Water shortage has become a limiting factor of sustainable development in Hong Kong, even in China. It can be ascribed to two formative ingredients, economic development and urbanization. Water shortage in Hong Kong would be aggravated in the next two decades. Dongjiang River would have exceeded the corresponding water resources carrying capacity. Seawater desalination is of extreme importance for increasing water supply in Hong Kong and inevitable strategy to undertake water scarcity in Hong Kong. Beyond considering of water price and cost or pros and cons of various technologies, Seawater desalination is of necessity due to sustainable social and economic development in Hong Kong. With advancement of membrane technologies, the gap between water prices from long distant water transfer from Dongjiang River and seawater desalination cost would shrink steadily. Water generated from seawater desalination will become practical and emerged as an important component in public water supply systems.
The inappropriate cost accounting system has confined the development and applications of seawater desalination in Hong Kong for the last two decades. Long distance water transfer projects are usually funded and financed by central or local governments and water are underpriced. Applications of seawater desalination have not to be financed and thus it is not as competitive as long distance water transfer. Due to the constraint of high desalination costs, many countries are unable to afford these technologies as a fresh water resource. Long term multidisciplinary and integrated R&D programs are needed for the purpose of making the seawater desalination techniques affordable worldwide. Active R&D work is required to be performed in order to constantly improve the technologies and reduce the cost of desalination.
For the GO sheet that could be used in desalination of water, the GO synthesis must be large in surface area to express the hydrophobic domains and low oxygen contain on the surface. But of the layer separation must be large enough for water pass through with high flux and smaller than the salt ions. As a result, reduced-graphene oxide is used in graphene membrane for seawater desalination.
Reduced-graphene oxide (RGO) is a material synthesis from graphene oxide by further reduction to slightly remove some of the functional group on the surface of graphene oxide that help the membrane become more insoluble in water for safer and more reliable Nano-filtration. Also the structure of RGO provides a lot of hydrophobic domains that enhance the flux of fluid. As a first attempt to answer to above question, we would prepare graphene/amine-functionalized composite, in which the graphene/ amine-functionalized structure acts as the conductive framework, while active amine-functionalized works as pseudocapacitor. In addition, the charge transfer between graphene and amine-functionalized was also enhanced by the introduction of amine domain. Amine-functionalized graphene oxide could provide a greater performance than normal graphene oxide because of the addition of special functional groups. The composite was characterized by IR spectrum and XRD.
We also would design and fabricate ultrathin graphene oxide derivative membranes with 2D nanochannels by the simple filtration-assisted assembly strategy and the corresponding reverse osmosis membrane evaluator. Next, we characterized the membranes of interlayer distance between two atomic graphene layers by X-ray diffraction analysis. The materials and methods include two parts, graphene oxide derivatives of surface modification with aliphatic amines and manufacture of reverse osmosis membrane evaluator. The first principle is attaching as much as amine onto the graphene oxide (GO), which is consist of GO preparation, surface modification, membrane synthesis and characterization. The second principle is the size of the evaluator matches the effective membrane size while withstanding hydraulic pressure up to 56bar.
Problems associated with prior arts include, but not limited to, short service life, formation of biofilm and low permeate flux. Therefore, we would design a prototype that is designed to filter sea water by means of membranes in order to achieve an effective sea water desalination with the aim of eliminating the problems mentioned above as much as possible.
Hong Kong now is one of the most promising market for seawater desalination. The annual increase rate is projected to be about 50%. Graphene membrane for seawater desalination will dominate Chinese seawater desalination market in the foreseeable future.