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Herein, Fe 3 O 4 magnetic nanoparticles (MNPs) were synthesized and characterized. Afterward, a magnetic carbon paste electrode (MCPE) was modified with MNPs via casting and drying MNPs on top of the MCPE (MCPE/MNP). Electrochemical behavior of the MCPE/MNP was studied by cyclic voltammetry in the presence of [Fe(CN) 6 ] 3−/4− as a redox probe, and surface p of MNPs was evaluated as 6.3 ± 0.1. The behavior of MCPE/MNP towards dopamine (DA) and ascorbic acid (AA) has been investigated by electrochemical methods, and the obtained results showed that the MCPE/MNP has adsorption behavior towards only DA. Based on this behavior, the DA molecules were pre-concentrated on top of the MCPE/MNP and followed with stripping in DA free solution. Subsequent to experimental and instrumental optimization, a calibration curve from 5.0 × 10 −6 to 1.0 × 10 −3 M DA with 2 = 0.999, DL = 7.6 × 10 −7 M DA, and RSD = 4.6%, was obtained in the presence of 1.0 × 10 −3 M AA. Performance of the MCPE/MNP was successfully tested in a pharmaceutical sample.

Fe 3 O 4 superparamagnetic nanoparticles (NPs) modified with zirconia (ZrO 2 ) were synthesized (Fe 3 O 4 @ZrO 2 ) using a chemical co-precipitation method and used as nanoadsorbent in removal excessive fluoride from aqueous solutions. This adsorbent combines the advantages of magnetic nanomaterial and Fsorbent floc, with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, and easy isolation from sample solutions by the application of an external magnetic field. The prepared Fe 3 O 4 @ZrO 2 magnetic nanoparticles were characterized by XPS, XRD, SEM, EDXA, BET, FTIR, and VSM techniques. Affecting parameters on removal of fluoride, such as mass ratio of Fe 3 O 4 to ZrO 2 , solution pH, adsorption time, initial fluoride concentration, and co-existing anions were investigated. The high adsorption capacity calculated by Langmuir equation was 158.6 mg g -1 for Fe 3 O 4 @ZrO 2 (2:5) in pH 2.5. The adsorption capacity increased with temperature and the kinetics followed a pseudo-secondorder rate equation. The enthalpy change (∆H 0 ) and entropy change (∆S 0 ) was 25.02 kJ mol −1 and 3.76 J mol −1 K −1 , which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe 3 O 4 @ZrO 2 NPs as adsorbent could reach 0.3 mg L −1 with an initial concentration of 20 mg L −1 . Also application of Fe 3 O 4 @ZrO 2 NPs for removal of fluoride from real samples was tested. All of the results suggested that the Fe 3 O 4 @ZrO 2 NPs with strong and specific affinity toward fluoride could be excellent adsorbent for treatment of fluoride contaminated water.

In the first section of this research, superparamagnetic nanoparticles (NPs) (Fe 3 O 4) modified with hydroxyapatite (HAP) and zirconium oxide (ZrO 2) and thereby Fe 3 O 4 /HAP and Fe 3 O 4 /ZrO 2 NPs were synthesised through co-precipitation method. Then Fe 3 O 4 /HAP and Fe 3 O 4 /ZrO 2 NPs characterised with various techniques such as X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Brunauer-Emmett-Teller, Fourier transform infrared, and vibrating sample magnetometer. Observed results confirmed the successful synthesis of desired NPs. In the second section, the antibacterial activity of synthesised magnetic NPs (MNPs) was investigated. This investigation performed with multiple microbial cultivations on the two bacteria; Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Obtained results proved that although both MNPs have good antibacterial properties, however, Fe 3 O 4 /HAP NP has greater antibacterial performance than the other. Based on minimum inhibitory concentration and minimum bactericidal concentration evaluations, S. aureus bacteria are more sensitive to both NPs. These nanocomposites combine the advantages of MNP and antibacterial effects, with distinctive merits including easy preparation, high inactivation capacity, and easy isolation from sample solutions by the application of an external magnetic field.

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