Electrochemical sensors for detection of bisphenols

The endocrine-disrupting chemicals (EDCs) are chemicals of very high concern that have hazards with serious consequences on human health. It influences on development of metabolic disorders, reproduction and respiratory problems. They can be found in our everyday life, from food, and personal care products to medical devices, dental products, special lenses and baby drink cans. Among several EDCs, banned Bisphenol A (BPA) and his substitute Bisphenol S (BPS) have attracted attention due to high usage during the manufacturing process for water and food packaging, in the production of epoxy resins, lacquer coating and can even be found in receipt. Due to that, there is a need for the fast, reliable and commercial detection of Bisphenols in everyday life. The gold standard for the detection of Bisphenols is chromatography and enzyme-linked immunosorbent assay, expensive and robust methods. Electrochemical sensors are a new approach to the detection of EDCs in very small quantities in complex environments. The aim of this research was to study commercial screen-printed electrodes (SPEs) as receptor elements in electrochemical sensors for the detection of BPA and BPS. Scanning electron microscopic (SEM) and Fourier transform infrared spectroscopy (FT-IR) were employed for examining the surface of the SPEs working electrodes. SPE electrodes showed very good voltammetric responses toward BPA and BPS oxidation with linear ranges between 0.5 and 50.0 μM and lower limits of detection of 0.15 μM and 0.37 μM, respectively

Electrochemical sensor for detection bisphenols in thermal paper

The substances of very high concern (SVHCs) can be found in a wide range of consumer products. These substances can negatively influence human health depending on the route of exposure, exposure time and duration, amount of intake the substance by body and other factors. Increased number of carcinoma, sterility, diabetes can be due to the contact with SVHCs in our everyday life. Bisphenol A (BPA) is one of the most commercialized SVHC chemicals and is used in many different products such as plastic packaging for water and food, storage media, and even in thermal paper. Thermal paper is used for receipts in stores and tickets for parking, bus, and trains. BPA is applied on thermal paper as a dye developer. As a dye developer, it is not chemically bound to the paper so it can easily migrate and be absorbed by the skin (fingers, palm). Studies showed that typical occupational exposures of work cashiers can increase concentrations of BPA and its metabolites in urine several times. Toxicokinetic studies showed that the route of exposure has a big effect on the concentration of BPA that circulates in the body. If BPA enters the body through dermal exposure, it metabolizes as unconjugated BPA, while oral exposure leads to a conjugated form of BPA. Studies showed that only the unconjugated form can bind to estrogen receptors, leading to the conclusion that the unconjugated form is hazardous. Due to that European Commission restricted usage of BPA to 0.02 mas%. The paper manufacturers replaced BPA with bisphenol S (BPS). It is expected that 61 % of all thermal paper in the EU will be BPS-based till now. However, the wide use of BPS in thermal paper raises concern because it was shown that BPS is also toxic. New studies of urine samples collected around the world showed the presance of BPS. Due to increasing production of BPS there is a need for the development of analytical methods for the detection of SVCHs. The most used are HPLCs with mass spectrometric detection, which are expensive and time-consuming. On a another hand, electrochemical sensors are low-cost and simple method for detection of SVCHs. The present study represents fast, reliable and commercial detection of bisphenols via screen-printed electrodes (SPEs) as receptor elements. Scanning electron microscopy (SEM) was used to study the surface of the SPEs working electrodes. SPE electrodes showed very good electrochemical responses toward BPA and BPS oxidation with linear ranges between 0.5 and 50.0 μM and lower limits of detection of 0.15 μM and 0.37 μM, respectively

Detection of bisphenol S via screen-printed electrodes

Screen-printed electrodes are economical, easy-to-use electrochemical sensors that can be used for in-situ real-time monitoring of toxic substances. This work represents a comparison of two SPEs electrodes for the detection of bisphenol S (BPS). BPS is an endocrine interrupts the hormonal system in humans and shows a genotoxic, cytotoxic and cancerpromoting effect. Fast and reliable detection of bisphenols is very important. Chromatographic and spectroscopic techniques are the most used methods for the detection of bisphenols, however they are expensive, complicated and consume a lot of time. On the other hand, electrochemical sensors are promising since they are fast, reliable and simple methods for in-situ measuring. In the present work the detection of BPS was performed via screen-printed electrodes with carbon nanoparticles and carbon single-wall nanotube working electrodes. Determination of BPS was carried out by cyclic voltammetry (CV) anddifferential puls voltammetry (DPV). The influence of different concentrations of BPS, scan rate and influencing BPA on detection were studied. Screen-printed electrodes showed very good electrochemical activity, sensitivity and repeatability. Screen-printed electrodes enable the miniaturization of sensors elements, using smaller volumes of samples, rapid and low cost detection without generating dangerous waste

