous stirring The product was first washed with ethanol and then with water to remove impurities and maintained the pH at 11 Then dried the samples in oven at 105 °C Finally, annealed the samples above 600°C (i.e at 800°C and 900°C in air ) as reported by M Augustina with T Balub [41], Leila Asadi Kafshgari et al [42], M.M Rashad [43], M.N Ashiq et al [44] and many other researchers (Fig 1) Mn2 + + Fe + + OH− + 1/2 O2 → MnFe2 O4 + 3H2 O (1) Fe + + 1/4 O2 + H+ → Fe3 + + 1/2 H2 O (2) Fe3 + + H2 O + H+ → Fe (OH )3 + H+ (3) Fe + (4) +2 OH− → Fe (OH )2 Mn2 + + OH− → Mn (OH )2 (5) Fe (OH )3 → FeOOH + H2 O (6) If pH > FeOOH + Mn (OH )2 → MnFe2 O4 + H2 O (7) Various factors may affect, such as concentration of hydroxide play important role in formation of MnFe2O4 When base is added to the solution two types of precipitates were formed i.e Fe(OH)3 and Mn (OH)2.This Fe(OH)3 may react with residual hydroxide which precipitate as Fe2O3 Second, Mn(OH)2 is oxidized via oxygen in the air to form MnOOH which then converted into Mn3O4 [32] Results and discussion 3.1 Micro-emulsion technique Mn (OH )2 + MnOOH → Mn3 O4 + H2 O In our oil in water synthesis scheme, the precursor is metal salt present in water-core For precipitation reaction, the precipitating agent during passing through the surfactant layer, slower downs the reaction rate Water droplets containing ions, when diffuse or collide with each other resulting into exchange of ions, which affects the formation of particles Surfactant walls of micro-droplets not only behave as a barrier in the way of particle nucleation but also as cages in the way of particle growth that results narrow size distribution of particles [27,28] In fact, long chain alkyl alcohols as co-surfactant with a hydrophilic head and hydrophobic end interact with monolayer of primary surfactant at the water/oil interface After this, they get distributed at the interface and stops further nucleation of micelle The polar functional segment (head) of the long chain alkyl alcohol orients its head towards the water phase and does cease the further nucleation (8) 3.2 Co-precipitation route Low reaction temperature, non-expensive, simple, better homogeneity, high yield (production rate) [33], contamination-free and ecofriendly are the main features of this method [34] Nanoparticle synthesis using co-precipitation route is complicated due to lack of control on crystallinity, morphology and particle size [35] Simple and widely used co-precipitation method yields nanoparticles with broadsized distribution and poor crystal chemistry, as it formed rapidly so disturbed the cations distribution from the equilibrium state [36,37] M Augustina with T Balub [38], Leila Asadi Kafshgari et al [39], M.M Rashad [40], M N Ashiq et al [41] and many other researchers synthesized ferrite using co-precipitation method, annealed the Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Fig A proposed graphic representation of formation of normal spinal manganese ferrites iron cations changed into hexa-coordinated aquo complexes Secondly, the hydroxylation of the cations on distinct pH ranges: hydroxylation of Fe (III) occurs from pH = to pH = 4–5 at room temperature while for Fe(II) cation is about pH = 7–9 (yields aquo-hydroxo complexes) After that, the condensation of Hydroxylated complexes proceeds via two basic mechanisms (olation and oxolation) The Olation mechanism is followed by aquo-hydroxo complexes, [Fe(OH)h(OH2)6−h] (z−h)+ in which condensation of complexes proceeds by elimination of water molecule which results hydroxo bridges [42–44] (Here, h is hydroxylation rate and z is charge on cation) Oxolation mechanism is followed by oxo-hydroxo complexes [FeOa (OH)b](z−2a−b)+ in which condensation of complexes proceeds in two steps which results oxo bridges [45] For divalent transition metals like Fe(II) and Mn(II) (in solution), there is possibility of formation of tetrameric polycation [Fe4(OH)4(OH2)12]4+ above pH = at the very first material in the range of 600 °C–800 °C and obtained single phase material finally Keeping in view of above cited research articles, we have also attempted to synthesize manganese ferrite (single-phase) by following these procedures in the same manners, but we