Poly(vinylidene fluoride) (b-PVDF) nanoporous membranes are obtained by heavy ion irradiation and track etching leading to cylindrical pores. Pores diameter measured by scanning electron microscopy and small angle neutron scattering lies in the 20-50 nm range. Electron paramagnetic resonance study gives evidence that radicals still remains in PVDF membrane after track-etching. These radicals allows acrylic acid polymerization to be initiated onto membrane. Radiografted and functionalized membranes are characterized using infrared spectroscopy and weighing. Finally, radiografted poly(acrylic acid) (PAA) has been selectively labeled by fluorophores and imaged by confocal laser scanning microscopy. Images show the localisation of PAA specifically inside nanopores.
Track-etched functionalized nanoporous -PVDF membrane electrodes, or functionalized membrane electrodes (FME), are thin-layer cells made from track-etched, poly(acrylic acid) (PAA) functionalized nanoporous -poly(vinylidene fluoride) (-PVDF) membranes with thin Au films sputtered on each side as electrodes. The Au film is thin enough that the pores of the membranes are not completely covered. The PAA functionalization is specifically localised in the walls of the nanoporous -PVDF membrane by radio grafting. The PAA is a cation exchange polymer that adsorbes metal ions, such as Pb 2+ , from aqueous solutions thus concentrating the ions into the membrane. After a calibrated time the FME is transferred to an electrochemical cell for analysis. A negative potential is applied to the Au film of the FME for a set time to reduce the adsorbed ions onto the Au film working electrode. The other metalized side of the FME functions as a counter electrode. Finally, square-wave anodic stripping voltammetry (SW-ASV) is performed on the FME to determine the metal ion concentrations in the original solution based on calibration. The calibration curve of charge versus log concentration has a Temkin isotherm form. The FME membranes are 9 m thick and have 40 nm diameter pores with a density of 10 10 pores/cm 2. This high pore density provides a large capacity for ion adsorption. Au ingress in the pores during sputtering forms a random array of nanoelectrodes. Like surface modified electrodes for adsorptive stripping voltammetry, the pre-concentration step for the FME is performed at open circuit. The zero current intercept of the calibration for Pb 2+ is 0.13 ppb (g/L) and a detection limit of 0.050 ppb based on 3S/N from blank measurements. Voltammetry (CV) and chronoapmerometry (CA) were used to characterize the system. The apparent diffusion coefficient (D) for Pb 2+ in the PAA functionalized pores was determined to be 2.44 x 10-7 cm 2 /s and the partition coefficient (pK M) was determined to be 3.08. The maximum allowable levels for toxic metals in water are now set at low ppb (g/L) levels. The maximum levels of Pb 2+ in potable water established the European Environmental Agency (EEA) the United States Environmental Protection Agency (EPA) and recommendations from the World health Organisation (WHO) are 7.2, 15.0, and 10.0 ppb respectively and the goal of the United States EPA is zero. 1-3 Reliable quantification of these low concentrations is difficult time consuming and expensive. Also, the analysis equipment is not portable so the samples have to be sent a centralised lab which typically involves a 24 hour turn around time, which means that pollution events can be missed, or detected too late. Electrochemical analysis techniques, such as anodic stripping voltammetry (ASV), are generally inexpensive, rapid and portable. The electrode of choice for measuring trace levels of toxic metal ions by ASV has been the dropping mercury electrodes (DME). 4 DMEs and mercury film electrodes are very sensitive, due to their high capa...
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