Green Processing and Synthesis 2021; 10: 384–391 Research Article Seham S. Alterary* and Anfal AlKhamees Synthesis, surface modification, and characterization of Fe3O4@SiO2 core@shell nanostructure https://doi.org/10.1515/gps-2021-0031 received March 02, 2021; accepted April 06, 2021 1 Introduction Abstract: In recent times, nanoparticles have been the In the recent decade, applications of nanotechnology focal point of research in nanoscience due to their wide have emerged with an increasing use of nanosized mate- scope of potential applications in all fields of science. rials in various fields due to their unique properties at the ( ) ( ) Iron oxide Fe3O4 nanoparticles NPs show incredible nanoscale in comparison with their bulk counterparts [1]. - magnetic saturation, stability, biocompatibility, and intui Integration of nanotechnology with other sciences has tive properties on the surface, which makes them ideal for resulted in the rapid development of novel research being utilized in several ways. In the present study, Fe3O4 areas, which will improve and revolutionize technology - NPs were synthesized by co precipitation and further coated in several industries [2]. ( ) - with silica SiO2 to avoid aggregation. Synthesized nanopar Magnetite and Fe O NPs provide a unique nanoplat- ( ) 3 4 ticles Fe3O4@SiO2 were individually functionalized using form and play a major role in providing a broad range of - glycine and malonic acid and characterized by various spec applications owing to their important magnetic property troscopies and microscopies techniques. XRD diffraction of superparamagnetism. The phenomenon shows that analysis showed that the presence of SiO did not alter the 2 ferromagnetic or ferrimagnetic nanoparticles would have diffraction pattern peaks, which represented the existence of zero magnetic remanence together with a high magnetic Fe3O4. The presence of Fe3O4 and SiO2 nanoparticles were susceptibility. Among them, Fe3O4 NPs stand out due to further confirmed using EDS. Transmission electron micro- their high biocompatibility, low toxicity, strong super- scope micrographs of the synthesized nanoparticles exhib- paramagnetic property, and easy preparation process, and ited spherical shape and confirmed the increase in particle thus, they have attracted increasing attention [3,4] in the size after coating with SiO Also, the analysis of dynamic 2. field of research. Fe O NPs do have their limitations, such light scattering showed that the particle size of Fe O @SiO 3 4 3 4 2 as rapid agglomeration, wide surface area, high chemical functionalized with malonic acid (229.433 nm) was greater than reactivity, and high surface energy, resulting in mag- those functionalized with glycine (57.2496 nm). However, the netism loss [5]. Therefore, appropriate surface modifica- surface area was greater in Fe O @SiO -glycine (104.8 m2/g) 3 4 2 tion of Fe O NPs is required to avoid the aforementioned than Fe O @SiO -malonic acid (26.15 m2/g).Thekeyfindings 3 4 3 4 2 problems. The coating is the most common surface modifi- suggest that the synthesized core-shell Fe O @SiO nanoparti- 3 4 2 cation method to conjugate organic or inorganic mate- cles are a promising candidate for a wide array of applications rials onto the surface of iron oxide nanoparticles. This in the field of medicine and environmental science. approach avoids not only the oxidation and agglomeration Keywords: core@shell, Fe3O4@SiO2,functionalization, but also provides the possibility of further functionaliza- nanostructure, surface modification tion [6,7]. Functionalization of magnetic NPs boosts up their physicochemical properties, making them ideal can- didates for catalysis or biomedicine purposes [8]. Many * Corresponding author: Seham S. Alterary, Department of studies are conducted on the synthesis of Fe3O4 nanopar- Chemistry, King Saud University, Riyadh, Saudi Arabia; ticles into composite structures with other materials. King Abdullah Institute of Nanotechnology, King Saud University, Chang et al. [9] and Sobhanardakani and Zandipak [10] Riyadh, Saudi Arabia, e-mail: [email protected] have reported the formation of silica layers on the surface Anfal AlKhamees: Department of Chemistry, King Saud University, Riyadh, Saudi Arabia, e-mail: [email protected] of stabilized magnetite nanoparticles using a surfactant ORCID: Seham S. Alterary 0000-0002-4176-2840 [11]. Amorphous SiO2 is the most representative material Open Access. © 2021 Seham S. Alterary and Anfal AlKhamees, published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License. Synthesis of nano Fe3O4@SiO2 characterization and surface modification 385 among potential candidates for constructing core-shell 2.2 Synthesis of silica-coated Fe3O4 NPs structures with Fe3O4.SiO2 is used because of its inherent (Fe3O4@SiO2 NPs) high thermal stability, physicochemical durability, and surface characteristics, which is because it retains a large A volume of 10 mL of deionized water, 30 mL of absolute [ ] ff number of surface hydroxyl