Research has demonstrated that the formation of composites of titanium dioxide (TiO₂) with silver phosphate (Ag₃PO₄) through the construction of heterojunctions can expand its light absorption range and suppress the recombination of photogenerated electron–hole pairs, thereby improving the photocatalytic performance. However, this method offers only limited performance improvements, and the composite photocatalysts are costly due to the expensive Ag₃PO₄. In this study, Ti₃C₂ MXene, which has good hydrophilicity and excellent electrical conductivity, is first used to form Schottky junction composites with bronze TiO₂ (TiO₂(B)) via electrostatic self-assembly. Then, Ag₃PO₄ quantum dots were further formed on the surface of the TiO₂(B)/Ti₃C₂ MXene by in situ self-growth, and Ag₃PO₄ formed heterojunctions and Schottky junctions with TiO₂(B) and Ti₃C₂ MXene, respectively. Finally, a ternary composite photocatalyst TiO₂(B)/Ti₃C₂ MXene/Ag₃PO₄ was jointly constructed by these functional junctions. Under the synergistic effect of these functional junctions, the mobility and fast separation performance of photogenerated electron–hole pairs of the composite photocatalyst were significantly improved, the recombination of photogenerated electron–hole pairs was effectively suppressed, and the light absorption performance was enhanced. As a result, the composite photocatalyst exhibited excellent photocatalytic performances.