Über die Adsorption in Lösungen

Alginate derivatization: a review of chemistry, properties and applications.

Use of silver and silver salts is as old as human civilization but the fabrication of silver nanoparticles (Ag NPs) has only recently been recognized. They have been specifically used in agriculture and medicine as antibacterial, antifungal and antioxidants. It has been demonstrated that Ag NPs arrest the growth and multiplication of many bacteria such as Bacillus cereus, Staphylococcus aureus, Citrobacter koseri, Salmonella typhii, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia, Vibrio parahaemolyticus and fungus Candida albicans by binding Ag/Ag+ with the biomolecules present in the microbial cells. It has been suggested that Ag NPs produce reactive oxygen species and free radicals which cause apoptosis leading to cell death preventing their replication. Since Ag NPs are smaller than the microorganisms, they diffuse into cell and rupture the cell wall which has been shown from SEM and TEM images of the suspension containing nanoparticles and pathogens. It has also been shown that smaller nanoparticles are more toxic than the bigger ones. Ag NPs are also used in packaging to prevent damage of food products by pathogens. The toxicity of Ag NPs is dependent on the size, concentration, pH of the medium and exposure time to pathogens.

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A review on biosynthesis of silver nanoparticles and their biocidal properties.

A review on application of flocculants in wastewater treatment

A straightforward, cheap and unique method to produce novel fibers with a diameter in the range of 100 nm and even less is related to electrospinning. For this goal, polymer solutions, liquid crystals, suspensions of solid particles and emulsions, are electrospun in the electric field of about 1 kV/cm. The electric force results in an electrically charged jet of polymer solution flowing out from a pendant or sessile droplet. After the jet flows away from the droplet in a nearly straight line, it bends into a complex path and other changes in shape occur, during which electrical forces stretch and thin it by very large ratios. After the solvent evaporates, birefringent nanofibers are left. Nanofibers of ordinary, conducting and photosensitive polymers were electrospun. The present review deals with the mechanism and electrohydrodynamic modeling of the instabilities and related processes resulting in electrospinning of nanofibers. Also some applications are discussed. In particular, a unique electrostatic field-assisted assembly technique was developed with the aim to position and align individual conducting and light-emitting nanofibers in arrays and ropes. These structures are of potential interest in the development of novel polymer-based light-emitting diodes (LED), diodes, transistors, photonic crystals and flexible photocells. Some other applications discussed include micro-aerodynamic decelerators and tiny flying objects based on permeable nanofiber mats (smart dust), nanofiber-based filters, protective clothing, biomedical applications including wound dressings, drug delivery systems based on nanotubes, the design of solar sails, light sails and mirrors for use in space, the application of pesticides to plants, structural elements in artificial organs, reinforced composites, as well as nanofibers reinforced by carbon nanotubes.

Electrospinning of Nanofibers from Polymer Solutions and Melts

Organic and inorganic flocculants are used in treatment of water and industrial effluents. Polymeric flocculants, synthetic as well as natural, because of their natural inertness to PH changes, low dosage, and easy handling, have become very popular in industrial effluent treatment. It has been established in the authors' laboratory that by grafting polyacrylamide branches on rigid backbone of polysaccharides, the dangling grafted chains have easy approachability to contaminants in effluents. Thus grafted polysaccharides are very efficient, shear stable and biodegradable flocculants. They also exhibit turbulent drag reducing characteristics. Among grafted guar gum, xanthan gum, carboxymethyl cellulose, and starch, grafted starch performs the best. Starch consists of amylose (a low molecular weight linear polymer) and amylopectin (a high molecular weight, branched polymer). The grafted amylopectin is found to be the best flocculant for various kinds of industrial effluents, providing credibility to the above-cited model. In the present paper, the details about grafted polysaccharides as turbulent drag reducers and flocculants are given, along with their applications.

Biodegradable drag reducing agents and flocculants based on polysaccharides: Materials and applications

The present paper describes a less time-consuming and eco-friendly method for the synthesis of silver nanoparticles (AgNPs) using an aqueous solution of silver nitrate and Amaranthus gangeticus Linn (Chinese spinach) leaf extract. The synthesized AgNPs which are to be used as an antimicrobial and Congo red dye is to be used as a toxic-degrading agent. AgNP was prepared by the reduction of silver nitrate solution by the leaf extract of Amarranthus Gangeticus Linn leaf extract in aqueous medium on heating for about 15 mins at 80 °C in presence of one drop 0.05 (M) NaOH. The size of the synthesized silver nanoparticles (AgNPs) using Amaranthus gangeticus Linn leaf extract and aqueous solution of silver nitrate (10−3 M) are formed at their stable condition within the range of 11–15 nm. AgNPs are obtained by this process within a couple of minutes of reaction without using reducing and stabilizing agents or harsh conditions. High-resolution transmission electron microscope (HR-TEM), selected area electron diffraction (SAED), ultraviolet-visible (UV-VIS) spectroscopy, and Fourier transform infrared spectroscopy (FTIR) are used to characterize the prepared AgNPs which show that the nanoparticles are globular in shape and polycrystalline. The synthesized silver nanoparticles showed inhibitory activity towards Gram positive, Gram negative bacteria and fungus and also showed good Congo red dye-degrading agents. The overall outcome of this study suggests that green synthesis AgNPs hold promise as a potent antibacterial and antifungal agent. The particles obtained were also found to degrade toxic Congo red dye.

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Green synthesis of silver nanoparticles with antimicrobial and azo dye (Congo red) degradation properties using Amaranthus gangeticus Linn leaf extract

Novel flocculating agent based on sodium alginate and acrylamide

The synthesis of sodium alginate-g-polyacrylamide was carried out by a ceric-ion-induced solution polymerization technique. Six grades of graft copolymers were synthesized by the variation of catalyst and monomer concentrations. These graft copolymers were characterized by intrinsic viscosity measurements, 13C-NMR spectroscopy, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. From the characterizations, it could be concluded that there was a substantial amount of grafting with a minimum formation of homopolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3296–3308, 2001

Characterization of polyacrylamide-grafted sodium alginate: A novel polymeric flocculant

Water is a scare commodity now. Recycling of municipal wastewater, industrial and mineral processing effluents require treatment with the inorganic or organic flocculants. Inorganic flocculants are used in large quantities, leave large amount of sludge and are very much affected by pH changes. Other polymeric flocculants are used in a very minute quantity, form large cohesive floc and are inert to pH changes. Both natural and synthetic polymers are used as flocculants. Natural polymers are biodegradable and are effective at very large dosages but are very shear stable. The synthetic polymers are highly effective flocculants at very small dosages and have high tailorability, but have poor shear stability. In the authors’ laboratory, a new class of flocculants has been developed by grafting polyacrylamide branches onto polysaccharide such as guargum, hydroxypropyl guargum, starch, amylopectin and sodium alginate. These grafted polysaccharides exhibit synergistic flocculation characteristics, shear stability and controlled biodegradability. Out of all the grafted polysaccharides, amylopectin grafted polysaccharides out performs most of the commercially available flocculants. The polacrylamide branches grafted on high molecular weight branched amylopectin have larger approachability to contaminants in the industrial effluents [1, 2].

Tridib Tripathy

Papers

Biodegradable drag reducing agents and flocculants based on polysaccharides: Materials and applications

Green synthesis of silver nanoparticles with antimicrobial and azo dye (Congo red) degradation properties using Amaranthus gangeticus Linn leaf extract

Novel flocculating agent based on sodium alginate and acrylamide

Characterization of polyacrylamide-grafted sodium alginate: A novel polymeric flocculant

Biobased polymeric flocculants for industrial effluent treatment