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Highly dispersed and debundled carbon nanotubes were prepared in an aqueous solution of lysozyme using a combination of ultrasonication and ultracentrifugation. The product is a pH-sensitive dispersion, which remains in a highly dispersed state at pH<8 and pH>11, but in an aggregated state at pH 8-11. Photoluminescence measurements show that by changing the pH value, a reversible conversion of the highly dispersed state to the aggregated state (or vice versa) could be observed. Circular dichromism analysis confirmed that the secondary structure, as well as the majority of the tertiary structure, remains intact. Some lysozyme molecules were irreversibly bound to the nanotubes, which is possibly due to pi-pi or hydrophobic interactions. However, these interactions alone are not enough to produce fine dispersions of the nanotubes. Protonated amine interactions on the defect sites of the nanotubes play a vital role in the stabilization of the nanotubes below the isoelectric point and amine adsorption on the sidewalls of nanotubes occurs in cases where the pH value is higher than the isoelectric point.

The interactions between biological substances and carbon nanotubes (CNTs) and their effect on the nanotubes are of significant importance in this emerging era of nanobiotechnology. Consequently, highly stable dispersions of debundled CNTs in aqueous solution are an important prerequisite for their applications and for the development of nanotube-based molecular electronic and nanobiomedical devices. Here, we report that proteins can work as tools to this end if their primary structure and the pH value of the system are chosen appropriately. Proteins containing a large number of basic residues, for example, histone, are found to be the most promising protein tools for the dispersion of nanotubes. Apart from other interactions, the polarity of the protein seems to play a vital role in obtaining high yields of debundled nanotubes. In addition, an enrichment of metallic nanotubes in the products is observed, which offers a facile approach for separating nanotubes according to their electronic properties in the bulk.

The applications of separation techniques using ultrafiltration in connection with functional soluble polymers for the removal of environmentally relevant and toxic substances from waters are reviewed. The types of interactions of the soluble polymers with low molecular mass compounds, the criteria for selecting the appropriate polymeric agents, and the binding conditions are discussed. Several factors influencing the separation of the target substances such as membrane type, solution composition, synergism, polymer adsorption, deformation of macromolecules, and hydrodynamics are evaluated and highlighted. Chemical, electrochemical, and thermal regeneration aspects are also covered. Finally, an overview on varius preparative and analytical application examples is presented.

Summary: This paper describes a simple and facile approach to fabricate well dispersed silver nanoparticles (AgNPs) in poly[N‐isopropylacrylamide‐co‐(sodium acrylate)] hydrogels. The silver nanoparticles formed are spherical in shape with a narrow size distribution in the hydrogel networks in which the nanoparticles are stabilized by the polymer network. Uniformly dispersed silver nanoparticles were obtained with poly[N‐isopropylacrylamide‐co‐[sodium acrylate)] hydrogels, whereas a poly(N‐isopropylacrylamide)/poly(sodium acrylate) IPN gel showed aggregated nanoparticles. It is demonstrated that the hydrogel network structure determines the size and shape of the nanoparticles. These particles are more stable in the gel networks compared to other reduction methods. The hydrogel/silver nanohybrids were well characterized by XRD, UV‐vis spectrometry, scanning electron microscopy and transmission electron microscopy.