Greener and size-specific synthesis of stable Fe-Cu oxides as earth-abundant adsorbents for malachite green.

A greener and sustainable pathway to the assembly of Fe, Cu -based adsorbent is described using Virginia creeper (Parthenocissus quinquefolia) leaf extracts in presence of oxalic acid which avoids the use of toxic chemicals. Characterization of the synthesized mixed Fe, Cu oxides are carried out by SEM, TEM, XRD, FT-IR, XPS, and BET techniques; SEM and TEM results disclosed particle size ranging from 160 nm to 1 μm in presence of varying oxalic acid amounts of 0 and 0.1 mol/L. The X-ray photoelectron spectroscopy studies revealed that the sample comprised of Fe, Cu-based hybrid oxides and oxalates. The ensuing results from altered operational parameters namely initial pH, initial malachite green (MG) concentration, the sample dosage and the reaction temperature suggest that the MG adsorption capacity of synthesized materials could be well structured by simply varying the amount of oxalic acid. The optimal sample (S3 sample) has a remarkably high maximum adsorptive capacity (~1399 mg/g) for aqueous MG removal at 303 K and natural pH (~ 6.58), which is superior to recently documented sorbents. The results demonstrate that the adsorption is spontaneous (i.e., ∆G < 0) via an endothermic process wherein the synthesized adsorbent displayed excellent characteristics: 1) maintained a high adsorption capacity under a wide range of pH conditions; 2) remained chemically stable under ambient storage environments to allow for extended stowage; and 3) portrayed high reusability with no waning effect after 4 adsorption/desorption cycles.