Diagnosis Of Remote Nitrogen Plasma And Modification Of PAN Ultrafiltration Membrane

Different modification effects were produced by different modification conditions,and the composition of active particles in nitrogen plasma is complex.In order to obtain better modification effect,the remote nitrogen plasma under different conditions has been diagnosed in this study.The free radical parameters in nitrogen plasma were diagnosed by emission spectrometry and the electron temperature and ion density in remote nitrogen plasma field under different conditions were measured by double suspension Langmuir probe.Finally,according to the diagnosis results,the polyacrylonitrile(PAN)ultrafiltration membrane was modified to obtain the change of the contact angle of the membrane under different conditions,and the optimum modification conditions of the polyacrylonitrile(PAN)ultrafiltration membrane were determined.The water flux and BSA flux of the membrane were measured under this condition.The flux attenuation rate,fouling rate and interception rate were calculated.The results showed that:(1)There were a lot of electrons,ions and free radicals in the remote nitrogen plasma,in which the wavelength range of the free radical spectra was mainly concentrated between300nm~500nm,and the NIII in the second positive band system of nitrogen was dominant(for example,NIII310.9,NIII337.4,NIII379.2),the wavelength of the maximum characteristic peak was 337 nm.There were also a few NI(such as NI670.3,NI870.3)and NⅡ(such as NⅡ359.5,NⅡ655.4,NⅡ889.3)between 500nm~1100nm.(2)The free radicals in the plasma were beneficial to the modification of the membrane surface,and the content of free radicals can be regulated by changing the discharge conditions.In the experiment,the intensity of free radical increased with the increase of discharge power and pressure,and the free radical content of 10Pa~15Pa was relatively high,and then decreased with the increase of remote distance,the intensity of free radical began to decrease at 35 cm time,and all the spectrum lines at 50 cm were no longer detected.In addition,the light intensity was also affected by the distance from the discharge center to the inlet.In this experiment,the intensity of light from the discharge center to the inlet 20 cm to the 50 cm was large and stable.(3)When the electron energy was high and the density was high,the surface of the material wold be etched and the structure of the material wold be destroyed.According to the diagnostic results of Langmuir probe,the electron temperature decreased with the increase of discharge power,increased with the increase of gas pressure,and increased at first and then decreased with the increase of remote distance.The electron density increased with the increase of discharge power,decreased with the increase of gas pressure and remote distance,and approached to zero at 30 cm.(4)On the basis of diagnosis,the PAN ultrafiltration membrane was modified by experiments.The optimum modification conditions were as follows: discharge power100 W,pressure 20 Pa,treatment time 95 s,remote distance 40 cm.The optimum conditions were as follows: discharge power 100 W,pressure 20 Pa,treatment time 95 s,distance 40 cm.The hydrophilicity of the modified membrane material was improved,and the contact angle was reduced from 57 °to 20 °of the original membrane.In the BSA filtration experiment,the flux decay rate of the modified PAN membrane decreased from 62% to48%,and the fouling rate decreased from 43% to 38%.The rejection rate increased from83% to 89%,and the anti-fouling performance of pan ultrafiltration membrane was improved.