One-pot preparation of MnOx impregnated cotton fibers for methylene blue dye removal

Abstract

Using natural cotton fibers (CF) as a matrix, a series of novel MnO_x impregnated cotton fibers (designated as Mn-X@BCF) were prepared in this study through a one-pot sono-assisted KMnO₄ reduction process with no additional reducers. The as-prepared Mn-X@BCF was covered by a uniform and dense layer of MnO_x nanospheres (10–30 nm), the amount of which was significantly improved by CF pretreatment and linearly correlated with KMnO₄ concentration. Specifically, when KMnO₄ concentrations increased from 5 mmol L⁻¹ to 100 mmol L⁻¹, the impregnation ratios of MnO_x on BCF increased from 0.34% to 14.98% accordingly. Mn-X@BCF showed substantial removal for the typical dye MB. Under the studied conditions, MB removal equilibrium was reached within 10 minutes and solution pH showed no significant influence over a wide pH range (2–11). MB adsorption by Mn-25@BCF obeyed the pseudo-second-order kinetic model and Langmuir model well. The calculated maximum adsorption capacity (Q_m) of Mn-25@BCF was 46.3 mg g⁻¹, close to the cumulative adsorption capacity (Q_c 45 mg g⁻¹) of MB determined during the eight cycles of adsorption. It was proposed that adsorption followed by partial oxidation was the main mechanism of MB removal by Mn-X@BCF. The as-prepared Mn-25@BCF has great potential as an efficient and low-cost material for dye wastewater treatment because of its inexpensive and renewable source of raw materials, fast MB removal kinetics, wide working pH range and easy solid–liquid separation.