Structure-Color And Gas Sensing Application Of Polysaccharide Nanocrystal Coating

Polysaccharides are widely distributed in the nature,such as cellulose,chitin,chitosan and so on.It has become a focus today to use them to make environmental friendly materials.In this work,according to the structure characteristics of cellulose and chitin,using reasonable methods to make them into cellulose nanocrystals(CNCs)and chitin nanocrystals(CHNs).And then spin coating method was used to make CNCs coating and CHNs coating.Then the coatings were used for gas sensing research.The CNCs suspension was prepared by sulphuric acid hydrolyzing and the CHNs suspension was prepared by hydrochloric acid hydrolyzing.Then the suspension was used for spin-coating to make optical coatings.Atomic force microscope(AFM)shows the nanocrystals of both CNCs and CHNs are uniform and attempted to align regularly in the axial-centrifuged direction.According to SEM testing results,the coatings both have layer structures.The polarization microscope(POM)display the colorful interference fringe.Afterwards,optical fiber spectrometer(OFS)was used to test the reflectance of the coating and the results indicate that the reflective wavelength of the coatings switched periodically along with their thickness.Accordingly,the color changed from blue to orange and then to blue.Then the coatings of CNCs and CHNs were used in vapor sensing.When the as-prepared CNCs and CHNs coatings were exposed to saturated ammonia vapor and distilled water vapor,the wavelength of the CNCs and CHNs coatings changed from about 540 nm to 590 nm and 542 nm to 589 nm respectively.On the other hand,when paced the CNCs coatings in saturated HCl and HAc vapors,a much larger shift of 85 nm and 105 nm were observed,respectively,corresponding to a clear color change.While a red shift of 70 nm and 85 nm were seen respectively when exposed the CHNs coatings to HCl and HAc vapors.The stronger swelling of HCl and HAc vapors to CNCs coating and CHNs coating makes the sensing results better than ammonia vapor and distilled water vapor.In addition,compared to recovery at room temperature,the CNCs coating exposed to NH3 H2O,H2O and HAc vapors could easily restore to the original state when recover under heating.While the coatings exposed in HCl vapor cannot recover to the initial state,and can only recover to 60%.Compared with CNCs coatings,the CHN coating had high recovery rate,while only recover 46%and 67%in HAc and HCl vapors respectively.The coatings made of polysaccharide are friendly to the environment and the naked-eye detectability of acid and base vapors could be realized by the clear change in color of the CNCs and CHNs coatings,which is of great importance in the development of chemical and biological sensors.