Enhancing the efficiency of magnetically driven carbon nitride-based nanocomposites with magnetic nanoflowers for the removal of methylene blue dye at neutral pH.

The present study focuses on the elaboration of magnetic nanocomposites by the in situ incorporation of magnetite (Fe3O4) nanoparticles (NPs) with spherical and nanoflower-like morphologies in graphitic carbon nitride (g-C3N4) sheets using two different synthetic routes. Nanomaterials are characterized by TEM, SEM, XRD, FTIR, BET, zetametry, vibrating sample magnetometry, and UV-vis absorption spectroscopy. The decoration of the carbon nitride matrix with the magnetic NPs enhanced optical and textural properties. The influence of the morphology of the magnetic NPs on the adsorptive and photocatalytic properties of the nanocomposites under different pH conditions (4.5, 6.9, and 10.6) was assessed from batch tests to remove methylene blue (MB) from aqueous solutions. In extreme pH conditions, the nanocomposites exhibited lower or equivalent MB removal capacity compared to the pure g-C3N4. However, at neutral medium, the nanocomposite with incorporated Fe3O4 nanoflowers showed a significantly higher removal efficiency (80.7%) due to the combination of a high adsorption capacity and a good photocatalytic activity in this pH region. The proposed nanocomposite is a promising alternative to remove cationic dyes from water by magnetic assistance, since no pH adjustment of the polluted effluent is required, reducing costs and environmental impact in the dyeing industry.

Hybrid magnetic CoFe2O4@γ-Fe2O3@CTAB nanocomposites as efficient and reusable adsorbents for Remazol Brilliant Blue R dye.

The main goal of the present survey was to elaborate, characterize and evaluate the efficiency of ferrite-based nanoparticles modified with cetyltrimethylammonium bromide (CTAB) as potential magnetic nanoadsorbents to remove Remazol Brilliant Blue R (RBBR) from water. It is proposed an innovative nanomaterial architecture based on highly magnetic and chemically stable core@shell nanoparticles covered by an adsorptive surface layer of CTAB (CoFe2O4@γ-Fe2O3@CTAB). Samples of two different mean sizes (7.5 and 14.6 nm) were synthesized using a hydrothermal coprecipitation followed by surface treatment and functionalization. Batch tests were performed to evaluate the influence of contact time, temperature, pH, shaking rate, presence of interferents and mean size on the performance of the proposed nanomaterials. The kinetics of the adsorption process followed the pseudo-second-order model with an equilibrium time of 20 min. The adsorption capacity was estimated by the Langmuir isotherm model and was found to be 56.3 mg/g (smaller size) and 45.6 mg/g (larger size) at pH = 3 and a shaking rate of 400 rpm. The process was spontaneous, exothermic, and showed increased randomness. Sulphate ions negatively impacted the removal of RBBR. The best performance of the nanoadsorbent based on smaller mean sizes can be correlated to its larger surface area. Regeneration and readsorption tests showed that the nanoadsorbents retain more than 80% of their original removal capacity, therefore they can be effectively recycled and reused.

A numerical study on the interplay between the intra-particle and interparticle characteristics in bimagnetic soft/soft and hard/soft ultrasmall nanoparticle assemblies.

A mesoscopic scale approach and the Monte Carlo (MC) method have been employed to study the exchange bias behaviour of MnFe2O4 (soft)/maghemite (soft) and CoFe2O4 (hard)/maghemite (soft) nanoparticles (NPs) of size ∼ 3 nm in dense and diluted assemblies at low temperatures. The analysis of our MC results clearly shows that in the powder samples the contribution to the exchange bias field (H ex) and the coercivity (H c) comes mainly from the intraparticle core/shell structure in the hard/soft sample and that the interplay between the internal characteristics and the interparticle interactions is more important in the soft/soft samples where the dipolar strength is enhanced. In the diluted frozen ferrofluid samples where interparticle exchange interactions are absent and the role of the dipolar interactions is not significant the exchange bias effects are reduced, and they come from the intra particle structure. The variation of H ex and H c with the applied cooling field well reproduces the experimental findings and sheds light on the key mechanisms of the observed magnetic behaviour. Our results demonstrate the possibility to control the magnetic behaviour of nanostructures by using properly chosen core/shell bimagnetic nanoparticles.

Core-Shell Bimagnetic Nanoadsorbents for Hexavalent Chromium Removal from Aqueous Solutions.

Novel nanoadsorbents based on core-shell bimagnetic nanoparticles (CoFe2O4@É£-Fe2O3) with two different mean sizes were elaborated, characterized and applied as potential sorbents for Cr(VI) removal from aqueous solutions through magnetically assisted chemical separation. The nanoadsorbents were characterized by XRD, TEM, FTIR, XPS, potentiometric-conductometric titrations, BET and vibrating sample magnetometry. The influence of contact time, shaking rate, pH, pollutant concentration, temperature and competing ions on Cr(VI) adsorption were evaluated. The results were analyzed in the framework of Langmuir and Freundlich models to evaluate the maximum adsorption capacity and the extent of affinity. The nanoadsorbents showed a good selectivity for Cr(VI) adsorption and were more effective at pH = 2.5, with a shaking rate of 400 RPM. The adsorption process was spontaneous, endothermic and presented an increased randomness. The contact time required to reach the equilibrium was relatively short and the kinetic date followed the pseudo-second-order model. The maximum adsorption capacity was nearly 40% higher for the nanoadsorbent of smaller mean size due to its higher surface area. Regeneration studies revealed that the nanoadsorbents can be recovered for reuse. These results indicate that prepared nanoadsorbents can be used as a powerful tool for Cr(VI) removal from contaminated water.