Synthesis of water dispersible phosphate capped CoFe2O4 nanoparticles and its applications in efficient organic dye removal

Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions

Impelled by the need to find solutions to new challenges of modern technologies new materials with unique properties are being explored. Among various new materials that emerged over the decades, magnetic fluids exhibiting interesting physiochemical properties (optical, thermal, magnetic, rheological, apparent density, etc.) under a magnetic stimulus have been at the forefront of research. In the initial phase, there has been a fervent scientific curiosity to understand the field-induced intriguing properties of such fluids but later a plethora of technological applications emerged. Magnetic nanofluid, popularly known as ferrofluid, is a colloidal suspension of fine magnetic nanoparticles, has been at the forefront of research because of its magnetically tunable physicochemical properties and applications. Due to their stimuli-responsive behaviour, they have been finding more applications in biology and other engineering disciplines in recent years. Therefore, a critical review of this topic highlighting the necessary background, the potential of this material for emerging technologies, and the latest developments is warranted. This review also provides a summary of various applications, along with the key challenges and future research directions. The first part of the review addresses the different types of magnetic fluids, the genesis of magnetic fluids, their synthesis methodologies, properties, and stabilization techniques are discussed in detail. The second part of the review highlights the applications of magnetic nanofluids and nanoemulsions (as model systems) in probing order-disorder transitions, scattering, diffraction, magnetically reconfigurable internal structures, molecular interaction, and weak forces between colloidal particles, conformational changes of macromolecules at interfaces and polymer-surfactant complexation at the oil-water interface. The last part of the review summarizes the interesting applications of magnetic fluids such as heat transfer, sensors (temperature, pH, urea detection, cations, defect detection sensors), tunable optical filters, removal of dyes, dynamic seals, magnetic hyperthermia-based cancer therapy and other biomedical applications. The applications of magnetic nanofluids in diverse disciplines are growing day by day, yet there are challenges in their practical adaptation as field-worthy or packaged products. This review provides a pedagogical description of magnetic fluids, with the necessary background, key concepts, physics, experimental protocols, design of experiments, challenges and future directions.

Formation Mechanism and Lattice Parameter Investigation for Copper-Substituted Cobalt Ferrites from Zingiber officinale and Elettaria cardamom Seed Extracts Using Biogenic Route

Biogenic routes for the synthesis of nanoparticles are environmentally friendly, nontoxic, biocompatible, and cost-effective compared to traditional synthesis methods. In this study, cobalt ferrite was synthesized using Zingiber officinale and Elettaria cardamom Seed extracts. Effect of copper contents (x = 0.0, 0.3, 0.6 and 0.9) on the plant extracted Cux(Co1−xFe2O4) was investigated by XRD, SEM, EDX, UV-Vis., PL, FE-SEM, FTIR and photocatalytic activity. XRD results revealed that nanoparticles exhibit a cubical spinel structure with an average diameter of 7–45 nm, calculated by the Debye Scherer formula. The value of the lattice parameter decreased from 8.36 Å to 8.08 Å with substitution of copper, which can be attributed to mismatch of ionic radii of Cu2+ (0.73 Å) and Co2+ (0.74 Å) ions. SEM analysis showed that nanoparticles exhibit a spherical shape (~13 nm diameter) for undoped samples and low Cu concentration, while they changed to a hexagonal structure at higher Cu concentration (x = 0.9) with a diameter ~46 nm and a decreased degree of agglomeration. FE-SEM further confirmed the nanoparticles’ size and shape. EDX analysis confirmed the presence of cobalt, iron, and oxygen without contamination. The optical absorption spectra of UV-vis and PL showed red-shift, which can be accredited to larger crystalline sizes of nanoparticles. FTIR spectra showed two main bands at 410 and 605 cm−1, indicating the presence of intrinsic vibrations of the octahedral and tetrahedral complexes, respectively. The photocatalytic activity of Co0.4Cu0.6 Fe2O4 nanoparticles was investigated using methylene blue (MB) and methyl orange (MO) dyes under visible light irradiation. The degradation rate (93.39% and 83.15%), regression correlation coefficient (0.9868 and 0.9737) and rate constant (0.04286 and 0.03203 rate·min−1) were calculated for MB and MO, respectively. Mechanisms for the formation and photocatalytic activity of Cu-substituted plant-extracted cobalt ferrite were discussed. The Co0.4Cu0.6 Fe2O4 nanoferrite was found to be an efficient photocatalyst, and can be exploited for wastewater treatment applications for MB/MO elimination.

