Rapid dry synthesis of nanosized potassium polytungstate via flame aerosol technology for benzene sensing

Polytungstates are oxygen-linked assemblies of highly oxidized tungsten polyhedra, valued for their tunability and stability in diverse applications. Traditional synthesis methods (hydrothermal, solvothermal, solid-state) offer material variety but are limited in scalability and their ability to yield nanostructured materials due to long reaction times and high temperatures. Here, we introduce flame aerosol synthesis as a single-step, rapid and dry method to prepare K 2 W 7 O 22 nanoparticulate powders and coatings. Thereby, monocrystalline and phase-pure K 2 W 7 O 22 with varying crystal sizes were obtained by controlling flame temperature, residence time and metal ion concentration during particle formation by nucleation, coagulation and sintering. X-ray diffraction and electron microscopy identified the high potassium tolerance of the K 2 W 7 O 22 lattice (K/W ratio up to 0.6) and phase stability up to 400 °C, before other polytungstates and WO 3 polymorphs were formed, respectively. Porous films of such K 2 W 7 O 22 nanoparticles featured n-type semiconductor behavior that was utilized for the chemoresistive quantification of the air pollutant benzene down to 0.2 parts-per-million at 20% relative humidity. Such sensors were quite selective over other compounds (e.g. alcohols, aldehydes, ketones, CO, NH 3 or H 2 ), in particular to chemically similar toluene and xylene (>18). • Nanostructured polytungstate K 2 W 7 O 22 was produced by single-step flame aerosol technology. • Modifying operational parameters allowed particle and crystal size optimization. • Thermal annealing revealed phase stability up to 400 °C. • Porous coatings of K 2 W 7 O 22 nanoparticles enable selective detection of trace-level benzene concentration.