H. N. M. Ekramul Mahmud

Structural and Optical Characterization of Metal Tungstates (MWO4; M=Ni, Ba, Bi) Synthesized by a Sucrose-Templated Method

BackgroundMetal tungstates have attracted much attention due to their interesting structural and photoluminescence properties. Depending on the size of the bivalent cation present, the metal tungstates will adopt structures with different phases. In this work, three different phases of metal tungstates MWO4 (M= Ba, Ni and Bi) were synthesized via the sucrose templated method.ResultsThe powders of BaWO4 (tetragonal), NiWO4 (monoclinic) and Bi2WO6 (orthorhombic) formed after calcination temperatures of 750, 650 and 600°C for 4 h respectively are found to be crystalline and exist in their pure phase. Based on Scherrer estimation, their crystallite size are of nanosized. BET results showed NiWO4 has the highest surface area. BaWO4 exhibited less Raman vibrations than the NiWO4 because of the increased lattice symmetry but Bi2WO6 showed almost the same Raman vibrations as BaWO4. From the UV-vis spectra, the band gap transition of the metal tungstates are of the order of BaWO4 > Bi2WO6 > NiWO4. Broad blue-green emission peaks were detected in photoluminescence spectra and the results showed the great dependence on morphology, crystallinity and size of the metal tungstates.ConclusionThree different phases of metal tungstates of BaWO4 (scheelite), NiWO4 (wolframite) and Bi2WO6 (perovskite layer) in their pure phase were successfully prepared by the simple and economical sucrose-templated method. The highest surface area is exhibited by NiWO4 while largest band gap is shown by BaWO4. These materials showed promising optical properties.

Influence of adsorption parameters on cesium uptake from aqueous solutions- a brief review

Due to rapid population growth, technological advancement and industrial revolution, the rate of generated waste effluents has become a grave concern. Cesium which possesses high fission yield is generally transferred to liquid wastes especially those emanated from the nuclear power plants, reprocessing of spent fuels, nuclear weapon testing and radionuclides production facilities for medical applications etc. Radiocesium (137Cs) is one of the hazardous radionuclides creating adverse effects on human health and environment. Due to its physical (T1/2 = 30.17y) and chemical characteristics (alkalinity, solubility etc.), it can be easily assimilated by the living organisms. As a result, the removal of cesium from wastewater is imperative from the health point of view. Several techniques are implemented but in recent time, adsorption has been gaining increasing attention to the scientific community owing to a number of reasons. Hence, this paper presents an overview on sorption of cesium from wastewaters. Consequently, several critical parameters such as sorption capacity, percentage efficiency and the influence of several factors on cesium uptake by various adsorbents have been reviewed in details.

OPTICAL BAND GAP AND CONDUCTIVITY MEASUREMENTS OF POLYPYRROLE-CHITOSAN COMPOSITE THIN FILMS

Electrical conductivity and optical properties of polypyrrole-chitosan (PPy-CHI) conducting polymer composites have been investigated to determine the optical transition characteristics and energy band gap of composite films. The two electrode method and I–V characteristic technique were used to measure the conductivity of the PPy-CHI thin films, and the optical band gap was obtained from their ultraviolet absorption edges. Depending upon experimental parameter, the optical band gap (Eg) was found within 1.30–2.32 eV as estimated from optical absorption data. The band gap of the composite films decreased as the CHI content increased. The room temperature electrical conductivity of PPy-CHI thin films was found in the range of 5.84 × 10−7–15.25 × 10−7 S·cm−1 depending on the chitosan content. The thermogravimetry analysis (TGA) showed that the CHI can improve the thermal stability of PPy-CHI composite films.

The effect of terminal substituents on crystal structure, mesophase behaviour and optical property of azo-ester linked materials

ABSTRACT A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH3, –OC2H5 and –OC3H7) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R12(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R22(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH3, –OC2H5 and –OC3H7) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λmax) of nearly 370 nm. GRAPHICAL ABSTRACT

Synthesis and characterization of a new conducting polymer composite

Organic conductive composite films have been synthesized by electropolymerization of pyrrole in the presence of chitosan and p-toluene sulfonic acid sodium salt. The obtained conductive polymer composite films have been characterized by Fourier Transform Infrared spectroscopy, dynamic mechanical analysis, scanning electron microscopy, X-ray diffraction and conductivity measurements. The prepared polymer composite films had the amorphous structure and exhibited the enhanced conductivity and mechanical properties due to the presence of chitosan in the composite films.