Effect of praseodymium in cation distribution, and temperature-dependent magnetic response of cobalt spinel ferrite nanoparticles

This work reports cation distribution, magnetic, structural, and morphological studies of rare-earth Pr doped cobalt ferrite nanoparticles CoFe_2-xPr_xO₄(x= 0, 0.02, 0.04, 0.06 at%) fabricated by sol-gel auto-combustion method. X-ray diffraction analysis, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier-transform infrared (FTIR) microscopy were utilized to study the structural and morphological characteristics of the prepared samples. Rietveld refinement by the Material Analyses Using Diffraction (MAUD) software showed the formation of mono-phase cubic spinel structure with Fd-3m space group; however, there was a trace of impure PrFeO₃phase for the sample CoFe_1.96Pr_0.04O₄(x= 0.06). Cation distribution was inferred from the XRD patterns using MAUD program. FESEM analysis revealed the spherical-shaped particles with dimensions close to the data extracted from XRD analysis and HRTEM images confirmed it. FTIR measurements revealed the presence of two prominent stretching vibrational modes confirming the successful formation of ferrite spinel structure. Magnetic properties of the nanoparticles were measured at two different temperatures 300 K and 10 K. For the low temperature of 10 K a high sensitive measurement method as Superconducting Quantum Interference Device (SQUID) magnetometry was used and Vibrating Sample Magnetometer (VSM) recorded the magnetic data at 300 K. Comparison of the magnetic results exhibited a significant enhancement with temperature drop due to the reduction in thermal fluctuations. Paramagnetic nature of rare-earth ions may be the main reason forM_Sdecrement from 76 emu g^-1(x= 0.0) to 60 emu g^-1(x= 0.02) at 300 K. At 10 K, the estimated cation distribution played a vital role in justification of obtained magnetic results. All the obtained data showed that the synthesized magnetic nanoparticles can be implemented in permanent magnet industry and information storage fields, especially when it comes to lower temperatures.

Organic Dyes versus Adsorption Processing

Even in the first quarter of the XXI century, the presence of organic dyes in wastewaters was a normal occurrence in a series of countries. As these compounds are toxic, their removal from these waters is a necessity. Among the separation technologies, adsorption processing appeared as one of the most widely used to reach this goal. The present work reviewed the most recent approaches (first half of the 2021 year) regarding the use of a variety of adsorbents in the removal of a variety of organic dyes of different natures.

Tuning the microstructural and magnetic properties of CoFe2O4/SiO2 nanocomposites by Cu2+ doping

Co–Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO₂ matrix were prepared by a sol–gel method. The effect of a small Cu²⁺ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mössbauer spectroscopy, and VSM. It was found that single cubic Co_1−xCu_xFe₂O₄ ferrite was formed in amorphous SiO₂ matrix. The average crystallite size of Co_1−xCu_xFe₂O₄ increased from 18 to 36 nm as Cu²⁺ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu²⁺ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu²⁺doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu²⁺ content increasing, the saturation magnetization (M_s) first increased, then tended to decrease, while the coercivity (H_c) decreased continuously, which was associated with the cation migration. The results suggest that the Cu²⁺ doping content in Co_1−xCu_xFe₂O₄ NPs plays an important role in its magnetic properties.

The Cu²⁺ doping content in Co_1−xCu_xFe₂O₄/SiO₂ plays an important role in tuning hyperfine interaction and magnetic properties.