Nitrate detection at Pd-Cu-modified carbon screen printed electrodes

Abstract

Carbon nanofibers (CNF) and single-walled carbon nanotubes (SWCNT) screen printed electrodes (SPEs) are used for bi-metal, Pd-Cu, modification. Pd nanoparticles (NPs) are deposited first on the pre-reduced carbon SPEs by means of a spontaneous electroless process in the absence of solute reductants. Copper is deposited in a next step under galavanostatic conditions. For both electrodes the Pd deposit consists of NPs with sizes in the 10-ths of nm range with a much denser population and larger amount of the metallic phase in the SWCNT case. The copper deposit on the Pd-modified SPEs differs markedly depending on the type of the underlying substrate with a three times larger mass ratio Pd/Cu of the deposited metals for the SWCNT electrode compared to the CNF one. Nitrate detection is studied on the Cu- and Pd-Cu-modified electrodes in slightly acidic sulfate solution by means of linear sweep voltammetry. The comparison of the mono- and bi-metal- modified electrodes shows a significant enhancement of the nitrate-related reductive currents at the Pd-Cu-modified carbon SPEs. Between the two bi-metal modified electrodes the SWCNT-based one has a higher sensitivity and a larger concentration range of reproducible electroanalytical signal. The non-linear concentration dependence of the nitrate reduction peak currents is modeled by means of a Langmuir type of equation and used for recovery measurements. The Pd-Cu-modified SWCNT-based SPE shows a good stability of the metallic phases over extended nitrate reduction measurements series.