obtained the final product as a mixed phase manganese ferrite The same reaction is taking place in co-precipitation method and in water pools of microemulsion method The following is the proposed reaction mechanism for formation of ferrites along with mixed oxides 3.3 Detailed mechanism and chemical reactions during MnFe2O4 ferrite formation Variable and stable oxidation states (II and III) on large acidic range, common reactivity of complexes of iron towards acid-base and simple condensation reactions make iron chemistry highly versatile Firstly, Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Fig (a) A Proposed Water in oil (b) oil in water Microemulsion (c) distribution of dodecanol during micelle formation mechanism Fig A proposed reaction pathway for formation of metal hydroxide estimated which may be oxidized as: stage of hydroxylation process (h = 1) Brucite structure of precipitated Fe (OH)2 (hydroxylated ferrous ions) is formed by ferrous complexes [Fe(OH)2(OH2)4]0 in anaerobic conditions at pH > 6–7 (The mechanism is same for Mn(OH)2) Ferrous complexes [Fe(OH)2(OH2)4]0, a precursor having bifunctional character condenses (by olation mechanism) to form dimmers which on condensation form tetramers and with the growth of nuclei leads a layered brucite structure [46](Fig 3) Ferric ions, when hydroxylated at pH > (by using a base) leads ferrihydrite which is unstable (thermodynamically) and transforms via different ways into different crystalline structures (phases) depending on the pH of the medium Ferrihydrite, at ≤ pH ≤ transforms via dehydration (In-situ) and local rearrangement into hematite (α-Fe2O3) of very small sized particles [47] Ferrihydrite, at pH < or pH > (having higher solubility) transforms easily into goethite (α-FeOOH) via dissolution–crystallization mechanism Formation of goethite may be explained by the condensation of planar tetramer [M4(OH)12(OH2)4]0 by olation originates the basic octahedral (planar) double chains which are further connected by oxolation When oxidation is carried out using H2O2 at pH = 7–8, feroxyhyte δ–FeOOH is produced [43,44] Simultaneous presence of Fe(II) and Fe (III) types of ions in solution directs the condensation process to form some definite phases, specifically the green rust, maghemite and magnetite (spinel) Their formation depends upon reaction pH, iron ions concentration and the composition of reaction system (especially) i.e, x = Fe3+/(Fe3+ + Fe2+) [48,49] Magnetite formation pathway: 2FeOOH + Fe + + 2OH− → Fe +Fe23 +O4 (Magnetite) + 2H2 O Fe + + Fe3 + + OH− → Fe3 O4 H2 O (14) Fe3 O4 + 0.25 O2 + 4.5 H2 O → 3Fe (OH )3 (15) At the start, oxidation of Fe ions takes place (Fe + O2 → Fe3+) which creates difficulty in maintaining Fe3+: Fe2+ ratio to (2:1) Two approaches were suggested In one, bubbling an inert gas like Nitrogen gas in reaction mixture not only reduces the oxidation process (for both Fe2+ ions and magnetite) but also the particle size [50,51] In second, (when reaction is in air environment) lowering the Fe3+: Fe2+ ratio < (2:1) so that after oxidation (Fe2+ → Fe3+) the ratio keeps to its original value (2:1) [52] (Fig 4) 2+ Iron ions → (In aqueous solution) 2+ [Fe(OH2)6]z+ (Hexa − coordinated aquo complex) [Fe (H2 O)6]z+ + H2 O Hydrolysis → [FeII (OH)(H2 O)5]+ + H3 O+ (Aqua hdroxo complex) [Fe (OH)(H2 O)5]+ Olation → Dimerizes [Fe2 (OH)2 (H2 O)8]2 + [Fe2 (OH)2 (H2 O)8]2 + Olation → Dimerizes [Fe4 (OH) (H2 O)12]4 + (9) (10) (11) (12) 3.4 Impact of annealing temperature and XRD investigations 3.4.1 Micro-emulsion method Reverse micelle process is very effective to obtained uniformed size and thermally stable nanoparticles Different calcinations temperatures were applied to study the phase formation High annealing temperature (13) Keeping molar ratio of Fe3+: Fe2+ (2:1) and pH of reaction mixture 7.5 to 14 in non-oxidizing(inert) medium, Fe3O4 precipitation is Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Fig A Proposed reaction mechanism for formation of Manganese ferrites along with mixed oxides Fig (a) XRD patterns of MnFe2O4 prepared by microemulsion methods using various routes (b) XRD patterns of MnFe2O4 prepared by water in Paraffin oil microemulsion method at different annealing temperatures