<p>The photoreduction of environmental contaminants such as nitrate (NO₃⁻) and carbon dioxide (CO₂) into clean and renewable fuels has emerged as a key strategy for mitigating global environmental challenges, in which perovskite photocatalysts offer a promising, cost-effective, and sustainable solution. In the current research, a novel CuBi₂S₄/Al₂WO₆/Ti₃C₂ MXene Schottky/Z-scheme ternary heterojunction photocatalyst was synthesized and developed for the efficient photoreduction of nitrate and carbon dioxide, as well as photocatalytic water splitting under visible-light irradiation. The nanocomposite integrates three distinct components: (i) zero-dimensional (0D) CuBi₂S₄ quantum dot (QDs) nanoparticles (acting as a metal-assisted sulfide perovskite photocatalyst), (ii) three-dimensional (3D) aluminum tungstate (Al₂WO₆) double perovskite (serving as the central oxide perovskite photocatalyst), and (iii) two-dimensional (2D) Ti₃C₂ MXene (functioning as a non-metallic co-catalyst facilitating interfacial charge transfer). A comprehensive assessment of operating factors revealed their significant influence on the photocatalytic behavior of the CuBi₂S₄/Al₂WO₆/Ti₃C₂ ternary photocatalyst. The CuBi₂S₄/Al₂WO₆/Ti₃C₂ photocatalyst achieved a nitrate reduction efficiency of 80%, with nitrogen gas (N₂) identified as the predominant reduction product (55% selectivity). The same catalyst also exhibited a CO₂ photoreduction efficiency of 70%, in which methane (CH₄) displayed the highest generation rate (13.87 mL·g⁻¹·h⁻1; 619 µmol·g⁻¹·h⁻¹) corresponding to a 50% selectivity. Moreover, the composite demonstrated an impressive hydrogen evolution rate of 16 mL·g⁻¹·h⁻¹ (714 µmol·g⁻¹·h⁻¹) during photocatalytic water splitting with an efficiency of 60%. Furthermore, the ternary heterojunction photocatalyst exhibited excellent reusability and structural stability, retaining its photocatalytic performance over five consecutive cycles.</p>