Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 μg L-1 and 0.6 μg L-1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals.

Gold nanoparticle-modified sustainable plastic sensor chip for voltammetric monitoring of Hg(II)

Mercury is a toxic environmental contaminant that can cause serious health problems. This work describes a new type of eco-friendly three-electrode plastic sensor chip for the determination of trace Hg(II) by means of anodic stripping voltammetry (ASV). The sensor chip is entirely fabricated by injection moulding, which is a sustainable manufacturing method, and consists of three conductive carbon-based electrodes embedded in a plastic holder while the reference electrode is coated with Ag using e-beam evaporation. The sample is spiked with Au(III) which deposits on the working electrode in the form of gold nanoparicles during the analysis; the target Hg(II) co-deposits on the gold nanoparticles forming a Au(Hg) amalgam in situ. The accumulated Hg is stripped off the electrode and quantified by an anodic square wave potential scan. The relevant conditions and the potential interferences are investigated. The limit of detection for Hg(II) is 0.4 μg L^-1 and the repeatability at the 20 μg L^-1 Hg(III) level (n = 10) is 5.3%. The sensor is applied to water, honey, fish oil and mussel samples with recoveries between 98 and 107%.

Application of activated persulfate for the inactivation of fecal bacterial indicators in water

Activated persulfate, as a member of the broad group of Advanced Oxidation Processes (AOPs), has emerged as a promising method for the elimination of microorganisms in aqueous matrices. This study evaluates the disinfection efficiency of this technique with respect to the inactivation of Escherichia coli and Enterococcus faecalis in water samples, as representative Gram negative and Gram positive bacterial indicators, respectively. In this perspective, various activators were employed, namely, ferric ion, heating, ultrasound application and UVA irradiation, which exhibited different bactericidal effect, depending on the operating conditions and the structural properties of each species. The highest disinfection rates were achieved with 200 mg/L of persulfate and ferric ion or heating as activators. For instance, 6 Log reductions were recorded within only 10-15 min when 30 mg/L of iron were applied, whereas the same bacterial removal was noted upon heat-activation at 50 °C, but in longer periods (i.e. 45-60 min). Nevertheless, in all cases E. faecalis was more resistant than E. coli, which was readily inactivated in shorter treatment periods. The overall process activity was deteriorated above the limit of 200 mg/L of persulfate. Ultrasound application exhibited lower performance, as even more prolonged treatment was required (120-150 min) for the same bacterial decay with the persulfate concentration not affecting substantially the process. In an attempt to improve the ultrasound activity, it was combined together with iron but with no synergistic results, as no actual enhancement of the method was observed. Finally, UVA did not seem to serve as an activator under the applied conditions, taking into account that it resulted in negligible loss of bacterial viability. Based on the current results, activated persulfate may be used successfully for disinfection purposes; however, the appropriate establishment of process variables is mostly required, considering the various resistance levels of aquatic microorganisms under stressed conditions.