Abstract: A high-performance composite photocatalyst was successfully fabricated in this study via noble metal functionalization methodology. The Pd nanoparticle-modified Na_0.9Mg_0.45T_i3.55O₈ (NMTO) composite photocatalyst was successfully synthesized via a water bath method. The Pd nanoparticles formed a favorable Schottky contact interface with the base material Na_0.9Mg_0.45Ti_3.55O₈, serving as efficient electron trapping centers and significantly improving the separation and transport efficiency of photogenerated charge carriers. Photoelectrochemical tests revealed that the optimized composite catalyst exhibited markedly enhanced photocurrent response and lower interfacial charge transfer resistance, confirming its superior charge separation capability. The system optimization revealed that when the Pd loading ratio reached 1.8%, the composite material exhibited optimal photocatalytic performance: it achieved a remarkable 98% degradation rate of RhB within 20 minutes of illumination, demonstrating significant enhancement compared to pure Na_0.9Mg_0.45Ti_3.55O₈. In the CO₂ photoreduction reaction, the production rates of CO and CH₄ reached 37.48 and 5.63 μmol/(g·h) within 1 hour, respectively. Mechanistic studies indicated that the formation of an interfacial Schottky barrier effectively suppressed charge carrier recombination, which is the key factor in the performance enhancement. This research provides new insights and experimental evidence for designing high-performance multifunctional photocatalysts.