Synthesis And Microwave Absorption Properties Of SnO₂ Nanomaterials

In recent years, electromagnetic (EM) wave absorbing materials have aroused great interest because of more and more civil, commercial and military applications in electromagnetic interference shielding in the gigahertz (GHz) band range. Traditionally electromagnetic wave absorbing materials, which are composed of magnetic metals or alloys particles, are restricted in application because of high specific gravity and formulation difficulty. It is hence desirable to have microwave absorbing materials that are lightweight, structurally sound, and flexible and show good microwave-absorbing ability in a wide frequency range. In terms of these criteria, one-dimensional nanostructures, which have a tremendous surface area and more dangling bond atoms on surface, appear to be good candidates. SnO2 has been paid attention in a variety of applications in chemical, optical, electronic, and mechanical fields, due to its unique high conductivity, chemical stability, photoluminescence, and gas sensitivity. However, the research on its dielectric property and microwave absorption capability has not been reported. Here, we focused on the microwave absorption properties of SnO2 nanowires synthesized by chemical vapor deposition(CVD) methods, undoped and Co doped nanograins synthesized by sol-gel method. The main contents, results and originalities of this researh are as follows:(1) undoped and Co doped SnO2 nanograins have been prepared by a sol-gel method and their microwave absorption properties have been investigated in detail. Complex permittivity and permeability of the SnO2 nanograins and paraffin composites with different proportion of 10,20,30,40,50% have been measured in a frequency range of 0.1-18 GHz, the value of both real partε'and imaginary partε" of the permittivity increase significantly with increasing SnO2 nanograins loading The value of maximum reflection loss for undoped SnO2 nanograins and paraffin composites with 40 vol% SnO2 NWs is-27.5 dB at 13 GHz with a thickness of 2.0 mm. This material was promising as a lightweight, hard corrosionand, wide-frequency microwave absorbent. The influence of Co element on the electromagnetic characters and microwave absorption capability of SnO2/paraffin composites were investigated.(2) SnO2 nanowires were fabricated by chemical vapor deposition(CVD) methods. The in-depth study of complex permittivity and permeability revealed that SnO2 nanowires and paraffin composites exhibit excellent microwave absorption properties, owing to the consequence of a proper EM match and the strong dipolar polarization. The value of maximum reflection loss to for the composites with 20 vol% SnO2 NWs is-32.5 dB at 14 GHz with a thickness of 5.0 mm. The measured results were compared with that calculated with effective medium theory (EMT). We found that Bruggeman equation could be only used as qualitative analyse, and led large error as quantitative analyse.(3) we demonstrated the simplified chemical vapor deposition (CVD) approach and prepared three-dimensional (3D) hierarchical SnO2 microstructures without introducing any templates, surfactants, or polymers. The correlation between the growth conditions and the resultant morphologies of SnO2 nanostructures were studied in details.