Design And Fabrication Of Highly Sensitive Optical Fiber Gas Sensors Based On Nanomaterials Coating

With the rapid development of heavy industry,a variety of toxic,harmful,flammable and explosive gases are discharged in large quantities,leading to environmental pollution and collective poisoning accidents.Therefore,the development of simple and reliable,highly sensitive,highly selective gas sensors has become an important research content in the field of gas sensing.Optical fiber gas sensor has the advantages of low electromagnetic interference,high sensitivity and strong corrosion resistance,so it has wide applications.However,the sensitivity,selectivity and recovery of simple optical fiber sensors still need to be improved.In this paper,the sensitivity and selectivity of micro-nano fiber devices for ammonia detection are improved by combining nano-materials with micro-nano fiber.Firstly,a various of metal oxides nanomaterials were synthesized via hydrothermal methods and sol-gel methods,including ZnO microsphere,ZnO nanoflower,ZnO nanowires and nanoflake,Fe₂O₃ nanotubes,ZnO nanosheets-graphene composite,ZnO nanospheres-graphene composites and other nanomaterials.Through adjusting the experimental parameters such as the temperature,reaction time and PH of the composition,the morphology of the materials can be controlled.The scanning electron microscope?SEM?,X-ray diffraction?XRD?and transmission electron microscopy?TEM?analysis were conducted to investigate the morphology and phase of the composite materials.The SEM and TEM images show that the nanomaterials possess a uniform morphology.Secondly,interferometric micro-nano fiber devices with different structures are fabricated by means of fused taping,and fiber gratings are written by means of phase mask method.For the interferometric micro-nano fiber devices,by controlling the stretching speed and stretching length of the linear translation platform,the interferometric micro-nano fiber devices with different waist diameter and different transition zone length can be obtained.For fiber Bragg gratings,micro-nano fiber Bragg gratings with different diameters are prepared by controlling the corrosion time and corrosion area of HF.It provides the foundation for the high performance microfiber gas sensor.Finally,the synthesized nanomaterials were coated on the micro-nano fiber surface and the response characteristics to ammonia gas?NH₃?of the as-fabricated devices were studied.The ZnO spheres and nanoflowers was coated on the interferometric multimode fiber optic sensor by the drop coating method.The results showed that the fiber optic sensors coated with ZnO spheres and nanoflowers demonstrated sensitivity of 0.57pm/ppm and 1.50pm/ppm,respectively,when the concentration of ammonia was 0-3480ppm.Similarly,the interferometric multi-core fiber optic sensor was coated with conical ZnO/graphene composites and graphene respectively.The experimental results showed that the sensitivity of the sensor was 4.92pm/ppm and 0.79pm/ppm respectively when the concentration of ammonia was 0-3480ppm.The sensors had excellent repeatability and selectivity at room temperature.The Fe₂O₃ nanotubes and flakes are coated on the surface of the micro-nano fibers grating respectively.The results show that the fibers coated with flake has a higher sensitivity.In conclusion,the combination of micro-nano fiber devices and nanomaterials can obtain high sensitive and selective gas sensors.It is found that with the decrease of nanomaterials size,the specific surface area of the particles increases,and the adsorption capacity of the sensor to the gas becomes stronger.Therefore,designing reasonable micro-nano structure for coating materials is an effective means to obtain high-sensitivity optical fiber sensors...