This study explores the development of cost-effective photocatalysts based on Prussian Blue (Iron(III) Hexacyanoferrate(II)) and its analogues (Cobalt(II) Hexacyanoferrate(II), Iron(III) Hexacyanocobaltate(III), and Cobalt(II) Hexacyanocobaltate(III)) combined with commercial anatase nanoparticles (particle size <25 nm, purity 99.7%) for UV-driven degradation of aqueous methylene blue (MB) solutions. The materials were characterized using XRF, FTIR, SEM, and XRD, confirming the successful formation of side-by-side composites without core@shell morphology. The formation of heterojunctions remains inconclusive.

Photocatalytic experiments demonstrated that the composites achieved high decolorization efficiencies (80–90%), significantly outperforming pure anatase (<25%). However, total organic carbon (TOC) analysis revealed only partial mineralization, with MB content reducing minimally (64.5 mg/L to 62.12 mg/L) under irradiation with a xenon and mercury UV lamp. Importantly, no bleaching of MB solutions occurred with pure Prussian Blue or its analogues alone.

Ecotoxicological assays using Scaptotrigona postica bees revealed that the photodegraded dye solution exhibited reduced toxicity compared to untreated MB, as evidenced by lower mortality risks (HR = 0.8973) and longer median lethal times (TL50 = 12 days vs. 11 days for untreated dye). Stingless bees exposed to untreated MB faced higher mortality risks (HR = 0.6161), emphasizing the ecological risks of untreated dyes.

Therefore, it is imperative to continue studying the development of innovative and sustainable photocatalytic systems, focusing on Prussian Blue composites, their efficient reuse, and their coupling with hydrogen peroxide and/or persulfate, to advance water treatment and the remediation of dyes in an economically viable and environmentally friendly manner.