The sensing measurements were performed using a Metrohm potentiostat and controlled via the accompanying NOVA 1.11 software.
Sensing based on changes of the surface potential was performed in open circuit potential (OCP) mode using an Autolab PGSTAT204 potentiostat. A coiled gold wire was used as counter electrode. OCP measurements were performed in a cell containing 10 ml of high purity water. Addition of the halogen ions was done during the running measurements by adding the desired volume of NaF or NaCl solution stepwise, resulting in maximum final concentrations of 4 mM.
Since for electrochemical impedance spectroscopy (EIS) a conductive solution is required from the beginning, 20 ml of 50 mM KNO3 aqueous solution was used as background electrolyte. Samples were measured in this electrolyte without, directly after and one day after the addition of 4 mM NaF. For EIS an Autolab PGSTAT128N potentiostat with an electrochemical impedance spectroscopy module (FRA32M) was used. A coiled Pt-wire served as counter electrode and a parallel capacitance of 1 mF was connected to the reference to reduce its impedance at high frequencies. Frequency spectra were recorded at open circuit potential with frequencies in a range from 10 mHz to 100 kHz using an amplitude with a round mean square (RMS) value of 20 mA.
Before starting each anion sensing measurement, samples were soaked in the starting electrolyte for at least 8 h to ensure diffusion into the porous structure. All data presented in this study result from a well balanced, regenerated sensor. To regenerate the samples they were soaked in 1 M KOH overnight after each fluoride detection measurement.
Sensing based on changes of the surface potential was performed in open circuit potential (OCP) mode using an Autolab PGSTAT204 potentiostat. A coiled gold wire was used as counter electrode. OCP measurements were performed in a cell containing 10 ml of high purity water. Addition of the halogen ions was done during the running measurements by adding the desired volume of NaF or NaCl solution stepwise, resulting in maximum final concentrations of 4 mM.
Since for electrochemical impedance spectroscopy (EIS) a conductive solution is required from the beginning, 20 ml of 50 mM KNO3 aqueous solution was used as background electrolyte. Samples were measured in this electrolyte without, directly after and one day after the addition of 4 mM NaF. For EIS an Autolab PGSTAT128N potentiostat with an electrochemical impedance spectroscopy module (FRA32M) was used. A coiled Pt-wire served as counter electrode and a parallel capacitance of 1 mF was connected to the reference to reduce its impedance at high frequencies. Frequency spectra were recorded at open circuit potential with frequencies in a range from 10 mHz to 100 kHz using an amplitude with a round mean square (RMS) value of 20 mA.
Before starting each anion sensing measurement, samples were soaked in the starting electrolyte for at least 8 h to ensure diffusion into the porous structure. All data presented in this study result from a well balanced, regenerated sensor. To regenerate the samples they were soaked in 1 M KOH overnight after each fluoride detection measurement.