Table XRD parameter calculations of various MnFe2O4 nanoparticles Sample Crystal lattice parameter a (Å) Cell Volume/ Vcell (Å3) Crystallite size (nm) X-ray density/ ρ X-ray (g/ cm3) M-1-900 °C M-2-900 °C M-3-400 °C M-4-400 °C M-4-800 °C C-1-800 °C C-2-800 °C C-3-800 °C C-4-800 °C 8.457 8.439 8.416 8.4878 8.439 8.7888 8.2160 9.0874 9.5613 604.85 600.99 596.09 611.48 601.00 678.873 554.60 750.445 874.079 21.67 20.77 13.57 16.33 19.84 18.70 17.24 18.40 18.57 5.07 5.11 5.15 5.02 5.11 4.52 5.53 4.09 3.51 and found the cubic spinel structure of MnFe2O4 The diffraction peaks at plane (220), (311), (222), (400), (422), (511) and (440) confirmed the cubic spinel structure Sample M-4 which was annealed at higher temperature showed manganese ferrite phase with some mixed oxides i.e FeMnO3, Mn2O7 and Fe2O3 Because at higher temperature MnFe2O4 is unstable in air and Mn2+ ions oxidize to convert into Mn3+ which results in the formation of other phases along with MnFe2O4 [55,56] The MnFe2O4 were oxidized into Fe2O3 along with Mn2O3 at high annealing temperature However, when sample was annealed at higher temperature even in vacuum, MnFe2O4 was oxidized and decomposed into Fe2O3 along with Mn2O3 It indicated that at higher temperature, Manganese ferrite was decomposed One of the reasons of spinel structure formation is the controlled oxidation i.e low temperature annealing under vacuum or some inert gases like nitrogen or Argon [57] (Fig 5b) Fig XRD pattern of MnFe2O4/hematite phase prepared by co-precipitation methods within a specific limit favors the formation of crystalline material [53,54] For Sample M-2/M-3 annealed at 900 °C, minute secondary phases were observed at higher temperature Literature reported that heat treatment after 600 °C started to decompose the ferrite For samples M-3 and M-4 (synthesized by facile water-in-paraffin oil/Toluene micro emulsion methods), all diffraction peaks were investigated and indexed to the (jacobsite) fd-3m structure (JCPDS#10–0319) which indicated the well crystalline manganese ferrite material The XRD patterns are given in Fig 5a The sharpness of the peaks was scanned Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Table Synthesis scheme for preparation of MnFe2O4 nanoparticles using co-precipitation methods Sample C-1 C-2 C-3 C-4 Salt solution 0.1M 0.1M 0.1M 0.1M 2+ Mn Mn2+ Mn2+ Mn2+ + + + + 0.2M 0.2M 0.2M 0.2M 3+ Fe Fe3+ Fe3+ Fe3+ Surfactant Precipitating agent (To maintain pH = 11) Washing solvent Annealing temperature Without surfactant CTAB SDS TBAB NH3 NH3 NH3 NH3 Ethanol/Water Ethanol/Water Ethanol/Water Ethanol/Water 800 °C(in 800 °C(in 800 °C(in 800 °C(in air) air) air) air) Fig TGA/DSC curve of un-annealed sample Fig SEM image of MnFe2O4 nanoparticles absence of O2 than spinel structure will produce If Sample was annealed at low temperature in vacuum than spinel Mn ferrite will not be oxidized However, when sample was annealed at higher temperature in vacuum than ∝ -Fe2O3 may produce It indicates that at higher temperature Mn ferrites may be decomposed To avoid oxidation samples were annealed in inert atmosphere [59] All samples were heated in air, due to this Mn2+ is oxidize into Mn3+ This oxidation of Mn3+ may effect on the spinel structure This oxidation may decrease the net magnetic moment When heating time increased, oxidation of Mn also increased that decrease the magnetic moment This oxidation may control using inert atmosphere [60] It is observed that when sample was annealed in air at higher temperature all Mn2+ were oxidized to Mn3+, which diminished the spinel phase and hematite phase were prepared [61,62] (Fig 6) (Tables and 3) Fig FTIR spectra's of MnFe2O4 nanoparticles 3.4.2 Co-precipitation method XRD patterns of samples prepared using different surfactants (CTAB, SDS, TBAB) showed the effect of surfactants The samples were annealed at 800 °C in air The results showed the low crystalline of samples forming hematite phase, hydroematite phase (JCPDS #2–0918) (Fig 6) No Mn/Fe mixed oxide phase was deducted in all samples It was studied that presence of Mn hinders the reduction process of Fe ions, as Fe was present in oxidation state Fe3+ along with Fe2+ converting into Fe3O4 and Fe2O3 species When base was added rapid