Molybdenum Trioxide (α-MoO₃) Nanoribbons for Ultrasensitive Ammonia (NH₃) Gas Detection: Integrated Experimental and Density Functional Theory Simulation Studies

Abstract

A highly-sensitive ammonia (NH3) gas sensor based on molybdenum trioxide nanoribbons was developed in this study. α-MoO3 nanoribbons (MoO3 NRs) were successfully synthesized via a hydrothermal method and systematically characterized using various advanced technologies. Following a simple drop-cast process, a high-performance chemiresistive NH3 sensor was fabricated through the deposition of a MoO3 NR sensing film onto Au interdigitated electrodes. At an optimal operation temperature of 450 °C, the MoO3 nanoribbon-based sensor exhibited an excellent sensitivity (0.72) at NH3 concentration as low as 50 ppb, a fast response time of 21 s, good stability and reproducibility, and impressive selectivity against the interfering gases such as H2, NO2, and O2. More importantly, the sensor represents a remarkable limit of detection of 280 ppt (calculated based on a signal-to-noise ratio of 3), which makes the as-prepared MoO3 NR sensor the most sensitive NH3 sensor in the literature. Moreover, density functional theory (DFT) simulations were employed to understand the adsorption energetics and electronic structures and thus shed light on the fundamentals of sensing performance. The enhanced sensitivity for NH3 is explicitly discussed and explained by the remarkable band structure modification because of the NH3 adsorption at the oxygen vacancy site on α-MoO3 nanoribbons. These results verify that hydrothermally grown MoO3 nanoribbons are a promising sensing material for enhanced NH3 gas monitoring.

Recent Progress in Chemiresistive Gas Sensing Technology Based on Molybdenum and Tungsten Chalcogenide Nanostructures

“…The response time (15 s) and recovery time (50 s) of the device was less than a minute for 1 ppm TMA in adverse condition (55% RH) at this optimal temperature, which indicates its practical application in TMA sensing. Kwak et al synthesized α‐MoO 3 nanoribbons via a hydrothermal route (as shown in Figure a,b) and found it highly sensitive (sensitivity = 0.72 at 50 ppb ammonia) toward ammonia gas at an optimal temperature of 450 °C 121. The response characteristic of the device (with a 1 V biasing voltage) to wide range of ammonia concentration (50 ppb–10 ppm) is shown in Figure 8c and a theoretical LOD was estimated to be as low as 280 ppt at a signal‐to‐noise ratio of 3.…”

“…f) Sensor responses to 25 ppm H 2 , NO 2 , and NH 3 and different contents of O 2 . Reproduced with permission 121. Copyright 2019, American Chemical Society.…”

Ultrathin MoOx/Graphene Hybrid Field Effect Transistor Sensors Prepared Simply by a Shadow Mask Approach for Selective ppb‐Level NH3 Sensing with Simultaneous Superior Response and Fast Recovery

“…[ 4 ] Recently, MoO 3 nanoribbons based sensors led to a low detection limit of 280 ppt for NH 3 with 72% response at 50 ppb, a short recovery time of 216.9 s and 21 repeatable cycles at an elevated temperature of 450 °C. [ 5 ] MoO 3 /Si nanoparticles based sensors could detect 1 ppm NH 3 with 22% response, and had a detection limit of 400 ppb and 7 min recovery time at 400 °C without repeatability and stability reported. [ 6 ] Pd nanoparticles decorated graphene sensors showed high selectivity toward 100 ppm NH 3 with incomplete recovery even after 25 min at 150 °C.…”

“…Most of the sensors above were prepared via lithography, etching, and evaporation processes [ 8,10,12 ] or only their electrodes were prepared by a shadow mask approach. [ 7,9,13 ] Furthermore, their sensing performances for NH 3 were improved by different degrees by extra heating, [ 2–9 ] light illumination [ 10,11 ] or so on, which would undoubtedly cause great inconvenience and/or increase fabrication cost. More unfortunately, use of these extra sources cannot even realize the simultaneous enhancement of overall sensing performances.…”

Enhancement of Lewis Acidity of Cr‐Doped Nanocrystalline SnO2: Effect on Surface NH3 Oxidation and Sensory Detection Pattern

“…Specifically, gas sensor response disturbance towards ammonia is caused by NO x compounds, formed during NH 3 oxidation on the surface of metal oxides . The use of MoO 3 ‐based materials has been proposed for ammonia detection, but considerable sensitivity towards organic compounds has been reported for such systems . Application of Ru‐modification for SnO 2 allows to significantly increase sensor response towards ammonia, but catalytic effect of Ru component also leads to the increase of response towards reducing gases, such as acetone .…”