Synthesis And Application Properties Of Nitrogenous Groups Modified Cellulose Nanocrystals

Cellulose nanocrystals(CNC)are derived from acid hydrolysis of cellulosic materials,such as straw,waste paper,wood biomass.CNC are excellent candidates for the design and development of nanomaterials in many applications due to several attractive features,such as high surface area,hydroxyl groups for functionalization,stability.Based on CNC,the nitrogenous groups modified cellulose nanocrystals were designed and synthesized by chemical reaction,and their application properties in the adsorption of metal ion and pH-responsive Pickering emulsions were studied.In this paper,cellulose nanocrystals were prepared through acid hydrolysis of filter paper with inorganic acids(sulfuric acid and hydrochloric acid).Dialdehyde cellulose nanocrystals(DAC)were prepared by the oxidation of CNC with sodium periodate.Cysteamine-modified cellulose nanocrystals(Cys-CNC)and L-cysteine-modified cellulose nanocrystals(Lcys-CNC),were prepared by reductive amination of DAC with cysteamine and L-cysteine.PEI-CNC was prepared by introducing hydrophilic polyethyleneimine onto the surface of DAC via a reductive amine reaction.PEI-CNC was then hydrophobically modified to synthesize three types of amphiphilic amino groups modified cellulose nanocrystals,benzyl-polyethyleneimine modified cellulose nanocrystals(Ben-PEI-CNC),amyl-polyethyleneimine modified cellulose nanocrystals(Amyl-PEI-CNC),octyl-polyethyleneimine modified cellulose nanocrystals(Oct-PEI-CNC).The molecular structure of the modified cellulose nanocrystals were confirmed by FT-IR,solid NMR and XPS characterization.The N content and S content in Cys-CNC and Lcys-CNC,and the content of hydrophilic groups and hydrophobic groups on the the amphiphilic cellulose nanocrystals(Ben-PEI-CNC,Amyl-PEI-CNC,Oct-PEI-CNC)were calculated by elemental analysis results.Cys-CNC and Lcys-CNC can selectively adsorb mercury ions in the presence of other coexisting metal ions;Cys-CNC and Lycs-CNC can reach adsorption equilibrium within 10 min and 5 min,respectively;the maximum Hg(?)adsorption capacities of Cys-CNC and Lcys-CNC are 849 mg g-1 and 923 mg g-1,respectively.Therefore,Cys-CNC and Lcys-CNC can selectively,quickly and efficiently adsorb mercury ions from aqueous solutions.In addition,the effect of pH,contact time and mercury ions initial concentration were thoroughly investigated to optimize the adsorption process.The adsorption of Hg(?)followed Langmuir model and pseudo-second order model.Hg?)-loaded Cys-CNC and Lcys-CNC can be recycled after treatment with eluent(2 M HCl and 0.5 M thiourea).Amphiphilic amino groups modified cellulose nanocrystals(Ben-PEI-CNC,Amyl-PEI-CNC and Oct-PEI-CNC)can be used to prepare Pickering emulsions,and the stability of the emulsions was controlled by pH.The pH response of Pickering emulsion prepared by Ben-PEI-CNC is ideal,at pH 7,the emulsion is stable;at pH 3,the emulsion is broken.The pH of the system was adjusted to achieve reversible emulsification-demulsification,recovery of the oil phase,and recycling of emulsifiers.The effects of pH,Ben-PEI-CNC mass concentration and oil/water volume ratio on the emulsion were also investigated in detail.