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

Qomaruddin Qomaruddin,Olga Casals,Tony Granz,Andris Šutka,Andreas Waag,Hutomo Suryo Wasisto,Cristian Fàbrega,Joan Daniel Prades

doi:10.3390/s20030850

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.

Highlights

Metal oxide semiconductors have shown the best characteristics in term of sensitivity, selectivity, and stability in gas sensor technology
We present a new p-type metal oxide used as a sensing material, which has several advantages over n-type counterpart [49], e.g., (1) ability to chemisorb the higher concentrations of oxygen molecules, since the formation of a hole-accumulation layer (HAL) in p-type oxide semiconductors is not limited by concentrations of free charge carriers [50]; (2) capability to promote selective oxidation of various volatile organic compounds (VOCs) [51,52]; and (3) lower humidity dependence [53]
CaFe2 O4 nanoparticles have been synthesized by a sol-gel auto-combustion method resulting in unconventional metal oxides with bandgap of around 1.9 eV, which is suitable for visible light spectra

Summary

Introduction

Metal oxide semiconductors have shown the best characteristics in term of sensitivity, selectivity, and stability in gas sensor technology. The high operating temperature is one of the main drawbacks of metal oxide-based gas sensors because it results in high power consumption and undesirable long-term drift problems caused by sintering effects in the metal oxide grain boundaries, yielding poor selectivity and stability [9,10]. Another disadvantage of the metal oxide-based gas sensors with the high operating temperature is Sensors 2020, 20, 850; doi:10.3390/s20030850 www.mdpi.com/journal/sensors. Light-activated sensors have shown high potential [26,27]

Methods

Results

Conclusion