Rational Integration of SnMOF/SnO₂ Hybrid on TiO₂ Nanotube Arrays: An Effective Strategy for Accelerating Formaldehyde Sensing Performance at Room Temperature

Abstract

Formaldehyde is ubiquitously found in the environment, meaning that real-time monitoring of formaldehyde, particularly indoors, can have a significant impact on human health. However, the performance of commercially available interdigital electrode-based sensors is a compromise between active material loading and steric hindrance. In this work, a spaced TiO2 nanotube array (NTA) was exploited as a scaffold and electron collector in a formaldehyde sensor for the first time. A Sn-based metal–organic framework was successfully decorated on the inside and outside of TiO2 nanotube walls by a facile solvothermal decoration strategy. This was followed by regulated calcination, which successfully integrated the preconcentration effect of a porous Sn-based metal–organic framework (SnMOF) structure and highly active SnO2 nanocrystals into the spaced TiO2 NTA to form a Schottky heterojunction-type gas sensor. This SnMOF/SnO2@TiO2 NTA sensor achieved a high room-temperature formaldehyde response (1.7 at 6 ppm) with a fast response (4.0 s) and recovery (2.5 s) times. This work provides a new platform for preparing alternatives to interdigital electrode-based sensors and offers an effective strategy for achieving target preconcentrations for gas sensing processes. The as-prepared SnMOF/SnO2@TiO2 NTA sensor demonstrated excellent sensitivity, stability, reproducibility, flexibility, and convenience, showing excellent potential as a miniaturized device for medical diagnosis, environmental monitoring, and other intelligent sensing systems.

The Challenges and Opportunities for TiO2 Nanostructures in Gas Sensing

“…The change of the width of the depletion layer and the carrier concentration has an impact on the adsorption and reaction of gas molecules at the interface, thus affecting the sensitivity and selectivity of the sensor. For an n–n heterojunction, the charge carriers will move from the material with a higher Fermi level (FL) to the one with a lower FL until the two FLs equilibrate (Figure e–h) . This leads to the formation of electron accumulation and depletion layers on the surfaces of the low-energy and high-energy states, respectively, which significantly changes the electronic properties and surface reaction characteristics of the material, thus affecting the performance of the gas sensor.…”

“…Schematic diagram of the electron depletion layer on SnMOF/SnO 2 @TiO 2 nanotubes (SnO 2 @TiO 2 forms the n–n heterojunction) (e) in air and (f) in formaldehyde and the potential barrier change (g) in air and (h) in formaldehyde. (Reproduced from ref . Copyright 2023 American Chemical Society.)…”

Quasicrystal Nanosheet/α-Fe2O3 Heterostructure-Based Low Power NO2 Sensors: Experimental and DFT Studies

“…Figure d and e shows the Fermi-energy diagrams in vacuum and after heterojunction formation between 2D QC nanosheets and α-Fe 2 O 3 . As a result, the surface carriers were depleted, leading to the formation of a depletion layer near the sensor surface and a potential barrier . Once the reaction reached equilibrium, a significant potential barrier equilibrium developed on the sensor surface, resulting in the generation of numerous active sites …”

“…Semiconducting metal oxide (SMO)-based chemiresistive gas sensors are gaining much interest due to their interesting characteristics, such as high sensitivity, cost-effectiveness, portability, small size, and easy integration at the chip level. − The ability to differentiate various kinds of gases is an area of concern due to the sensitivity of the sensors to a wide range of gases . Hematite (α-Fe 2 O 3 ) is one of the promising SMOs that can exhibit significant potential for practical applications due to its physicochemical and optoelectronic properties, earth abundance, and low toxicity. , α-Fe 2 O 3 is the prevalent polymorph and has been used in multiple forms, including thin films, hierarchical structures, nanoparticles, nanotubes, nanobelts, and so on, to detect gaseous analytes. − The development of gas sensors based on α-Fe 2 O 3 , decorated with metal nanostructures, opens up new possibilities.…”

Customizing Wettability of Defect-Rich CeO2/TiO2 Nanotube Arrays for Humidity-Resistant, Ultrafast, and Sensitive Ammonia Response

“…Among them, MOS-based sensing devices have gained prominence owing to their robustness and cost-effectiveness . In our previous work, spaced TiO 2 nanotube arrays (NTAs) have been shown to have excellent potential as scaffold and electron collector alternatives to conventional interdigital electrodes in gas sensors . In general, MOSs containing frustrated Lewis pairs (FLPs) usually act as active sites, owing to their ability to activate small molecules .…”