Mixed bandgap and bandgap tunability in semiconductors is critical in expanding their use. Composition alterations through single-crystal epitaxial growth and the formation of multilayer tandem structures are often employed to achieve mixed bandgaps, albeit with limited tunability. Herein, self-assembled one-dimensional coordination polymers provide facile synthons and templates for graphitic C-doped mesoporous oxides, gC-β-Ga2O3 or gC-In2O3 via controlled oxidative ligand ablation. These materials have mixed bandgaps and colors, depending on amount of gC present. The carbon/oxide interface leads to induced gap states, hence, a stoichiometrically tunable band structure. Structurally, a multiscale porous network percolating throughout the material is realized. The nature of the heat treatment and the top-down process allows for facile tunability and the formation of mixed bandgap metal oxides through controlled carbon deposition. As a proof of concept, gC-β-Ga2O3 was utilized as a photocatalyst for CO2 reduction, which demonstrated excellent conversion rates into CH4 and CO.