Satyawati S. Joshi

Fluorescence Behavior of Cysteine-Mediated Ag@CdS Nanocolloids

Ag@CdS quantum dots were synthesized by a colloidal method. CdS nanoparticles stabilized by L-cysteine were doped with varying silver concentrations. Ag@CdS nanoparticles were characterized by UV-visible spectroscopy, steady-state and time-resolved fluorescence, X-ray diffraction, Fourier transform infrared resonance (FTIR), and transmission electron microscopy. The effect of dopant concentration and effect of aging of Ag@CdS colloids were studied. At low silver content, emission was found to enhance, while at high silver content, emission quenching was observed after aging. Ag-CdS nanocolloids exhibited multiexponential decay with tau2 being a long-lived component. X-ray diffraction spectra of as prepared samples indicated that silver occupies an interstitial position, while for annealed samples, Ag+ ions get oxidized to Ag2+ and substituted for Cd2+ in the CdS lattice. FTIR studies have shown that cysteine acts as a monodentate ligand for cadmium and silver for as-prepared sample, whereas it acts as a tridentate ligand for annealed samples toward silver. Transmission electron microscopy of as-prepared samples showed spherical-shaped composites with a uniform layer of capping molecules.

Effect of method of crystallization on the IV–III and IV–II polymorphic transitions of ammonium nitrate

A study has been undertaken on the effect of crystallization method on the IV<-->III transition of ammonium nitrate (AN). AN is crystallized in three different ways, viz. recrystallization, evaporative crystallization and melt crystallization. When the samples were crystallized from saturated aqueous solution, ideal crystals were formed, which behaved differently from the crystals formed from the other methods. The DTA examination of the crystals showed that the crystals have different transition behaviour. The moisture uptake of the samples determined were found to have influenced by the mode of crystallization. The samples were further analyzed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The present study showed that the parameters like thermal history, number of previous transformations and moisture content have a very negligible influence on the IV<-->III transition of AN as compared to the method of crystallization.

Use of potassium ferrocyanide as habit modifier in the size reduction and phase modification of ammonium nitrate crystals in slurries.

Ammonium nitrate (AN) is an inorganic crystalline compound used as a solid propellant oxidizer and as a nitrogenous fertilizer. The practical use of AN as solid propellant oxidizer is restricted due to the near room temperature polymorphic phase transition and hygroscopicity. A good deal of effort has been expended for last many years to stabilize the polymorphic transitions of AN, so as to minimize the storage difficulties of AN based fertilizers and to achieve more environmentally benign propellant systems. Also, particles with aspect ratio nearer to one are a vital requirement in fertilizer and propellant industries. In the present study AN is crystallized in presence of trace amount of potassium ferrocyanide (K(4)Fe(CN)(6)) crystal habit modifier and kept for different time intervals. And the effect of K(4)Fe(CN)(6) on the habit and phase modification of AN was studied. Phase modified ammonium nitrate (PMAN) with a particle aspect ratio nearer to one was obtained by this method and the reasons for this modifications are discussed. The morphology changes were studied by SEM, the phase modifications were studied by DSC and the structural properties were studied by powder XRD.

Optical and photocatalytic properties of single crystalline ZnO at the air-liquid interface by an aminolytic reaction.

Crystalline flowerlike ZnO was synthesized by an aminolytic reaction at the air-liquid interface in an aqueous media at an alkaline pH. A thin visible film was formed at the air-liquid interface by self-assembly of flowerlike ZnO. Diffraction studies show rearrangement of the single crystalline units at the air-liquid interface leading to the formation of nanobelts. These nanobelts overlap systematically to form petals of the flowerlike structure; individual petals get curved with time. Each nanobelt is found to be single crystalline and can be indexed as the hexagonal ZnO phase. The organic product formed in the aminolytic reaction and dissolution-reprecipitation mechanism is the driving force for the formation of flowerlike ZnO at the air-liquid interface. A clear relationship between the surface, photocatalytic, and photoluminescent properties of ZnO is observed. The flowerlike structure exhibits a blue shift (3.56 eV) in the band emission as compared to bulk ZnO (3.37 eV). The photodegradation of methylene blue over the flowerlike ZnO catalyst formed at the air-liquid interface and in the sediments shows enhanced photocatalytic activity. The sub-bands formed due to surface defects facilitate separation of charge carriers increasing their lifetime, leading to enhanced photocatalytic activity of flowerlike ZnO.

