A facile approach to synthesis of cobalt ferrite nanoparticles with a uniform ultrathin layer of silicon carbide for organic dye removal

A review on synthesis, capping and applications of superparamagnetic magnetic nanoparticles

Magnetic nanoparticles (MNPs) have garnered significant attention from researchers due to their numerous technologically significant applications in diverse fields, including biomedicine, diagnostics, agriculture, optics, mechanics, electronics, sensing technology, catalysis, and environmental remediation. The superparamagnetic nature of MNP is exploited for many applications and remains fascinating to study many fundamental phenomena. The uniqueness of this review is that it gives an in-depth review of different synthesis approaches adopted for preparing magnetic nanoparticles and nanoparticle formation mechanisms, functionalizing them with different capping agents, and applying different functionalized magnetic nanoparticles. The important synthesis techniques covered include coprecipitation, microwave-assisted, sonochemical, sol-gel, microemulsion, hydrothermal/solvothermal, thermal decomposition, and mechano-chemical synthesis. Further, the advantages and disadvantages of each technique are discussed, and tables show important results of prepared particles. Other aspects covered in this review are the dispersion of magnetic nanoparticles in the continuous matrix, the influence of surface capping on high-temperature thermal stability, the long-term stability of ferrofluids, and applications of functionalized magnetic nanoparticles. For effective utilization of the ferrite nanoparticles, it is essential to formulate thermally and colloidally stable magnetic nanoparticles with desired magnetic properties. Capping enhances the phase transition temperature and long-term colloidal stability. Magnetic nanoparticles capped or functionalized with specific binding species, specific components like drugs, or other functional groups make them suitable for applications in biotechnology/biomedicine. Recent studies reveal the tremendous scope of MNPs in therapeutics and theranostics. The requirements for nanoparticle size, morphology, and physio-chemical properties, especially magnetic properties, functionalization, and stability, vary with applications. There are also challenges for precise size control and the cost-effective production of nanoparticles in large quantities. The review should be an ideal material for researchers working on magnetic nanomaterials and an excellent reference for freshers.

Synthesis of pozzolan and sugarcane bagasse derived geopolymer-biochar composites for methylene blue sequestration from aqueous medium

In this study, four pozzolan-based geopolymers GP₀, GP₅, GP₁₀, and GP₂₀ were synthesized by alkaline activation and by substituting 0, 5, 10, and 20% of the precursor with sugarcane bagasse-derived biochar, respectively. The composites were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM/EDX), and Brunauer-Emmett-Teller (BET) surface area analyses, and applied to sequester methylene blue (MB) dye in an aqueous medium in batch mode. The alkaline activation of pozzolan-biochar blends resulted in the formation of poly (Ferro-sialate-siloxo)-biochar chains. The adsorption capacity increased with an increase in biochar content from 24.44 to 455.46 mg/g (18-fold) for GP₀ and GP₁₀, respectively. The sorption kinetics of MB onto the composites followed pseudo-second-order kinetics while the equilibrium data were best described by the Sips isotherm model. The adsorption process was thermodynamically spontaneous, endothermic (ΔH = 14.32-32.20 kJ/mol), and physical. The amount of adsorbent required for the removal of 99% of a fixed amount of MB in different volumes of effluent was predicted. Cost-analysis indicates that the composites are efficient and cheaper eco-adsorbents than commercial activated carbon and are suitable alternative candidates for the removal of dyes from water.

Controlled synthesis of graphene oxide/silica hybrid nanocomposites for removal of aromatic pollutants in water

