Heavy-metal pollution of surface water, sediment and fish have been seen as a major global problem, with a significant proportion of developing countries like Bangladesh. This study assessed the intensity of alarming six toxic substances (Cr, Zn, Fe, Cu, Pb and Ni) throughout the River water, sediments as well as soft tissues of three widely consumed fishes (Heteropneustes fossilis, Channa punctatus and Channa striata) obtained from two urban streams of the Buriganga and Turag in the Dhaka metropolitan. For evaluating the comparative seasonal variation of heavy-metal concentration, water and sediment samples were collected from five selected sites for two different seasons (viz. 10 from winter seasons and 10 from summer seasons). Finally, a total of 20 water samples, 20 sediment and 12 fish samples were investigated by flame atomic absorption spectroscopy (FAAS) and graphite furnace atomic absorption spectrometer (GFAAS) corrected with the Zeeman effect background correction system. The hierarchy of mean concentration of selected heavy metals in Buriganga water is found to be Fe > Cr > Ni > Zn > Cu > Pb in the winter season whereas during the summer season the order is Fe > Cr > Zn > Ni > Cu > Pb. For the River Turag, the order is Fe > Zn > Cu > Ni > Cr > Pb and Fe > Zn > Ni > Cu > Cr > Pb during winter and summer season, respectively. The level of metals studied surpassed the acceptable level of drinkable water, implying the ineptitude of drinking and cooking water from these Rivers. However, this hierarchy of heavy metals for sediments of Buriganga River changed to Fe > Cr > Ni > Zn > Cu > Pb for the winter season and Fe > Cr > Ni > Cu > Zn > Pb for the summer season. Whereas, for the Turag River, the decreasing trend of metal concentration found in sediment was Fe > Zn > Cr > Ni > Cu > Pb for both seasons. For probable human health hazard implications, contamination factor (CF) and pollution load index (PLI) were studied. The CF values revealed the low-to-moderate pollution of sediment. The PLI value above one shows the degradation of the consistency of the sediments. Fe, Ni, Pb, Cr, Zn and Cu concentrations in fish species were found to be 19.66–45.1, 0.07–12.18, 1.2–10.18, 20.18–187.07, 11.08–68.25, 2.07–10.4 mg/kg, respectively. The metals studied differed considerably among organisms and seasons. Bioconcentration factor (BCF), the daily average consumption of metal (EDI), as well as target threat quotients (THQs) for specific metal indicated that Cr and Pb are harmful in fish muscles and possible risks remain for fish consumers. The obtained concentrations of some metals are higher than the WHO/FAO’s permissible limit, suggesting that the water and fish found in these Rivers are like to be harmful to the human being. This study shows that attention should be given to the risk assessment for heavy metals in these Rivers.

The bandgap energy range of multiferroic bismuth ferrite is 2.2-2.7 eV, making it a promising candidate for photovoltaic (PV) applications. But its efficiency is still very low (<2%). This report thus focusses on the application of bismuth ferrite (BFO) engineered with cobalt (Co) doping and on the tuning of its bandgap energy (E g). BiFeO 3 is a unique multiferroic material that simultaneously displays both ferromagnetic and ferroelectric properties at room temperature. Co doped with pure BiFeO 3 (BiFe (1−x) Co x O 3 ; x = 0, 0.05, 0.1 and 0.15) was synthesized by the sol-gel method and annealed at 600 • C. X-ray diffraction shows the well-arranged crystalline structure and peaks of pure and doped-BiFeO 3 nanoparticles. A suitable reduction of E g has been observed for Co-doped BiFeO 3 , which may be appropriate for the effective use in PV solar cells. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the thermal decomposition character of the xerogel powder and the pattern of pure and doped BiFeO 3 phases. Field emission scanning electron microscopy images show the surface crystallography of pure and Co-doped BiFeO 3. Co-doped BiFeO 3 has considerably reduced the crystallite and particle size of the samples. We have calculated the E g of pure and doped BiFeO 3 using a UV-Vis-NIR spectrophotometer and the results show the important reduction of E g (1.60 eV) of the Co-doped samples, which may have potential applications in PV solar cells.

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We report the synthesis of Y-substituted Mg-Zn [Mg 0.5 Zn 0.5 Y x Fe 2−x O 4 (0x0.05)] ferrites using conventional standard ceramic technique. The samples were characterized by x-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), FTIR spectroscopy, UV-Vis spectroscopy and quantum design physical properties measurement system (PPMS). XRD patterns confirm the single phase cubic spinel structure up to x=0.03 and appearance of a secondary phase of YFeO 3 for higher Y contents. FESEM images depict the distribution of grains and EDS spectra confirmed the absence of any unwanted element. Completion of solid state reaction and formation of spinel structure has been revealed from FTIR spectra. The FTIR data along with lattice constant, bulk density and porosity were further used to calculate the stiffness constant (C ij ), elastic constant and Debye temperatures. Mechanical stability of all studied compositions is confirmed from C ij using Born stability conditions. Brittleness and isotropic nature are also confirmed using Poisson's ratio and anisotropy constants, respectively. The enhancement of dc electrical resistivity (10 5 Ω cm to 10 6 Ω cm) with Y content is observed. The energy band gap (increased with Y contents) is found in good agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase change has been observed from the field dependent high temperature magnetization curves. The magnetic moments and saturation magnetization were found to be decreased with increasing temperature. The Curie temperature (T c ) has been measured from temperature dependent magnetic moment (M-T) and initial permeability (μ′ i -T) measurements and found to be in good agreement with each other. Decrease in T c with Y content is due to redistribution of cations and weakening of the exchange coupling constant. The magnetic phase transition has been analyzed by Arrott plot and found to have second order phase transition. The dc resistivity endorses the prepared ferrites are suitable for high frequency and high temperature magnetic device applications as well.Mg-Zn ferrite is one of the most used soft ferrites because of its high electrical resistivity, low cost, low dielectric loss, high mechanical hardness and superior environmental stability [13]. Mg-Zn ferrites with higher resistivity (10 6 -10 7 Ω cm) make its suitability in high frequency applications [13]. Most of (∼ 90%) Mg 2+ ions are located on the B-sites and small fraction (∼10%) occupies in the A-sites [14,15]. However, the Zn 2+ ions have a preference to occupy A-sites in the spinel lattice [16,17]. The Fe 3+ ions are distributed on both A-and B-sites [18]. Therefore, the physical properties of the Mg-Zn ferrites are determined by the cations distribution over the A-and B-sites. The physical properties can be altered by introducing the different metallic ions results the cations distribution modification on the A-and B-sites. The factors that determine cation distributions are ionic radius, charge, site preference and le...