Ultra-fast and highly-reversible dyes adsorption using a prepared in-situ Fe(PO3)2/biochar composite from corn cob

Abstract

Fe(PO3)2/biochar composite was obtained for the first time by H3PO4-activation and subsequent pyrolysis at 500 °C of an iron-rich corn cob (from Zea mays var. amylacea). The effect of the activation process and Fe(PO3)2 phase on the biochar's structural, surface, and chemical properties was evaluated. The removal capacity of dyes was studied through batch experiments to determine the effect of temperature, pH, ionic strength, initial concentration, and contact time. In addition, the thermodynamic, isotherm and kinetic parameters were determined by non-linear fitting to well-known models. The composite exhibited a maximum adsorption capacity of 372.92 mg·g−1 for methylene blue and 333.14 mg·g−1 for methyl orange. It also showed an ultra-fast adsorption (97 % removal in 0.5 min, initial concentration = 100 mg·L−1) for single and dye-mixed solutions. For both dyes, the adsorption process on the prepared composite was spontaneous, the kinetics were determined as pseudo-second-order and the dye adsorption process was well-fitted to the Freundlich isotherm model, suggesting the presence of high and low-affinity sites toward each dye. Furthermore, an efficient and selective desorption of the dyes was achieved through lixiviation, allowing that the obtained material be reused for more that adsorption-desorption cycles without considerable efficiency losses.