What is the synthesis and characterization of highly selective magnetite nanoparticles by in situ precipitation?
Preface: Based on the application of iron oxide nanoparticles in many fields, in situ precipitation method is widely used to synthesize iron oxide nanoparticles, however, the reaction rate and rate constant for the formation of ferrotetroxide magnetite phase have not been thoroughly studied, and the reaction rate is required to design the scale-up of the process.
In this study, the iron oxide nanoparticles of the magnetite phase were synthesized by in situ precipitation and the total reaction rate was evaluated based on the concentration of magnetite produced in the process, using X-ray diffraction, energy-dispersing X-ray spectroscopy, and Raman spectroscopy to determine which higher proportion of magnetite was responsible for the superior magnetic performance of the final product74.615emu.
The morphological changes of these nanoparticles at different time intervals of the reaction were reported by transmission electron microscopy. The results show that spherical nanoparticles synthesized at different time intervals of the reaction have a very narrow range of particle sizes, i.e. 9-15 nm. Detailed analysis revealed that magnetite is converted to magnetite at the beginning of the reaction and eventually converted to magnetite at the end of the reaction, thereby enhancing the magnetic strength of the nanoparticles.
To date, about 16 different iron oxide phases have been reported. All of these iron oxide phases are crystalline, with the exception of two, Schwitmannite and hydroironite. In therapeutic and diagnostic applications, such as magnetic resonance imaging, the production of metal nanoparticles and the use of their superparamagnetism are very common.
These iron oxides are used as catalysts, adsorbents, pigments, flocculant coatings, gas sensor wastewater treatment, and for lubrication. Similarly, these nanoparticles can also be used in different advanced processes to form nanoreactors, added to polymer films and other products, based on their excellent magnetic properties.
These applications fabricate supermagnetic nanoparticles of ferric oxide and require the development and improvement of this synthesis process with minimal operating costs. According to the magnetism of iron oxide crystals, the three main phases are known for their high magnetic strength, with magnetite topping the list, followed by magnetite and hematite.
There are several different methods for producing iron oxide nanoparticles, sol-gel, hydrothermal solution, emulsion precipitation, microemulsion and microwave-assisted hydrothermal techniques. However, the focus is on magnetite phases with high purity iron oxides. In this case, the solid phase is generated by neutralization reactions and rapid mixing, which is essential for controlling grain size and magnetism.
Precipitation and surface morphology are the result of several mechanisms, namely nucleation, molecular growth, and secondary processes such as aggregation/coalescence and fragmentation of particles, and the driving force generated by nanoparticles is supersaturation. Nucleation is the first step in the formation of nanoparticles and occurs when a critical number of molecules combine to form an embryo.
Stable embryos from the nucleus act as seeds in solution for precipitating other molecules. Aggregation and growth lead to the attachment of two particles and the growth of these nanoparticles, respectively. Aggregation is characterized by a slow velocity, occurring after particle formation, depending on the force by which the two particles collide. Most collisions don't have enough energy to gather particles, which bounce back into the system.
Most metal oxide nanoparticles also have surface charges, and the strength of these surface charges also reduces the chance of particles aggregating or coalescing. The breakup of particles depends on the different forces acting on the particles as they move in the fluid. Particles with sharp edges and uneven surfaces are more likely to break into two or more smaller particles, depending on the balance of force on the particles.
However, this phenomenon is very rare in metal oxide nanoparticles. Compared to the surface forces acting on the particles, the mechanical forces in metal oxides are very high and can be assumed to be zero in the case of nanoparticles. In a turbulent mixing state, the precipitation of iron salts with strong alkaline solutions creates supersaturation and causes newly formed particles to migrate to ultra-highly saturated regions.
In the high mixing state, the small particles produced by the high nucleation rate and the growth of these nanoparticles depend on the mixing efficiency. Since the precipitation reaction is very fast, the effect of mixing is significant at the micromixing level. This phenomenon is more pronounced at high mixing rates and will depend on the flow regime in the reactor.
In this study, nano-ferric oxide was prepared by co-precipitation, and one of the main contributions of the current work is to report the change of magnetite concentration with reaction time. The co-precipitation reaction between the iron salt and the precipitant is very fast, resulting in the formation of different products when the first drop is mixed into the solution.
However, magnetite formation is based on slow reactions that require relatively long reaction times. The selectivity of magnetite production in solution is very sensitive and depends on operating parameters such as pH, reaction temperature, concentration and molar ratio of iron salts. Therefore, the goal of this work is to synthesize superparamagnetic iron oxide nanoparticles, i.e. magnetite with high purity. First, the experimental setup and process of co-precipitation are described. The concentration of nanoparticles in different crystals in the product is then characterized, and finally the size and magnetic strength of these nanoparticles are reported.
Iron oxide nanoparticles were prepared by co-precipitation using a precursor mixture of ferric chloride and ferric chloride. The nanoparticles were generated with a good yield of high impurities, and the reaction rate value of 7.5×10-3 was −4 moles, the minimum −1 rate constant was 2.074×10−4 moles−2 parts−1.
The XRD results supported by Raman spectroscopy showed that most of the magnetite was formed early in the reaction, while as the reaction progressed, the magnetite was converted to magnetite and increased the selectivity of magnetite nanoparticles to 98.2%, and the ζ potential of these nanoparticles was found to be 41 at the end of the reaction, indicating that the nanoparticles were stable.
conclusion
The surface charge leads to significant resistance to the aggregation and coalescence of the nanoparticles, TEM analysis shows that the structure of these nanoparticles is spherical and gives a porous structure, these impurity-free magnetic nanoparticles with round and porous surfaces can be used as additives in different polymer materials due to their excellent magnetic and mechanical properties.