The remarkable characteristics of graphene make it a model candidate for boosting the effectiveness of nano-adsorbents with high potential owing to its large surface area, π–π interaction, and accessible functional groups that interact with an adsorbate. However, the stacking of graphene reduces its influence adsorption characteristics and also its practical application. On the other hand, the widespread use of aromatic compounds in the industry has aggravated the contamination of the water environment, and how to effectively remove them has become a research hotspot. Herein, we develop the functionalization of silica nanoparticles on graphene oxide nanosheet (FGS) by a facile, cheap, and efficient synthesis protocol for adsorption of Trypan Blue (TB) and Bisphenol A (BPA). It was demonstrated that chemical activation with KOH at high autoclaving temperature successfully transformed rice husk ash (RHA) into FGS. The graphene oxide layered interlamination was kept open by using SiO₂ to expose the interlayers' strong adsorption sites. XRD, EDX, FTIR, Raman spectroscopy, SEM, HR-TEM, and BET surface area are used to investigate the chemical composition, structure, morphology, and textural nature of the as-produced FGS hybrid nanocomposite. The various oxygen-containing functional groups of the hybrid nanocomposites resulted in a significantly increased adsorption capacity, according to experimental findings. In addition, FGS2, the best composite, has a specific surface area of 1768 m²g⁻¹. Based on Langmuir isotherms, the maximal TB dye and BPA removal capacity attained after 30 min were 455 and 500 mg/g, respectively. The Langmuir isotherm model, a pseudo-second-order kinetic model, and an intraparticle diffusion model have all been used to provide mechanistic insights into the adsorption process. This suggests that BPA and TB adsorption on FGS2 is mostly chemically regulated monolayer adsorption. Due to its unique sp²-hybridized single-atom-layer structure, the exposed graphene oxide nanosheets' extremely hydrophobic effect, hydrogen bonding, and strong—electron donor–acceptor interaction contributed to their improved adsorption of BPA and TB. According to adsorption thermodynamics, FGS2 adsorption of TB and BPA is a spontaneous exothermic reaction that is aided by lowering the temperature. For adsorption-based wastewater cleanup, the produced nanocomposites with a regulated amount of carbon and silica in the form of graphene oxide and silica can be used. These findings suggest that functionalized GO/SiO₂ hybrid nanocomposites could be a viable sorbent for the efficient and cost-effective removal of aromatic chemicals from wastewater.

Computer-Aided Modeling, Simulation, and Exergy Analysis of Large-Scale Production of Magnetite (Fe3O4) Nanoparticles via Coprecipitation

Magnetite nanoparticles present attractive properties including high magnetization, low toxicity, adsorption capacity, and simple preparation, making them efficient in water purification processes, soil remediation, and biomedical applications. In this sense, there is growing interest in the production of magnetite nanoparticles; therefore, evaluating the performance of this process on a large scale gives relevant information to process designers. In this work, the simulation and exergy analysis of large-scale production of magnetite nanoparticles via coprecipitation were performed using computer-aided tools. The process was modeled for the production of 807 t/year of magnetite nanoparticles; the data for the simulation were obtained from the literature, and experimental results were developed by the authors. The exergy efficiency of the process was estimated at 0.046%. The exergy of waste was estimated to be 105 313 MJ/h, while the unavoidable exergy losses were 2941 MJ/h. Washing 2 and 3 represented the most critical stages of the process, contributing 95.12% of the total irreversibilities due to the waste exergy, which corresponds to the water and ethanol exergy discarded in these stages. These results show that the process must be improved from the energy point of view and require the implementation of process optimization strategies to reach a more sustainable design.

A Novel Trace-Level Ammonia Gas Sensing Based on Flexible PAni-CoFe2O4 Nanocomposite Film at Room Temperature

In this study, we developed a new chemi-resistive, flexible and selective ammonia (NH3) gas sensor. The sensor was prepared by depositing thin film of polyaniline-cobalt ferrite (PAni-CoFe2O4) nanocomposite on flexible polyethylene terephthalate (PET) through an in situ chemical oxidative polymerization method. The prepared PAni-CoFe2O4 nanocomposite and flexible PET-PAni-CoFe2O4 sensor were evaluated for their thermal stability, surface morphology and materials composition. The response to NH3 gas of the developed sensor was examined thoroughly in the range of 1-50 ppm at room temperature. The sensor with 50 wt% CoFe2O4 NPs content showed an optimum selectivity to NH3 molecules, with a 118.3% response towards 50 ppm in 24.3 s response time. Furthermore, the sensor showed good reproducibility, ultra-low detection limit (25 ppb) and excellent flexibility. In addition, the relative humidity effect on the sensor performance was investigated. Consequently, the flexible PET-PAni-CoFe2O4 sensor is a promising candidate for trace-level on-site sensing of NH3 in wearable electronic or portable devices.

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.