Microwave Assisted Hydrothermal Synthesis Of Ternary Ferrites And Their Gas Sensing Properties

As the most dangerous disease to human health globally,lung cancer has become the focus of researchers in many fields.How to realize the noninvasive screening of early cancer has always been the focus of researchers.There are many methods for lung cancer detection,such as chest CT and histopathological examination.These methods are of great importance for cancer diagnosis,but they also have obvious disadvantages,such as radiation,high cost,complex operation,and trauma.Moreover,they are limited by detection equipment and are difficult to be popularized on a large scale,so they are not suitable for large-scale screening in the early stage of cancer.With a research foundation in disease detection,exhalation analysis can provide a simple,convenient,noninvasive,and low-cost detection method.Many sensing technologies have been reported for disease detection.Among them,semiconductor metal oxide gas sensor shows excellent development potential in disease detection because of their advantages of simple preparation,cost-effectiveness,and easy integration.Isop ropanol is a typical biomarker gas of lung cancer.It’s concentration in exhaled breath is low,usually less than one part per million(ppm).Exhaled breath detection is intended to detect the concentration change of VOCs including isopropanol in exhaled breath to distinguish healthy people from patients with early lung cancer.The sensor needs to have high sensitivity and excellent selectivity.In order to prepare highly sensitive gas sensing materials,two different kinds of ternary ferrites were prepared with the optimal synthesis conditions confirmed by controlling variables,and their gas sensing performance with low-concentration isopropanol was studied.Considering the application conditions of exhaled breath detection,the influence of humidity on the gas sensing properties of materials is also studied in this paper.Firstly,during the synthesis process of materials,microwave synthesis conditions greatly influence the properties of gas sensing materials,including synthesis temperature,reaction time,and power.On the one hand,the phase composition,micromorphology and specific surface area of materials are affected.On the other hand,microwave synthesis conditions affect the gas sensing performance of materials on the response strength and response speed of the target gas.Under the optimum working temperature,bismuth ferrite has excellent gassensing performance and can detect 0.2 ppm ultra-low concentration of isopropanol.In the gas sensing experiment for 0.2-1 ppm isopropanol,a fine linear relationship exists between the response value and the concentration,which can be used as the basis for measuring isopropanol content.Secondly,to explore the influence of humidity on the sensor’s performance,the gas sensing tests are carried out in the range of 20-100%relative humidity atmosphere.It is found that humidity has some influence on the gas sensing performance of bismuth ferrite material.With the increase of humidity,the gas sensing response intensity of the material decreases.However,the response value of bismuth ferrite to 1 ppm isopropanol is still as high as 3.9 with 100%relative humidity.In order to explore the selectivity of bismuth ferrite materials,experiments were carried out on the other seven gases in exhaled gas.It was found that bismuth ferrite had excellent response to acetone,ethanol,and isopropanol,but a weak response to ammonia,carbon dioxide,and other gases.Finally,LnFeO3(Ln=Nd,Eu,Dy,Er)gas sensing materials were rapidly synthesized by microwave hydrothermal synthesis.Under the optimal working temperature,LnFeO3 has excellent gas sensing properties for isopropanol,like high sensitivity,humidity resistance,good selectivity,and good long-term stability.With the change of lanthanides,LnFeO3 shows slightly different gas sensing properties.Its excellent gas sensitivity is due to the low binding energy of Ln-O bond,which is easy to fracture and chemical reaction.