Metal oxide QD based ultrasensitive microsphere fluorescent sensor for copper, chromium and iron ions in water.

Herein we developed a rapid, cheap, and water-soluble ultra-sensitive ZnO quantum dot (QD) based metal sensor for detecting different hazardous metal ions up to the picomolar range in water. Various spectroscopic and microscopic techniques confirmed the formation of 2.15 ± 0.46 µm of ZnO QD conjugated CMC microspheres (ZCM microspheres) which contain 5.5 ± 0.5 nm fluorescent zinc oxide (ZnO) QDs. Our system, as a promising sensor, exhibited excellent photostability and affinity towards various heavy metal ions. The detection limits were calculated to be 16 pM for Cu2+ and 0.18 nM for Cr6+ ions which are better than previously reported values. The simple fluorescence 'turn off' property of our ZCM microsphere sensor system can serve a two-in-one purpose by not only detecting the heavy metals but also quantifying them. Nonetheless, pattern recognition for different heavy metals helped us to detect and identify multiple heavy metal ions. Finally, their practical applications on real samples also demonstrated that the ZCM sensor can be effectively utilized for detection of Cr6+, Fe3+, Cu2+ present in the real water samples. This study may inspire future research and design of target fluorescent metal oxide QDs with specific functions.

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.

Silver-nano biohybride material: synthesis, characterization and application in water purification.

A green chemical synthesis of silver nanoparticles (AgNPs) through in situ reduction of silver nitrate (AgNO(3)) by a fungal strain of Rhizopus oryzae is described along with the promising eco-friendly role of the synthesized nano-silver bioconjugate (NSBC) material in water purification process. The NSBC has been characterized using UV-vis spectroscopy, high resolution transmission electron (HRTEM) microscopy, and Fourier transform infrared (FTIR) spectroscopy. The NSBC exhibits strong antibacterial activity against Escherichia coli and Bacillus subtilis and high adsorption capacity towards different organophosphorous pesticides. Fluorescence and electron microscopic images reveal NSBC binds on the bacterial cell wall, which cause irreversible membrane damage eventually leading to cell death. Proteomic analysis further demonstrates down regulation of protein expression, inhibition of cytosolic and membrane proteins and leakage of cellular content following binding of NSBC with bacterial cell wall. NSBC has been exploited to obtain potable water free from pathogens and pesticides in one step process.

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.