Vasile Coman

A membrane-, mediator-, cofactor-less glucose/oxygen biofuel cell

We report the fabrication and characterisation of a non-compartmentalised, mediator and cofactor free glucose-oxygen biofuel cell based on adsorbed enzymes exhibiting direct bioelectrocatalysis, viz. cellobiose dehydrogenase from Dichomera saubinetii and laccase from Trametes hirsuta as the anodic and cathodic bioelements, respectively, with the following characteristics: an open-circuit voltage of 0.73 V; a maximum power density of 5 microW cm(-2) at 0.5 V of the cell voltage and an estimated half-life of > 38 h in air-saturated 0.1 M citrate-phosphate buffer, pH 4.5 containing 5 mM glucose.

An advanced study on the hydrometallurgical processing of waste computer printed circuit boards to extract their valuable content of metals

This study refers to two chemical leaching systems for the base and precious metals extraction from waste printed circuit boards (WPCBs); sulfuric acid with hydrogen peroxide have been used for the first group of metals, meantime thiourea with the ferric ion in sulfuric acid medium were employed for the second one. The cementation process with zinc, copper and iron metal powders was attempted for solutions purification. The effects of hydrogen peroxide volume in rapport with sulfuric acid concentration and temperature were evaluated for oxidative leaching process. 2M H2SO4 (98% w/v), 5% H2O2, 25 °C, 1/10 S/L ratio and 200 rpm were founded as optimal conditions for Cu extraction. Thiourea acid leaching process, performed on the solid filtrate obtained after three oxidative leaching steps, was carried out with 20 g/L of CS(NH2)2, 6g/L of Fe(3+), 0.5M H2SO4, The cross-leaching method was applied by reusing of thiourea liquid suspension and immersing 5 g/L of this reagent for each other experiment material of leaching. This procedure has lead to the doubling and, respectively, tripling, of gold and silver concentrations into solution. These results reveal a very efficient, promising and environmental friendly method for WPCBs processing.

Graphite electrodes modified with Neurospora crassa cellobiose dehydrogenase: Comparative electrochemical characterization under direct and mediated electron transfer

The electrochemical characterization of a class II cellobiose dehydrogenase (CDH), from the ascomycete fungus Neurospora crassa, adsorbed on graphite (G), was performed in regard to direct (DET) and mediated electron transfer (MET). The effects of the applied potential, mediator (1,4 benzoquinone) concentration and flow carrier pH on the amperometric response of the G/CDH modified electrodes were investigated under flow conditions. From the calibration curves, recorded at two pH values (5.2 and 7.0) for nine different sugars, the kinetic and the analytical parameters were evaluated under DET and MET operation modes. These results together with those obtained from long term operational stability measurements showed that: (i) for all nine investigated sugars the sensitivity was higher for MET than for DET and for pH 5.2 compared to pH 7.0; (ii) irrespective of DET or MET operation mode, the sensitivity of the new enzyme towards the investigated sugars decreased in the following sequence: cellobiose>lactose>(cellotriose≈cellopentaose) >>(maltotriose≈maltotetraose≈maltopentaose)>(maltose≈glucose); (iii) for all tested substrates, the apparent CDH affinity was roughly higher in DET than in MET operation mode.