Cobalt-embedded nitrogen-doped carbon nanosheets with enhanced oxidase-like activity for detecting perfluorooctane sulfonate

Abstract

In this study, we used leaf-like zeolitic imidazolate framework (ZIF-L) as the precursor, CoAc2⋅4H2O as the Co source, and 1,10-phenanthroline (Phen) as the N source to synthesize the cobalt-embedded nitrogen-carbon nanosheet (CoNCN) with enhanced enzyme-like activity. A variety of characterizations proved that the ultra-thin two-dimensional nanosheet structure of the CoNCN with both micropores and mesopores exposes more Co-Nx active sites, which makes it easier for the colorimetric substrate to contact the CoNCN’s surface. Compared with the Co-NC (the synthesized product without using Phen) and NC (the synthesized product without using CoAc2⋅4H2O) controls, the optimized CoNCN nanozyme exhibits 2.3-fold and 12.3-fold enhancement of oxidase-like activity, and 1.3-fold and 25.0-fold enhancement of catalase-like activity, respectively. In addition, the CoNCN has a high affinity for TMB, with a Km value of 0.53 mM and a Vmax value of 3.24 × 10-7 M s−1. The mechanism investigation indicated that the •OH, O2•− and 1O2 were reactive oxygen species responsible for the oxidase-like activity of CoNCN. The perfluorooctane sulfonate (PFOS) can fade the blue oxTMB. Based on this, an analytical method based on a colorimetric strategy coupled to classical univariate calibration was established for the sensitive detection of PFOS, with a linear range of 0.01 to 100 μM, and the limit of detection (LOD) of 20 nM according to modern IUPAC definition. The proposed method was successfully used to determine the concentration of PFOS in actual water samples.