Development of high performance nanofibrous composite membranes by optimizing polydimethylsiloxane architectures for phenol transport

Phenol removal and recovery from wastewaters are highly demanded in industries due to its high toxicity and industrial importance. It can transport through the silicon-based rubber polydimethylsiloxane (PDMS) via the solution-diffusion mechanism. To improve the phenol removal efficiency in extractive processes, dense PDMS membranes with different macromolecular structures have been developed and evaluated in this work. The condensation-cured PDMS membranes (PA) with network architecture exhibited higher phenol partition coefficients (K) than the hydrosilylation-cured PDMS membranes with linear and branch architectures. This was attributed to the four-armed quaternary-siloxy linkages formed in the three-dimensional network structure, increasing the free volume for phenol passage and hydrogen bonding between phenol and PDMS matrix. The K of PA was further enhanced by optimizing the PDMS precursor chain length and cross-linker amount, and the corresponding membrane mechanical properties and phenol overall mass transfer coefficients (k0) were examined. The optimal PA formulation was utilized to fabricate a highly effective nanofibrous composite membrane via spray coating. The resultant composite membrane exhibited a k0 of 18.3 ± 1.3 × 10−7 m/s in an aqueous-aqueous extractive process, significantly outperforming the commercial counterpart with 45% increment. This is the first demonstration of the importance of PDMS macromolecular structures on phenol extraction. The newly-developed condensation-cured PDMS could contribute to the fabrication of highly effective composite membranes for various extractive processes.