Abstract: Graphitic carbon nitride（C₃N₄）has a graphitic-like planar nanostructure with special optical and electrical properties. Bulk C₃N₄ was prepared from melamine with high-temperature calcination，then the acidification was processed with nitric acid，the sonication-exfoliation was used for C₃N₄-H⁺.The product C₃N₄-H⁺ was characterized with SEM，FTIR，XRD and UV-vis. Besides retaining the basic properties of C₃N₄，C₃N₄-H⁺ exhibits excellent water dispersion stability，large specific surface area and enhanced fluorescence properties. It can be used as a fluorescent probe material. The C₃N₄-H⁺ was taken as fluoresent sensing material，the copper ion was choosed as detection target，the results showed that：in the copper ion concentration range of 0-200. 0μmol/L，change of fluorescence intensity (F₀ /F) of C₃N₄-H⁺ and concentration of copper ion had a certain linear relationship. It is expected to be used for detecting of copper ion in water.

Key words: graphene carbon nitride, acidification, copper ion, fluorescent detection