Highly sensitive detection of phosphate using well-ordered crystalline cobalt oxide nanoparticles supported by multi-walled carbon nanotubes

Abstract

Phosphates are well-known groundwater and surface water contaminants, with even modest increases in their concentration contributing to the eutrophication of lakes and coastal waterways and thus potentially harming the environment. Consequently, sensors capable of detecting phosphate ions at concentrations below the eutrophication threshold (0.1 μM) are highly sought after. Herein, cobalt oxide nanoparticles (CoONPs) supported by polybenzimidazole (PBI)-modified multi-walled carbon nanotubes (MWCNTs) were prepared and shown to feature uniform size (3.5–5.5 nm) and limited Co phase mainly containing hexagonal Co₃O₄ and a minor amount of CoO. The synthesized NPs exhibited better phosphate sensing performance than previously reported polycrystalline Co wires, i.e., the CoONPs/PBI/MWCNT-modified glassy carbon electrode could detect phosphate at pH 4 and 7 at levels of 0.1 to 100 nM, that is, below the eutrophication threshold of 0.1 μM.