Rajib Dey

Review: biofunctionalized quantum dots in biology and medicine

Quantum dot (QD) nanocrystals which have important optical properties, in particular, the wavelength of their fluorescence, depend strongly on their size. Colloidal QDs once dispersed in a solvent are quite interesting fluorescence probes for all types of labelling studies because of their reduced tendency to photo bleach. In this review, we will give an overview on how QDs have been used so far in cell biology. In particular, we will discuss the biologically relevant properties of QDs and focus on four topics: labeling of cellular structures and receptors with QDs, incorporation of QDs by living cells, tracking the path and the fate of individual cells using QD labels, and QDs as contrast agents. QDs are seen to be much better in terms of efficacy over radioisotopes in tracing medicine in vivo. They are rapidly being applied to existing and emerging technologies but here this review deals with a comprehensive compilation of the biological relevance of quantum dots. It covers important information from 1999 till 2008 with few from 1982 to 1997.

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Abstract Silicon nitride (Si3 N4) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si3 N4 nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.

Mineralogy and carbothermal reduction behaviour of vanadium-bearing titaniferous magnetite ore in Eastern India

Vanadium-bearing titaniferous magnetite bands hosted by Precambrian gabbro-norite-anorthositic rocks or their metamorphic equivalents were discovered in some parts of Eastern Indian Shield, containing 48%–49% Fe (total), 10%–25% TiO2, and 0.3%–2.20% V2O5 by mass. Mineralogical and petrological study, composition, and characterization of the vanadium-bearing titaniferous magnetite ore were carried out by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), wave length X-ray florescence (WDXRF), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), etc. Chemical beneficiation for valuable metals, such as Fe, Ti, and V, was performed by reduction roasting. The direct and indirect reduction were investigated by mixing the lump ore with solid activated charcoal in a closed reactor and purging the reducing gas mixture in standard reducibility index apparatus at different temperatures and time intervals. The reduction roasting parameters were optimized. Finally, the reduced samples were crushed and upgraded by magnetic separation. The results show that, the maximum mass fractions of magnetic and nonmagnetic parts achieved are 69.36% and 30.64%, respectively, which contain 10.6% TiO2 and 0.84% V2O5 in the magnetic part and 36.5% TiO2 and 0.22% V2O5 in the nonmagnetic part.

Oxidation behaviour and phase characterization of titaniferous magnetite ore of eastern India

Abstract Titaniferous magnetite ore is a kind of symbiotic complex ore which comprises ilmenite, magnetite, hercynite and magnesio-hercynite spinel minerals. The ore collected from eastern India was characterized by XRD, WDXRF, SEM and Mossbauer spectroscopy. The oxidation behaviour of fine ore was investigated by TG-DTA analysis under oxygen atmosphere. Subsequent isothermal oxidation experiments were carried out under oxygen and air atmospheres, holding the samples for different periods of time at different temperatures from 873 K to 1473 K. It was observed that ilmenite phase transformed to hematite and titanium dioxide at lower temperature, whereas ferric-pseudobrookite phase was found at higher temperature. Direct reduction of oxidized sample-coke cylindrical briquettes was successfully achieved for phase transition from titaniferous magnetite to iron and titanium dioxide at 1473 K.

Biofunctionalised quantum dots for sensing and identification of waterborne bacterial pathogens

Harmful bacteria are the most common cause of food- and waterborne illnesses. Infection often leads to bloody diarrhoea, and occasionally to kidney failure. Several strains of the bacteria Escherichia coli produce a powerful toxin which causes serious illness. Food and water can be contaminated with other bacteria like Salmonella, Coliform, Pseudomonas, etc. Hence, it has become important to rapidly detect and identify infectious bacteria. Colloidal luminescent semiconductor nanocrystals or quantum dots (QDs) have elicited a great deal of interest in the biosensing community due to their unique fluorescent properties. Here ZnS : Mn2+ QDs are synthesised and biofunctionalised with chitosan. They are attached to the anionic cell wall of E. coli bacteria and different properties of this compound system are studied. These nanocrystals may offer cost effective and quicker alternative to detect single bacterium compared to other conventional methods. The process of the synthesis of QDs, biofunctionalisation and detection of bacteria have been characterised by XRD, UV-Vis spectroscopy, FTIR, photoluminescence spectroscopy, AFM, high-resolution transmission electron microscopy and confocal microscopy. The particle size calculated is approximately 8–10 nm. The blue shift of PL peak has been observed after the bacteria get attached.

Microbial leaching of chromite overburden from Sukinda mines, Orissa, India using Aspergillus niger

Leaching of nickel and cobalt from two physical grades (S1, 125–190 μm, coarser and S3, 53–75 μm, finer) of chromite overburden was achieved by treating the overburden (2% pulp density) with 21-d culture filtrate of an Aspergillus niger strain grown in sucrose medium. Metal dissolution increases with ore roasting at 600°C and decreasing particle size due to the alteration of microstructural properties involving the conversion of goethite to hematite and the increase in surface area and porosity as evident from X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (DT-TGA), and field emission scanning electron microscopy (FESEM). About 65% Ni and 59% Co were recovered from the roasted S3 ore employing bioleaching against 26.87% Ni and 31.3% Co using an equivalent amount of synthetic oxalic acid under identical conditions. The results suggest that other fungal metabolites in the culture filtrate played a positive role in the bioleaching process, making it an efficient green approach in Ni and Co recovery from lateritic chromite overburden.

