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Nanoporous Polystyrene Fibers Functionalized by Polyethyleneimine for Enhanced Formaldehyde Sensing

Author: ZhangChunYan
Tutor: PanNing；YuJianYong；DingBin
School: Donghua University
Course: Textile Material and Textiles Design
Keywords: Polyethylene imine (PEI) Polystyrene (PS) Surface modification Electrostatic spinning porous nanofibers Formaldehyde sensor Quartz crystal microbalance (QCM)
CLC: X830.2
Type: Master's thesis
Year: 2011
Downloads: 102
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Abstract

Formaldehyde is a volatile organic toxic substances, can cause great harm to the human body. Traditional formaldehyde gas detection methods, it is difficult to trace formaldehyde at room temperature to make real-time, accurate, low-cost detection. QCM sensor can detect a small mass (ng) the instrument of change. To detect trace amounts of formaldehyde by the QCM electrode surface functionalization has aroused extensive attention of scholars at home and abroad. But now such studies face a difficult problem: smooth-aware film unit area limit the amount of formaldehyde gas adsorption point. This project to design a new efficient QCM technology-based formaldehyde gas sensor, combined with electrospinning technology and surface modification of nanomaterials technology achieved a major breakthrough in this field, the preparation of a high sensitivity, good selectivity and can be repeated short reaction time of nano-porous fibers formaldehyde gas sensor, and the establishment of the theory of the relationship between the three-dimensional nano-porous fiber structure and sensor performance. This topic first step electrospinning prepared by nano-fiber membranes having a porous ultra-high-specific surface area of ??three-dimensional polystyrene (PS). The experiment used THF / DMF (mass ratio of 1:4) mixed volatile organic solvent as PS electrostatic spinning liquid solvent. The electrospinning process parameters as well as the nature of the PS spinning solution PS electrospinning process and, accordingly, determine the optimum spinning process parameters: PS spinning solution concentration of 7wt%, 10wt% and 13wt%, The high-voltage power supply voltage of 20kV, and the reception distance of 15cm, the syringe advancing speed of 4ml / h, and the laboratory temperature and humidity were 25 ℃ and 40% RH. Subsequently PS nanofiber membranes prepared three scanning electron microscopy (FE-SEM), and the use of fiber diameter the Acrobat Photoshop image analysis software and mathematical statistics method. The results showed that the three kinds of PS nanofibers have a porous structure and the surface of the perforated beaded structure; the greater the concentration of the spinning solution, and under the same conditions, the collected fiber membrane is thicker, the greater the fiber diameter. Also, the PS fiber membrane obtained a BET specific surface area of ??the test, and a nitrogen adsorption - desorption testing, and the test results are analyzed using ASAP2020 surface area analysis software. The results showed that with the increase of the concentration of the spinning solution, PS nanofiber specific surface area increases, and larger specific surface area than the smoothing film under the same conditions than a dozen times; noteworthy is the diameter of the fiber is gradually increased (not conducive to a specific surface area increases), which shows the pore distribution in the fiber is affected than the surface area of ??the dominant factor; also been found that the size of the fiber in the hole belonging to the mesoporous and macroporous range; And with the increasing concentration of the same hole width condition, the unit a pore volume in the quality of the fiber becomes large. These holes can be formed by phase separation theory to explain. Then, by the drop casting method of the polyethylene imine (PEI), the direct spinning to the the PS nanofiber membrane on the QCM electrode function modification. PEI in the hydroxyl group may be a reversible chemical reaction occurs with formaldehyde molecules, is an ideal material for formaldehyde gas detection. PEI almost can not by electrospinning directly pick the QCM electrode, so the experiment using the drop casting method. FE-SEM uses the same method on the drop casting PEI fiber membrane morphology characterization. Experimental discovery of PEI particles successfully attached to the three fibers in the sample, and the greater the concentration of the spinning solution, the more the number of particles of fiber adsorbed PEI; addition, the presence of PEI PS porous nanofiber film morphology. Finally, the prepared PEI-PS formaldehyde gas sensor placed the Stanford QCM200 test systems for detection. The experimental test PS spinning solution concentration of PEI amount of formaldehyde gas sensor performance drop casting. The results show that the same PS and PEI load case, the higher the concentration of the spinning solution, the better the sensor performance; of PEI drop casting the more the amount, the better the sensor performance, but experiments have found that the PEI drop casting exceeds 6000Hz easy caused by QCM electrodes overload and over 1000Hz PS load causes fiber membrane was non-rigid state. Selective tests show that the performance of the sensor is not subject to interference from other common organic volatile gases. In addition, this topic is also considering the results of all tests, the theoretical relationship between the three-dimensional PS porous nano fiber membrane morphology and the final system performance of the sensor, the experimental and theoretical basis for future similar sensor.

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