Research Topics
1. Transformation and Degradation of Graphene Nanomaterials in the Environment
Given the exponential increase in production of graphene-family nanomaterials, it is likely that they will be released into the environment, but the impacts of engineered graphene and its breakdown products are not known. Hence, understanding the fate, transport and transformation of graphene-based nanomaterials in environment is crucial for the sustainable applications of these emerging materials. Due to their extraordinary physicochemical properties, graphene family nanomaterials are being considered for numerous current and future applications in the electronic, medical, energy, and environmental sectors. The structure of graphene is very similar to polyaromatic hydrocarbons (Geim 2009). Historically aromatic hydrocarbons are of significant environmental concern due to their carcinogenic properties. Once in the environment, graphene may transform and degrade to numerous combinations of polyaromatic hydrocarbons.
Our preliminary data show that graphene oxide nanomaterials can be degraded by sunlight and free chlorine, and water and wastewater disinfection in the United States is accomplished almost solely by chlorination. In fact, the degradation process of graphene begins with the creation of holes in the basal planes of the material, and this is where functional groups are located in graphene oxide. Although we know that chlorinated polyaromatic hydrocarbons are formed in graphene degradation, we do not know how the addition of functional groups to graphene nanomaterials affects the toxicity or mobility of the degradation products.
There is, therefore, a critical need to identify the degradation and transport mechanisms of graphene-family nanomaterials in the environment. Given the increasing use of these emerging pollutants in consumer and industrial products, the lack of this knowledge could result in the unwitting release of toxins both to the environment and human health. Our long-term goal is to define the structure–function relationship between graphene-family nanomaterials in their degradation to provide the basis for the design of more sustainable implementation of this technology. Our preliminary data provide evidence that graphene oxide nanomaterials can be degraded by sunlight and free chlorine, and form chlorinated polyaromatic hydrocarbons, which may be potentially more mobile and toxic than parent compounds. Our objective in this proposed project is to identify the transformation and degradation mechanisms of graphene family nanomaterials during the disinfection process.
2.Nanomaterial Based Smart AntiFouling Membranes for Water Filtration
Membrane-based water treatment is rapidly becoming the method of choice for producing potable water. Membranes filters have the potential to solve the global fresh water challenge and therefore an important field of environmental nanotechnology research is based upon synthesizing new NMs (e.g., magnetic NMs or Nano membranes). Nano filtration and reverse osmosis are capable of purifying wastewater and seawater. The advancement of membrane technology is severely hampered by the long-standing problem of fouling, which is caused by the accumulation of foreign substances on membrane surfaces or inside pores.
Fouling can deteriorate membrane performance by lowering water permeability, worsening product water quality, increasing energy consumption, shortening membrane life etc. Biofouling, undesirable overgrowth of microorganisms on surfaces, is especially difficult to treat and could lead to low water quality, pathogen development, and corrosion, which often requires intensive chemical cleaning or membrane replacement. Rapid advances in nanotechnology have brought about numerous nanomaterials with superb properties that can be potentially useful in membrane processes. Among these nanomaterials, emerging two dimensional nanostructures have exhibited numerous unprecedented properties that can be exploited to make novel membranes. Two dimensional nanomaterials are one-atom thick (~1 nm), which can significantly reduce the thickness of the membranes. Two dimensional graphene family nanomaterials have both antibacterial and anti-corrosive properties, which can be utilized in membranes.
2D transition metal dihalcogenide nanostructures including molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are highly hydrophobic and have extremely low friction, which can deter settlement of fouling organisms and provide low adhesion of any fouling that occurs. Moreover, 2D nanostructures have unique electrical properties, which can utilize the high concentrations of ions in water for deterring attachment of microorganisms. Furthermore, 2D nanostructures are usually one atom thick, which is perfect for membranes and coatings. These innovative smart antifouling membranes will work best in the water with high salt concentration (sea water, wastewater) by activating their electrical properties as well as the usual antimicrobial, anti-corrosion and anti-friction properties of 2D nanostructure-based membranes.
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