Novel technique for synthesis of silicon nitride nanowires

Abstract Abstract Silicon nitride nanowires have been prepared by carbothermal reduction followed by nitridation of silica gel by in situ generation of ultrafine carbon as well as nitrogen over a temperature range of 1200–1350°C. Before the heat treatment dry silica gel is subjected to repeated evacuation followed by purging with ammonia. Ammonia is adsorbed on the silica gel surface and forms a ≡Si–NH2 bond which acts as a source of in situ generation of nitrogen and decomposition of dextrose provides ultrafine carbon respectively at the reaction temperature. During a high temperature heat treatment ultrafine carbon reduces the partial pressure of oxygen required for the generation and stabilisation of silicon nitride nanowires. The nanowires synthesised by this process are of 20–40 nm diameter and ∼1 μm length. The nanowires are characterised by XRD and filed emission SEM and EDAX.

A Novel Devolatilization Technique of Pre-reduction of Iron Ore Using Lean Grade Coal

The problem of properly utilizing non-coking coals in alternative iron making processes dates back to long ago. Lean grade coals with higher ash and volatile matter content (e.g. boiler grade coals) have always challenged the metallurgists to develop a suitable process for their utilization. The aim of this work is to achieve an energy efficient method for the reduction of briquetted iron ore fines using ‘SYNGAS’—which is the gaseous product (enriched with reducing agents) generated by pyrolysis of coal along with fine sized carbon particles produced during pyrolysis. A laboratory scale reduction furnace with pyrolysis facility has been designed and fabricated after in depth thermo-gravimetric analysis (TGA), differential thermal analysis (DTA), and gas chromatograph (GC) studies. A particular temperature profile has been maintained inside the furnace to achieve the optimum reduction temperature. The briquettes are reduced in the pyrolysis furnace and the extent of reduction has been calculated from the weight loss. The reduced specimens are characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX), field emission scanning electron microscope (FESEM), and chemical analysis method. It is observed that iron ore can be significantly reduced to metallic iron by using the devolatilization product of lean grade coal.ZusammenfassungDas Problem der richtigen Anwendung von nichtkokenden Kohlen in alternativen Eisenherstellungsverfahren ist schon lange bekannt. Minderwertige Kohlen mit höherem Aschegehalt und flüchtigen Bestandteilen (z. B. Kesselkohlen) und die Entwicklung eines geeigneten Verfahrens zu ihrer Nutzung haben schon immer die Metallurgen herausgefordert. Das Ziel dieser Arbeit ist die Entwicklung eines energieeffizienten Verfahrens zur Reduktion des brikettierten Feineisenerzes unter Verwendung von SYNGAS. SYNGAS ist das gasförmige Produkt einer Kohleentgasung, welches mit feinen Kohlepartikeln vermischt wird. Dazu wurde ein Reduktionsofen im Labormaßstab mit Entgasungsmöglichkeit nach thermo-gravimetrischen Analysen (TGA), Differentialthermoanalysen (DTA) und Gaschromatographie (GC) Untersuchungen entwickelt. Um die optimale Reduktionstemperatur zu erreichen, wird ein besonderes Temperaturprofil innerhalb des Ofens eingestellt. Die Briketts werden im Pyrolyseofen reduziert, und das Ausmaß der Reduktion wird aus dem Gewichtsverlust berechnet. Die reduzierten Proben werden unter Verwendung von Röntgen-Diffraktometrie (XRD), Rasterelektronenmikroskopie (REM), energiedispersive Röntgenspektrometer (EDX), Feldemissions-Rasterelektronenmikroskop (FE-REM) und chemischen Analyseverfahren charakterisiert. Es wurde beobachtet, dass Eisenerze durch Verwendung des Entgasungsprodukts aus minderwertigen Kohlen zu einem hohen Anteil zu metallischen Eisen reduziert werden können.

Statistical optimisation parameter for lean grade self-reducing nuggets by surface response modelling to produce pig iron

Iron ore fines, lean grade coal and coke dust fines have always challenged the metallurgists to develop a suitable process for its optimum use. The aim of this study is to utilise the inferior quality of iron ore fines, coal and plant waste coke dust for reduction. At first mechanical properties of iron ore nuggets are assessed through shatter and abrasion test and subsequent to which cold bonded self-reducing nuggets are directly reduced in standard reducing furnace. The maximum extent of reduction achieved in the present study is 87.2%. The reduced specimens are further characterised using XRD, SEM, EDX and chemical analysis method. Finally, the statistical model of Box Behnken Design (BBD) method is successfully utilised to optimise the process parameter for reduction experiments. The optimised sample thus obtained is subjected to melting for laboratory scale pig iron production. Better slag metal separation is achieved when calcined lime is used as a flux. The microstructure of the metallic iron is studied and it shows ferrite phase with dispersed carbon.

Reduction behaviour of agglomerated iron ore nuggets by devolatisation of high-ash, high-volatile lignite coal for pig iron production

High-quality coking coals all over the world are gradually approaching extinction. These days, steel industries are trying to focus more on the utilisation of non-coking grades of coal. The present work involving high-ash, high-volatile lignite coal can be used indirectly in iron-making processes. Direct use is not possible due to low amount of carbon and high value of ash. High ash content leads to huge sulphur content, and this leads to high cost involvement in secondary processes. On the other hand, huge amount of iron ore fines are generated during mechanised mining, sizing, screening, transportation, beneficiation and sintering processes. Iron ore nuggets are formed from inferior quality iron ore fines using suitable binders with the applied pressure. Mechanical properties of iron ore nuggets are also assessed through shatter and abrasion test. A furnace was designed, to indirectly utilise high-ash, high-volatile lignite coal, for pre-reduction iron ore nuggets. Iron ore nuggets were partly reduced by CO, H2 and fine carbon produced from volatilisation of coal. Optimized pre-reduced nuggets, having high mechanical stability was directly charge in the raising hearth furnace for pig iron production.