Heterogeneous, Porous 2D Oxide Sheets via Rapid Galvanic Replacement: Toward Superior HCHO Sensing Application

Abstract

2D heterogeneous oxide nanosheets (NSs) have attracted much attention in various scientific fields owing to their exceptional physicochemical properties. However, the fabrication of 2D oxide NSs with abundant p-n interfaces and large amounts of mesopores is extremely challenging. Here, a facile synthesis of highly porous 2D heterogeneous oxide NSs (e.g., SnO 2 /CoO x ) is suggested through a 2D oxide exfoliation approach combined with a fast galvanic replacement reaction (GRR). The ultrathin (<5 nm) layered CoO x NSs are simply prepared by ion-exchange exfoliation and a subsequent GRR process that induces a rapid phase transition from p-type CoO x to n-type SnO 2 metal oxides (<10 min). The controlled GRR process enables the creation of heterogeneous SnO 2 /CoO x NSs consisting of small SnO 2 grain sizes (<10 nm), high porosity, numerous heterojunctions, and sub-10 nm thickness, which are highly advantageous characteristics for chemiresistive sensors. Due to the advantage of these features, the porous SnO 2 /CoO x NSs exhibit an unparalleled HCHO-sensing performance (R air /R gas > 35 @ 5 ppm with a response speed of 9.34 s) with exceptional selectivity compared to that of the state-of-the-art metal oxide-based HCHO gas sensors.

High UV and Sunlight Photocatalytic Performance of Porous ZnO Nanostructures Synthesized by a Facile and Fast Microwave Hydrothermal Method

“…Among ZnO nanomaterials, porous nanostructures with nanoscale thicknesses have received special attention due to their large specific surface area, which can enhance their performance in numerous applications [ 44 , 45 , 46 , 47 , 48 , 49 ]. Porous ZnO nanostructures can be obtained by the thermal decomposition of layered zinc hydroxide (LZH) materials [ 20 ].…”

Liquid‐phase exfoliation method to access cobalt oxide nanosheets in pH‐neutral solutions

“…Prepared through a two-step (i.e., acidbase ionic exchange reaction in the interlayer) liquidphase exfoliation method first reported by Kim et al, 21 CONs typically lack in lateral size. Free-standing CONs obtained from the bulk layered particles larger than approximately 400 nm × 400 nm in lateral size have yet to be reported in the literature 21,27,33,35 other than our recent report focusing on the cation deficiency in LCO after the acid treatment. 24 Therefore, there is little-to-no information relating to the intrinsic physical, chemical, electrical, or optical properties of monolayer and multilayer CONs, since larger lateral dimensions for a 2D material typically allow for more facile measurement of their properties.…”

“…Most commonly exfoliated from lithium cobalt oxide (LCO) 21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] (with many reports coming from our research group [23][24][25]28,29,34,36 ), CONs have been implemented in Liion batteries, thermoelectric devices, armored polymer particles, and layer-by-layer films. 21,23,27,30,31 CONs have also been synthesized through bottom-up techniques, but are not the focus of this work.…”

“…Thus far, characterization of CONs obtained using traditional softchemical ion-exchange exfoliation methods have been limited to transmission electron microscopy (TEM) and/or atomic force microscopy (AFM). 21,24,27,33,35 Herein, we discuss a liquid-phase exfoliation method for producing multilayer CONs in pH-neutral aqueous solutions. Furthermore, details on the size, thickness, structure, and inherent properties were examined for selected CONs.…”

Porous ZnO Nanostructures Synthesized by Microwave Hydrothermal Method for Energy Harvesting Applications

“…Porous oxide semiconductor nanomaterials, particularly two-dimensional (2D) materials with nanoscale thickness, are promising candidates due to their usually large specific surface areas that can improve their performance in several applications [46][47][48][49][50][51]. These nanomaterials can inclusively assemble into three-dimensional (3D) hierarchically structures with controlled morphology and dimensions which can lead to novel properties and applications [52].…”