Applications In Aqueous Media Research Articles

Luminescent Eu(III) hybrid sensors for in situ copper detection

In this work we used the sol–gel technique to develop luminescent Eu(III) transparent films deposited on glass slides to build for sensor devices capable of monitoring transition metal ions in aqueous solutions. The films were obtained from a bis(trialkoxysilyl) organic precursor synthesized from the amide of the 2,6-pyridinedicarboxylic acid (DPA) with aminopropyltriethoxysilane (APTES) in the presence or absence of cetyl trimethyl ammonium bromide (CTAB) surfactant as templating agent and triethylethoxysilane (TEOS) as crosslinker. These sensor devices were used to perform in situ quenching experiments by Cu(II), Fe(III), Co(II) and Ni(II) ions. The results indicate that the templated films allow the detection and quantification of these metals down to ppb levels by means of the values of the Stern–Volmer constants. In particular, it was shown that Cu(II) acts as an extremely efficient quencher ( K SV = 3.5 × 10 5 M −1) when compared with the results obtained for the other metals, opening the possibility to use these devices as potential Cu(II) sensors for actual applications in aqueous media.

Immobilization of a lipoxygenase in silica gels for application in aqueous media

The encapsulation of soybean lipoxygenase-1 (LOX-1) in silica gels and its application in an aqueous medium, were studied. The main silica precursor was tetramethoxysilane (TMOS) but the introduction of hydrophobic SiCH 3 groups brought with methyltrimethoxysilane (MTMS) was evaluated. Other sol–gel synthesis parameters investigated comprised partial or complete drying by evaporation and CO 2 supercritical drying. The influence on LOX-1 activity of the various chemicals with which the enzyme was in contact during encapsulation (acetone, methanol, polyvinyl alcohol), as well as the temperature and pH, were examined. The activity of free and encapsulated LOX-1 was assayed on the oxygenation reaction of linoleic acid by dioxygen from air dissolved in aqueous medium, in a UV–vis spectrophotometer. With free LOX-1, the reaction advancement could be followed in continuous in the spectrophotometer. With the gels, in a first approach, the conversion was simply determined after 15 min reaction after filtration of the liquid, to discriminate between active and inactive gels. For the most interesting gels, the kinetics were then assessed by continuous recording in the UV spectrophotometer, after placing a small piece of gel (≈15 mg) directly in the cell. The best gels had an activity ≈30% of free LOX. The present studies, supplemented by characterization of the gels texture and structure, respectively by nitrogen adsorption and 29Si MAS NMR, showed that drying a gel before use in aqueous media was detrimental to the activity. This effect is due to a contraction of the gel network which occurs when a dry aerogel sample is dipped in water after drying. Hence gels containing LOX-1 enzyme must not be dried but kept in water impregnated state, for optimum use.

Surface and Electrochemical Studies of Thin Film Diamond

ABSTRACTThe behavior of diamond electrodes for electrochemical applications in aqueous media containing the protein bovine serum albumin has been explored, to examine the degree of electrode poisoning which occurs. Although the diamond electrode retains good activity in such solutions, electrode fouling is found at long contact times due to protein adsorption. Two adsorption processes are observed. The first is a simple physical adsorption mechanism, and can be simply reversed by washing the electrode in water. The second mechanism is only observed when negative potentials are applied to the diamond electrode and is attributed to the attraction and reaction of the positively charged protein at the electrode interface. Electrode poisoning is also observed in the presence of power ultrasound, although the electrochemical signals are usefully enhanced under these conditions due to enhanced mass transport to the electrode surface.

Advances in solvent-resistant nanofiltration membranes: experimental observations and applications.

