Amphiphilic Nanocomposite Membranes for Oil in Water Separation and Fouling Resistance

Abstract

This dissertation presents a comprehensive study on developing nano-engineered composite membranes for oily wastewater treatment by synthesizing and incorporating 2D nanomaterials of MoS2 and MXene. In the first phase of this study, an amphiphilic MoS2/cellulose acetate membrane was designed, fabricated, and assessed for the separation of emulsified oil from water, aiming to address the persistent challenge of oily wastewater treatment. This membrane has a hydrophobic component of MoS2 nanoparticles embedded in the hydrophilic cellulose acetate (CA) polymer matrix. The hydrophobic (oleophilic) component of MoS2 nanoparticles captured the oil droplets, whereas the hydrophilic component of the CA polymer allowed water passage. This unique heterogeneous wettability enabled the membrane to have dual functionality: adsorption of oil droplets and enhanced fouling resistance with high water permeation due to the hydration layer formed by CA. Tested under various conditions, the membrane exhibited a high pure water flux (132.2±2 L m−2 h−1 at 0.5 bar), with oil removal efficiencies between 96±0.5% and 99±0.5%. Remarkable regeneration capabilities were confirmed, with water flux recovery rates of 92.6±1.0% after flushing and 98.7±1.0% after chemical cleaning. The secondary phase of the research utilized the MoS2/cellulose acetate membrane to assess its effectiveness in maintaining flux stability and fouling mitigation while processing emulsified oily wastewater over a long operational time. The nanocomposite membrane displayed a significant oil removal rate (up to 83.1%) with minimal flux decline (<10% over 80 minutes; 16.2% over 4-6 hours), markedly outperforming the CA membrane without the nanomaterials. The enhanced fouling resistance and sustained flux were also attributed to the catalytic generation of reactive oxygen species (ROS) by MoS2 and of H2O2 catalytic interaction, effectively breaking down oil components and opening the membrane pores. In the final phase of this research, a hybrid 2D nanocomposite membrane was fabricated by incorporating MXene and MoS2 in the polymeric matrix to enhance oil removal from water further. The feed consisted of petroleum emulsion and lecithin as an oil droplet stabilizer was used to simulate oily wastewater. The added 2D MXene material in the membrane improved the removal efficiency of petroleum to 89.45%, compared to 80.86% without the MXene in the membrane. This hybrid 2D nanocomposite membrane was used as pre-treatment of a feed containing both oil and petroleum organic chemicals before the nanofiltration membrane; an excellent removal of both oil and dissolved organic matter was achieved as high as 95-96%, compared to NF alone which only achieved 84% removal. In addition, the coupled 2D nanocomposite and NF membranes demonstrated promising membrane performance with low fouling and high oil and organic matter removal. The successful use of functional 2D nanomaterials such as MoS2 and MXene in fabricating amphiphilic membranes has significantly enhanced oil removal, fouling resistance, catalytic degradation, and durability in oily wastewater treatment. This research contributes to developing low-energy consumption membrane technology solutions for solving the pressing industrial oily wastewater challenges and promotes innovations in water treatment technologies.

Date of Award	22 Jul 2024
Original language	American English
Supervisor	Linda Zou (Supervisor)