Application of Graphene in Water Filtration

Worldwide, more than two billion people do not have access to clean water. 90% of this population live in rural or remote areas. Similarly, one in every nine persons does not have access to drinking water that is not contaminated. The challenge is felt most in developing countries; 80% of sewage is emptied directly into water bodies without any treatment, and the consequence is the reported 3.5 million annual deaths from causes directly related to inadequate water supply, sanitation, and hygiene. It is heart-warming that the United Nations has identified the water problem as one of the goals of the 2015 Sustainable Development Goals, but experts in climate say the problem may soon be unprecedented.

There is a need for clean water to improve the standard of living of people and communities and rapidly drive urbanization, but unfortunately, the quest for industrialization has seen domestic, agricultural, and industrial activities impairing the quality of water, giving rise to the need for water treatment. Water treatment is a collective name for a group of [commonly industrial] processes that make water more suitable for its use, including domestic and industrial uses. The conventional approach to industrial water treatment is via boiler water treatment, cooling water treatment, and wastewater treatment. But recently, certain water purification technologies, like the use of graphene, are challenging these approaches to tackle this water problem.

Graphene is a carbon material considered a constituent of graphite. It has some interesting features: it is lightweight, a good conductor of electricity, and has unique degrees of light absorption. It is also a good hydrophile that forms a stable, oxidized graphene dispersion when dispersed in water—a property that is particularly interesting to its use in a new water filtration method. Graphene oxide is the most popular derivative of graphene. When added to ionized water, it is convenient to be used in preparing the graphene oxide membrane which has seen tremendous research progress in water filtration. It is noteworthy that the oxidation of graphene to graphene oxide would increase the solubility of the graphene in water molecules. However, a modification of the graphene oxide membrane can alter the surface properties of graphene oxide to improve the hydrophilicity of the membrane; for instance, the use of a silane-modified graphene file improves the adhesion between the graphene and the base film.

It’s interesting that the water purification membrane produced by this new filtration method not only removes pollutants but also extracts them physically. Researchers say that billions of nanoscrolls stacked in layers can filter pollutants selectively. The two-dimensional structure of graphene makes it possible for scientists to cram sheets of graphene, producing a thin-layered membrane. Molecular simulation results have shown that water molecules can pass through appropriate pore sizes of oxidized graphene pellets. This filtration benefit of graphene may be credited to the low resistance flow of the monolayers of water molecules between graphene sheets.

The application of this new water filtration method gives you water that has the basic properties of pure water: odorless, colorless, and tasteless. The challenge, however, has been in the scalability of this filtration method to serve a commercial purpose.

A team of engineering researchers at the Massachusetts Institute of Technology has developed a scalable technology that requires seamless, high-quality graphene to be manufactured and tailored towards membrane applications. The idea of membrane application of graphene towards water filtration is not new but given the resemblance of a single sheet of graphene to an atomically thin wire that is constituted of carbon atoms interwoven in a pattern that makes it highly impervious and gives it its high tensile strength, the production of graphene membranes have been limited to only small batches in laboratories. Commercialization of the graphene membrane technology for filtration would require a production that is continuous and reliable—and this is something the researchers from MIT have recognized and deciphered in their novel technology.

The process involves a “roll-to-roll” system where spools connected via a conveyor belt at both ends unwinds (at the first spool) clean copper foils, which is passed through a furnace, and (at the second spool) processed copper foils which carry deposits of methane and hydrogen that form graphene in dispersed parts that aggregate together to form a continuous sheet. Copper is etched out of the graphene and the graphene is supported by a porous polymer. 5 centimeters of graphene are created per minute via this technology. The researchers say if they were in a factory, it would be running 24 hours a day, seven days a week.

The application of this new water filtration technique has wide applications, including in military operations. The US Army Engineer Research and Development Centre's Environmental Laboratory has applied a graphene water filtration system that employs graphene oxide to recycle wastewater. With the use of chitosan—a cheap material made up of the shells of crustaceans—graphene oxide is bound into a recyclable membrane that can filter up to 600 gallons of wastewater per hour. The technology has been patented by the US army and is also available to industry.

In summary, Clean Water and Sanitation for All are one of the 17 Sustainable Development Goals set out by the United Nations for adoption by world leaders, and this goal is essential in reaching other goals as well, including Health and Wellness and Zero Wellness. Researchers have continuously challenged themselves on how to improve the quality of water to attain these goals and improve the quality of life. An emerging class membrane-based water purification technology has attracted the interests of researchers and scientists worldwide. Graphene has been touted to revolutionize water treatment/filtration methods given some of its fine and startling physical and structural properties. Until recently, its commercial scalability has been in doubts due to its limited production quantities (restricted to only for use in laboratory quantities), but emerging research has shown that there is a pathway to commercialization of this technology, that this carbon material is not just the future of water filtration method but also the present.