(351ar) CVD Graphene Based Membrane for Water Desalination

Although almost 70% of the world is covered by water, less than 3% of it is fresh. The remainder—the vast majority of Earth’s water—is saline. To meet humanity’s increasing and unavoidable need for water, we must convert saline water into fresh water through desalination. Many desalination technologies are available, and membrane-based technologies, such as reverse osmosis (RO), are widely used. Though RO is especially common because of slightly fast transport of water molecules through a membrane while obstructing all ions, but desalination through RO faces several challenges. For example, high operation cost due to high pressure during the process or its degradable polymeric active layer in contact with Chlorine-containing compounds. Polymeric membranes are also susceptible to various foulants, such as biofouling, which become more problematic in the absence of treatments like chlorine. In terms of general functionality, water transport through membranes could still be improved by increasing membrane permeability, but progress in this area has been impeded by a lack of data about how polymer membrane chemistry and structure affect fundamental transport properties. Consequently, improvements in membrane permeability have been relatively slow. Current composite membranes have permeability less than two times higher than those produced twenty years ago.

One of the most famous and recently studied candidates for use in RO or NF membranes is Graphene which has excellent chemical, and mechanical stability and it is the most prominent thinnest possible membrane with its one atom thickness acting as the membrane. In a further benefit, graphene manifests greater resistance to chlorine than current polyamide membranes. This research focused on developing graphene membranes with higher flux and better ion/molecule selectivity compared to the RO/NF membranes currently available on the market.

In this study, the process of transferring Chemical Vapor Deposition (CVD) graphene on to a hydrogel will be discussed. The process of transferring the membrane to the substrate is challenging: CVD graphene is fragile and can easily be torn if it is directly transferred to the support structure. To allow transference without damage, a hydrogel substrate—polyvinyl alcohol (PVA)—has been synthesized and cross-linked. The degree of crosslinking, the thickness of the casting, can affect the permeability of a PVA membrane. The graphene is transferred onto the PVA support by a simple but unique approach to decreasing the chance that defects will form.

Making tunable nanometer pores by plasma: As reported by O’Hern et al. , using plasma through the graphene can create sub-nanometer pores that make the graphene more selective. Consequently, it will be discussed the results of the plasma cleaner with the different condition that was used to apply nanometer pores on the graphene surface.

Experimental work combined with membrane characterization methods (FESEM, AFM, and, LEXT) and membrane performance studies by using a RO system to examine the graphene as RO/NF membrane will be presented. These results will be compared with the other synthesized membrane and different types of supports.

This research will provide insights into developing CVD graphene-based membranes with high water permeability and excellent size selectivity, membranes that will be highly attractive for water purification and desalination because of their high energy-efficiency.