Graphitic carbon nitride (g-C₃N₄) nanosheets have attracted widespread interest in the construction of advanced separation membranes. However, dense stacking and a single functionality have limited the membrane development. Here, an advanced two-/three-dimensional (2D/3D) g-C₃N₄/TiO₂@MnO₂ membrane is constructed by intercalating 3D TiO₂@MnO₂ nanostructures into g-C₃N₄ nanosheets. The 3D flower-like nanostructures broaden the transport channels of the composite membrane. The membrane can effectively separate five oil-in-water (O/W) emulsions, with a maximum flux of 3265.67 ± 15.01 L·m⁻²·h⁻¹·bar⁻¹ and a maximum efficiency of 99.69% ± 0.45% for toluene-in-water emulsion (T/W). Meanwhile, the TiO₂@MnO₂ acts as an excellent electron acceptor and provides positive spatial separation of electrons–holes (e⁻–h⁺). The formation of 2D/3D heterojunctions allows the material with wider light absorption and smaller bandgap (2.10 eV). These photoelectric properties give the membrane good degradation of three different pollutants, with about 100% degradation for methylene blue (MB) and malachite green (MG). The photocatalytic antibacterial efficiency of the membrane is also about 100%. After cyclic experiment, the membrane maintains its original separation and photocatalytic capabilities. The remarkable multifunctional and self-cleaning properties of the g-C₃N₄ based membrane represent its potential value for complex wastewater treatment.