Arun K. Guha

GOLD NANOPARTICLES: MICROBIAL SYNTHESIS AND APPLICATION IN WATER HYGIENE MANAGEMENT

A green chemical method to synthesize nanogold-bioconjugate and its eco-friendly promising role to purify contaminated waters has been described. Gold nanoparticles of 10 nm average diameter are produced on the surface of Rhizopus oryzae , a fungal strain, by in situ reduction of chloroauric acid (HAuCl(4)). The nanogold-bioconjugate (NGBC) showed strong adsorption capacity toward different organophosphorous pesticides. The EDXA study confirms adsorption of pesticides on the conjugate material surface. Morphological changes of the NGBC material after adsorption of organophosphorous pesticides were detected by atomic force micrographs. NGBC shows high antimicrobial activity against several Gram-negative and Gram-positive pathogenic bacteria as well as the yeasts Saccharomyces cerevisiae and Candida albicans . The treatment of microbial cells with NGBC caused rupture of cell membrane as revealed in scanning electron and fluorescence micrographs. These unique characteristics of NGBC have been successfully utilized to obtain potable water free from pathogens and pesticides in a single operation.

Jute stick powder as a potential biomass for the removal of congo red and rhodamine B from their aqueous solution.

Jute stick powder (JSP) has been found to be a promising material for adsorptive removal of congo red (C.I. 22120) and rhodamine B (C.I. 45170) from aqueous solutions. Physico-chemical parameters like dye concentration, solution pH, temperature and contact time have been varied to study the adsorption phenomenon. Favorable adsorption occurs at around pH 7.0 whereas temperature has no significant effect on adsorption of both the dyes. The maximum adsorption capacity has been calculated to be 35.7 and 87.7mg/g of the biomass for congo red and rhodamine B, respectively. The adsorption process is in conformity with Freundlich and Langmuir isotherms for rhodamine B whereas congo red adsorption fits well to Langmuir isotherm only. In both the cases, adsorption occurs very fast initially and attains equilibrium within 60min. Kinetic results suggest the intra-particle diffusion of dyes as rate limiting step.

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.

Microbial Synthesis of Multishaped Gold Nanostructures

The development of methodologies for the synthesis of nanoparticles of well-defined size and shape is a challenging one and constitutes an important area of research in nanotechnology. This Full Paper describes the controlled synthesis of multishaped gold nanoparticles at room temperature utilizing a simple, green chemical method by the interaction of chloroauric acid (HAuCl4 x 3H20) and cell-free extract of the fungal strain Rhizopus oryzae. The cell-free extract functions as a reducing, shape-directing, as well as stabilizing, agent. Different shapes of gold nanocrystals, for example, triangular, hexagonal, pentagonal, spherical, spheroidal, urchinlike, two-dimensional nanowires, and nanorods, are generated by manipulating key growth parameters, such as gold ion concentration, solution pH, and reaction time. The synthesized nanostructures are characterized by UV/Vis and Fourier-transform infrared spectroscopy, transmission electron microscopy, and energy dispersive X-ray analysis studies. Electron diffraction patterns reveal the crystalline nature of the nanoparticles and a probable mechanism is proposed for the formation of the different structural entities.

Adsorption of rhodamine B on Rhizopus oryzae: role of functional groups and cell wall components.

The role of different functional groups (i.e. amino, carboxyl, hydroxyl as well as phosphate) and cell wall components (such as chitin, chitosan, glucan and phosphomannan) of Rhizopus oryzae on adsorption of rhodamine B is described. The functional groups were chemically modified to determine their contribution in the present adsorption process. Fourier transformed infrared spectroscopic (FTIR) study was used to characterize the modification of the functional groups due to chemical treatments. Carboxyl and amino groups were identified as most important moieties involved in the binding process. Different cell wall components were also isolated from the cell wall to explore their role involved in the binding process. Phosphomannan fraction adsorbed higher amounts of rhodamine B compared to the other cell wall components. Fluorescence microscopic images also supported the differential adsorption capacity of the various cell wall components.

Adsorption behavior of copper ions on Mucor rouxii biomass through microscopic and FTIR analysis

Mucor rouxii biomass (MRB) was found to be most potent sorbent for the removal of copper from its aqueous solution. Maximum adsorption was noted within pH range 5.0-6.0, and the process follows Langmuir adsorption isotherm (r2=0.998). Adsorption process is very fast initially and reaches equilibrium very quickly following pseudo second order rate kinetics. Amino, carboxyl and phosphate groups present on the cell surface of the biomass are involved in chemical interaction with copper ion as revealed from FTIR and SEM-EDX study and also by blocking experiments. Both SEM and AFM micrographs revealed the formation of metal nanostructure on the biomass surface due to copper adsorption. Biomass surface modification indicates the major involvement of amino functional group for the binding probably through the chelation. Copper ion can be eluted from the adsorbed biomass with 0.1M hydrochloric acid.

