▎ 摘　　要

NOVELTY - Preparing nitrogen and sulfur co-doped pH responsive graphene quantum dots involves mixing the carbon source compound and the nitrogen and sulfur source compound containing nitrogen and sulfur, carrying out a hydrothermal reaction, centrifuging and filtering the reacted solution to prepare nitrogen and sulfur co-doped pH responsive graphene quantum dots. USE - Method for preparing nitrogen and sulfur co-doped pH responsive graphene quantum dots used in pH value responsive reagent for selective iron (Fe3+) detection (all claimed). ADVANTAGE - The preparation method is simple in process and low in cost, and the prepared graphene quantum dot solution not only has a good linear relationship between pH=2-7, serves as a fluorescent probe for detecting metal ions, and quickly detects metal ions Fe3+ in water within 30 seconds. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: i. nitrogen and sulfur co-doped pH responsive graphene quantum dots; ii. selective iron (Fe3+) detection method, which involves carrying out detection of Fe3+by fluorescence spectrophotometry, where the solution used in the fluorescence spectrophotometry is formed by mixing phosphate buffered saline (PBS) buffer solution, ferric nitrate solution and N, S co-doped graphene quantum dots. iii. A pH value responsive reagent in aqueous solution, which comprises nitrogen and sulfur co-doped pH responsive graphene quantum dots, where the response range of nitrogen and sulfur co-doped pH responsive graphene quantum dots in the aqueous solution is 2.5-7.5.