Organic Vapors Sensitive Photonic Crystal Film Visual Sensors

Volatile organic compounds（VOCs） have strong stimulation to skin, respiratory tract mucous membrane and eye mucous. They are even carcinogenic and have a serious impact on human health. Therefore, it is very important for human health and environmental protection to highly efficiently detect volatile organic pollutants in the atmosphere, soil and water.This thesis fabricated the functional molecules infiltrated Si O₂ inverse opal photonic crystal（IOPC） film sensors by using the photonic stopband property of photonic crystal（PC）. Combined with the reversible chemical/physical properties between the functional molecules and organic vapors, and high specific surface area of the IOPC’s three-dimensional macroporous structure, the average refractive index of the PC sensors can be tuned reversibly, which results in the reversible change of photonic stopbands and can be shown in the reversible shifts of reflectance spectra. By selecting proper PCs, reflectance spectra of the prepared sensors can be shifted in the region of visible light when exposed to the atmosphere of the gaseous analytes, which induces the changed film’s color. The color change can be observed clearly by naked-eyes. Thus, the visual detection of target molecules can be realized, and finally, the organic vapors sensitive PC film visual sensors can be obtained. The main contents are as follows:1. A diethyl ether/petroleum ether vapors sensitive PC film sensor were obtained from infiltrating hexaphenylsilole（HPS） into the voids of Si O₂ IOPC, which were fabricated by sacrificing template methods. The reversible color change of the prepared sensor can be obtained by alternating its exposure to different vapor environments.When the film was put in diethyl ether or petroleum ether vapor, a stopband red shift of more than 100 nm could be clearly observed, while the color changed from green to red. When exposed to air, the stopband underwent a blue shift and the color changed back to green. The result is attributed to the HPS molecules, which can be transformed reversibly between the crystal and amorphous state when alternately exposed to air and vapors of diethyl ether/petroleum ether. When crystal HPS changed to amorphous HPS in an atmosphere of organic vapors, both the specific surface area and refractive index of HPS increased. The higher specific surface area of HPS improved the adsorption behavior of organic vapors. Both the improved adsorption and higher refractive index of HPS increased the average refractive index of the sensor, which resulted in the red shift of the stopband and the corresponding color change. Based on the reversible aggregation state transfer and the adsorption-desorption of organic vapors, the average refractive index of the sensor film varied repeatedly, which caused the reversible stopband shift and color change. The visual detection of organic vapors can be realized because of the remarkable color change of the sensor, which provides a simple route for monitoring VOCs, and is important for chemical and biological sensors.2. A tetrahydrofuran/acetone vapors sensitive sensor, based on a tetraphenylethene polymer（TPEP） infiltrated Si O₂ IOPC, was fabricated and used for visual detection of these two kinds of vapors by the color change. When the sensor was exposed to organic vapors, a red shift of the stopband of more than 50 nm could be clearly observed; meanwhile, the film’s color changed from violet to cyan. Subsequently, when exposed to air, the stopband underwent a blue shift and the color returned to violet. The reason for the observed change is that a reversible adsorption-desorption process occurs on alternate exposure of the sensor to organic vapors and air, due to the high specific surface area of the inverse opal macroporous structure and the high affinity of TPEP to tetrahydrofuran and acetone. The adsorption of vapor analytes can increase the PC’s average refractive index, which will induce the stopband red shift and the resulting color change according to Bragg’s Law. The reversible adsorption-desorption of organic vapors varied the average refractive index of the sensor repeatedly, causing the reversible stopband shift and color change, and providing a general method for the design of visual vapor sensors.3. The visual sensors for volatile aldehydes（including formaldehydes, acetaldehydes, propaldehydes, butaldehydes and valeraldehydes） were fabricated by infiltrating functional polymer poly（allylaminehydrochloride）（PAH） into the voids of Si O₂ IOPC. When the sensor was exposed to volatile aldehyde vapors, the photonic stopband had a red shift of more than 100 nm accompanying with a color change from initial violet to yellow green. This is attributed to that the inverse opal macroporous structure is benefit for the gaseous diffusion and adsorption on the pore walls, in which the nucleophilic addition reaction between amino group of PAH and formyl group occurs. In addition, partly vapors can condense on the pore walls. All the aboved-mentioned factors can increase the average refractive index of the sensor film. Subsequently, when exposed to air, the stopband underwent a blue shift and the color returned to violet due to the decreased average refractive index of the film caused by the reversible nucleophilic addition reaction and desorption of organic vapors. The prepared sensor realizes the visual detection of volatile aldehydes and can be reused, which provides a simple way for fabricating new vapors sensitive sensors.