Fe3O4-multiwalled carbon nanotubes-bentonite as adsorbent for removal of methylene blue from aqueous solutions.

The contamination of water due to present of dyes, poses serious health problems. Therefore, treatment of contaminated water is necessary to resolve this problem. A tailored co-precipitation technique has been successfully used to prepare Fe3O4-multiwalled Carbon Nanotubes (MWCNTs)-Bentonite nanocomposite. The methylene blue present in aqueous solutions was removed using synthesized nanocomposite as adsorbent. The synthesized novel nanocomposite was analyzed by various characterization techniques. The scanning electron microscope analysis shows that Bentonite and Fe3O4 nanoparticles are well decorated with the MWCNTs matrix. The nanocomposite exhibited a high BET surface area of 204.01 m2/g with a pore volume of 0.367 cm3/g. The BJH adsorption average pore diameter was analyzed to be 7.2 nm. Moreover, the adsorption model was in agreement with the Redlich-Peterson model with adsorption capacity of 48.2 mg/g with a high nonlinear regression coefficient (R2 = 0.985) and a low chi-square value (χ2 = 6.18). Kinetics data were described well by pseudo-first-order and pseudo second order, models with a high non-linear regression coefficient (R2 = 0.993). Adsorption of MB dye was determined to be a non-spontaneous and endothermic process since the values of ΔG, and ΔH were positive, and the entropy value was negative. Thus, the synthesized nanocomposite established itself as a promising candidate for the water treatment process.

Carbon-coated Fe3O4 core-shell super-paramagnetic nanoparticle-based ferrofluid for heat transfer applications.

Herein, we report the investigation of the electrical and thermal conductivity of Fe3O4 and Fe3O4@carbon (Fe3O4@C) core-shell nanoparticle (NP)-based ferrofluids. Different sized Fe3O4 NPs were synthesized via a chemical co-precipitation method followed by carbon coating as a shell over the Fe3O4 NPs via the hydrothermal technique. The average particle size of Fe3O4 NPs and Fe3O4@C core-shell NPs was found to be in the range of ∼5-25 nm and ∼7-28 nm, respectively. The thickness of the carbon shell over the Fe3O4 NPs was found to be in the range of ∼1-3 nm. The magnetic characterization revealed that the as-synthesized small average-sized Fe3O4 NPs (ca. 5 nm) and Fe3O4@C core-shell NPs (ca. 7 nm) were superparamagnetic in nature. The electrical and thermal conductivities of Fe3O4 NPs and Fe3O4@C core-shell NP-based ferrofluids were measured using different concentrations of NPs and with different sized NPs. Exceptional results were obtained, where the electrical conductivity was enhanced up to ∼3222% and ∼2015% for Fe3O4 (ca. 5 nm) and Fe3O4@C core-shell (ca. 7 nm) NP-based ferrofluids compared to the base fluid, respectively. Similarly, an enhancement in the thermal conductivity of ∼153% and ∼116% was recorded for Fe3O4 (ca. 5 nm) and Fe3O4@C core-shell (ca. 7 nm) NPs, respectively. The exceptional enhancement in the thermal conductivity of the bare Fe3O4 NP-based ferrofluid compared to that of the Fe3O4@C core-shell NP-based ferrofluid was due to the more pronounced effect of the chain-like network formation/clustering of bare Fe3O4 NPs in the base fluid. Finally, the experimental thermal conductivity results were compared and validated against the Maxwell effective model. These results were found to be better than results reported till date using either the same or different material systems.

Synthesis of highly stable γ-Fe2O3 ferrofluid dispersed in liquid paraffin, motor oil and sunflower oil for heat transfer applications.

This article aims at the synthesis of highly stable γ-Fe2O3 magnetic nanoparticles and their ferrofluids using different base liquids such as liquid paraffin, motor oil and sunflower oil for heat transfer applications. Phase and morphology of the synthesized nanoparticles were probed using XRD, SEM and FTIR spectroscopy. The average nanoparticle size of γ-Fe2O3 magnetic nanoparticles was found to be 13 nm. Stability of the ferrofluids was monitored by visually observing the aggregation nature of the nanoparticles for 180 days. The ferrofluid prepared using motor oil as a base fluid exhibited high stability (for more than 1 year) and a mean enhancement of 77% in thermal conductivity at 1.5 vol% nanoparticles was observed as compared to base fluid. The viscosity of the ferrofluids was also measured and found to be 18, 38 and 8 cP at 27 °C for the liquid paraffin based, motor oil based and sunflower oil based ferrofluid, respectively.