nucleation of ferrihydrite [FeO(OH)x] was occur Mn2+ ions coexist along with these ferrihydrite species retarding hematite formation [58] The samples (C-1,C-2, C-3, C-4) for MnFe2O were annealed in air at different temperatures The results of XRD were studied in detail and found that all samples were oxidized and no spinel structure was found The MnFe2o4 were oxidized into Fe2O3 along with Mn2O3 It was found from results that O2 in air oxidize the metal.If samples were annealed in 3.5 Thermogravimeteric analysis (TGA) The TGA/DSC curves from 50 °C to 1000 °C at 10 °C/min of the samples are shown in Fig Different regions of weight loss are shown in the thermogram The sample was heated up to 1000 °C which comprised three steps Firstly, evaporation of adsorbed water molecules Secondly, removal of some residues of hydrocarbon (surfactant and Oil) that attached to the surface of the ferrite particles and hard to remove even after washing procedure Thirdly the phase development i.e formation of ferrite (conversion of sample into oxides) resulted some weight loss After heating around 121 °C, weight loss was increased up to 85% that is attributed to the evaporation of adsorbed water After Ceramics International xxx (xxxx) xxx–xxx M.M Baig, et al Fig 10 EDX data of MnFe2O4 nanoparticles manganese ion in ferrite system is co-precipitation reaction in protective media i.e water-in-paraffin oil Dodecanol being more hydrophobic (a long chain alcohol) stabilized the particles by adsorbing on the colloid at the smaller size, which prevents and suppresses further growth of colloid that results in reduction of particle size Oxidation of spinel ferrite is controlled by using low temperature annealing under vacuum It is also revealed that samples prepared using dodecanol as oil phase show thermal stability even at 900 °C.This stability may be due to two steps mechanism First, solubilization and distribution of dodecanol during micellar formation and secondly, coating of dodecanol over particles results rigid and hard spheres of ferrite particles Furthermore, it is suggested that utilization of micro-emulsion technique (water in paraffin oil), thermal treatment at low temperature under vacuum endorses (leads to the formation of) the single phase, spinel and nanocrystalline manganese ferrite Table EDX data of Manganese Ferrites nanoparticles Element Weight (%) Atomic (%) CK OK Na K Mn K Fe K Total 21.57 25.70 2.56 17.26 32.93 100 40.65 36.37 2.52 7.11 13.35 that up to 500 °C, second weight loss is noticed because a possible conversion of hydroxides into oxides When we studied the DSC results, the endothermic DSC peak at about 106.02 °C indicated the loss of water and ethanol contents An exothermic peak at around 319.16 °C was observed, which showed that after that temperature oxidation of residual surfactant molecules and formation of crystalline phase may started This exothermic peak showed that after 320 °C formation of spinel phase may started Acknowledgements Authors from King Saud University highly acknowledge the sincere appreciation of King Saud University Riyadh (Saudi Arabia) for Research Grant (RG-1438-068) Other authors are thankful to the Islamia University of Bahawalpur (Pakistan) and Higher Education Commission-Islamabad-45320, Pakistan (6276/Punjab/NRPU/R&D/ HEC/2016) 3.6 FTIR results The FTIR spectra of samples M-3 & M-4 annealed at 400 °C in vacuum confirmed the spinel structure of MnFe2O4 showed in Fig The two main absorption bands of metal oxygen bond in the range of 400 cm−1 to 600 cm−1 were observed which confirmed the spinel structure The ν1(high frequency band) located in the range of 500–600 cm−1 is due to M-O (Mn2+ and Fe3+) bond stretching showing the tetrahedral groups formation while ν2 band (low frequency band) located in range of 400 cm−1 - 500 cm−1 confirming the octahedral metal 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molecules Secondly, removal of some residues of hydrocarbon (surfactant and Oil) that attached to the surface of the ferrite particles... dodecanol during micellar formation and secondly, coating of dodecanol over particles results rigid and hard spheres of ferrite particles Furthermore, it is suggested that utilization of micro-emulsion