A Facile Wet Synthesis of Nanoparticles of Litharge, the Tetragonal Form of PbO
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A Facile Wet Synthesis of Nanoparticles of Litharge, the Tetragonal Form of PbO Tommy J. Wilkinson, Dale L. Perry1, Erik Spiller, Paul Berdahl, Stephen E. Derenzo, and Marvin J. Weber Lawrence Berkeley National Laboratory Berkeley, CA 94720. 1 Author to contact regarding correspondence. Lawrence Berkeley National Lab, 1 Cyclotron Road, MS 70A-1150, Berkeley, CA 94720. ABSTRACT The red, tetragonal form of lead oxide, α-PbO, litharge, has been synthesized in the nanoparticle range using a rapid, one-step reaction sequence using water as the reaction medium. The product was characterized by powder x-ray diffraction and scanning electron microscopy. With time at room temperature, the original material slowly changed in color intensity, indicating its alteration to β-PbO, massicot. Grinding the aged material converted it back to the original litharge form. The role of impurities in the experimental synthesis of the material and microstructural variations in the final product are discussed, along with the PbOphase compositions of commercial products.
INTRODUCTION Lead(II) oxide exists in essentially two structural polymorphs, with the phase being produced by previous synthetic techniques being dependent on experimental parameters such as
Figure 1. The structures of the α-PbO (litharge) (a) and β-PbO (massicot) (b) phases of lead(II) oxide. The solid lines represent the unit cell frameworks of the molecules. W6.13.1
temperature, pH, and concentration of the lead(II) starting solution. One form is the red tetragonal form, α-PbO, while the other form is the yellow orthorhombic one, β-PbO (Figure 1). Additionally, microstructural phase changes---ones slightly different from the two principal phases normally reported for the compound---can result as a result of the synthetic route and experimental conditions used to prepare the material. The resulting phase is also partially dependent on contaminant species of various other elements present in the reaction solution in addition to the lead(II) ion itself. Both forms of PbO are photoactive semiconductors with bandgap energies of 1.92 and 2.7 eV for α-PbO and β-PbO, respectively, and have been discussed with respect both to their use in a variety of applications and their electronic properties [1-3]. The different synthetic approaches to the bulk preparation of lead(II) oxide have been reported in the research literature, with many of them being ambiguous with respect to the exact products formed. All basically concentrate on the use of a starting salt of lead(II) and its reactions with some type of base. Narita et al [4] have reported the hydrolysis of lead(II) nitrate with sodium hydroxide, a procedure which results in the formation of both α- and β-PbO and four different types of lead(II) hydroxide nitrates. A somewhat similar hydrolysis-based reaction sequence used lead(II) alkoxides as the starting material, followed by their aqueous hydrolysis and subsequent dehydration of the resulting complex lead(II) oxide hydrates [5]. A very different approach was the ball milling
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