Studies of simultaneous electrochemical sensing of Hg2+ and Cd2+ ions and catalytic reduction properties of 4-nitrophenol by CuO, Au, and CuO@Au composite nanoparticles synthesised using a graft copolymer as a bio-template

Abstract

An efficient and selective electrochemical sensor for the simultaneous detection of Hg²⁺ and Cd²⁺ ions in an aqueous medium is developed using bimetallic CuO@Au composite nanoparticles prepared using a novel graft copolymer, sodium alginate-g-poly(allylamine-co-acrylic acid), as a bio-template. The graft copolymer is synthesized via a solution-phase graft copolymerization technique. The same graft copolymer is also used for the preparation of monometallic Au and CuO composite nanoparticles. The developed polymer and composite nanoparticles are characterized using several characterization techniques. All three composite nanoparticles are globular in shape with an average particle size of 5.5 nm for the CuO NPs, 7.5 nm for the Au NPs and 13 nm for the CuO@Au NPs, and are well polydispersed. Metal ion sensing is carried out electrochemically using the linear sweep voltammetry (LSV) technique. The sensing ability of the bimetallic composite nanoparticles towards Hg²⁺ and Cd²⁺ ions is sufficient, with limit of detection values (LODs) of 0.99 nM and 0.78 nM for [Hg²⁺] and [Cd²⁺], respectively. The catalytic activities of the three metal NPs are evaluated by the reduction of 4-nitrophenol to 4-aminophenol. Here, the developed bimetallic composite nanoparticles also show excellent results superior to those of the other two monometallic composite nanoparticles, as well as those of some other reported materials, with a K_app value of 0.556 min⁻¹.