Highly luminescent graphene core N-doped carbon nanodots prepared under spatial nanoconfinement

Nitrogen-dopped carbon nanodots (CNDs) with an extremely high quantum yield of photoluminescence (up to 95%) have been obtained by thermal treatment of citric acid embedded in the porous structure of silica with immobilized N-[3-(Trimethoxysilyl)propyl]ethylenediamine. Spatial isolation of molecular precursors in nanoreactors permits the preparation of high-quality nanoparticles with spheroidal geometry and size 2-5 nm. The particles obtained at 110-180 degrees C for 60-600 min demonstrate excitation-independent photoluminescence at 453 nm. HRTEM reveals that the CNDs demonstrate ordered crystalline structures of graphic materials, indicating the catalytic effect of the nanoreactor. The high-resolution XPS experiment proves the N-doping of CNDs with 4.0 at. % of nitrogen atoms incorporated into the graphene core as pyrrolic and ternary fragments.