Co3O4 nanosheet-built hollow spheres containing ultrafine neck-connected grains templated by PS@Co-LDH and their ppb-level gas-sensing performance

Abstract

Through the hydrothermal approach, cobalt-based layered double hydroxide (Co-LDH) nanosheets were grown on the surfaces of polystyrene spheres (PSs), forming core–shell PS@Co-LDH composites. By calcinating such PS@Co-LDH composites at a low temperature, Co3O4 hollow spheres were then synthesized with a skeleton comprising many ultrathin (5.1 nm) porous nanosheets. Each nanosheet consisted of numerous primary grains approximately 5 nm in size and closely neck-connected with each other, as well as a large number of pores approximately 2–3 nm in size. The use of the Co3O4 nanosheet-built hollow spheres in high-performance gas sensors was found to be advantageous, as revealed by the low detection limit of 4.3 ppb for ethanol vapor and the short detection time of 4 s for dimethyl sulfide. To our knowledge, this detection limit for ethanol vapor is the lowest value in the actual test among p-type metal oxide semiconductor resistance-type gas sensors. Furthermore, a conduction model of the connected hole accumulation layer was proposed to explain the excellent gas sensing performances from Co3O4 nanosheet-built hollow spheres.