Citation: Niemiec, B.; Zambrzycki,
M.; Piech, R.; Wardak, C.;
Paczosa-Bator, B. Hierarchical
Nanocomposites Electrospun Carbon
NanoFibers/Carbon Nanotubes as a
Structural Element of Potentiometric
Sensors. Materials 2022, 15, 4803.
https://doi.org/10.3390/
ma15144803
Academic Editor: Deepak Kukkar
Received: 16 May 2022
Accepted: 7 July 2022
Published: 9 July 2022
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Article
Hierarchical Nanocomposites Electrospun Carbon
NanoFibers/Carbon Nanotubes as a Structural Element of
Potentiometric Sensors
Barbara Niemiec
1
, Marcel Zambrzycki
1
, Robert Piech
1
, Cecylia Wardak
2
and Beata Paczosa-Bator
1,
*
1
Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza 30,
30-059 Krakow, Poland; bniemiec@agh.edu.pl (B.N.); zambrzycki@agh.edu.pl (M.Z.); rpiech@agh.edu.pl (R.P.)
2
Department of Analytical Chemistry, Faculty of Chemistry, Institute of Chemical Sciences,
Maria Curie-Sklodowska University in Lublin, Maria Curie-Sklodowska Sq. 3, 20-031 Lublin, Poland;
cecylia.wardak@poczta.umcs.lublin.pl
* Correspondence: paczosa@agh.edu.pl; Tel.: +48-0126175021; Fax: +48-0126341201
Abstract:
This work proposes new carbon materials for intermediate layers in solid-contact electrodes
sensitive for potassium ions. The group of tested materials includes electrospun carbon nanofibers,
electrospun carbon nanofibers with incorporated cobalt nanoparticles and hierarchical nanocompos-
ites composed of carbon nanotubes deposited on nanofibers with different metal nanoparticles (cobalt
or nickel) and nanotube density (high or low). Materials were characterized using scanning electron
microscopy and contact angle microscopy. Electrical parameters of ready-to-use electrodes were
characterized using chronopotentiometry and electrochemical impedance spectroscopy. The best
results were obtained for potassium electrodes with carbon nanofibers with nickel-cobalt nanoparti-
cles and high density of nanotubes layer: the highest capacity value (330
µ
F), the lowest detection
limit (10
−6.3
M), the widest linear range (10
−6
–10
−1
) and the best reproducibility of normal potential
(0.9 mV). On the other hand the best potential reversibility, the lowest potential drift (20
µ
V
·
h
−1
) in
the long-term test and the best hydrophobicity (contact angle 168
◦
) were obtained for electrode with
carbon nanofibers with cobalt nanoparticles and high density of carbon nanotubes. The proposed
electrodes can be used successfully in potassium analysis of real samples as shown in the example of
tomato juices.
Keywords:
hierarchical nanocomposites; carbon nanotubes/carbon nanofibers; potentiometric sen-
sor; potassium determination; hydrophobic material
1. Introduction
In the field of potentiometry, research is largely focused on the development and
modification of ion-selective electrodes. The simplest structure of an ion-selective electrode
(ISE), called a coated disc electrode, is a conductive substrate directly covered by an ion-
selective membrane (ISM) [
1
]. However, such a simple design is quite unreliable due to
the following problems: (i) instability of the potential; (ii) poor reproducibility caused by
the direct connection of materials of different types of conductivity. The charge-transfer
process at the interface between electronically conducting substrates and ISM is disturbed,
which results in deterioration of the potentiometric response. The easiest way to eliminate
these problems is to place an additional electroactive material between the substrate and
the ion-selective membrane. Such structured electrodes are called solid-contact electrodes.
However, many materials have been tested as intermediate layers, new solutions are still
sought [2,3].
Nanomaterials are one of the groups of materials used as intermediate layers [
4
]. The
physical and chemical properties of nanomaterials make them very useful in the construc-
tion of potentiometric sensors. The large contact area with the ion-selective membrane
Materials 2022, 15 , 4803. https://doi.org/10.3390/ma15144803 https://www.mdpi.com/journal/materials
