Preparation And Mass Transport Performance Of Vertically Aligned Carbon Nanotube/Polymer Composite Membranes

The contradiction between the permeability and the selectivity has always been a challenge for the nanofiltration membranes.Nanofiltration membranes with high permeance and high selectivity is the key and the premise to satisfy the industry requirement.Due to the adsorption force and the friction were reduced,as the gas transport through the inner bores of carbon nanotubes is “constraints”,and the atomically smooth inner surface structure,carbon nanotube membranes were expected to get high permeability and high selectivity.This research designed a new VACNT/polymer composite membranes technology,with filling the gap of the VACNT,and successfully prepared nanocomposite membranes with the inner bores of VACNT as gas transport channels.For the gas transport performance tests,the gas permeability and the selectivity values in this work were high.The main research is summarized as bellow:?1?VACNT forests were synthesized by the water assisted chemical vapor deposition.This paper research the influence rule which the effect of gas flow rate,temperature,H2 ratio,and water content conditions on the height,crystal quality and the growth rate by SEM,HRTEM,Raman,etc.The results show that,with the increase of the temperature,the weight,growth rate,crystallization quality and thermal stability of the VACNT forests were increase slightly,but the catalyst life expectancy;With the increase of gas flow,the height and yield of the VACNT decreased,growth rate reduced,crystal quality and improving thermal stability;With the improvement of H2 ratio,the height and yield of the VACNT increase,crystal quality and the thermal stability was reduced.?2?The growth conditions of the VACNT forest: total flow rate 650 mL/min,temperature 815 ?,Ar/H2 ratio 6/4,C2H4 flow rate 100 mL/min,water flow rate 100 mL/min.The height of the VACNT forest is 5-1 000 ?m,diameter ?5-?10 nm,density 10×1011 cm-2,and the height of the forest is about 10?m,with ideal structure used in the preparation of nanofiltration membranes.?3?The gaps of the VACNT forest were in situ sealing filling parylene by low pressure chemical vapor deposition.Research the influence rule which the annealing temperature and holding time on the structure.The results show that with the increase of annealing temperature,filling state change obviously.At the low temperature,not filled completely;At high temperature,the structure of the VACNT were destroyed;When the annealing temperature is 375 ? and holding 1 h,the surface of the CNT/Parylene composite membrane uniform,and the array structure intact.?4?Ar/O₂ plasma treatment was used to etch extra parylene and expose the CNT tip,to get the composite nanofiltration membrane device.Research the influence rule which gas composition,pressure,power and time on the CNT open.The conditions of the plasma etching: Ar/O₂ flow rate 20/50 mL/min,pressure 100 Pa,power 100 W,etching time 90 min.The vertical alignments of CNTs were found to be well maintained after polymer infiltration.?5?CNT/parylene composite membrane was fixed in a home-made permeation testing device.Transport properties of various of gases including pure H2,He,N2,Ar,O₂ and CO₂ through the CNT/parylene membranes were investigated.Research the influence which gas composition,pressure and temperature on the permeability and selectivity.The results show that with the increase of gas molecular weight,the permeability follow Knudsen theoretical model;With the increase of temperature,the permeability increased before 50 ? and then reduced,with the peak at 2.48 mol·m-2·s-1·Pa-1.The enhancement factors were more than 50,indicating much higher transport rate than Knudsen diffusion.This is mainly due to the atomically smooth channels of the CNTs,and the gas transport in CNT as the form of specular reflection without resistance.The selectivity of H2/CO₂ is 5.45.?6?The VACNT forests were subsequently pushed over and stacked into dense membranes by mechanical rolling.For gas transport and liquid permeability research,the gaps of the CNT were as the filtering channel.Study the transport of H2,He,N2,O₂,Ar,water,ethanol,hexane and kerosene through the nanofiltration membranes.The results show that porosity of the membrane is 4.38%,and the enhancement factors were more than 30,the liquid penetration rate higher than the calculated value of 4 orders of magnitude.Successful filter nano silver solution and nano gold solution with particle size 15 nm and 10 nm respectively.