Fabrication of carboxylated g-C3N4 with excellent adsorption and photocatalytic properties

[Display omitted] •Carboxylated g-C3N4 (g-C3N4-HNO3) was derived from g-C3N4 treated by 10 M HNO3.•Carboxyl group played an important role in the process of adsorption and degradation.•The g-C3N4-HNO3 exhibited an excellent adsorption property towards MO, LRB and Cr(VI).•The g-C3N4-HNO3 showed a good photocatalytic degradation property towards RhB and MB.•The g-C3N4-HNO3 could effectively purify the organic and heavy metal wastewater. Graphitic carbon nitride (g-C3N4) was prepared by thermal annealing urea and melamine. And then the carboxylated g-C3N4 (g-C3N4-HNO3) was successfully fabricated from the g-C3N4 treated through 10 M nitric acid at 80 °C for 24 h. Several characterization data suggested that g-C3N4-HNO3 assembled by 30–190 nm thinner nanosheets possessed lots of carboxyl functional groups, higher specific surface area (88.5173 m2/g) and larger pore volume (0.481684 m3/g). A series of contrast experiments indicated that the g-C3N4-HNO3 exhibited an excellent adsorption property towards methyl orange (MO), Lissamine rhodamine B (LRB) and Cr(VI) due to the hydrogen bonding, higher surface area and electrostatic interaction, and a good photocatalytic degradation property towards rhodamine B (RhB) and methylene blue (MB) due to suitable band gap and better electrical conductivity. The g-C3N4-HNO3 with excellent adsorption and photocatalytic properties could be used to effectively purify the actual wastewater through adsorption and photodegradation roles.