A green approach for decolorising azo dyes by using AlCrFeMn-based high-entropy alloys doped with nonmetallic elements (S, P and C)

The effects of nonmetallic elements Sulfur (S), Phosphorus (P) and Carbon (C) on the decolorisation of azo dye direct blue 6 (DB6) by using ball-milled (BM) Co-free AlCrFeMn (S0) high-entropy alloy (HEA) are presented for the first time in this work. We report the approach of adding S, P and C into S0 HEA in a single step by ball milling, and it is environment friendly method. Moreover, HEAs added with S, P and C do not cause secondary pollution of water during decolorisation recation. DB6 dye solution (200 mg/L) can be fully decolorised in 0.3, 1.9 and 3.3 min with 0.5 g/L of BM AlCrFeMnS (SS), AlCrFeMnP (SP), and AlCrFeMnC (SC), which are about 42, 6.6 and 3.8 times faster than that of S0, respectively. The efficiency of SS for DB6 is 126,000 times that of commercially available pure iron powders. The activation energy of SS is 36.3 kJ/mol, which is lower than that of S0 (54.6 kJ/mol). The extremely high decolorisation efficiency is closely related with the formation of a large number of galvanic cells in SS, SP and SC between the metal and nonmetal elements, which greatly increases the amount and efficiency of electron transfer. The decolorisation efficiency of DB6 solution is assessed by ultraviolet–visible absorption spectrophotometry. The decolorisation rate follows pseudo-first-order reaction kinetics with respect to dye concentration. The results of this study provide some enlightenment for researchers in the application of HEAs in wastewater treatment.