Efficient and recyclable photocatalytic degradation of methylene blue dye in aqueous solutions using nanostructured Cd_1 − xCo_xS films of different doping levels

This study outlines the impact of Co doping on the structures, morphologies, optical, and photochemical activities of nanoporous CdS films for efficient solar energy conversion. A sequence of nanotextured films of cadmium cobalt sulfide (Cd_1 − xCo_xS; where x = 0, 0.02, 0.04, 0.06, and 0.08) were grown on glass substrates using spray pyrolysis method followed by annealing at 300 °C for 2 h. The grown Cd_1 − xCo_xS films are of single wurtzite phase and polycrystalline nature. The preferential crystallographic growth of Cd_1 − xCo_xS nanocrystallites along the (002) is changed to (101) direction for x ≥ 0.06. The crystallite size and lattice parameters are decreased for x ≤ 0.04. Also, the absorption is increased and the optical bandgap is decreased to 2.40 eV at 6% Co-doping. The morphological study reveals the growth of agglomerated pure CdS nanorods. The incorporation of Co increases the density of nanorods, which self-assembled to form nanoporous surface at 2 and 4%. A random distribution of irregular nanorods accompanied by patterned spherical clusters is observed at 6%, which is assembled to a nanoporous pattern at 8%. The photocatalytic performances and reaction kinetics of the films are investigated for methylene blue dye decomposition under sunlight and artificial light illumination. The 6% Co-doped film reached the complete removal after 240 min under sunlight irradiation. This film showed higher stability than pure CdS film for 7 runs. Therefore, the combination of spray pyrolysis and adjustable doping level is a viable way for producing large-scale and reusable photocatalytic films for eco-friendly removal of dyes from industrial wastewater.