Click the "blue word" button above to subscribe to the latest paper "superhydrophobic electron PVDF memories with silanization and fluorosilation co functional CNTs for improved direct contact" by Professor Li Ying, Department of mechanical engineering, Texas A & M University, published online in the Journal of engineered Science in January 2020 In this paper, the preparation of superhydrophobic electrospun PVDF membrane by siliconization and fluorosilication co functionalization CNT and its application in direct contact membrane distillation are described in detail. (DOI: 10.30919/es8d905)。
The shortage of clean water is one of the global problems affecting millions of people around the world, and it is becoming more and more serious due to population growth, industrial development and climate change. In order to solve this problem, many advanced technologies have been developed, such as reverse osmosis (RO) and nanofiltration. Direct contact membrane distillation (DCMD) is a heat driven technology, which uses the temperature difference to generate steam pressure through the hydrophobic membrane between the hot feed side and the cold distillation side. Therefore, the water vapor is transported from the hot side through the membrane and condensed through the cold side, while the salt and pollutant remain in the hot side, as shown in Figure 1. Since the working temperature of the feed side may be in the range of 30? C to 90? C, which is lower than the boiling point of water, the technology can use industrial waste heat, solar energy and some renewable energy to heat the feed side, so as to achieve energy saving and economic friendly effect.
Figure 1 Schematic diagram of DCMD setting
Direct contact membrane distillation (DCMD) is a promising method for water purification. It is very important to manufacture membrane with high porosity, uniform pore size distribution and high surface hydrophobicity to improve the efficiency of this method. In this study, CNTs with two functionalized surfaces, silanization and fluorosilicylation, were mixed with polyvinylidene fluoride (PVDF) to prepare electrospun composite nanofiber membranes for DCMD.
Fig. 2 salt removal efficiency of membrane
In this paper, the effects of functionalization on the dispersion, pore size, porosity, hydrophobicity and DCMD properties of CNTs were studied. The results show that the hydrophobicity of the film is improved by CNTs, and the surface functionalization of CNTs further improves this property. It is found that in the tested membrane, the membrane with cofunctionalized CNT achieves the highest distillate flux (? 45 lm-2 h-1) and desalination rate (? 99.99%), as shown in Figure 2.
Figure 3 contact angle of water drop on different films
The flux of CNT was 14% and 46% higher than that of CNT and CNT. The characterization shows that the excellent properties are attributed to the improvement of CNT dispersion by CO functionalization, high porosity (? 85.5%), large average pore diameter (? 0.89? M) and superhydrophobic surface (contact angle? 153?), as shown in Figure 3. This work shows that the functionalization of CNT is a potential way to improve the performance of PVDF membrane in DCMD applications.
Fig. 4 possible mechanism of improving DCMD performance by functionalized CNT in electrospun PVDF film
Fig. 4 shows the possible mechanism of improving DCMD performance by functionalized CNT in electrospun PVDF film. First of all, it is reported that CNT has a very high ability of rapid adsorption and desorption, providing a way for water vapor diffusion, so that it can benefit from the membrane. Vapor transport. Secondly, the surface energy and van der Waals force between CNTs can be reduced by surface fluorosilication, which will help to improve the dispersion of CNTs in polymer matrix and make full use of functionalized CNTs. Thirdly, fluorosilanized functionalized carbon nanotubes have high hydrophobicity, which can increase the surface roughness of nanofibers by forming protrusions on the surface of nanofibers. Fourth, two surface groups with different chain lengths are introduced into the CNT surface by combining surface silanization and fluorosilicylation, as shown in Fig. 4. The surface roughness of CNT and nanofibers was further increased to improve hydrophobicity. As a result, these functionalized CNTs improve the hydrophobicity and moisture resistance of the membrane, thus helping the superhydrophobic pore wall repel the water vapor molecules, thus reducing the friction between the pore wall and the water vapor molecules, thus promoting the water vapor transportation.
Professor Li Ying, Department of mechanical engineering, Texas A & M University, is the corresponding author of this paper. Gao Chongjie and Deng Wei are the co first authors of this paper. This paper is supported by the Texas A & M Energy Institute and the center for material characterization, Texas A & M University.
Paper link:
http://www.espublisher.com/journals/articledetails/208/
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