Toxic Gas Detectors Based on a MnSb2O6 Oxide Chemical Sensor

*José Trinidad Guillen Bonilla, Héctor Guillen Bonilla, Maricela Jiménez Rodríguez, Alex Guillen Bonilla, Verónica María Rodríguez Betancourtt, Víctor Manuel Rangel Cobian, María Eugenia Sánchez Morales and Antonio Casillas Zamora*

### **Abstract**

We synthesized the semiconductor oxide MnSb2O6 through a wet chemical process assisted by low-power microwave radiation. A gas-sensitive sensor was elaborated from the MnSb2O6 powders obtained by calcination at 600°C. The sensor was electrically characterized in static CO and C3H8 atmospheres by measuring direct current signals at 100, 200, and 300°C. The toxic gases' concentrations were 1, 5, 50, 100, 200, 300, 400, and 500 ppm of C3H8; and 1, 5, 50, 100, 200, and 300 ppm of CO. From the MnSb2O6's electrical resistance results, a sensor's operational point and a low-cost analog circuit were proposed, obtaining two new prototypes: one for detecting C3H8 and a second one for detecting CO. We selected the response at 200°C and 5 ppm for both cases. Notably, this concentration (5 ppm) is selectable with a calibration resistance, generating an alarm signal of ≈11*:*3 *V* at a supply voltage of 120 V AC. The toxic gas detectors showed excellent functionality. The resistive sensor showed high sensitivity and good electrical response, while the analog circuit presented a rapid response. Due to the operating temperature employed (200°C), these devices could find practical applications, for example, exothermic generators and heaters.

**Keywords:** semiconductor oxide MnSb2O6, sensor was electrically characterized, good electrical response, resistive sensor, CO and C3H8 atmospheres, toxic gas detectors, analog circuit

### **1. Introduction**

The detection of polluting gases is of great importance worldwide because an alarming increase in respiratory, ocular, skin, and lung diseases has been detected [1, 2]. There is no adequate control on the emission of toxic gases into the atmosphere by many large industries and transportation systems [2]. Therefore, a huge effort in research and synthesis of new materials capable of detecting different levels of toxic

gases has been undertaken. The current aim is the development of new inexpensive, reliable, sensitive, efficient, and thermally stable detectors in toxic atmospheres (like in CO, CO2, C3H8, NO2, etc.) [1–4]. The most widely studied semiconductors for their application as gas detectors are the p and n-type binary oxides (like SnO2, ZnO, NiO, CuO, In2O3, WO3, Fe2O3, etc.) [4–6], as well as the ternary perovskite-type oxides (like YCoO3 and LaFeO3) [7, 8], and the oxides with spinel-type structure (like CoFe2O4 and ZnFe2O4) [9, 10]. However, recent reports informed that other transition-metal ternary semiconductors with a trirutile-type crystalline structure (AB2O6, where A and B possess divalent and pentavalent bonds, respectively) are alternative materials for toxic-gas sensors [11, 12]. Among these materials are the CoSb2O6 [11], the NiSb2O6 [12], the MgSb2O6 [13], and the ZnSb2O6 [14]. These oxides have been studied in CO2, CO, C3H8, LPG, H2S, and NO2 atmospheres [11–17].

The MnSb2O6 oxide (manganese antimonite, where in this case the Mn ion substitutes the A) can show a hexagonal crystalline structure with the spatial group P321 [18] or a trigonal chiral-type crystalline structure [19]. The MnSb2O6 possesses good catalytic activity in toxic atmospheres (such as CO) at temperatures above 100°C [20, 21]. In Ref. [20], it was reported that the MnSb2O6 showed a maximum sensitivity magnitude (S) of �8.98 at 300 ppm of CO and 300°C. At 500 ppm of C3H8 (propane), the response was �0.439 at the same temperature. In Ref. [21], the MnSb2O6 was synthesized by the colloidal method and it showed increased sensitivity as a function of the increase in the operating temperature and the gases' concentrations. The response in 500 ppm of propane had a maximum of �165.66 at 300°C. In 300 ppm of CO, the maximum response was �14.929, also at 300°C. The good MnSb2O6's electrical response was attributed to the nanometric particle's microstructure (porosity, morphology, and size) obtained during the synthesis process.

We studied the MnSb2O6 regarding its application as a gas detector and found little information on the application of the oxide in devices for detecting C3H8 and CO, which form atmospheres with a high risk of explosion (propane) or intoxication (CO). In this work, we designed two novel gas detectors: one of them detects C3H8 concentrations and the second one detects CO concentrations. Both are analog detectors and were designed based on the oxide's electrical response. They are capable to detect concentrations of 5 ppm, which can be modified through a calibrating resistance. They generate an alarm signal at � 11*:*3 V, use a supply voltage of 120 V in alternate current (AC), and an operating voltage of Vcc ¼ 12 V. They possess rapid response, and are easy to build, install, and repair. Both are ideal for industrial applications where combustion is involved.
