Synthesis and application of transition metal ions co-doped CdS photocatalyst for tetracycline hydrochloride degradation

Photocatalytic degradation of resistant antibiotics based on metal sulfide is regarded as an important method of wastewater treatment. However, the low photocatalytic activity and photocorrosion of CdS restrict its application in the photocatalytic degradation of resistant antibiotics. In order to comprehensively investigate the impact of co-doping transition metal ions into CdS on its photocatalytic activity, we successfully prepared a Fe³⁺/Co²⁺/Ni²⁺ co-doped CdS catalyst (Fe_0.1Co_0.05Ni_0.05/CdS) featuring a lamellar agglomeration structure. The specific surface area of Fe_0.1Co_0.05Ni_0.05/CdS (77.0 m²·g⁻¹) was increased evidently, while pure CdS was only 44.3 m²·g⁻¹. Additionally, the photocatalytic degradation efficiency of tetracycline hydrochloride (TCH) by Fe_0.1Co_0.05Ni_0.05/CdS was significantly enhanced, and the TCH’s removal rate can reach 88.9% within 50 min. This is due to Fe³⁺ doping altering CdS's bandgap for more visible-light absorption, Co²⁺ addition reducing electron–hole pairs recombination, and Ni²⁺ introduction enhancing photocorrosion resistance. Moreover, sample Fe_0.1Co_0.05Ni_0.05/CdS retained excellent photocatalytic stability after four cycles. The active species of h⁺ and ·O₂⁻ play the major role in TCH degradation; thus, we hypothesized the TCH’s photocatalytic mechanism and degradative pathway. This finding can assist in designing high-efficiency catalysts by co-doping non-noble metal ions, which will enhance the catalysts’ photocatalytic efficiency through their synergistic action.