Photocatalytic Degradation of Allura Red Dye (Red No. 40) Using GdCoO3 as a Photocatalyst Under Solar Irradiation

Allura Red AC (R40) is a widely used water-soluble monoazo food colorant whose potential genotoxic effects have raised environmental and health concerns. This study evaluates the photocatalytic degradation of R40 using GdCoO3 under natural sunlight. GdCoO3 perovskite was synthesized via a combustion-assisted route and calcined at 1100 °C for 6 h. Characterization revealed a highly agglomerated coral-like morphology with a mean maximum Feret diameter of 1.835 ± 0.734 μm and a broad optical response with an apparent transition energy of approximately 2.0 eV. Under direct solar irradiation, GdCoO3 (40 mg in 30 mL of 1.5 × 10−4 mol L−1 R40) achieved 38.5% apparent degradation after 240 min, whereas the corresponding dark system showed a 21.9% concentration decrease mainly attributable to adsorption. The photocatalytic data were best described by the Elovich model (R2 = 0.9854). H2O2 addition significantly enhanced photodegradation, reaching 73.46%, 90.28%, and 98.77% after 180 min using 10, 20, and 30 wt% H2O2 working solutions, respectively. Reactive-species modulation supported a predominant contribution from hole-mediated oxidation together with an important secondary contribution from superoxide-related pathways. After six reuse cycles, the systems retained approximately 83.1–87.5% of their initial activity, supporting the short-term operational reusability of GdCoO3 under the evaluated conditions.