Synthesis of Birnessite in the Presence of Phosphate, Silicate, or Sulfate.
Layered manganese (Mn) oxides, such as birnessite, are versatile materials in industrial applications and common minerals mediating elemental cycling in natural environment. Many of birnessite properties are controlled by Mn(III) concentration and particle sizes. Thus, it is important to synthesize birnessite nanoparticles with controlled Mn(III) concentrations and sizes so that one can tune its properties for many applications. Birnessite was synthesized in the presence of oxyanions (phosphate, silicate, or sulfate) during reductive precipitation of KMnO4by HCl and characterized using multiple synchrotron X-ray techniques, electron microscopy, and diffuse reflectance UV-vis spectroscopy. Results indicate that all three anions decrease MnO6sheet sizes, attributed to oxyanion adsorption on edges of the sheets, inhibiting their lateral growth. As a result of decreased sizes, sheets undergo significant structural contraction. Meanwhile, Mn(III) concentration significantly increases with increasing oxyanion/Mn ratio. The increased Mn(III) concentration, along with the decreased size, enlarges both direct and indirect band gaps of birnessite. Phosphate imposes the strongest influence, followed by silicate and then by sulfate, consistent with their decreasing adsorption affinity. Reacting with 1 M KOH solution effectively removed the adsorbed oxyanions while leading to increased sheet sizes, probably due to oriented attachment-driven particle growth mechanisms. The results have important implications for developing highly performed birnessite materials, for example, small size Mn(III)-rich birnessite for photochemical and catalytic applications, as well as for understanding chemical compositional variations of naturally occurring birnessite.
Department of Ecosystem Science and Management, University of Wyoming , Laramie, Wyoming 82071, United States.
Qian
Q
Wang
Department of Ecosystem Science and Management, University of Wyoming , Laramie, Wyoming 82071, United States.
Xianya
X
Liao
Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
Wenqian
W
Xu
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Yang
Y
Ren
Materials Characterization and Processing Center, Department of Materials Science and Engineering, The Johns Hopkins University , Baltimore, Maryland 21218, United States.
Kenneth J
KJ
Livi
Department of Ecosystem Science and Management, University of Wyoming , Laramie, Wyoming 82071, United States.
Mengqiang
M
Zhu