In the present work, the seedless, highly aligned and vertical ZnO nanorods in 3 dimensions (3D) were grown on the nickel foam substrate. The seedless grown ZnO nanorods were characterised by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) techniques. The characterised seedless ZnO nanorods in 3D on nickel foam were highly dense, perpendicular to substrate, grown along the (002) crystal plane, and also composed of single crystal. In addition to this, these seedless ZnO nanorods were functionalized with trans-dinitro-dibenzo-18-6 crown ether, a selective iron (III) ion ionophore, along with other components of membrane composition such as polyvinyl chloride (PVC), 2-nitopentylphenyl ether as plasticizer (NPPE), and tetrabutyl ammonium tetraphenylborate (TBATPB) as conductivity increaser. The sensor electrode has shown high linearity with a wide range of detection of iron (III) ion concentrations from 0.005 mM to 100 mM. The low limit of detection of the proposed ion selective electrode was found to be 0.001 mM. The proposed sensor also described high storage stability, selectivity, reproducibility, and repeatability and a quick response time of less than 10 s.
Iron has remained important for the different biosystems such as haemoglobin, myoglobin, and hem enzymes and also plays role as cofactor in enzyme activities as well as in oxygen transport and electron transport. It has also harmful effects on the various biological systems either in form of being alone or combined state. Due to deficiency of iron anaemia is usually diagnosed, and excess of iron can also be a cause of many health problems. Diseases like cancer, heart problems, and other illnesses such as hemochromatosis are also linked to high level of iron in the body [
Recently, one-dimensional (1D) semiconductor nanomaterials are getting more interest due to their significant contribution in the development of nanoscale-based electronic and optoelectronics devices [
In this work, seedless ZnO nanorods were grown in 3D on nickel foam substrate. Moreover, trans-dinitro-dibenzo-18-6 crown ether as selective iron (III) ion ionophore was used for the functionalization of seedless grown ZnO nanorods in 3D on nickel foam substrate. The present iron sensor electrode demonstrated good linearity, selectivity, sensitivity, fast response time, and high stability.
The zinc acetate dihydrate Zn(CH3COO)2·2H2O, 25% ammonia (NH3), ferric nitrate hexahydrate (Fe(NO3)3·6H2O, potassium nitrate (KNO3), tetrahydrofuran (THF), selective iron (III) ionophore trans-dinitro-dibenzo-18-6 crown ether, polyvinyl chloride (PVC), 2-nitopentylphenyl ether as plasticizer (NPPE), tetrabutyl ammonium tetraphenylborate (TBATPB) as conductivity increaser were purchased from Sigma Aldrich, Sweden. The nickel foam was purchased from Good fellow Cambridge Limited, England. The nickel foam has thickness and porous size in order (thickness: 1.6 mm, Pores/cm: 20 and with 95% porosity), respectively. All other chemical reagents used were of analytical grade. All the concentrations of analyte were prepared in deionized water.
The seedless ZnO nanorods were fabricated on nickel foam using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and 25% ammonia aqueous solutions [
The seedless grown ZnO nanorods were functionalized with membrane solution consisting of the following composition: 2% trans-dinitro-dibenzo-18-6 crown ether, 63% 2-nitopentylphenyl ether as plasticizer (NPPE), 29% PVC, and 2% tetrabutyl ammonium tetraphenylborate (TBATPB) in 5 mL of THF [
The potential response of the functionalised seedless grown ZnO nanorods in 3D on nickel foam was measured using pH meter model 744 and Keithley 2400 an electrical instrument applied for the measurement of response time of the proposed sensor electrode at 25°C. The cell assembly consisted of two-electrode system; the functionalised seedless grown ZnO nanorods on nickel foam were used as working electrode and the silver/silver chloride (Ag/AgCl) as reference electrode.
Figures
The (FESEM) images of fabricated ZnO nanorods.
The (HRTEM) images.
(XRD) analysis of synthesised ZnO nanorods.
The functionalized seedless grown ZnO nanorods based sensor electrode was used for the detection of iron (III) ions from ferric nitrate electrolytic solution. The sensing mechanism of the developed iron ion sensor using ZnO nanorods on nickel foam is described through the schematic diagram as shown in Figure
The schematic diagram of the fabricated iron (III) ion sensor.
Calibration graph of EMF versus log of iron ion concentrations.
The repeatability of any of the sensor electrode describes its potential reusability for the certain period of time. In this study, the same ion selective electrode was tested for three consecutive days, and in these three experiments the sensor electrode exhibited almost the same response to the detected range of concentrations as shown in Figure
Calibration for repeatability of the proposed iron ion sensor.
The reproducibility of the ion selective electrode is important for the observation of a relatively similar response to another electrode prepared under similar set of conditions. In this part of experiment, six independent sensor electrodes were fabricated and functionalised with selective iron (III) ion ionophore and tested into 5 mM electrolytic solution. The sensor electrode revealed good reproducibility with less than 5% standard deviation as shown in Figure
Reproducibility response of different independent iron ion sensor electrodes.
Selectivity of the ion selective electrodes is the back bone parameter for defining their characteristics in the presence of common interferents. It was observed, during the use of the functionalised seedless grown ZnO nanorods based sensor electrode into the solutions of different metals, both mono and divalent cation ions such as sodium, potassium, calcium, magnesium, Zinc, nickel, cobalt, silver, and copper ions, that the proposed sensor electrode is highly selective towards iron (III) ions and shows negligible response to these common interferents.
The shelf life of sensor electrode depends on the storage conditions provided for the sensor electrode. Before and after the measurement each sensor electrode was kept at 4°C and used for more than 3 weeks. It was observed that the sensor electrode maintained good storage stability, same sensitivity, and reusability for this period of time.
Besides other characteristics, the proposed iron (III) ion sensor electrode showed the quick output voltage response with respect to time. The proposed iron (III) ion sensor demonstrated a fast response time of 10 s, and the sensor electrode revealed the fast electrochemical signal transfer speed among the highly exposed ZnO nanorods on nickel foam and iron (III) ions in the analyte solution as shown in Figure
Response time of the present iron ion sensor based on the seedless ZnO nanorods.
For describing the working pH range of the present iron ion sensor electrode, a series of pH range was selected from 3–12 as shown in Figure
Effect of pH on the output response of proposed iron ion sensor.
In this study, highly perpendicular to substrate seedless ZnO nanorods were grown in 3D on the nickel foam and functionalised with selective iron (III) ion ionophore. The seedless grown ZnO nanorods grown on nickel foam were characterised by FESEM, HRTEM, and XRD techniques. The sensor electrode based on these functionalised seedless grown ZnO nanorods on the nickel foam detected the wide range of iron (III) ions concentrations with good sensitivity of 41 mV/decade and exhibited a fast response time of 10 s. Along these features, the proposed iron (III) ion sensor electrode shows better repeatability, reproducibility, and storage stability. All the obtained results provided the clear evidence for the usability of the present iron ion sensor electrode for the determination of iron ion from the blood samples, clinical, environmental, and other iron containing samples.
The authors do not have any conflict of interests with Sigma Aldrich, Sweden, because this is just a chemicals supplier, and the amountis paid for these chemicals by Linköping university Sweden. Moreover, all authors agreed for the submission of paper.