Ronald D. Sanderson

Review of electro-assisted methods for water purification

Many different methods for improving the hygienic quality of waste, industrial and drinking water are already established. These include pressure-driven membrane-based methods such as reverse osmosis, ultrafiltration and microfiltration, biological treatment, treatment of water by means of various chemicals such as ozone or chlorine, and treatment with UV radiation. This review deals with electro-assisted methods for water purification which stand apart from the well-established technologies. Although electrodialysis is a competitive electro-assisted method for water treatment, electrochemical systems for water treatment have, in general, not yet attracted adequate attention. Electrochemistry, a link between physical chemistry and electronic science, has proved to be a clean, versatile and powerful tool for the development of new advanced methods for water purification. The freedom of choice in adjusting the electrode potential and electrode material, to meet almost any demand, makes electrochemistry extremely selective and flexible. This survey covers both established and recent developments in the field of electrochemical technologies for waste water and drinking water treatment.

Magnetic nanoparticles: Properties and potential applications

Magnetic particles may be used to selectively attach and manipulate or transport targeted species to a desired location under the influence of an external magnetic field. By virtue of their size, magnetic nanoparticles are superparamagnetic, offering great potential in a variety of applications in their bare form or through coating with a surface coating and functional group chosen for a specific application. In this paper, and in order to illustrate this concept, three applications for the use of magnetic nanoparticles will be discussed, namely, in magnetic liquids for densimetric separation, in therapeutic and diagnostic testing, and in effluent processing and metal ion removal.

Sol-gel film-preparation of novel electrodes for the electrocatalytic oxidation of organic pollutants in water

Abstract The electrochemical oxidation of phenol as a model contaminant, has been studied using different electrode materials (Ebonex, Ebonex PbO 2 , Ti SnO 2 ) in water by means of cyclic voltammetry. Best results have been obtained with doped SnO2-films on titanium foils prepared by a sol-gel dip-coating technique. The cyclovoltam-mograms reveal a high overpotential for oxygen-evolution, resulting in a well separated peak for the oxidation of phenol. Improvements of the conductivities of the films and higher current densities for the oxidation were obtained by doping the film sol-gel solution with 10% Sb. Doping with fluoride increased the conductivity, but decreased the oxidation peaks. The PbO2-coated Ebonex-electrodes were obtained by the galvanostatic deposition in an acidic PbNO3-solution. Upon the addition of phenol to the electrolyte, however, the electrodes did not show a separated oxidation peak. The oxidation peak is partially hidden by oxygen evolution. The electrochemical characteristics of the electrode material Ebonex is not significantly changed by the addition of phenol to the electrolyte.

Nano-structure phosphorus-containing polyurethane dispersions: synthesis and crosslinking with melamine formaldehyde resin

Abstract Nano-particle-size phosphated polyurethane dispersions were synthesised from phosphorus-containing macroglycol, bis (hydroxymethyl) propionic acid and methylene-bis-(4-isocyanatocyclohexane) (H 12 MDI). After the carboxylic acid groups of the phosphated polyurethane were neutralised by suitable bases, water was added to form the phosphated polyurethane dispersion. Chain flexibility affected particle-size reduction because flexible particles are more deformable in a shear field. During phase inversion the dispersed phase can more easily be broken into smaller particles. Depending on the number of hydrophilic groups present, the dispersion can be obtained in a very finely divided form, so that it practically has the appearance of a solution. Crosslinking of the dispersions with melamine showed that hexamethoxymethyl melamine does not self-condense during the curing and co-condensation was predominant. It was further shown that the cure response of the polyurethane dispersions was affected by the nature of the neutralising amine. Triethanolamine neutralised dispersions gave very poor cure response compared with triethylamine due to the low-volatility and the tendency to enter side reaction with the melamine.

Direct monitoring of membrane fouling and cleaning during ultrafiltration using a non-invasive ultrasonic technique

An ultrasonic technique has been applied as a non-destructive, real-time, in situ measuring technique for the non-invasive study of fouling and cleaning during ultrafiltration (UF) with polysulfone (PSU) membranes. Paper mill effluent from a wastewater treatment plant was used as a feed solution. Firstly, an asymmetric, composite polysulfone membrane, its compaction and fouling were detected by the ultrasonic technique. The experimental results showed a good correspondence between the ultrasonic signal responses and the development of the fouling layer on the membrane surface. Secondly, the ultrasonic technique was successfully used for monitoring membrane cleaning and evaluating the cleaning effectiveness of various cleaning methods. Moreover, the technique provided a means of producing a differential signal (an echo signal of a fouling layer) by comparing reference and test waveforms. The differential signal indicates the state and progress of the fouling layer on a membrane surface and gives warning of advanced fouling during realistic operation. Results showed the nature and thickness of the fouling layer as a function of operating time. Traditional flux measurements and analysis of the membrane surface by microscopy corroborated the ultrasonic response results. The ultrasonic technique is a useful technique for the non-destructive investigation of fouling and cleaning in membrane applications.

