Rapid sonochemical preparation of shape-selective lead iodide
Graphical abstract
SEM morphologies of various PbI2 products obtained with the iodine concentration of 6.7 g/L and irradiation time of 1 minute at the reaction temperatures of 35 °C (a), 25 °C (b), and 15 °C (c).
Highlights
► PbI2 with various morphologies were rapidly formed at room temperature. ► We could well control the morphologies of PbI2 by changing reaction conditions. ► The PbI2 films could better resist rolling in a liquid media.
Introduction
Architectural control of semiconductor crystals with well-defined nano/micro structures has attracted considerable attention for potential applications due to their physical and chemical properties which are strongly influenced by their shapes and dimensions. Thus, morphology-controlled synthesis of semiconductor nano/micro structures has been the topic of intensive investigation in recent years [1]. Sonochemical method, which allows the rapid synthesis of many inorganic materials under ambient conditions, has been recently investigated as a promising alternative technique for the fabrication of inorganic materials that exhibited controllable nano/micro structures [2], [3], [4], [5], [6]. It depends on the cavitation effects which are produced by collapsing bubbles in liquids [7], [8], [9]. Different from other means, the sonochemical route always has some special advantages: straightforward, fast, surfactant/template free, low-cost, and low temperature (always at room temperature) [10].
Lead iodide (PbI2) has been paid particular attention for a long time owning to its attractive optical and electrical properties as well as technological application for photocell, X-ray and γ-ray detectors, and medical imaging arrays [11], [12], [13], [14], [15] because of wide band gap energy (Eg = 2.3–2.5 eV) [16], high resistivity (ρ > 1013 Ω cm), and good chemical stability [17]. There are so far many synthetic approaches [18], [19], [20], [21], [22], [23], which have been used to fabricate PbI2 films/crystals with nano/microstructures for the above applications. Also, in our previous work, the hydrothermal/solvothermal approaches were successfully introduced to grow epitaxial PbI2 films composed of perfect hexagonal single crystals [24], [25]. However, long reaction time and rigorous experimental conditions such as high temperature or high vacuum were always needed in such approaches. Herein, we employ a rapid in situ liquid-solid reaction route for the growth of PbI2 films/crystals on lead foils at room temperature by the sonochemical technique. And the effects of different reaction parameters including irradiation time, reaction solvents, iodine concentration, ultrasonic power, and reaction temperature on the morphologies of various PbI2 products were systematically studied. The understanding of these parameters is very important for us to further exploit the rapid and morphology-controlled growth of PbI2 films/crystals for their following use for photocell, X-ray, and γ-ray detectors.
Section snippets
Synthesis
All reagents were of analytical grade and used without further purification. In a typical procedure, a certain dose of elemental iodine and 45 mL absolute ethanol were loaded into a 50 mL beaker to form a transparent solution. A piece of lead foil (Sinopharm Chemical Reagent Co., purity: >99.9%, thickness: 0.1 mm) was placed into the bottom of the above beaker. The lead foil was ultrasonically cleaned in advance with a 1 M HNO3 solution for several seconds and rinsed with distilled water for
Phase and chemical composition of the resulting PbI2 films/crystals
In the present study, we firstly used XRD to characterize the resulting metal iodide films. Fig. 1 shows the typical XRD patterns of the PbI2 films/crystals with various nano/micro morphologies in different reaction medium/systems. Three strong peaks at 31.30°, 36.25°, and 52.21° are respectively correlated to the (1 1 1), (2 0 0), and (2 2 0) planes of the pure lead foil (JCPDS file No. 4-686), respectively. While the other weaker peaks can be readily indexed to hexagonal phase of PbI2 (JCPDS file
Conclusions
In this study, lead iodide films/crystals with various nano/micro morphologies (Nanoflake, block, and microrod) were rapidly and directly prepared on lead foils by the simple sonochemical technique in a controlled way. The PbI2 crystals with perfect nanoflake structures could be formed with the irradiation time as short as 36 s at room temperature, which drastically shortened the reaction time generally needed in other chemical methods. The surface morphologies of the resulting PbI2 could be
Acknowledgements
This work was supported by National Natural Science Foundation of China (Grant Nos. 20873118, 21007053, 51102204, and 61106125), Science & Research Program of He’nan Province (Grant No. 082102230036), Leading Young Teachers in Henan Provincial Institutions of Higher Education of China (Grant No. 2010GGJS-175), Foundation of He’nan Educational Committee (Grant Nos. 2010B150026 and 2009B150023).
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