In this era, nanotechnology is gaining enormous popularity due to its ability to reduce metals, metalloids and metal oxides into their nanosize, which essentially alter their physical, chemical, and optical properties. Zinc oxide nanoparticle is one of the most important semiconductor metal oxides with diverse applications in the field of material science. However, several factors, such as pH of the reaction mixture, calcination temperature, reaction time, stirring speed, nature of capping agents, and concentration of metal precursors, greatly affect the properties of the zinc oxide nanoparticles and their applications. This review focuses on the influence of the synthesis parameters on the morphology, mineralogical phase, textural properties, microstructures, and size of the zinc oxide nanoparticles. In addition, the review also examined the application of zinc oxides as nanoadsorbent for the removal of heavy metals from wastewater.

Single crystalline nickel ferrite (NiFe2O4) which has an inverse spinel structure is reported to exhibit a mixed spinel structure when its grain size is reduced to nanometer range. It is known that structural transformations in the nanosize regime are not akin to those of bulk crystals. Additionally, magnetic properties like superparamagnetism and contribution to it by surface layers are critically influenced by the synthesis route of the samples. In this article, we present an investigation on the structural transformation of nanostructured NiFe2O4 using x-ray diffraction (XRD), Mössbauer and magnetization measurements, and Fourier transform infrared (FTIR) and micro-Raman spectroscopy. Nanostructured NiFe2O4 samples were synthesized by a coprecipitation technique followed by thermal processing. Four samples having average grain sizes 13, 20, 26, and 51 nm were synthesized. XRD results confirmed the samples to be nanostructured NiFe2O4 and gave evidence for the mixed spinel structure of the samples of lower grain sizes. Mössbauer study of the smallest and largest grain-sized samples revealed surface spin canting and change in coordination of the iron ions at tetrahedral and octahedral sites with reduction in grain size. The spin canting angle and the coordination factor were determined from the Mössbauer spectra. Vibrating sample magnetometer measurements gave a lower value of magnetization for the samples of lowest grain size and this observation could be explained on the basis of a structural transformation of the sample from inverse to mixed spinel. FTIR and micro-Raman spectroscopic studies also yielded convincing evidence for a transformation of the structure. The results of the present study lead to the inference that the properties of nanosized NiFe2O4 particle emerged from a transformation of their structure from inverse spinel structure to mixed spinel.

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Road deposited sediments contain toxic metals which can pollute terrestrial as well as aquatic environments when these pollutants are mobilized during storm runoff. Assessment of toxic metals in the road deposited sediments of Suleja streets was carried out. 30 samples were collected from seven selected streets. The road sediment samples were digested with a mixture of HNO 3 and HClO 4 (2:1 v/v), and analyzed for the metals Pb, Cu, Cr, Zn, Cd and Ni using Atomic Absorption Spectrophotometer. Results showed that metal concentrations were in the order Zn>Pb>Cu>Ni>Cd>Cr. Geo-accumulation Index indicated that the contamination degree ranged from unpolluted to moderately polluted areas. Potential Ecological Risk Index demonstrated that overall risk caused by metals ranges from moderate to low. Only Cd constitutes considerable risk and contributed 60.15% of the total risk.