Nanofiltration (NF) and reverse osmosis (RO) are well-established membrane technologies for applications involving aqueous streams. The principles of NF transport (diffusion, convection, and Donnan exclusion) are effectively used to develop novel membrane materials and applications in aqueous medium. Use of NF in a non-aqueous medium holds strong potential for the food, refining, and pharmaceutical industries because of the low energy costs involved with such membrane processes. Further understanding and development of solvent-resistant NF membranes provides opportunities for various hybrid processing ranging from reactor-membrane to distillation-membrane combinations. This paper provides a comprehensive overview of literature results and our own work in the area of non-aqueous systems. For solvent-based systems, potential membrane swelling and solvent-solute coupling needs to be considered for membrane design and transport theories. A simplified transport theory for pure solvents has been developed using solvent (molar volume, viscosity) and membrane properties (membrane surface energy). This model and has been verified with literature data for both hydrophilic and hydrophobic membranes. Membrane characterization and preconditioning aspects need to be given serious consideration for evaluating membrane performance. In addition to permeability and separation results, some novel applications of NF in non-aqueous solvents are included in this paper.

Alumina and titania multilayer membranes for nanofiltration: preparation, characterization and chemical stability

The preparation and characterization of porous ceramic multilayer nanofiltration (NF) membranes is described. During preparation, special care was given to each sub-layer that forms a part of the multilayer configuration: the macroporous substrate, the membrane interlayers and the NF toplayers. High-quality macroporous supports are prepared from α-Al 2O 3. Three types of colloidal sol–gel derived mesoporous interlayers are considered: Al 2O 3, TiO 2 and mixed Al 2O 3–TiO 2. The active NF toplayer is a very thin and fine textured polymeric TiO 2 toplayer. Optimized α-Al 2O 3/γ-Al 2O 3/anatase and α-Al 2O 3/anatase/anatase multilayer configurations show high retentions for relatively small organic molecules (molecular weight cut-off <200). Different membrane layers have very different crystallographic properties resulting in a considerably different chemical stability. Corrosion measurements showed that application of a multilayer configuration including weakly crystallized γ-Al 2O 3 layers is restricted to mild aqueous media (pH 3–11) or non-aqueous media (organic solvents). For NF applications in aqueous media with a lower or higher pH, the multilayer membrane composed of anatase on a α-Al 2O 3 support is to be preferred.

Polyimide, a new shielding layer for sensor applications

In sensor applications it is often necessary to cover the sensor surface or the interacting area of the sensor with a shielding layer. We present a well reproducible and easy method to shield a sensor surface with an aromatic polyimide layer. The shielding capacity was tested with surface acoustic wave (SAW) devices which are commercially available and furthermore meet the requirements for (bio)sensor applications in aqueous media. All experiments described here were done with these devices. One major advantage of this technique was the prevention of corrosion processes on the sensor surface, especially the damage of interdigital transducers which often consist of aluminium, because this material is known to have the best acoustoelectric properties for SAW-devices. Besides, we show that a thin polyimide film enhance the typical sensor characteristics in terms ‘of sensitivity and stability’.

Covalent photolinker-mediated immobilization of an intermediate dextran layer to polymer-coated surfaces for biosensing applications

A new method is presented for the covalent binding of dextran as an intermediate layer on surface acoustic wave (SAW) devices. For biosensing applications in aqueous media commercially available SAW devices require surface passivation to prevent corrosion of the aluminum device structures in electrolytes. Thin films of polyimide and parylene revealed exceptional passivation properties. They were used as a base for dextran immobilization. Covalent binding of dextran to polymer-coated surfaces was achieved by photoimmobilization. Aryldiazirine-functionalized bovine serum albumin served as the multifunctional light-activable linking agent (photolinker polymer). Dextran and photolinker polymer were mixed and photobonded to sensor surfaces. Essential photoimmobilization parameters were optimized. The binding of proteins to dextran applying carbodiimide chemistries was exemplified with anti-urease antibodies and the feasibility of specific immunosensing was investigated on SAW sensors connected to a fluid handling system.

The role of carrier fluid in the tribological behaviour of metallic stearates

It is shown that the carrier fluid has a marked effect on the performance of metallic stearates. Some metallic stearates in water provide improved tribological activities and thus their application in aqueous media may be useful in the reduction of pollution arising from oil components in many metal-working processes. With calcium, strontium and barium stearates the range of lubrication in aqueous media can be extended. The interaction of calcium stearate with graphite has been shown to be beneficial in improving antiseize properties. In these cases it is thought that a layer formulation of metallic stearates may partly explain the lubrication mechanism.