Coercivity increase of the recycled HDDR Nd-Fe-B powders doped with DyF3 and processed via Spark Plasma Sintering & the effect of thermal treatments

The magnetic properties of the recycled hydrogenation disproportionation desorption recombination (HDDR) Nd-Fe-B powder, doped with a low weight fraction of DyF3 nanoparticles, were investigated. Spark plasma sintering (SPS) was used to consolidate the recycled Nd-Fe-B powder blends containing 1, 2, and 5 wt.% of DyF3 grounded powder. Different post-SPS sintering thermal treatment conditions (600, 750, and 900 °C), for a varying amount of time, were studied in view of optimizing the magnetic properties and developing characteristic core-shell microstructure in the HDDR powder. As received, recycled HDDR powder has coercivity (HCi) of 830 kA/m, and as optimally as SPS magnets reach 1160 kA/m, after the thermal treatment. With only 1−2 wt.% blended DyF3, the HCi peaked to 1407 kA/m with the thermal treatment at 750 °C for 1 h. The obtained HCi values of the blend magnet is ~69.5% higher than the starting recycled HDDR powder and 17.5% higher than the SPS processed magnet annealed at 750 °C for 1 h. Prolonging the thermal treatment time to 6 h and temperature conditions above 900 °C was detrimental to the magnetic properties. About ~2 wt.% DyF3 dopant was suitable to develop a uniform core-shell microstructure in the HDDR Nd-Fe-B powder. The Nd-rich phase in the HDDR powder has a slightly different and fluorine rich composition i.e., Nd-O-F2 than in the one reported in sintered magnets (Nd-O-F). The composition of reaction zone-phases after the thermal treatment and Dy diffusion was DyF4, which is more abundant in 5 wt.% doped samples. Further doping above 2 wt.% DyF3 is ineffective in augmenting the coercivity of the recycled HDDR powder, due to the decomposition of the shell structure and formation of non-ferromagnetic rare earth-based complex intermetallic compounds. The DyF3 doping is a very effective single step route in a controlled coercivity improvement of the recycled HDDR Nd-Fe-B powder from the end of life magnetic products

Influence of Ga on the formation of phases in cast Al–Mn-based alloys

This work deals with the influence of gallium addition on the constitution and formation of the phases in the Al-rich corner of the Al–Mn system during casting. Al-rich binary Al–Mn and ternary Al–Mn–Ga alloys were cast into a copper mould with a cavity diameter of 5 mm. The microstructures of the produced alloys were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction. The characterization revealed the presence of α$_{Al}$, Al$_6$Mn, λ-Al$_4$Mn, L-Al$_4$Mn, icosahedral quasicrystals (IQCs) and decagonal quasicrystals (DQCs). As the amount of gallium in the synthesized alloys increased, the proportion of the phases varied and IQCs and DQCs were formed. Microanalysis revealed that IQCs contained more gallium and less manganese than DQCs

The Influence of a Surface Treatment of Metallic Titanium on the Photocatalytic Properties of TiO2 Nanotubes Grown by Anodic Oxidation

Titanium dioxide (TiO2) nanotubes obtained by the anodic oxidation of titanium metal foils can be used for the photocatalytic degradation of organic pollutants. The aim of our study was to determine the influence of the titanium foil’s surface treatment on the final morphology of the TiO2 nanotubes and their photocatalytic activity. In our experiments, we used two different titanium foils that were electropolished or untreated prior to the anodic oxidation. The morphologies of the starting titanium foils and the resulting TiO2 nanotube layers were investigated and the photocatalytic activities measured by the decomposition of caffeine under UV irradiation. Our results showed that electropolishing of the starting foils produced a more uniform and smoother TiO2 nanotubes surface. In contrast, the TiO2 nanotube surfaces from untreated titanium foils mimic the initial surface roughness of the titanium foil. A comparison of the photocatalytic properties of the TiO2 nanotube layers obtained from the untreated and electropolished titanium foils showed that electropolishing does not necessarily improve the photocatalytic properties of the resulting TiO2 nanotube layer. It was found that the determining factors influencing the photocatalytic activity are the chemical impurities (Ti-nitride) on the surface of the titanium foils and the surface roughness of the TiO2 nanotube layer. The highest photocatalytic activity was achieved with the anodized untreated foil with the minimal presence of Ti-nitride and a relatively high roughness of the TiO2 nanotubes