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Abstract A massive release of harmful substances especially heavy metal ions and dyes to the environment has been a major concern due to many people disregards the proper protocols in the waste management. The freshwater supplies are threatened and huge discharge of pollutants result from various anthropogenic activities may pose a major threat to the living organisms and negatively affect the ecosystem stability. This article reviews the development of magnetic iron oxide nanocomposites for removal of heavy metal ions and dyes from water. The highlight will be focused on current research activities for controlled size and dispersion of magnetic iron oxide nanoparticles within solid matrices including zeolites, silica, clays, carbon, activated carbon, graphene and graphene oxide. The magnetic properties of the nanocomposites will be evaluated to determine whether they possessed sufficient magnetization for easy separation by an external magnet. The unique features of the synthesized materials will be investigated along with their application in the removal of heavy metal ions and dyes. The advantages and limitations of the magnetic nanocomposites will be highlighted to determine their adsorption ability. The effect of various parameters such as pH, contaminants concentration, adsorbent dosage, contact time and temperature will be summarized to identify the best condition for effective pollutants removal. Graphical abstract Image 1 Highlights • Synthesis, properties and application of magnetic iron oxide NCs for the adsorption of heavy metal ions and dyes. • Methods for the preparation of magnetic iron oxide NCs with control over the size, morphology and the magnetic properties. • Factors affecting the adsorption of heavy metal ions and dyes in water by magnetic iron oxide NCs. • Influence of the iron oxide loading and specific surface area of NCs on removal of heavy metal ions and dyes in water. [ABSTRACT FROM AUTHOR]

This paper presents a green, facile and rapid method to prepare magnetite/zeolite-nanocomposites (NCs) in one step procedure at ambient temperature. The powder X-ray diffraction (PXRD) pattern of iron oxide nanoparticles (NPs) with the sole zeolite showed the broadening of zeolite peaks attributed to the incorporation of Fe 3 O 4 . Field-emission scanning electron microscopy (FESEM) analysis depicted that the Fe 3 O 4 ‒NPs were formed on the surface of porous zeolite framework. Transmission electron microscopy (TEM) analysis displayed the Fe 3 O 4 nanoparticles (NPs) were mostly in spherical shape with a mean diameter and standard deviation of 2.40 ± 0.41 nm. The selected-area electron diffraction (SAED) pattern confirmed the presence of cubic Fe 3 O 4 phase. The vibrating sample magnetometer (VSM) results indicated the as-synthesized sample has a saturation magnetization of around 6.52 emu g −1 . The magnetite/zeolite-NCs can be considered as a low-cost alternative catalyst for oxygen reduction reaction (ORR) process. The electrochemical measurement showed that the performance of magnetite/zeolite-NCs towards the ORR increased as the scan rate increased from 20 mV s −1 to 500 mV s −1 . The ORR is a diffusion-controlled process in the alkaline medium. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of OH concentration on the size of Fe3O4 nanoparticles (Fe3O4-NPs). Fe3O4-NPs with different cubic nanocrystal structure and percentage Fe3O4 content were successfully prepared, by use of the chemical co-precipitation method, on the exterior surface of talc, as solid substrate, by an environmentally friendly process. Ferric chloride, ferrous chloride, and sodium hydroxide were used as iron oxide precursors and reducing agent. The results showed that the morphology of the Fe3O4-NPs can be adjusted by changing the reaction conditions, for example volume of reducing agent and concentration of iron salts. Different size, dispersal, and the magnetic properties were obtained by changing the concentration of iron salts and NaOH. The products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. The reaction was conducted in a non-oxidizing, oxygen-free environment. Because the interlamellar spacing of the talc was almost unchanged (ds = 0.94-0.87 nm), the Fe3O4-NPs were formed on the exterior surface of the talc. The average diameter of the Fe3O4-NCs could be varied from 6.62-8.13 nm in adjusting the concentration of NaOH. The size of the nanoparticles decreased as the amount of reducing agent was increased. These talc-Fe3O4nanocomposites (talc-Fe3O4-NCs) may have potential applications in the chemical and biological industries. [ABSTRACT FROM AUTHOR]