<p>The development of economically viable, efficient, and highly reusable visible-light-responsive photocatalysts can substantially enhance the practical feasibility and large-scale applicability of photocatalytic technologies for the remediation of organic wastewater contaminants. The present investigation reports the fabrication of a cost-effective MOF-geopolymer heterostructure composite synthesized by the decoration of bimetallic Co/Ni-BTC metal–organic framework onto calcium-doped, fly ash-derived geopolymer substrate, with the objective of valorizing fly ash, a major by-product of coal-based power plants. The geopolymer matrix served as a stable support enabling the homogeneous growth of Co/Ni-BTC crystallites via a solvothermal route. Comprehensive physicochemical analyses were conducted to elucidate the microstructural, morphological, optical, and electronic attributes of the engineered composite, followed by the evaluation of its photocatalytic potential towards crystal violet (CV) and methylene blue (MB) as model pollutants. Under optimized conditions, the catalyst achieved high degradation efficiencies of 95.59% for CV within 35&#xa0;min and 95.93% for MB within 90&#xa0;min through an advanced oxidative photo-Fenton-like pathway. This enhancement is primarily ascribed to the rapid cycling of Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ redox pairs, which accelerated charge separation and promoted sustained generation of reactive oxygen species. Further, the oxygen-rich geopolymer network promoted the adsorption of dye molecules, thereby increasing the local concentration and availability of contaminant molecules to catalytic active sites. Simultaneously, the geopolymer facilitated efficient transfer of photogenerated holes toward its negatively charged domains, markedly suppressing charge recombination, as corroborated by photoluminescence studies. The degradation mechanism was interpreted through HR-LCMS identification of intermediate species, VB-XPS analysis, and radical scavenging experiments. Photocatalytic kinetics were also investigated, encompassing the discussion of systematic variations of operational parameters, water matrices, dissolved organic matter, co-existing ions, and solution pH, thereby substantiating the practical viability of the proposed system. The degradation process obeyed a pseudo-first order kinetic model with a rate constant of 6.64 × 10^–2&#xa0;min⁻¹ and 2.48 × 10^–2&#xa0;min⁻¹ for CV and MB, respectively. Collectively, the study highlights the dual significance of the MOF-geopolymer heterostructure as a highly interesting photocatalyst and as a paradigm for the sustainable valorization of industrial waste toward eco-efficient wastewater remediation.</p>