Synthesis of α‐Fe2O3 Nanocubes

Nanocubes of α‐Fe2O3 were successfully synthesized by aqueous polymer thermolysis method in air. The synthesis of hematite nanoparticles has been carried out using a habit modifier polyvinyl alcohol of different molecular weights. The influence of annealing temperature from 300 to 500°C on structural and thermal properties of α‐Fe2O3 nanoparticles was investigated systematically using X‐ray diffraction and thermogravimetric analysis. The smallest grain size of 12 nm after calcinations was found in presence of PVA of 1,25,000 molecular weight. The binding and microstructural features of polycrystalline samples of iron oxide were studied by FTIR, SEM and TEM. Infrared spectra reveal the formation of α‐Fe2O3 and the removal of organic matter at higher temperatures.

Structural phase behavior and vibrational spectroscopic studies of biofunctionalized CdS nanoparticles.

Biomodified CdS nanoparticles were synthesized using l-cysteine as a capping agent in the colloidal state as a function of pH. The role of pH on the size and structure of CdS nanoparticles was investigated in detail. At pH 7.4 and 9.1, X-ray diffraction spectra of as prepared samples showed the presence of a mixture of cubic and hexagonal phases while cubic phase was formed at pH 11.2. A gradual transition to the hexagonal phase was observed for refluxed samples at pH 9.1 and 11.2. Whereas, at pH 7.4, the sample remains in a mixture of cubic and hexagonal phase even after refluxing. The particle size of as prepared samples was about 2 nm, and for refluxed samples the size increased up to 10 nm. The binding of cadmium through thiol group is evidenced by infrared spectra. An intense band due to C-C-N vibration was observed after 24 h of reflux. The formation of a specific molecular cluster determines the growth of a particular phase. Transmission electron microscopy (TEM) studies support the X-ray diffraction (XRD) studies and exhibit well separated spherical particles while refluxed samples show clustering.

Photochemically assisted one-pot synthesis of PMMA embedded silver nanoparticles: antibacterial efficacy and water treatment

One-pot synthesis of polymer embedded silver nanoparticles (AgNPs) by the UV irradiation method was performed and thoroughly characterized. Electron microscopy analysis revealed that AgNPs (17.30 nm) were embedded into the PMMA matrix. High-resolution transmission electron microscopy (HRTEM) study indicates that the silver–poly(methyl methacrylate) (Ag–PMMA) nanocomposite exhibited internal highly ordered lattice fringes of the Ag (111) lattice plane. The Ag–PMMA nanocomposite had a lower tendency to agglomerate than borohydride reduced AgNPs as evaluated by stability experiments. The nanocomposite shows a zeta potential of −63.9 mV confirming the high stability of the nanocomposite. Organic reagent tests reveal that the synthesized nanocomposite contains a greater amount of Ag0-state particles and a lesser amount of Ag+ ions. Fourier transform infrared spectroscopy (FTIR) studies evidenced that the carbonyl group of PMMA binds to AgNPs. The nanocomposite exhibited excellent antibacterial performance against Gram negative Escherichia coli, Pseudomonas aeruginosa and Gram positive, Staphylococcus aureus. Moreover, the possible mechanism for the antibacterial activity of the Ag–PMMA nanocomposite with E. coli bacteria was discussed. In addition, the Ag–PMMA nanocomposite solution was loaded onto a membrane (the ‘treated membrane’) for water treatment applications and characterized by spectroscopy techniques. Sludge water was passed through the treated membrane and the effluent water was analyzed for viable bacteria. Deactivation of bacteria by percolation through the treated membrane occurred. Consequently, the filter effluent contains dead bacteria, which indicates that the treated membrane exhibits antibacterial properties. Interestingly, microwave plasma-atomic emission spectrometry (MP-AES) analysis estimated that silver loss in the treated membrane was less than 0.1 ppm.

