Cu2-xO-functionalized plastic optical fiber for H2S sensing

Abstract

A Plastic Optical Fiber (POF) in U-shape, functionalized with a thin film of copper oxide, was developed as a hydrogen sulfide gas sensor. Unlike resistive-type Semiconductor Metal Oxide (SMOX) gas sensors, the present optical sensing probe is neither electrically charged nor demands a heating system as it functions at room temperature (25 °C). Pulsed Laser Deposition (PLD) method was used to coat optical fibers with copper, nickel and tin oxides. However, only CuO-functionalized fibers demonstrated a detectable signal to the H2S exposure. The PLD copper oxide thin films were composed of a dominantly amorphous structure and embedded Cu2-xO crystallites. Fourier Transform Infrared Spectroscopy (FTIR) demonstrated that the PLD process created negatively charged oxygen species adsorbed on the surface of the Cu2-xO, which react with H2S are responsible for the sensing mechanism. A state-of-the-art modification in the fiber’s geometry, with more curves, was presented and improved the Signal to Noise Ratio (SNR). The sensor demonstrated a response time as low as 1 min during an exposure to 200 ppm H2S and a minimum detectable H2S concentration, CH2S, around 10 ppm. The experimental data led to an interpolation that estimates a logarithmic relationship between the saturated signal and CH2S. The sensor demonstrates a remarkable selectivity to H2S. Furthermore, the saturated signal represents an inverse relation with the Relative Humidity (RH).