Characterisation of hexagonal birnessite with a new and rapid synthesis method-comparison with traditional synthesis

Birnessite is one of the most important manganese oxides that can control the geochemical behaviors of pollutants or can be applied to form industrial products. Many studies have been conducted on the synthesis of hexagonal birnessite because different synthesis methods can affect the structural, morphological, and physicochemical properties of hexagonal birnessite. However, there are still some defects in these synthesis methods. Therefore, a new synthesis method that is rapid, simple, and low-cost was proposed in this study involving the reduction of KMnO₄ by H₂O₂ in a H₂SO₄ solution without controlling the pH, temperature and pressure. Using a series of XRD, chemical composition, AOS, SSA, SEM, FTIR, and TGA analyses, Bir-H₂O₂ was found to have lower crystallinity than Bir-HCl. However, the AOS and SSA of Bir-H₂O₂ were 3.87 and 103 m² g^-1 higher than those of Bir-HCl, i.e., 3.70 and 22 m² g^-1, respectively. Moreover, both Bir-H₂O₂ and Bir-HCl had similar particle morphology and thermal stability; in addition, the maximum adsorption content of Pb²⁺ on Bir-H₂O₂ (∼3006 mmol kg^-1) was ∼30% greater than that on Bir-HCl (∼2285 mmol kg^-1) at pH 5.5; this indicated that the adsorption of Pb²⁺ on Bir-H₂O₂ was better and belonged to a pseudo-second-order model. All the abovementioned results indicate that Bir-H₂O₂ synthesized herein using the proposed synthesis method can have large application value.