Metal nanoparticle catalyzed charge rearrangement in selenourea probed by surface-enhanced Raman scattering

The adsorption behavior of selenourea (SeU) on noble metal silver (Ag) and gold (Au) nanoparticles (NPs) was investigated using the surface-enhanced Raman scattering (SERS) technique in combination with X-ray photoelectron spectroscopy (XPS) and density functional theoretical (DFT) calculations. SeU contains two different anchoring groups, firstly, a selenium atom and secondly, two amino groups. SERS, XPS and DFT studies provided useful insight into the metal–molecule interaction, thus, illustrating the active sites of SeU and the metal substrates being directly involved in binding. The SERS and DFT results provided further insight into the tautomerism of SeU, suggesting that as a solid, the selenone form is exclusively found. On the Ag NP surface, signatures of the selenol form were predominant which indicates charge rearrangement within the molecule while on the Au NP surface, contributions from both selenone and selenol tautomers were observed. In addition, the preferential binding affinity of the anchoring groups in SeU towards Ag and Au was exploited for the synthesis of metal–molecule–metal sandwiched nanoassemblies that further suggested possible charge rearrangement within the molecule.

Irreversible phase transition in BiVO4 nanostructures synthesized by a polyol method and enhancement in photo degradation of methylene blue

Structure and bonding in metal oxides has been studied extensively using Raman vibrational spectroscopy and is found to provide complementary information to the crystallographic observations. In this study, BiVO4 nanostructures with pure and stable crystal phases were synthesized selectively by reaction between Bi(NO3)3·5H2O and NH4VO3 in ethylene glycol at temperatures between 80 °C to 140 °C. A high temperature tetragonal scheelite (t-s) phase was obtained directly at synthesis temperature, whereas calcination at 600 °C resulted in phase transformation to a monoclinic scheelite (m-s) crystal structure. Distortion of the VO43− tetrahedron, being the reason for the phase transition that results in two sets of V–O bonds, was confirmed by bond length and bond strength calculations with the help of Raman spectroscopy. Irreversibility of the phase transition was observed through Differential Scanning Calorimetric (DSC) analysis and X-Ray Diffraction (XRD). The band gap was found to vary between 1.97 to 2.33 eV with respect to synthesis temperature as well as calcination temperature. Nanostructures synthesized at 110 °C and calcined at 600 °C for 3 h had a band gap of 2.25 eV and were found to bring about the highest photocatalytic degradation of MB under visible light irradiation. Increase in the distortion of the VO43− tetrahedron in terms of increase in the difference between bond lengths of two sets of V–O bonds was found to be the reason for the enhancement in the photodegradation of MB over BiVO4 catalysts with a monoclinic scheelite crystal structure.

Enhanced in vitro cytotoxicity and cellular uptake of DNA bases functionalized gold nanoparticles in HeLa cell lines

The aggregation of nanoparticles (NPs) in the tumour environment has been hypothesized to enhance retention and cellular uptake, crucial for NP-assisted cancer treatment. Gold nanoparticles (AuNPs) are synthesized by reducing gold chloride with sodium borohydride and are appended with mono and paired DNA bases (adenine, cytosine, and thymine). The AuNPs–DNA base nanoconjugates show aggregation which was characterized by UV-Vis spectroscopy and TEM. An intense surface plasmon resonance (SPR) band in the visible region at 520 nm was observed for the synthesized AuNPs, while addition of mono and pair of DNA bases exhibited colour change and generation of a new band at higher wavelengths. FTIR studies evidenced the mode of interaction of the DNA bases with the AuNPs. A zeta-potential study indicates that functionalized AuNPs were negatively charged and showed zeta-potential values in the range of −53 to −24.5 mV. These functionalized AuNPs were internalized to a greater extent with high cellular uptake than AuNPs into HeLa cells, quantitatively examined using MP-AES and visualized by optical microscopy. MP-AES results estimated the highest (51.43%) cellular uptake for AuNPs–CT among other NPs. A cytotoxicity study demonstrates that functionalized AuNPs possess a higher toxicity than AuNPs against HeLa cells.