https://www.ucl.ac.uk/~ucaptt0/NANTODay.pdf

Functionalisation of nanoparticles for biomedical applications

Magnetite nanoparticles were synthesized via the chemical co-precipitation method using ammonium hydroxide as the precipitating agent. The size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through the surface modification. Herein, the hexanoic acid and oleic acid were introduced as the coating agents during the initial crystallization phase of the magnetite. Their structure and morphology were characterized by the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and the field-emission scanning electron microscopy (FE-SEM). Moreover, the electrical and magnetic properties were studied by using a conductivity meter and a vibrating sample magnetometer (VSM), respectively. Both of the bare magnetite and the coated magnetite were of the cubic spinel structure and the spherical-shaped morphology. The reaction temperature and the surface modification critically affected the particle size, the electrical conductivity, and the magnetic properties of these particles. The particle size of the magnetite was increased through the surface modification and reaction temperature. In this study, the particle size of the magnetite nanoparticles was successfully controlled to be in the range of 10–40 nm, suitable for various biomedical applications. The electrical conductivity of the smallest particle size was 1.3 × 10−3 S/cm, within the semi-conductive materials range, which was higher than that of the largest particle by about 5 times. All of the magnetite nanoparticles showed the superparamagnetic behavior with high saturation magnetization. Furthermore, the highest magnetization was 58.72 emu/g obtained from the hexanoic acid coated magnetite nanoparticles.

Synthesis and characterization of magnetite nanoparticles via the chemical co-precipitation method

Magnetic magnetite (Fe3O4) nanoparticle synthesis and applications for lead (Pb2+) and chromium (Cr6+) removal from water.

Magnetite nanoparticles (Fe₃O₄) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C₂H₅)₄NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

https://www.mdpi.com/1996-1944/6/12/5549/pdf

Room Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles in a Large pH Window with Different Bases

The performance of magnetic nanoparticles is intimately entwined with their structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique way of engineering the magnetic response by modifying the strength of the dipolar interactions between particles. Here we report on an experimental and theoretical analysis of magnetic hyperthermia, a rapidly developing technique in medical research and oncology. Experimentally, we demonstrate that single-domain cubic iron oxide particles resembling bacterial magnetosomes have superior magnetic heating efficiency compared to spherical particles of similar sizes. Monte Carlo simulations at the atomic level corroborate the larger anisotropy of the cubic particles in comparison with the spherical ones, thus evidencing the beneficial role of surface anisotropy in the improved heating power. Moreover we establish a quantitative link between the particle assembling, the interactions and the heating properties. This knowledge opens new perspectives for improved hyperthermia, an alternative to conventional cancer therapies.

/pdf/learning-from-nature-to-improve-the-heat-generation-of-iron-2jw0yo897h.pdf

Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications

Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles

We investigate the effect of digestion time and alkali addition rate on the size and magnetic properties of precipitated magnetite nanoparticles. It is observed that the time required to complete the growth process for magnetite nanocrystals is very short (∼300 s), compared to long digestion times (20−190 min) required for MnO and CdSe nanocrystals. The rapid growth of magnetite nanoparticles suggests that Oswald ripening is insignificant during the precipitation stage, due to the low solubility of the oxides and the domination of a solid-state reaction where high electron mobility between Fe2+ and Fe3+ ions drives a local cubic close-packed ordering. During the growth stage (0−300 s), the increase in the particle size is nominal (6.7−8.2 nm). The effect of alkali addition rate on particle size reveals that the nanocrystal size decreases with increasing alkali addition rate. The particle size decreases from 11 to 6.8 nm as the alkali addition rate is increased from 1 to 80 mL/s. During the size decrease, ...

Effect of Digestion Time and Alkali Addition Rate on Physical Properties of Magnetite Nanoparticles

We report a simple method for producing magnetic nanoparticles with enhanced maghemite (?-Fe2O3) to haematite (?-Fe2O3) phase transition temperature. By controlling the properties of the solvent media, we have been able to tune the particle size from 2.3 to 6.5?nm. Nanoparticles with higher transition temperatures have been achieved by using NaOH as an alkali during the co-precipitation. The maghemite to haematite phase transition was complete at a temperature below 600??C for nanoparticles prepared using ammonia, whereas the phase transition was not complete until 750??C for the samples prepared with NaOH. The increase in average particle size after heat treatment at 600??C is attributed to coalescence of particles by solid state diffusion, where the system reduces its free energy by reducing the surface area. The final particle diameters of the haematite after the heat treatment were 35.4, 31.38 and 26.85?nm respectively for nanoparticles of initial diameters 5, 7 and 9.8?nm. Our studies on the effect of the initial particle size on the transition temperature show that the transition temperature decreases with decreasing particle size due to the reduced activation energy of the system.

https://iopscience.iop.org/article/10.1088/0957-4484/17/23/023/pdf

Magnetic nanoparticles with enhanced γ-Fe 2 O 3 to α-Fe 2 O 3 phase transition temperature

In this paper, we report the variations in the crystal structure, average particle size, and magnetic properties of ZnFe2O4 nanoparticles on thermal annealing, using in situ high temperature x-ray diffraction (XRD). Fine powder of ZnFe2O4 nanoparticles with an average particle size of 9.3nm, prepared through coprecipitation technique, has been used in these studies. The powder is heated from room temperature to 1000°C, under vacuum in steps of 100°C and the XRD pattern is recorded in situ. A sudden drop in the lattice parameter from 8.478to8.468A is observed at 800°C, above which it increases with increasing temperature. After annealing at 1000°C, the lattice parameter reduces from 8.441to8.399A and the magnetization value increases from 5to62emu∕g, suggesting the possibility of a conversion of the cubic structured ZnFe2O4 from normal to inverse spinel structure due to canting of ions between the tetrahedral and octahedral interstitial sites. During annealing, the Zn2+ ions move from tetrahedral site to o...

Effect of thermal annealing under vacuum on the crystal structure, size, and magnetic properties of ZnFe2O4 nanoparticles

We study the effects of surfactant monolayer coating on the reduction of Fe3O4 nanoparticles under vacuum thermal annealing. Oleic acid coated and uncoated Fe3O4 nanoparticles were synthesized by a simple coprecipitation technique. In the temperature range of 300−700 °C, the particle size and lattice constant of uncoated Fe3O4 nanoparticles increased from 9 to 18 nm and from 8.357 to 8.446 A, respectively. On further heating (above 700 °C), Fe3O4 decomposed into γ-Fe2O3 and FeO phases. In the range of 800−1000 °C, the FeO phase was predominant, and its size grew significantly from 30 to 44 nm. Conversion of oleic acid coated Fe3O4 phase to metallic α-Fe commenced at 500 °C and continued up to 800 °C. After vacuum annealing at 800 °C, the magnetic behavior of the sample changed from ferrimagnetic to ferromagnetic. The activation energies for the phase transitions of uncoated and oleic acid coated nanoparticles were estimated to be 30.304 and 17.349 kJ/mol, respectively. Thermogravimetric analysis (TGA) cou...

G. Gnanaprakash

Papers

Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles

Effect of Digestion Time and Alkali Addition Rate on Physical Properties of Magnetite Nanoparticles

Magnetic nanoparticles with enhanced γ-Fe 2 O 3 to α-Fe 2 O 3 phase transition temperature

Effect of thermal annealing under vacuum on the crystal structure, size, and magnetic properties of ZnFe2O4 nanoparticles

Effect of Surfactant Monolayer on Reduction of Fe3O4 Nanoparticles under Vacuum