Enhancing microwave absorption of TiO₂ nanocrystals via hydrogenation

Abstract

TiO 2 has attracted tremendous research interest for photocatalytic water splitting, solar hydrogen generation, environmental pollution removal, dye-sensitized solar cells, lithium-ion batteries, supercapacitors, and field emission. Microwave absorption materials (MAMs) play important roles in many military (e.g., the stealth coating on the B-2 bomber) and civil (e.g., telecommunications, noise reduction, information security, signal, and data protection) applications. However, TiO 2 is not a good MAM due to its poor absorption in the microwave region. Here, we report that via hydrogenation excellent and tunable microwave absorption is achieved with hydrogenated TiO 2 nanocrystals. After hydrogenation, 4.3x and 103x improvements have been obtained in storing and dissipating the electric energy of the microwave electromagnetic field. Their permittivity values are higher than those of the current carbonaceous MAMs. Instead of relying on the dipole rotation or ferromagnetic resonance mechanisms for traditional MAMs, the hydrogenated TiO 2 nanocrystals work as good MAMs based on a newly proposed collective-movement-of-interfacial-dipole (CMID) mechanism. Although there is still no direct physical evidence of the interface effects of the CMID mechanism, the CMID as a hypothesis at this point successfully explained the origin of the enhanced microwave absorption of the hydrogenated TiO 2 nanoparticles. This study thus may open new applications for TiO 2 nanocrystals and also stimulate new approaches for new MAM development.

EFEK SUBSTITUSI Fe2+ DAN Fe3+ TERHADAP STRUKTUR KRISTAL, SIFAT OPTIK DAN MAGNETIK PADA NANOPARTIKEL ANATASE Ti1-d(d %Fe)O2

“…Bukan mengandalkan rotasi dipol atau mekanisme resonansi feromagnetik, nanokristal TiO 2 terhidrogenasi bekerja berdasarkan pada gerakan kolektif dari hadirnya dipol antarmuka. Namun hipotesis ini masih belum mampu dijelaskan secara langsung dari efek antarmuka dari mekanisme gerakan kolektif hadirnya dipol antarmuka ini [10].…”

Modifying oxide nanomaterials’ properties by hydrogenation

“…[45] As the crystalline/disordered core/shell nanostructure is formed for hydrogenated TiO 2 nanoparticles, there is apparent electronic structural mismatch between the crystalline phase and the disordered phase. [4,77,78] The interface in between is expected to have structural and chemical defects with dangling bonds and charge imbalance. Meanwhile, the various defects help the charge diffusion and transport with smaller resistance.…”

“…[79] The propagation of the microwave electromagnetic field through the material will cause rapid switching of the polarizing direction and charge accumulation at these interfaces based on a collective-movement-of-interfacial-dipoles (CMID) mechanism. [77,78] Hydrogenated TiO 2 nanoparticles can thus show excellent microwave absorption performance. [77,78] Changing the hydrogenation condition can tune the anatase/rutile ratios and the size of the individual core/shell nanoparticles to achieve microwave absorption with adjustable frequencies.…”

“…[77,78] Hydrogenated TiO 2 nanoparticles can thus show excellent microwave absorption performance. [77,78] Changing the hydrogenation condition can tune the anatase/rutile ratios and the size of the individual core/shell nanoparticles to achieve microwave absorption with adjustable frequencies.…”

“…[77,78] This discovery has been expanded to hydrogenated ZnO and BaTiO 3 nanoparticles for enhanced microwave absorption. [80,81] Hydrogenated TiO 2 nanoparticles have recently been demonstrated with promising medical application due to their extended absorption in the infrared region.…”