Tailored preparation of porous aromatic frameworks in a confined environment

The growth of porous aromatic frameworks (PAFs) on the surface of polymer brushes is reported for the first time. In contrast to PAFs formed in solution, polymer brushes provide a confined environment for PAF growth, resulting in nanosized and homogeneous spherical PAFs formed amongst the polymer brushes. 4-Bromobenzene functionalities from the polymer brushes are utilized to induce PAF growth by a Yamamoto-type Ullman coupling reaction. The size of PAFs can be tailored from 30 nm to 500 nm by subtly changing the structural parameters: e.g. reaction time, grafting density, and concentration of 4-bromobenzene on the surface. The established strategy is not only applicable to the preparation of PAF-1, but can also be extended to the controlled preparation of PAF-5. In addition, free-standing and flexible PS/PAF-1 hybrid membranes are obtained via dissolving the oxidized layer between the polymer layer and the silicon substrate, which can be transferred to any flat substrate. The obtained PS/PAF-1 membrane is proven to show high efficiency in removing dye from water and is promising for eliminating other foulants, such as microorganisms and trace organics.