Electromagnetic Interference Shielding Effectiveness of New Conducting Polymer Composite

Electrical conductivity and shielding effectiveness (SE) of conductive polymer composite of polypyrrole-chitosan (PPy-CHI) have been studied. It was shown that chitosan can improve electrical and thermal properties of polypyrrole. The applicability of PPy-CHI composite films to the electromagnetic wave shielding in the microwave frequency range from 8 to 12 GHz were investigated. The SE of the composite films had a strong dependence on chitosan content. The SE of the composite films was obtained by Simon formalism. Comparison of the experimental and theoretical values revealed good correspondence of the shielding of the composite films at high conductivity and frequency.

An overview of detection techniques for monitoring dioxin-like compounds: latest technique trends and their applications

Dioxin-like compounds (DLCs) are considered persistent bioaccumulative toxicants with a number of continuing issues in the fields of ecotoxicology and bioassay. In spite of the great need to monitor these compounds, the only analytical technique with sufficient sensitivity and selectivity for determination of DLCs is a combination of high-resolution gas chromatography and high-resolution mass spectrometry. However, these methods require aseptic techniques, long incubation times, and sophisticated technical expertise for getting accurate results. Nowadays, biological techniques such as biomarkers, bioassays, enzyme immunoassays (EIAs), or other methods have been greatly developed as more sensitive, cost-effective and rapid techniques to determine the presence of DLCs in trace levels of environmental and biological samples. The main aim of this study is to review the latest analytical and bioanalytical detection methods (BDMs) for diagnosis and monitoring of DLCs. Likewise, this work characterizes the latest techniques and trends based on their application, advantages and shortcomings for the various BDMs and their differences are also noted.

Removal of Nickel Ions from Aqueous Solution by Polypyrrole Conducting Polymer

Polypyrrole (PPy) conducting polymer prepared by chemical oxidation method using FeCl3.6H2O as an oxidant has exhibited 100% adsorption efficiency for the removal of nickel ions from aqueous solution. At pH 7, 100% nickel absorption was found by the prepared polypyrrole as measured by atomic absorption spectrophotometry. At both acidic and alkaline solutions, the adsorption efficiency of PPy was substantially lowered. The effects of pH, the initial concentration of nickel stock solution and the contact time on the uptake of nickel ions were also investigated. With the variation of initial concentration from 1-5 ppm, the initial concentration of 1 ppm nickel has been found to be adsorbed fully (100%) by the prepared polypyrrole. The contact time of 8 hours has been found to be the highest effective contact hours as beyond this there was no adsorption effect. The FTIR results confirmed the presence of nickel ions in the polymer matrix after adsorption.

Development and Characterization of Polypyrrole-Based Nanocomposite Adsorbent and Its Applications in Removal of Radioactive Materials

Development of environmental friendly materials is desirable in the fields of science and engineering for various purposes. In environmental science, they find applications commonly in environmental remediation and the recovery of valuable metals. This aspect is of particular concern to health sciences due to the toxic effects and non-biodegradable nature of many substances that have found their way into the human body via environmental media. As for instance, though cobalt possesses some importance in diet it has been linked to health problems like cardiomyopathy, asthma etc. via overexposure. As a result, removal of this substance from the aqueous media of our environment is crucial. In this study, polypyrrole conducting polymer incorporated with biomass waste (sawdust) was prepared by simple chemical oxidative polymerization as a composite adsorbent for 57Co radionuclide removal from aqueous solution. The as-prepared composite material was characterized by FESEM, XRD and BET surface analysis. In the 57Co adsorption studies, the effects of several factors such as adsorbent dosage, contact time and competitive metal ions were investigated for real wastewater treatment applications. The results indicated that the removal process was rapid and reached saturation within 3 hours of contact of adsorbent and adsorbate at ambient temperature. Both Na+ and K+ coexisting ions were found to affect 57Co adsorption and the uptake percentage was reduced from 54.9 to ~ 20% at 0.1M of both Na+ and K+ ions. Langmuir isotherm model was used to fit the maximum sorption capacity.