Soft template assisted hydrothermal synthesis of phosphorus doped porous carbon spheres with tunable microstructure as electrochemical nanozyme sensor for distinguishable detection of two flavonoids coupled with derivative voltammetry

A variety of phosphorus doped porous carbon spheres (P-PCSs) with tunable microstructure are facilely prepared by hydrothermal method using xylan as a carbon source, phosphoric acid as an activator and dopant, surfactants as soft templates. Surfactants are beneficial to the development of pore structure and the decrease of particle size. In particular, the introduction of polyvinylpyrrolidone (PVP) facilitates the formation of hierarchically porous structure and nanoscale dimension. The activation of phosphoric acid can improve the graphitization degree, enrich the surface oxygen-containing groups, realize phosphorus doping, and increase the specific surface area. The prepared PVP-P-PCS as a highly conducting electrocatalyst with well dispersed nano-sized spherical morphology of 50–150 nm, large specific surface area of 1558.14 m2/g and hierarchical porosity with coexisted micropores, mesopores and macropores, displays enhanced current responses of about 55-fold enhancement for luteolin and 52-fold enhancement for baicalin compared with bare GCE, intrinsic oxidase-like (nanozyme) characteristics, excellent electrocatalytic ability for luteolin with a low limit of detection (LOD) of 0.77 nM in linear ranges of 0.05–1 μΜ, and baicalin with a LOD of 3.3 nM in linear range of 0.05–1 μM. First-order derivative voltammetry is selected for realizing distinguishable determination of two flavonoids, which demonstrates satisfactory results in the practical application.