The Fabrication Of Photonic Crystal Sensing Films And Their Applications In The Detection Of Gases

The vapors derived from volatile organic and inorganic compounds are poisonous,irritant and corrosive.They are harmful to the human's eyes,skin and mucous membranes.For a long-term exposure,there is a potential risk of mutagenesis,carcinogenesis and even death.Therefore,it is very important for humans to high efficiently,real-time and conveniently detect these poisonous vapors.In this thesis,the chemical sensors based on photonic crystal?PC?film for highly efficient detection of vapors were fabricated by infiltrating functional molecules into the voids of inverse opal photonic crystals?IOPC?.The main contents include:?1?Upon combining the special affinity between functional molecules and the target vapors with the three-dimensional macroporous structures and high surface area of IOPC,the visual detection for target vapors were realized by changing the average refractive index of PC films.It changed the photonic stopbands and the reflectance spectra shifted.?2?The fluorescence enhancement effect arisen from slow photon effect of PC improved the detection sensitivity and realized the quick,high efficient and real-time detection for analytes.The main contents are as follows:1.Acopolymer,poly?2-hydroxyethylmethacrylate-comethylacrylate??P?HEMA-co-MA??,infiltrated SiO₂ inverse opal as visual sensor for the detection of volatile alcohols vapors.The constructed sensor generates remarkable stopband red-shifts when exposed to an atmosphere of volatile alcohols.Particularly for isopropanol and butanol,a red-shift of more than 85 nm can be obtained and the color of the film changes from green to red,which can be observed by the naked eye.This can be attributed to the increased effective refractive index of the inverse opal caused by the diffusion and adsorption of alcohol molecules into the pores.This is based on a combination of a three-dimensional macroporous structure of the inverse opal and strong affinity of the copolymer to alcohols.The exposure to air can reactivate the sensor because of the volatilization and desorption of alcohols.The selectivity,sensitivity and the reusability of the sensor have been investigated by monitoring the reflectance spectra.The results demonstrate that the prepared sensor can be used as visual sensors for detecting volatile alcohol vapors.2.A visual sensor for highly efficient detection of p-xylene vapor was fabricated by infiltrating poly?4-vinylbenzyl chloride-co-methyl methacrylate??P?VBC-co-MMA??into the voids of SiO₂ IOPC,in which P?VBC-co-MMA?was synthesized by free radical copolymerization.When the as-prepared sensor was exposed to p-xylene vapor,the reflectance spectra made a red shift of more than 50 nm,and the film's color changed from yellow-green to orange-red.The reason is that the p-xylene diffused into the voids of the IOPC and was absorbed and condensed onto the air pores wall based on high affinity between P?VBC-co-MMA?and p-xylene.That increased the average refractive index of the PC film and induced the red shift of the reflectance spectra.However,after exposure to air,the reflectance underwent a blue shift and the film color returned to yellow-green because of the decreased average refractive index.Here the air with low refractive index replaced the p-xylene with low refractive index due to the volatilization of p-xylene.The reversible absorption and desorption of organic vapors endowed the sensor with good reusability,which provides a simple and cost-effective strategy for the detection of p-xylene.3.We fabricated a 2-?2-acetoxyphenyl?quinoline-4?3H?-one?HPQ-Ac?infiltrated SiO₂ IOPC fluorescence sensor for the highly efficient detection of ammonia.In the environment of ammonia,the sensor emitted strong fluorescence at a wavelength of 492nm with 30 s.This is because a fluorescence product generated from the HPQ-Ac and ammonia and its fluorescence intensity was enhanced by the slow photon effect of PC.There is a 25.6-fold fluorescence enhancement for the optimized sensor compared to the control sample and the limit of detection is 0.46 mg dm^-3.In addition,the quick response was realized because the three-dimensional macroporous structure is helpful to the fast diffusion of vapors and its high surface area provides more active sites for the analytes.Furthermore,the sensor can be reactivated and reused by exposure to HCl atmosphere.The reason is that HCl can efficiently quench its fluorescence by disrupting the intramolecular hydrogen bond in the HPQ molecule and blocking the intramolecular proton transfer process.The proposed method provides a new strategy for highly efficient detection of ammonia and a platform for developing new fluorescence sensor of gases.