Héctor Guillén-Bonilla

A Novel Gas Sensor Based on MgSb2O6 Nanorods to Indicate Variations in Carbon Monoxide and Propane Concentrations

Bystromite (MgSb2O6) nanorods were prepared using a colloidal method in the presence of ethylenediamine, after a calcination step at 800 °C in static air. From X-ray powder diffraction analyses, a trirutile-type structure with lattice parameters a = 4.64 Å and c = 9.25 Å and space group P42/mnm was identified. Using scanning electron microscopy (SEM), microrods with sizes from 0.2 to 1.6 μm were observed. Transmission electron microscopy (TEM) analyses revealed that the nanorods had a length of ~86 nm and a diameter ~23.8 nm. The gas-sensing properties of these nanostructures were tested using pellets elaborated with powders of the MgSb2O6 oxide (calcined at 800 °C) at temperatures 23, 150, 200, 250 and 300 °C. The pellets were exposed to different concentrations of carbon monoxide (CO) and propane (C3H8) at these temperatures. The results showed that the MgSb2O6 nanorods possess excellent stability and high sensitivity in these atmospheres.

Dynamic Response of CoSb2O6 Trirutile-Type Oxides in a CO2 Atmosphere at Low-Temperatures

Experimental work on the synthesis of the CoSb2O6 oxide and its CO2 sensing properties is presented here. The oxide was synthesized by a microwave-assisted colloidal method in presence of ethylenediamine after calcination at 600 °C. This CoSb2O6 oxide crystallized in a tetragonal structure with cell parameters a = 4.6495 and c = 9.2763 Å, and space group P42/mnm. To prove its physical, chemical and sensing properties, the oxide was subjected to a series of tests: Raman spectroscopy, Scanning Electron Microscopy (SEM) and impedance (Z) measurements. Microstructures, like columns, bars and hollow hemispheres, were observed. For the CO2 sensing test, a thick film of CoSb2O6 was used, measuring the impedance variations on the presence of air/CO2 flows (0.100 sccm/0.100 sccm) using AC (alternating current) signals in the frequency-range 0.1–100 kHz and low relative temperatures (250 and 300 °C). The CO2 sensing results were quite good.

CO and C 3 H 8 sensitivity behavior of zinc antimonate prepared by a microwave-assisted solution method

ZnSb2O6 has been synthesized by a microwave-assisted solution method in order to test its possible application as a gas sensor. Zinc nitrate, antimony trichloride, and ethylenediamine were used as precursors and deionized water as solvent. Microwave radiation, with a power of ∼350 W, was applied for solvent evaporation. The thermal decomposition of the precursors leads to the formation of ZnSb2O6 at 600°C. This oxide crystallized in a tetragonal structure with cell parameters a = 4.66 A, c = 9.26 A and space group P42/mnm. Microwires and microrods formed by nanocrystals were observed by means of scanning and transmission electron microscopies (SEM and TEM, resp.). Pellets of the oxide were tested as gas sensors in flowing atmospheres of carbon monoxide (CO) and propane (C3H8). Sensitivity increased with the gas concentration (0-300 ppm) and working temperatures (ambient, 150 and 250°C) increase. The results indicate high sensitivity of ZnSb2O6 in both gases at different concentrations and operating temperatures.

Synthesis, Characterization, and Sensor Applications of Spinel ZnCo2O4 Nanoparticles

Spinel ZnCo2O4 nanoparticles were synthesized by means of the microwave-assisted colloidal method. A solution containing ethanol, Co-nitrate, Zn-nitrate, and dodecylamine was stirred for 24 h and evaporated by a microwave oven. The resulting solid material was dried at 200 °C and subsequently calcined at 500 °C for 5 h. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, confirming the formation of spinel ZnCo2O4 nanoparticles with average sizes between 49 and 75 nm. It was found that the average particle size decreased when the dodecylamine concentration increased. Pellets containing ZnCo2O4 nanoparticles were fabricated and tested as sensors in carbon monoxide (CO) and propane (C3H8) gases at different concentrations and temperatures. Sensor performance tests revealed an extremely high response to 300 ppm of CO at an operating temperature of 200 °C.

Facile Synthesis, Microstructure, and Gas Sensing Properties of NdCoO3 Nanoparticles

NdCoO3 nanoparticles were successfully synthesized by a simple, inexpensive, and reproducible solution method for gas sensing applications. Cobalt nitrate, neodymium nitrate, and ethylenediamine were used as precursors and distilled water as solvent. The solvent was evaporated later by means of noncontinuous microwave radiation at 290 W. The obtained precursor powders were calcined at 200, 500, 600, and 700°C in a standard atmosphere. The oxide crystallized in an orthorhombic crystal system with space group Pnma (62) and cell parameters  A,  A, and  A. The nanoparticles showed a diffusional growth to form a network-like structure and porous adsorption configuration. Pellets prepared from NdCoO3 were tested as gas sensors in atmospheres of carbon monoxide and propane at different temperatures. The oxide nanoparticles were clearly sensitive to changes in gas concentrations (0–300 ppm). The sensitivity increased with increasing concentration of the gases and operating temperatures (25, 100, 200, and 300°C).

