Novel dual-functional manganese stannate thin film for acetone gas sensing and photocatalytic methyl orange degradation

Abstract

Increasing health concerns due to pollution has led to the development of various materials to control exposure to pollutants such as toxic gases and contaminated water. In this study, novel manganese stannate (MTO) composite thin films were synthesized via sol-gel spin coating and their structural, morphological, and chemical properties were extensively characterized. In addition, their photocatalytic and gas-sensing abilities were evaluated. In photocatalysis, degradation efficiency measures of how well a photocatalyst can degrade pollutants or dyes under light exposure. Remarkably, the MTO film exhibited a high degradation efficiency of 67% for methyl orange (MO) dye when exposed to UV light for 150 minutes. We also examined the gas-sensing properties of the MTO thin films, particularly their response to acetone. In gas sensors, sensitivity is often reported as a percentage, indicating the relative change in the sensor's response per unit change in analyte concentration. Herein, the sensors displayed a linear response within the 1-9 ppm range of acetone concentration at an operating temperature of 200 °C. They also exhibited excellent selectivity, sensitivity, and repeatability, thus emerging as promising candidates for acetone gas-sensing applications. A sensitivity of 22% was achieved by the sensors, allowing for a low detection limit of 1 ppm, which indicated their high sensitivity towards acetone gas. Moreover, the MTO sensor exhibited response and recovery times of 15 and 16 seconds, respectively. Based on these results, the MTO thin film is a potential material for photocatalytic MO degradation and a gas sensor for acetone detection.

Fig. 1. (a) XRD patterns of MTO thin films fabricated with varying Mn/Sn ratios, where the identified peaks correspond to the @-Mn₂O₃ phase and #-Mn₂SnO₄ phase, (b) morphology (FESEM) of the samples with unique nano-level features (scale bar is 1 μm) and (c) topography (AFM) of the samples showing roughness variation due to a change in the cation ratio.

Fig. 2. (a) TEM images of the sample with a Mn/Sn molar ratio of 2. (b) Selected area electron diffraction (SAED) pattern indicating the presence of crystalline phases. (c) HRTEM image showing the mixed phases of Mn₂SnO₄ and Mn₂O₃. (d) Elemental composition.

Fig. 3. (a) Survey scan to identify all the essential elements in the Mn/Sn = 2 and 2.5 materials; (b) and (c) deconvoluted narrow scans of Mn/Sn (2) and Mn/Sn (2.5) thin films for O 1s, Mn 2p, and Sn 3d.

Fig. 4. (a) Acetone sensing at different operating temperatures using the Mn/Sn = 2 based sensors; (b) sensing of various concentrations of acetone at a 200 °C operating temperature; (c) response and recovery times for the MTO sensor for acetone sensing; (d) sensitivity of the MTO films for different gases; (e) repeatability of the sensing performance to check the stability of the film for long time usage.

Fig. 5. Linear fitting plot of sensitivity versus gas concentration.

Fig. 6. (a) Contact angle measurements for the Mn/Sn = 2 and 2.5 thin films showing their highly hydrophilic natures; (b) photocatalytic degradation of MO using MTO as a thin film catalyst; (c) degradation efficiency of MTO films as a catalyst to degrade MO dye.