In recent years, there has been increasing concern about the usage of a broad range of organic substances, heavy metals and aromatic compounds in the aquatic environment due to their wide distribution and potential adverse health effects. The presence of toxic contaminants in water effluent, even at very low concentrations, is extremely harmful and undesirable. Various treatment processes have been investigated to reduce these toxic pollutants from wastewater. Because of the chemical stability of the contaminants, these technologies have proved to be ineffective for handling waste effluents. Nanotechnology offers the possibility of efficient removal of pollutants as nanoparticles have a smaller size and higher adsorptive surface area. From the past few years, nanoscale iron oxides such as magnetite, maghemite, and hematite have been used for the separation and removal of organic and inorganic contaminants. In this review we summarize the use of iron oxide nanomaterials performed over the last few years for the removal of dyes, heavy metals and aromatic compounds.

The current research work focuses on the synergistic effect of Ni doped ZnO nanoparticles and ultrasonication for the degradation of anionic (Fast Green) and cationic (Victoria Blue) dyes. Well crystalline monodispersed Ni doped ZnO nanoparticles have been synthesized by quick and simple co-precipitation technique at low temperature. Synthesized nanoparticles have been characterized by X-ray diffraction, UV-vis spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The effects of operating parameters such as catalyst dosage, pH, power dissipation, temperature and dye initial concentration have been investigated, and the enhancement in degradation capability of Ni doped ZnO with undoped ZnO has also been discussed. The degradation of both the dyes follows pseudo-first-order kinetics. In concert with superior activity and reuse performance, the current route is promising for the application of ZnO-based catalysis for water decontamination.

The present paper reports the applicability of magnetite (Fe3O4) nanoparticles as an adsorbent for the removal of three dyes viz. Acridine orange (cationic dye), Comassie Brilliant Blue R-250 (anionic dye) and Congo red (azo dye) from their aqueous solution. The Fe3O4 nanoparticles were synthesized via simple chemical precipitation method using CTAB, as surfactant. The as-prepared nanoparticles were characterized in terms of their morphological, structural and optical properties by using transmission electron microscopy X-ray diffraction and UV-visible spectroscopic measurements. The dye removal efficiency of Fe3O4 NPs have been determined by investigating several factors such as effect of pH, amount of adsorbent dose and effect of contact time on different dye concentrations. Langmuir and Freundlich adsorption isotherms have also been studied to explain the interaction of dyes. The experimental data indicate that the adsorption rate follows pseudo- second-order kinetics for the removal of all the three dyes. Moreover, the nanoparticles and the adsorbed dyes were desorbed. The identities of recovered nanoparticles as well as the three dyes have been found, as same and were reused.

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