Nickel-Palladium Nanoparticles Modified Glassy Carbon Electrode as an Electrochemical Nanosensor for Quantitative Detection of Formaldehyde in Water
Nachaki, Ernest Ojiambo
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Formaldehyde is one of the smallest organic molecules with a wide range of uses in the society. It is used in cosmetics as a preservative. Formaldehyde and formaldehyde releasers are contained in some cosmetics; hair products, shampoos, nail products, lip and dental care products, deodorants, antiperspirants, shaving products, swipes, among others. It is also used in the pharmaceutical industry and in the manufacture of resins and adhesives, permanent press fabric treatments, tissue preservatives, lawn fertilizers and disinfectants. Despite its significance, there are concerns about its toxicity. The United States’ Occupational Health and Safety Administration (OSHA) has set an exposure limit of 2 ppm (for a short period of 15 minutes). Formaldehyde electrooxidation has become a subject of major interest in the recent past, this is due to its potential application in fuel cell technology, and the need for its detection at trace levels as a result of its toxicity. The existing methods of analysing formaldehyde such as; high-performance liquid chromatography, gas chromatography and spectrophotometry, are expensive, require bulky instrumentation and sometimes require the use of toxic reagents. In addition, they are impractical for real-time measurements because o f the time required for apparatus set-up. Hence there is need to continually develop simple and sensitive methods of formaldehyde determination at trace levels. Many studies have been conducted on formaldehyde electrooxidation, most of which suffer electrode passivation as a result of adsorbed intermediates such as carbon monoxide adsorbed (COads) and formic acid adsorbed (H2COOads) formed from electrooxidation of formaldehyde. The objective of this work was to modify a Ni-Pd/GCE sensor for quantitative detection of formaldehyde in water and determine the optimum pH, scan rate and potential window for the electrochemical oxidation of formaldehyde on the Ni-Pd/GCE. Thus, the glassy carbon electrode (Ni-Pd/GCE) was modified with Ni and/or Pd nanoparticles for electrooxidation of formaldehyde. Palladium nanoparticles were electrochemically deposited onto the bare Glassy Carbon Electrode (GCE) from 2 mM PdCl2 in 0.1 M H2SO4 supporting electrolyte, at a controlled potential of -0.14 V for 240 seconds. The Nickel nanoparticles were electrochemically deposited onto the Pd/GCE from 0.5 M NiSO4 in 0.1 M H2SO4 supporting electrolyte, at a controlled potential of -1.25 V for 40 seconds. The modified glassy carbon electrode (Ni-Pd/GCE) was conditioned in 0.5 M NaOH for about 50 cycles or more to obtain a reproducible voltammogram. The assembled electrode was characterized using; Cyclic Voltammetry (CV), and Chronoamperometry (CA). The analytical performance characteristics of the assembled electrode were also determined. The results show that the electrode has significant electrocatalytic properties with respect to formaldehyde electrooxidation as a result of the synergistic effect of Ni and Pd nanoparticles combined with the glassy carbon technology. A sensitive oxidation peak for 1 mM formaldehyde was observed at about +0.43 V vs. Ag/AgCl/KCl (3 M) in 0.5 M NaOH, with a current density of 17 mA cm-2. It had a linear detection range from 10 μM to 1 mM (R=0.9985), and a detection limit of 5.4 μM. The electrode showed significant electrocatalytic activity towards the electrooxidation of formaldehyde in aqueous solution, is selective, reproducible and stable, hence can be used to detect formaldehyde to concentrations of up to 1.45 ppm (18 μM) and can find application in fuel cells.