**4.2 Oxygen doping**

By doping oxygen into g-C3N4, Wei *et al*. [18] significantly increased photocatalytic performance. **Figure 3** shows the process of making oxygen-doped g-C3N4 nanospheres. The copolymerization of the precursor can be used to adjust the degree of oxygen doping. As a result, oxygen-doped g-C3N4 demonstrated exceptional photocatalytic performance, with a Rhodamine B visible light degradation rate of 0.249 min−1 which was greater than traditional g-C3N4, respectively. Zhang et al. [19] also doped varied oxygen element concentrations in typical carbon nitride materials by introducing different quantities of oxalic acid. Photocatalysis efficiency has been significantly enhanced. The addition of oxygen to the energy band structure can change the energy band structure and boost visible light absorption.
