Preparation Mechanism Of Coaxial Electrospun Poly (Aspartic Acid) Nanofibers And Its Application In Ions Detection

Poly?aspartic acid??PASP?is a kind of poly?amino acids?and falls under the category of polypeptides.Owning to its low cost,excellent degradability,strong complexation ability and good water solubility,PASP has potential applications in various fields including water treatment,cleaning products,sanitary,agriculture and biomedical engineering.However,PASP is generally used in solution system due to its water solubility,which limits its application.Electrospinning is a simple and effective technology to prepare nanofibers,and most polymers are able to be fabricated into nanofibers by electrospinning.The electrospun nanofibrous membranes not only possess the advantages of high specific surface and controllable nanofibrous structure,but also can be functionalized by the regulation of chemical composition or structure.Manufacturing the PASP into nanofibrous structure membrane can extend its application fields.In this thesis,a novel,biodegradable colorimetric chemosensor for Cu²⁺ ions detection in aqueous water was designed using PASP nanofibers,based on the strong complexation ability of PASP and the high porosity of nanofibrous membrane.To prepare PASP nanofibers,the polysuccimide?PSI?,as the intermediate of PASP,was electrospun into nanofibers firstly.Then PASP nanofibers were obtained by the crosslinking and hydrolysis treatment of PSI nanofibers.The coaxial electrospinning approach was employed to enhance the mechanical properties of PASP nanofibers.PASP nanofibers with different structure were prepared into colorimetric sensor for Cu²⁺ detection.This low-cost,biodegradable and reversible sensor had a good application prospect for metal ions detection in real water samples and provided a new insight into the design of colorimetric sensor based on nanofibers.The main contents of this thesis are summarized as follows:In Chapter 2,the PASP nanofibers were successfully manufactured by crosslinking and hydrolysis of electrospun PSI nanofibers.Firstly,we demonstrated the synthesis of PSI with high molecular weight for electrospinning,and the influence of electrospinning parameters on PSI nanofibers morphology was investigated.PSI with excellent electrospinnability was prepared by heat polymerization of L-apartic acid with phosphoric acid as catalyst.Single factor experiment of PSI electrospinning parameters showed that the PSI nanofibers diameter increased as the solution concentration and applied voltage increasing.With working distance increasing,the PSI nanofibers diameter decreased firstly and then increased.On the basis of single factor experiments,response surface methodology was utilized to analyze the quantitative relationship between PSI electrospinning parameters and the PSI nanofibers diameter.It indicated that the influence of the working distance on PSI nanofibers diameter was mainly depended on the solution concentration and applied voltage to some extent.And the working distance parameter was not orthogonal to other two parameters.In addition,the quadratic regression equation based on response surface methodology was able to predict the diameter of PSI nanofibers effectively.Then the novel PASP nanofibers were obtained by crosslinking and hydrolysis of electrospun PSI nanofibers.In Chapter 3,the properties of PASP nanofibers were investigated and thermoplastic polyurethane/PSI?PU/PSI?core-sheath nanofibers were fabricated.When PASP nanofibers were crosslinked in the aqueous solution,the crosslinking agent concentration had a significant influence on swelling ratio and the structural integrity of PASP nanofibers.The largest swelling ratio of PASP nanofibers achieved to 260.8 g/g and the optimal crosslinking concentration was ranging from 0.10-0.20 mol/L.This novel PASP nanofibers exhibited significant hydrogel characteristics with fast swelling,high water absorption,pH-sensitivity.Moreover,it also had excellent degradability.The nanofibrous structure endowed PASP nanofibrous membranes morphological robustness and stability.However,the PASP nanofibers had poor mechanical properties after swelling,which limited its practical application.PU with good mechanical properties was employed to reinforce PASP nanofibers,and the PU/PSI nanofibers were fabricated utilizing coaxial electrospinning.The PU/PASP nanofibers were obtained by crosslinking and hydrolysis of the PSI component in PU/PSI nanofibers.And the PU/PASP nanofibers exhibited good mechanical properties.In Chapter 4,force analysis of electrospinning jet was investigated to regulate core-sheath structure of PU/ PSI nanofibers.For the single needle electrospinning process,according to the mass conservation,charge conservation and momentum equation,we derived that the flow-rate Q,jet diameter r and the axial distance z from nozzle were scaled with:R-Q^1/2·s^-1/2.Then the compound jet in coaxial electrospinning process was discussed.When core flow rate Q_i matched the sheath flow rate Q_e,the PU and PSI solution in compound jet had the same speed and the core-to-sheath jet diameter ratio was scaled with: r/R-?Q_i/?Q_i+Q_e??^1/2.If the core flow rate and sheath flow rate did not match,the speed of PU and PSI solution in compound jet varied and the core-to-sheath jet diameter ratio changed irregularly.Then the influence of coaxial electrospinning parameters on PU/PSI nanofibers morphology was studied.And the PU/PASP nanofibers with smooth surface were prepared based on the mechanism analysis of coaxial electrospinning.In Chapter 5,novel colorimetric chemosensors for Cu²⁺ ions naked-eye detection in pure aqueous water were designed using PASP nanofibers,based on the strong complexation ability of PASP and the high adsorption capacity of nanofibers.The PASP nanofibers sensor exhibited highly sensitive and selective properties toward Cu²⁺ ions over other competing anions with a detection limit of 0.5 mg/L.After Cu²⁺ sorption and preconcentration by PASP nanofibers in pure aqueous water,the copper-PASP complexes showed a color change from white to purple under alkaline conditions.When the PASP nanofibers were employed as filter membrane for Cu²⁺ naked-eye detection,the color change was able to be observed without any further treatment.And the PASP nanofibers can also be used as a colorimetric sensor for Fe³⁺ detection with naked-eye detection limit of 0.03 mg/L.When PU/PASP nanofibers with good mechanical properties and stable dimension were employed as colorimetric sensor,the color change can still be observed with Cu²⁺ concentration of 1 mg/L.Moreover,the reinforced PASP nanofibers based colorimetric sensor can be reused after the metal ions were removed from PASP nanofibers by acid treatment.