Attributing to its significantly low bandgap of 1.32 eV, the as-synthesized FeCoNiCuZn HEA 18 can degrade up to 86%, 94%, 80%, and 99% of TC, SMX, IBP, and DCF, respectively within 19 120 min of visible light exposure. In order to gain insights into the underlying photocatalytic 20 degradation mechanism, the role of various reactive oxygen species, as well as the diverse 21 intermediates formed during the photocatalytic reaction, are elucidated. Furthermore, the 22 evaluation of the probable toxicity of the treated PhAC solutions reveals that the photocatalysis end-products do not pose any conceivable public health threats. More importantly, the as-1 developed HEA demonstrates a relatively stable cycling performance for prolonged operation, 2 without any significant metal leaching. To the best of our knowledge, this is the first report which