Synthesis of char-based adsorbents from cotton textile waste assisted by iron salts at low pyrolysis temperature for Cr(VI) removal

Char-based adsorbents (char-FeCl₃, char-FeCl₂, and char-FeCit) derived from cotton textile waste (CTW) were synthesized by one-step low-temperature pyrolysis approach with different iron salts. The properties of the samples were conducted by BET, SEM, EDS, XRD, XPS, TEM, and FTIR. The results suggested that the surface areas of char-FeCl₃ and char-FeCl₂ were higher than those of char-FeCit. The presence of Fe₂O₃ as well as pyrolysis gas (HCl (g) and H₂O (g)) could catalyze the formation of porosity. Meanwhile, FeCl₃ showed the strongest catalysis effect to decompose cellulose to produce char. The pyrolysis process analysis was investigated by means of thermogravimetry-DSC. FeCl₃ and FeCl₂ could accelerate the breakage of cellulose structure whereas FeC₆H₅O₇ was not beneficial to form char at low temperature as the incomplete decomposition of citrate. The adsorption property of Cr(VI) for the chars was evaluated. Adsorption processes were fitted well with the Freundlich model, and char-FeCl₃ presented the best adsorptive capacity (70.39 mg/g). Thus, this low-temperature pyrolysis method was economical and technologically simplified as well as efficient adsorption capacity of Cr(VI) removal. Graphical abstract.