Abstract：Nitrogen-defective g-C3N4 catalytic materials were synthesized by nitric acid-assisted high-temperature polycondensation of melamine. The microstructure and spectroscopic characteristics were analyzed by scanning electron microscope (SEM)，Brunauer Emmett Teller (BET)，X-ray diffraction (XRD)，Ultraviolet-visible spectroscopy (UV-Vis)，X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy(FTIR). The modified material of sem images exhibits a smaller pore size and a rougher surface resembling a “flower” shape, indicating that the addition of nitric acid significantly changes the structure of the material. The BET spectrum clearly shows that the nitric acid-assisted synthetic material exhibits a large specific surface area and pore size. The XRD pattern shows that the modified material not only maintains the general structural characteristics of the carbon nitride material, but also changes the peak width and angle at both peaks, indicating that assistance of the acid can change the structure of the raw material. It is seen from the UV-Vis spectrum that the modified material has a significant red shift phenomenon, indicating that the material has a certain enhancement to the visible light compared to the original carbon nitride material. The FTIR spectrum shows that the modified material has a change in the carbon-nitrogen single bond and an increase in the amino group on the basis of maintaining the original material groups. From the image of the XPS spectrum, it was found that the binding energy of the modified material and the peak area changed, and the N element content was significantly improved. It is speculated that the conversion of the melamine caused by the action of nitric acid caused the increase of nitrogen. Finally, the Catalytic performance of the materials was tested under visible light and sunlight. The results show that the method is not only simple, the consumption of nitric acid is also low, and the synthesized g-C3N4 material has better micro-structure advantages such as porous structure, smaller particle size and higher specific surface area, and more importantly, The C/N ratio of the materials synthesized by this method has a significant downward trend, and the amino groups also have an increased performance, which may be caused by the chemical reaction between nitric acid and melamine during high-temperature sintering. The results of catalytic degradation of RhB by visible light and sunlight showed that the catalytic effect of g-C3N4 was the best when the volume of nitric acid was 2 mL, and the degradation rate reached 99%, which was 2.8 times and 2.5 times than non-nitric acid materials, respectively. The cyclic degradation test of the material indicates that the material has high recyclability. This materials which include highly efficient, easy-to-industrial and recyclable provides an excellent reference for future practical applications.
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