▎ 摘　　要

NOVELTY - Preparing nitrogen-doped carbon dot-graphene oxide composite material involves mixing a carbon source and a nitrogen source, performing hydrothermal reaction, performing solid-liquid separation to obtain a nitrogen-doped carbon dot solution, mixing, stirring graphene oxide and a reducing agent, reacting, performing solid-liquid separation, taking a solid phase, dissolving to obtain a pre-reduced graphene oxide solution, mixing ultrasonically the obtained nitrogen-doped carbon dot solution and the obtained pre-reduced graphene oxide solution, dropping the mixture on an electrode, and reducing by cyclic voltammetry to obtain the nitrogen-doped carbon dot-graphene oxide composite material. USE - Method for preparing nitrogen-doped carbon dot-graphene oxide composite material that is used for detecting heavy metal ion, and electrochemical sensor (all claimed). ADVANTAGE - The prepared nitrogen-doped carbon dot-graphene oxide composite material has a high specific surface area, excellent conductivity and electron transfer rate, and abundant active site. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an electrochemical sensor, which comprises: a nitrogen-doped carbon dot-graphene oxide composite material prepared by the preparation method.