Preparation Of Bio-based Nanofibrous Membranes And Its Applications In The Field Of Water Treatment

In the water treatment process,the common substances that need to be treated include the toxic and harmful substances,suspended matter,polluted oil and dyes,etc.The main advantage of the traditional water treatment method is that the treatment speed is fast,but meanwhile traditional method dependents on large machinery with low efficiency.In addition,it is easy to cause secondary pollution problems.Therefore,water treatment has been a major issue to be addressed.Electrospinning technology provides a very reliable prospect for this field.Nanofibrous membranes has a huge specific surface area so that it can become an excellent carrier for adsorption of metal ions.Additionally,the adsorption function of the membranes is reversible and renewable,which will be very conducive to environmental protection and the cost savings.Therefore,the electrospinning nanofibrous membranes is a promising material for water treatment and water filtration.In this paper,the application of electrospinning nanofibrous membrane in the field of water treatment is studied from the following three parts:the first part is the preparation of high strength polyimide nanofibrous membrane and the study of Oil-water separation performance.The polyamide acid（PAA）was synthesized by low temperature polymerization,and then electrospun into a fiber film by electrospinning technology.After program heating during the nitrogen atmosphere,the PAA nanofibrous membranes were transferred to polyimide（PI）,then the fiber membrane was coated and modified by using the polydopamine solution and PTFE dispersion solution respectively and the superhydrophobic PDA/PTFE-PI membrane was obtained for the oil-water separation.The second part is the preparation of a green super hydrophilic nanofibrous film.The raw polymers used for electrospinning are two biodegradable polymers-polyvinyl alcohol（PVA）and glucomannan（KGM）.Then the electrospun PVA/KGM membrane was modified by cellulose nanocrystalline（NCC）to enhance the hydrophilic properties.The obtained NCC-PVA/KGM membranes were used in the field of separation of oil and water mixtures.The third part of this paper is based on the second part.We studied the adsorption properties of the obtained NCC-PVA/KGM membranes for heavy metal ions in water,including the copper ions,lead ions,mercury ions and cadmium ions.The specific works carried out in the paper are as follows:1.After program heating in the nitrogen atmosphere,we prepared the low-cost PI membranes with high strength successfully.Then we modified the PI membranes with the polydopamine solution and PTFE dispersion solution respectively and got the PDA/PTFE-PI membranes finally.The PDA/PTFE-PI membranes can separate the oil-water mixtures efficiently（higher than 99%）with a high flux(6000±200 L·m^-2·h^-1).Additionally,the manufactured PDA/PTFE-PI membranes are fairly stable in extremely harsh environments（ultra-high temperatures,strong acids and strong alkalinity）and still have good separation efficiency and flux after 10 cycles.2.The nanofibrous membranes were prepared by electrospinning the mixed aqueous solution of glucomannan and polyvinyl alcohol polymers.In order to increase the water resistance and stability of the KGM/PVA,the membranes were heated in a vacuum oven for crosslinking.Then we selected the cellulose nanocrystalline（NCC）dispersion solution to modify the fiber film for enhanced wettability of the KGM/PVA membranes.The characterization methods including the SEM,TEM,Fourier infrared transformation,TGA analysis are carried to character the physical properties of the membranes.Through the oil-water separation experiment,the flux was calculated to the 2000L·m^-2·h^-11 and the efficiency was all above 98%.So the NCC-KGM/PVA membranes can be used for the commercial separation materials.3.The adsorption experiments of CNC-KGM/PVA nanofibrous membranes on the four kinds of heavy metal ions including Hg²⁺,Cu²⁺,Pb²⁺,Cd²⁺were studied in this part and the influence of time and pH value on the adsorption capacity of membranes were investigated.The conclusion is as follows:Electrostatic spinning NCC-KGM/PVA nanofibrous membranes have certain adsorption ability to these four kinds of ions,among which,the adsorption capacity of Cu²⁺ions is the greatest,the adsorption capacity of other three kinds of ions is relatively low.And with the increase of pH value,the adsorption amount of Cu²⁺will also increase and the adsorption amount was the highest when pH=5.3 while there was no obvious law on the adsorption amount of other three ions with the change of pH.The maximum adsorption amount of Pb²⁺was about 4.5 in pH and the adsorption amount to Hg²⁺was the smallest when pH=3.2 while the adsorption amount of Cd²⁺increased with the increase of pH and the adsorption amount was the largest when pH=5.2.In summary,a series of high-throughput electrospinning nanofibrous membranes for oil-water separation were fabricated in this paper.These membranes not only showed good performance in the field of oil and water separation,but also had broad applications,including the adsorption of heavy metal ions in sewage.On this basis,we can develop a series of multi-functional membrane-based separation materials for the use of oil-water separation,sewage treatment and so on with a good prospect.