Ultra-filtration is a membrane separation process driven by pressure with filtration precision between micro-filtration and nanofiltration. The membrane flux, anti-pollution performance and service life of the ultrafiltration membrane are closely related to the membrane material. In order to increase the performance of ultrafiltration membrane, organic-inorganic modification of membrane materials is a common method. The modified membrane has both excellent characteristics of organic and inorganic membrane, and its physicochemical stability, anti-pollution ability, the separation characteristics, permeability and the perfection degree of membrane pore structure are greatly improved. In recent years, the rapid development of inorganic nanomaterials has opened up a new direction for the development and design of membrane materials. Inorganic Nanomaterials, such as titanium dioxide (TiO_2), alumina (Al_2o_3), silicon dioxide (SiO_2) and carbon nanotubes (CNT), have stable properties and are easy to be prepared, it promoted the development of nano composite films. After inorganic nanomaterials are combined with membrane matrix, the larger surface area and pore channel increase the hydrophilicity of the membrane, and at the same time comprehensively and effectively improve the overall separation efficiency of the membrane.
The latest progress and application of inorganic nanomaterials in ultrafiltration membrane in recent years are reviewed, mainly including TiO_2, Al_2o_3, SiO_2, CNT, silver nanoparticles and other inorganic nanomaterials, and the effect of its application in ultrafiltration membrane is described in detail. The particle size of nano-TiO_2 is only 1% to 1‰ of that of ordinary TiO_2, I .e. 10~100nm. Nanometer TiO_2 has chemical stability, corrosion resistance, strong oxidation and reduction, strong self-cleaning ability, high selectivity and reaction activity at the same time, coupled with its insoluble, non-toxic and low cost properties, it has broad application prospects in the field of environmental protection. The application of TiO_2 in the ultrafiltration membrane can increase the hydrophilicity of the composite membrane. As the research finds, adding nano-TiO_2 can increase the hydrophilicity of PES ultrafiltration membrane.
TiO 2 can also improve the antifouling performance of the ultrafiltration membrane. For example, after the activated sludge operation and mechanical cleaning treatment in the sewage plant, the recovery rate of the membrane flux of the modified PES ultrafiltration membrane is 25 higher than that of the unmodified PES ultrafiltration membrane. 3%. Adding nano-TiO_2 can also improve the internal structure of the membrane, and nano-TiO_2 can make the surface of TiO_2 /PVDF composite membrane have smaller average aperture and more internal pores of the membrane, therefore, the structure and performance of the membrane can be improved, and the anti-pollution performance of the membrane can be improved. Adding TiO_2 nanoparticles into PVDF casting solution, it is found that the microporous structure, mechanical properties, thermal stability, hydrophilicity, permeability and pollution resistance of the composite membrane are all improved.
In addition, the PVDF/TiO_2 composite membrane prepared by nano-TiO_2 particles with different contents (0 - 4%) has a faster removal rate than that of pure membrane, and the sterilization effect is the best when the content of nano-TiO_2 is 4%. Under the condition of UV illumination, compared with pure PVDF membrane, the photocatalytic properties of PVDF/TiO_2 composite membrane are obviously enhanced, the composite membrane with the content of 2-4% nano-TiO 2 has good anti-pollution and self-cleaning performance, and after the membrane is polluted, the trans-membrane pressure and water flux of the composite membrane can be recovered quickly through UV treatment. Nano-Al_2o_3 acts on ultrafiltration membrane, which has the characteristics of high mechanical strength, good chemical stability, strong antimicrobial ability, long service life and so on. At present, it is widely used in sewage treatment, seawater desalination, drinking water purification, drug concentration separation and other fields. It is found that the flux recovery rate of inorganic nano composite ultrafiltration membrane is 6.8% higher than that of pure membrane by applying the mixed stuffing of Al_3 /TiO_2 to polyvinylidene fluoride (PVDF) ultrafiltration membrane and treating with emulsified oil wastewater.
The nano-composite ultrafiltration membrane is made of Polyether sulfone (PES) membrane with 1% al_2o_3, and the differential pressure is 0. Under 5Mpa, the membrane porosity of pure PES membrane and nano composite ultrafiltration membrane are 68 and 66 respectively. 6%, after whey protein feed treatment, its initial flux is 1. 2 and 1. 99L/m2h, pure water flux is 3. 9 and 4. 63L/m2h, Flux recovery rates were 58 respectively. 2 and 96. 1%. When the addition amount of Al_2o_3 is 0. 4% after adding pure PES membrane, the membrane porosity of pure PES membrane and nanocomposite ultrafiltration membrane are 52 and 62% respectively. After the treatment with serum protein, it was found that the pure water membrane flux was 181 and 209L/m2h respectively. The size effect and macroscopic quantum tunneling effect of nano-SiO_2 (particle size ≤100nm) make it produce siltation effect, which can go deep into the unsaturated bond of polymer chain, it acts with the electron cloud of unsaturated bond to improve the thermal stability, optical stability and chemical stability of polymer materials, so as to improve the anti-aging performance and chemical resistance of products.
