Visible Light-Driven p-Type Semiconductor Gas Sensors Based on CaFe2O4 Nanoparticles

Abstract

In this work, we present conductometric gas sensors based on p-type calcium iron oxide (CaFe2O4) nanoparticles. CaFe2O4 is a metal oxide (MOx) with a bandgap around 1.9 eV making it a suitable candidate for visible light-activated gas sensors. Our gas sensors were tested under a reducing gas (i.e., ethanol) by illuminating them with different light-emitting diode (LED) wavelengths (i.e., 465–640 nm). Regardless of their inferior response compared to the thermally activated counterparts, the developed sensors have shown their ability to detect ethanol down to 100 ppm in a reversible way and solely with the energy provided by an LED. The highest response was reached using a blue LED (465 nm) activation. Despite some responses found even in dark conditions, it was demonstrated that upon illumination the recovery after the ethanol exposure was improved, showing that the energy provided by the LEDs is sufficient to activate the desorption process between the ethanol and the CaFe2O4 surface.

Ethanol Gas Sensors Using Semi-Hedgehog-like CuO Nanostructures: Studying the Role of Oxygen Vacancies, Unsaturated Cu-Sites, and Hole Accumulation Layer

“…It is of note that unlike in the n-type MOX, where the adsorbed oxygen molecules create oxygen ionic species by capturing electrons from the conduction band, resulting in an electron depletion layer and band bending, in p-type MOX, the situation is different: the adsorbed oxygen molecules create oxygen ionic species by trapping electrons from the valence band of CuO that results in a high-conductivity hole-accumulation region and upward band bending, i.e., the energy bands bend upward near the surface of CuO (Figure ) in comparison with the flat band situation before any surface reaction. , When the ionic oxygen species interact with reducing gases or undergo competitive adsorption, the adsorbed oxygen is replaced by other molecules, which reduces and sometimes reverses the band bending, resulting in increased resistance . Upon the application of this process, the captured electrons return to the valence band, resulting in electron–hole compensation and eventually the suppression of the HAL.…”

Recent advancements in CaFe2O4-based composite: Properties, synthesis, and multiple applications

“…The principal purposes of photocatalytic activity are to use solar energy for the production of power and the protection of the environment. 35,36 In the photocatalysis process, an electron is transferred from the valence band to the conduction band in this condition, generating photo-induced holes in the valence band. Photo-induced electrons are readily absorbed in the conduction band by dissolved oxygen molecules, resulting in the formation of a reactive superoxide anionic free radical.…”

Electrospun Nanofibers for Quartz Crystal Microbalance Gas Sensors: A Review

“…Unlike traditional chemoresistive gas sensors, the QCM-based sensors basically need neither conductor nor semiconductor materials as their sensing layers. , They work at room temperature with lower power consumption compared to the conventional chemoresistive sensors that need additional heating or lighting sources for their activation. ,− Moreover, QCM-based gas sensors also offer overall higher selectivity and a diverse range of coating materials . Nonetheless, to be used in commercial devices, they still have to meet the typical characteristics of chemoresistive sensors (e.g., good sensing stability, convenient replacement, high reproducibility, and humidity resistance , ).…”