groups 12,13 .Thiso ers a ethanol (CH3CH2OH ≥99.8%; Sigma-Aldrich), and 1 mL of mode to overcome the limitations encountered during ammonia (30% NH3; Applichem Panreac) were added to the synthesis of Fe3O4 nanoparticles. Among the methods 0.5 g Fe3O4 nanoparticles. This mixture was incubated in of synthesis used, chemical co-precipitation is the most an ultrasonic tank for 30 min, after which we added common method both for the laboratory purpose and on 2.5 mL of tetraethylorthosilicate (TEOS ≥99.0%; Fluka) a larger scale for industrial processes since it is highly while stirring for 22 h. The coated Fe3O4@SiO2 was dried advantageous. The process has easy processing operation, at room temperature [19,20]. high yield product, low temperature, and time of reaction in comparison with methods like thermal decomposition and hydrothermal and utilizes inorganic reactants and environmental-friendly solvents such as water [14].To 2.3 Surface modification of Fe3O4@SiO2 NPs make a core-shell structure, there is a major deficiency by glycine and malonic acid in using Fe3O4 nanoparticles obtained by co-precipitation - - due to the large surface to volume ratio, high surface A total of 0.15 g of Fe3O4@SiO2 NPs was added to 7.5 mL energy, and magnetic dipole–dipole attractions between of deionized water in ultrasonic tanks. Then, 0.15 g of the particles, and magnetic nanostructures are highly glycine (WINLAB) or malonic acid (LOBA Chemie) was prone to aggregation. To synthesize well-dispersed silica- added to the solution by stirring at 90°C for 20 min. – coated Fe3O4 NPs, sol gel method, the Stöber method, and After the reaction was complete, the precipitate was microemulsion are the most common methods for coating washed three times with deionized water and dried under [ ] the surface of Fe3O4 nanoparticles with silica 15,16 . vacuum for 12 h at 50°C [21,22]. With this premise, the present study was carried out to use the Fe3O4 nanoparticle as a magnetic core coated by SiO2 shell and then modified by organic and inorganic reagents to synthesize the Fe3O4@SiO2 as an efficient 2.4 Characterization techniques nanomagnetic catalyst. Initially, the magnetic iron oxide nanoparticles (Fe3O4 NPs) were produced using the co- The FTIR spectra of Fe3O4,Fe3O4@SiO2,Fe3O4@SiO2-gly- precipitation method and then coated with SiO2. The cine, and Fe3O4·SiO2-malonic acid nanoparticles were coated particles are then functionalized with glycine analyzed by Fourier transform infrared spectrophotometer and malonic acid. (Perkin-Elmer Spectrum BX) to examine the functional chemicals groups of the prepared samples using the potassium bromide (KBr) disk method. The structural analyses of the collected samples were carried out using 2 Materials and methods XRD and Bruker D5005 diffractometers using CuK5-007 radiation (5-007 = 1.5418 A0). The average particle size of the prepared nanoparticles was calculated according to 2.1 Co-precipitation method synthesized of the Scherrer equation. The particle size distribution was Fe3O4 NPs investigated by a dynamic light scattering (DLS) tech- nique using a Zetasizer (HT Laser, ZEN3600 Malvern A volume of 500 mL of 1.5 M NaOH (BdH Laboratory Instruments, Malvern, UK). To determine particle size, Supplies) was added with a dropper with continual stir- morphology, and composition of Fe3O4,Fe3O4@SiO2 and ring at 80°C to the mixture of FeCl3·6H2O (LOBA Chemie; acquired samples were examined using a JEOL JSM-6300 0.04 mol, 10.8 g) and FeSO4·7H2O (UNI-CHEM; 0.02 mol, SEM with an EDS and a JEM-200CX TEM. The Brunau– 5.5 g) dissolved in 50 mL of 0.5 M HCl (Salzsäure rau- Emmet–Teller (BET) method was employed to measure chend). Thereafter, the prepared Fe3O4 precipitant was the surface area of Fe3O4@SiO2-glycine and Fe3O4@SiO2- collected with a magnet, washed several times with deio- malonic acid nanoparticles with a Micromeritics Gemini nized water, and dried for 7 h at 50°C [17,18]. 2360 surface area analyzer. Nitrogen gas molecules were 386 Seham S. Alterary and Anfal AlKhamees adsorbed onto the solid surface, which allows measure- 140 ment of the surface area of the nanoparticles. Fe3O4@SiO2 Fe3O4@SiO2-Mal 120 Fe3O4 Fe3O4@SiO2-Gly 2.5 Statistical analysis 100 80 All experiments were performed in triplicate. Results ± (n = ) were expressed as means standard deviation 3 . 60 The size of nanoparticles was measured from the scan- Transmitance (%) ning electron microscope (SEM) and transmission elec- 40 tron microscope (TEM) pictures using ImageJ software. 20 4000 3500 3000 2500 2000 1500 1000 500 -1 3 Results and discussion Wavenumber (cm ) Figure 1: FTIR spectra of the synthesized nanoparticles. 3.1 FTIR analysis corresponds to CO2 asymmetric stretching, and the bands −1 The chemical compositions of Fe3O4,Fe3O4@SiO2,Fe3O4@SiO2- at 3,206 and 3,400 cm correspond to the O–Hstretching glycine, and Fe3O4@SiO2-malonic acid nanoparticles vibration and intramolecular C–H stretching vibration, were characterized using FTIR spectroscopy as shown respectively [27].