Carboxyl-rich g-C3N4 nanoparticles: Synthesis, characterization and their application for selective fluorescence sensing of Hg2+ and Fe3+ in aqueous media

•Carboxyl-rich g-C3N4 was prepared through hydrothermal oxidation of g-C3N4 nanosheet.•A facile one-pot method was proposed for synthesizing of graphitic carbon nitride nanosheet containing heptazine motif.•The surface groups of g-C3N4 structures were measured by ninhydrin test and acid-base titrations.•Carboxyl-rich g-C3N4 was used as a fluorescence sensor for selective detection of Hg2+ and Fe3+.•The prepared sensor was a highly selective On-Off fluorescence sensor for detection of Hg2+ and CN−.

A new method has been introduced for synthesizing of carboxyl-rich g-C3N4 nanoparticles through a facile procedure from g-C3N4 nanosheets prepared by one-pot thermal polymerization of dicyandiamide under nitrogen atmosphere. The formation of these nanosheets was confirmed by the AFM, XRD, FESEM and FTIR analyses. These nanosheets subsequently were transformed to carboxyl-rich nano structures through hydrothermal oxidation and were characterized by XRD, AFM, DRS, FESEM, Zeta-potential and FTIR. AFM studies revealed that the thickness and lateral size of these nano structures were 6 and 35-50 nm, respectively. In the present work, carboxyl-rich g-C3N4 was used as a selective sensor for detection of Hg2+ and Fe3+ which showed 12 and 190 nM detection limits, respectively. In addition, CN− was added as a discriminative agent to the aqueous media of these ions that enhanced and quenched PL intensities of Hg2+ and Fe3+, respectively.

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