Bio-inspired fabrication of silver nanoparticles on nanostructured silica: characterization and application as a highly efficient hydrogenation catalyst

The design and facile green synthesis of supported metal-engineered nanoparticles with efficient catalytic activity has significant industrial importance. A biosynthetic and ecofriendly one-step reduction strategy has been developed through the protein-mediated in vitro biosynthesis of AgNPs on the surface of nanosilica. The as-synthesized silver nanoparticles supported on nanosilica (Ag@Nanosilica) were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDXA) elemental mapping, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The spectroscopic and electron microscopic studies demonstrated that the immobilized protein on the nanosilica surface served as a reducing, capping and stabilising agent, while sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed that the three proteins of 48, 38 and 36 kDa participated in the formation of Ag@Nanosilica material. The formation mechanism of AgNPs on nanosilica explained the origin of the biomineralization of metal nanoparticles in nature. The novel reusable Ag@Nanosilica exhibited enhanced catalytic activity for the hydrogenation of a model compound, namely, 4-nitrophenol. Overall our results will help to understand metal nanoparticle formation in the Earth’s crust and aid the design of “green” syntheses of novel nanoreactors.

Interaction of malathion, an organophosphorus pesticide with Rhizopus oryzae biomass

Adsorption of malathion on Rhizopus oryzae biomass (ROB) with special reference to binding mechanism has been described. ROB has been found to adsorb approximately 85% of malathion from its aqueous solution as against 47-68% by other fungal biomasses. Hydrogen ion concentration does not influence the adsorption of malathion by ROB which follows Langmuir-Freundlich dual equilibrium isotherm model (r(2)=0.998). Both physical and chemical interactions are responsible for binding of malathion on ROB. Scanning electron micrographs and EDXA spectra exhibit adsorption of the pesticide on cell surface of ROB. Studies with cell surface polysaccharides show that chitosan through its amine groups contributes largely in the adsorption of malathion. Extraction of lipids from ROB decreases its adsorption capacity to the extent of 36.37-94.02%, depending on the polarity of the solvent.

Adsorption profile of lead on Aspergillus versicolor: A mechanistic probing

The adsorption of lead on Aspergillus versicolor biomass (AVB) has been investigated in aqueous solution with special reference to binding mechanism in order to explore the possibilities of the biomass to address environmental pollution. AVB, being the most potent of all the fungal biomasses tested, has been successfully employed for reducing the lead content of the effluents of battery industries to permissible limit (1.0 mg L(-1)) before discharging into waterbodies. The results establish that 1.0 g of the biomass adsorbs 45.0 mg of lead and the adsorption process is found to depend on the pH of the solution with an optimum at pH 5.0. The rate of adsorption of lead by AVB is very fast initially attaining equilibrium within 3h following pseudo second order rate model. The adsorption process can better be described by Redlich-Peterson isotherm model compared to other ones tested. Scanning electron micrograph demonstrates conspicuous changes in the surface morphology of the biomass as a result of lead adsorption. Zeta potential values, chemical modification of the functional groups and Fourier transform infrared spectroscopy reveal that binding of lead on AVB occurs through complexation as well as electrostatic interaction.

Mechanistic studies on the binding of Acid Yellow 99 on coir pith

The interaction of Acid Yellow 99 (AY 99) with coir pith has been investigated in aqueous medium to understand the mechanism of adsorption and explore the potentiality of this biomass towards controlling pollution resulting from textile dyes. The obtained results establish that one gram of coir pith can adsorb 442.13 mg of AY 99. The adsorption process is found to be a function of pH of the solution, the optimum pH value being 2.0. The process follows Langmuir-Freundlich dual isotherm model. Scanning electron microscopic analysis demonstrates that on dye adsorption the biomass develops uneven and irregular surface. X-ray diffraction study indicates incorporation of the dye into the micropores and macropores of the adsorbent and thereby enhancing its degree of crystallinity. The results of Fourier transform infrared (FTIR) spectroscopy and chemical modification of the functional groups establish that binding of AY 99 on coir pith occurs through electrostatic and complexation reaction.