Effect of cobalt doping on the physicochemical and photocatalytic properties of Cu ₂ BaSnS ₄ thin films

Cobalt (Co)-doped Cu₂BaSnS₄ (CBTS) thin films were synthesized <i>via</i> the sol-gel dip-coating method to investigate the effect of Co incorporation on their physicochemical properties and photocatalytic activity. X-ray diffraction confirmed that the films crystallize in a trigonal structure, with a slight shift of the favored (104) peak toward higher angles, while X-ray photoelectron spectroscopy verified effective Co incorporation into the CBTS lattice. Surface morphology and roughness, examined by scanning electron microscopy and atomic force microscopy, revealed a reduction in particle size and distinct morphological changes with increasing Co content. UV-vis spectroscopy showed a blueshift in the absorption edge, with the optical band gap widening from 1.78 eV (undoped) to 1.91 eV at 8 at%. The optimized CBTS: Co (6 at%) film achieved 95% degradation efficiency of RhB dye after 120 min and retained high reusability over five cycles. Quenching experiments and electron spin resonance (ESR) analysis identified superoxide radicals (˙O₂ ^-) as the dominant reactive species, with the degradation process following pseudo-first-order kinetics. These findings demonstrate that Co doping effectively tunes the physicochemical properties of CBTS thin films, enhancing their photocatalytic efficiency and stability, and highlighting their potential as sustainable, non-toxic, and earth-abundant photocatalysts.