Using Ce /SiO_2 as stuffing and adding the ultrafiltration membrane made by PES, the differential pressure across the membrane is 0. Under 05Mpa, the membrane porosity of pure PES membrane and nano composite ultrafiltration membrane are 78 respectively. 6 and 41.7%, after treatment with emulsified oil wastewater, the retention rate is 98 respectively. 3% and 98. 9%. The ultrafiltration membrane made of cellulose diacetate (CA) was added with SiO_2 as the filler, and the addition amount was 4%. After being treated with serum protein, it was found that the initial flux was 5 respectively. 2 and 19. 8L/m2h, pure water flux is 15. 6 and 46. 7L/m2h, retention rate is 94 and 81%, Flux recovery rate is 61 and 75%, respectively. Using SiO_2 as filler and adding polysulfone (PS) membrane to make the ultrafiltration membrane, the addition amount is 3%, and the porosity of pure PS membrane and nano composite ultrafiltration membrane is 36 respectively. 2 and 79. 17%, after being treated with emulsified oil wastewater, it is found that the initial flux is 1. 08 and 19. 32L/m2h, Flux recovery rates were 10 respectively. 3 and 34. 01%. CNT is composed of hexagonal grid structure, which has good mechanical strength, thermal conductivity, electrical conductivity and chemical stability. It can be easily chemically modified to improve their dispersibility and enhance their adsorbability.
CNT was first used by Choi et al as nanometre stuffing for ultrafiltration membrane, and mixed 1.5% CNT and Polysulfone in carboxylate. It was found that this synthetic nanometre composite material could increase the pure water flux. Dr. Wu Huiqing of Fudan University in our country loads carboxated multi-walled carbon nanotubes (MWNTs) into the matrix of brominated Polyphenylene ether (bcvd) to make hybrid ultrafiltration membrane, it is found that the pure water flux of the membrane increases sharply with the increase of MWTNs content. When the membrane does not contain MWTNs, the flux of the membrane is only 197L/m2h, while when the content of MWTNs in the membrane is 5wt%, its flux reaches the maximum 487L/m2h, if the MWTNs content is increased, the membrane flux will decrease, but it is still higher than that of pure polymer membrane without MWTNs.
The water flux of the pure PES membrane and the nano-composite ultrafiltration membrane are 124 and 184L/m2h respectively, which are made of the ultrafiltration membrane made of PES membrane as The Matrix and 1% CNT addition, the pass recovery rates were 27 and 46%, respectively. However, the method of constructing carbon nanotube polymer complex membrane with directional arrangement structure is very complicated and involves expensive chemical reagents, which is not suitable for actual industrial production and use. Therefore, seeking a simple and effective construction approach is the future development direction of carbon nanotube modified ultrafiltration membrane. Since the size of nano-silver belongs to the category of nano-scale, it has three main features of nano-materials at the same time: quantum effect, small size effect and huge specific surface area, so the antibacterial effect is better than that of conventional antibacterial agents, and the sterilization effect is more lasting, a very small amount of nano silver particles can kill a large number of bacteria.
The antibacterial mechanism of nano-silver particles is that nano-silver can adsorb with microorganisms and bacteria, which can damage the bacteria to accelerate the oxidation of reactive oxygen free radicals and induce deoxyenzyme inactivation, and promote the leakage of thallus contents, and interrupt cell signal transduction to kill bacteria. The results of the membrane's ultrafiltration performance show that the water flux of the polysulfone plate membrane and hollow fiber membrane modified by nano silver particles and the interception rate of bovine serum protein solution are both higher than those of the unmodified Polyether irony membrane. The results of Flux recovery rate show that the anti-bovine serum protein contamination ability of PS membrane modified by nano silver particles is stronger than that of PES membrane not modified. In addition, the PES membrane modified by nano silver particles has obvious inhibitory effect on the reproduction of Escherichia coli and can improve the anti-biological pollution ability of the membrane.
The nanocomposite ultrafiltration membrane made of 4% silver nanoparticles added to PS membrane has a differential pressure of 0. Under 3Mpa, the contact angles of pure PS membrane and nano composite ultrafiltration membrane are 81 respectively. 2 and 60. 9%, the initial flux is 42 and 147L/m2h respectively, the pure water flux is 48 and 168L/m2h respectively, and the retention rate is 64 and 97% respectively. Add 0. The nano-composite ultrafiltration membrane made of 5% silver nanoparticles has a differential pressure of 0. Under the condition of 3Mpa, the contact angles of pure PS membrane and nano-composite ultrafiltration membrane are 70 and 60% respectively. After treatment with BSA feed, the initial flux is 94 respectively. 2 and 43. 2L/m2h. Other inorganic nanomaterials that can be used for ultrafiltration membranes include zirconia (ccl), graphene oxide (GO), Meg (MMT), zeolite (zcolite), etc. Based on the tubular ceramic microfiltration membrane, the composite ultrafiltration membrane made by the ZrO membrane can improve the retention rate of the membrane, the Nano-GO can improve the hydrophilicity of the PVDF membrane, and the nano-Meg can improve the mechanical properties of the PVC membrane, modified zeolite pre-coating can improve the flux of ultrafiltration membrane.
