Sequential Elemental Dealloying Approach for the Fabrication of Porous Metal Oxides and Chemiresistive Sensors Thereof for Electronic Listening

Abstract

Highly porous materials, with large surface area and accessible space, variable chemical compositions, and porosity at different length scales, have captivated the attention of researchers in recent years as an important family of functional materials. Here, we report a novel approach to grow porous metal oxides (PMOs) by sequential elemental dealloying in which a highly mobile element gets dealloyed first under the thermal treatment (annealing) and facilitates the formation of PMOs. Subsequently, a chemiresistive sensor based on porous SnO was fabricated for humidity sensing at room temperature which shows a high sensitivity of 348 in a fully humid [>99% relative humidity (RH)] atmosphere with an accuracy of 1% RH change. In addition, the sensor is highly durable and reproducible. Eventually, the chemiresistive sensor has been exploited for electronic listening toward speaking, whistling, and breath monitoring. Overall, the results advocate the fabrication of PMOs and the development of resistive humidity sensors for electronic listening as well as for biomedical applications.

Harvesting energy via stimuli‐free water/moisture dissociation by mesoporous SnO 2 –based hydroelectric cell and CuO as a pump for atmospheric moisture

“…The absorption spectrum shown in Figure 1D reveals a sharp absorption edge at~340 nm related to the direct band edge transition of SnO 2 . 18,25,26 Here, the strong electrostatic field, generated due to presence of oxygen vacancies 27,28 (existence of oxygen vacancies were confirmed with photoluminescence spectra shown in Figure S1), dissociates the water molecules (as seen in Figure 2B) according to Tauc plot, as shown in the inset of Figure 1D, confirms a direct bandgap of~3.62 eV and is in accordance with earlier report.…”

“…18 Removal of Zn atoms from the kink site creates vacancies near surface region which get accumulated with time and guide the highly mobile interstitial Zn atoms to diffuse toward the surface and less mobile atoms diffuse outward. Sintered composites of weight 2.22 gm were than pelletized in 1-inch diameter (5-cm 2 surface area) under high pressure of 130 kN.…”

“…The schematic of the setup is shown in Figure 1A and is utilized in the subsequent experiments. The mesoporous SnO 2 is synthesized using a simple sequential elemental dealloying technique discussed in the work of Solanki et al 18 Figure 1B shows the optical and SEM images of mesoporous SnO 2 pellet. Figure 1A displays the schematic of an experimental setup utilized for voltage generation from water that uses mesoporous SnO 2 .…”

“…Mesoporous SnO 2 has been synthesized by elemental dealloying via thermal assisted sequential removal of highly mobile elements which promises the formation of hierarchical porous structures in green way, 18 ie, without using hazardous chemicals such as H 2 SO 4 , and HNO 3 , which are otherwise essential for electrochemical dealloying process. 19,20 To synthesize the porous SnO 2 , the Cu-Zn-Sn-Cl-O composite was fabricated using hydrothermal route and dealloyed thermally.…”

“…19,20 To synthesize the porous SnO 2 , the Cu-Zn-Sn-Cl-O composite was fabricated using hydrothermal route and dealloyed thermally. The detailed synthesis procedure is reported in the work of Solanki et al 18 In brief, SnCl 4 •5H 2 O, CuCl 2 , and Zn (NO 3 ) 2 •6H 2 O were mixed and dissolved in an equal volume of deionized (DI) water and ethanol at 100°C under continuous stirring for 30 minutes. A light blue colored viscous solution was obtained via adding 1M NaOH dropwise.…”