Electrochemical Detection of Dissolved Hydrogen Sulfide By Platinum-Modified Multi-Walled Carbon Nanotubes Sensors

Abstract

Multi-walled carbon nanotubes (MWCNTs) were synthesized by thermal chemical vapor deposition (CVD) technique on stainless steel substrates. To catalyze the growth of nanotubes, a thin layer of cobalt catalyst nanoparticles was electrodeposited on the substrates under the optimum deposition potential of −1.1 V vs. SCE, leading to the formation of bamboo-shaped MWCNTs. The structural and chemical characterization of carbon nanotubes by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) confirmed the growth of vertically aligned carbon nanotubes with close ends. The fabricated MWCNTs were subjected to a purification treatment by electrochemical oxidation in sulfuric acid solution. Fourier transform infrared (FTIR) spectroscopy verified the formation of oxygenated functional groups (primarily carbonyl and hydroxyl) at the nanotubes sidewalls after the treatment, and the morphological analyses demonstrated the opening of the nanotubes tips blocked by Co nanoparticles. To improve the catalytic activity of the functionalized MWCNT electrodes and boost their electrochemical performance as biosensors, surface modification of the nanotubes was carried out by the potentiostatic and pulse potential electrodeposition of platinum nanoparticles. The optimum operating parameters were determined as E = −0.6 V, t = 100 s and Eon = −0.6 V, Ton = 100 s, Eoff = −0.35 V, Toff = 10 s in the potentiostatic and pulse potential deposition techniques, respectively. The structural characterizations revealed that the Pt/MWCNT electrode prepared by pulse potential deposition possessed a highly uniform and compact structure of more refined Pt nanoparticles as compared to the Pt/MWCNT electrode modified by the potentiostatic electrodeposition technique. The methanol oxidation reaction (MOR) performance of the fabricated electrodes was investigated by the cyclic voltammetry (CV) tests in an electrolyte containing sulfuric acid and methanol, and the pulse-deposited Pt/MWCNT electrode exhibited superior electrocatalytic activity and anti-CO poisoning capability. The performance of the pulse-deposited Pt/MWCNT electrode as an electrochemical sensor for the detection of dissolved hydrogen sulfide was evaluated. The oxidation of sulfide anions on the designed sensor involved the formation of sulfate species, rather than elemental sulfur, through an irreversible diffusion-controlled process, with a sensitivity of 0.632 μA μM−1 cm−2 and a detection limit of 0.26 μM. These data indicate the remarkable capabilities of the fabricated sensor as a promising candidate for numerous applications in water and wastewater treatment technologies.