Preparation And Homologues Detection Performance Of Hollow Mesoporous Silica Sphere Photonic Crystals

Photonic crystals?PCs?are optical materials with periodic modulation of the refractive index and photonic band gap properties.Based on adjustable photonic band gap of PCs,PCs have been widely applications in many areas,such as anti-counterfeiting,display,green printing,photo-catalysis,and advanced sensors and dection.There are many reports that PCs consist of solid spheres have been used to detect common analytes.However,it is difficult to distinguish chemical species with similar refractive indices?such as homologues and isomers?by the stopband shifts.Here,we prepared novel hollow mesoporous silica spheres?HMSSs?to assemble HMSS PCs for the first time,and homologues and isomers were successfully distinguished by three different ways of static reflection spectrum?SRS?,dynamic reflection spectrum?DRS?and dual-stopband shifts based on HMSS PCs with high specific surface areas,pore volume and absorption capacity.Firstly,the monodispersed HMSSs are synthesized by using polystyrene latex spheres as the template and cationic surface active agent as pore former through a simple templating method.The monodispersed and high sphericity HMSSs with different inner diameters and shell thicknesses are synthesized by adusting quantity of tetraethoxysilane,reaction temperture,reaction time and ratio of solvents.Then the monodispersed HMSSs were assembled into 3D ordered HMSS PCs using a vertical deposition technique.Comparing to the only one reflection peak of PCs formed from solid spheres,all reflection spectra of HMSS PCs contain two obvious reflection peaks,corresponding to the first-and second-order Bragg reflection peaks of HMSS PCs,the first reflection peak arises from the FCC?111?planes in the HMSS PCs;the second reflection peak is attributed to the synergetic effect of other planes such as?200?and?311?planes.The positions of the first-and second-order reflection peaks are closely related to the inner and outer diameters of the HMSSs.When the HMSS PC sensors are infiltrated with 10?L of liquid homologues or isomers,the first reflection peaks shift differently between 60 and 200 nm according to different chemicals,while the positions of the second reflection peaks remain nearly unchanged.The HMSS PCs with high specific surface areas,pore volume and absorption capacity result in different effective refractive indices,so the HMSS PCs show high sensitivity and selectivity to detect trace liquid homologues and isomers.For example,difference in the refractive indices of n-propanol and iso-propanol is only 0.008,stopband shifts of the two chemicals are 145 and 120nm,respectively,the difference in the stopband shifts is approximately 25 nm.To further improve the sensitivity and high precision of the HMSS PCs for detecting analytes,we use a dynamic reflection spectrum method to distinguish gaseous homologues and isomers.When 50?L of chemicals diffuse into the HMSS PCs,different adsorption and desorption processes of the HMSS PCs response to the chemicals lead to enormous difference in evolution of reflection spectra with time,which results in high precision detection for trace gaseous homologues and isomers.For isomers of n-butanol and iso-butanol,although difference in the refractive indices of the two chemicals is only 0.001,the adsorption and desorption processes of the HMSS PC responsed to n-butanol and iso-butanol are remarkably different according to the color-filled contour map derived from DRS.DRS pattern of the adsorption process of n-butanol is composed of six reflection bands,while it is five for iso-butanol.The average reflection peak position shift speed of n-butanol(14.2×10^-2 nm/s)is slower than that of iso-butanol(20.4×10^-2 nm/s)in initial 100 s,the average reflection peak position shift speeds of the two chemicals are 7.0×10^-2and 8.3×10^-2 nm/s during the second 100 s,respectively.Compared to stopband shifts of SRS,DRS is more comprehensive and high precision detection method to distinguish gaseous homologues and isomers according to difference of various parameters,such as stopband shift,color change,adsorption-desorption balance time,reflection peak shift speed and the evolution of color bands.The two reflection peaks of the HMSS PCs have red shifts when the HMSS PC sensors exposure to trace gaseous homologues and isomers for a long time,and the shift of the first-order reflection peak is larger than that of the second-order reflection peak.For example,when the HMSS PC sensors exposure to gaseous n-butanol and iso-butanol,the stopband 1 shifts of the HMSS PCs response to the two chemicals are 44.1 and 50.6 nm,and the stopband 2 shifts are 21.9 and 22.9 nm,respectively,their dual-stopband shifts are obviously different.Comparing to the only one stopband shift of detection of PCs formed from solid spheres,the trace gaseous homologues and isomers can be accurately distinguished due to different dual-stopband shifts of HMSS PCs.Here,we provide three different ways of static reflection spectrum,dynamic reflection spectrum and dual-stopband shifts to detect chemical species with similar refractive indices such as alcohol compounds,benzene series,alkylolamines and chloride based on HMSS PCs.Moreover,the three kinds of detection methods are fully reversible,and demand for analytes is trace.Detection of chemical species with similar refractive indices based on HMSS PCs will have wide applications in chemical diffusion,environmental monitoring,chemical reaction assessment,life science and medicine in the future.