In situ Preparative Strategy for Novel Nano-enhanced Membrane with Improved Antifouling Performance

Promovendus/a: Xin Li

Promotor(en): Prof. dr. ir. Bart Van der Bruggen

Water is a critical resource in our daily lives. Its safety and availability are inextricably linked to public health, energy production and economic development. Although significant progress has been made in the field of water treatment in the 20th century, fresh water for the world's inhabitants seem to be moving in the wrong direction. As estimated by World Water Council, 3.9 billion people in the world will live in water-scarce regions by 2030. About 1.2 billion people lack access to safe drinking water. Membrane technology is a fast-growing industry, contributing substantially to advances in water treatment and response to water crisis. Although some degree of success has been witnessed for the development of traditional membrane technologies in water treatment, the membrane fouling are gradually pushing them to their limits.

Many attempts have been made to improve the antifouling performance of membranes by tailoring their characteristics. Among these, the incorporation of nanoparticles into membranes for water treatment has been the focus of numerous investigations with ever accelerating technical achievements and dramatic expansion of knowledge in this field. With this strategy, the obtained nano-enhanced membranes can lead to remarkable changes in membrane properties such as permeability, selectivity, mechanical resistance and hydrophilicity. However, the aggregation and leaching of nanoparticles restrain their further development, which compromise the comprehensive properties of obtained membranes.

In this thesis, an in situ preparative technique was developed to design novel nano-enhanced membrane for controlling the aggregation and leaching of nanoparticles. By integrating the formation of both nanoparticles and membrane into one composite system, the morphology and microstructure of membranes were tailored. Moreover, the antifouling performance of the obtained membranes was also improved. The detailed conclusions are as follows:

1) In situ chemical reduction and the in situ sol-gel process were designed to prepare novel nano-enhanced membrane. AgNO3, NiCl2, TBT and Zn(NO3)2 were selected as the precursors of Ag, Ni, TiO2, and ZnO nanoparticles, respectively. This technique provides leapfrogging opportunities to develop next-generation water supply systems.

2) The in situ preparative technique realizes a good dispersion of nanoparticles in the casting solution or in the membrane matrix, which effectively restrained the aggregation of nanoparticles. The size of in situ formed nanoparticles can be controlled around 10 nm.

3) The leaching of nanoparticles from the membrane matrix could be controlled with the in situ sol-gel process. For the design of self-assembled nano-enhanced membrane with TiO2 nanoparticles, the hydrogen bonds between -OH groups of TiO2 nanoparticles and the PEO segment of F127 enhanced the stability of sol-gel formed TiO2 nanoparticles during the filtration process.

4) The in situ addition of nanoparticles accelerated the demixing process of the casting solution, which increased the mean pore size and porosity, thus tailoring the morphology of the obtained membranes. The surface hydrophilicity and pure water flux of membrane were also improved. Meanwhile, the BSA rejection was maintained at an acceptable level (higher than 90%).

5) The in situ preparative technique effectively improved the antifouling performance (e.g., antibacterial activity, antibiofouling and organic antifouling performances) of composite membranes. By measuring the foulant-membrane and foulant-foulant intermolecule adhesion forces, AFM revealed the fouling behavior of composite membranes. Moreover, the filtration model confirmed that the standard blocking and cake filtration were the main factors to induce membrane fouling.