Construction of CeCu_<i>x</i>-BTC/CN S-type heterojunctions and photocatalytic CO₂ reduction to CO and CH₄

S-type heterojunction photocatalysts (CeCu _<i>x</i> -BTC/CN) of cerium-copper bimetallic organic framework (CeCu _<i>x</i> -BTC) and graphitic carbon nitride (g-C₃N₄) were constructed by a simple solvothermal method using cerium nitrate, copper nitrate, and urea as the raw materials, and 1,3,5-benzene-tricarboxylic acid as the ligand for the photocatalytic CO₂ reduction to CO and CH₄. The results show that the built-in electric field constructed by Fermi energy level flattening transfers the electrons in an S-type manner, which not only preserves the strong reducing properties of the electrons in the material but also provides the maximum redox capacity and enables the composite samples to obtain higher visible-light trapping capacity and improve the separation efficiency of the carriers while refining the crystal particles. With the addition of only 1 mL of H₂O as the proton supply source, CeCu_0.05-BTC/CN exhibits the optimal photocatalytic performance. The CO and CH₄ yields were 64.44 and 0.5575 μmol g^-1, which were 7.56 and 2.42 times higher than those of g-C₃N₄, respectively, and the catalytic performances were basically stable after cycling tests.