Preparation And Sensing Application Of Chitin Nanocrystals

Chitin is the second most abundant natural polysaccharide after cellulose on earth and has largest number of nitrogen functional groups.Due to the fact that chitin is naturally abundant,non-toxic,biocompatible and biodegradble,it has attracted much attention in recent years.Chitin nanocrystals(CHNs)can be extracted and prepared generally through strong acid hydrolysis.It is known that the treatment of chitin by HCl acid or TEMPO oxidizing agent can introduce some Cl-,CIO-,Br ions to the system.However because these methods introduce such ions,large-scale application of their future large-scale application of CHN prepared by this method is limited since these ions has the tendency of causing environmental problems.In this paper,two green methods to prepare CHN suspensions are proposed.The first,enzymatic hydrolysis and secondly,the use of hydrogen peroxide(H2O2)to produce CHN from chitin nanofibrils(CNFs).The structure and properties of CHNs were characterized by FTIR.WXRD?SEM?TEM and POM.In addition,The chitin nanocrystals were used as a coating material to coat silicon substrates,using the relatively technology known as a spin coater or spin processor.The chitin films coated silicon substrates were used to detect the acidic and alkaline vapor gases.This chitin films will be used in the field of environmental monitoring.This innovation of this work was as follows:In this paper,two green methods to prepare CHN suspensions are proposed.The first,enzymatic hydrolysis and secondly,the use of H2O2 hydrolysis.CHN spin coated films were used in sensing for acid and alkaline vapor gases,the values is significantly after exposure to the acid and alkaline vapor gases.The primary content and conclusion of this work was as follows:CHNs were prepared by a green way of mechanical-assisted enzyme hydrolysis.Several nanowhisker fractions were successfully separated by centrifugation at three different centrifugal speed,respectively.The results showed that the particle size was decreased with an increase of enzyme concentration or hydrolysis time.Another green hydrolysis method was used to prepare CHNs,H2O2 hydrolysis CNFs.The size,morphology and crystalline form of nanocrystals were analyzed using FTIR and WXRD,the results showed that the CHNs still had their original molecular and crystalline structures,even after H2O2 hydrolysis.The POM revealed a fingerprint like pattern at 0.7 wt%concentration that indicates the existences of cholesteric phase.Also,SEM showed the self-assembly process of CHNs.The CHNs with uniform size and stable dispersion wree prepare thought HCl hydrolysis.Chitin nanocrystals spin coated films were used in sensing for acidic and alkaline vapor gases,the color of spin coated films changes significantly after exposure to the acidic and alkaline vapor gases,and a "red shift" phenomenon of the reflecting wavelength was observed.