Fathima Laffir

Colloidal synthesis of wurtzite Cu2ZnSnS4 nanorods and their perpendicular assembly

The quaternary copper chalcogenide Cu(2)ZnSnS(4) is an important emerging material for the development of low-cost and sustainable solar cells. Here we report a facile solution synthesis of stoichiometric Cu(2)ZnSnS(4) in size-controlled nanorod form (11 nm × 35 nm). The monodisperse nanorods have a band gap of 1.43 eV and can be assembled into perpendicularly aligned arrays by controlled evaporation from solution.

Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control.

A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π-π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.

Spontaneous room temperature elongation of CdS and Ag2S nanorods via oriented attachment.

Spontaneous elongation from nanorod to nanowire in the presence of an amine is reported for nanocrystals of cadmium sulfide and silver sulfide (cation exchanged from CdS). Elongation occurs instantaneously where the final aspect ratio is a controllable multiple of the original nanorod length. Transmission electron microscopy (TEM) analysis reveals the influential factors on the attachment process are the concentration of amine, duration and temperature of the reaction. The elongated nanorods are further characterized by X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS). A mechanism of oriented attachment is evidenced by the doubling in length of asymmetrically gold tipped CdS nanorods with the corresponding absence of elongation in symmetrically tipped nanorods.

Biomineralization Mechanism of Gold by Zygomycete Fungi Rhizopous oryzae

In recent years, there has been significant progress in the biological synthesis of nanomaterials. However, the molecular mechanism of gold biomineralization in microorganisms of industrial relevance remains largely unexplored. Here we describe the biosynthesis mechanism of gold nanoparticles (AuNPs) in the fungus Rhizopus oryzae . Reduction of AuCl(4)(-) [Au(III)] to nanoparticulate Au(0) (AuNPs) occurs in both the cell wall and cytoplasmic region of R. oryzae . The average size of the as-synthesized AuNPs is ~15 nm. The biomineralization occurs through adsorption, initial reduction to Au(I), followed by complexation [Au(I) complexes], and final reduction to Au(0). Subtoxic concentrations (up to 130 μM) of AuCl(4)(-) in the growth medium increase growth of R. oryzae and induce two stress response proteins while simultaneously down-regulating two other proteins. The induction increases mycelial growth, protein yield, and AuNP biosynthesis. At higher Au(III) concentrations (>130 μM), both mycelial and protein yield decrease and damages to the cellular ultrastructure are observed, likely due to the toxic effect of Au(III). Protein profile analysis also confirms the gold toxicity on R. oryzae at high concentrations. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis shows that two proteins of 45 and 42 kDa participate in gold reduction, while an 80 kDa protein serves as a capping agent in AuNP biosynthesis.

Assembly of CuIn1-xGaxS2 Nanorods into Highly Ordered 2D and 3D Superstructures

Here, we report self- and directed assembly of CuIn(1-x)Ga(x)S(2) (CIGS) nanorods into highly ordered 2D and 3D superstructures. The assembly protocol is dictated by the ligand environment and is hence chemically tunable. Thiol capped nanorods spontaneously assemble into 3D aligned nanorod clusters over a period of hours with end to end and side to side order. These clusters can be disassembled by ligand exchange with an amine and subsequently reassembled either at a substrate interface or as free floating 2D sheets by directed assembly protocols. This dimensional control of CIGS nanorod assembly, extending over device scale areas with high degrees of order, is highly attractive for applications utilizing these important quaternary photoabsorbers.

A facile aqueous sol–gel method for high surface area nanocrystalline CeO2

Thermally stable high surface area nanocrystalline CeO2 was synthesized via an aqueous sol–gel method using cerium hydroxide and urea as precursors. The CeO2 sol is yellow colored and absorbs light over the range 200–500 nm. Nanocrystalline CeO2 particles derived from the sol are spherical in shape and range from 9 to 13 nm in diameter. The CeO2 powder has a high surface area of up to 85 m2 g−1 and a band gap of 3.1 eV. The method of preparation is facile, utilises low cost reagents and can be performed on a large scale.

