Preparation And Characterization Of Chitosan- Oligosaccharide Derived In-situ N-doped Mesoporous Carbon

N-doped mesoporous carbon materials have broad applications in the fields of biomacromolecular separation and biocatalysis,adsorption separation,drug carriers,and electrode materials,due to it's high surface areas,large pore volume,high mechanical stability and chemical inertness.At present,N-doped mesoporous carbon materials is prepared mainly by soft-template method.Moreover,most of carbon sources are the phenolic resins synthesized by phenol and formaldehyde,which has toxicity and limit their application in drug carriers.In addition,N-doped nitrogen-containing carbon source need to prepare in advance to improve it's poor wettability and electrochemical properties,which is very cumbersome and highly cost.Therefore,in order to obtain non-toxicity in-situ nitrogen-doped mesoporous carbon materials with narrow pore size distribution,it is nessecarry to find a suitable new carbon and nitrogen source.Moreover,when molecular weight of the carbon precursor is small enough in soft template method,the carbon source can self-assemble around the soft template micelle.Chitosan oligosaccharide is a low molecular weight alkaline polysaccharide is degraded by chitosan.It is a good carbon and nitrogen source,it has abundant reserves,low price,good biocompatibility and rich carbon and nitrogen resource..The C3 and C6 positions on the chitooligosaccharide contain hydroxyl group,which can be self-assembled by hydrogen bonding with an ether bond on the block copolymer.The amine group of C2can be cross-linked with a Schiff base reaction of a difunctional aldehyde such as glyoxal to form a stable rigid structure,thereby it is possible for preparation by soft template method.In addition,compared with chitosan,chitosan oligosaccharides have better water solubility,but are not soluble in organic solvents such as ethanol,and are more suitable for aqueous phase synthesis.The preparation of mesoporous carbon by soft template method using chitosan oligosaccharide as carbon source has not been reported.Therefore,a low molecular weight chitosan-oligosaccharide was selected as a new carbon and nitrogen source.A series of in-situ nitrogen-doped mesoporous carbon materials with high void ratio and narrow pore size distribution were prepared by hydrothermal synthesis.the effect of reaction conditions on the pore volume and pore size of carbon materials were investigated.The specific research contents are as follows:?1?Preparation of Chitosan-oligosaccharide N-doped Mesoporous Carbon:Chitosan-oligosaccharide derived N-doped mesoporous carbon materials with high void ratio and worm-like pore structure were prepared by hydrothermal synthesis using chitosan-oligosaccharide as a new carbon-nitrogen source and F127 as a soft template.The effects of calcination temperature,mass ratio of F127/chitosan-oligosaccharide,reaction temperature and reaction stirring time on the pore volume of carbon materials were studied.The results show that mesoporous carbon materials with high void ratio can also be obtained by hydrothermal treatment of chitosan-oligosaccharides alone.The specific surface area,pore volume and average pore diameter were 482.350m²·g^-1,0.526 cm³·g^-1and 16.015 nm respectively.The soft-template F127 can effectively increase the porosity of mesoporous carbon.When the calcination temperature is 700?,the mass ratio of F127/chitosan-oligosaccharide is0.5,the reaction temperature is 50?and the reaction stirring time is 4 h,the mesoporous carbon pore volume is the largest.The specific surface area,pore volume and average pore diameter were 470.629m²·g^-1,0.972 cm³·g^-11 and 16.015 nm,respectively.The surface nitrogen content of mesoporous carbon measured by XPS can reach 6.88 wt%,and the doping form is mainly pyridinium nitrogen and quaternary ammonium nitrogen.?2?Preparation of Chitosan-oligosaccharide N-doped mesoporous carbon with narrow pore size distribution using glyoxal as crosslinking agent:Nitrogen-doped mesoporous carbon materials with narrow pore size distribution were successfully prepared by low-concentration hydrothermal synthesis using chitosan oligosaccharide as new carbon-nitrogen source,F127 as soft-template and glyoxal as cross-linking agent.The effects of the mass ratio of F127/chitosan-oligosaccharide,the adding order and the amount of glyoxal on the pore size distribution were studied.The results showed that when the mass ratio of F127/chitosan-oligosaccharide was 0.333,the adding order was that chitosan-oligosaccharide solution added dropwise to the F127solution and the amount of glyoxal added was 2 ml,the material with narrowest pore size distribution could be get.The average pore diameter,pore volume and specific surface area of the carbon material were 7.620nm,0.498 cm³·g^-1 and 472.517 m²·g^-1,respectively.The pore diameter were concentrated mainly at 5-10 nm.The surface nitrogen content of the carbon material measured by XPS reached at 4.84 wt%,and its morphology is mainly pyrrole nitrogen,imine nitrogen,pyridinium nitrogen and quaternary ammonium nitrogen.?3?Preparation of glyoxal crosslinked chitosan oligosaccharide N-doped mesoporous carbon with adjustable pore size:By adjusting the reaction temperature,reaction time,hydrothermal temperature and hydrothermal time during the preparation of glyoxal cross-linked chitosan-oligosaccharide derived N-doped mesoporous carbon materials,a series of N-doped mesoporous carbon materials with pore diameter adjustable were obtained,which pore diameter in the range of 3.794 to10.681 nm.