Hydrophilic metal-chelated membrane for biocatalytic membrane reactor application

Membrane filtration via polymer membranes is widely used to remove pollutants in various industrial applications. For instance, it has been used to remove phenolic chemicals such as Bisphenol-A (BPA) from wastewater generated by the pharmaceutical and plastic industries. BPA can be degraded to its non-phenolic compound with an enzyme. To ensure the stability of an enzyme, a polymer membrane has to be slightly hydrophilic. However, a polymer membrane was found to be dominant to its hydrophobic nature, exhibiting high trans-membrane pressure, and fouling tends to occur. Hence, modification of a membrane surface is necessary to avoid these shortcomings. Therefore, a metal-chelated membrane is proposed in this research, which later will act as a support to immobilize laccase for biocatalytic removal of BPA. The hydrophobicity of the PVDF membrane was altered by dopamine (DA) and polyethyleneimine (PEI). At the same time, iminodiacetic acid (IDA) was introduced as a metal chelator to bind different types of metals, i.e., Mn2+ and Ni2+, to improve the enzyme’s stability during immobilization. The modified membranes were characterized by permeate flux, contact angle measurement, Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) and Fourier-transform Infrared Spectroscopy (FTIR). The results proved that the PVDF membrane hydrophilicity has improved after several modifications. The contact angle decreased by 15% and 10%, and the permeate flux increased to 181.55 L/m2.h and 178.01 L/m2.h for Mn and Ni-chelated membranes, respectively. In addition, in different SEM-EDX images and peaks detected by FTIR, researchers found the successful coating of metals, where the EDX findings detected 0.4% of Mn attached to the Manganese chelated membrane and only 0.1% of Ni was found on the Nickel chelated membrane.