In situ photoexcitation of silver-doped titania nanopowders for activity against bacteria and yeasts

Photocatalytic and in situ microbial activity of the amorphous and annealed states of Ag-doped and un-doped titania were examined. Studies on their structure, morphology, composition, and the photo-absorption characteristics of these materials were performed. These results were correlated with the photocatalytic and microbial activity against methicillin resistant Staphylococcus aureus K324 (MRSA), methicillin susceptible S. aureus ATCC 25923 (MSSA), Escherichia coli PA 170, and yeasts Candida albicans ATCC 90028. The annealed powders containing anatase form of titania exhibited relatively higher photocatalytic activity,corresponding to activity against MRSA,when exposed to UV-A radiation. In comparison, amorphous powders exhibited low photoactivity and showed poor antibacterial performance against MRSA under UV-A exposure. Doping of amorphous titania with Ag resulted in an anti-MRSA effect without exposure to UV radiation. In the Ag-doped crystalline anatase samples, the size of Ag primary nanocrystallites increased, which led to the decrease in the surface concentration of Ag and detriment anti-MRSA activity.

Surface Immobilization of a Tetra-Ruthenium Substituted Polyoxometalate Water Oxidation Catalyst Through the Employment of Conducting Polypyrrole and the Layer-by-Layer (LBL) Technique

A tetra Ru-substituted polyoxometalate Na10[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2] (Ru4POM) has been successfully immobilised onto glassy carbon electrodes and indium tin oxide (ITO) coated glass slides through the employment of a conducting polypyrrole matrix and the layer-by-layer (LBL) technique. The resulting Ru4POM doped polypyrrole films showed stable redox behavior associated with the Ru centres within the Ru4POM, whereas, the POMs tungsten-oxo redox centres were not accessible. The films showed pH dependent redox behavior within the pH range 2-5 whilst exhibiting excellent stability towards redox cycling. The layer-by-layer assembly was constructed onto poly(diallyldimethylammonium chloride) (PDDA) modified carbon electrodes by alternate depositions of Ru4POM and a Ru(II) metallodendrimer. The resulting Ru4POM assemblies showed stable redox behavior for the redox processes associated with Ru4POM in the pH range 2-5. The charge transfer resistance of the LBL films was calculated through AC-Impedance. Surface characterization of both the polymer and LBL Ru4POM films was carried out using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Initial investigations into the ability of the Ru4POM LBL films to electrocatalytically oxidise water at pH 7 have also been conducted.

Titania–silver and alumina–silver composite nanoparticles: Novel, versatile synthesis, reaction mechanism and potential antimicrobial application

Titania-silver (TiO(2)-Ag) and alumina-silver (Al(2)O(3)-Ag) composite nanoparticles were synthesised by a simple, reproducible, wet chemical method under ambient conditions. The surface of the oxides was modified with oleic acid, which acted as an intermediate between the oxide surface and the silver nanoparticles. The resulting composite nanoparticles were thoroughly characterised by XRD, TEM, XPS, FTIR and TGA to elucidate the mode of assembly of Ag nanoparticles on the oxide surfaces. Epoxy nanocomposites were formulated with TiO(2)-Ag and Al(2)O(3)-Ag to examine potential applications for the composite nanoparticles. Preliminary results from disc diffusion assays against Escherichia coli DH5α and Staphylococcus epidermidis NCIMB 12721 suggest that these TiO(2)-Ag and Al(2)O(3)-Ag composite nanoparticles have potential as antimicrobial materials.

Redox switching of polyoxometalate-methylene blue-based layer-by-layer films.

Iron-substituted crown-type polyoxometalate (POM) [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) has been successfully immobilized onto glassy carbon electrode surfaces by means of the layer-by-layer (LBL) technique employing the cationic redox active dye, methylene blue (MB). The constructed multilayers exhibit pH-dependent redox activity for both the anionic POM and the cationic dye moieties, which is in good agreement with their solution behavior. The films have been characterized by alternating current impedance, atomic force microscopy, and X-ray photoelectron spectroscopy, whereby the nature of the outer layer within the assemblies was found to have an effect upon the films behavior. Preliminary investigations show that the POM dye-based films show electrocatalytic ability toward the reduction of hydrogen peroxide, however, only when there is an outer anionic POM layer.