Chemical and morphology characteristics of mimic enzyme Zinc-cyclen integrated with polyvinyl alcohol (PVA) - polyethersulfone (PES) membrane

Carbon dioxide (CO2) released from fossil fuel industries into the atmosphere had contributed to the global warming effect and climate change. The development of CO2 separation process through membrane technology had been introduced to capture CO2 from the flue gas. Integration between membrane technology with the biological approach using carbonic anhydrase (CA) enzyme has been explored to enhance carbon capture technology. However, because of the pH and temperature changes, the CA activity had been permanently disturbed. Thus, in this present study, amimic enzyme (Zn-cyclen) was introduced to resemble the active site of CA enzymes and mimic the bio-catalytic process of CA. Mimic enzyme (Zn-cyclen) was synthesized using the precipitation method of Zinc perchlorate salt solution. The white precipitate of Zn-cyclen was analyzed and characterized for functional group, morphology, and crystallinity behaviour. Then, the developed Zn-cyclen was mixed with the polyvinyl alcohol (PVA) solution and cast onto polyethersulfone (PES) membrane using the dip-coating method to form a complex PES + PVA + Zn-cyclen membrane. The effect of mimic enzyme (Zn-cyclen) loading in the PVA solution were evaluated for swelling and hydrophilic characteristic. The finding shows that Zn-cycle possesses a crystalline structure that is significant in catalytic reaction and the functioning group analysis indicated that the presence of N-H and O-H groups at 1630 cm−1 and 3274 cm−1, respectively, which reflect the protein molecular structure of CA. Integration of Zn-cyclen onto PVA membrane shows that Zn-cyclen has improved the swelling ability of the membrane and increased the hydrophilicity of the complex membrane. Thin film PVA with 3 mg of Zn-cyclen gave the lowest contact angle at 36.4° which possesses the highest hydrophilic. Furthermore, higher swelling ability was observed at Zn-cyclen loading less than 6 mg. The presence of Zn-cycle in the complex PES + PVA membrane was validated with the appearance of the peaks associated with the N – H group at 1629 cm−1. The surface of the complex membrane was rough and the presence of Zn-cyclen cluster or aggregate was observed on the surface of the membrane. The finding indicated addition of Zn-cyclen particle into the PES + PVA membrane formulation has improved the swelling and hydrophilic characteristic of the PES + PVA membrane which is significant in the CO2 hydration application.