Metal-deposited bismuth oxyiodide nanonetworks with tunable enzyme-like activity: Sensing of mercury and lead ions

In this study, we demonstrate that the enzyme-like activity of bismuth oxyiodide (BiOI) nanonetworks can be regulated through homogeneous deposition of metal atoms/ions or nanoparticles. Bismuth oxyhalide (BiOX; X = Cl, Br or I) nanostructures were prepared from a simple mixture of bismuth ions (Bi³⁺) and halide ions (X^-) in aqueous solution. The BiOI nanonetworks exhibited much stronger (>25-fold) peroxidase-like activity than BiOCl or BiOBr nanosheets. In situ formation and deposition of gold nanoparticles (Au NPs) onto BiOI nanonetworks greatly enhanced the oxidase-like activity of the nanocomposites. The deposition of Ni, Zn or Mn on the BiOI nanonetworks boosted their peroxidase-like activity by at least 3-fold. Moreover, the catalase-like activity of the BiOI nanonetworks was elevated after deposition of MnO₂ or ZnO nanoparticles. The enzyme-like activity of BiOI regulated by the deposition of metals was mainly due to the changes in the electronic and band structures of the BiOX nanonetworks, and the existence of surface metal atoms/ions in various oxidation states. We used the Au NPs/BiOI nanocomposites and NiO NPs/BiOI nanocomposites for the detection of Hg²⁺ and Pb²⁺ heavy metal ions, respectively, based on the suppression of the enzyme-like activity of the nanocomposite after deposition of these metal ions. These BiOI nanocomposite-based probes allow the selective detection of Hg²⁺ and Pb²⁺ down to nanomolar quantities. The practicality of these two nanozyme probes was validated by analysis of Hg²⁺ and Pb²⁺ ions in environmental water samples (tap water, river water, lake water, and sea water).