Efficient Adsorption of Azo Dye Acid Brilliant Red on Graphite Carbon Nitride in Aqueous Solution

In this study, two types of graphite carbon nitrides were prepared by directly calcinating urea (U-g-C3N4) and melamine (M-g-C3N4) in a muffle furnace. Their adsorption performances on acid brilliant red (ABR) from aqueous solution were examined and compared. Results showed that, at the optimum calcination temperature of 580 degrees C, both the adsorption capacity of U-g-C3N4 and that of M-g-C3N4 increased strongly with decreasing solution pH. U-g-C3N4 exhibits higher adsorption capacity than M-g-C3N4 at an initial pH > 2.0. However, at an initial pH of 1.0, M-g-C3N4 displayed a much higher adsorption capacity than U-g-C3N4, where the maximum adsorption capacity of M-g-C3N4 can reach 25 635.64 mg g(-1), being the highest reported to date. Adsorptions of both adsorbents followed pseudo-second-order kinetic models and the Langmuir adsorption isothermal models. The adsorption is spontaneous and exothermic and occurs mainly through electrostatic attraction between the protonated g-C3N4 and the negatively charged ABR. In addition, the used U-g-C3N4 can be easily regenerated with ethanol and the renewed U-g-C3N4 possesses comparable adsorption capability of its original form, showing its superior recyclability and broad industrial application prospects.