Electrochemical degradation and mineralisation of organic dyes in aqueous nitrate solutions

Electrochemical treatment of organic matter for environmental remediation necessitates the development of cheap and robust electrodes that are chemically and structurally stable. To address this challenging requirement, we demonstrate a new electrochemical approach using a simple copper electrode under cathodic conditions to electrochemically generate reactive nitrosonium ions for the degradation of different classes of synthetic organic dyes. This could be achieved in an aqueous HNO₃/KNO₃ electrolyte at a relatively low cathodic potential of -0.5 V RHE at room temperature. UV-visible absorption spectroscopy, Raman spectroscopy, liquid chromatography - mass spectrometry and total organic carbon measurements revealed the rapid decolorisation and mineralisation of several dye types such as triarylmethane dyes (crystal violet, cresol red), an azo dye (methyl orange) as well as a sulfur containing thiazine dye (toluidine blue). The total organic carbon content of a 50 mg L^-1 methyl orange solution was found to decrease by 83% after 1 h of electrolysis. Promisingly, locally sourced river and creek water samples spiked with 50 mg L^-1 methyl orange were also successfully treated for up to 6 cycles at a simple Cu electrode, demonstrating potential for the remediation of polluted waterways.

Gold-Deposited Nickel Foam as Recyclable Plasmonic Sensor for Therapeutic Drug Monitoring in Blood by Surface-Enhanced Raman Spectroscopy

A sensitive and recyclable plasmonic nickel foam sensor has been developed for surface-enhanced Raman spectroscopy (SERS). A simple electrochemical method was used to deposit flower-shaped gold nanostructures onto nickel foam substrate. The high packing of the gold nanoflowers onto the nickel foam led to a high enhancement factor (EF) of 1.6 × 10¹¹. The new SERS sensor was utilized for the direct determination of the broad-spectrum β-lactam carbapenem antibiotic meropenem in human blood plasma down to one pM. The sensor was also used in High Performance Liquid Chromatography (HPLC)-SERS assembly to provide fingerprint identification of meropenem in human blood plasma. Moreover, the SERS measurements were reproducible in aqueous solution and human blood plasma (RSD = 5.5%) and (RSD = 2.86%), respectively at 200 µg/mL (n = 3), and successfully recycled using a simple method, and hence, used for the repeated determination of the drug by SERS. Therefore, the new sensor has a strong potential to be applied for the therapeutic drug monitoring of meropenem at points of care and intensive care units.

Rapid detection of mercury contamination in water by surface enhanced Raman spectroscopy

Mercury (Hg) is a potent neurotoxin in fish, wildlife, and humans.