Hierarchically porous indium oxide nanolamellas with ten-parts-per-billion-level formaldehyde-sensing performance

Hierarchically porous indium oxide nanolamellas with two levels of nanopores have been designed and synthesized by low-temperature dehydration. Each nanolamella consists of nanoparticles, where nanogaps of 5–50 nm are present between the nanoparticles and concave nanopits of 3 nm exist in the surface of each nanoparticle. The nanopits bring negative curvatures to the surfaces of the nanoparticles, leading to a high density of atomic steps and then enhancing the surface activity. Consequently, the indium oxide nanolamellas have exhibited a formaldehyde-detection limit of 80 ppb (parts per billion) with response and recover times as short as 5 s and 1.3 s respectively. The 80-ppb detection limit is lower than the previously reported values from gas-sensing semiconductors and the health standard limitation on the concentration of formaldehyde in indoor air. The detection signal also has an excellent linearity with the formaldehyde concentration. Moreover, the strategy to synthesize the nanolamellas is just two-step heating and easy to scale up. Therefore, the hierarchically porous indium oxide nanolamellas are ready for industrialization and practical applications.