Advances in Colloid and Interface Science (v.145, #1-2)

Membrane-based techniques for the separation and purification of proteins: An overview by Arunima Saxena; Bijay P. Tripathi; Mahendra Kumar; Vinod K. Shahi (1-22).
Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as microfiltration, ultrafiltration, emerging processes as membrane chromatography, high performance tangential flow filtration and electrophoretic membrane contactor. Membrane-based processes are playing critical role in the field of separation/purification of biotechnological products. Membranes became an integral part of biotechnology and improvements in membrane technology are now focused on high resolution of bioproduct. In bioseparation, applications of membrane technologies include protein production/purification, protein–virus separation. This manuscript provides an overview of recent developments and published literature in membrane technology, focusing on special characteristics of the membranes and membrane-based processes that are now used for the production and purification of proteins.
Keywords: Protein separation; Membrane technology; Membrane filtration; Microfiltration; Ultrafiltration; Electro-ultrafiltration; Membrane contactor; Membrane chromatography;

Photoemission and absorption spectroscopy of carbon nanotube interfacial interaction by N.H. Tran; M.A. Wilson; A.S. Milev; J.R. Bartlett; R.N. Lamb; D. Martin; G.S.K. Kannangara (23-41).
Element-specific techniques including near edge X-ray absorption fine structure, extended X-ray absorption fine structure and X-ray photoemission spectroscopy for the characterization of the carbon nanotube interfacial interactions are reviewed. These techniques involve soft and hard X-rays from the laboratory-based and synchrotron radiation facilities. The results provided information of how the nano-particles of catalysts are involved in the initial stage of nanotube growth, the nanotube chemical properties after purification, functionalization, doping and composite formation.
Keywords: Surface; Interface; Thin film; X-ray photoemission spectroscopy (XPS); Extended X-ray absorption fine structure (EXAFS); Near edge X-ray absorption fine structure (NEXAFS); Single walled carbon nanotube (SWCNT); Double walled carbon nanotube (DWCNT); Multi walled carbon nanotube (MWCNT); Chemical vapour deposition (CVD);

The use of bitumen as a construction material dates back to antiquity. The materials in use then were mostly naturally occurring in contrast to modern bitumens which have become highly technical artificial materials.This article reviews the current understanding of bitumen structure and the consequences in terms of properties, with a strong emphasis on the rheological properties. The links between chemistry, structure and mechanical properties are highlighted in the framework of an updated colloidal picture of bitumen. It shows that a simple solvation parameter allows quantifying the effect of the asphaltenes on the rheological properties of bitumen. This appears as a promising approach in order to understand more complex phenomena such as bitumen ageing or the diffusion of rejuvenating oils into an older bitumen.From this structural modelling, the effect of several modifiers, such as polymers, acids or mineral fillers, is explained using fundamental results from the mechanics of colloidal suspensions and multiphase materials through the Palierne model. Thus, relevant parameters describing polymer-bitumen or mineral fillers-bitumen interactions can be extracted, as detailed from literature data. In the case of mineral filler, volume fraction is the key parameter but particle size comes also into play when fine fillers are considered. In the case of polymer-modified bitumens, the swelling extent of the polymer controls all other parameters of importance: volume fraction of dispersed phase and mechanical properties of both dispersed and continuous phases. In addition, interesting rheological features due to droplet shape relaxations are described in polymer-modified bitumens.Although a general picture of bitumen structure is shown to emerge, the many fundamental points that remain to be addressed are discussed throughout the paper.
Keywords: Bitumen; Mineral fillers; Polymer-modified bitumen; Rheology; Multiphase materials;

Silver nanoparticles: Green synthesis and their antimicrobial activities by Virender K. Sharma; Ria A. Yngard; Yekaterina Lin (83-96).
This review presents an overview of silver nanoparticles (Ag NPs) preparation by green synthesis approaches that have advantages over conventional methods involving chemical agents associated with environmental toxicity. Green synthetic methods include mixed-valence polyoxometallates, polysaccharide, Tollens, irradiation, and biological. The mixed-valence polyoxometallates method was carried out in water, an environmentally-friendly solvent. Solutions of AgNO3 containing glucose and starch in water gave starch-protected Ag NPs, which could be integrated into medical applications. Tollens process involves the reduction of Ag(NH3)2 + by saccharides forming Ag NP films with particle sizes from 50–200 nm, Ag hydrosols with particles in the order of 20–50 nm, and Ag colloid particles of different shapes. The reduction of Ag(NH3)2 + by HTAB (n-hexadecyltrimethylammonium bromide) gave Ag NPs of different morphologies: cubes, triangles, wires, and aligned wires. Ag NPs synthesis by irradiation of Ag+ ions does not involve a reducing agent and is an appealing procedure. Eco-friendly bio-organisms in plant extracts contain proteins, which act as both reducing and capping agents forming stable and shape-controlled Ag NPs. The synthetic procedures of polymer-Ag and TiO2–Ag NPs are also given. Both Ag NPs and Ag NPs modified by surfactants or polymers showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. The mechanism of the Ag NP bactericidal activity is discussed in terms of Ag NP interaction with the cell membranes of bacteria. Silver-containing filters are shown to have antibacterial properties in water and air purification. Finally, human and environmental implications of Ag NPs to the ecology of aquatic environment are briefly discussed.
Keywords: Silver colloid nanoparticles; Environmentally friendly synthesis; Irradiation; Silver-titanium dioxide nanoparticles; Antibacterial;

A review of the considerable, but often contradictory, literature examining the specific surface reactions associated with copper adsorption onto the common metal sulfide minerals sphalerite, (Zn,Fe)S, and pyrite (FeS2), and the effect of the co-location of the two minerals is presented. Copper “activation”, involving the surface adsorption of copper species from solution onto mineral surfaces to activate the surface for hydrophobic collector attachment, is an important step in the flotation and separation of minerals in an ore. Due to the complexity of metal sulfide mineral containing systems this activation process and the emergence of activation products on the mineral surfaces are not fully understood for most sulfide minerals even after decades of research.Factors such as copper concentration, activation time, pH, surface charge, extent of pre-oxidation, water and surface contaminants, pulp potential and galvanic interactions are important factors affecting copper activation of sphalerite and pyrite. A high pH, the correct reagent concentration and activation time and a short time delay between reagent additions is favourable for separation of sphalerite from pyrite. Sufficient oxidation potential is also needed (through O2 conditioning) to maintain effective galvanic interactions between sphalerite and pyrite. This ensures pyrite is sufficiently depressed while sphalerite floats. Good water quality with low concentrations of contaminant ions, such as Pb2+and Fe2+, is also needed to limit inadvertent activation and flotation of pyrite into zinc concentrates. Selectivity can further be increased and reagent use minimised by opting for inert grinding and by carefully choosing selective pyrite depressants such as sulfoxy or cyanide reagents. Studies that approximate plant conditions are essential for the development of better separation techniques and methodologies.Improved experimental approaches and surface sensitive techniques with high spatial resolution are needed to precisely verify surface structures formed after copper activation. Sphalerite and pyrite surfaces are characterised by varying amounts of steps and defects, and this heterogeneity suggests co-existence of more than one copper–sulfide structure after activation.
Keywords: Flotation; Copper activation; Collector; Sphalerite; Pyrite;