Synthesis of ZnMn2O4 Nanoparticles by a Microwave-Assisted Colloidal Method and their Evaluation as a Gas Sensor of Propane and Carbon Monoxide

Spinel-type ZnMn2O4 nanoparticles were synthesized via a simple and inexpensive microwave-assisted colloidal route. Structural studies by X-ray diffraction showed that a spinel crystal phase of ZnMn2O4 was obtained at a calcination temperature of 500 °C, which was confirmed by Raman and UV-vis characterizations. Spinel-type ZnMn2O4 nanoparticles with a size of 41 nm were identified by transmission electron microscopy. Pellet-type sensors were fabricated using ZnMn2O4 nanoparticles as sensing material. Sensing measurements were performed by exposing the sensor to different concentrations of propane or carbon monoxide at temperatures in the range from 100 to 300 °C. Measurements performed at an operating temperature of 300 °C revealed a good response to 500 ppm of propane and 300 ppm of carbon monoxide. Hence, ZnMn2O4 nanoparticles possess a promising potential in the gas sensors field.

Sensitivity Tests of Pellets Made from Manganese Antimonate Nanoparticles in Carbon Monoxide and Propane Atmospheres

Nanoparticles of manganese antimonate (MnSb2O6) were prepared using the microwave-assisted colloidal method for its potential application as a gas sensor. For the synthesis of the oxide, manganese nitrate, antimony chloride, ethylenediamine and ethyl alcohol (as a solvent) were used. The precursor material was calcined at 800 °C in air and analyzed by X-ray diffraction. The oxide crystallized into a hexagonal structure with spatial group P321 and cell parameters a = b = 8.8054 Å and c = 4.7229 Å. The microstructure of the material was analyzed by scanning electron microscopy (SEM), finding the growth of microrods with a size of around ~10.27 μm and some other particles with an average size of ~1.3 μm. Photoacoustic spectroscopy (PAS) studies showed that the optical energy band (Eg) of the oxide was of ~1.79 eV. Transmission electron microscopy (TEM) analyses indicated that the size of the nanoparticles was of ~29.5 nm on average. The surface area of the powders was estimated at 14.6 m2/g by the Brunauer–Emmett–Teller (BET) method. Pellets prepared from the nanoparticles were tested in carbon monoxide (CO) and propane (C3H8) atmospheres at different concentrations (0–500 ppm) and operating temperatures (100, 200 and 300 °C). The pellets were very sensitive to changes in gas concentration and temperature: the response of the material rose as the concentration and temperature increased. The results showed that the MnSb2O6 nanoparticles can be a good candidate to be used as a novel gas sensor.

Synthesis Characterization of Nanostructured ZnCo2O4 with High Sensitivity to CO Gas

In this work, nanostructured ZnCo 2 O 4 was synthesized via a microwave-assisted colloidal method, and its application as gas sensor for the detection of CO was studied. Typical diffraction peaks corresponding to the cubic ZnCo 2 O 4 spinel structure were identified at calcination temperature of 500°C by X-ray powder diffraction. A high degree of porosity in the surface of the nanostructured powder of ZnCo 2 O 4 was observed by scanning electron microscopy and transmission electron microscopy, faceted nanoparticles with a pockmarked structure were clearly identified. The estimated average particle size was approximately 75 nm. The formation of ZnCo 2 O 4 material was also confirmed by Raman characterization. Pellets fabricated with nanostructured powder of ZnCo 2 O 4 were tested as sensors using CO gas at different concentrations and temperatures. A high sensitivity value of 305–300 ppm of CO was measured at 300°C, indicating that nanostructured ZnCo 2 O 4 had a high performance in the detection of CO.

CHAPTER 3 – CO2 Response of Nanostructured CoSb2O6 Synthesized by a Nonaqueous Coprecipitation Method

Publisher Summary This chapter discusses the CO2 response of nanostructured CoSb2O6 synthesized by a nonaqueous coprecipitation method. CO2 plays an important role in preserving the average atmospheric temperature; the emission of this gas in large amounts during recent decades is producing a phenomenon of great concern to mankind, global warming. With the goal of developing reliable solid-state gas sensors, notable scientific research has been made worldwide. As a result, several compounds such as SnO2, ZnO, WO3, TiO2, and other inorganic oxides have been intensively tested for the detection of toxic gases like CO and NO2. In addition to the oxides already mentioned, several oxides possessing different crystal structures have been studied for gas-sensing purposes. A nonaqueous coprecipitation method based on PVP in ethyl alcohol was used for the preparation of CoSb2O6. Using this simple method, CoSb2O6 was obtained at a low calcination temperature, with good control on the stoichiometry. The synthesis of nanostructured CoSb2O6 by a nonaqueous coprecipitation method using polyvinyl pyrrolidol (PVP), cobalt nitrate, and antimony trichloride in ethyl alcohol is also discussed in this chapter. The relationship between the PVP concentration in solution and the surface morphology is investigated in the study. The potential application of nanostructured CoSb2O6, as an environmental gas-sensor material, is studied by measuring the dynamic variation of resistance in air, CO2, and O2. The CO2-sensing response is also studied by recording intensity vs. voltage graphs at different CO2 concentrations.