The Controlled Synthesis of Birnessite Nanoflowers via H2O2 Reducing KMnO4 For Efficient Adsorption and Photooxidation Activity.

Birnessite nanoflowers composed of layers have been proven to be the strongest adsorbent and oxidant in the surface environment. However, the current synthesis methods of birnessite nanoflowers are suffering from long reaction time and high reaction temperature. Based on these, this paper explores a new method for the rapid and controlled synthesis of layered manganese oxides. The method relies on the molar ratios of KMnO4 and H2O2 redox reacting species to drive the production of birnessite nanoflowers under acidic conditions. The molar ratios of KMnO4 and H2O2 are the key to the crystal structure of the as-prepared. It was found that when the molar ratios of KMnO4 and H2O2 is from 1:1.25 to 1:1.90, the sample is birnessite nanoflowers, and when the ratio is increased to 1:2.0, the sample is a mixture of birnessite nanoflowers and feitknechtite nanoplates. Among the as-prepared samples, BF-1.85 (molar ratios of KMnO4 and H2O2 is 1:1.85) shows the highest capacity for Pb2+ adsorption (2,955 mmol/kg) and greatest degradation efficiency of phenol and TOC. The method proposed herein is economical and controllable, and it yields products with high efficiency for the elimination of inorganic and organic pollutants.

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.