The effect of surface fluorination on the wettability of high density polyethylene

Abstract High-density polyethylene (HDPE) samples have been fluorinated and oxyfluorinated for different times. Dynamic contact angle analysis was used to determine the effect of fluorine gas mixtures on the surface of HDPE. The total surface tension of HDPE increased drastically with the length of oxyfluorination treatment, but levelled off after longer treatments. Fluorination resulted in a marked decrease in the total surface tension of HDPE. During fluorination, the dispersive component of the surface tension decreased progressively with fluorination time, while the polar component increased initially but decreased again with longer fluorination treatments. This indicates that short fluorination times lead to increased wettability by polar liquids, while longer fluorination times have the opposite effect. Fluorinated and oxyfluorinated surfaces were exposed to elevated temperatures. Whereas it was found that fluorinated surfaces changed measurably, oxyfluorinated surfaces changed dramatically upon heating at 100 °C. Photoacoustic FT-IR spectroscopy indicated that this was probably due to migration of surface polar groups into the bulk of the polymer, rather than chemical change.

Surface fluorination of polypropylene: 1. Characterisation of surface properties

Abstract Polypropylene (PP) was exposed to various fluorine-gas mixtures and the fluorinated PP surfaces were characterised by means of X-ray photoelectron spectroscopy, Rutherford backscattering, attenuated total reflectance infrared spectroscopy, solid–liquid contact angles and thermogravimetric analysis. The surface wettability and surface tensions of PP, as functions of fluorination and oxyfluorination times, were also determined and discussed.

Modification, crosslinking and reactive electrospinning of a thermoplastic medical polyurethane for vascular graft applications.

Thermoplastic polyurethanes are used in a variety of medical devices and experimental tissue engineering scaffolds. Despite advances in polymer composition to improve their stability, the correct balance between chemical and mechanical properties is not always achieved. A model compound (MC) simulating the structure of a widely used medical polyurethane (Pellethane) was synthesized and reacted with aliphatic and olefinic acyl chlorides to study the reaction site and conditions. After adopting the conditions to the olefinic modification of Pellethane, processing into flat sheets, and crosslinking by thermal initiation or ultraviolet radiation, mechanical properties were determined. The modified polyurethane was additionally electrospun under ultraviolet light to produce a crosslinked tubular vascular graft prototype. Model compound studies showed reaction at the carbamide nitrogen, and the modification of Pellethane with pentenoyl chloride could be accurately controlled to up to 20% (correlation: rho=0.99). Successful crosslinking was confirmed by insolubility of the materials. Initiator concentrations were optimized and the crosslink densities shown to increase with increasing modification. Crosslinking of Pellethane containing an increasing number of pentenoyl groups resulted in decreases (up to 42%, p<0.01) in the hysteresis and 44% in creep (p<0.05), and in a significant improvement in degradation resistance in vitro. Modified Pellethane was successfully electrospun into tubular grafts and crosslinked using UV irradiation during and after spinning to render them insoluble. Prototype grafts had sufficient burst pressure (>550 mm Hg), and compliances of 12.1+/-0.8 and 6.2+/-0.3%/100 mm Hg for uncrosslinked and crosslinked samples, respectively. It is concluded that the viscoelastic properties of a standard thermoplastic polyurethane can be improved by modification and subsequent crosslinking, and that the modified material may be electrospun and initiated to yield crosslinked scaffolds. Such materials hold promise for the production of vascular and other porous scaffolds, where decreased hysteresis and creep may be required to prevent aneurismal dilation.

Characterization of electroless plated palladium–silver alloy membranes

Abstract Palladium and silver coated membranes were prepared using electroless plating. Palladium–silver alloy membranes were synthesized by successive palladium and silver depositions on the same membrane support. Full characterizations of the pure palladium and pure silver membranes were performed using scanning electron microscopy (SEM), X-ray diffractometry (XRD) and proton induced X-ray emission (PIXE). Metal coated membranes were heat treated for 5 h in a hydrogen atmosphere at 650°C. The effect of the palladium and silver deposition sequence on coating adhesion and metal distribution in the alloy matrix after heating were investigated. By depositing first silver and then palladium, the palladium to silver ratio across the thickness of the film remained constant after heat treatment and it resulted in only a small amount of the alloy penetrating into the support membrane pores. However, when palladium was deposited first, the alloy penetrated at least 3 μm into the support and the palladium and silver concentration profiles across the thickness of the film were asymmetric.

Highly asymmetrical carbon membranes

Abstract Carbon membranes have been produced by thermo-oxidative stabilization and carbonization of polyacrylonitrile-based hollow-fibre precursors. The inner layer of coarse pores, the system of channels which penetrate through most of the wall, and the dense outer skin form the highly asymmetrical structure of the membrane. Transmission electron microscopy images of Pt/C replicas of the membranes outer surfaces revealed that the pore sizes and shapes in the outer surfaces revealed that the pore sizes and shapes in the outer skin could be altered by the use of polymers of different intrinsic viscosities as a precursor material as well as changing the stabilization atmosphere and carbonization temperature.